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1
Mancera, Ricardo Luis. "Understanding the hydrophobic effect". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627110.
Testo completo
2
Pazhianur, Rajesh R. "Hydrophobic Forces in Flotation". Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28066.
Testo completoAbstract (sommario):
An atomic force microscope (AFM) has been used to conduct force measurements to better understand the role of hydrophobic forces in flotation. The force measurements were conducted between a flat mineral substrate and a hydrophobic glass sphere in aqueous solutions. It is assumed that the hydrophobic glass sphere may simulate the behavior of air bubbles during flotation. The results may provide information relevant to the bubble-particle interactions occurring during flotation. The glass sphere was hydrophobized by octadecyltrichlorosilane so that its water contact angle was 109 degrees. The mineral systems studied include covellite (CuS), sphalerite (ZnS) and hornblende (Ca₂(Mg, Fe)₅(Si₈O₂₂)(OH,F)₂). The collector used for all the mineral systems studied was potassium ethyl xanthate (KEX).
For the covellite-xanthate system, a biopotentiostat was used in conjunction with the AFM to control the potential of the mineral surface during force measurements. This was necessary since the adsorption of xanthate is strongly dependent on the electrochemical potential (Eₕ) across the solid/liquid interface. The results show the presence of strong hydrophobic forces not accounted for by the DLVO (named after Derjaguin, Landau, Verwey and Overbeek) theory. Furthermore, the potential at which the strongest hydrophobic force was measured corresponds to the potential where the flotation recovery of covellite reaches a maximum, indicating a close relationship between the two.
Direct force measurements were also conducted to study the mechanism of copper-activation of sphalerite. The force measurements conducted with unactivated sphalerite in 10⁻³ M KEX solutions did not show the presence of hydrophobic force while the results obtained with copper-activated sphalerite at pH 9.2 and 4.6 showed strong hydrophobic forces. However, at pH 6.8, no hydrophobic forces were observed, which explains why the flotation of sphalerite is depressed in the neutral pH regime.
Direct force measurements were also conducted using hornblende in xanthate solutions to study the mechanism of inadvertent activation and flotation of rock minerals. The results show the presence of long-range hydrophobic forces when hornblende was activated by heavy metal cations such as Cu²⁺ and Ni²⁺ ions. The strong hydrophobic forces were observed at pHs above the precipitation pH of the activating cation. These results were confirmed by the XPS analysis of the activated hornblende samples.
Force measurements were conducted between silanated silica surfaces to explore the relationship between hydrophobicity, advancing contact angle (CA), and the magnitude (K) of hydrophobic force. In general, K increases as Contact Angle increases and does so abruptly at Contact Angle=90°. At the same time, the acid-base component of the surface free energy decreases with increasing CA and K. At CA>90°, GammaSAB approaches zero.
Based on the results obtained in the present work a mathematical model for the origin of the hydrophobic force has been developed. It is based on the premise that hydrophobic force originates from the attraction between large dipoles on two opposing surfaces. The model has been used successfully to fit the measured hydrophobic forces using dipole moment as the only adjustable parameter. However, the hydrophobic forces measured at CA>90° cannot be fitted to the model, indicating that there may be an additional mechanism, possibly cavitation, contributing to the appearance of the long-range hydrophobic force.Ph. D.
3
Cochin, D., P. Hendlinger e André Laschewsky. "Polysoaps with fluorocarbon hydrophobic chains". Universität Potsdam, 1995. http://opus.kobv.de/ubp/volltexte/2008/1734/.
Testo completoAbstract (sommario):
A series of amphiphilic copolymers is prepared by copolymerization of choline methacrylate with 1,1,2,2-tetrahydroperfluorooctyl methacrylate in varying amounts. The copolymers bearing fluorocarbon chains are studied concerning their effects on viscosity, solubilization and surface activity in aqueous solution, exhibiting a general behavior characteristic for polysoaps. The results are compared with the ones obtained for an analogous series of amphiphilic copolymers bearing hydrocarbon chains.
4
Quyum, Abdul. "Water migration through hydrophobic soils". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ65008.pdf.
Testo completo
5
Singh, Baljit. "Studies on hydrophobic dendrimer nanoparticles". Thesis, University College London (University of London), 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428133.
Testo completo
6
Matthews, Andrew Ernest. "Synthesis of hydrophobic crosslinkable resins". Thesis, Kingston University, 1989. http://eprints.kingston.ac.uk/20528/.
Testo completoAbstract (sommario):
After reviewing the literature relating to the synthesis and properties of hydrophobic materials, and then considering potential methods for their synthesis, a route for the preparation of novel materials was chosen. A reaction scheme involving the condensation of an excess of 1,4-bis (chloromethyl) benzene with bisphenolic compounds, and conversion of the resultant chloromethyl products to their vinyl analogues is described. A variety of methods were used to accomplish the initial etherification. The use of dimethyl acetamide and potassium carbonate was found to reduce the incidence of side reactions. The vinylation stage, using the Wittig reaction was also studied. The products were characterised by NMR and IR spectroscopy and by gel permeation and high perfonnance liquid chromatography. The curing reaction of the vinyl terminated material was studied using differential scanning calorimetry. The reaction product derived from bisphenol A was cured into various specimens, and the physical properties of the material examined. The polymer combines reasonable mechanical properties with one of the lowest water absorption maximov reported in the literature for non-fluorinated thennosets. On immersion in water at 700 C. the absorption maximov was 0.28% by weight. The thermooxidative degradation of the base material was also examined.
7
Pan, Lei. "Hydrophobic Forces in Wetting Films". Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/76918.
Testo completoAbstract (sommario):
Flotation is an important separation process used in the mining industry. The process is based on hydrophobizing a selected mineral using an appropriate surfactant, so that an air bubble can spontaneously adhere on the mineral surface. The bubble-particle adhesion is possible only when the thin film of water between the bubble and particle ruptures, just like when two colloidal particles or air bubbles adhere with each other. Under most flotation conditions, however, both the double-layer and dispersion forces are repulsive, which makes it difficult to model the rupture of the wetting films using the DLVO theory.
In the present work, we have measured the kinetics of film thinning between air bubble and flat surfaces of gold and silica. The former was hydrophobized by ex-site potassium amyl xanthate, while the latter by in-site Octadecyltrimetylammonium chlroride. The kinetics curves obtained with and without theses hydrophobizing agents were fitted to the Reynolds lubrication theory by assuming that the driving force for film thinning was the sum of capillary pressure and the disjoining pressure in a thin film. It was found that the kinetics curves obtained with hydrophilic surfaces can be fitted to the theory with the disjoining pressure calculated from the DLVO theory. With hydrophobized surfaces, however, the kinetics curves can be fitted only by assuming the presence of a non-DLVO attractive force (or hydrophobic force) in the wetting films. The results obtained in the present work shows that long-range hydrophobic forces is responsible for the faster drainage of wetting film.
It is shown that the changes in hydrophobic forces upon the thin water film between air bubble and hydrophobic surface is dependent on hydrophobizing agent concentration, immersion time and the electrolyte concentration in solution. The obtained hydrophobic forces constant in wetting film K132 is compared with the hydrophobic forces constant between two solid surfaces K131 to verify the combining rule for flotation.Master of Science
8
Boyett, Robin Ernest. "Computational studies of hydrophobic porphyrins". Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241621.
