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1
Avateffazeli, Maryam. "Characterization, Exfoliation, and Applications of Boron Nitride and Molybdenum Disulfide from Compressible Flow Exfoliation." University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1607085667908185.
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Nassar, Nashaat. "Melt exfoliation in montmorillonitepolystyrene nanocomposites." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19613.
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Polymer clay nanocomposites (PCN) exhibit many advantages over conventional composites, while using substantially smaller quantities of filler. For various reasons, it is desirable, in nanocomposite manufacturing, to employ processes based on melt exfoliation of modified clay particles. While various researchers have studied the effects of processing variables and material properties on the effectiveness of melt exfoliation, many issues remain unresolved. This study attempts to deal with some of these. In this study an amorphous polymer, atactic polystyrene (PS), has been chosen to avoid complications related to crystallization. Three grades of (PS), having different molecular weight, were pre-blended with Cloisite® 1OA (a modified montmorillonite) in a twin-screw extruder (TSE). The TSE blends were subsequently fed to a single screw extruder, fitted with one of three specially designed attachments at the front of the screw. The attachments were designed to provide combinations of shear and elongational deformations. The resins, TSE blends, and final nanocomposites were characterized for the degree of exfoliation, mechanical properties, and rheological behavior using capillary and rotational rheometers, FTIR, XRD and TEM. The effects of molecular weight, mixing time, and levels of shear and elongational stresses, on the degree of intercalation and the properties of the nanocomposites were studied. Surprisingly, the complex and shear viscosities of the nanocomposites were found to be lower than the corresponding viscosities of the virgin polystyrene. Intercalation was achieved with in a short residence time. However, the degradation of the clay intercalant increased with residence time which causes degradation of PS.
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Roscher, Sarah [Verfasser], and Oliver [Akademischer Betreuer] Ambacher. "Reduktive elektrochemische Exfoliation von Graphenflocken." Freiburg : Universität, 2020. http://d-nb.info/1221959921/34.
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Zhu, Xiaowen. "Exfoliation of Two-Dimensional Materials." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428063152.
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Butler, Sheneve. "Exfoliation and Air Stability of Germanane." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366295898.
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Suter, Theo M. "Crystalline carbon nitrides : characterisation, intercalation and exfoliation." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10045282/.
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In recent years there has been significant interest in, and research into, carbon nitride materials for use in applications such as photocatalysis. The most commonly described C/N materials are referred to as graphitic carbon nitride (gCN), though due to the layered amorphous nature structural characterisation is difficult. Polytriazine imide (PTI) is a crystalline layered carbon nitride that is less explored within the literature compared to gCN due to its more difficult synthetic procedure. In this thesis the synthesis, characterisation, intercalation chemistry and exfoliation of PTI is explored. The synthesis of a related material, triazine based graphitic carbon nitride (TGCN) is explored and the product characterised in detail. PTI refers to the carbon, nitrogen and hydrogen framework (C6N9H3) within which different ionic intercalants can be accommodated; then give rise to several different crystalline materials with the same underlying carbon nitride backbone. The structure of these crystalline, layered PTI was synthesised by reversibly removing and replacing the intercalated ions without affecting the carbon nitride structure. The structures of these new materials was investigated and how changing the intercalant can be used to tune the structures and properties. This methodology may facilitate the fine-tuning and optimisation of carbon nitrides for a number of applications. I have also explored the exfoliation of the layered PTI materials. A number of methods have been used including intercalation and ultrasonication. Remarkably, however I found that the PTI gently, and even spontaneously dissolves to form solutions in highly polar organic solvents and even in water. This process takes place without the need for mechanical mixing, sonication or centrifugation. The resultant separated nanosheets solutions are characterised indepth. Few layer stacks of undamaged crystallites are observed. The photoluminescence of the nanosheets have been found to depend on the number of stacked layers, presenting exciting opportunities for optoelectronic devices.
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Webb, Melanie. "Blistering and exfoliation of ion-implanted GaAs." Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/844157/.
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This thesis investigates a technique of transferring thin layers of GaAs onto other substrates, called the ion-cut (or smart-cut) process. The process, and the progress that had already been made to optimise and understand it is described in detail in the first chapter, and the project aims are presented in the context of these developments. The following chapter describes the experimental setups used in this work, with the main techniques involving ion beam analysis, x ray diffraction and Nomarksi, atomic force and electron microscopy. The development of a new method for controlling the flux and temperature of implantation is described in this thesis, and is now available to other users of the Ion Beam Centre at the University of Surrey. A new method for interpreting the channelling RBS (Rutherford Backscattering Spectrometry) spectra in blistered samples has been developed, and is described in chapter 4. The results presented in this thesis show that the ion-cut process is dependent on the flux of ion implantation, and demonstrate that this can be explained in terms of the relative concentration of damage introduced by the ion implantation process. In addition, the role of implant temperature on the process has also been investigated in detail for the first time. Finally, the suitability of implanting helium or neon under different conditions instead of hydrogen has been investigated and it is shown that while helium is more effective than hydrogen (around half the dose is required for helium implantation compared with hydrogen), neon is not a suitable alternative. Such an investigation is essential for optimisation of this process, which has eclectic applications including the fabrication of lasers, solar cells and the integration of GaAs and silicon materials on a single chip.
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Petitjean, Dominique. "Synthèse et exfoliation de composés graphite-acide." Nancy 1, 1992. http://www.theses.fr/1992NAN10413.
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Le thème principal de ce mémoire est l'étude générale de l'exfoliation des composés graphite-acide nitrique, sulfurique, perchlorique. La synthèse et la caractérisation de ces composés sont présentées dans une première partie. L'étude du système graphite acide perchlorique commercial (70%) a été particulièrement développée. Les conditions d'insertion de cet acide sont précisées et les propriétés structurales et de transport : résistivité électrique, ont été abordées. L'exfoliation de ces composés est étudiée dans la seconde partie de ce travail. L'analyse des travaux antérieurs et les recherches expérimentales ont permis d'établir une classification des types d'expansion. Il est ainsi distingué et analysé l'expansion endothermique réversible obtenue par chauffage lent d'un composé d'insertion et l'exfoliation irréversible observée à la suite d'un chauffage à vitesse modérée ou rapide. Un nouveau mode d'exfoliation est étudié : l'expansion par décompression brusque. Des mécanismes de l'exfoliation sont présentés et l'influence de divers paramètres discutés. Les recherches expérimentales se sont poursuivies par l'étude de l'exfoliation exothermique qui est obtenue soit par voie chimique en phase liquide, soit par chauffage d'un composé dont l'espèce intercalée est instable thermiquement.
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Trantow, Colleen. "Genetic pathways of Lyst and exfoliation syndrome." Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/896.
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Human eyes with exfoliation syndrome (XFS) exhibit a distinctive pattern of iris transillumination defects that are recapitulated in Lyst mutant mice carrying the beige allele. Here I present the identification and characterization of the B6-Lystbg-J mouse model of XFS, modifiers of Lyst mediated ocular phenotypes, mechanisms of intraocular pressure (IOP) pathology related to circadian rhythms, and mechanisms of iris transillumination defects in the B6-Lystbg-J mice.
Clinical and histological analysis shows that the B6-Lystbg-J mice have multiple similarities to human XFS including: iris transillumination defects, production of an exfoliative-like material, and pronounced pigment dispersion. Despite these insults, Lyst mutation does not cause increased IOP or optic nerve damage within the context of a C57BL/6J genetic background. However, defects in the circadian rhythm regulation of IOP were identified. Sequence analysis identifies that the beige mutation is predicted to delete a single isoleucine from the WD40 domain of the LYST protein. I identified CSNK2B as a binding partner of LYST and showed that LYSTbg-J completely disrupts the interaction. CSNK2B function in regulating E-cadherin and β-catenin binding is subsequently disrupted. These results lead to a working hypothesis that aspects of the XFS phenotype involve LYST and CSNK2B pathways, likely influencing cell-cell adherens junctions.
Epistasis experiments were used to test for genetic modifiers of Lyst, which demonstrated that albino Lyst mutant mice exhibited complete rescue of Lyst-dependent iris phenotypes. In a genetic background-driven approach, a DBA/2J strain of congenic mice was created. The DBA/2J background, which harbors multiple mutations influencing melanosomal-proteins, enhanced Lyst dependent iris phenotypes. Thus, both experimental approaches implicated melanosomes, a potential source of oxidative stress, as mechanistically contributory. Supporting a contributory role of oxidative damage, Lyst mutation resulted in genetic context sensitive changes in iris lipid hydroperoxide levels, being lowest in albino and highest in DBA/2J mice. These results identified an association between oxidative damage to lipid membranes and severity of Lyst-mediated phenotypes, uncovering a new mechanism contributing to pathophysiology involving LYST. In conclusion these results demonstrate that mutation of the Lyst gene can produce ocular features of human XFS and suggests that LYST or LYST-interacting genes may contribute to XFS.
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Zhao, Xinyan. "Exfoliation corrosion kinetics of high strength aluminum alloys." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1140154773.
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Uribe, Calderón Jorge Alonso. "Melt intercalation andor exfoliation of polystyrene-montmorillonite nanocomposites." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79267.
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Thermal stability of organoclays and polystyrene (PS) intercalation in organoclays by melt processing were studied. The effects of polymer viscosity, processing conditions, type of mixing and the type of fillers on the intercalation process were evaluated. The resulting nanocomposites were tested to characterize structure, thermal stability and mechanical properties.Two new organoclays were used in this study exhibited good thermal stability. This suggested their potential use in the preparation polymer nanocomposites at high processing temperatures.
Batch mixing promoted polymer intercalation in most cases. PS nanocomposites showed a combination of intercalated and unintercalated or collapsed structures. In general, thermal stability and mechanical properties of PS were enhanced by incorporation of organoclays. Processing conditions in the batch mixer had only a small influence on intercalation behavior. However, they had a strong effect on thermal stability and mechanical properties. The degree of intercalation was dependant on the type of organoclay. As a result thermal stability and mechanical properties were influenced by the type of organoclay used. The best mechanical properties were obtained with Cloisite 10-A.
Mixing in the twin screw extruder promoted intercalation of low viscosity PS. Thermal stability was increased in all cases, but mechanical properties did not improve significantly.
The tensile modulus of nanocomposites was calculated using five models reported in the literature. The results were compared to experimental data obtained in this study. Up to 1% wt Cloisite 10-A content, the experimental results showed very good agreement with the predictions of the Halpin-Tsai and Brune models, which predicted the highest modulus values. The experimental values fell rapidly bellow theoretical predictions above 1% wt clay content.
