Dissertations / Theses: 'Hydrophobicitet'

1

Jönsson, Ingrid. "Bio-based water/dirt repellant wood coating." Thesis, KTH, Fiber- och polymerteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298182.

Full text

Abstract:

Syftet med detta examensarbete var att utveckla en helt bio-baserad vatten- och smutsavstötande ytbehandling för trä med ambitionen att ersätta en icke bio-baserad referens produkt på marknaden. Flera emulsioner med oljor och vaxer har framställts och analyserats utefter emulsionernas stabilitet och kvalitet. Flera av dessa emulsioners vattenabsorption, kontaktvinkel, pH värde vid ytan och åldrande i utomhusmiljö testades också efter att olika typer av trä behandlats med formuleringarna. En del av formuleringarna verkade ge liknande vattenabsorption som referensen på de olika typerna av trä med undantag för trä typ 4 där de bio-baserade formuleringarna presterade bättre än referensen. Vidare bildade även de bio-baserade formuleringarna en mindre gul och sträv yta jämfört med referensen och de genomgick dessutom en mindre fysisk förändring efter placering utomhus. Dock var stabiliteten för de bio-baserade emulsionerna sämre än för referensen. Dessutom resulterade de bio-baserade formuleringarna till en mindre pH sänkning på trä typ 3 med alkaliskt.
The aim of this thesis project was to develop a fully bio-based water and dirt repellent wood coating with the ambition to replace the current non-bio-based reference product on the market. Several wax and oil emulsions were made and analyzed in terms of emulsion quality and stability. Several formulations were also tested on different types of wood in terms of water absorption, weathering, surface pH and contact angle. Some formulations seam to give similar water absorption as the reference, the not bio-based product and performs similar on different types of wood with an exception on Wood type 4 where the bio-based formulations performs better than the current reference product. Secondly the bio-based formulations form a less yellow and rough coating compared to the current reference product. According to the weathering test the bio-based formulations seams to perform better. However, the stability of the bio-based formulation is not as good as the current reference product. Also, the developed bio-based conceptual formulations exhibited limited pH lowering on Wood type 3 with alkaline pH.

APA, Harvard, Vancouver, ISO, and other styles

2

Jones, Amanda Kay. "Hydrophobicity in polysaccharide gelation." Thesis, Cranfield University, 1992. http://dspace.lib.cranfield.ac.uk/handle/1826/4595.

Full text

Abstract:

The role of hydrophobic substituents on the gelation mechanism of highly esterified pectin and the cellulose derivatives methylcellulose and hydroxypropylmethylcellulose (HPMC) has been explored by monitoring the behaviour of the amphiphilic polysaccharides in varying combinations of an ethylene glycoVwater solvent. The gelling ability (mechanical spectroscopy, visual observation) of very highly esterified (- 100%) pectin in high concentrations of ethylene glycol (>60%) is greatly reduced, however, the polymer still undergoes conformational ordering (CD, OR). A model for gel formation involving a two stage process has been proposed, comprising adoption of the ordered structure stabilised by hydrogen bonding between OH groups of contiguous polysaccharide chains, followed by (or coincident with) aggregation of the ordered sequences by 'hydrophobic' clustering of the fundamental structural subunits to form the three dimensional gel network. It has been found that ethylene glycol promotes the fIrst stage (ordering) but is antagonistic to the second (aggregation). The reversibility (mechanical spectroscopy) of the thermo-gelling cellulose derivatives can be largely abolished in the presence of ethylene glycol (40% for methylcellulose, 10% for HPMC), attributed to solubilisation of the proposed ordered 'bundle' structure at low temperatures removing the enthalpic advantage (DSC) of gel melting. The increased sensitivity of HPMC to modification of the solvent environment is due to the presence of the polar hydroxypropyl substituent causing an inceptive destabilisation of the 'bundle' structure. It is suggested that gelation is driven by the entropic advantage of melting-out 'cages' of structured water surrounding the hydrophobic groups giving rise to intermolecular 'hydrophobic' aggregation.

APA, Harvard, Vancouver, ISO, and other styles

3

Jäger, Robert. "Quantification and localization of molecular hydrophobicity." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=960539999.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Crawford, Russell J., and n/a. "Particle size, hydrophobicity and flotation response." Swinburne University of Technology, 1986. http://adt.lib.swin.edu.au./public/adt-VSWT20070828.150946.

Full text

Abstract:

Quartz particles of various discrete particle size ranges have been methylated to varying known mounts using trimethylchlorosilane and their flotation behaviour has been assessed in a modification of the Hallimond tube. For each particle size there is a definite degree of. surface coverage below which the particles do not float. A 'flotation domain' is identified which shorvs that both coarse (-100pm) and fine (-10pm) particles require a greater degree of surface coverage to initiate flotation than do intermediate (-40pm) particles. Water contact angles have been measured on quartz plates and powders which have been methylated (under the same conditions) with trimethylchlorosilane. Both advancing and receding water contact angles measured on quartz plates as a function of degree of surface methylationare in good agreement with the angles predicted by the Cassie equation. Advancing water contact angles measured on quartz particles as a function of degree of surface methylation are also in good agreement with angles predicted by the Cassie equation up to surface coverages of'about 70%. The angles measured at higher surface coverages are less than those anticipated by the Cassie equation. The flotation behaviour of the particles has been compared with that predicted by existing flotation theories. It has been shown that coarse particle behaviour is predicted by the kinetic theory of flotation proposed by Schulze. Fine particle behaviour, however, only qualitatively agrees with Scheludko's theory of fine particle behaviour. Calculated induction times, in conjunction with observed flotation behaviour, indicate that the bubble-particle attachment process is most efficient for particles of about 38pm in diameter ander the set experimental conditions used in this study. Flotation rate trials were performed for three particle size ranges and rate constants were evaluated for the various degrees of surface coverage. It was found that the dependence of rate constant on particle size is essentially linear.

APA, Harvard, Vancouver, ISO, and other styles

5

Fergusson, Christian. "Hydrophobicity of Low Temperature Vibrating Surfaces." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5589.

Full text

Abstract:

This study proposes a method to enhance the anti-icing capabilities of superhydrophobic surfaces by utilizing vibration to further reduce contact time of an impacting droplet in addition to keeping the droplet in the Cassie-Baxter regime, where surface adhesion is lower than the opposing Wenzel regime. We tested this with two methods: by investigating the effects of vibration normal to the plane of a superhydrophobic surface being impacted by water droplets in a room temperature environment, with the surface horizontal in a room temperature environment and tiled in a subzero degree environment. The amplitude and frequency of the vibration were varied in our experiments. Our results show that the mean contact time of a 10µL droplet consistently decreased linearly as the vibration frequency increased, though the standard deviations drastically increased. The ice accretion in the second phase of the testing also had significant variance, which obfuscated any reliable trend from the introduction of vibration.

APA, Harvard, Vancouver, ISO, and other styles

6

Arbabzadeh, Sima-Dokht. "Functionality hydrophobicity relationships of selected food proteins." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69580.

Full text

Abstract:

Commercial food proteins were used in order to study the relationship between hydrophobicity and two functional properties: emulsification and foaming. Hydrophobicity determined by sodium dodecyl sulfate (SDS) binding method and the cis-parinaric acid (CPA) fluorescence probe method gave poor statistical correlation with foaming and emulsification. The SDS binding method gave higher hydrophobicity and higher correlation values with foaming and emulsifying, than the fluorescence probe CPA method.
Fourier Transform Infrared (FTIR) spectroscopy was used to study the secondary structures, of the commercial food proteins. Infrared spectra of the protein samples with or without denaturing agents (SDS, urea, and guanidine) in the region of the amide I and II bands were determined in deuterium oxide (D$ sb{2}$O) buffer. Fourier self-deconvolution was used to study infrared band positions. BSA was an $ alpha$-helix protein, and in the presence of SDS, due to protein unfolding, exhibited a random coil structure. By correlating their infrared spectra to predetermined peak positions in the protein samples, it was shown that the legume proteins contained $ beta$-structure, and as SDS was added, exhibited non-ordered structures. The spectra of gluten samples were obtained only in the presence of SDS, showing either random coil, or non-ordered structures.

APA, Harvard, Vancouver, ISO, and other styles

7

Chacko, Blesson. "Hydrophobicity, solvation and structure formation in liquids." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/27536.

Full text

Abstract:

In this thesis we use density functional theory (DFT) to study the solvent mediated interactions between solvophobic, solvophilic and patchy nanostructures namely rectangular cross section blocks. We calculate both the density profiles and local compressibility around the blocks and the results obtained for our model system provide a means to understanding the basic physics of solvent mediated interactions between nanostructures, and between objects such as proteins in water, that possess hydrophobic and hydrophilic patches. Our results give an improved understanding of the behaviour of liquids around solvophobic objects and solvophobicity (hydrophobicity) in general. Secondly, we look into the physics incorporated in standard mean-field DFT. This is normally derived by making what appears to be a rather drastic approximation for the two body density distribution function: ρ(2)(r,r′) ≈ ρ(r)ρ(r′), where ρ(r) is the one-body density distribution function. We provide a rationale for why the DFT often does better than this approximation would make you expect. Finally, we develop a lattice model to understand the nature of the pattern formation exhibited by certain systems of particles deposited on liquid-air interfaces and in particular the nature of the transitions between the different patterned structures that are observed. This is done using Monte Carlo computer simulations and DFT and links the observed microphase ordering with the micellisation process seen e.g. in surfactant systems.