Testo completo
9
Yang, Fan 1980. "Solvent mediated interaction between hydrophobic spheres". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84087.
Testo completoAbstract (sommario):
We develop a coarse grained methodology to study solvent mediated interactions between two or more hydrophobic spheres. The free energy of a configuration of two hydrophobic hard spheres is calculated as a function of their separation to understand the thermodynamic force between them mediated by water. The range of the hydrophobic interaction is found to be of the order of the equilibrium correlation length of water; beyond this range the hydrophobicity induced force is negligible. We also examine the free energy landscape corresponding to the two interacting hydrophobic spheres, and find a new intermediate state between the two states of separate and non-interacting spheres and a weakly bound cluster. The nature of this intermediate state changes depending on the size of the spherical particles, and even disappears beyond a minimum critical radius. Our results are relevant to the understanding of hydrophobic mediated interactions in coarse grained models of protein folding and protein protein interactions which, to date, have only accounted for hydrophobicity in an empirical way.
10
Lipnizki, Frank. "Hydrophobic pervaporation : process integration and optimisation". Thesis, University of Bath, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343775.
Testo completo
11
Baines, Fiona Louise. "Water-soluble hydrophilic-hydrophobic block copolymers". Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283139.
Testo completo
12
Baba, N. M. "Hydrophobic polymers and nanocomposites from cassava". Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1435602/.
Testo completoAbstract (sommario):
This project aims to benefit the sub-Saharan African economies by exploiting cassava for chemical feedstock for materials production. It anticipates the industrial changes that will follow from increased petroleum price and regulatory control of embedded fossil carbon. It offers a way to integrate industrial and agricultural sectors. Initially, glucose and fructose were dehydrated by reactive distillation over a sulfated zirconia catalyst and 1-butyl-3-methylimidazolium chloride (BMIM Cl) ionic liquid as solvent under a nitrogen atmosphere at 180 oC to produce 5-(hydroxymethyl) furan (5-HMF) as a precursor for polymeric materials. Solvent, catalyst and reaction conditions were varied to improve the yield of 5-HMF. Yields of 82% and 65% were obtained using fructose and glucose substrates with this catalyst. Secondly, 2,5-furandicarboxylic acid (FDCA) and 2,5-bis-(hydroxymethyl)furan (BHMF) were synthesised as monomers from 5-HMF. The aldehyde group of 5-HMF was oxidized using potassium permanganate to FDCA with 80% yield achieved. BHMF was synthesised from 5-HMF using sodium borohydride with 88% yield achieved. The third part focuses on the polymerization of FDCA with the following diols: 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol and BHMF via esterification reactions at 160-200 oC using titanium (IV) n-butoxide catalyst. All diols produced polymers under the same conditions. The difference within this family of polymers was the number of carbon atoms in the linking diols and that BHMF had a different diol structure with a furan ring attached. Furthermore, a study of the interaction of all the monomers and the 5-HMF with Na-montmorillonite clay was made. It was observed that all were intercalated into the clay paving the way for the manufacture of nanocomposites. Finally, all the polymers were shown to be hydrophobic with PBH-2,5-F more hydrophobic with a contact angle of 91o compared to others. Water absorption, dielectric constant and mechanical properties of the polymers were recorded.
13
Ghasemi, Mohsen. "Evaporation of Water in Hydrophobic Confinement". Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1503094472074141.
Testo completo
14
Wang, Jihang. "Modeling Hydrophobic Effects at different lengthscales". VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/161.
Testo completoAbstract (sommario):
Understanding hydrophobic effects at different length scales is relevant to many complex and poorly understood everyday phenomena in materials science and biology. In this thesis, a variety of theory/computational methods in statistical physics and statistical mechanics are used to address three separated, but interconnected problems: (1) How solvation free energy scales with a partical size that is charged? This problem has never been attempted to solve before despite its immense importance in colloidal and protein solutions (J. Wang, D. Bratko, K. Leung and A. Luzar, Hydrophobic hydration at different length-scales: manipulating the crossover by charges, to be submitted to J. Stat. Phys. (Special issue on Water and Associated Liquids)); (2) Can onset to capillary evaporation, seen in some protein complexes with large hydrophobic areas be predicted in a simple way? A simple coarse-grained model of water/protein system, which is developed here shows the conditions for wet and dry hydrophobic protein cavities, and is able to reproduce all atom simulation results. The method should serve as an intermediate step between the initial screening of protein hydrophobic cavities and expensive molecular simulations (J. Wang, S. Kudesia, and A. Luzar, Computational probe of dewetting events in protein systems, in preparation for submission to J. Phys. Chem. B); (3) How to predicts hydrophobicity of a mixed surface from the knowledge of its pure constituents? To this end, wetting free energy on synthetic and biological heterogeneous surfaces is studied. Two distinct mechanisms responsible for their non-additivity have been identified in each case (J. Wang, D. Bratko and A. Luzar, Probing surface tension additivity on heterogenous surfaces: a molecular approach, Proc. Natl. Acad. Sci, under revision)
15
Gupta, Vipul. "Deposition and Characterization of Hydrophobic Coatings". BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3859.
Testo completoAbstract (sommario):
Hydrophobic coatings find application in various sectors of the economy including to electronics, textiles, optical devices, and in scientific and commercial equipment. These different applications demand that different hydrophobic coatings posses a range of properties that may include smoothness or roughness, thicknesses on the order of a monolayer or a micron, robustness or the ability to dissolve quickly, transparency or opacity, water resistance or water permeability, electrical conductivity, oleophobicity, etc. However, whatever the final/desired properties, deposition via dry-deposition processes offers significant advantages, including greater reproducibility, increased environmental friendliness, and cost effectiveness on an industrial scale. Herein I explore the chemical vapor deposition of silanes and the characterization of a commercial, hydrophobic coating to better prepare and understand hydrophobic coatings on different materials. One of the characterization techniques I used frequently in these studies is X-ray photoelectron spectroscopy (XPS). Accordingly, in Chapter 2 of this thesis I discuss this technique vis-à-vis the chemical shifts it detects, which reflect the oxidation states of materials being probed. In particular, I discuss a recommendation made over a decade ago by Gion Calzaferri for 'fixing' the problem of oxidation numbers as applied to organic materials and show how XPS confirms his suggestion. In Chapter 3 I introduce hydrogen as an etch/cleaning gas for silicon wafers. I first show that, like argon and oxygen plasmas, hydrogen plasmas will effectively clean silicon wafers. However, I then show that hydrogen plasma treatment leads to a silicon surface that is chemically different than those prepared with the other plasmas and that undergoes silanization to a greater extent -- the resulting surfaces have higher water contact angles and thicknesses. In Chapter 4 I study the deposition of a potential barrier layer for water, which was prepared from an aza silane: N-n-butyl-aza-2,2-dimethoxysilacyclopentane (1) in a molecular layer deposition (MLD)-like process using either water or ammonium hydroxide as the second half reactant. This molecule has the interesting property of undergoing self-limiting growth, where the termination of this growth is accelerated by use of an ammonium hydroxide catalyst. Interestingly, films of 1 are considerably thicker on nylon than on silicon, which is explained by nylon acting as a water reservoir in the reaction. In Chapter 5 I show the careful characterization of the hydrophobic coating on an Apple iPod nano, which was probed by ToF-SIMS, wetting, and XPS. I could identify that the coating is only applied to the touchscreen of the device. SIMS suggested that the fluorinated coating contains oxygen, which should add to its biodegradability. Finally, in Chapter 6 I make recommendation for future work in these areas.
