Letteratura scientifica selezionata sul tema "Covalent functionalisation"

The thermal and electrical properties of a polymer nanocomposite are highly dependent on the dispersion of the CNT filler in the polymer matrix. Non-covalent functionalisation with a PVP polymer is an excellent driving force towards an effective dispersion of MWNTs in the polymer matrix. It is shown that the PVP molecular weight plays a key role in the non-covalent functionalisation of MWNT and its effect on the thermal and electrical properties of the polymer nanocomposite is reported herein. The dispersion and crystallisation behaviour of the composite are also evaluated by a combination of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC).

Chemical functionalisation is one of the most active areas of graphene research, motivated by both fundamental science and the opportunities to adjust or supplement intrinsic properties. There is increasing interest in understanding and controlling the locus of reaction.

Here we demonstrate the application of a dynamic covalent chemistry methodology for the synthesis of [2]- and [3]-rotaxanes not only in solution, but also on solid supports with 65% rotaxane functionalisation of the polymer resins observed.

In this paper, a renewable carbon catalyst was developed based on the non-functionalisation method. Three different pyrolysis temperatures at 400°C (SC400), 500°C (SC500) and 600°C (SC600) were used to prepare amorphous carbon. The non-covalent functionalisation was carried out by 1-pyrenesulfonic acid (1-PSA) in organic solvents such as ethanol, heptane and dimethylformamide (DMF), and characterised by total acidity, TGA, FT-IR, SEM-EDX, particle size, BET Porosity, and XRD. The total acidity was found to be 1.58 mmol/g for catalyst SC400. The functional groups –COOH, –OH, –SO3H and π-π stacking were detected. The amorphous carbon was stable until 500°C. The sulphur content was found to be 0.013mmol/g for SC400. This research approach focused on the direct interaction of carbonaceous support with pyrene moieties and terminal groups (–SO3H) acting as catalytic acid sites that open a new way to be explored for performing liquid-phase heterogeneous acid-catalysed reactions.Keywords: Non-covalent functionalization, Amorphous carbon, sulfonation, surface morphology, D-Glucose carbon

AbstractFor functionalisation of a representative C30 fullerene nanostructure by pyrrole-n-carboxylic acid (PnCA; n=2, 3) their stabilities and properties were investigated based on density functional theory calculations. Parallel calculations were also done for C60 fullerene as evidence for comparing the results. Non-covalent interactions are considered to make the functionalised structures. In contrast with the spherical shape of C60, the shape of C30 fullerene is elliptical; therefore, the functionalisation processes were done for both axial and equatorial elliptical positions (AC30 and EC30). The results indicated that both the positions of C30 have almost equivalent chances to be functionalised by PnCA; but functionalisation by P2CA is slightly more favourable than P3CA, either for C60. The illustrated molecular orbitals’ distributions indicated that the direction of charge transfer could be considered from PnCA counterparts to fullerene counterparts. The molecular properties indicated more reactivity for C30 than for C60 fullerene. Finally, the atomic scale quadrupole coupling constants indicated different roles for N and O atoms of PnCA in the functionalised models.