APA, Harvard, Vancouver, ISO, and other styles

8

Ho, Thu. "DEVELOPMENT OF MAGNETIC FABRICS WITH TUNABLE HYDROPHOBICITY." VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/400.

Full text

Abstract:

Polystyrene (PS) fiber mats incorporating iron (Fe) particles were fabricated by electrospinning and the hydrophobicity of the resulting magnetic fabrics was investigated with and without an applied magnetic field. The results show that the hydrophobicity (as measured using water droplet contact angle) increases in the presence of a magnetic field and the hysterisis in the advancing/receding contact angle (a measure of the stickiness of the surface) decreases in the presence of a magnetic field. It is also shown that the contact angle and hysterises increase with decreasing fiber diameter and mat thickness.

APA, Harvard, Vancouver, ISO, and other styles

9

Melki, Safi. "Etude du mouillage de structures fibreuses multi échelles : robustesse de l’hydrophobicité." Thesis, Mulhouse, 2014. http://www.theses.fr/2014MULH8863/document.

Full text

Abstract:

Ces travaux ont pour but d’étudier le comportement au mouillage spontané (statique et dynamique) ainsi que le mouillage forcé, sous l’effet de la compression, de différentes structures textiles hydrophobes. Le mouillage forcé a permis d’évaluer la robustesse de l’hydrophobicité des structures textiles. En parallèle, un nouveau dispositif automatisé et plus approprié à l’étude du mouillage forcé a été mis au point. Les principaux résultats ont montré qu’une bonne hydrophobicité ne conduit pas forcément à une bonne robustesse : spontanément, la structure floquée est la seule à favoriser une configuration de Cassie-Baxter, cependant, sa robustesse est plus faible que celle des tissus. Les différents essais ont mis en évidence l’influence importante et majeure de certains paramètres, appropriés à chaque structure textile, sur son hydrophobicité et sa robustesse comme la densité et la finesse des poils pour les tissus floqués. Ils ont également montré que certains facteurs pouvaient améliorer l’hydrophobicité mais pas sa robustesse ou inversement. Ainsi, la robustesse de l’hydrophobicité n’est pas prévisible à partir des mesures du mouillage spontané
This work aims to study the spontaneous (static and dynamic) and the forced (under the effect of compression) wetting behaviour of different water-repellent textile structures. Forced wetting allowed to evaluate the robustness of the hydrophobicity of textile structures. In parallel, a new automated and more suitable device was developed for the study of forced wetting. The main results showed that a good hydrophobicity does not necessarily lead to a good robustness: spontaneously, the flocked structure is the only one to foster the Cassie-Baxter state, however, its hydrophobicity’s robustness is lower than that of the tissue. The different tests have highlighted the important and major influence of some parameters, adapted to each textile structure, on its hydrophobicity and its robustness such as the density and fineness of bristles for flocked fabrics. They also showed that some factors can improve the hydrophobicity but not its robustness or vice versa. Thus, the robustness of the hydrophobicity is not predictable from the measures of spontaneous wetting

APA, Harvard, Vancouver, ISO, and other styles

10

Akhtar, Mst Alpona. "Hydrophobicity of Magnetite Coating on Low Carbon Steel." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1248389/.

Full text

Abstract:

Superhydrophobic coatings (SHC) with excellent self-cleaning and corrosion resistance property is developed on magnetite coated AISI SAE 1020 steel by using a simple immersion method. Roughness measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), contact angle measurement (CAM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), and qualitative characterization of self-cleaning behavior, antifouling property and durability of the coatings are assessed. A water contact angle as high as 152o on the coated surface with excellent self-cleaning and resistivity to corrosion and good longevity in atmospheric air is obtained. Self-cleaning test results prove that these surfaces can find applications in large scale production of engineering materials. Potentiodynamic polarization tests and EIS tests confirm that the superhydrophobic low carbon steel surfaces have better resistance to corrosion compared to bare steel and magnetite coated steel in 3.5% NaCl solution. But the longevity of the coated steel surfaces in 3.5% salt solution is limited, which is revealed by the immersion durability test. However, hydrophobic coatings (HC) have better stability in normal tap water, and it can stay unharmed up to 15 days. Finally, hydrophobic coatings on low carbon steel surface retains hydrophobic in open atmosphere for more than two months. Results of this investigation show surface roughness is a critical factor in manufacturing hydrophobic steel surfaces. Higher contact angles are obtained for rougher and more uniform surfaces. A linear mathematical relationship (y =6x+104; R2 = 0.93) is obtained between contact angle (y) and surface roughness (x).

APA, Harvard, Vancouver, ISO, and other styles

11

Lamour, I. A. "Preparation and application of metal coatings with extreme hydrophobicity." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501304.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Hayoun, Pascaline. "Partial wetting of thin liquid films in polymer tubes." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066202/document.

Full text

Abstract:

Les tubes polymères, de PDMS ou de PVC, sont des matériaux hydrophobes polyvalents et peu couteux. Ils sont très largement utilisés dans l'industrie pour transférer des fluides plus ou moins complexes tels que de l'eau potable, des émulsions (e.g lait), des suspensions (e.g café), ou encore des solutions de molécules actives (e.g médicament). La plupart de ces applications mettent en jeux des écoulements intermittents répétés de liquide qui peuvent contaminer le matériau. Cette étude a pour but de mieux comprendre comment ces écoulements de fluides complexes entraînent la contamination des tubes. Nous étudions expérimentalement et théoriquement les régimes d'un segment de liquide de faible viscosité s'écoulant dans un tube en conditions de mouillage partiel. Deux processus sont en compétition : à cause de la vitesse élevée du segment de liquide, un film de liquide se forme à l'arrière du segment, alors qu'à cause de des conditions de mouillage partiel le film de liquide démouille. Nous montrons qu'au-delà de la limite en vitesse correspondant à la transition de mouillage dynamique qui est bien inférieure à la prédiction de Cox-Voinov, un régime précédemment inconnu avec un film épais, dont l'épaisseur dépend de la vitesse, est obtenu bien avant la formation classique d'un film de Landau-Levich-Derjaguin. Nos simulations numériques sont en partie en accord avec nos observations
Polymer tubes, made of PDMS or PVC, are versatile, low cost, hydrophobic materials. They are heavily used in industry for transferring more or less complex fluids such as drinkable water, emulsions (e.g milk), suspensions (e.g coffee), or solution of active molecules (e.g pharmaceutics). Most of these applications involve repeated, intermittent flow of liquids which can lead to unwanted contamination. This study aims at better understanding the mechanisms of contamination for intermittent flow. We experimentally and theoretically investigate the flow regimes of low viscosity liquid slugs flowing down a vertical tube under partial wetting condition. Two processes are in competition: because of the large slug velocity, a liquid film tends to be created at the back of the slug whereas because of the partial wetting condition, the liquid film dewets. We investigate how this competition controls film deposition in hydrophobic tubes. We show that above the threshold velocity for dynamic wetting which is much lower than predicted by Cox-Voinov, a previously unknown regime is found where we observe a velocity dependent thick film well before the classical Landau-Levich-Derjaguin regime

APA, Harvard, Vancouver, ISO, and other styles

13

Schmidt, Anette Skammelsen. "An investigation of the partition behaviour of proteins based on their physico-chemical properties in aqueous two-phase systems." Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239470.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Cao, Liwen. "Effects of heat on the hydrophobicity of EPDM composite insulators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0010/MQ52522.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Hu, Yongan. "Influences of monomer hydrophobicity on secondary nucleation in emulsion polymerization." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555602067112746.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Pouzet, Martial. "Modification de l’énergie de surface du bois par fluoration." Thesis, Université Clermont Auvergne‎ (2017-2020), 2017. http://www.theses.fr/2017CLFAC086/document.