16
Piotto, Chiara. "Nanostructured materials for hydrophobic drug delivery". Doctoral thesis, Università degli studi di Trento, 2019. https://hdl.handle.net/11572/367644.
Testo completoAbstract (sommario):
Porous silicon (Psi) and nanocellulose (NC) hydrogels are nanostructured materials with several properties that make them promising for drug delivery applications. In this work, β-carotene (BC) and clofazimine (CFZ) are used as model molecules to investigate the physical and chemical processes governing the interactions of hydrophobic molecules with both inorganic (Psi) and organic (NC) nanostructured carriers. Despite the large number of advantages, Psi does not perform well as carrier for BC, since it stimulates the molecule degradation even if its surface is carefully passivated. Furthermore, during the release experiments, BC tends to nucleate on Psi surface forming aggregates whose dissolution is much slower than the BC molecules release, thus they negatively impact on the control over the drug release. On the other hand NC hydrogels do not pose heavy issues to the release of lipophilic drugs, provided that a suitable surfactant (either Tween-20 or Tween-80) mediates the molecule solvation and its subsequent release into aqueous media. Moreover, NC gels protect BC from degradation much better than its storage in freezer or in organic solvent, making these carriers interesting for DD.
17
Piotto, Chiara. "Nanostructured materials for hydrophobic drug delivery". Doctoral thesis, University of Trento, 2019. http://eprints-phd.biblio.unitn.it/3575/2/Piotto_thesis.pdf.
Testo completoAbstract (sommario):
Porous silicon (Psi) and nanocellulose (NC) hydrogels are nanostructured materials with several properties that make them promising for drug delivery applications. In this work, β-carotene (BC) and clofazimine (CFZ) are used as model molecules to investigate the physical and chemical processes governing the interactions of hydrophobic molecules with both inorganic (Psi) and organic (NC) nanostructured carriers. Despite the large number of advantages, Psi does not perform well as carrier for BC, since it stimulates the molecule degradation even if its surface is carefully passivated. Furthermore, during the release experiments, BC tends to nucleate on Psi surface forming aggregates whose dissolution is much slower than the BC molecules release, thus they negatively impact on the control over the drug release. On the other hand NC hydrogels do not pose heavy issues to the release of lipophilic drugs, provided that a suitable surfactant (either Tween-20 or Tween-80) mediates the molecule solvation and its subsequent release into aqueous media. Moreover, NC gels protect BC from degradation much better than its storage in freezer or in organic solvent, making these carriers interesting for DD.
18
Ermeydan, Mahmut Ali. "Wood cell wall modification with hydrophobic molecules". Phd thesis, Universität Potsdam, 2014. http://opus.kobv.de/ubp/volltexte/2014/7132/.
Testo completoAbstract (sommario):
Wood is used for many applications because of its excellent mechanical properties, relative abundance and as it is a renewable resource. However, its wider utilization as an engineering material is limited because it swells and shrinks upon moisture changes and is susceptible to degradation by microorganisms and/or insects. Chemical modifications of wood have been shown to improve dimensional stability, water repellence and/or durability, thus increasing potential service-life of wood materials. However current treatments are limited because it is difficult to introduce and fix such modifications deep inside the tissue and cell wall. Within the scope of this thesis, novel chemical modification methods of wood cell walls were developed to improve both dimensional stability and water repellence of wood material. These methods were partly inspired by the heartwood formation in living trees, a process, that for some species results in an insertion of hydrophobic chemical substances into the cell walls of already dead wood cells,
In the first part of this thesis a chemistry to modify wood cell walls was used, which was inspired by the natural process of heartwood formation. Commercially available hydrophobic flavonoid molecules were effectively inserted in the cell walls of spruce, a softwood species with low natural durability, after a tosylation treatment to obtain “artificial heartwood”. Flavonoid inserted cell walls show a reduced moisture absorption, resulting in better dimensional stability, water repellency and increased hardness. This approach was quite different compared to established modifications which mainly address hydroxyl groups of cell wall polymers with hydrophilic substances. In the second part of the work in-situ styrene polymerization inside the tosylated cell walls was studied. It is known that there is a weak adhesion between hydrophobic polymers and hydrophilic cell wall components. The hydrophobic styrene monomers were inserted into the tosylated wood cell walls for further polymerization to form polystyrene in the cell walls, which increased the dimensional stability of the bulk wood material and reduced water uptake of the cell walls considerably when compared to controls. In the third part of the work, grafting of another hydrophobic and also biodegradable polymer, poly(ɛ-caprolactone) in the wood cell walls by ring opening polymerization of ɛ-caprolactone was studied at mild temperatures. Results indicated that
polycaprolactone attached into the cell walls, caused permanent swelling of the cell walls up to 5%. Dimensional stability of the bulk wood material increased 40% and water absorption reduced more than 35%. A fully biodegradable and hydrophobized wood material was obtained with this method which reduces disposal problem of the modified wood materials and has improved properties to extend the material’s service-life.
Starting from a bio-inspired approach which showed great promise as an alternative to standard cell wall modifications we showed the possibility of inserting hydrophobic molecules in the cell walls and supported this fact with in-situ styrene and ɛ-caprolactone polymerization into the cell walls. It was shown in this thesis that despite the extensive knowledge and long history of using wood as a material there is still room for novel chemical modifications which could have a high impact on improving wood properties.Der nachwachsende Rohstoff Holz wird aufgrund seiner guten mechanischen Eigenschaften und der leichten Verfügbarkeit für viele Anwendungszwecke genutzt. Quellen und Schrumpfen bei Feuchtigkeitsänderungen des hygroskopischen Werkstoffs Holz limitieren jedoch die Einsatzmöglichkeiten. Ein weiteres Problem stellt der mitunter leichte Abbau – u.a. bei feuchtem Holz - durch Mikroorganismen und/oder Insekten dar. Durch chemische Modifizierungen können die Dimensionsstabilität, die Hydrophobizität und die Dauerhaftigkeit verbessert und damit die potentielle Lebensdauer des Werkstoffes erhöht werden. Dabei ist die dauerhafte Modifikation der Zellwand nur äußerst schwer realisierbar. Inspiriert von der Kernholzbildung in lebenden Bäumen, ein zellwandverändernder Prozess, der Jahre nach der Holzbildung erfolgt, wurden im Rahmen dieser Arbeit neue Ansätze zur chemischen Modifizierung der Zellwände entwickelt, um die Dimensionsstabilität und Hydrophobizität zu erhöhen. Der erste Teil der Arbeit ist stark vom Prozess der Kernholzbildung inspiriert, eine abgeleitete Chemie wurde verwendet, um die Zellwände von Fichte, einem Nadelholz von geringer natürlicher Dauerhaftigkeit, zu modifizieren. Kommerziell verfügbare hydrophobe Flavonoide wurden nach einem Tosylierungsschritt erfolgreich in die Zellwand eingebracht, um so „artifizielles Kernholz“ zu erzeugen. Die modifizierten Holzproben zeigten eine verringerte Wasseraufnahme, die zu erhöhter Dimensionsstabilität und Härte führte. Dieser Ansatz unterscheidet sich grundlegend von bereits etablierten Modifikationen, die hauptsächlich hypdrophile Substanzen an die Hydroxylgruppen der Zellwand anlagern. Der zweite Teil der Arbeit beschäftigt sich mit der Polymerisation von Styren in tosylierten Zellwänden. Es ist bekannt, dass es nur eine schwache Adhäsion zwischen den hydrophoben Polymeren und den hydrophilen Zellwandkomponenten gibt. Die hydrophoben Styren-Monomere wurden in die tosylierte Zellwand eingebracht und zu Polystyren polymerisiert. Wie bei der Modifikation mit Flavonoiden konnte eine erhöhte Dimensionsstabilität und reduzierte Wasseraufnahme der Zellwände beobachtet werden. Im dritten Teil der Arbeit wurde das biologisch abbaubare, hydrophobe poly(ɛ-caprolacton) in der Zellwand aufpolymerisiert. Die Ergebnisse deuten darauf hin, dass Polycaprolacton in der Zellwand gebunden ist und zu einer permanenten Quellung führt (bis zu 5 %). Die Dimensionsstabilität nahm um 40 % zu und die Wasseraufnahmerate konnte um mehr als 35 % reduziert werden. Mit dieser Methode kann nicht nur dimensionsstabileres Holz realisiert werden, auch biologische Abbaubarkeit und damit eine einfache Entsorgung sind gewährleistest.
