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This work focused on the design of functional capsules made of chemically modified polysaccharides. The layer-by-layer capsules have attracted great interest due to their Indeed, as an advanced multifunctionality which can be advantageously used for pharmaceutical and biomedical applications. Polysaccharides, which are generally biocompatible and biodegradable, are very attractive materials for the construction of bio-related multilayer systems. Considering the intrinsic antibacterial properties of chitosan (CHI), this polysaccharide was selected and quaternized to prepare in physiological conditions contact-killing capsules by combination with hyaluronic acid (HA). The relationship between the antibacterial activity of the quaternized chitosan derivatives (QCHI) and that of QCHI-based capsules was investigated. Then, in order to encapsulate small hydrophobic drugs within the wall of capsules, alkylated derivatives of HA were used as the negatively charged partner of QCHI for the capsules formation. The encapsulation of the hydrophobic dye, nile red (NR), in the hydrophobic shell of capsules was determined. At last, to release the payload under mild conditions was studied by synthesizing rapidly degradable capsules composed of hydrolysable cationic dextran derivatives and HA. The degradation of the layer-by-layer assemblies, both multilayer films and microcapsules is discussed. / Ce travail de thèse porte sur la conception de capsules fonctionnelles à base de polysaccharides chimiquement modifiés. Les capsules couche par couche connaissent actuellement un essor important lié à leur multifonctionnalité pouvant être avantageusement mise à profit dans les domaines pharmaceutique et biomédical. Les polysaccharides, généralement biocompatibles et biodégradables, constituent des matériaux de choix pour la construction de systèmes multicouches. Compte tenu des propriétés antibactériennes intrinsèques du chitosane (CHI), ce polysaccharide a été choisi puis quaternisé afin de préparer dans des conditions physiologiques des capsules par complexation avec l'acide hyaluronique (HA), capables de tuer les bactéries par simple contact. La relation entre l'activité antibactérienne des dérivés quaternisés du chitosane (QCHI) et celle des capsules préparées à partir de QCHI a été étudiée. En outre, afin d'encapsuler des médicaments hydrophobes dans la paroi des capsules, des dérivés alkylés du HA ont été utilisés en tant que partenaire chargé négativement du QCHI pour la formation des capsules. L'encapsulation d'une sonde fluorescente hydrophobe, le nile rouge (NR), dans le réservoir hydrophobe des capsules a été réalisée avec succès. Enfin, pour libérer des médicaments encapsulés dans des capsules dans des conditions douces, des capsules rapidement dégradables comprenant des dérivés cationiques hydrolysables du dextrane et de HA ont été préparées. La dégradation des assemblages couches par multicouches a été analysée par différentes approches à la fois à partir de capsules et de films plans.

Master of Science / Department of Grain Science and Industry / X. Susan Sun / Soybean protein modified with sodium bisulfite behaves like latex adhesives, with adhesive strength comparable to formaldehyde-based adhesives. β-conglycinin and glycinin are two major protein components of the adhesive system. The objective of this research was to investigate the effect of sodium bisulfite on the physicochemical, morphological, and adhesion properties of glycinin and β-conglycinin in order to better understand the function of glycinin and β-conglycinin in the formation of the soy latex adhesive. Sodium bisulfite broke the disulfide bonds that linked acidic and basic polypeptides of glycinin, and the reducing effect was enhanced with increasing sodium bisulfite concentration. Although cleavage of disulfide bonds was expected to destabilize proteins, the thermal stability of glycinin increased as the sodium bisulfite concentration increased. Sodium bisulfite modified glycinin had higher surface hydrophobicity, which facilitated hydrophobic interations between molecules and aggregation of glycinin. The balance between hydrophobic interactions and electrostatic forces makes glycinin form unique chain-like structures. Adhesive performance of glycinin dropped significantly at lower sodium bisulfite concentration and then increased as sodium bisulfite concentration increased up to 24 g/L. Excess sodium bisulfite was detrimental to adhesive strength and water resistance. High-molecular-weight aggregates were observed in unmodified β-conglycinin, but these aggregates were dissociated by sodium bisulfite treatment. Similar to glycinin, the thermal stability of β-conglycinin was improved by the modification. However, the denaturation enthalpy of β-conglycinin decreased significantly at high level of sodium bisulfite (36 g/L). The turbidity at pH 4.8 also dropped extensively at the concentration of 36 g/L. The contact angle of β-conglycinin reached its minimum at 6 g/L sodium bisulfite on cherry wood and 24 g/L on glass. Morphology study proved that sodium bisulfite modification made the β-conglycinin solution more dispersed. At pH 9.5, water resistance of β-conglycinin was improved to a small extent by 6 g/L sodium bisulfite. At pH 4.8, adhesive performance was enhanced by 3 g/L and 6 g/L sodium bisulfite. High level of sodium bisulfite at 36 g/L reduced the adhesive performance of β-conglycinin drastically.