Full text

Abstract:

La disponibilité, les aspects écologiques et économiques du bois sont autant d’avantages qui expliquent le large champ d’applications de ce matériau dans plusieurs domaines tels que la papeterie, l’ameublement, la menuiserie ou la construction. Cependant, le bois est un matériau hygroscopique très sensible aux variations d’humidité et de température ambiante. Le gonflement et le retrait causés par l’adsorption et la désorption de l’eau engendrent des fissures et des déformations dans le bois, le rendant incompatible avec certaines applications.Dans cette étude, une méthode originale a été appliquée sur des échantillons de bois (douglas et sapin) pour diminuer leur caractère hydrophile : la fluoration directe par du fluor moléculaire F2. Le greffage covalent des atomes de fluor sur la surface du bois, grâce à une substitution des groupements C-OH par des liaisons C-F, a été validé par spectroscopie infrarouge et par Résonance Magnétique Nucléaire du 19F.Le bois, qui est intrinsèquement hydrophile, acquiert un caractère hydrophobe comparable à celui du Téflon grâce à la fluoration. Des études de vieillissements sous atmosphère ambiante et irradiation UV ont permis de déterminer une bonne durabilité du traitement. De plus, ce traitement permet d’obtenir un caractère hydrophobe sans changements structuraux (morphologie, densité et couleur) ou mécaniques majeurs. Grâce au caractère surfacique de la fluoration, la conservation de ces propriétés après la fluoration s’avère être un remarquable avantage par rapport aux autres traitements physiques et chimiques classiquement utilisés dans l’industrie du bois
The availability, the ecological and economic characteristics of wood are advantages which explain the very wide scope of applications of this material in several domains such as the paper industry, furniture, carpentry and construction. However, wood is a hygroscopic material, highly sensitive to ambient humidity and temperature. The swelling and the shrinking caused by water adsorption and desorption cycles lead to cracking and deformation in the wood volume, making it incompatible for some applications.In this study an original surface treatment was applied to wood samples (douglas and silver fir species) to decrease their hydrophilic character: direct fluorination using F2 gas. The covalent grafting of fluorine atoms onto extreme wood surfaces through a conversion of C-OH groups into C-F was evidenced by Fourier-Transform infrared spectroscopy and 19F solid state Nuclear Magnetic Resonance.The wood which is initially hydrophilic acquires a hydrophobic character comparable to that of Teflon, thanks to fluorination. Good durability of this treatment under ambient atmosphere and UV irradiation was also highlighted. Moreover, because it affects only the extreme surface, this treatment allowed us to obtain a hydrophobic character without major structural (morphology, density and colour) or mechanical changes. The maintaining of these properties after fluorination appears to be a remarkable advantage over other traditional physical and chemical wood treatments

APA, Harvard, Vancouver, ISO, and other styles

17

Cao, Feishu. "Caractérisation de l'hydrophobie des polymères extracellulaires (PEC) extrait de biofilms : une étude basée sur la technique de la résine DAX-8." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1048/document.

Full text

Abstract:

Les propriétés hydrophobes des polymères extracellulaires (PEC) exercent l’influence profonde sur les propriétés de la surface cellulaire. Cependant, de nombreux facteurs tels que les méthodes d'extractions, le type de substrat influencent les caractéristiques des PEC et les informations concernant des caractéristiques hydrophobes sont rarement documentées. L'objectif principal de cette étude est de développer une méthode appropriée pour étudier l'hydrophobicité des PEC, puis d'étudier les caractéristiques hydrophobes des PEC.Le fractionnement hydrphobe par la résine Supelite™ DAX-8 a d'abord été appliqué sur les PEC extraits de boues granulaires anaérobies, deux conditions de pH d'élution (pH 2 et 5) ont été testées. L'impact de sept méthodes d'extraction sur les caractéristiques hydrophobes des PEC a été évalué. Les résultats ont montré que les méthodes d'extraction et le pH de la solution extraitante ont influencé la composition des PEC et leur hydrophobicité. En outre, les extraitants des PEC, par exempe le formaldéhyde, l'éthanol, le dodécylsulfate de sodium (SDS) et Tween 20, ont non seulement introduit une teneur supplémentaire en carbone pendant la mesure du carbone organique total (COT), mais ils ont également interagit avec la résine DAX-8. En comparant la répartition du poids moléculaire apparent (aMW) des échantillons des PEC non traités et ajustés au pH détectés par chromatographie d'exclusion stérique (en anglais SEC), l’information plus complète d’aMW a été préservée à pH 5. Ainsi, le fractionnement hydrophobe par la résine DAX-8 à pH 5 et les méthodes physiques d'extraction PEC ont été préférés dans cette étude.Une analyse qualitative détaillée des caractéristiques hydrophobes des EPS a été étudiée par la technique de la matrice de fluorescence d’excitation-emission (EEM). Les résultats ont montré que les substances de type humique (HS-like) représentaient la majorité des composés organiques des PEC extraits de la boue granulaire anaérobie, et constituaient également le principal support moléculaire de l'hydrophobicité des extraits. Ces composés hydrophobes de type HS étaient essenciellement des molécules petites tailles de 8 kDa à <1 kDa. L’hydrophobité contributée par les protéines (PN) et les polysaccharides (PS) présentait un moindre rapport.Afin d’explorer les propriétés hydrophobes de PN et de PS, ainsi évaluer l'impact de l'addition de Ni(II) sur l'hydrophobicité des extraits des champignons, fongi Phanerochaete chrysosporium a été choisi. Les résultats ont montré que la teneur de PN et de PS dans les PEC extrait de ce type de fongi variait en fonction de la concentration de Ni(II). Avec une augmentation de la concentration de Ni de 0 mg/L à 25 mg/L, la teneur en PN a diminué alors que celle de PS a été augmentée. L'hydrophobicité des PEC du fongi, déterminée par le traitement de la résine DAX-8, a diminué lors que la concentration de Ni augmentait. Par ailleurs, l'intensité du pic de SEC correspondant aux molécules PN-like (Ex/Em = 225/345 nm) de 1,9 × 103 à 10 kDa a été augmentée par l'addition Ni; en même temps, la distribution d’aMW des composés organiques totaux (UV/210) dans les PEC restait presque stable. Ces résultats ont indiqué que les composés de type PN-like peuvent avoir déterminé l'hydrophobicité des PEC fongique dans des conditions de stress.Dans l’extrait plus hétérogène des PEC de boues granulaires anaérobies, des composés HS-like représentaient le composant organique majeur, ainsi le principal support moléculaire de l'hydrophobicité des PEC. En étudiant les caractéristiques hydrophobes des PEC extrait du champignon Phanerochaete chrysosporium, le PN et le PS des PEC jouaient un rôle actif dans la protection du champignon sous le Ni. La concentration élevée de Ni a diminué l'hydrophobicité des PEC fongique, mais elle a augmenté l'hydrophobicité de la surface cellulaire du champignon. Il semble que la présence de Ni favorise l'apparition d'un champignon plus hydrophobe
The hydrophobic properties of extracellular polymeric substances (EPS) exert a profound influence on the cell surface properties. However, many factors such as EPS extractions methods, substrate type influence EPS characteristics, and limited information regarding to the hydrophobic features of EPS can be found. The main aim of this study is to develop a proper method to study EPS hydrophobicity, and then investigate the hydrophobic features of EPS.The hydrophobic fractionation by Supelite™ DAX-8 resin was first applied on the EPS extracted from anaerobic granular sludge, two elution pH conditions i.e. pH 2 and 5 were tested. The impact of seven EPS extraction methods on the hydrophobic features of EPS was assessed. The results showed that the extraction methods and bulk solution pH dramatically influenced the EPS composition and their hydrophobicity. Besides, the EPS extracting reagents namely formaldehyde, ethanol, sodium dodecyl sulfate (SDS) and Tween 20 not only introduced extra carbon content during total organic carbon (TOC) measurement, but also interacted with the DAX-8 resin. By comparing the apparent molecular weight (aMW) distribution of the untreated and pH-adjusted EPS samples detected by size exclusion chromatography, more complete EPS aMW information was preserved at pH 5. Thus, the hydrophobic fractionation by DAX-8 resin at pH 5 and physical EPS extraction methods were preferred in this study.After identifying the proper conditions for DAX-8 resin fractionation, detailed qualitative analysis of the EPS hydrophobic features was further investigated. The results showed that the humic-like substances (HS-like) were the major organic constituent of the EPS extracted from the anaerobic granular sludge, and they were also the main molecular support of the EPS hydrophobicity. Those hydrophobic HS-like compounds were mainly small molecules ranging from 8 kDa to <1 kDa. Proteins (PN) and polysaccharides (PS) contributed to the EPS hydrophobicity to a lesser extent.The role of PN and PS in the EPS hydrophobicity was difficult to be shown. It is known that the major organic constituents of the EPS extracted from bacteria, algae and fungi are PN and PS. Therefore, to explore the hydrophobic features of PN and PS, as well as to investigate the impact of Ni(II) addition, on the EPS hydrophobicity, the fungus Phanerochaete chrysosporium was chosen. The results showed that the contents of PN and PS in the extracted fungal EPS varied with the Ni(II) concentration. With an increase in the Ni concentration from 0 mg/L to 25 mg/L, the PN content was decreased whereas the PS content was increased. The fungal EPS hydrophobicity, determined by the DAX-8 resin treatment, was decreased as the Ni concentration increased.Besides, the peak intensity on the size exclusion chromatography (SEC) corresponding to the PN-like molecules (Ex/Em = 225/345 nm) ranging from 1.9×103 to 10 kDa were intensified by the Ni addition, while the aMW distribution of the total organics (UV/210) in the EPS remained almost stable. These results indicated that those PN-like compounds may determine the hydrophobicity of fungal EPS under stress conditions.For the more heterogeneous EPS extracted from anaerobic granular sludge, HS-like compounds were identified as the major organic component, as well as the main molecular support of the EPS hydrophobicity. By studying the hydrophobic features of the EPS extracted from the fungus Phanerochaete chrysosporium, it showed that the PN and PS in the EPS played an active role in protecting the fungus under Ni stress. The increased Ni concentration decreased the hydrophobicity of fungal EPS, but it increased the cell surface hydrophobicity of the fungus. It seems that the presence of Ni promoted the fungus becoming more hydrophobic

APA, Harvard, Vancouver, ISO, and other styles

18

Acharya, Hari. "Hydrophobicity, heat transfer, and momentum transfer at hard and soft aqueous interfaces." Thesis, Rensselaer Polytechnic Institute, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3600990.