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Brent, John. "Exfoliation and synthesis of two-dimensional semiconductor nanomaterials." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/exfoliation-and-synthesis-of-twodimensional-semiconductor-nanomaterials(289ba930-19ff-4fae-8d84-e46560620c18).html.
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2-Dimensional (2D) materials are characterised by atomic thickness and significantly larger edge-lengths, producing particles which are highly confined in 1 direction. Reducing a material to one or few atomic layers gives rise to structural and electronic properties that deviate significantly from those of the bulk crystal. For this reason 2D nanosheets have been investigated for potential application in sensing, catalysis, capacitance, photovoltaics and for flexible circuits (among others).Despite rapid progress in understanding the synthesis and properties of 2D nanosheets in recent years, there remain significant problems surrounding the development of scalable production methods, understanding and tuning fundamental properties, and controlling the size and monodispersity of semiconductor crystals. In addition, new materials with novel properties are constantly sought in order to meet specific requirements. Although the tools developed over the last 12 years can often be applied to the fabrication of these materials, understanding their behaviour and limitations is ongoing. The following thesis discusses the routes to the fabrication of 2-dimensional materials and explores the production of MoS2, black phosphorus and tin(II) sulfide nanosheets. The aim of each piece of work is determined by the level of development of the field; MoS2 nanosheets have been known for several years and therefore the work presented was motivated by a desire to impart size control for specific applications. The study of phosphorene and 2D tin(II) sulfide is in its infancy; as such the focus remains on scalable nanosheet exfoliation and developing an understanding of their properties. The following studies on phosphorene report the exfoliation of nanosheets in organic and aqueous surfactant solutions and an investigation of the stability and breakdown products of the resulting colloidal suspensions. The stabilisation of phosphorene in aqueous media paves the way for its use in biological systems. Band-gap tuning in IV-VI analogues of phosphorene is demonstrated by size-selection of exfoliated SnS nanosheets. Although the physical characteristics of nanosheets and their incorporation into devices receive some attention, this thesis will focus mainly on the synthetic aspects of 2D materials research.
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Forsberg, Viviane. "Liquid Exfoliation of Molybdenum Disulfide for Inkjet Printing." Licentiate thesis, Mittuniversitetet, Avdelningen för naturvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-29181.
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Since the discovery of graphene, substantial effort has been put toward the synthesis and production of 2D materials. Developing scalable methods for the production of high-quality exfoliated nanosheets has proved a significant challenge. To date, the most promising scalable method for achieving these materials is through the liquid-based exfoliation (LBE) of nanosheetsin solvents. Thin films of nanosheets in dispersion can be modified with additives to produce 2D inks for printed electronics using inkjet printing. This is the most promising method for the deposition of such materials onto any substrate on an industrial production level. Although well-developed metallic and organic printed electronic inks exist on the market, there is still a need to improve or develop new inks based on semiconductor materials such as transition metal dichalcogenides (TMDs) that are stable, have good jetting conditions and deliver good printing quality.The inertness and mechanical properties of layered materials such as molybdenum disulfide (MoS2) make them ideally suited for printed electronics and solution processing. In addition,the high electron mobility of the layered semiconductors, make them a candidate to become a high-performance semiconductor material in printed electronics. Together, these features make MoS2 a simple and robust material with good semiconducting properties that is also suitable for solution coating and printing. It is also environmentally safe.The method described in this thesis could be easily employed to exfoliate many types of 2D materials in liquids. It consists of two exfoliation steps, one based on mechanical exfoliation of the bulk powder utilizing sand paper, and the other inthe liquid dispersion, using probe sonication to liquid-exfoliate the nanosheets. The dispersions, which were prepared in surfactant solution, were decanted, and the supernatant was collected and used for printing tests performed with a Dimatix inkjetprinter. The printing test shows that it is possible to use the MoS2 dispersion as a printed electronics inkjet ink and that optimization for specific printer and substrate combinations should be performed. There should also be advances in ink development, which would improve the drop formation and break-off at the inkjet printing nozzles, the ink jetting and, consequently, the printing quality.Sedan upptäckten av grafen har mycket arbete lagts på framställning och produktion av 2D-material. En viktig uppgift har varit att ta fram skalbara metoder för produktion av högkvalitativa nanosheets via exfoliering. Den mest lovande skalbarametoden hittills har varit vätskebaserad exfoliering av nanosheets i lösningsmedel. Tunna filmer av nanosheets i dispersion kan anpassas med hjälp av tillsatser och användas för tillverkning av halvledare strukturer med inkjet-skrivare, vilket är den mest lovande metoden för på en industriell produktions nivå beläggaden typen av material på substrat. Även om det finns välutvecklade metalliska och organiskabläck för tryckt elektronik, så finns det fortfarande ett behov av att förbättra eller utveckla nya bläck baserade på halvledarmaterial som t.ex. TMD, som är stabila, har goda bestryknings egenskaper och ger bra tryckkvalitet. Den inerta naturen tillsammans med de mekaniska egenskaperna som finns hosskiktade material, som t.ex. molybdendisulfid (MoS2), gör demlämpliga för flexibel elektronik och bearbetning i lösning. Dessutom gör den höga elektronmobiliteten i dessa 2D-halvledaredem till en stark kandidat som halvledarmaterial inom trycktelektronik. Det betyder att MoS2 är ett enkelt och robust material med goda halvledaregenskaper som är lämpligt för bestrykning från lösning och tryck, och är miljömässigt säker.Den metod som beskrivs här kan med fördel användas föratt exfoliera alla typer av 2D-material i lösning. Exfolieringensker i två steg; först mekanisk exfoliering av torr bulk med sandpapper, därefter används ultraljudsbehandling i lösning för att exfoliera nanosheets. De dispersioner som framställts i lösning med surfaktanter dekanterades och det övre skiktetanvändes i trycktester med en Dimatix inkjet-skrivare.Tryckprovet visar att det är möjligt att använda MoS2 -dispersion som ett inkjet-bläck och att optimering för särskildaskrivar- och substratkombinationer borde göras, såsom förbättringav bläcksammansättningen med avseende på droppbildning och break-off vid skrivarmunstycket, vilket i sin tur skulleförbättra tryckkvaliteten.
KM2
Paper Solar Cells
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Jackson, N. "Factors Affecting The Exfoliation Corrosion Of Aluminium Alloys." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/11281.
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Aluminium alloys suffer from localised attack termed exfoliation corrosion which is
intergranular in nature where the attack proceeds around the elongated grains present in
the microstructure. The formation of a more voluminous corrosion product than the
original material results in the lifting of grains giving the characteristic of exfoliation
corrosion - lamellar attack. This results in surface degredation in the form of pitting,
flaking or blistering. The precipitates present within the microstructure and the grain shape
can alter how susceptible the material is to exfoliation corrosion. The distribution of
precipitates present can be altered by heat treatment which affects the exfoliation
corrosion susceptibility. A study on the effects of heat treatment and grain shape on
exfoliation corrosion has been completed for two AlCuMg alloys (2014 and 2024) and
two aluminium - lithium alloys (8090 and 2091). A MASTMAASIS salt - spray cabinet
was used to determine the exfoliation corrosion susceptibility of all the alloys. A four -
point bend test was developed to determine the depth of penetration and compared to
depths measured metallographically.
The results for the 2XXX series alloys suggest that as the grain aspect ratio
increases the exfoliation susceptibility increases. Although the aspect ratio did not differ
greatly between each alloy, the different phases present in the two alloys seem to
contribute more markedly to the susceptibility. Heat treatment in the 2024 alloy suggested
that the peak - aged condition gave a higher susceptibility to corrosion than the under -
aged and over - aged conditions. Results indicated that the heat treatment has a greater
effect on exfoliation corrosion than the grain aspect ratio, showing that the grain
boundary microstructure is an important factor in the exfoliation process. The four - point
bend test tended to underestimate the depth of attack by virtue of measuring the whole
area of the specimen whereas metallographic measurements only took into account the
attacked areas. End grain testing suggested that the attack can not only proceed
longitudinally but also "short - circuit" down the transverse path of the elongated grains
in the 2XXX series alloys. For the aluminium - lithium alloys the over - aged condition
showed more resistance to attack than the under - aged and peak - aged conditions but
the under - aged was more resistant to attack for the 2091 alloy. Stress corrosion
cracking showed trends similar to exfoliation corrosion.
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Jackson, Neal C. "Factors affecting the exfoliation corrosion of aluminium alloys." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/11281.
Full textAbstract:
Aluminium alloys suffer from localised attack termed exfoliation corrosion which is intergranular in nature where the attack proceeds around the elongated grains present in the microstructure. The formation of a more voluminous corrosion product than the original material results in the lifting of grains giving the characteristic of exfoliation corrosion - lamellar attack. This results in surface degredation in the form of pitting, flaking or blistering. The precipitates present within the microstructure and the grain shape can alter how susceptible the material is to exfoliation corrosion. The distribution of precipitates present can be altered by heat treatment which affects the exfoliation corrosion susceptibility. A study on the effects of heat treatment and grain shape on exfoliation corrosion has been completed for two AlCuMg alloys (2014 and 2024) and two aluminium - lithium alloys (8090 and 2091). A MASTMAASIS salt - spray cabinet was used to determine the exfoliation corrosion susceptibility of all the alloys. A four - point bend test was developed to determine the depth of penetration and compared to depths measured metallographically. The results for the 2XXX series alloys suggest that as the grain aspect ratio increases the exfoliation susceptibility increases. Although the aspect ratio did not differ greatly between each alloy, the different phases present in the two alloys seem to contribute more markedly to the susceptibility. Heat treatment in the 2024 alloy suggested that the peak - aged condition gave a higher susceptibility to corrosion than the under - aged and over - aged conditions. Results indicated that the heat treatment has a greater effect on exfoliation corrosion than the grain aspect ratio, showing that the grain boundary microstructure is an important factor in the exfoliation process. The four - point bend test tended to underestimate the depth of attack by virtue of measuring the whole area of the specimen whereas metallographic measurements only took into account the attacked areas. End grain testing suggested that the attack can not only proceed longitudinally but also "short - circuit" down the transverse path of the elongated grains in the 2XXX series alloys. For the aluminium - lithium alloys the over - aged condition showed more resistance to attack than the under - aged and peak - aged conditions but the under - aged was more resistant to attack for the 2091 alloy. Stress corrosion cracking showed trends similar to exfoliation corrosion.