Since metals in general, and steels in particular, are vital construction materials in our modern society, the corrosion protection of said materials is of great importance, both to ensure safety and to reduce costs associated to corrosion. Previously, chromium (VI) and other harmful substances were effectively used to provide corrosion protection to steel, but since their use was heavily regulated around year 2000, no coating has yet been developed that, in a fully satisfactory manner, replaces their corrosion protective properties.In this thesis, the use of hydrophobic and superhydrophobic surface coatings as part of corrosion protective coating systems has been studied. Since the corrosion mechanism relies on the presence of water to take place, the use of a superhydrophobic coating to retard the penetration of water to an underlying metal surface is intuitive. The evaluation of corrosion protective properties of the hydrophobic and superhydrophobic surfaces was performed using mainly contact angle measurements and electrochemical measurements in severely corrosive 3 wt% NaCl water solution.First, the differences in corrosion protection achieved when employing different hydrophobic wetting states were investigated using a model alkyl ketene dimer wax system. It was found that superhydrophobicity in the Lotus state is superior to the other states, when considering fairly short immersion times of less than ten days. This is due to the continuous air film that can form between such a superhydrophobic surface and the electrolyte, which can retard the transport of electrolyte containing corrosive ions to the metal surface to the point where the electrical circuit is broken. Since corrosion cannot occur unless an electrical current is flowing, this is a very efficient way of suppressing corrosion.An air layer on an immersed superhydrophobic surface is, however, not stable over long time, and to investigate long-term corrosion protection using hydrophobic coatings a polydimethylsiloxane formulation containing hydrophobic silica nanoparticles was developed. This system showed enhancement in corrosion protective properties with increasing particles loads, up until the point where the particle load instead causes the coating to crack (at 40 wt%). The conclusion is that the hydrophobicity of the matrix and filler, in combination with the elongatedivdiffusion path supplied by the addition of particles, enhanced the corrosion protection of the underlying substrate.To further understand how hydrophobicity and particle addition affect the corrosion protective properties of a coating a three layer composite coating system was developed. Using this coating system, consisting of a polyester acrylate base coating, covered by TiO2 particles (with diameter &lt; 100 nm) and finally coated with a thin hexamethyl disiloxane coating, it was found that both hydrophobicity and particles are needed to reach a great enhancement in corrosion protective properties also for this system. / Eftersom metaller, och då särskilt stål, är viktigta konstruktionsmaterial i vårt moderna samhälle är korrosionsskydd av stor betydelse, både för att garantera säkerhet och för att minska kostnader som uppkommer i samband med korrosion. Tidigare har sexvärt krom och andra skadliga ämnen använts för att på ett effektivt sätt skydda stål från korrosion, men efter att deras användning kraftigt reglerades runt år 2000 har ännu ingen beläggning utvecklats som helt kan ersätta krombeläggningarna med avseende på funktion.I denna avhandling har hydrofoba och superhydrofoba ytbeläggningar och deras möjliga applikation som en del av ett korrosionsskyddande beläggningssystem studerats. Eftersom korrosionsmekanismen är beroende av närvaron av vatten, är användandet av en superhydrofob beläggning för att fördröja transporten av vatten till den underliggande metallytan intuitiv. De korrosionsskyddande egenskaperna hos superhydrofoba ytbeläggningar