Full text

Abstract:

Advancements in science and technology increasingly involve systems operating at the nanoscale. Interfaces are often present in these systems. Nanoscopic interfaces are ubiquitous in biological systems, nanofluidic devices, and integrated circuits. Properties at the interface may be quite different from the bulk, and in fact a true bulk may not be present in these systems. At the nanoscale the ratio of interface to volume is large, and the interface may have the dominant role in determining system behavior. Interfacial characteristics and their connection to interfacial properties are the focus of my thesis. Using molecular simulations of model interfaces we characterize how properties like chemistry, composition, and topography affect such phenomena such as hydrophobicity, heat transfer, and momentum transport at the nanoscale. An interface is defined simply as where two materials meet and a change in some structure or order parameter is observed. In aqueous systems, the type studied here, these changes are relatively sharp and occur within a distance of nanometers. Water molecules near the interface are expected to display sensitivity to the underlying surface. Indeed, water near a hydrophobic surface is more deformable and has greater fluctuations. The hydrophobicity of chemically heterogeneous surfaces and proteins are characterized using these nanoscopic measures. We find the effect of mixing hydrophobic and hydrophobic head group chemistries is asymmetric, i.e., it is easier to make a hydrophobic surface hydrophilic than the reverse. The role of hydrogen bonding in hydrophobic and ion hydration is also characterized using a short range water model. Hydrophobic and ion hydration are reasonably captured with the short range water model. These studies show the importance of chemical composition and local hydrogen bonding in determining surface hydrophobicity. Interfaces also lead to anomalous behavior in heat and momentum transport. Interfaces disrupt local structure and create boundary resistances that manifest in temperature discontinuities and interfacial slip. We explore the effects of chemical heterogeneity, nanoscale surface roughness, and directionality on thermal conductance across model solid-water interfaces. Interfacial conductance is directly influenced by the coupling strength or wettability of the surface. For chemically mixed surfaces, interfacial conductance does not precisely match with wettability. Surface roughness in general enhances conductance, but the improvement cannot be completely attributed to increased solvent accessible surfaced area. Momentum transport displays similar discontinuities at aqueous interfaces. These effects can be reduced through the use of osmolytes. Collectively this work highlights the influence of interfaces on heat and momentum transport. Insights are provided for modifying interfacial behavior and altering the property of interest.

APA, Harvard, Vancouver, ISO, and other styles

19

Hillborg, Henrik. "Loss and recovery of hydrophobicity of polydimethylsiloxane after exposure to electrical discharges." Doctoral thesis, KTH, Polymer Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3082.

Full text

Abstract:

Silicone rubber based on polydimethylsiloxane is used ashigh voltage outdoor insulation, due to its ability to preservethe hydrophobic surface properties during service and evenregain hydrophobicity after exposure to electrical discharges.The underlying processes for the hydrophobic recovery arediffusion of low molar mass siloxanes from the bulk to thesurface and reorientation by conformational changes ofmolecules in the surface region. Only little is known of whichfactors are responsible for the long-term stability of thishydrophobic recovery. It is therefore important to increase theknowledge about the fundamental mechanisms for the loss andrecovery of hydrophobicity of silicone rubbers, exposed toelectrical discharges. Addition-cured polydimethylsiloxanenetworks, with known crosslink densities, were exposed tocorona discharges and air/oxygen-plasma and the loss andrecovery of hydrophobicity was characterised by contact anglemeasurements. The degree of surface oxidation increased withincreasing exposure time with a limiting depth of 100- 150 nm,as assessed by neutron reflectivity measurements. The oxidationrate increased with increasing crosslink density of the polymernetwork, according to X-ray photoelectron spectroscopy. Withinthe oxidised layer, a brittle, silica-like layer was graduallydeveloped with increasing exposure time. The hydrophobicrecovery following the corona or air/oxygen- plasma exposuresoccurred at a slow pace by diffusion of cyclic oligomericdimethylsiloxanes through the micro-porous but uncrackedsilica-like surface layer or at a much higher pace by transportof the oligomers through cracks in the silica-like layer. Theoligomers were present in the bulk, but additional amounts wereformed during exposure to corona discharges. High-temperaturevulcanised silicone rubber specimens were aged in a coastalenvironment under high electrical stress levels (100 V/mm). Thechanges in surface structure and properties were compared tothe data obtained from specimens exposed to coronadischarges/plasma. The dominating degradation mechanism wasthermal depolymerisation, initiated by hot discharges. Thisresulted in the formation of mobile siloxanes, of which the lowmolar mass fraction consisted of cyclic oligomericdimethylsiloxanes. Oxidative crosslinking resulting insilica-like surface layers was not observed during theseconditions.

Keywords:silicone rubber, polydimethylsiloxane,hydrophobicity, corona, air-plasma, oxygen-plasma, surfacecharacterisation, degradation products, crosslink density.

APA, Harvard, Vancouver, ISO, and other styles

20

Thompson, Troy David. "Remediation of Soil Hydrophobicity on a Coastal USGA Sand-Based Golf Green." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/303.

Full text

Abstract:

Managing soil hydrophobicity caused by localized dry spots (LDS) on sand based golf greens has become one of the greatest challenges for golf course superintendents and managers, especially as water restrictions intensify. The purpose of this study was to evaluate the effectiveness of thirteen soil surfactants in eliminating LDS and in maximizing root zone soil moisture on a sand based USGA golf green located on the California Central Coast. Potential water repellency of air dried cores (measured utilizing the water droplet penetration time (WDPT) method), phytotoxicity, and climate were analyzed during two experimental trials. Phytotoxicity data was collected for Trial I using visual quality ratings and for Trial II using a chlorophyll meter. Phytotoxicity decreased during Trial I. Differences in phytotoxicity as measured using chlorophyll index were not at all significant during Trial II (p = 1). Ten of the thirteen wetting agent treatments significantly (p < 0.001) decreased soil hydrophobicity compared with the other wetting agent treated plots and the non-treated control. More frequent application of Cascade Plus resulted in a more significant reduction in soil hydrophobicity. Increasing the application rates also resulted in the reduction of soil hydrophobicity. Wetting agent treatment 6-CP(10day) maintained the highest volumetric water content (VWC) but treatment 13-2079337 maintained the highest levels for wetting agents treated monthly.

APA, Harvard, Vancouver, ISO, and other styles

21

Mao, Laiqun. "Application of Extended DLVO Theory: Modeling of Flotation and Hydrophobicity of Dodecane." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/29232.

Full text

Abstract:

The extended DLVO theory was used to develop a flotation model by considering both hydrodynamic and surface forces involved in the process. A stream function was used to estimate the kinetic energies for thinning the water films between bubbles and particles, which were compared with the energy barriers, created by surface forces, to determine the probability of adhesion. A general expression for the probability of detachment was derived from similar mechanism for chemical reaction, and the kinetic energy for detachment was estimated with French and Wilson's model. The hydrophobic force parameter (K132) calculated from the rate constants of single bubble flotation tests showed that, K132 for bubble-particle interaction were close to the geometric means of K131 for particle-particle interactions and K232 for bubble-bubble interaction, indicating that the combining rules developed for dispersion forces may be useful for hydrophobic forces. The model was used to predict flotation results as functions of several important parameters such as contact angle, double-layer potentials, particle size, bubble size, etc. The predictions were consistent with experience, and could be explained in view of the various subprocesses considered in the model development. Furthermore, the model suggested optimum conditions for achieving the maximum separation efficiency. The extended DLVO theory was also used to determine the hydrophobic force between two oil/solution interfaces from the equilibrium film thicknesses of dodecylammonium chloride (RNH3Cl) solutions obtained using Thin Film Balance (TFB) technique. The results showed that, the oil droplets were inherently hydrophobic, and the hydrophobic force played an important role in the stability of emulsions. This force decreased with increasing surfactant concentration, and also changed with pH and the addition of electrolyte. The interfacial area occupied by molecules indicated that, the dodecane molecules might present between two surfactant ions at interface, thus the hydrophobicity of oil/solution interface was less sensitive to the addition of the surfactant than that of air/solution interface. Thermodynamic analysis suggested that, there might exist a relationship between the interfacial hydrophobicity and the interfacial tension.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

22

Liu, Qi. "The role of mineral surface composition and hydrophobicity in polysaccharide/mineral interactions." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28861.