19
Etmimi, Hussein Mohamed. "Hydrophobic core/shell particles via miniemulsion polymerization". Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019/539.
Testo completo
20
Chen, C. H. "Phase ordering of monoglyceride in hydrophobic solutions". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597547.
Testo completoAbstract (sommario):
In Chapter 1 the fundamentals of MG and MG-water are reviewed before embarking on studying the mixtures of MG and oils. The typical phase ordering and crystallisation process are reviewed. Understanding the physical properties of lipids is fundamentally important, hence, relevant theories regarding the phase behaviour are discussed in the following section. Chapter 2 introduces synthesis, characterisation and experimental techniques used throughout the thesis. Particular attention is given to assess the limitations of these techniques when probing the phase ordering of MG-oil. In Chapter 3 the phase diagram and the microstructure of MG in oils are presented by a set of experimental data from different techniques. Chapter 4 presents the experimental findings of the water effects in MG-oil systems. Chapter 5 considers the aging and metastability of MG-oil and its hydrated system (MG-oil with 3 wt\% water). The aging phenomena are quantified by the increase of melting enthalpy in differential scanning calorimetry (DSC) heating scans and the mechanism is understood by applying infrared spectroscopy. The changes of hydrogen bonding patterns by adding small quantity of water slows the aging process significantly. In Chapter 6 the effect of colloidal dispersions is discussed to modify the MG gel. Lipids such as MG form the gel-like material which can be widely applied in the food industry, cosmetics and other personal products. It is hoped that this thesis will provide stimulating insight into the lipid composite field and furthermore, motivate research in industry toward improvement of existing materials and discovery of innovative new products.
21
Moradi, Sona. "Super-hydrophobic nanopatterned interfaces : optimization and manufacturing". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46588.
Testo completoAbstract (sommario):
This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence, scanning speed and scanning overlap) on the wettability of the resulted micro/nano-patterned morphologies on stainless steel. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nanostructures. All of the produced structures were classified according to a newly defined parameter, the Laser Intensity Factor (LIF) that is a function of scanning speed and fluence of laser. By increasing LIF, the ablation rate and the periodicity of the asperities increase. In order to decrease the surface energy, all of the surfaces were coated with a fluorinated alkylsilane agent. Analysis of the wettability in terms of contact angle (CA) and contact angle hysteresis (CAH) revealed enhanced superhydrophobicity for most of these structures, particularly that possessing triple roughness pattern. This also exhibited a low CAH. The high permanent superhydrophobicity of this pattern is due to the special micro-nano structure of the surface that facilitates the Cassie-Baxter state.
A new two-dimensional (2D) thermodynamic model is developed to predict the contact angle (CA) and contact angle hysteresis (CAH) of all types of surface geometries, particularly those with asperities having non-flattened tops. The model is evaluated by micro/nano sinusoidal and parabolic patterns fabricated by laser ablation. These microstructures are analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium CA and CAH. The effects of the geometrical details on maximizing the superhydrophobicity of the nano-patterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters, which may lead to lotus effect (high CA>150° and low CAH<10°) or petal effect (high CA>150° and high CAH>>10°).
22
Charalambous, Antonia. "Lipid oil nanodroplets for hydrophobic drug delivery". Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/21956/.
Testo completoAbstract (sommario):
Delivery of anti-cancer drugs to tumours is a fundamental requirement for cancer treatment. However, failure of drugs to reach tumours at sufficient concentrations due to poor bioavailability, rapid metabolism and elimination compromises effective treatment. A substantial number of potent anti-cancer drugs, exhibit hydrophobic properties that hinder their clinical use. Therefore, there is an urgent need for the development of a hydrophobic drug delivery system (DDS) that aims to effectively deliver and controllably trigger the release of these agents. This may improve drug bioavailability, efficacy and reduce severe side effects. Lipid-Oil-NanoDroplets (LONDs) are nanosized nanoemulsions and are proposed as a novel hydrophobic DDS for colorectal cancer (CRC) treatment. LONDs were produced using a two-step high pressure homogenisation process, producing LONDs with size ranges between 100-300 nm. The hydrophobic vascular disrupting agent Combretastatin A4 (CA4) was encapsulated and used as a proof-of-concept for LOND evaluation in vitro and in vivo. CA4 was dispersed in triacetin or tripropionin oil to form the LOND core, stabilised by a phospholipid-shell. Using a microfluidic production platform, CA4 LONDs were attached on-chip to gas-filled, phospholipid-shelled therapeutic microbubbles (thMBs). CA4 thMBs were targeted to vascular endothelial growth factor receptor 2 (VEGFR-2) and used as LOND delivery vehicles. An external ultrasound (US) destruction pulse applied at the tumour site was used to trigger targeted release and enhance delivery. This project showed CA4 release and/or uptake from LONDs in both endothelial and human CRC cells by immunofluorescence and flow cytometry. Intratumoural delivery of CA4 LONDs was observed and quantified in CRC xenografts using liquid chromatography tandem mass spectrometry (LS-MS/MS). Administration of CA4 LONDs resulted in a modest tumour growth inhibition in vivo, while a reduction in tumour perfusion was observed with CA4 thMBs. Combination therapy of CA4 thMBs with a chemotherapeutic agent, irinotecan, further reduced tumour growth compared to irinotecan alone, potentially through reduction in tumour perfusion. These results suggest that LONDs may serve as a novel hydrophobic DDS, while thMBs could further enhance tumour specific delivery.
23
Crick, C. R. "The chemistry and CVD of hydrophobic surfaces". Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1332890/.