utvärderades här främst med hjälp av kontaktvinkelmätningar och elektrokemisk utvärdering i korrosiv lösning bestående av 3 vikts% NaCl i vatten.Först undersöktes skillnaden i korrosionsskydd som uppnås vid användandet av ytbeläggningar med olika hydrofoba vätningsregimer med hjälp av ett modellsystem bestående av ett alkylketendimer vax. Det konstaterades att superhydrofobicitet i Lotusregimen är överlägset bättre än de andra hydrofoba vätningsregimerna, i alla fall när man ser till relativt korta exponeringstider, typiskt mindre än tio dagar. Detta beror på att den kontinuerliga luftfilm som kan bildas på en sådan typ av superhydrofob yta kan minska transporten av elektrolyt (som innehåller korrosiva joner) till metallytan till den grad att den elektriska kretsen bryts. Eftersom korrosion inte kan ske utan en sluten elektrisk krets är detta ett mycket effektivt sätt att förhindra korrosion från att ske.Ett luftskikt på en superhydrofob yta nedsänkt i vatten är dock inte stabilt under lång tid. För att undersöka möjligheten till korrosionsskydd under längre tid med hjälp av hydrofoba beläggningar utvecklades en hydrofob ytbeläggning bestående av polydimetylsiloxan och hydrofoba nanopartiklar av kiseldioxid. Detta system visade en förbättring av korrosionsskyddet vid ökat partikelinnehåll upp till den koncentration (40 wt%) där i stället sprickbildning i ytbeläggningen observerades. Från detta system kunde slutsatsen dras att matrisens och partiklarnasvihydrofobicitet i kombination med den längre diffusionsvägen som partiklarna orsakade förbättrade korrosionsskyddet av den underliggande metallen.För att ytterligare förstå hur hydrofobicitet och partikeltillsatser påverkar en ytbeläggnings korrosionsskyddande egenskaper har dessutom ett treskikts kompositbeläggningssystem utvecklats. Genom att använda detta beläggningssystem, som består av en basbeläggning av polyesterakrylat, ett lager TiO2-partiklar (med en diameter på &lt;100 nm) slutligen belagt med ett tunt ytskikt bestående av hexametyldisiloxan så kunde slutsatsen dras att både en hydrofob matris och partiklar behövs för att nå en markant förbättring av ytbeläggningens korrosionsskyddande egenskaper. / <p>QC 20151015</p>

The time-dependent wettability of nickel nanorod arrays was studied by measuring their water contact angles as a function of "aging" time in air. The nickel nanorod arrays were deposited on silicon substrates by DC magnetron sputtering using an oblique angle of 85° with respect to the substrate normal. By changing the deposition time from 10 to 90 min., the diameter, height, and separation of the nanorods were varied. The water contact angles of each sample were then periodically measured from a minimum aging time of 30 min. after deposition and exposure to air, up to a maximum aging time of three months. The initial water contact angles for all samples were approximately equal to 8o, indicating that the nickel nanorod arrays were initially superhydrophilic. As the samples aged in air, however, they all showed increasing contact angles as a function of time that were nonlinear with different rates. The results can be grouped into two categories: thinner samples with shorter deposition times (10 to 55 min) demonstrated faster rates of increase in contact angle, and thicker samples with longer deposition times (60 and 90 min.) showed slower rates. The increase in contact angle with time indicates that the Ni nanorods become more hydrophobic with aging time in air. Surface chemical analysis demonstrates that this increase in hydrophobicity may be due to oxidization and hydrocarbon contamination, which depend on the nanorod morphology. X-ray photoelectron spectroscopy results indicate that thinner samples (10-55 min. deposition time) have more adsorbed carbon as compared to thicker samples (60 and 90 min.). It appears that the reactivity of the Ni nanorods with air ambient is enhanced for shorter, smaller-diameter nanorods.