Full text

Abstract:

The interactions of polysaccharides (dextrin, amylopectin and carboxymethyl cellulose (CMC)) with variously modified quartz samples were investigated using floatability, wettability, electrokinetic and adsorption tests, supplemented by conventional titration and infrared spectroscopic studies. The quartz samples were treated either by methylation (rendered hydrophobic), lead coating (introduction of metallic adsorption centres), or both forms of surface modification. The presence of metal ionic sites on a quartz surface played a decisive role in polysaccharide adsorption. The adsorption densities of both dextrin and CMC on lead-coated quartz were both much higher and much more pH-dependent than those on uncoated quartz. The "hydrophobic bonding" of dextrin with mineral surfaces as reported in the literature was not observed with hydrophobic (methylated) quartz. However, if the quartz contained surface lead ionic sites and was also methylated, it adsorbed more dextrin than unmethylated, lead-coated quartz. This was also true for the adsorption of CMC onto similarly modified quartz samples. To obtain a rational understanding of the importance of metal ions in polysaccharide adsorption, studies of the solution chemistry of polysaccharides and metal ions were conducted. CMC co-precipitated with both metal cations and metal hydroxy complexes, (including metal hydroxides), whereas dextrin co-precipitated only with metal hydroxides. Co-precipitation involving either polysaccharide caused a decrease in the solution pH. Dextrin-metal co-precipitation occurred at pH optima of 7.5, 8, 9, 11, and 12 for ferric, aluminum, cupric, lead and magnesium ions, respectively. Infrared spectroscopic studies of the precipitates revealed the elimination of glucose ring deformation, suggesting a chemical basis for the interaction between dextrin and metal hydroxides. The surfaces of sulphide minerals behaved like hydroxide during dextrin adsorption. Since copper and lead hydroxides form over different pH ranges, the pH ranges for optimum adsorption of dextrin on copper sulphides and lead sulphides were different. The results of preliminary flotation tests indicated that dextrin could be utilized in the differential flotation of Cu-Pb sulphides. Small scale flotation tests conducted on synthetic mixtures of chalcopyrite and galena confirmed this point.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

APA, Harvard, Vancouver, ISO, and other styles

23

McDonagh, James L. "Computing the aqueous solubility of organic drug-like molecules and understanding hydrophobicity." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6534.

Full text

Abstract:

This thesis covers a range of methodologies to provide an account of the current (2010-2014) state of the art and to develop new methods for solubility prediction. We focus on predictions of intrinsic aqueous solubility, as this is a measure commonly used in many important industries including the pharmaceutical and agrochemical industries. These industries require fast and accurate methods, two objectives which are rarely complementary. We apply machine learning in chapters 4 and 5 suggesting methodologies to meet these objectives. In chapter 4 we look to combine machine learning, cheminformatics and chemical theory. Whilst in chapter 5 we look to predict related properties to solubility and apply them to a previously derived empirical equation. We also look at ab initio (from first principles) methods of solubility prediction. This is shown in chapter 3. In this chapter we present a proof of concept work that shows intrinsic aqueous solubility predictions, of sufficient accuracy to be used in industry, are now possible from theoretical chemistry using a small but diverse dataset. Chapter 6 provides a summary of our most recent research. We have begun to investigate predictions of sublimation thermodynamics. We apply quantum chemical, lattice minimisation and machine learning techniques in this chapter. In summary, this body of work concludes that currently, QSPR/QSAR methods remain the current state of the art for solubility prediction, although it is becoming possible for purely theoretical methods to achieve useful predictions of solubility. Theoretical chemistry can offer little useful additional input to informatics models for solubility predictions. However, theoretical chemistry will be crucial for enriching our understanding of the solvation process, and can have a beneficial impact when applied to informatics predictions of properties related to solubility.

APA, Harvard, Vancouver, ISO, and other styles

24

Jefferson, Bruce. "Mechanisms of particle capture in dissolved air flotation." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/32107.

Full text

Abstract:

The dissolved air flotation process experiences process stability problems that are attributed to a poor understanding of the fundamental mechanisms. A detailed review of the literature revealed that the mechanisms of flotation are fairly well understood in mineral flotation application but that the transfer of knowledge to water treatment application is poor, particularly regarding the differences between particle and floc flotation.

APA, Harvard, Vancouver, ISO, and other styles

25

Lemaître, Christelle. "Purification et caractérisation de protéines hydrophobes extraites du mucus épidermique de carpe (cyprinus carpio). Relations entre activités ionophores et antibactériennes." Rouen, 1996. http://www.theses.fr/1996ROUES056.

Full text

Abstract:

Le rôle de défense contre les microorganismes a déjà été démontré parmi les nombreuses fonctions du mucus épidermique du poisson. En effet, les sécrétions épidermiques de la carpe (cyprinus carpio) contiennent des composés dont l'activité est comparable à celle des peptides de défense, connus chez les bactéries, les insectes, les amphibiens et les mammifères, actifs par la formation de pores dans les membranes cellulaires. Le mucus épidermique possède lui aussi la faculté de générer des canaux ioniques dans des bicouches lipidiques planes et les substances responsables de cette activité ionophore ont été mises a jour. Ainsi, pour la première fois, des protéines de masses moléculaires de 31 kDa et 27 kDa hydrophobes ont été purifiées à partir du mucus épidermique de carpe, solubilisé dans une fraction détergent (octylpolyoxyéthylène). Ces deux protéines forment des canaux transmembranaires, non voltage-dépendants et très légèrement sélectifs pour les anions (31-kDa) ou pour les cations (27-kDa). Les deux protéines sont des antibiotiques très efficaces puisqu'elles agissent à des CMI entre 0. 16 et 0. 18 microM contre les bactéries Gram + et Gram -. D'autre part, des caractérisations préliminaires ont permis de montrer que la glycoprotéine 27-kDa possède une structure secondaire majoritairement en hélice-α. Par contre, la protéine 31-kDa qui n'est pas glycosylée a une structure secondaire qui est organisée en feuillet-β. La question concernant l'origine de synthèse de ces deux protéines a été étudiée afin de déterminer s'il s'agissait d'une sécrétion épidermique ou d'une contamination bactérienne. Les faits sont que (i) les protéines sont actives contre les bactéries pathogènes revivifiées du poisson, (ii) elles ne possèdent pas d'homologue recensé dans les banques protéiques et (iii) ce phénomène existe chez d'autres poissons contenant des protéines ionophores différentes dans leurs sécrétions épidermiques. A ce jour, tout semblerait indiquer que les protéines 31-kDa soient de nouvelles protéines antibiotiques, sécrétées par le mucus épidermique de carpe.

APA, Harvard, Vancouver, ISO, and other styles

26

Powell, Ashley Ann. "Bile acid biological activity in colon cancer cells: From hydrophobicity to gene activation." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280045.

Full text

Abstract:

Bile acids, known for millennia to play a role in health and disease, are currently being studied for their pivotal contribution to the development and possible prevention of colon cancer. Some bile acids have long been suspected to play a role in the development of colon cancer. Particularly, highly hydrophobic bile acids, such as deoxycholic acid (DCA), are known to promote the formation of colon tumors in animal models. However, one moderately hydrophobic bile acid, ursodeoxycholic acid (UDCA), has been shown to be a colon cancer chemopreventive agent, although its mechanism of action is unknown. Originally, it was believed that increased hydrophobicity caused high levels of cell membrane perturbation and digestion, thus resulting in cell death. In addition, it was believed that bile acids could cross membranes to a level related to their hydrophobicity and interact with intracellular molecules to induce biological responses. My studies have shown that while bile acid biological activity is related to hydrophobicity, bile acids do not have the innate ability to cross colon cell membranes. While highly hydrophobic bile acids cause a rapid induction of apoptosis and moderately hydrophobic bile acids cause growth arrest in colon cells, no evidence could be found to show that bile acids could enter colon cells. In fact, my data indicate that bile acids activate signaling cascades through transmembrane receptors on the plasma membrane. It is the activation of these signaling pathways, which result in DCA-induced apoptosis or UDCA-induced growth arrest. My studies have shown that DCA has the ability to activate GADDI53, FADD, and caspase 8 and that activation of these molecules is necessary to produce apoptosis. Additionally, I discovered that UDCA activates Rb and GADD153 and has the ability to induce GI growth arrest and protect cells from DCA induced apoptosis. Interestingly, I found that while DCA and UDCA cause drastically different cellular responses, my data suggest that they signal through shared pathways. I show that UDCA could abrogate DCA activity. These studies also show two possible by which UDCA acts as a chemo-preventive agent: by causing growth arrest and by preventing DCA-induced apoptosis.

APA, Harvard, Vancouver, ISO, and other styles

27

Yancey, Dennis Dwayne. "Controlling changes in cell surface hydrophobicity reduces mass transport limitations in Rhodococcus biotransformations /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Chen, Jiadong. "Shape and Hydrophobicity Effects of Titanium Dioxide Nanoparticles on Blood Plasma Protein Adsorption." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1595977372164445.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Akita, Emmanuel E. "Lipophilization of beta-lactoglobulin : effect on hydrophobicity, surface functional properties, digestibility and allergenicity." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27789.