Testo completoAbstract (sommario):
This thesis details the use of chemical vapour deposition (CVD) to deposit hydrophobic surfaces, in addition to this, the functional properties are investigated and further characterisation of the surfaces extreme water repulsion (superhydrophobicity) is made. The design and manufacture of surfaces that repel water (hydrophobic) draws much inspiration from the natural world, including examples of superhydrophobic leaves. The way water can interact with a surface is characterised, with many examples of superhydrophobic surface generation provided from the literature, along with general routes toward their formation. The main aspects of CVD depositions are addressed and examples of hydrophobic surfaces using this technique are cited. The novel deposition of thermosetting and thermosoftening polymers has been investigated, with the role of the CVD deposition mechanism emphasised. The deposition of the polymer occurs via the preformation of polymer particles, which is not typical in CVD, these were then deposited onto the substrate. The result was an easy-to-produce and robust superhydrophobic thin film, constructed from an inherently hydrophobic material. The same principle is then expanded to silica microparticles, films of the particles were deposited on to a substrate with hydrophilic surfaces originally deposited. The silica films were subsequently rendered exceptionally superhydrophobic by a simple post-treatment. The formation of copper films is then reported, using copper nitrate precursors a relatively flat metallic copper film was formed. The films were then roughened by reaction to form copper hydroxide nano-crystals, this hydrophilic surface is again functionalised to render it superhydrophobic. All films deposited were characterised using energy dispersive X-ray analysis, glancing angle X-ray diffraction, UV/Vis spectroscopy, infra-red/Raman spectroscopy and scanning electron and atomic force microscopy were used to study surface morphology, with the hydrophobicities of each surface quantified. The superhydrophobic elastomer films underwent microbiological testing in order to examine the adhesion of bacteria. A substantial reduction in the ability of bacteria to attach to the superhydrophobic surfaces was observed and rationalised through a reduction in available contact between the media of the bacteria (water) and the surface material. The dynamic interaction between water and surfaces was examined through water bouncing. The dependence of water bouncing on surface hydrophobicity and microstructure was studied, in addition to the effect of water droplet volume and impact velocity. A new definition and scale for superhydrophobicity is proposed, through the ability of water droplets to bounce on a surface. Finally the insight gained from previous work carried out is used in developing a device for separating mixtures of oil and water, through the use of superhydrophobic meshes.
24
Gan, Haiying. "Self-Assemblies Driven by the Hydrophobic Effect". ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/1389.
Testo completoAbstract (sommario):
Water is a simple molecule but is an essential part of life. One key aspect of the properties of water is the hydrophobic effect, and whilst there is an appreciation of this phenomenon at the macro-scale (raindrops falling off leaves) and the micro-scale (the structure of cellular systems), a complete understanding at the molecular level still eludes science. Addressing this issue, our studies involve synthetic supramolecular compounds that assemble in water via the hydrophobic effect.
First of all, a novel water-soluble deep-cavity cavitand was synthesized. It possesses four endo methyl groups on top rim of the cavitand, eight water-solubilizing carboxylic acid groups coated on the cavitand exterior, and a relatively large hydrophobic interior. Compared to a previous well-studied water-soluble deep-cavity cavitand octa-acid (OA), this novel cavitand (TEMOA) possesses a non-monotonic assembly profile in the presence of a homologous series of straight-chain alkanes. Three supramolecular species were observed: 1:1, 2:2, and 2:2 and they are approximately isoenergetic. Second, we examined the guest-controlled self-sorting in assemblies. A mixture of OA and TEMOA formed hetero-capsular complex driven by the hydrophobic effect. The extent of homo- or hetero-dimerization is intimately tied to the size of the guest being encapsulated. TEMOA is less predisposed to dimerize than OA, thus TEMOA possesses the ability to form various self-assembled states, such as tetrameric and hexameric assemblies. Furthermore, we also discussed our observation of how external stimuli such as changing the nature or concentration of a co-solute salt influences a unique, unusual transition from one assembled state to another.
25
Jones, Alan Wayne III. "Advancement of the Hydrophobic-Hydrophilic Separation Process". Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89067.
Testo completoAbstract (sommario):
Froth flotation has long been regarded as the best available technology for ultrafine particles separation. However, froth flotation has extreme deficiencies for recovering ultrafine particles that are less than 30-50 μm in size for coal and 10-20 μm for minerals. Furthermore, dewatering of flotation products is difficult and costly using currently available technologies. Due to these problems, coal and mineral fines are either lost to tailings streams inadvertently or discarded purposely prior to flotation. In light of this, researchers at Virginia Tech have developed a process called hydrophobic-hydrophilic separation (HHS), which is based originally on a concept known as dewatering by displacement (DbD). The process uses non-polar solvents (usually short-chain alkanes) to selectively displace water from particle surfaces and to agglomerate fine coal particles. The resulting agglomerates are subsequently broken (or destabilized) mechanically in the next stage of the process, whereby hydrophobic particles are dispersed in the oil phase and water droplets entrapped within the agglomerates coalesce and exit by gravity along with the hydrophilic particles dispersed in them. In the present work, further laboratory-scale tests have been conducted on various coal samples with the objective of commercial deployment of the HHS process. Test work has also been conducted to explore the possibility of using this process for the recovery of ultrafine minerals such as copper and rare earth minerals. Ultrafine streams produced less than 10% ash and moisture consistently, while coarse coal feed had no observable degradation to the HHS process. Middling coal samples were upgraded to high-value coal products when micronized by grinding. All coal samples performed better with the HHS process than with flotation in terms of separation efficiency. High-grade rare earth mineral concentrates were produced with the HHS process ranging from 600-2100 ppm of total rare earth elements, depending on the method and reagent. Additionally, the HHS process produced copper concentrates assaying greater than 30% Cu for both artificial and real feed samples, as well as, between 10-20% Cu for waste samples, which all performed better than flotation.Master of Science
Froth flotation has long been regarded as the best available technology for separating fine particles. Due to limitations in particle size with froth flotation, and high downstream dewatering costs, a new process has been developed called the hydrophobic-hydrophilic separation (HHS) process. This process was originally based on a concept known as dewatering by displacement (DbD) which was developed by researchers at Virginia Tech in 1995. The process uses hydrocarbon oils, like pentane or heptane, to selectively collect hydrophobic particles, such as coal, for which it was originally developed. In coal preparation plants, a common practice is to purposefully discard the ultrafine stream that flotation cannot recover and has an increased dewatering cost. The HHS process can effectively recovery this waste stream and produce highgrade salable product, with significantly reduced cost of dewatering. In the work presented, laboratory-scale tests have been conducted on various coal samples with the objective of commercial deployment of the HHS process. In this respect, several varying plant streams have been tested apart from the traditional discard stream. Additionally, test work has expanded into mineral commodities such as copper and rare earth minerals. In this work, salable high-value coal products were achievable with the HHS process. Ultrafine streams consistently produced less than 10% ash and moisture. Coarse coal feeds had no observable degradation to the HHS process and were able to produce single digit ash and moisture values. Middling coal samples were upgraded to high-value coal products when micronized by grinding. All coal samples performed better with the HHS process than with flotation in terms of separation efficiency. High-grade rare earth mineral concentrates were produced with the HHS process ranging from 600- 2100 ppm of total rare earth elements depending on the method and reagent. Additionally, the HHS process produced copper concentrates assaying greater than 30% Cu for an artificial and feed samples, as well as, between 10-20% Cu for waste samples, which all performed better than flotation.