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.

Les réseaux de polymères interpénétrés (IPNs) combinent les propriétés de leurs différents composants. Ils possèdent une bonne résistance thermique, mécanique et chimique, et s’avèrent très intéressants pour pallier les inconvénients des réseaux homopolymères. Une méthode de synthèse rapide et efficace fait appel à la photopolymérisation. Les IPNs photopolymérisés sont donc très attractifs pour l’obtention de revêtements industriels présentant des propriétés de surface avancées. Cette thèse porte sur la réalisation de revêtements hydrophobes présentant des propriétés d’auto-régénération suite à un endommagement. Le concept mis en œuvre repose sur la ségrégation vers la surface de groupements fonctionnels liés chimiquement à un réseau IPN photopolymère, par différence de tension superficielle entre la surface et l’intérieur du matériau. L’auto-régénération de la fonctionnalité de surface nécessite une distribution homogène et une mobilité suffisante des groupements fonctionnels dans la matrice polymère. Des surfaces auto-régénérantes basées sur un réseau acrylate photopolymérisé ont d’abord été développées afin de démontrer la faisabilité du concept. Des IPNs photopolymérisés sous lumière UV et naturelle, combinant deux polymères (acrylates et époxydes) possédant des Tgs faibles et élevées (auto-régénération combinée avec résistance mécanique), et présentant des morphologies différentes ont ensuite été étudiés. Des surfaces auto-régénérantes possédant une Tg plus élevée compatible avec des applications industrielles ont été obtenues. / Interpenetrating polymer networks (IPNs) combine properties of their different components. They exhibit high mechanical strength, good thermal stability and chemical resistance. They are thus interesting to overcome the limitations of stand-alone networks. One of the easy and efficient ways to produce IPNs involves light curing. Considering these features, photocured IPNs are very attractive materials for functional polymeric surfaces in the coating industry. This thesis reports the development of hydrophobic coatings showing self-replenishing properties upon surface damage. This concept relies on the segregation of functional groups chemically bound to a light-cured IPN network towards the surface, thanks to the energy difference between surface and bulk. Surface functionality self-repairing mechanism requires a homogeneous distribution and a sufficient mobility of functional groups in the polymeric network. Self-replenishing hydrophobic surfaces based on a UV-cured acrylate network have been firstly developed in order to demonstrate the proof of concept. In a second part, UV and visible-light cured IPNs combining two polymers (acrylates and epoxides) with low and high Tgs (self-replenishing together with mechanical resistance), showing different morphologies have been investigated. Finally, self-replenishing hydrophobic surfaces with enhanced Tg more suitable for industrial applications have been obtained.

Ph. D., Faculty of Science, University of the Witwatersrand, 2011 / Different cadmium, cobalt and zinc complexes of substituted thioureas, dithiocarbamates and thiuram di/monosulfides were synthesized using ethanol or water as solvents. The synthesis of dithiocarbamates complexes were performed at room temperature while the rest were refluxed at 70 oC. The complexes were easy to synthesize, of low cost and stable in air and were obtained in good yields. The complexes were characterized using various instruments, such as infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy, elemental analyzer, thermogravimetric analysis (TGA) and X-ray crystallography. The complexes were found to coordinate the ligands through sulphur atom, instead of nitrogen atom. This was concluded after shifts to higher or lower wavenumbers were observed from the infrared spectra of the complexes as compared to their free ligands. The 1H NMR also depicted formation of the complexes, with complexes peaks shifting to downfield as compared to the free ligands. There were also signs of broad NH peaks especially for substituted thiourea complexes. The crystals grown from complex II (diphenylthiourea cadmium complex) depicted a tetrahedral geometry, with two sulphur and two chlorine atoms binding to the central atom which is cadmium. The easily synthesized complexes were thermolysed in HDA, TOPO or a mixture of the two to form metal sulphide nanoparticles. The role of the above capping agents or ligands was to control particles growth and prevent them from aggregation. A single source precursor route was employed in synthesizing hydrophobic semiconductor nanoparticles, which are also known as (QDs) quantum dots. Various shapes, which are rods (mono-, bi- and tripods), spheres and hexagonal were revealed through transmission electron microscope (TEM). The sizes of these particles ranged from 1 to 12 nm in diameter. Other instruments used for characterising the as-synthesized semiconductor nanoparticles include X-ray diffractometer (XRD), UV-Visible and Photoluminescence spectroscopy. The optical properties of the particles as determined by the UV-Visible spectroscopy revealed some differences as compared to the bulk materials. All the absorption spectra were blue shifted to the bulk materials signifying finite size of the particles. The XRD peaks observed were broad as compared to the bulk ones, which also signified small particles size. Two phases, which are hexagonal and cubic, were revealed from the XRD. viii The hydrophobic semiconductor nanoparticles or quantum dots synthesized were then transferred into water soluble using ligand exchange method. The chloroform and pyridine routes were used to synthesize hydrophilic semiconductor nanoparticles, with pyridine route being preferred. The shape and size of the particles were not influenced by the transfer into water soluble since the experiments were performed at room temperature. This was confirmed by TEM analysis. The capping agents used after displacing water insoluble capping agents were sugars, which were soluble in water. The XRD pattern of the semiconductor nanoparticles/QDs (CdS) capped by sugars after ligand exchange through pyridine yielded multiple peaks which were difficult to assign. The attempt to employ ligand exchange method in transferring hydrophobic CoxSy and ZnS nanoparticles to hydrophilic CoxSy and ZnS nanoparticles proved unsuccessful. When the materials were centrifuged after the sugars were introduced as capping agents, some solid material settled at the bottom, with some floating on top of the solution. This was an indication that the materials were not miscible. The hydrophilic CdS, CoxSy and ZnS nanoparticles were also synthesized using direct method. In this method, the metal sources and capping (sugars) were dissolved in ethylene glycol at 100 oC. The sulphur sources were also dissolved separately in the same solvent. Upon completion, the latter solution was added to the former one. The particles were grown at 160 oC for an hour with ethylene glycol as a solvent. The morphology of the particles dominated through this method was spherical-like in shape. The crystallinity of CdS and ZnS nanoparticles depicted hexagonal and cubic phases depending on the complexes used. The XRD indicated the armophous nature of the cobalt sulphide nanoparticles, irrespective of the precursor used. Due to the toxicity problem of the quantum dots, especially CdS, the water soluble CdS capped by glucuronic acid, glucose and sucrose after ligand exchange were chosen for that study. However, results showed that the CdS used were not toxic. It was measured or deduced by checking the viability which remained above 90%. Add a bit of deductions about toxicity study here, just some of the general trends.

Neste trabalho estudamos o efeito hidrofóbico no sistema benzenoágua. Nossa estratégia é avaliar as propriedades das ligações de hidrogênio entre as moléculas de água nas proximidades da molécula e benzeno. Utilizamos as ferramentas da mecânica quântica e o método de simulação computacional para este estudo. A análise estrutural e energética detalhada dos clusters benzenoágua mostra que a ligação de hidrogênio é mais forte quando na presença do benzeno. A investigação pelo método de simulação Monte Carlo corrobora estas conclusões e ainda fornece os efeitos da variação de tempeatura. Verificamos que o aumento da temperatura afeta todas as moléculas aumentando a desordem líquida, no entanto, constatamos a manutenção de uma estrutura de ligações de hidrogênio mais fortes as proximidades do benzeno. A interação entre duas moléculas de benzeno também foi analisada, mostrando que a interação benzenobenzeno é bem mais forte na presença da água. / The hydrophobic effect is studied for the benzene-water system. The properties of the hydrogen bond between the water molecules around the benzene is evaluated using both classical and quantum mechanical methods. Hydrophobic hydration analysis shows that the hydrogen bond interaction is stronger in the presence of benzene. This is verified both by ab initio quantum mechanical methods and classical Monte Carlo simulation. Temperature dependence is investigated. Although increasing temperature increases the disorder the hydrogen bonds between the water molecules are still stronger for those in the proximities of the benzene. Hydrophobic interaction is also investigated. It is seen that the benzene-benzene interaction is stronger in the water environment.