Full text

Abstract:

In this research, beta-lactoglobulin was chemically modified by attaching different levels of stearic acid to the protein. The effect of this modification on hydrophobic!ty, emulsifying and foam properties, digestibility and allergenicity of the protein was investigated. It was found that the effect of fatty acid attachment or lipophilization depended on the amount of fatty acids attached to the protein. Incorporation of the hydrophobic ligands led to increased hydrophobic interactions, resulting in a decreasing solubility with extent of incorporation. Furthermore, the surface hydrophobicity measurements showed that the two fluorescence probes 8-anilinonaphthalene-l-sulfonate (ANS) and cis-parinaric acid (CPA) used for the surface hydrophobicity measurements were not equivalent This may support the. observation by earlier workers that ANS measures aromatic hydrophobicity and CPA aliphatic hydrophobicity. The studies on surface functional properties i.e. emulsifying and foaming properties, indicated that there was some improvement in these functional properties at low and medium levels of incorporation which decreased as the extent of fatty acid attachment further increased. The improvement, of these functional properties could be attributed to improved amphiphilicity of the proteins at these levels of incorporation. This research also showed that both high solubility and high ANS surface hydrophobicity is needed for the best emulsifying properties. In vitro digestibility studies showed a decrease in digestibility of the modified proteins with increased lipophilization. From the passive cutaneous anaphylaxis experiments, it was found that the level of fatty acid attachment to the protein had a significant effect on its ability to elicit IgE antibodies. Increased ability to elicit IgE antibodies was observed at a low level of fatty acid. When a medium level of fatty acid was attached the ability to elicit antibodies was reduced and almost completely destroyed when a higher level of fatty acid was incorporated. The above observations could be explained by the fact that the low level incorporation of fatty acid led to changes in the protein structure which exposed more allergenic sites. The almost complete destruction of the allergenicity could be attributed to denaturation of the protein which reduced or destroyed available allergenic sites. The antigenicity or binding of the modified proteins to the IgG antibodies raised against the native protein was studied by both direct and competitive enzyme linked immunosorbent assay. It was found that at low and medium levels of incorporation, the proteins demonstrated increased binding ability compared to the native protein. This was attributed to the increased exposure of antigenic sites on the protein with fatty acid incorporation. However, the protein with high level of incorporated fatty acid showed decreased binding ability.
Land and Food Systems, Faculty of
Graduate

APA, Harvard, Vancouver, ISO, and other styles

30

Shakeri, Fard Parvin. "Production and purification of biosurfactants and study of their influence on surface properties of stainless steel and Teflon." Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10006/document.

Full text

Abstract:

Dans cette étude, un ensemble de molécules biosurfactantes a été choisi en fonction de leur diversité structurale et leur aptitude à être produites dans des procédés industriels. Cet ensemble contient des membres des trois familles de composés lipopeptidiques produits par des souches de Bacillus subtilis comprenant la surfactine S1, l’iturine A et la mycosubtiline (deux membres de la famille des iturines) et la fengycine, ainsi que des rhamnolipides produits par Pseudomonas aeruginosa PTCC 1637. Après purification et/ou caractérisation par plusieurs méthodes analytiques, ces composés ont été étudiés pour leur aptitude à modifier l’hydrophobicité de surface de deux substrats, l’acier inoxydable et le Téflon. Ces modifications ont été évaluées par des mesures d’angle de contact de l’eau. Les effets dépendent de la biomolécule, de sa concentration et du substrat. Le traitement de l’acier inoxydable avec différentes concentrations, entre 1 et 100 mg l-1, de surfactine S1 et de rhamnolipides a montré une augmentation de l’hydrophobicité. Sur le même substrat, la fengycine augmente l’hydrophobicité jusqu’à sa concentration micellaire critique (6,25 mg l-1). Avec des concentrations plus élevées en fengycine, une réduction de l’hydrophobicité est observée. La surfactine, la mycosubtiline et l’iturine diminuent l’hydrophobicité sur le Téflon. Des analyses par XPS de surfaces traitées par les lipopeptides ont confirmé la présence des différentes biomolécules. Les relations entre structure, CMC et les propriétés de modifications de surface sont discutées. L’adhésion de spores de Bacillus cereus 98/4, à des surfaces conditionnées par ces biosurfactants, a ensuite été étudiée. Il y a une bonne correlation entre les modifications de l’hydrophobicité et l’adhésion des spores de B. cereus 98/4 à ces surfaces. L’augmentation de l’hydrophobicité des surfaces augmente l’adhésion des spores et vice versa
In this study, a set of biosurfactant molecules was chosen in function of their structural diversity and their ability to be easily produced in industrial processes. This set contains members of three families of lipopeptidic compounds produced by Bacillus subtilis strains including surfactin S1, iturin A and mycosubtilin (two members of the iturin family) and fengycin, as well as rhamnolipids produced by Pseudomonas aeruginosa PTCC 1637. After purification and/or characterization by several analytical methods, these compounds were examined for their ability to modify the surface hydrophobicity of the two substrata stainless steel and Teflon.These modifications were evaluated by water contact angle measurements. The effects depend on the biomolecule, the concentration, and the substratum. Treatment of stainless steel with different concentrations between 1 and 100 mg l-1 of surfactin S1 and rhamnolipids showed an increase in the hydrophobicity. On the same substratum, fengycin increased hydrophobicity up to its critical micelle concentration (6.25 mg l-1). With higher concentrations of fengycin, a decrease in hydrophobicity was observed. Surfactin, mycosubtilin and iturin A decreased hydrophobicity on Teflon. XPS analyses of surfaces treated by lipopeptides confirmed the presence of the different biomolecules. Relationships between structure, CMC, and modifications of surface properties are discussed.Then, the attachment of Bacillus cereus 98/4 spores to conditioned surfaces by these biosurfactants was studied. There are promising correlations between hydrophobicity modifications of surfaces and the attachment of B. cereus 98/4 spores to these surfaces. Enhancement in hydrophobicity of surfaces increases the number of adhering spores to them and vice versa. Finally, a strategy was developed to overproduce a less studied lipopeptide from Bacillus licheniformis, lichenysin which was structurally slightly different from surfactin

APA, Harvard, Vancouver, ISO, and other styles

31

Pezzotti, Simone. "DFT-MD simulations and theoretical SFG spectroscopy to characterize H-Bonded networks at aqueous interfaces : from hydrophobic to hydrophilic environments Structural definition of the BIL and DL: a new universal methodology to rationalize non-linear χ(2)(ω) SFG signals at charged interfaces, including χ(3)(ω) contributions What the Diffuse Layer (DL) Reveals in Non-Linear SFG Spectroscopy 2D H-Bond Network as the Topmost Skin to the Air-Water Interface Combining ab-initio and classical molecular dynamics simulations to unravel the structure of the 2D-HB-network at the air-water interface 2D-HB-Network at the air-water interface: A structural and dynamical characterization by means of ab initio and classical molecular dynamics simulations Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface Molecular hydrophobicity at a macroscopically hydrophilic surface Graph theory for automatic structural recognition in molecular dynamics simulations DFT-MD of the (110)-Co3O4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLE008.

Full text

Abstract:

Améliorer notre connaissance de la structure de l'eau dans l'environnement spécial offert par une interface est essentiel pour la compréhension de nombreux phénomènes naturels et applications technologiques. Pour révéler cette structure interfaciale de l'eau, des techniques capables de fournir des informations microscopiques, de manière sélective, pour cette couche interfaciale (BIL) sont nécessaires. Dans le présent travail de thèse, nous avons donc étudié les interfaces aqueuses au niveau moléculaire, en couplant la modélisation théorique à partir de simulations DFT-MD avec les spectroscopies SFG et THz-IR. En développant de nouveaux protocoles/outils d'investigation associant simulations DFT-MD et spectroscopie SFG, en particulier pour la rationalisation plus complexe des interfaces chargées, nous avons fourni une compréhension globale de l'effet des conditions interfaciales d'hydrophilicité, de pH, de force ionique sur le réseau des liaisons-H formé dans la couche interfaciale BIL, sur ses signatures spectroscopiques et sur son impact sur les propriétés physico-chimiques. Nous avons montré pour la première fois que, dans des conditions suffisamment hydrophobes, l'eau interfaciale crée des réseaux des liaisons-H bidimensionnels, révélé expérimentalement par les spectres THz-IR. Le réseau-2D dicte la dynamique de l'eau interfaciale, le potentiel de surface, l'acidité de surface, la tension superficielle et la thermodynamique d'hydratation des solutés hydrophobes. Cet "ordre horizontal" aux interfaces hydrophobes est opposé à "l'ordre verticale" obtenu aux interfaces hydrophiles. Nous avons aussi révélé comment les ions et les conditions de pH modifient ces arrangements structuraux
Improving our knowledge on water H-Bonded networks formed in the special environment offered by an interface is pivotal for our understanding of many natural phenomena and technological applications. To reveal the interfacial water arrangement, techniques able to provide detailed microscopic information selectively for the interfacial layer are required. In the present thesis work, we have hence investigated aqueous interfaces at the molecular level, by coupling theoretical modeling from DFT-MD simulations with SFG & THz-IR spectroscopies. By developing new investigation protocols/tools, coupling DFT-MD simulations and SFG spectroscopy, in particular for the more complex rationalization of charged interfaces, we have provided a global comprehension of the effect of various interfacial conditions (hydrophilicity, pH, ionic strength) on the HB-Network formed in the interfacial layer (BIL), on its spectroscopic signatures and on its impact on physico-chemical properties. We have shown for the first time that, in sufficiently hydrophobic conditions, BIL interfacial water creates special 2-Dimensional HB-Networks, experimentally revealed by one specific THz-IR marker band. Such 2D-network dictates HBs and orientational dynamics of interfacial water, surface potential, surface acidity, water surface tension and thermodynamics of hydration of hydrophobic solutes. Such "horizontal ordering” of water at hydrophobic interfaces is found opposite to the “vertical ordering” of water at hydrophilic interfaces, while coexistence of the two orders leads to disordered interfacial water in intermediate hydrophilic/hydrophobic conditions. Both DFT-MD and SFG further revealed how ions & pH conditions alter these BIL-water orders