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Xie, Aozhen. "Exfoliation of Transitional Metal Dichalcogenides (TMDS) and the Application of Co-Exfoliation of MoS2/Natural Graphite in Lithium Ion Battery (LIB)." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1396966667.
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Shiravand, Fatemeh. "Study of the exfoliation process in epoxy-clay nanocomposites." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/283195.
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Cured epoxy resins are highly cross-linked polymers which are increasingly important in high performance engineering field due to the stiffness, high strength, heat resistance and solvent resistance. However one major drawback is their poor resistance to impact and crack initiation. Consequently, there is a need to improve the toughness while maintaining desirable properties. Various approaches were suggested for improving the toughness including the addition of silicate layered clay.
The aim of this investigation is to develop the exfoliation process in the epoxy-silicate layered nanocomposites. It is generally considered that, in order to maximize the degree of exfoliation, the intra-gallery reaction, which is associated to the epoxy homopolymerization reaction between clay galleries, should occur before the extra-gallery reaction, which is related to the cross-linking reaction between epoxy groups and amines, hence for enhancement the rate of intra-gallery reaction, these different possibilities were considered to improve the exfoliation degree in cured nanocomposites as follow:
1. Select suitable cure temperature and curing program,
2. Pre-conditiong the epoxy/clay mixture
3. Incorporation of the cationic initiator in clay galleries
4. Addition of the hyperbranched polymer to epoxy/clay mixture
5. Select the appropriate type of silicate layered clay
In support of these statements, TGAP (Araldite MY0510) as tri-functional epoxy resin, montmorillonite (Nanomer I.30E, MMT) as silicate layered clay and diamino diphenyl sulphone (Aradur 976-1, DDS) as curing agent were chosen as experimental system to study the influence of these strategies on improvement of the final nanostructure. The curing behavior and the thermal properties of epoxy silicate layered nanocomposites which is prepared based on the above procedures were separately examined with differential scanning calorimetry (DSC and TOPEM) and Thermogravimetric analysis (TGA) and also the fully cured nanostructure in each case is characterized by transition electron microscopy (TEM) and the x-ray scattering (SAXS) and moreover, the mechanical properties are studied by dynamic mechanical analysis (DMA), impact test and scanning electron Microscopy (SEM). Although in each case we obtained the intersecting results which are presented in our papers, the real goal is to fabricate the highly exfoliated nanostructure which is obtained from the first three procedures.
Among these three procedures, it is difficult to decide which one is more effective on the exfoliation process based on the TEM images which shows the small part of the nanostructure. Therefore, the mechanical properties such as modulus, impact test and fracture surface which display the behavior of the whole nanostructure are helpful tools to compare the degree of exfoliation between these cases. As results, the mechanical properties measurements suggested that incorporation of the cationic initiator is the best protocol to achieve the highly exfoliated epoxy/clay nanocompositesResinas epoxi curados son polímeros reticulados altamente que son cada vez más importante en el campo de la ingeniería de alto rendimiento debido a la rigidez, alta resistencia, resistencia al calor y resistencia a los disolventes. Sin embargo, una desventaja importante es su pobre resistencia al impacto ya la iniciación de grietas. En consecuencia, hay una necesidad de mejorar la tenacidad a la vez que mantiene propiedades deseables. Se han sugerido varios enfoques para mejorar la tenacidad incluyendo la adición de silicato arcilla estratificada. El objetivo de esta investigación es desarrollar el proceso de exfoliación de las capas de nanocompuestos - epoxi silicato. Es generalmente se considera que, con el fin de maximizar el grado de exfoliación, la reacción intra - galería, que se asocia a la reacción de homopolimerización epoxi entre galerías de arcilla, debe ocurrir antes de la reacción adicional - galería, que está relacionada con la reacción de reticulación entre los grupos epoxi y aminas, por lo tanto, para la mejora de la velocidad de reacción dentro de la galería, estos se consideraron diferentes posibilidades para mejorar el grado de exfoliación en nanocompuestos curados de la siguiente: 1. Seleccionar temperatura de curado adecuado y el programa de curado 2. Pre- conditiong la mezcla epoxi / arcilla 3. Incorporación del iniciador catiónico en galerías de arcilla 4. La adición del polímero hiperramificado de epoxi / mezcla de arcilla 5. Seleccione el tipo apropiado de arcilla en capas de silicato. En apoyo de estas afirmaciones, TGAP (Araldite MY0510) como la resina epoxi trifuncional, montmorillonita (Nanomer I.30E, MMT) como silicato en capas de arcilla y diamino difenil sulfona (Aradur 976-1, DDS) como agente de curado fueron elegidos como experimentales sistema para estudiar la influencia de estas estrategias en la mejora de la nanoestructura definitiva el comportamiento de curado y las propiedades térmicas de silicato de nanocompuestos epoxi en capas que se presenta de acuerdo a la procedimientos anteriores se examinaron por separado con calorimetría diferencial de barrido (DSC y TOPEM) y el análisis termogravimétrico (TGA) y también la nanoestructura completamente curado en cada caso se caracteriza por la transición de electrones microscopía (TEM) y la dispersión de rayos x ( SAXS ) y, además, las propiedades mecánicas son estudiados por dinámico análisis mecánico (DMA), la prueba de impacto y microscopía electrónica de barrido (SEM). Aunque en cada caso se obtuvo la intersección de los resultados que se presentan en nuestros papeles, el verdadero objetivo es fabricar la nanoestructura muy exfoliada que se obtiene a partir de los tres primeros procedimientos. Entre estos tres procedimientos, es difícil decidir cuál es el más eficaz en el proceso de exfoliación a base de las imágenes de TEM que muestra la pequeña parte de la nanoestructura. Por lo tanto, las propiedades mecánicas tales como el módulo, prueba de impacto y la superficie de fractura que muestran el comportamiento de toda la nanoestructura son herramientas útiles para comparar el grado de exfoliación entre estos casos. Como resultados, las propiedades mecánicas mediciones sugirieron que incorporación del iniciador catiónico es el mejor protocolo para alcanzar los nanocompuestos epoxi / arcilla altamente exfoliadas.
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Risley, Mason J. "Surfactant-assisted exfoliation and processing of graphite and graphene." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48980.
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Surfactant assisted solution exfoliation of expanded graphite by means of sonication was carried out in an attempt to produce non-covalent charge functionality on the surface of graphene for the directed self assembly of graphene films on patterned substrates via electrostatic interactions. This thesis includes the results of experimental research associated with: 1) quantifying the effectiveness of various di-functionalized dithienothiophene surfactant small molecules, 2) further understanding the surface affinity and interaction mechanism between these surfactant molecules and the surface of expanded graphite and graphene and 3) experimentally testing the feasibility of the directed self-assembly of graphene films by means of charge functionalization of graphene by the surfactant molecules adsorbed onto the surface of exfoliated graphene.
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Armstrong, Christopher Paul. "A characterisation of the exfoliation behaviour of natural graphites." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238713.
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Yang, Sheng [Verfasser]. "Exfoliation of conductive layered materials in solutions / Sheng Yang." Mainz : Universitätsbibliothek Mainz, 2018. http://d-nb.info/1156623782/34.
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Jones, S. P. "Stress-corrosion and exfoliation of high strength aluminium alloys." Thesis, Cranfield University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.352939.
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Abro, Mehwish. "Modelling the exfoliation of graphite for production of graphene." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-272339.
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The aim of my thesis is to make a theoretical model of data obtained from liquid-phase exfoliation of graphene. The production of graphene in the liquid phase exfoliation is a cost efficient method One part of this work is devotedto learn the method of production of graphene by the shear mixing technique from the graphite and to estimate some important parameters which are crucial for the process. Other part of my work is based on studying the liquid-phase exfoliation mechanism of graphene through ultrasonication technique. This method is time consuming as compared to shearmixing.
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Shulga, Y. M., S. A. Baskakov, E. I. Knerelman, G. I. Davidova, E. R. Badamshina, S. Y. Shulga, E. A. Skrileva, A. L. Agapov, D. N. Voylov, and A. P. Sokolov. "Carbon Nanomaterial Produced by Microwave Exfoliation of Graphite Oxide." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35118.
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Carbon-based graphene-like material was obtained through microwave stimulated exfoliation of graph-ite oxide (GO). Properties of this material were investigated by multiple techniques including element analysis, X-ray photoelectron spectroscopy (XPS), mass-spectroscopy, infrared (IR) and Raman spectrosco-py, scanning electron microscopy (SEM) and broadband dielectric spectroscopy. Specific surface area and volume of microwave exfoliated graphite oxide (MEGO) reached 600 m2/g and 6 cm3/g, respectively. It is shown that during such explosive reduction process the sample emits CO2, CO and H2O and, in some cases, SO2 gases. The resulting reduced material exhibits IR spectra similar to that of graphite and a dc-conductivity of 0.12 S/cm. It is also shown that prolonged storage in ambient conditions leads to elevated oxygen content and decrease of specific surface area of the samples.
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Eredia, Matilde. "2D materials : exfoliation in liquid-phase and electronics applications." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF008/document.
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Cette thèse est consacrée à la production de matériaux 2D en phase liquide, en utilisant des approches pouvant permettre la production en masse de graphène et de matériaux apparentés. Notre objectif est de surmonter certains problèmes critiques pour le traitement et l'utilisation pratique des encres à base de matériaux 2D et de fournir une compréhension approfondie de la relation structure-propriétés dans ces matériaux, constituant des étapes obligatoires pour leurs applications futures. Cette thèse porte principalement sur l'UILPE et l'exfoliation électrochimique du graphène et du disulfure de molybdène (MoS2), qui ont été choisis comme matériaux prototypes à 2 dimensions. Les approches synthétiques sont combinées à une caractérisation physico-chimique des matériaux produits, à l'aide de techniques telles que l'AFM, la microscopie électronique, la spectroscopie XPS et Raman, ainsi qu'à une caractérisation électrique. Des applications dans le domaine de la détection et de l'électronique ont été explorées et ont permis de démontrer que des approches d'exfoliation en phase liquide pouvaient être utilisées pour obtenir un contrôle précis des propriétés des matériaux 2D ouvrant la voie à leur intégration en tant que matériaux actifs dans de nouveaux dispositifs multifonctionnelsThis thesis is devoted to the production in liquid-phase of two-dimensional materials, by using approaches that may enable mass production of graphene and related materials. We aim to overcome some issues that are critical for the processing and practical use of 2D materials-inks and to provide a deep understanding of the structure-properties relationship in such materials being mandatory steps toward their future applications. This thesis mainly focuses on ultrasound-induced liquid-phase exfoliation and electrochemical exfoliation of graphene and molybdenum disulfide, which have been chosen as prototypical 2D materials. The synthetic approaches have been combined with a multiscale physico-chemical and electrical characterization of the produced materials, by employing techniques such as AFM, XPS and Raman spectroscopy. Applications in the field of sensing and electronics have been explored and allowed to demonstrate that liquid-phase exfoliation approaches can be conveniently employed to achieve a fine control on the properties of 2D materials paving the way to their integration as active materials in novel multifunctional devices
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Bernardo, Philippe. "Influence des propriétésdu graphite sur le premier cycle d'intercalation du lithium." Thesis, Mulhouse, 2011. http://www.theses.fr/2011MULH5212.
