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An atomic force microscope (AFM) has been used to conduct force measurements to better understand the role of hydrophobic forces in flotation. The force measurements were conducted between a flat mineral substrate and a hydrophobic glass sphere in aqueous solutions. It is assumed that the hydrophobic glass sphere may simulate the behavior of air bubbles during flotation. The results may provide information relevant to the bubble-particle interactions occurring during flotation. The glass sphere was hydrophobized by octadecyltrichlorosilane so that its water contact angle was 109 degrees. The mineral systems studied include covellite (CuS), sphalerite (ZnS) and hornblende (Ca₂(Mg, Fe)₅(Si₈O₂₂)(OH,F)₂). The collector used for all the mineral systems studied was potassium ethyl xanthate (KEX). For the covellite-xanthate system, a biopotentiostat was used in conjunction with the AFM to control the potential of the mineral surface during force measurements. This was necessary since the adsorption of xanthate is strongly dependent on the electrochemical potential (Eₕ) across the solid/liquid interface. The results show the presence of strong hydrophobic forces not accounted for by the DLVO (named after Derjaguin, Landau, Verwey and Overbeek) theory. Furthermore, the potential at which the strongest hydrophobic force was measured corresponds to the potential where the flotation recovery of covellite reaches a maximum, indicating a close relationship between the two. Direct force measurements were also conducted to study the mechanism of copper-activation of sphalerite. The force measurements conducted with unactivated sphalerite in 10⁻³ M KEX solutions did not show the presence of hydrophobic force while the results obtained with copper-activated sphalerite at pH 9.2 and 4.6 showed strong hydrophobic forces. However, at pH 6.8, no hydrophobic forces were observed, which explains why the flotation of sphalerite is depressed in the neutral pH regime. Direct force measurements were also conducted using hornblende in xanthate solutions to study the mechanism of inadvertent activation and flotation of rock minerals. The results show the presence of long-range hydrophobic forces when hornblende was activated by heavy metal cations such as Cu²⁺ and Ni²⁺ ions. The strong hydrophobic forces were observed at pHs above the precipitation pH of the activating cation. These results were confirmed by the XPS analysis of the activated hornblende samples. Force measurements were conducted between silanated silica surfaces to explore the relationship between hydrophobicity, advancing contact angle (CA), and the magnitude (K) of hydrophobic force. In general, K increases as Contact Angle increases and does so abruptly at Contact Angle=90°. At the same time, the acid-base component of the surface free energy decreases with increasing CA and K. At CA>90°, GammaS^AB approaches zero. Based on the results obtained in the present work a mathematical model for the origin of the hydrophobic force has been developed. It is based on the premise that hydrophobic force originates from the attraction between large dipoles on two opposing surfaces. The model has been used successfully to fit the measured hydrophobic forces using dipole moment as the only adjustable parameter. However, the hydrophobic forces measured at CA>90° cannot be fitted to the model, indicating that there may be an additional mechanism, possibly cavitation, contributing to the appearance of the long-range hydrophobic force. / Ph. D.

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.

Betulin is a naturally abundant compound in the outer bark of birch and can be easily obtained by solvent extraction. Herein, solutions of betulin were used to treat cellulosic textile fibers and improve their water repellency. Cotton fabrics impregnated in a 7.5 g L-1 solution of betulin in ethanol showed the highest water contact angle of about 153° while the impregnation in a 3.75 g L-1 solution resulted in a close effect. A terephthaloyl chloride-betulin copolymer was synthesized and dissolved in tetrahydrofuran to afford a solution with a concentration of 3.75 g L-1. The cotton fabric impregnated in this solution showed a water contact angle of 150°. Changes in morphology of the cellulose fibers before and after the treatment were observed by scanning electron microscopy, and the water repellency was measured by a standard spray test. The marketing strategy of the potential product, which will be developed based on this technique, was discussed.

Protein sequences may evolve to avoid highly hydrophobic local regions of sequence, in part because such sequences promote nonnative aggregation. Hydrophobic local sequences are avoided in proteins even in buried regions, where native structure requirements tend to favor them. In this dissertation, I describe three explorations of this hydrophobic suppression. In Chapter 2, I examine the occurrence of hydrophobic and polar residues in completely buried β-strand elements, and find evidence for hydrophobic suppression that decreases as a β-strand becomes more exposed. In Chapter 3, I present a generalized study of the tendency of local sequences to deviate from the hydropathy (hydrophobicity) expected based on their solvent exposure. First, I examined the hydropathy of local and nonlocal sequence groups over a large range of solvent exposures, within folded protein domains in the ASTRAL Compendium database; second, I calculated the tendency of residues within 10 positions of a nonpolar or polar reference residue to deviate from the hydropathy expected based on their structural environment. Both analyses suggested that protein sequences exhibit 'local hydropathic balance' across a range of 6-7 residues, meaning that polar and nonpolar residues are more dispersed in the sequence than expected based on solvent exposure patterns. This balance occurs in all major fold classes, domain sizes and protein functions. An unexpected finding was that it partly arises from a tendency of buried or exposed residues to be flanked by polar or nonpolar residues, respectively. This relationship may result from evolutionary selection for folding efficiency, which might be enhanced by reduced local competition for buried or exposed sites during folding. Finally, in Chapter 4, I present several exploratory analyses, including a decision-tree approach, to visualize the influence of a large number of sequence-structure properties on residue hydrophobicity. Overall, the work in this dissertation confirms that hydrophobic suppression and local hydropathic balance in general are intrinsic properties of folded proteins. I speculate that local hydropathic balance results from selection for reduced aggregation propensity, increased folding efficiency and increased native state specificity. The concept of local hydropathic balance might be used to improve the properties of designed and engineered proteins.