26
Kroeger, Thomas William 1952. "Hydrophobic partitioning of the bacteriophage MS-2". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276963.
Testo completoAbstract (sommario):
In batch experiments at pH's 5 and 7, the partitioning of MS-2 between water and silica (unbonded) was compared with the partitioning between water and silica with 6.5 percent of the surface covered by hydrophobic C18 chains (bonded). The roles of double-layer and van der Waals forces in partitioning were explored by modeling the potential energies of interaction. MS-2 adsorption to unbonded silica was negligible at pH 7, but did occur at pH 5. Adsorption was independent of pH with the bonded silica and approximately 2.6 orders of magnitude greater than the unbonded at pH 5, suggesting the importance of hydrophobic partitioning. The total potential energies of interaction, which closely approach the pH-independent van der Waals potentials, are similar in magnitude for all pH's or silica types, and have no positive (repulsive) values. The insignificant contribution of the double-layer potentials suggests that these pH-dependent forces may not account for the pH-dependent adsorption observed with the unbonded silica.
27
Cardin, Karl Jeffrey Theodore. "Jet Rebound from Hydrophobic Substrates in Microgravity". PDXScholar, 2019. https://pdxscholar.library.pdx.edu/open_access_etds/4830.
Testo completoAbstract (sommario):
We experimentally investigate the phenomena of large jet rebound, a mode of fluid transfer following oblique jet impacts on hydrophobic substrates. We initially seek to describe the jet rebound regimes in tests conducted in the weightless environment of a drop tower. A parametric study reveals the dependence of the flow structure on the relevant dimensionless groups such as Reynolds number and Weber number defined on the velocity component perpendicular to the substrate. We show that significantly larger diameter jets behave similarly as much smaller jets demonstrated during previous terrestrial investigations is some parameter ranges while the flow is fundamentally different in others. Level-set numerical predictions are provided for comparisons where practicable. Simple models are developed predicting landing geometry and the onset of instability that are found to yield good agreement with experiments and simulations. Improving our understanding of such jet rebound opens avenues for unique transport capabilities.
28
Ronchi, Laura. "Synthesis of Hydrophobic Zeolites for Energetic Applications". Thesis, Mulhouse, 2017. http://www.theses.fr/2017MULH0678/document.
Testo completoAbstract (sommario):
Les zéolithes sont des solides microporeux cristallins largement utilisés en adsorption, catalyse, échange ionique et comme tamis moléculaires. Les zéolithes hydrophobes purement siliciques (zéosils) peuvent être utilisées pour le stockage et l’absorption de l’énergie mécanique par intrusion d’eau à haute pression. En fonction du système “zéosil-eau”, lorsque la pression est relâchée (extrusion), le système peut restituer, dissiper ou absorber l’énergie mécanique fournie pendant la compression (intrusion) et donc, il peut montrer un comportement de type ressort, amortisseur ou pare-chocs. Récemment, il a été remarqué que l’intrusion de solutions salines peut améliorer considérablement les performances énergétiques de ces systèmes par une augmentation de la pression d’intrusion. Pendant ce travail, l’intrusion d’eau et de solutions de LiCl a été étudiée pour différentes zéosils pour mieux comprendre la relation qui existe entre la structure des zéosils (dimension des pores, type et dimensionnalité du système poreux) et le comportement ou les performances énergétiques du système “zéosil-liquide intrusé”.Les expériences avec des zéosils qui présentent une structure à cage ont confirmé une pression d’intrusion plus faible par rapport à celles observées par les zéosils ayant une structure à canaux. La pression d’intrusion augmente fortement avec la concentration de LiCl pour les zéosils caractérisés par de petites ouvertures des pores, spécialement pour ceux qui ont des cages, tandis que cette augmentation est plus faible lorsque de grandes ouvertures de pores sont présentes. Il a été aussi montré une influence de la concentration du sel sur le comportement, probablement, due à la nature particulière des solutions très concentréesZeolites are microporous crystalline solids widely used in adsorption, catalysis, ion exchange and molecular sieving. Hydrophobic pure-silica zeolites (zeosils) can be used for mechanical energy absorption and storage by high pressure intrusion-extrusion of water. Depending on the “zeosil-water” system, when the pressure is released (extrusion), the system is able to restore, dissipate or absorb the supplied mechanical energy during the compression step (intrusion) and therefore to display a spring, shock absorber or bumper behavior. Recently, it was found that the use of aqueous salt solutions could considerably improve the energetic performances of such systems by an increase of the intrusion pressure.In this work the intrusion of water and LiCl solutions was studied for different zeosils in order to understand the relationship between the structure of zeosils (pore size, pore system type and dimensionality) and the behavior or the energetic performances of “zeosil-liquid” systems. The experiments with cage-type zeosils confirmed a lower intrusion pressure in comparison with channel-type ones. The intrusion pressure strongly increases with the LiCl content for the zeosils with small pore openings, particularly, for the cage-type ones, while for larger pores this increase is less important. An influence of salt concentration on the behavior of “zeosils-liquid” systems probably due to the particular nature of highly concentrated solutions was also shown
29
Macdonald, Ryan. "The Effects of Trimethylamine-N-Oxide and Guanidinium Chloride on Aqueous Hydrophobic Contact-Pair Interactions". Elsevier - Biophysical Chemistry, 2013. http://hdl.handle.net/1993/30162.
Testo completoAbstract (sommario):
Trimethylamine-N-oxide (TMAO) and guanidinium chloride (GdmCl) are both highly studied molecules in the field of protein folding/unfolding. Thermodynamic studies have shown that TMAO, an organic osmolyte, is a strong stabilizer of the protein folded state, while GdmCl is known to be one of the most effective protein denaturants. Although TMAO and GdmCl are well studied the mechanism by which they stabilize and denature proteins, respectively, is not well understood. In fact there are few studies looking at their effects on hydrophobic interactions. In this work we determine the effect of TMAO and GdmCl on hydrophobic interactions, by looking at the model system of phenyl and alkyl hydrophobic contact pairs. Contact pair formation is monitored through the use of fluorescence spectroscopy, i.e., measuring the intrinsic phenol fluorescence being quenched by carboxylate ions. Hydrophobic interactions are isolated from other interactions through a developed methodology. The results show that TMAO addition to the aqueous solvent destabilizes hydrophobic contact-pairs formed between phenol and carboxylate ions. The TMAO acts as a “denaturant” for hydrophobic interactions. For GdmCl the data shows that for small alkyl groups, acetate and propionate, hydrophobic contact-pairs are slightly stabilized or are not affected, respectively. For the larger alkyl groups GdmCl disrupts contact pair formation and destabilizes them. GdmCl’s effect on hydrophobic interactions shows a size dependence on carboxylate ion size, i.e., as carboxylate ion tail length increases the contact pair formed with phenol is destabilized to a greater degree.
30
Darne, P. "Sophorolipid assisted enhanced solubility of hydrophobic biomolecules and development of nano-carriers as advanced drug delivery systems". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2018. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4587.