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Les batteries à ions lithium alimentent la plupart des petits appareils électriques, portables. Elles font usage du graphite comme électrode négative. Pour optimiser celle-ci, il faut réduire la perte spécifique de charge du premier cycle d’intercalation du lithium. Cette perte est principalement due à la formation d’une couche passive par décomposition de l’électrolyte. Les propriétés du graphite qui l’influencent sont partiellement connues. En particulier, une meilleure compréhension de l’exfoliation du graphite, responsable d’une grande perte spécifique de charge, est souhaitée. Ce phénomène est provoqué par la co-intercalation de solvant à travers les plans de bord des particules. Des paramètres comme la cristallinité, la chimie de surface et la réactivité du graphite semblent jouer un rôle. Une étude systématique a été entreprise afin de déterminer leur influence sur le premier cycle dans un électrolyte standard à base de carbonate d’éthylène et de diméthyle. Il apparaît que les complexes de surface oxygénés ne jouent pas de rôle particulier tandis que les complexes hydrogénés favorisent la co-intercalation de solvant. De plus, les graphites ayant une faible teneur en sites actifs constituant l’Active Surface Area (ASA), mesurée par chimisorption d’oxygène, sont plus enclins à exfolier. Comme les atomes de bord à deux voisins sont les plus réactifs en raison de la présence d’un électron célibataire, la plus grande sensibilité à la co-intercalation de solvant des graphites de faible ASA peut s’expliquer par la formation d’une couche passive inappropriée sur des plans de bord peu réactifs laissant passer le solvantIn the field of small portable electrical devices, lithium-ion batteries are common. Graphite is used as the negative electrode. To improve its electrochemical performances, the first cycle specific charge loss must be decreased. It is predominantly attributed to the electrolyte reduction into a passivation layer. The graphite properties which influence this charge loss are not clearly identified. In particular, the graphite exfoliation which is responsible for a huge specific charge loss must be better understood. This dramatic phenomenon is due to solvent co-intercalation through the particle edge planes. Many graphite parameters such as crystallinity, surface chemistry and reactivity are thought to play a role. A systematic study was carried out in which the influence of each parameter on the first cycle was assessed in a standard ethylene and dimethyl carbonate based electrolyte. It appears that the presence of oxygen surface complexes does not have any influence whereas C6H bonds cause slight exfoliation. In addition, graphite samples containing low amount of active sites : the so-called Active Surface Area (ASA), quantified by oxygen chemisorption, are more likely to exfoliate. Since graphite active sites are mainly the edge atoms because of unpaired electron presence, low ASA graphite exfoliation can be explained by the formation of inappropriate passivation layer on the edge planes letting solvent molecules co-intercalate
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Mollet, Vincent. "Characterization of exfoliation and intercalation in polymer layered silicate nanocomposites." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82620.
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A microstructural and morphological analysis of polymer/layered silicate nanocomposites (PLSN) is proposed. The analysis employs wide angle x-ray diffraction (WAXD) and to a larger extent, transmission electron microscopy (TEM).Polyamide-6 (PA) and polystyrene (PS) nanocomposites were produced by melt processing the resins with several grades of organically modified clay in a twin screw extruder (TSE). The TSE was operated in two different configurations (C and A). The effects of the type of organoclay, TSE configuration, clay concentrations and addition of a compatibilizing agent in the matrix were evaluated.
Both WAXD and TEM analysis revealed exfoliated or intercalated structures for PA-based nanocomposites depending on the organoclay, whereas PS-based nanocomposites mainly exhibited intercalated structure. A quantitative analysis of the diffraction peaks was carried out in order to identify the ambiguous nature of the secondary reflection peak. Depending on the case, it is proposed that the secondary reflection peak could be due to a combination of secondary reflection of the intercalated structure and a primary reflection of a collapsed structure of the layered silicate particles.
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Cox, Kathleen Marie. "Characterisation of two dimensional nanomaterials produced via spontaneous liquid exfoliation." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10052324/.
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Developing scalable nanomaterial production methods is necessary for realising nanomaterial commercialisation. In principle, production via Liquid Phase Exfoliation satisfies this need. However, techniques reliant on energy input damage the material via mechanical stress, yielding suspensions of multi-layer stacks, stable only for days, and necessitating centrifugation for manipulation. An alternative, emerging technique relies upon the charging of material to allow spontaneous dissolution of pristine 2d nanomaterials. Here this is explored for pnictogen chalcogenide layered materials, focusing on unanswered questions relating to the practicality of the method. In this thesis, ion intercalated Bi2Te3 and Sb2Te3 were dissolved within the aprotic solvents: N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF). Successful exfoliation of undamaged, hexagonal 2d nanomaterials was confirmed. A range of complementary experimental techniques were used including TEM, AFM, and SAXS. From the analysis of thousands of nanosheets it was found that gradual diffusion of nanosheets, as a result of their spontaneous exfoliation, lead to fractionation of nanosheets of differing lateral width throughout the liquid volume without need for centrifugation. Nanosheet lateral dimension was also controlled by stoichiometry of the intercalant metal, with an optimum intercalant stoichiometry of 0.1 < x < 1.5 for Kx. Bi2Te3 for production of pristine nanomaterial. The chemical stability of the solution was investigated in relation to exposure to air, water, and heating, with a focus on tellurium impurities. Using SEM and TEM it was shown that tellurium impurities resulted from the presence of alkali metal polytellurides, which could be minimised by optimising the Kx. Bi2Te3 stoichiometry. However, the existence of nanosheets in a 16 month old solution demonstrates stability of these liquids when handled under inert conditions. Together these results demonstrate that this scalable method allows material manipulation and tailoring of nanosheet dimensions, whilst also giving weight to the argument that the liquids can be described as true thermodynamic solutions.
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Kottegoda, Mahavithanage Nilwala Svetlana. "Synthesis and exfoliation of layered double hydroxides : characterisation and applications." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613738.
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Mortezaee, Reza. "Computational Modeling of Graphene Oxide Exfoliation and Lithium Storage Characteristics." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1369612628.
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Wang, Weiling. "Development of Nanocomposites Using Graphene Synthesized by Solvent Exfoliation Method." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418217334.
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Winchester, Andrew. "LIQUID PHASE EXFOLIATION OF 2D LAYERED MATERIALS AND THEIR APPLICATION." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1417.
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In this work, several materials possessing a layered structure were investigated using a technique of exfoliation in liquid phase to produce few- to mono-layers of the material. Materials exfoliated in such a way included graphite, boron nitride, molybdenum disulfide and tungsten disulfide. Subsequent transmission electron microscopy and accompanying electron diffraction patterns revealed that few and mono layer forms of these materials have been realized through this exfoliation method. Ultraviolet-visible spectroscopy confirmed the shifting of the band gaps in molybdenum and tungsten disulfides that is predicted in reducing the number of layers of these materials and was also used to confirm the band gap of the boron nitride. As a potential application, exfoliated molybdenum disulfide was used in the construction of electrodes for electrical charge storage in an electrochemical double layer capacitor, or supercapacitor, style device. Cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy measurements were performed using three different electrolytes, which showed good capacitive behavior for these devices. Using the data from electrochemical impedance spectroscopy, equivalent circuit models were generated to represent the systems in different electrolytes. From this, it was determined that the capacitive behavior of these systems was partially diffusion limited.
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Bordes, Emilie. "Graphène dans des liquides ioniques : interactions aux interfaces, exfoliation, stabilisation." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC052.
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L'exfoliation en phase liquide du graphite est l'une des méthodes les plus prometteuses pour augmenter la production et la disponibilité commerciale du graphène. Le processus d'exfoliation peut être décrit, de manière conceptuelle, en quatre étapes: le contact du graphite avec le liquide, l'intercalation du solvant entre les feuillets de graphène, la dispersion du matériau à deux dimension et sa stabilisation en phase liquide. Comme les liquides ioniques peuvent être facilement obtenus avec différentes structures moléculaires et donc des propriétés physicochimiques modulables, ils ont été utilisés dans cette thèse comme milieux liquides pour l'exfoliation du graphite. Notre objectif est d'optimiser l'exfoliation du graphite à travers la compréhension des mécanismes moléculaires et des interactions impliquées dans chaque étape du processus. Les énergies interfaciale graphite-liquide ont été calculées à partir de tensions de surface et d'angles de contact mesurées entre des liquides ioniques et du graphite pour déterminer l'affinité de différents liquides à la surface du graphite. Afin d'étudier cette interface liquide - solide, des simulations en dynamique moléculaire ont été menées pour analyser l'organisation des liquides ioniques à la surface du graphite. De même, l'énergie libre nécessaire pour créer des cavités au sein du liquide ionique a été calculée.Des simulations moléculaires ont également été réalisées pour modéliser l'exfoliation d'un feuillet de graphène à partir de graphite en apportant une vue microscopique de l'intercalation des molécules de solvant. L'énergie nécessaire à l'exfoliation a pu être calculée en présence de différents liquides. Des composés polyaromatiques ont été considérés comme des modèles pour le graphène car ils peuvent être facilement obtenus purs, sans variabilité de structure, défauts ou groupes fonctionnels non contrôlés. Les enthalpies de dissolution du naphtalène, anthracène et pyrène dans différents liquides ioniques ont été mesurées par calorimétrie en solution et liées à leur solubilité. L'organisation des ions autour de ces composés modèles a été étudiée par simulation moléculaire et spectroscopie Infra-Rouge.Après l'exfoliation, les échantillons de graphène en suspension dans différents liquides ioniques ont été caractérisés expérimentalement en termes de taille de feuillets (microscopie électronique à transmission et microscopie à force atomique), nombre de couches de graphène (microscopie à force atomique, spectroscopie Raman), concentration totale (spectroscopie UV-visible) et pureté du matériau exfolié (spectroscopie de photoélectrons~X). Vingt liquides ioniques différents à base de cations imidazolium, pyrrolidinium et ammonium et d'anions bis (trifluorométhylsulfonyl)imide, triflate, dicyanamide, tricyanométhanide et méthylsulfate ont été testés. Les interactions moléculaires permettant d'établir de règles de conception pour les liquides ioniques capables d'exfolier les matériaux carbonés ont été identifiées. Le cation pyrrolidinium a montré des résultats prometteurs dans toutes les étapes du processus d'exfoliation, par rapport au cation imidazolium ou ammonium. La sélection d'un grand anion flexible a réduit l'énergie interfaciale avec le graphite, dispersé les nanocarbones en augmentant l'entropie du système et stabilisé le graphite exfolié en plus grande quantité. Un petit anion tel que le triflate semble être favorable à l'obtention de graphène, même si la taille des couches et leur quantité sont réduites. Un liquide ionique ayant une partie apolaire importante facilitera l'insertion et la dispersion du nanomatériau de carbone. Pour la stabilisation du graphite, les interactions alkyle-π et π- π sont décisivesThe liquid-phase exfoliation of graphite is one of the most promising methods to increase production and commercial availability of graphene. The exfoliation process can be conceptually described in four steps: the contact of the graphite with liquid, the intercalation of the solvent between layers, the dispersion of the two dimensional material, and its stabilization in the liquid-phase. Because ionic liquids can be easily obtained with chosen molecular structures and tunable physicochemical properties, they were used in this study as liquid media for the exfoliation of graphite. Our aim is to optimize the exfoliation of graphite through the understanding of the molecular mechanisms and of the interactions involved in each step of the process.The liquid-graphite interfacial energies from measured surface tensions and contact angles, between ionic liquids and pristine graphite surface, were used to determine the affinity of different liquids at the surface of graphite. In order to investigate this interface, molecular dynamics simulations were conducted to analyse the ordering of ionic liquids at the surface of graphite. The free energies necessary to create cavities inside the bulk ionic liquid have also been studied.Molecular simulations were also used to study the exfoliation of one graphene layer from a stack of graphite and hence provide a microscopic view of the intercalation of solvent molecules. The energies involved in the process have been calculated.Polyaromatic compounds were regarded as models for graphene as they can be easily obtained pure, without structure variability, defects or uncontrolled functional groups. Enthalpies of dissolution of polyaromatic hydrocarbons (naphthalene, anthracene and pyrene) in different ionic liquids were measured by solution calorimetry and related with their solubility. The ordering of the ions around this model compounds were studied by molecular simulation and spectroscopy Infra-Red.After exfoliation, samples of suspended graphene in different ionic liquids have been characterized experimentally in terms of flake size (using transmission electron microscopy and atomic force microscopy), number of layers (atomic force microscopy, spectroscopy Raman), total concentration (UV-visible spectroscopy) and purity of the exfoliated material (X-ray photoelectron spectrometry).Twenty different ionic liquids based on imidazolium, pyrrolidinium and ammonium cations and on bis(trifluoromethylsulfonyl)imide, triflate, dicyanamide, tricyanomethanide, and methyl sulfate have been tested. The molecular interactions have been identified thus allowing the establishment of design rules for ionic liquids capable of exfoliating carbon materials. The pyrrolidinium cation has shown promising results in all the steps of exfoliation process, compared to the imidazolium or ammonium cation. Selecting a large and flexible anion reduced the interfacial energy with graphite, dispersed the nanocarbons by increasing the entropy of the system and stabilized the exfoliated graphite in larger quantity. A small anion such as triflate appears to be favorable for obtaining graphene, whereas the size of the layers and their quantity is reduced. An ionic liquid having an important apolar portion will facilitate the insertion and dispersion of graphene layers. For the stabilization of graphite, the alkyl-π et π -π interactions are decisive
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Qiu, Xiaoyu. "Procédé d'exfoliation du graphite en phase liquide dans des laboratoires sur puce." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI056/document.
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L’exfoliation en phase liquide du graphite est un procédé simple susceptible de produire du graphène à faible coût. Ces dernières années, de nombreuses équipes ont exploité la cavitation acoustique et la cavitation hydrodynamique comme moyen d’exfoliation. La cavitation acoustique ne peut traiter qu’une quantité limitée de fluide et génère des défauts sur la structure du graphène,tandis que la cavitation hydrodynamique dans une solution en écoulement n’agit que localement pendant une durée très brève. Les équipes de recherche utilisant ce dernier procédé compensent cette brièveté en imposant à la solution chargée en graphite des différences de pression très fortes, et utilisent alors des infrastructures macroscopiques lourdes pour lesquelles il est difficile de distinguer le rôle du cisaillement de celui de la cavitation. Nous avons cherché à développer un nouveau procédé d’exfoliation basé sur l’utilisation de microsystèmes fluidiques capables de générer un écoulementcavitant avec un débit supérieur à 10 L/h pour une différence de pression modérée n’excédant pas 10 bar. Une nouvelle génération de laboratoires ‘sur puce’ a ainsi été imaginée et réalisée, permettant de traiter des solutions surfactées chargées en microparticules de graphite. Il est apparu que laconcentration solide et la durée de traitement sont des paramètres cruciaux pour l’efficacité du procédé. Par rapport à un écoulement monophasique laminaire microfluidique, l’écoulement cavitant produit plus de produits exfoliés et de graphène, avec un rendement de l’ordre de 6%. Ceci indique que l’implosion des bulles et la turbulence favorisent également les interactions entre particules. Ce procédé d’exfoliation microfluidique, qui ne nécessite une puissance que de quelques Watts, permet d’envisager à terme une production économe et écologique de graphène en suspensionLiquid phase exfoliation of graphite is a simple and low-cost process, that is likely to produce graphene. The last few years, many researchers have used acoustic or hydrodynamic cavitation as an exfoliating tool. Acoustic cavitation is limited to low volumes and defects are present on the graphenesheets ; hydrodynamic cavitation inside a flowing solution acts briefly. So, people are using big reactors running with high pressure drops, and it is difficult from a fundamental point of view to know the physical role of shear rate versus cavitation, in the exfoliation process. We have tried to develop a new process funded on hydrodynamic cavitation ’on a chip’, with flow rates above 10 L/h and pressure drop below 10 bar. A new generation of ’labs on a chip’ has been designed and performed, processing with aqueous surfactant graphite solutions. The solid concentration and the duration of the process have proved to be key parameters. Cavitating microflows have exhibited a better efficiency (up to ~6%) than laminar liquid microflows, for the production of graphene flakes. Collapsing bubbles and turbulence are also likely to enhance particles interactions. Such a microfluidic process, which requires an hydraulic power of a few Watt, makes possible a further low-cost and green production of graphene sheets
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Knick, Cory. "Modeling the Exfoliation Rate of Graphene Nanoplatelet Production and Application for Hydrogen Storage." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1347767528.
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Kosidowski, Maria-Laura S. "The preparation and characterisation of intercalation compounds." Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/584.
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Kelly, D. J. "Exfoliation and stress corrosion cracking of the aluminium-lithium alloy 8090." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302803.
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Golub, A. S., N. D. Lenenko, E. P. Krinichnaya, O. P. Ivanova, I. V. Klimenko, and T. S. Zhuravleva. "Nanostructured Films of Semiconducting Molybdenum Disulfide Obtained Through Exfoliation-Restacking Method." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35055.
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Preparing MoS2 films in mild conditions, using deposition of suspended MoS2 nanoplatelets onto the substrate is described. For this purpose, the nanosized MoS2 particles were obtained via restacking of MoS2 single layers produced by chemical exfoliation of bulk MoS2 crystals in liquid media. X-Ray diffraction study of the films showed that the basal planes of MoS2 crystallites are mainly oriented in the plane paral-lel to the substrate. Atomic force microscopy examination revealed the dependence of the film surface to-pography, as well as the roughness characteristics on the film thickness, which varied in the range of 0.03-2.2 m. Optical absorption spectra of the obtained MoS2 films were found to contain the same absorption bands as the spectra of thin natural MoS2 single crystals. Dark conductivity of the films was determined to be ~ 10–3 S∙сm–1 at 300 K. The present MoS2 films were found to be photosensitive in the range of 300-800 nm, providing the maximum value of photocurrent under photoexcitation at ~ 440 nm.
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Kim, Yunjo. "Interface engineering for exfoliation and integration of heteroepitaxial III-V films." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127049.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 78-82).
Compound semiconductors composed of III-V alloys play an essential role in modern optoelectronics and high frequency communication due to their superior optical properties and electron mobilities compared to silicon. However, the use of compound semiconductors devices has not seen the same level of wide-spread use compared to silicon owed in part to the significant cost of substrates required for processing III-V devices. To encourage the adoption of III-V technology, many strategies have been proposed to enable monolithic integration of III-V devices on Si to be compatible with Si CMOS technology. One approach to alleviate the cost of integrated III-V devices is to design a process that can selectively release the III-V device layer from its substrate for later heterointegration onto Si, while preserving the substrate for continuous reuse.
In this work, we introduce two novel processes for the exfoliation of III-V devices that also enable the reuse of the substrate for continuous processing. We first investigate a novel epitaxial process, termed 'remote epitaxy', that utilize graphene as a platform for epitaxial growth while also enabling the release of III-V devices. In our work, we have found that monolayer graphene interfaced on III-V substrate mildly screens the atomic interaction between the substrate and epitaxial film, enabling epitaxial films to grow with atomic registry to the parent substrate 'remotely' from the surface of graphene. In addition, remote epitaxially grown films could be readily released from the graphene interlayer by application of mechanical stress on the film, preserving the integrity of the substrate and device layer. The process of remote epitaxy and exfoliation of epitaxial films was demonstrated for a range of III-V compound semiconductors, GaAs, InP and GaP.
Secondly, we investigate an alternative strategy for thin-film exfoliation and wafer reuse based on a previously established controlled spalling process. In controlled spalling, mechanical stress is imparted onto a substrate by deposition of a stressed metal film in order to induce fracturing of the substrate at a specified depth from the surface. Using this process, the device layer can be released from the substrate at the sacrifice of damaging the substrate. In this work, we propose a non-destructive controlled spalling process that utilizes a mechanical sacrificial buffer layer between the substrate and device layer where selective fracturing can take place. Subsequent to exfoliation, the damaged buffer layer can be selectively etched to recover the original substrate for reuse.
This process, termed cleavage plane assisted exfoliation (CPEx), was applied to a GaAs/Ge/GaAs system utilizing Ge epitaxial film as the mechanical sacrificial buffer for the exfoliation of GaAs epitaxial films and reclamation of the original GaAs substrate.
by Yunjo Kim.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Schlierf, Andrea. "Graphene organic hybrid materials." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAF050/document.
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En 2004, le carbone, la base de toute vie connue sur Terre, a marqué les esprits une fois de plus: Les scientifiques de l’Université de Manchester au Royaume Uni ont pu extraire une matière carbonée complètement nouvelle, le graphène à partir d’un morceau de graphite comme celui qui compose les crayons. À l’aide d’un ruban adhésif, ils ont obtenu une paillette de carbone de l’épaisseur d’un atome seulement, à une époque où beaucoup pensaient qu’un matériaux cristallin aussi fin ne pouvait pas être stable. Le graphène parfait est une couche monoatomique composée d’atomes de carbone hybridés sp2, arrangés en structure alvéolaire; sa structure chimique particulière lui donne des propriétés physiques et chimique remarquable. Le graphène est devenu rapidement la matière carbonée la plus intensivement étudiée parmi celles «possiblement révolutionnaires», avec ses applications potentielles s’étendant de la microélectronique aux composites, des énergies renouvelables à la médecine. En 2010, Geim et Novoselov ont été récompensés par le prix Nobel de physique pour leurs «expériences révolutionnaires sur les matériaux bi-dimensionnels en graphène» qui a ouvert une nouvelle ère dans la science des matières carbonées.La chimie non-covalente du graphène est exploitée et étudiée dans cette thèse dans le but de concevoir, produire, transformer et caractériser les nouveaux matériaux hybrides graphène-organique. L’étendue de ce travail couvre les aspects mécanistiques de l’exfoliation en phase liquide du graphène avec des colorants, les aspects fondamentaux des interactions entre le graphène et le chromophore, en phase liquide et solide, ainsi que l’élaboration de suspensions hybrides de graphène dans le but d‘applications en électronique organique et dans les matériaux composites polymères fonctionnelsIn 2004, carbon, the basis of all known life on earth, has surprised once again: Researchers from University of Manchester, UK, extracted a completely new carbon material, graphene, from a piece of graphite such as is found in pencils. Using adhesive tape, they obtained a flake of carbon with a thickness of just one single atom, at a time when many believed it impossible for such thin crystalline materials to be stable. Pristine graphene is a mono-atomic sheet of, sp2 hybridized carbon atoms arranged in a honeycomb network; this particular chemical structure gives rise to its outstanding physical and chemical properties. Graphene rapidly became the most intensively studied among the ‘possibly revolutionary’carbon materials, with its potential applications reaching from microelectronics to composites, from renewable energy to medicine. In 2010, Geim and Novoselov were honored with the Nobel Prize in Physics for their “ground breaking experiments regarding the two-dimensional material graphene” that started a new era in the science of carbon materials.In this thesis we exploit and study the non-covalent chemistry of graphene to design, produce, process and characterize novel graphene organic hybrid materials. The scope of this work covers mechanistic aspects of graphene liquid phase exfoliation with dyes, fundamental aspects of graphene chromophore interactions in liquid and solid phase and the formulation of graphene hybrid suspensions towards application in organic electronics and functional polymer composite materials
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Bailey, J. A. "Studies on the effect of diet on exfoliation in the human colon." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596262.
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In this Thesis a non-invasive, reliable and reproducible technique for the isolation of exfoliated colonocytes from human stool was developed. Exfoliated colonocytes were shown histologically and immunocytochemically to be gut derived although the exact area of the large bowel from which they were derived was not clear. To investigate factors determining the numbers of recovered exfoliated cells, cells were obtained from three studies in which diet was carefully controlled in human volunteers over periods of 10-15 days. On analysis of variance, there was a significant individual effect (p < 0.001), indicating that the recovery technique was reliable. High polyunsaturated diets supplemented with vitamin E, and low starch high sugar diets were probably associated with increased cell recoveries (p < 0.002). In a fourth study, there was a clear effect of alcohol on increasing the numbers of cells recovered (p = 0.004). Transit time and stool weight were not reliably associated with increased cell recovery, but stool consistency was a significant (p < 0.010) factor influencing cell recovery in all three studies investigated. Exfoliated cells are a source of genomic DNA which was successfully isolated from 93.3% of samples, but only 11.7% of these extractions produced DNA yields of 3μg or more, so that quantification of adduct levels could not be determined by a sensitive immunoslot blot analysis. However, direct visualization of diet related adduct formation was possible, and could be quantified as percentages of cells staining positive for the N-nitroso compound (NOC) related adduct, O6 carboxymethyl guanine. A red meat diet significantly (p = 0.001) increased percentages of isolated cells staining positive for this adduct compared with a vegetarian diet, and there was a significant correlation (r = 0.66) between measures of faecal ATNC concentration and the percentages of positive cells on an individual basis.
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Xu, Bo. "Proton NMR relaxation investigations of particle exfoliation and distribution in polymer/clay nanocomposites." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/42936.
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In the past two decades polymer/clay nanocomposites (PCNs) have emerged as promising materials that exhibit remarkably improved properties when compared to conventional composites and pristine polymers. Such improvements strongly depend on the dispersion of clay nanoparticles in the polymer matrix. In spite of great efforts expended in characterizing clay dispersion, effective, simple and quantitative techniques are still needed. This work addresses this challenge by presenting new aspects of 1H solid-state NMR for quantifying clay dispersion in PCNs filled with clay containing paramagnetic ions. Employing these 1H solid-state NMR methods, some structure-processing-deformation relationships of PCNs were derived, and basic insights into nuclear relaxation and spin diffusion in PCNs were gained as well.
Detailed models and analyses were described for 1H spin-lattice relaxation in the presence of paramagnetic clays in PCNs. Relaxation recovery was analytically correlated to clay dispersion in two ways: one is the initial relaxation recovery which is related to clay surface area, and the other is the spin-lattice relaxation time which is related to interparticle spacing. These two NMR observables were employed to quantitatively observe the evolution of clay morphology in poly(propylene)/clay (PP/MMT) nanocomposites upon equibiaxial stretching, as well as upon in situ uniaxial deformation. The initial relaxation recovery was independently utilized to determine the polymer-clay interfacial surface area and the degree of clay exfoliation. We demonstrated the capabilities of our models in quantitatively characterizing several materials, including poly(vinyl alcohol), nylon 6, poly(å-caprolactone) (PCL), poly(lactic acid) (PLA) and PP nanocomposites. These results were used to examine the dependence of clay morphology upon processing (strain ratio, strain rate, temperature), deformation (extension), component characteristics (polymer molecular weight, clay surface modification) and clay content. Effects of paramagnetic Fe3+ concentration and external magnetic field strength on 1H spin-lattice relaxation in PCNs were also investigated and discussed. In particular, low field separates the initial relaxation recovery into two stages: one related to clay content and the other related to the polymer-clay interfacial surface area. The low field was observed to enhance the paramagnetic contribution to the spin-lattice relaxation rate, increasing its sensitivity to clay morphology. In addition, measurements of long-distance spin diffusion coefficients for a variety of polymers and paramagnetic characteristics of organically modified clay were explored. Overall, the utility of NMR relaxometry in characterizing PCNs has been significantly expanded and successfully demonstrated in this dissertation.
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Ma, Liguo, Maojun Zheng, Shaohua Liu, Qiang Li, Yuxiu You, Faze Wang, Li Ma, and Wenzhong Shen. "Synchronous exfoliation and assembly of graphene on 3D Ni(OH)2 for supercapacitors." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A30329.
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Nowadays, new approaches to fabricate high-performance electrode materials are of vital importance in the renewable energy field. Here, we present a facile synthesis procedure of 3D Ni(OH)2/graphene hybrids for supercapacitors via synchronous electrochemical-assisted exfoliation and assembly of graphene on 3D Ni(OH)2 networks. With the assistance of an electric field, the electrochemically exfoliated high-quality graphene can be readily, uniformly assembled on the surfaces of 3D Ni(OH)2. When serving as electrode materials for supercapacitors, the resulting 3D Ni(OH)2/graphene composites exhibited excellent specific capacitance (263 mF cm−2 at 2 mA cm−2), remarkable rate capability and super-long cycle life (retention of 94.1% even after 10 000 continuous charge–discharge cycles), which may be attributed to their highly porous, stable 3D architecture as well as uniform, firm anchoring of ultrathin graphene on their surfaces. Therefore, our approach provides a facile strategy for the large-scale synthesis of high-quality graphene based composites towards various applications.
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Ma, Liguo, Maojun Zheng, Shaohua Liu, Qiang Li, Yuxiu You, Faze Wang, Li Ma, and Wenzhong Shen. "Synchronous exfoliation and assembly of graphene on 3D Ni(OH)2 for supercapacitors." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-224917.
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Nowadays, new approaches to fabricate high-performance electrode materials are of vital importance in the renewable energy field. Here, we present a facile synthesis procedure of 3D Ni(OH)2/graphene hybrids for supercapacitors via synchronous electrochemical-assisted exfoliation and assembly of graphene on 3D Ni(OH)2 networks. With the assistance of an electric field, the electrochemically exfoliated high-quality graphene can be readily, uniformly assembled on the surfaces of 3D Ni(OH)2. When serving as electrode materials for supercapacitors, the resulting 3D Ni(OH)2/graphene composites exhibited excellent specific capacitance (263 mF cm−2 at 2 mA cm−2), remarkable rate capability and super-long cycle life (retention of 94.1% even after 10 000 continuous charge–discharge cycles), which may be attributed to their highly porous, stable 3D architecture as well as uniform, firm anchoring of ultrathin graphene on their surfaces. Therefore, our approach provides a facile strategy for the large-scale synthesis of high-quality graphene based composites towards various applications.
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Dalla, Francesca Kevin. "Exfoliation du graphène par voie liquide en vue d'une application aux contacts électriques." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS134/document.
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Le graphène est un matériau carboné exceptionnel de par ses propriétés électriques (mobilité électronique à température ambiante de 200 000 cm²V-¹s-¹), mécaniques (module d'Young de 1,5 TPA) et sa capacité à protéger un substrat de l’atmosphère. Cela en fait un candidat idéal comme revêtement de protection pour les dispositifs de connexion dont la partie active (le contact électrique) peut subir des dégradations sévères au cours du temps.. Un tel revêtement de protection doit en effet avoir des propriétés de robustesse et de conduction la plupart du temps antinomiques. La première étape de ce travail a consisté à mettre en œuvre un procède d’exfoliation en phase liquide afin de produire des suspensions de graphène ou de matériaux de type graphène. Différents type de caractérisations structurelles et électriques à l’échelle microscopique ont permis de déterminer des conditions d’exfoliation favorables en variant la nature du solvant et les conditions de sonication. Il s’est agi ensuite d’évaluer différents modes de dépôts permettant d’obtenir un revêtement de protection à partir de feuillets individuels. Les méthodes de trempé, évaporation, spray et filtration ont été caractérisées et ont montré leurs avantages et inconvénients. La méthode de filtration donne les films les plus couvrants mais pose le problème du transfert vers la surface à protéger : on a mis en évidence une contamination résiduelle difficile à éliminer. Les premiers résultats avec une méthode de spray industriel sans buse ont montré une grande réduction du frottement mais aussi la complexité des mécanismes régissant la qualité des dépôts. Les limites des différentes méthodes de dépôt pourraient être dépassées par l’utilisation de films composites polymère-graphèneGraphene is a special carbon material due to its electrical properties (electron mobility at room temperature 200 000 cm²V-¹s-¹), mechanical (Young modulus of 1.5 TPA) and ability to protect a substrate of atmosphere. This makes it an ideal candidate as a protective coating for connecting devices including the active portion (electrical contact) may suffer severe damage over time .. Such a protective coating must indeed have properties and robustness conducting most of the contradictory time. The first step of this work was to implement an exfoliation proceeds in the liquid phase to produce suspensions of graphene and graphene-like materials.Different types of structural and electrical properties at the microscopic scale have determined favorable conditions for exfoliation by varying the nature of the solvent and conditions of sonication. He then acted deposits evaluate different methods to obtain a protective coating from individual sheets. The methods of dip coating, drop casting, spray and filtration have been characterized and have shown their advantages and disadvantages. The filtration method gives the most covering films, but the problem of the transfer to the surface to be protected: it showed residual contamination difficult to remove. The first results with an industrial spray without nozzle method showed a large reduction in friction but also the complexity of the mechanisms governing the quality of deposits. Limitations of different deposit methods could be exceeded by the use of graphene-polymer composite films
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Haar, Sébastien. "Supramolecular approaches to graphene : generation of functional hybrid assemblies." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAF040/document.
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Cette thèse démontre le potentiel dont dispose l’exfoliation en phase liquide du graphite dans le but d’obtenir des feuillets de graphène dispersés dans un solvant organique. Ainsi le mécanisme d’exfoliation a été étudié en profondeur, en particulier, l’influence de plusieurs paramètres (température, puissance et solvants). Le choix de ses paramètres se montre crucial dans le contrôle du procédé, et pour l’obtention des feuillets de graphène ayant une taille ciblée. Il est donc possible de fabriquer des nano-feuillets de quelques dizaines de nanomètre qui en plus possèdent des propriétés de photoluminescence.Dans le but de comprendre le mécanisme d’exfoliation en phase liquide assistée par des molécules, une nouvelle approche a été mise au point : l’approche supramoléculaire. Cette approche se base sur l’utilisation de surfactants d’un nouveau type. En effet, les molécules sélectionnées possèdent une longue chaine alkyle. Cette chaine s’adsorbe sur la surface du graphène et permet de stabiliser les feuillets lors de l’exfoliation. L’influence de la taille de la chaine alkyle de ces molécules lors de l’exfoliation a été vérifiée. De plus, ces molécules ont été équipées de différentes fonctions supramoléculaires afin qu’elles puissent former des dimères sur la surface du graphène. L’ajout de ces molécules augmente non seulement le rendement d’exfoliation mais aussi le nombre de mono-feuillets présents dans ces dispersions. Ces dispersions présentent des propriétés conductrices lorsqu’elles sont déposées sur des substrats. Une nouvelles méthode de déposition a été mise au point afin d’améliorer et d’augmenter la conductivité mais aussi le pourcentage de transparenceThis thesis demonstrates the potential of exfoliation of the graphite in the liquid phase in order to obtain graphene sheets dispersed in an organic solvent. Thus the exfoliation mechanism has been studied, in particular, the influence of several parameters (temperature, power and solvents). The choice of parameters is actually crucial for the control of the process, and to obtain graphene sheets having a targeted size. It is therefore possible to manufacture nanosheets of several tens of nanometers, which in addition exhibit photoluminescence properties.In order to understand the exfoliation mechanism in liquid phase assisted by molecules, a new approach has been developed: the supramolecular approach. This approach is based on using a new type of surfactant. Indeed, the selected molecules carry a long alkyl chain. This chain is adsorbed on the surface of graphene and can stabilize the sheets during exfoliation. The influence of the size of the alkyl chain of these molecules during exfoliation was verified. Furthermore, these molecules have been equipped with various supramolecular functions, which can form dimers on the surface of graphene. The addition of these molecules not only increases exfoliation performance but also the number of mono-layers present in these dispersions. These dispersions have conductive properties when deposited on substrates. A new deposition method was developed to enhance and increase conductivity but also the percentage of transparency
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Harju, Mika. "Exfoliation glaucoma : studies on intraocular pressure, optic nerve head morphometry, and ocular blood flow." Helsinki : University of Helsinki, 2001. http://ethesis.helsinki.fi/julkaisut/laa/kliin/vk/harju/.
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Herraiz, Michael. "Graphène et fluorographène par exfoliation de graphite fluoré : applications électrochimiques et propriétés de surface." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC094/document.
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Sa conductivité électronique ou encore sa transparence optique sont autant de propriétés physico-chimiques singulières du graphène qui expliquent le nombre accru de méthodes d’exfoliation de précurseurs graphitiques développées pour l’obtention de ce matériau. Pour palier à l’utilisation d’un oxyde de graphite/graphène caractérisé par une chimie de surface mal maitrisée, des graphites fluorés, de cristallinité mais aussi de concentration en fluor variables, ont été préparés par fluoration de graphite sous fluor moléculaire pur après optimisation des paramètres. Les précurseurs, que ce soit par fluoration dynamique ou statique, ainsi obtenus ont été caractérisés finement : diffraction des rayons X, spectroscopies IR et Raman et leur texture sondée par Microscopie Electronique à Balayage et à Transmission. Suite à cela, trois méthodes d’exfoliation ont été mises en place, basées sur des mécanismes différents : i) une exfoliation par choc thermique, déjà connue mais dont les mécanismes de décomposition ont été affinés dans cette étude, ii) une exfoliation en voie liquide, avec l’utilisation pour la première fois d’un graphite fluoré pour la synthèse de graphène fluoré multi feuillets par voie électrochimique pulsée, et enfin iii) une méthode originale, peu conventionnelle, basée sur l’interaction laser femtoseconde/graphite hautement fluoré pour induire des mécanismes de réduction contrôlée, et surtout d’exfoliation de la matrice. Ces méthodes ont permis de mettre en évidence l’intérêt de la présence de fluor dans la course actuelle pour la synthèse de graphène, et ont montré l’obtention de matériaux graphéniques,possédant une fonction résiduelle fluorée intéressante pour certaines applicationsIts electronic conductivity or its optical transparency are unequaled physicochemicalproperties of graphene which explain the increased number of exfoliation methods based ongraphitic precursors to obtain this material. To overcome the use of a graphite/graphene oxidecharacterized by a poorly controlled surface chemistry, graphite fluorides, with variablecrystallinity and also fluorine concentration, were prepared by fluorination of graphite under puremolecular fluorine atmosphere after optimization of the process parameters. The obtainedprecursors, whether by dynamic or static fluorination, were characterized : X-Ray diffraction, FTIRand Raman spectroscopies for the structure, and their texture probed by Scanning andTransmission Electron Microscopy. After that, three methods of exfoliation were developed, basedon different mechanisms: i) a thermal shock, already known but decomposition mechanisms wererefined in this study, ii) an exfoliation within liquid medium by pulsed electrochemical treatment,using for the first time a fluorinated graphite for the synthesis of few-layered fluorinated grapheneand finally iii) an unconventional method, based on the interaction between femtosecond laser andhighly fluorinated graphite to induce mechanisms like controlled reduction, and especially for thisstudy exfoliation of the matrix. These methods have permit to highlight the interest of fluorine inthe current race for the synthesis of graphene, and have shown the production of graphenematerials, having an interesting fluorinated residual functionalization for some applications
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Hervé, Lucile. "L’exfoliation des cellules épithéliales mammaires : mécanismes de régulation, rôle dans la détermination du nombre de cellules dans la glande mammaire et influence sur la production laitière." Thesis, Rennes, Agrocampus Ouest, 2017. http://www.theses.fr/2017NSARB304/document.
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Le lait est produit par les cellules épithéliales mammaires (CEM). La quantité de lait produit est déterminée par le nombre de CEM et leur activité métabolique. Le nombre de CEM dépend de l’équilibre entre la prolifération cellulaire et l’apoptose. Le processus d’exfoliation, défini comme le décrochage des CEM de l’épithélium mammaire et leur évacuation dans le lait, a été proposé comme participant aussi à la régulation du nombre de CEM. Les objectifs de cette thèse étaient d’identifier les mécanismes biologiques impliqués dans la régulation de ce processus et d’étudier son rôle dans la régulation du nombre de CEM et son influence sur la production laitière. Nos résultats montrent qu’une partie des CEM est exfoliée entre deux traites consécutives.Cependant, la majorité des CEM sont exfoliées au moment de la traite suite à la contraction des cellules myoépithéliales et à la perte d’intégrité de l’épithélium induites par la décharge d’ocytocine. Le cortisol, au contraire, participerait à la restauration de l’intégrité de l’épithélium mammaire après la fin de la traite et limiterait l’exfoliation. Nous avons montré que les variations du taux d’exfoliation étaient opposées aux variations de production laitière dans le cas d’une restriction alimentaire et après la fin d’un traitement à l’hormone de croissance mais pas dans le cas d’un changement de fourrage, de l’inhibition de la prolactine et pendant un traitement à l’hormone de croissance. Le processus d’exfoliation des CEM participe donc à la régulation de la production laitière mais pas de façon systématiqueMilk is synthesized by mammary epithelial cells (MEC). Milk yield is determined by the number of MEC in the mammary gland and the metabolic activity of these cells. It is well known that MEC number depends on the balance between cell proliferation and apoptosis. The MEC exfoliation process, defined as the shedding of MEC from the mammary epithelium into milk, is another process that might participate in the regulation of MEC number in the udder and thus in milk yield variations. The aims of this thesis were to identify the mechanisms that regulate the exfoliation process and to study the potential role of this process in regulating the number of MEC and milk yield.Our results showed that some MEC are exfoliated between milkings. Most of the MEC are, however, exfoliated during milking as a consequence of the myoepithelial cell contraction and the disruption of mammary epithelium integrity, both of which are caused by milking-induced oxytocin release. Cortisol may play a role in limiting MEC exfoliation by restoring mammary epithelium integrity after milking. We showed that the exfoliation process participates in regulating milk yield during feed restriction and after a treatment with bovine growth hormone but did not participate in regulating milk yield when forage in the ration was changed, when prolactin secretion was inhibited, or during a treatment with bovine growth hormone. These results suggest that the MEC exfoliation process likely participates in regulating milk yield but not systematically
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Etmimi, Hussein Mohamed. "New approaches to the synthesis and exfoliation of polymer/functional graphene nanocomposites by miniemulsion polymerization." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20119.
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Thesis (PhD)--Stellenbosch University, 2012.ENGLISH ABSTRACT: New methods are described for the synthesis of polymer/graphite nanocomposites using the miniemulsion polymerization process. Natural graphite was functionalized by oxidation to produce graphite oxide (GO) nanosheets. Poly(styrene-co-butyl acrylate) (poly(St-co-BA)) nanocomposite latices containing GO nanosheets were successfully synthesized using miniemulsion as a one-step nano-incorporation technique. The approach followed included expanding the GO nanosheets in situ during the miniemulsification step and then polymerizing the monomers in the presence of these expanded nanosheets. Styrene (St) and butyl acrylate (BA) were mixed with GO and then emulsified in the presence of a surfactant and a hydrophobe to afford pre-miniemulsion latex particles. The stable pre-miniemulsions were then polymerized to yield poly(St-co-BA)/GO nanocomposite latices. The polymerization proceeded with relatively high monomer conversion and produced stable nanocomposite latex particles. The nanocomposites exhibited mainly an intercalated morphology, irrespective of the percentage of GO filler loading. The synthesis of exfoliated polymer nanocomposites made with modified GO is described. GO was modified with a surfmer (reactive surfactant), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), which widened the gap between the GO nanosheets and facilitated monomer intercalation between its nanogalleries. The AMPS-modified GO was used for the synthesis of poly(St-co-BA)/GO nanocomposite latices using a similar miniemulsion procedure. The obtained nanocomposites had exfoliated morphologies and the GO nanosheets were largely exfoliated (about 2–5 nm thick) in the resultant films obtained from the synthesized nanocomposite latices. The synthesized nanocomposites had enhanced thermal and mechanical properties compared to pure polymer as a result of the presence of AMPSmodified GO. Furthermore, the nanocomposites made with AMPS-modified GO had better thermal and mechanical properties than the unmodified GO. The mechanical properties of the nanocomposites depended on the AMPS-modified GO loading in the nanocomposites. The synthesis of polystyrene/GO (PS-GO) nanocomposites using the reversible additionfragmentation chain transfer (RAFT) mediated polymerization method is also described. The GO was synthesized and immobilized with a RAFT agent to afford RAFT-functionalized GO nanosheets. The RAFT-immobilized GO was used for the synthesis of PS nanocomposites in a controlled manner using miniemulsion polymerization. The molar mass and dispersity of the PS in the nanocomposites depended on the amount of RAFT-grafted GO in the system, in accordance with the features of the RAFT-mediated polymerization. X-ray diffraction and transmission electron microscopy analyses revealed that the nanocomposites had exfoliated morphology, even at relatively high GO content. The thermal stability and mechanical properties of the PS-GO nanocomposites were better than those of the neat PS polymer. Furthermore, the mechanical properties were dependent on the modified-GO content (i.e., the amount of RAFT-grafted GO). The hydrophobicity and barrier properties of the resulting films prepared from the synthesized poly(St-co-BA)/GO nanocomposite latices to water and water vapor were also investigated. The hydrophobicity of the synthesized nanocomposite films was determined using contact angle measurements. The water permeability was determined by measuring the moisture vapor transmission rate of the films. The GO in the nanocomposites was reduced to its original form (i.e., graphite), and the barrier properties of the obtained nanocomposite films were determined and compared to films containing the unmodified GO (as-prepared GO). Results showed that reduction of GO had a significant impact on the water affinity of the resultant films prepared from the synthesized nanocomposite latices. The presence of reduced-GO (RGO) instead of unmodified GO in the miniemulsion formulation significantly improved the hydrophobicity and barrier properties of the final films to water. However, the barrier properties of the nanocomposites were unaffected by the amount of RGO in the nanocomposites.
AFRIKAANSE OPSOMMING: Nuwe metodes is beskryf vir die sintese van polimeer/grafiet nanosamestellings deur gebruik te maak van die miniemulsie polimerisasieproses. Natuurlike grafiet is gefunksionaliseer dmv oksidasie om grafietoksied (GO) nanovelle te vorm. Polistireen-ko-butielakrilaat (poli[St-ko- BA]) nanosamestellinglatekse wat GO nanovelle bevat is suksesvol gesintetiseer deur gebruik te maak van miniemulsie polimerisasie as ‘n een-stap nano-insluitingstegniek. Die benadering wat gevolg is het die uitbreiding van die GO nanovelle, in situ, gedurende die miniemulsifiseringstap behels, gevolg deur die polimerisasie van die monomere in die teenwoordigheid van hierdie uitgebreide nanovelle. Stireen (St) en butielakrilaat (BA) is met GO gemeng en daarna emulgeer in die teenwoordigheid van ‘n seepmiddel (surfactant) en ‘n hidrofoob om pre-miniemulsielateksdeeltjies te lewer. Die stabiele pre-miniemulsies is gepolimeriseer om poli(St-ko-BA)/GO nanosamestellinglatekse te vorm. Die polimerisasie het met redelike hoë monomeeromskakeling verloop en het stabiele nanosamestellinglateksdeeltjies gelewer. Hierdie nanosamestellings het hoofsaaklik geïnterkaleerde morfologie, onafhanklik van die persentasie GO vullers, getoon. Die sintese van afgeskilferde polimeernanosamestellings berei met gewysigde GO is beskryf. GO is gewysig met ‘n ‘surfmer’ (reaktiewe seepmiddel), 2-akrielamido-2-metiel-1- propaansulfoonsuur (AMPS), wat die gapings tussen die GO nanovelle vergroot het en die monomeer interkalering tusssen sy nanogange fasiliteer. Die AMPS-gewysigde GO is gebruik vir die sintese van poli(St-ko-BA)/GO nanosamestellinglatekse deur gebruik te maak van ‘n soortgelyke miniemulsie prosedure. Die nanosamestelling sό verkry het ‘n afgeskilferde morfologie getoon en die GO nanovelle was grootendeels afgeskilfer (ongeveer 2–5 nm dik) in die films wat berei is van die gesintetiseerde nanosamestellinglatekse. Laasgenoemde het verhoogde termiese en meganiese eienskappe gehad in vergelyking met die suiwer polimeer, as gevolg van die teenwoordigheid van die AMPS-gewysigde-GO. Die meganiese eienskappe van die nanosamestellings hang af van persentasie AMPS-gewysigde GO vullers in die nanosamestellings. Die sintese van PSt/GO nanosamestellings dmv die omkeerbare-addisie-fragmentasieoordrag- (OAFO-, Eng. RAFT-) bemiddelde polimerisasie metode is ook beskryf. Die GO is berei en geïmmobiliseer met ‘n RAFT verbinding om GO nanovelle met RAFT funksionaliteit te lewer. Die RAFT-geïmmobiliseerde GO is gebruik vir die sintese van PSt nanosamestellings in ‘n gekontrolleerde manier mbv miniemulsie polimerisasie. Die molêre massa en dispersie van die PSt in die nanosamestellings hang af van die hoeveelheid RAFTgeënte GO in die sisteem, in ooreenstmming met die kenmerke van RAFT-bemiddelde polimerisasie. X-straaldiffraksie en transmissie-elektronmikroskopie analises het bewys dat die nanosamestellings, selfs by relatiewe hoë GO inhoud, ‘n afgeskilferde morfologie gehad het. Die termiese stabiliteit en meganiese eienskappe van die PSt-GO nanosamestellings was beter as dié van die suiwer PSt polimeer. Verder was die meganiese eienskappe afhanklik van die gewysigde-GO-inhoud (dws, die hoeveelheid RAFT-geënte-GO). Die hidrofobisiteit en spereienskappe van die films berei vanaf die gesintetiseerde poli(St-ko- BA)/GO nanosamestellinglatekse teenoor water en waterdamp is ook ondersoek. Die hidrofobisiteit is ondersoek deur gebruik te maak van kontakhoekmeting. Die waterdeurlaatbaarheid is bepaal deur die waterdampoordragtempo van die films te bepaal. Die GO in die nanosamestellings is gereduseer tot sy eenvoudigste vorm (grafiet) en die spereienskappe van die nanosamestellingfilms is bepaal en vergelyk met die films wat die ongewysigde GO bevat het. Resultate het getoon dat reduksie van GO ‘n groot invloed gehad het op die wateraffiniteit van die films wat berei is vanaf die gesintetiseerde nanosamestellinglatekse. Die teenwoordigheid van die gereduseerde-GO (RGO) in plaas van die onveranderde GO in die miniemulsie formulasie het die hidrofobisiteit en spereienskappe van die finale films, teenoor water, baie verbeter. Die spereienskappe van die nanosamestellings is egter nie beïnvloed deur die hoeveelheid RGO in die nanosamestellings nie.
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Ahmed, Shafkat. "Interactions of Gas Particles with Graphene during Compressible Flow Exfoliation: A Molecular Dynamics Simulations Study." University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1588278674983556.
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