Des efforts importants sont déployés pour manipuler le graphène avec un contrôle à la fois local et chimique, afin d’ajuster ses propriétés électroniques. Nous avons utilisé la microscopie à force atomique (AFM) pour étudier la lithographie par sonde locale catalytique (cSPL) afin de fonctionnaliser de manière covalente du graphène supporté. Nous avons montré que le graphène est coupé pour des forces de pointe plus petites dans un liquide que dans l'air. L'époxydation par cSPL avec un système catalytique à base de manganèse s’est montrée inefficace, mais le balayage AFM a ouvert la voie à l'étude des repliements du graphène par la méthode "cut and fold". En mode contact, le balayage AFM a formé des repliements nanométriques de graphène, en coupant et poussant avec la pointe des zones micrométriques de quelques couches de graphène (FLG). Les microscopies électronique à transmission et Raman ont révélé la création de graphène multicouche (MLG) turbostratique, avec une distance entre plan de 0.36 nm, et la présence de défauts linéaires dus aux bords des repliements. La méthode "cut and fold" transforme le FLG initial en un type de MLG particulier, qui a des propriétés du graphène suspendu et empilé aléatoirement, et qui est électroniquement différent du FLG. Enfin, nous avons effectué des tests préliminaires de la déformation réversible du graphène par l'isomérisation E/Z photoinduite des azobenzènes greffés formant des structures pontées. Nous avons confirmé la fonctionnalisation par Raman et XPS et observé des changements de résistance induits par irradiation UV
Many efforts are put in manipulating graphene with local and chemical control to tune its electronic properties, enabling its application in device fabrication. We have used atomic force microscopy (AFM) to investigate catalytic scanning probe lithography (cSPL) as a method to functionalise covalently a supported chemical vapour deposition graphene. We have shown that supported graphene is cut at smaller tip forces in liquid than in air. So far, the cSPL epoxidation with a manganese-based catalytic system was inefficient to functionalise graphene, but AFM scanning has opened the way for studying graphene folding by the “cut and fold” method. We have explored contact mode AFM scanning of micrometric zones of few-layer graphene (FLG), where graphene is cut and pushed at the top of scanned zones, forming wide folded stacks. Transmission electron microscopy and Raman analyses have revealed the creation of a turbostratic multilayer graphene (MLG), consisting of folded stacks of 10–20 layers, with an interlayer distance of 0.36 nm. Linear defects are introduced by folding, likely due to loops and folding edges. Thus, the cut and fold method creates a particular kind of MLG from initial FLG, sharing properties of free-standing and free-stacked graphene, and electronically different from the FLG. Finally, we have done preliminary tests of the reversible distortion of graphene by covalently grafted bridged azobenzene structures, using photoinduced E/Z isomerisation. We have confirmed functionalisation by Raman and XPS and observed UV-induced electric resistance changes

Carbon nanotubes (CNTs) have attracted considerable research interest owing to their exciting properties and potential for a wide range of applications. However, major challenges must be overcome before these applications can be realised. As-prepared CNT material contains a significant proportion of impurities, such as amorphous carbon, fullerenes and metal catalyst particles. The raw CNT material must be purified before the CNTs can be studied and utilised. Also, CNTs tend to aggregate into bundles or "ropes”, and have poor solubility in common solvents, making their handling and processing extremely difficult. Also, many applications require individually separated CNTs. To improve the solubility of CNTs, and amenability to processing on a large scale, chemical modification of CNT surfaces is necessary. To this end, non-covalent as well as covalent strategies have been developed. However, chemical modification may perturb the electronic structure of CNTs, thereby compromising their interesting properties. The challenge, therefore, is to develop chemical modification routes that improve CNT solubility while not seriously affecting their properties. In this work, we firstly study the problem of purification of as-produced CNT material. We have resolved a major controversy concerning the use of oxidising acids for purifying CNTs, which has profound implications for the spectroscopy and subsequent chemical modification of the CNTs. Secondly, we have developed a route for the non- covalent modification of CNTs by tertiary phosphines. This method has the advantages of significantly improving the solubility of CNTs in organic solvents while being extremely simple, not seriously perturbing the CNT electronic structure, as well as not rendering large areas of the CNT inaccessible^ Thirdly, we describe a method for the covalent derivatisation of CNTs based on reduction, followed by electrophilic substitution. This route is considerably more facile and versatile than other covalent functionalisation methods reported to date, and does not cause significant disruption of the CNT electronic structure. Finally, we demonstrate the covalent attachment of formyl (-CHO) groups to CNT walls, which could potentially open the gateway for a plethora of of coupling and modification reactions.

1D and 2D graphitic materials (carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs)) are of great interest due to their extraordinary electrical, thermal, mechanical and optical properties rarely found in bulk materials. The transfer of such properties to polymers has been limited and the development of scalable, cost-effective, multi-functional composite materials not fully realised. Polymers filled with 1D and 2D graphitic nanomaterials have uses in a wide range of applications and industries ranging from aerospace and automotive to personal care and high-tech products. Growing global economic development has sharply increased the world’s energy needs and in particular, our energy storage needs. In addition, they have potential applications in electronics, sensors and energy conversion. Another application in the area of personal care has shown that CNT-polymer composites can be used to speed up the process of bone-regeneration by being used as tissue scaffold materials. An application of interest is to use graphitic nanomaterials to produce composites with high mechanical performance (stiffness and strength) with low filler quantity providing innovative light-weighting solutions. Further potential applications of 1D and 2D graphitic nanomaterials include; touch screens, capacitors, spintronic devices, fuel cells, conductive films, high frequency circuits and flexible electronics. The development of such innovative materials requires the nanofiller to be homogenously dispersed within the polymer matrix, e.g. poly(propylene)(PP). The formation of an interconnected filler network structure at a low percolation threshold will result in the enhancement of electrical and thermal conductivity. In addition, efficient interfacial adhesion and stress transfer between filler and polymer results in improved mechanical strength and stiffness. However, poor compatibility between filler and the PP matrix prevents efficient homogenous dispersion and network formation. To address this major technical challenge, the use of a polymer compatibiliser which non-covalently functionalised graphitic nanomaterials was explored. By way of example, poly(lauryl acrylate) P[LA] was selected based upon its known compatibility with PP and it was proposed that it would also non-covalently functionalise such fillers via CH-π wrapping. P[LA] was synthesised using controlled living radical polymerisation methods and was shown to both be thermally stable for extrusion and physisorbed onto the surface of MWCNTs. For composites of PP, P[LA] and either MWCNTs or GNPs evidence was obtained confirming that P[LA] improved filler dispersion however, the most notable observation was a significant reduction in Tg of PP which was associated with P[LA] plasticising PP. Further polymer compatibilisers based on copolymers (statistical and block) of P[LA] and poly(2-phenyl ethyl acrylate) P[2PEA] where also synthesised and their potential to non-covalently functionalise CNTs and GNPs via both CH-π wrapping and π-π stacking examined. A range of characterisation techniques were employed to thoroughly understand the behaviour of these compatibilisers when added to composites of MWCNTs/GNPs and PP. Evidence for π-π stacking of P[2PEA] onto the surface of both graphitic fillers was observed from extensive electron microscopy observations. The potential of P[LA-co-2PEA] block copolymers as compatibilisers for 1D and 2D graphitic materials and PP was proven. The use of poly(acrylate)s as compatibilisers to assist the dispersion of 1D and 2D graphitic nanofillers in a PP has proven to be a concept with limited potential to alter the mechanical, electrical and thermal properties of polymers. The excellent thermal stability demonstrated by poly(acrylate)s for the purpose of melt blending with PP provides scope for further work through alternative functionalisation strategies e.g. covalent functionalisation. Throughout the project, the discussion has centred around the use of P[LA] and P[2PEA] due their potential to adsorb onto surface of 1D and 2D graphitic fillers and promote their dispersion in a PP matrix however, further work should investigate a range of poly(acrylate)s with various structures, chemistries, molecular weights and dispersities. For example, the use poly(acrylate)s with longer side chains such as poly(octadecyl acrylate) or poly(acrylate)s containing aromatic side chains with a greater number of benzene rings such as pyrene, for example pyrene acrylate. It is evident that the viscosity of the compatibilising polymer influences the extent of dispersion of the compatibiliser in the PP and matrix and therefore, it would be interesting to investigate if there is a correlation between the viscosity of the polymer compatibiliser and the extent of its dispersion in the PP matrix. GNPs with a greater aspect ratio are predicted to achieve percolation at lower loadings, increase electrical and thermal conductivity as well as improve the mechanical properties. Additionally, it would be interesting to explore what GNP quantity is required to achieve electrical and rheological percolation with the same type of GNPs and correlate those findings with graphenes with different aspect ratios to understand the role of flake dimensions. It is clear, P[LA] is not particularly successful in compatibilising the GNPs used in this study. In addition, it would useful to conduct dynamic cross-polarized optical microscopy and WAXS/SAXS scattering experiments during heating and cooling to investigate transcrystallinity phenomena at the interface between GNPs and the PP matrix.

L’objectif de ce travail est d’élaborer des matériaux composites modèles nanotubes de carbone/polymères permettant de tirer profit des propriétés des nanotubes de carbone à l’échelle macroscopique. L’obtention de tels matériaux nécessitant une fonctionnalisation homogène entre les nanotubes de carbone et les polymères, les nanotubes de carbone utilisés doivent être individuels et de même réactivité chimique, donc de même diamètre. Ainsi, ils doivent être synthétisés par CVD par des nanoparticules catalytiques monodisperses et supportées. Dans la première partie, nous avons élaboré une nouvelle méthode générique de synthèse de nanoparticules d’oxydes métalliques supportées. Nous avons principalement détaillé la synthèse de nanoparticules de Fe2O3 dont la distribution en taille est de 1.1 ± 0.3 nm. Dans la deuxième partie, après avoir étudié la stabilité thermique de ces nanoparticules, nous les avons utilisées pour catalyser la croissance des nanotubes de carbone monofeuillets individuels par CVD. La caractérisation des nanotubes obtenus par Raman indique une distribution en diamètre exceptionnellement étroite de 1.27 ± 0.15 nm. Dans la troisième partie, nous avons tout d’abord étudié la mise en solution des nanotubes de carbone par fonctionnalisation non covalente avec un polymère hydrosoluble le POE portant un motif pyrène en bout de chaîne et mis en évidence un phénomène de déplétion qui limite la solubilisation des nanotubes. Nous avons ensuite élaboré des matériaux composites nanotubes de carbone/rrP3HT par fonctionnalisation covalente et non covalente et nous avons étudié l’efficacité de séparation de charge dans les deux cas de fonctionnalisations
The aim of this work is to develop composite materials carbon nanotubes/polymers to take advantage of properties of carbon nanotubes at macroscopic scale. To get such materials, homogeneous functionalization between carbon nanotubes and polymers is required, carbon nanotubes must be individual with the same chemical reactivity, therefore the same diameter. Thus, they must be synthesized by CVD from monodispersed and supported catalyst nanoparticles. In the first part, we developed a new universal method for the synthesis of metal oxide supported nanoparticles. We mainly detailed the synthesis of Fe2O3 nanoparticles with size distribution of 1.1 ± 0.3 nm. In the second part, after studying the thermal stability of these nanoparticles, we used them to catalyze the growth of individual single wall carbon nanotubes by CVD. The caracterisation of the obtained nanotubes by Raman show exceptionally narrow diameter distribution of 1.27 ± 0.15 nm. In the third section, we first studied the dispersion of carbon nanotubes by noncovalent functionalization withhydro-soluble polymer POE with pyrene as end group and revealed depletion phenomena that limit the solubilization of nanotubes. Then we developed composite materials carbon nanotubes/rrP3HT by covalent and noncovalent functionalisation and we studied the efficiency of charge separation in both cases of functionalization

Hybrid nanocomposites based on graphene derivatives decorated with inorganic nanoparticles (NPs) have attracted the interest of the scientific community for advanced technology applications, due to the synergistic combination of the superior properties of graphene with the unique size- and shape-dependent functionalities of the inorganic matter, at the nanoscale. Such a combination is able not only to enhance the properties of the single components, but also to achieve original and unprecedented functionalities, thus motivating significant efforts in developing innovative solutions for preparing multifunctional nanocomposites. This chapter provides a comprehensive overview of the latest bottom-up and top-down methods, and often unconventional chemical and physical approaches, for the in situ decoration of graphene derivatives with inorganic NPs, and also offers insights into the origin of their structure- and morphology-related properties, in view of their potential applications. After a general description of the properties of graphene derivatives, their covalent and non-covalent functionalisation routes, selected examples of in situ and ex situ methods for preparing nanocomposites with inorganic NPs, polymers and molecules are addressed, and a comprehensive discussion of the latest unconventional in situ routes for manufacturing functional hybrid nanocomposite materials and their technological application in devices is reported.