Baigiamojo darbo tikslas – ištirti vilnos pluošto paviršiaus hidrofobiškumo įtaką dažiklių sorbcijai vilnos pluošte ir dažinių fizikinėms savybėms. Naujų antrachinoninių dažiklių RB 5-37 Mėlynojo ir RB 4-35 Žaliojo sintezė buvo atlikta Kauno Technologijos universitete, Organinės chemijos katedroje, prof. V. Mickevičiaus grupėje. Siekiant nustatyti, kokį pluoštą ir kokiomis sąlygomis intensyviausiai dažo naujieji dažikliai, atlikti parengiamieji tyrimai su multipluoštiniu audiniu (ISO 105 F10 DW), kurį sudaro vilna, poliakrilatas, poliesteris, poliamidas, medvilnė ir diacetatas. Bandymo metu buvo nustatyta, jog tiriamieji antrachinoniniai dažikliai intensyviausiai dažo vilną ir poliamidą. Tolimesni tyrimai atlikti naudojant standartinį vilnonį audinį (ISO 150/F – 1985 (E)). Siekiant įvertinti hidrofobinio paviršinio barjero įtaką dažiklių difuzijai jame, bandymai atlikti su standartiniu vilnos audiniu ir su audiniu, nuo kurio paviršiaus buvo pašalintas hidrofobinis sluoksnis. Vilnos pluošto ekstrakcija buvo atlikta naudojant metanolio ir chloroformo tirpiklių mišinį, Soksleto aparatu, 10 ciklų. Taip pat buvo atlikti dažymo kinetiniai tyrimai bei dažyto audinio pavienių siūlų mechaninių savybių tyrimai, t. y. vilnonio siūlo trūkimo jėga bei vilnonio siūlo trūkimo ištįsa, naudojantis dinamometru. Atlikus tyrimą su dviem naujai susintetintais dažikliais nustatyta, kad Žaliasis Dažiklis, kuris skyrėsi nuo Mėlynojo nitro funkcine grupe, intensyviau sorbavosi vilnos pluošte... [toliau žr. visą tekstą] / The aim of this work was to evaluate the effect of the hydrophobicity of wool fibre surface on the sorption of the dyes and on the physical properties of dyed wool fibre. New Anthraquinonic RB 5-37 Blue and Green RB 4-35 dyes synthesis was carried out by Professor V. Mickevičius group at Kaunas University of Technology, Department of Organic Chemistry. The multifiber fabric (ISO 105 F10 DW), composed of wool, polyacrylates, polyester, nylon, cotton and the diacetate was used in order to determine the fiber and the conditions under which the new dyes intensively dye. The dyeing results showed that new dyes wool fibers and polyamide dyed intensively. The standard wool fabric (ISO 150 / F - 1985 (E)) was used for further dyeing experiments. The standard wool fabric without pretreatment and wool fabric extracted with methanol and chloroform solvents mixture were used in order to evaluate hydrophobic wool surface barrier effect on dye diffusion in to wool fabric. It has also been done a kinetic study of dyeing process and dyed wool fiber single thread mechanical properties testing, i.e. breaking force and extension at break using a dynamometer. The investigation of the dyeing kinetic using two newly synthesized dyes showed that the Green dye which differs from the Blue by NO2 functional group, better penetrates into the wool fabric, irrespective of what was the composition of the dyeing solution. The data of equilibrium dye concentration indicates that independently of the... [to full text]