Testo completo
31
Motornov, Mikhail. "Herstellung und Untersuchung schaltbarer Polymerschichten mit hydrophobem, hydrophilem Charakter (Fabrication and study of switchable polymerlayers with hydrophobic, hydrophilic behavior) /". [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11513723.
Testo completo
32
Coskuner, Orkide. "Investigation of hydrophobic interactions by Monte Carlo simulation". [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968831664.
Testo completo
33
To, Chi Shung Brian. "Protein retention and transport in hydrophobic interaction chromatography". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 2.12 Mb., 319 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3205434.
Testo completo
34
Hawe, Andrea. "Studies on Stable Formulations for a Hydrophobic Cytokine". Diss., lmu, 2006. http://nbn-resolving.de/urn:nbn:de:bvb:19-59638.
Testo completo
35
Spagnolo, David. "Low temperature oxidation of methanol using hydrophobic catalysts". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21640.pdf.
Testo completo
36
Koziarz, Jacob. "Adhesion and immobilization of bacteria on hydrophobic cloths". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ36934.pdf.
Testo completo
37
Yu, Zhimin. "Flocculation, hydrophobic agglomeration and filtration of ultrafine coal". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/NQ39010.pdf.
Testo completo
38
Pomroy, Neil Christopher. "Solubilization of hydrophobic peptides by reversible cysteine PEGylation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0005/MQ45500.pdf.
Testo completo
39
Al-Jamal, Khuloud Taysir Yousef. "Studies on cationic hydrophobic dendrons and hydrophilic dendrimers". Thesis, University College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414002.
Testo completo
40
Lee, Jobina J. N. "Investigations into sustained-release hydrophobic matrix pellet formulations". Thesis, University of Strathclyde, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275167.
Testo completo
41
Tio, Evelyn. "Electrowetting study of jumping droplets on hydrophobic surfaces". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92210.
Testo completoAbstract (sommario):
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (page 27).
Recent studies have shown that jumping-droplet-enhanced condensation has higher heat transfer than state-of-the-art dropwise condensing surfaces by -30-40%. Jumping-droplet condensation occurs due to the conversion of surface energy to kinetic energy during the coalescence of microscale droplets, resulting in droplet ejection from the condenser surface. This conversion of energy is fundamentally studied by using electrowetting to decrease the equilibrium contact angle, increasing droplet surface area. Releasing the voltage allows the droplet to release excess surface energy, causing the droplet to jump off the surface. In contrast with previous work, droplets were initially held at a static deformed state. Here, jumping from the surface from this static electrowetting-induced state is demonstrated for the first time. Releasing the voltage caused droplets to jump as high as -2 mm with a maximum conversion efficiency between surface and potential energy of -5%.
by Evelyn Tio.
S.B.
42
Agarwal, Abhinandan. "An experimental study of nanobubbles on hydrophobic surfaces". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34104.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 123-127).
With the recent development of microfluidic systems, miniaturization of flow devices has become a real challenge. Microchannels, however, are characterized by a large surface area-to-volume ratio so that surface properties strongly affect flow resistance in sub-micrometer devices. Recent studies in the literature have opened up the possibility of a controlled realization of nanobubbles- found to exist primarily on hydrophobic surfaces- that can play all important role in changing the hydrodynamic boundary condition at the fluid-solid interface giving rise to considerable reduction in friction of the fluid flow past the solid boundaries. In this study, we seek to increase our understanding of the formation, morphology, and stability of nanobubbles. Further. we seek to exploit the dependence of nanobubble formation on surface to provide a means for controlling hydrodynamic boundary conditions at the solid-liquid interface. The formation of nanobubbles at solid-liquid interfaces has been studied using the atomic force microscopy (AFM) imaging technique. Nanobubble formation strongly depends on both the hydrophobicity of the solid surface and the polarity of the liquid subphase.
(cont.) First, a number of homogeneous surfaces are used as solid substrates to understand and analyze the formation and distribution of nanobubbles on homogeneous surfaces with differing degrees of hydrophobicity. While nanobubbles do not form on flat hydrophilic surfaces immersed in water. they appear spontaneously at the interface of water against smooth, hydrophobic surfaces. From the experimental evidence, we draw the conclusion that the features observed in the AFM images are deformable, air-filled bubbles. In addition to the hydrophobicity of the solid surface, differences in solubility of air between two miscible fluids can also lead to nucleation and growth of nanobubbles. We observe that nanobubbles appear at the interface of water against hydrophilic silicon oxide surfaces after in-situ mixing of ethanol and water in the fluid-cell. While for most part, the shapes of the nanobubbles are well approximated by spherical caps with width much larger than the height; in the vicinity of the three phase contact line, the shapes deviate significantly from the spherical cap profile to merge with the solid surface at a slope of < 0.05. This deviation in the interfacial profile from the spherical cap shape is due to long-range van der Waals forces, which are relevant at a spatial scale of few nanometers from the solid surface.
(cont.) We quantify the morphological distribution of nanobubbles by evaluating several important bubble parameters including surface coverage and radii of curvature. In conjunction, with an analytical model available in the literature, we use this information to estimate that the present nanobubble morphology may give rise to slip lengths [approx.]1/'2 micrometer in pressure driven flows for water flowing over a typical hydrophobic surface. The consistency of the calculated slip length with experimental values reported recently in the literature, suggests that the apparent fluid slip observed experimentally at hydrophobic surfaces may indeed arise from the presence of nanobubbles. Further, trends are established between different morphological parameters and surface hydrophobicity. Bubbles are found to get bigger, wider and less-frequent in number with increasing surface hydrophobicity. The pressure inside the bubble is found to decrease with an increase in the surface hydrophobicity. The presence of nanobubbles is controlled using nanopatterned surfaces possessing repeating patterns of polystyrene (hydrophobic domains) and polymethyl-methacrylate (hydrophilic domains).
(cont.) For nanobubbles to be present, we find that, in addition to controlling the degree of surface hydrophobicity, it is important for the spatial dimensions of the hydrophobic domains on the nanopatterned surface to be commensurate with the equilibrium topology of the nanobubbles. To the best of our knowledge, this is the first experimental study in which chemically inhomogeneous surfaces are used to probe the existence of nanobubbles. Thermodynamic issues related to formation and stability of nanobubbles are also discussed. The effects of line tension at the three-phase contact line is discussed for the observed set of nanobubbles. Further, the length-scale of a typical nanobubble is found to be comparable to the mean-free-path of gas molecules inside the bubble. The above fact suggests that the Young-Laplace equation- used in continuum theories for calculating pressure difference across an interface- may not be applicable in its unmodified form for the case of nanobubbles. It is noteworthy that the anomalously high pressure values obtained using this equation for nanobubbles have been the reason for much debate on the stability of nanobubbles.
by Abhinandan Agarwal.
S.M.
43
Damak, Maher Ph D. Massachusetts Institute of Technology. "Droplet deposition on hydrophobic surfaces for agricultural sprays". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101814.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 51-55).
This thesis presents a study of the in-situ precipitation of polyelectrolytes during droplet impacts and its applications in enhancing the retention efficiency of sprays. Large amounts of agricultural sprays are wasted worldwide, due to the poor retention on hydrophobic plants. As the harmful effects of pesticides in particular are more and more pointed out, there is an increasing pressure to reduce their use and make their spraying more efficient. Current solutions, mainly based on surfactants, all have limitations. Here, we present a novel idea based on the modification of the surface of the plant. By precipitating opposite polyelectrolytes, in-situ, we create sparse pinning sites that pin the contact lines of the impacting droplets from the spray and prevent them from bouncing off. We first study the behavior of the impact of two droplets containing oppositely charged polyelectrolytes on a hydrophobic surface. We then study the precipitation process of two polyelectrolytes and develop a model that predicts the outcome of a double drop impact. Finally, we show the macroscopic applications of this study, by using simultaneous spraying. Simultaneously spraying dilute opposite polyelectrolytes on a superhydrophobic surface leads to a large increase in the liquid retention and the coverage of the surface. The behavior has been shown to hold for different polyelectrolytes and surfaces, making this method suitable for a range of applications.
by Maher Damak.
S.M.
44
Lim, Wendel Alan. "The role of hydrophobic core in protein folding". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13897.
Testo completo
45
Prendergast, Daniel P. (Daniel Patrick). "Optimization of hydrophobic meshes for oil spill recovery". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82848.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references.
Widespread use of petrochemicals often leads to accidental releases in aquatic environments, occasionally with disastrous results. Recent advances in the understanding of selectively wetting surfaces have led to the development of functionalized steel meshes with hydrophobic and oleophilic surfaces. These meshes can perform oil/water separation in situ, continuously, via capillary action. The goal of this study is to determine the potential of hydrophobic meshes as oil spill recovery devices. A fabrication method was developed using steel mesh dip-coated in a hot solution of low-density polyethylene (LDPE) in xylene. The mesh gained a rough, hydrophobic coating of LDPE, with tunable pore sizes and surface roughness. The coating was characterized using microscopy techniques and contact angle analysis, in order to identify surface features relevant to oil/water separation. Oil was found to persistently wet the mesh, attenuating any effects from roughness. Next, a key performance metric, the water breakthrough pressure, was predicted using a modified version of the Young-Laplace equation incorporating an unpinned meniscus. The model was successful for meshes with pore radii between 7 - 220 tm, which could hold back up to 40 cm of water. Finally, a bench-scale apparatus was built to test the oil permeate flux at steady state under capillary-driven flow. The mesh successfully recovered oil from the surface of a pool of water, with less than 1% water recovered by mass, with a representative flux of 1 L-m-²-s. These results were used to discuss implications for the feasibility of field-scale devices.
by Daniel P. Prendergast.
S.M.
46
Chao, Michelle (Michelle L. ). "Hydrophobic nanostructured glass surfaces using metal dewetting process". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111342.
Testo completoAbstract (sommario):
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (page 18).
This project aims to create a hydrophobic surface through a top down fabrication process of a nanostructure surface on a glass surface. The nanostructure is created through reactive ion etching utilizing silver as a mask. The silver mask is the result of a solid state thermal dewetting process which is controlled by varying the temperature and time of the process. Using this fabrication process, contact angles up to 137 degrees was achieved. Further surface modification resulted in contact angles exceeding 150 degrees. Superhydrophobic surfaces were made with the addition of a secondary roughness feature and the a PDMS coating.
by Michelle Chao.
S.B.
47
Hu, Xiao Wen. "Hydrophobic interactions and liquid crystallisation in collagen assembly". Thesis, University of Winchester, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.697554.
Testo completo
48
Smith, Kara E. "Cleaning and Dewatering Fine Coal using Hydrophobic Displacement". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/33416.
Testo completoAbstract (sommario):
A new processing technique, known as hydrophobic displacement, was explored as a means of simultaneously removing both mineral matter and surface moisture from coal in a single process. Previous thermodynamic analysis suggests that coal moisture will be spontaneously displaced by any oil with a contact angle greater than ninety degrees in water. Based on these results, six methods of hydrophobic displacement were evaluated: hand shaking, screening, air classification, centrifugation, filtration, and displacement. In the first five methods hydrophobic displacement took place during the cleaning stage. A recyclable non-polar liquid (i.e. pentane) was used to agglomerate coal fines followed by a physical separation step to remove the coal agglomerates from the mineral-laden slurry. Bench-scale tests were performed to identify the conditions required to create stable agglomerates. Only the last method, displacement, did not utilized agglomeration and performed hydrophobic displacement during dewatering, not cleaning. A procedure was also developed for determining moisture content from evaporation curves so that the contents of water and pentane remaining in a sample could be accurately distinguished.
Two primary coal samples were evaluated in the test program, i.e., dry pulverized 80 mesh x 0 clean coal and 100 mesh x 0 flotation feed. These samples were further screened or aged (oxidized) to provide additional test samples. The lowest moisture, 7.5%, was achieved with centrifugation of the pulverized 80 mesh x 0 clean coal sample. Centrifugation provided the most reliable separation method since it consistently produced low moisture, high combustible recoveries, and high ash rejections. Hand shaking produced the next lowest moisture at 16.2%; however, the low moistures were associated with a drop in combustible recovery. There was also a great deal of error in this process due to its arbitrary nature. Factors such as oxidation, size distribution, and contact angle hysteresis influenced the concentrate moistures, regardless of the method utilized.
Master of Science
49
Mastropietro, Dean J. "Interfacial Phenomena and Surface Forces of Hydrophobic Solids". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/48966.
Testo completoAbstract (sommario):
At the molecular level the entropic “hydrophobic effect” is responsible for high interfacial energies between hydrophobic solids and aqueous liquids, the low solubility of apolar solutes in aqueous solvents, and self-assembly in biological processes, such as vesicle formation and protein folding. Although it is known that a strong attraction between apolar molecules exists at the molecular level, it is not clear how this force scales up to objects with dimensions in the range 100 nm–1 m. This work sets out to measure the forces between particles with a radius of about 10 µm. Because we can only measure the total force, which includes the van der Waals force and the electrostatic forces, it is important to isolate the effect of “hydrophobicity”. We do this by measuring for systems where the particles are very hydrophobic (water contact angle, θ ~110°) and the van der Waals and electrostatic forces are very small. Under these conditions we find that the total force is very small: it is similar to the van der Waals force at separations exceeding 5 nm.
Many early works on the hydrophobic force reported surface force at over 100 nm of separation. However, many of these strong, long-ranged attractive forces are likely caused by submicron interfacial bubbles, known as nanobubbles. Nanobubbles were imaged with an atomic force microscope to better understand their stability and dependence on solution properties, such as initial concentration of dissolved gas and changes in gas concentration. We found that nanobubbles still formed in degassed solutions and that lowering the dissolved gas concentration did not reduce the bubble size, implying that nanobubbles do not form from dissolved gas in the liquid phase or do not contain gas and are instead water vapor. Furthermore, addition of an oxygen scavenger agent, sodium sulfite, to a liquid phase that had been pressured with oxygen did not reduce bubble size which could be evidence that nanobubbles are impermeable to gas diffusion across the gas liquid interface, do not form from the dissolved gas in the surrounding liquid, or do not contain gas and are instead water vapor.Ph. D.
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Wang, Xueyuan. "Control and Characterization of Textured, Hydrophobic Ionomer Surfaces". University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1341290657.
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