APA, Harvard, Vancouver, ISO, and other styles

32

Radulovic, Jovana. "Experimental and theoretical investigation of the interfacial phenomenon associated with wetting of trisiloxane surfactant solutions." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4710.

Full text

Abstract:

Surface active agents have been successfully employed in numerous industrial, agricultural and biomedical applications for decades. Trisiloxane surfactants in particular have proved to be exceptionally effective as wetting enhancers; hence the name ‘superspreaders’. Since the early ‘90s these extraordinary surfactants have become an irreplaceable component in various products and processes. However, the true nature of their specific wetting behaviour has not been fully revealed and their underlying wetting mechanisms are still poorly understood despite substantial scientific interest during the last decades. In this thesis is an attempt to shed light on specific wetting and spreading behaviour of trisiloxane solutions. Commercial superspreader products were tested in various environments in order to get further insight into their performance in specific practical applications. Experimental investigation of wetting of superspreader solutions on surfaces of different hydrophobicity and comparison to that of a conventional surfactant revealed superiority of trisiloxanes. Exceptional interfacial activity was explained in terms of the specific chemical structure and ‘T’-shape of the molecule. However, sensitivity of the trisiloxane head to low pH and long-time ageing in aqueous environment was revealed. Performance of binary mixtures of commercial superspreaders and conventional surfactant was also assessed. Behaviour of trisiloxanes in the capillary action was studied. Finally, a comprehensive mathematical model for trisiloxane wetting, which incorporates diffusion as the governing factor of the wetting process, was developed.

APA, Harvard, Vancouver, ISO, and other styles

33

Hobden, Carole Lesley. "A study of the cell surface properties of Candida albicans." Thesis, University of Essex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295552.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Elliott, Craig Julian. "Analysis and prediction of protein structure." Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284165.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Patel, Mayank Mukesh. "Spermine-nucleic acid interactions : roles of hydrophobicity, polynucleotide sequence-dependence and nature of polynucleotide /." Connect to full text via ProQuest. IP filtered, 2006.

Find full text

Abstract:

Thesis (Ph.D. in Pharmaceutical Sciences) -- University of Colorado at Denver and Health Sciences Center, 2006.
Typescript. Includes bibliographical references (leaves 130-149, 177-182). Free to UCDHSC affiliates. Online version available via ProQuest Digital Dissertations;

APA, Harvard, Vancouver, ISO, and other styles

36

Doerr, S. H. "Soil hydrophobicity in wet Mediterranean pine and eucalyptus forests, Agueda Basin, north-central Portugal." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636454.

Full text

Abstract:

This thesis investigates soil hydrophobicity in a comparatively wet (>1500 mm/yr) mediterranean environment focusing on unburnt and burnt commercial Eucalyptus globulus and Pins pinaster forests in north-central Portugal. Principal aims were to assess (i) its severity and spatial and vertical variability, (ii) the impact of fire, (iii) variations between soil particle size fractions and (iv) the causal factors and mechanisms involved. Hydrophobicity in all forest types was found to be amongst the most severe reported in the literature (MED 24%, WDPT >1h). Findings differ from most previous studied: (1) Hydrophobicity was neither of patchy distribution nor confined to distinct layers, but a consistent property of all forest soils. This is thought to be due to the comparatively high release and thorough distribution of hydrophobic substances from the species involved, aided by the relatively wet climate and the uniform character of the forests. (2) Burning had little impact on hydrophobicity. This is attributed to: (i) pre-burn hydrophobicity being so severe that hydrophobic compounds released from litter during burning contribute to detectable additional hydrophobic effects and (ii) soil temperatures reached being insufficient to destroy hydrophobicity. (3) Fine soil particle fractions are as, or more hydrophobic than coarse ones. A high supply of hydrophobic substances is thought to allow a hydrophobic coating on all particles. (4) After wetting, hydrophobicity is not re-established in soils simply by drying, but a fresh input of hydrophobic substances is thought to be required. Soils under E. globulus are more hydrophobic than those under P. pinaster. Hydrophobicity develops within a year of planting E. globulus. The litter layers of both species, and the root zone of E. globulus, are identified as sources of hydrophobic substances. Models are developed regarding the establishment of, fire-effects on, and short-term temporal variations of hydrophobicity. Hydrogeomorphological and land management implications are discussed.

APA, Harvard, Vancouver, ISO, and other styles

37

Backéus, Anders. "Tribological behaviour of nano-composite UHMWPE on ski surfaces and the role of hydrophobicity." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-244163.

Full text

Abstract:

Ultra High Molecular Weight Polyethylene (UHMWPE) has been used as a ski sole material for many years due to its good tribological properties, good wear resistance and low friction coefficient. Recent studies have showed improved performance on wear rate and hydrophobicity with nanoparticle reinforced UHMWPE. In this study, different kinds of nano-composite UHMWPE’s were tested on snow to investigate if they are suitable as a ski sole material and to find the type of nano-composite UHMWPE that has the greatest potential. Further, the mechanisms of hydrophobicity and its influence on the friction level were examined. The friction coefficient was measured in a ski test rig and simple demonstrations under a microscope were made to simulate how water is dragged along the ski sole in contact with wet snow. Mechanical properties were measured with a CSM Nanoindentation Instrument and surface topography was examined in a Wyko Optical Profiler. The cross-linked UHMWPE material showed the lowest friction coefficient on snow. The hydrophobic demonstrations, together with the ski test results, questions the suggestion that high hydrophobicity enhances the ski glide. Nanoindentation was proved to give valuable data for mechanical properties, but it should be questioned whether it is a good technique for comparing different nano-composite UHMWPE materials. The ski tests show the importance of the characteristics of snow.

APA, Harvard, Vancouver, ISO, and other styles

38

Werner, Marco, Jens-Uwe Sommer, and Vladimir A. Baulin. "Homo-polymers with balanced hydrophobicity translocate through lipid bilayers and enhance local solvent permeability." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139304.

Full text

Abstract:

Recent experimental studies indicate that polymeric structures with a well-adjusted balance of amphiphilic parts may translocate through self-assembled phospholipid bilayers and enhance the passive trans-membrane transport of smaller molecules. Using a coarse grained lattice Monte Carlo model with explicit solvent we investigate self-assembled lipid bilayers interacting with a linear polymer chain under variation of the hydrophobicity of the chain. Here, we focus on the relationship between the chain's hydrophobicity and its translocation behavior through the membrane as well as induced membrane perturbations. We show, that there is an adsorption transition of the polymer at the bilayer interface, where effectively the solvent phase and the tail phase of the bilayer are equally repulsive for the polymer. Close to this adsorption threshold of the polymer both the translocation probability of the polymer as well as the permeability of the membrane with respect to solvent are enhanced significantly. The frequency of polymer translocation events can be understood quantitatively assuming a simple diffusion along a one-dimensional free energy profile, which is controlled by the effective lipophilicity of the chain and the tail-packing in the bilayer's core
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

APA, Harvard, Vancouver, ISO, and other styles

39

Al-Marhoon, Mohammed Salem Ahmed. "The relationship between CagA Helicobacter pylori, gastric mucus gel thickness, hydrophobicity and gastric cancer." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396542.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Werner, Marco, Jens-Uwe Sommer, and Vladimir A. Baulin. "Homo-polymers with balanced hydrophobicity translocate through lipid bilayers and enhance local solvent permeability." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27821.