A produção de filmes biodegradáveis à base de amido representa um desafio tecnológico, pois estas matrizes são altamente sensíveis à água. Neste sentido, as pesquisas estão sendo realizadas a fim de melhorar as caraterísticas de hidrofobicidade sem afetar a integridade estrutural das matrizes. Dentre os compostos comumente empregados para melhorar as características de filmes biodegradáveis, pode-se mencionar os óleos e ácidos graxos. O óleo de sementes de melancia apresenta alto potencial de aplicação em matrizes filmogênicas, pois além da possibilidade de melhorar as propriedades de barreira, apresenta compostos fitoquímicos com atividade antioxidante, que podem conferir um caráter ativo aos materiais produzidos. Neste contexto, o objetivo deste trabalho foi desenvolver e caracterizar filmes à base de amido modificado de mandioca e óleo de sementes de melancia. O óleo de sementes de melancia foi extraído por batelada com etanol pressurizado, sob diferentes temperaturas de extração (40, 60 e 80°C) e diferentes comprimentos de leito de extração (L1 = 4,2 cm, L2 = 9,8 cm e L3 = 15,8 cm). A cinética de extração foi matematicamente descrita utilizando-se o modelo de Peleg e os óleos caraterizados quanto à atividade antioxidante. Posteriormente foram testados quatro amidos modificados de mandioca (amido reticulado, AR; amido acetilado, AA; amido não modificado, ANM e amido duplamente modificado, AAR) com a finalidade de selecionar o que apresentasse melhores caraterísticas na produção de filmes quanto ao caráter hidrofóbico. Os filmes foram produzidos pela técnica de casting, utilizando - se concentrações fixas de amido e sorbitol (4 e 1,2 g/100g de solução filmogênica, respectivamente). O caráter hidrofóbico das matrizes foi avaliado pela determinação da solubilidade, grau de inchamento, permeabilidade ao vapor de água e ângulo de contato. Adicionalmente, foram produzidas emulsões através da técnica de Pickering, com diferentes concentrações de óleo e amido e caraterizadas quanto à estabilidade, tamanho de partículas e polidispersidade. A emulsão com maior estabilidade foi incorporada na formulação de filmes à base de AR em concentrações de 0 a 0,5 g de óleo na emulsão/100 g de solução filmogênica. Todos os filmes foram caracterizados quanto às propriedades mecânicas, microscopia, espectroscopia de infravermelho (FTIR), difração de raios X, cor, solubilidade, inchamento, permeabilidade ao vapor de água e ângulo de contato. Os resultados da extração de óleos mostraram rendimentos superiores sob temperaturas de 80°C e melhor atividade antioxidante a 60°C. O modelo de Peleg apresentou um bom ajuste, observando-se coeficientes de correlação altos (R2 > 0,90). A caraterização dos filmes produzidos com diferentes amidos modificados mostrou que o AR formou matrizes com maior ângulo de contato, menor grau de inchamento e maior resistência mecânica. As emulsões com maior de estabilidade foram produzidas com altas concentrações de óleo e amido (15 e 12 g/100 g de emulsão, respectivamente). Os filmes produzidos com incorporação de óleo na forma de emulsão Pickering apresentaram caráter mais hidrofóbico, sendo também alteradas as caraterísticas estruturais com o aumento da concentração de óleo. Os filmes produzidos com a incorporação de óleo em forma de emulsão apresentaram conteúdos de fenólicos totais de 0,19 a 5,68 mg equivalente de ácido gálico/100g de filmes. No entanto, os filmes não apresentaram atividade antioxidante frente ao radical DPPH•. / The production of biodegradable films based on starch represents a technological challenge because these matrices are highly sensitive to water. In this sense, the research is being carried out in order to improve the characteristics of hydrophobicity without affecting the structural integrity of the matrices. Among the compounds commonly used to improve the characteristics of biodegradable films, the oils and fatty acids can be highlighted. The oil of the watermelon seeds presents high potential of application in filmogenic matrices because in addition to the possibility of improving the barrier properties, it presents phytochemical compounds with antioxidant activity, which can impart an active characteristic to the produced materials. In this context, the objective of this work was to develop and characterize films based on modified cassava starch and watermelon oil. The watermelon oil was extracted in batches with pressurized ethanol under different extraction temperatures (40, 60, and 80°C) and different extraction bed lengths (L1 = 4.2 cm, L2 = 9.8 cm, and L3 = 15.8 cm). The kinetics of extraction were mathematically described using the Peleg model and the oils characterized for antioxidant activity. Four modified starches of cassava (reticulated starch, AR, acetylated starch, AA, unmodified starch, ANM, and doubly modified starch, AAR) were then tested in order to select the material with the best hydrophobic characteristics. The films were produced by the casting technique, using fixed concentrations of starch and sorbitol (4 and 1.2 g/100 g of film-forming solution, respectively). The hydrophobic characteristic of the matrices was evaluated by determining the solubility, degree of swelling, permeability to water vapor, and contact angle. In addition, emulsions were produced using the Pickering technique with different concentrations of oil and starch and then, characterized for stability, particle size, and polydispersity. The results of the extraction showed higher yields under temperatures of 80°C and better antioxidant activity at 60°C. The Peleg model presented a good fit, observing high correlation coefficients (R2> 0.90). The characterization of the films produced with different modified starches showed that AR formed matrices with higher contact angle, lower degree of swelling, and higher mechanical resistance. Emulsions with the highest degree of stability were produced with high concentrations of oil and starch (15 and 12 g/100 g of emulsion, respectively). The films produced with oil incorporation in the form of Pickering emulsion presented a more hydrophobic characteristic, and the structural characteristics were also altered with the increase of oil concentration. The films produced with the incorporation of oil in emulsion form presented total phenolic contents of 0.19 to 5.68 mg of gallic acid equivalent/100 g of films. However, the films did not present antioxidant activity against the DPPH• radical.