A super-hidrofobicidade é uma característica presente em diversas superfícies encontradas na natureza, conferindo-lhes determinadas características como a autolimpeza. Um dos mais conhecidos exemplos de superfície super-hidrofóbica autolimpante é a da folha de Lótus, que apresenta uma camada de retenção de ar importante entre as cavidades da superfície. Essa retenção de camada de ar entre cavidades é característica marcante de determinadas superfícies super-hidrofóbicas, e tem atraído grande atenção nos últimos anos, por ser de alto interesse tecnológico, econômico e ecológico. Algumas espécies apresentam superfície que retêm essa camada de ar por apenas algumas horas, ou dias. Em outras espécies, porém, ela se mantém por longos períodos. Uma das superfícies mais complexas é a da samambaia flutuante Salvinia, que é capaz de manter uma camada de ar estável durante várias semanas, mesmo quando submersa na água. Diversos estudos têm sido promovidos para fins de desenvolver tecnologias capazes de promover a retenção de ar na superfície por períodos longos, as quais têm grande potencial de aplicação no setor naval, por exemplo, pois serviriam para reduzir o arrasto hidrodinâmico quando utilizadas no revestimento de embarcações, diminuindo o consumo de combustível. Neste trabalho, buscou-se obter, através da mimetização da estrutura da Salvinia e suas espécies, uma superfície super-hidrofóbica retentora de camada de ar capaz de reduzir o arrasto hidrodinâmico. Desenvolveram-se, para tanto, revestimentos formados em duas etapas: uma base formada por fibras de poliamida para gerar rugosidade – aplicadas por flocagem eletroestática –, as quais foram cobertas, via spray, por um organosilano (hidrofóbico). Então, foram caracterizadas as propriedades dos revestimentos quanto à morfologia, ângulo de contato, ângulo de rolamento e volume de ar preso na superfície, bem como realizados testes para verificar sua capacidade de redução de arrasto hidrodinâmico. Os revestimentos super-hidrofóbicos desenvolvidos neste trabalho apresentaram camada de ar sobre a superfície e os testes demonstraram redução de arrasto hidrodinâmico de até 30%. / Super-hydrophobicity is a characteristic found in several surfaces of nature, which gives them certain features such as self-cleaning. One of the most well-known examples of a super-hydrophobic self-cleaning surface is the one present on the Lotus leaf, that contains an important layer of air retention between the cavities of the surface. This layer of air retention between cavities is a characteristic of some superhydrophobic surfaces, and has attracted a lot of attention recently, from technological, economic and ecological fields. Some species have a surface that holds this layer of air for only a few hours or days. Other species, however, maintain that for long periods of time. One of the most complex surfaces is the floating fern Salvinia - able to maintain a stable air layer for several weeks, even when submerged in water. Several studies have been carried out to develop technologies able to keep the air retention on surface for long periods, as they have a great potential to be applied in the naval sector, for instance, because they could reduce the hydrodynamic drag when used in the coating of boats, also reducing fuel consumption.The aim of this work is to obtain, by mimicking Salvinia’s structure and its species, a super-hydrophobic air-layer retaining surface, capable of reducing hydrodynamic drag. For this purpose, coatings composed in two stages were developed: a base composed by polyamide fibers to generate roughness - applied by electrostatic flocking - and covered by an organosilane (hydrophobic) spray. Then, the properties of the coatings were characterized in terms of morphology, angle of contact, rolling angle and volume of air hold on the surface, as well as tests to check their hydrodynamic drag reduction capacity. The super-hydrophobic coatings developed in this work have presented an air layer on surface and the tests has shown a hydrodynamic drag reduction for of up to 30%.