Full text

Abstract:

Recent experimental studies indicate that polymeric structures with a well-adjusted balance of amphiphilic parts may translocate through self-assembled phospholipid bilayers and enhance the passive trans-membrane transport of smaller molecules. Using a coarse grained lattice Monte Carlo model with explicit solvent we investigate self-assembled lipid bilayers interacting with a linear polymer chain under variation of the hydrophobicity of the chain. Here, we focus on the relationship between the chain's hydrophobicity and its translocation behavior through the membrane as well as induced membrane perturbations. We show, that there is an adsorption transition of the polymer at the bilayer interface, where effectively the solvent phase and the tail phase of the bilayer are equally repulsive for the polymer. Close to this adsorption threshold of the polymer both the translocation probability of the polymer as well as the permeability of the membrane with respect to solvent are enhanced significantly. The frequency of polymer translocation events can be understood quantitatively assuming a simple diffusion along a one-dimensional free energy profile, which is controlled by the effective lipophilicity of the chain and the tail-packing in the bilayer's core.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

APA, Harvard, Vancouver, ISO, and other styles

41

Vessigaud, Sandrine. "Re-mobilisation des hydrocarbures aromatiques polycycliques de terres industrielles de cokerie et mécanismes impliqués dans le "vieillissement" du fluoranthène." Phd thesis, Institut National Polytechnique de Lorraine - INPL, 2007. http://tel.archives-ouvertes.fr/tel-00339421.

Full text

Abstract:

Les HAP font partie de la classe des polluants organiques persistants dans les sols. Dans le cadre de la réhabilitation d'anciennes friches industrielles, il est nécessaire de comprendre l'origine de leur forte rétention et de connaître leurs possibilités de re-mobilisation à l'eau. Pour cela, une évaluation du potentiel de re-mobilisation à l'eau de matrices industrielles polluées a été réalisée sur 6 mois à l'aide de réacteurs fermés dont la solution est renouvelée mensuellement. Des expériences d'adsorption/désorption du 14C-fluoranthène sur ces mêmes matrices ainsi que sur une terre agricole ont confirmé que le fluoranthène s'adsorbe par interaction hydrophobe. L'affinité exceptionnelle des HAP pour les matrices présentant une pollution amassée est associée à leur re-mobilisation limitée par le faible contact de l'eau avec les surfaces de ces matrices hydrophobes. Notre étude met également en évidence la désorption plus lente de HAP "natifs" par rapport à des HAP ajoutés récemment, traduisant une modification du comportement de HAP au cours du temps. Afin de comprendre les mécanismes impliqués dans ce "vieillissement" au sein de terres industrielles, une expérience d'incubation de petites colonnes de sol, contaminées par du 14C-fluoranthène, a été conduite sur 6 mois. Dans les matrices à pollution amassée, le fluoranthène reste sous une forme extractible. Dans les matrices présentant une pollution moins importante et non amassée, le devenir des résidus du 14C-fluoranthène est contrôlé par l'activité de la microflore. Il est montré en particulier que les produits de dégradation sont en effet plus mobiles et peuvent pénétrer dans la porosité et y être séquestrés.

APA, Harvard, Vancouver, ISO, and other styles

42

Ekeroth, Sebastian. "Study of protein adsorption on structured surfaces using ellipsometry." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-72165.

Full text

Abstract:

In order to measure the thickness of a protein layer on a structured surface of silicon rubber, we have used ellipsometry and Fourier transform infrared (FTIR)-spectroscopy. The aim was to determine whether this type of measurement method can be used on protein layers or not. By hot-embossing a specific pattern of micrometre-sized pillars was created on the surface of the silicon rubber, which then was exposed to a phosphate buffer solution (PBS) containing human serum albumin (HSA) protein. FTIR measurements confirmed that proteins had attached to the surface. Ellipsometric studies were made and even though the protein layer was too thin to be measured, a simulation was made that revealed that a protein layer needs to be at least 1,5 nm to be measured properly with this method. We can also see that the protein molecules can get out of the solution, to find their way into the small pits of the samples.

APA, Harvard, Vancouver, ISO, and other styles

43

Sabio, Darlene Danette. "Surface Characteristics of Bacillus Spores." VCU Scholars Compass, 2004. http://hdl.handle.net/10156/1715.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Dominic, Justin. "Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/76796.

Full text

Abstract:

Presented in this paper are experiments to test the hypothesis that drag reduction is possible over hydrophobic surfaces in the Wenzel state during laminar and turbulent flows. Quantification of surface drag reduction in rectangular channel flow over walls with specific hydrophobic or hydrophilic properties was obtained with pressure drop measurements along the channel for a range of Reynolds numbers between 350 and 5900. Several commercially available materials and coatings were chosen in order to span a range of contact angles between 30° and 135°. The results are within the bounds of the theoretical values calculated with the Colebrook equation, and do not show any reduction in wall shear stress as a function of material properties or surface chemistry. The differences between this experiment and others measuring pressure drop over hydrophobic surfaces is the macro-scale conditions and the hydrophobic surfaces being fully wetted. These experiments are further proof of the importance of a liquid-vapor interface for increasing the shear free area to produce drag reduction.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

45

LIU, ANPING. "PREDICTION OF ORIENTATION OF α-HELICES IN HETEROPOLAR ENVIRONMENTS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1016465178.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Wang, Qiaoyun. "HYDROPHOBICALLY MODIFIED POLYELECTROLYTES TO TUNE THE PROPERTIES OF COACERVATES." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1590750104889183.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Hergert, Alexander [Verfasser]. "Test methods for evaluating the dynamic properties of hydrophobicity of polymeric insulating materials / Alexander Hergert." München : Verlag Dr. Hut, 2017. http://d-nb.info/1135597049/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Kinoshita, Takashi 1958. "Effects of pH and hydrophobicity on the transport of viruses and bacteria in saturated media." Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/192056.

Full text

Abstract:

Effects of pH and hydrophobicity on attachment-detachment of PRD-1 and MS-2 in three different soils, and Pseudomonas fluorescens P17 and Bacillus subtils TF-32 in 0.5-mm silica beads, were investigated in laboratory-column experiments. Attachment and detachment of hydrophobic virus PRD-1 may be predominantly controlled by hydrophobic interactions in soil media, while those of less-hydrophobic virus MS-2 may be mainly controlled by pH. Bacteria tend to exhibit hydrophobic interactions, since their surface contains hydrophobic substances. Soil media can exhibit strong hydrophobic interactions as well as electrostatic interactions. Parameters for three different transport models were estimated. The equilibrium model fits to the breakthrough curves of MS-2 in Cape-Cod soil resulted in dispersion coefficients similar to those of the conservative tracer (NaCl). The first-order and two-site model parameters indicated non-equilibrium conditions in all cases. Calculations of the two-site model were less stable than the first-order model for these breakthrough curves.

APA, Harvard, Vancouver, ISO, and other styles

49

Franco, Telma Teixeira. "Use of modified proteins in aqueous two-phase systems : effect of surface hydrophobicity and charge." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332663.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Khan, Sami Ph D. Massachusetts Institute of Technology. "Hydrophobicity of rare-earth oxide ceramics and their application in promoting sustained drop-wise condensation." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104029.

Full text

Abstract:

Thesis: S.M. in Technology and Policy, Massachusetts Institute of Technology, Institute for Data, Systems, and Society, Technology and Policy Program, 2016.
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 93-106).
Hydrophobic surfaces that are robust can have widespread applications in various industries including energy, hydropower, and transportation. In particular, hydrophobic materials promote dropwise condensation, which results in heat transfer coefficients that can be an order of magnitude higher than those seen in conventional filmwise condensation. Existing durable materials such as metals and ceramics are generally hydrophilic and require polymeric modifiers to render them hydrophobic, but these modifiers deteriorate in harsh environments. Therefore, robust hydrophobic surfaces have been difficult to realize and their widespread applicability has been limited. In this thesis, the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is studied for their hydrophobic potential. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Despite being inherently hydrophobic, the presence of excess surface oxygen on REOs can lead to increased hydrogen bonding and thereby reduce their hydrophobicity. Using X-ray Photoelectron Spectroscopy (XPS) and wetting measurements, surface stoichiometry and surface relaxations have been shown to impact wetting properties of REOs. Specifically, freshly sputtered ceria is shown to be hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ~3), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (~2.2) and becomes hydrophobic. Further, airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and relaxed REOs are intrinsically hydrophobic. This thesis also demonstrates that thin-film coatings (~300 nm) of relaxed hydrophobic REOs show sustained dropwise condensation behavior for over 100 hours at accelerated saturated steam conditions without compromising structural integrity or hydrophobicity, and produce a tenfold enhancement in the heat transfer co-efficient (103 ± 5 kW/m 2K) compared to conventional filmwise condensation (usually <10 kW/m2K). Finally, the political economy of rare-earths has been studied to understand the causes for market failure. A knowledge assessment exercise finds that rare-earth prices greatly depend on the rise of competing technologies and alternative resources, and international trade policies. It is envisioned that robust hydrophobic rare-earth oxide ceramics will have far reaching technological applications, especially in dropwise condensation.
by Sami Khan.
S.M. in Technology and Policy
S.M.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Hydrophobicitet'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles