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Recently, surface tension has been shown to be important in emerging high technologies, such as in pumping and control of flow in microfluidic devices, in microchemical analysis of complex fluids, and in rapid DNA screening, etc. Advances in these new technologies will depend strongly on the availability of flexible methods for controlling surface tension. Photo-control using a photoresponsive surfactant is a potentially attractive route to accomplishing many of the tasks required in these processes. Photoresponsive surfactants typically incorporate an azobenzene group as the functional unit which experiences reversible trans-to-cis photoisomerization under different irradiation conditions. The photoisomerization usually causes a change in surface tension. Obviously, a large change in surface tension under different illumination conditions will be highly desirable in practical applications. However, the largest change in surface tension as reported in the literature is only 3 mN/m which is too small to generate any significant effect. In this presentation, we report a new class of photoresponsive surfactants which exhibit excellent performance in surface tension control. Under different illumination conditions, the change in surface tension can be as large as 11.0 mN/m. Experimental results are presented for two new photoresponsive surfactants. A discussion of experimental results follows. / Singapore-MIT Alliance (SMA)

This thesis is concerned with aspects of the surface and colloid chemistry of various microemulsion systems stabilised by pure nonionic surfactants and alcohol as well as mixtures of nonionic and anionic surfactants. Phase equilibria and interfacial characteristics of the systems are studied with a view to their potential usefulness for enhanced oil recovery, in which salinity and temperature are important parameters. The equilibrium microemulsion phases are scanned at different temperatures and salinities and thus interfacial boundaries can be determined and optimum salinity scans can be performed accurately using a modified spectrophotometer. Several analytical techniques (e.g., high performance liquid chromatography, gas chromatography, ion-exchange chromatography, mass spectrometry, viscometry, electrical conductivity, photon correlation spectroscopy, UV-spectrophotometry, thermogravimetric analysis, transmission electron microscopy, surface and interfacial tension techniques) have been used to characterise and understand the microchemistry of the microemulsion systems. Ultra-low interfacial tensions (>0.1 µN/m) can be achieved in the microemulsion systems. Surfactant transfer between phases, and phase inversion of micro emulsions are shown to occur around the condition which produces minimum interfacial tension. Adsorption of the surfactants from aqueous and nonaqueous solutions has been investigated and the results show that the extent of adsorption can be reduced significantly in the presence of alcohols (co-solvent). The extent of adsorption increases with increasing temperature and salinity; however, it decreases with an increase in the hydrophilic head group of the surfactant. Adsorption of nonionic surfactants on quartz from the nonaqueous solution (decane) is much greater than from aqueous solution. In microemulsion applications, droplet combustion of w/o microemulsions is also studied for different surfaces (i.e. silica, oxidised Fecralloy and catalyst coated Fecralloy) in the temperature range of 313-573K. Formaldehyde and acetaldehyde are formed as intermediate combustion products. Thus the microemulsion combustion can lead to new oxygenate products. The w/o microemulsion route is used to synthesize colloidal silica of controlled particle size and morphology. The particle size can be varied by changing the molar ratio of water to TEOS using a water pH of 10.5.

Nous décrivons dans ce manuscrit la synthèse et l'étude de surfactifs à base de poly(2-méthyl-2-oxazoline) et de corps gras. Pour cela, deux voies de synthèse ont été réalisées. La première qui consiste à amorcer la polymérisation avec un alcool gras tosylé. La deuxième voie de synthèse a été réalisée en amorçant la polymérisation par un alcane iodé. Les surfactifs ainsi obtenus ont une chaîne grasse saturée ayant douze ou dix-huit atomes de carbone et des longueurs de chaînes polymères variables.Ces surfactifs sont examinés afin d'évaluer leur aptitude à la formulation. Ainsi, la valeur de leur concentration micellaire critique a été déterminée par tensiométrie et spectrofluorimétrie. Ensuite, l'évaluation de leurs pouvoirs mouillant et moussant, de leur HLB, de leur température de point de trouble… ont été déterminés afin de les comparer avec leurs homologues POE, les Brij®. Dans l'optique d'une application à la formulation, des tests d'évaluation de leur toxicité ont également été réalisés. Enfin, des préparations cosmétiques ont été formulées, à base de ces surfactifs et des Brij®. Parallèlement, une étude a été menée démontrant l'intérêt du carbonate de glycérol tosylé comme amorceur de la polymérisation de la 2-méthyl-2-oxazoline. Cet amorceur a permis de fonctionnaliser les polyoxazolines en extrémité de chaîne par des fonctions terminales (hydroxy)uréthane. / In this manuscript, we describe the synthesis and the study of surfactants based on poly(2-methyl-2-oxazoline) and vegetable oil derivatives. Two ways for the synthesis are realized. The first path consists to initiate the polymerization with a tosylate fatty alcohol. The second synthetic route was realized by initiating the polymerization by an iodoalkane. The obtained surfactants have au saturated fatty chain with twelve or eighteen carbon atoms and various lengths of polymeric chain. This surfactants are reviewed to assess their suitability for the formulation. Thus, the value of their critical micelle concentration was determined by tensiometry and spectrofluorimetry. After, the evaluation of their wetting and foaming powers, their HLB, their cloud point temperature… was determinded in order to compare with their homologous POE, the Brij®. In the context of an application in the formulation, evaluation tests of toxicity were also made. Next, cosmetic preparations were realized, based on this surfactants and Brij®. In parallel, a study was conducted to demonstrate the tosylate gycerol carbonate interest as initiator in the 2-methyl-2-oxazoline polymerization. This initiator enable to fonctionalize the polyoxazoline in the chain end with (hydroxy)uréthane terminal function.

The ability of surfactants to form micelles and solubilise hydrophobic substances in aqueous environments has been widely exploited in formulation science. In spite of extensive studies over the past few decades by both experimental and theoretical methods, however, it remains difficult to predict key micellar parameters such as their size, shape and nanostructure which is essential for their successful implementation in the solubilisation of active ingredients. This is partly due to the vast number of surfactants commercially available but, in addition, the fragmentation of the field of surfactant science, over recent years, has made it more difficult to identify general trends and properties of surfactant systems. A further challenge is in characterising systems of heavily mixed surfactants since our knowledge on pure surfactant systems may not allow us to predict the behaviour of these systems. The broad aim of this thesis was to contribute to these aspects of surfactant science. The first part of the thesis reports a systematic study of the surfactant structure-micellar structure relationship of pure alkyl ethoxylate (CmEn) surfactants. This was done by independently varying the lengths of the alkyl chain and ethoxylate group and measuring the micellar structural properties. The next part of the thesis reports the effects of solubilisation of two model pesticides, Cyprodinil and Diuron, on the size, shape and internal structure of these surfactant micelles. These pesticides were chosen because they were structurally representative of different features of those widely used in agrochemicals. The final part of the thesis reports the work on binary surfactant mixtures that rationalise the general structural features of mixed micelles and their impact on pesticide solubilisation. Various experimental techniques were used including small angle neutron scattering (SANS), nuclear magnetic resonance (NMR), nuclear Overhauser effect spectroscopy (NOESY NMR), dynamic light scattering (DLS) and UV spectroscopy. The key findings of the thesis were that the micellar core volumes could be predicted with reasonable accuracy using the hydrophilic-lipophilic balance (HLB) of the surfactants in pure micelles. NOESY results revealed protrusions of the terminal methylene groups into the ethoxylate shell, thus providing evidence for the theoretically predicted phenomenon referred to as the-shell interface. SANS revealed that solubilisation of both pesticides caused micellar growth, with the long axial lengths of the micelles growing much longer. These structural changes were associated with the dehydration of the ethoxylate shells. Although a partitioning experiment predicted that the pesticides would be solubilised in the hydrated ethoxylate micellar shell, NOESY measurements revealed that the solubilisation occurred predominantly in the micellar cores. The discrepancy was caused by alkyl chain-ethoxylate mixing leading to the formation of dehydrated palisade regions that entrapped the pesticides towards the cores. The results from the binary mixed micelles showed some signs of synergistic behaviour but no enhancement of pesticide solubilisation.

The aim of this thesis work was to investigate theadsorption of surfactants to different nonpolar interfaces.Particularly, the effects of the polar group and the nature ofthe hydrophobic interface were elucidated. The interfacialbehavior of the liquid-vapor interface was investigated bymeans of surface tension measurements. Here the effect of thepolar group and the hydrocarbon chain length was investigatedin a systematic manner. It was found that the shorter of thetwo chains examined, decyl, generated a larger surface pressurecontribution than the longer, dodecyl. Furthermore, the sugarbased surfactants behaved differently as compared to theethylene oxide based ones. The former could be modelled byassuming a hard disc behavior of the head group while thelatter displayed polymeric behavior. The influence of saltconcentration on the surface tension behavior of an ionicsurfactant, sodium dodecyl sulphate, was investigated. Theresult could be rationalized by employing the Gouy- Chapmanmodel to the polar region. Furthermore, mixtures of two sugarbased surfactants were investigated by surface tensionmeasurements and the adsorbed amount of the two components atthe interface atdifferent concentrations and fractions in thebulk were obtained by applying the Gibbs surface tensionequation. It was found that the molecule with the smaller headgroup adsorbed preferentially, and more so as the totalsurfactant concentration was increased. These findings could beexplained by considering the interactions generated by thedifferent head groups. The adsorption of sugar surfactants toan isolated hydrophobic surface was studied by means of wettingmeasurements and the behavior was similar to that at theliquid-vapor interface. Wetting isotherms were measured on twodifferent hydrophobic surfaces where the covalently attachedhydrophobic layers were in a crystalline and fluid state,respectively. The wetting results revealed that the sugarsurfactants anchored in the fluid hydrophobic layer. This had asignificant influence on the force profile. For example, at thecrystalline surface the surfactant monolayers were easilyremoved as the surface came into contact at relatively lowapplied loads. This was not the case when the hydrophobic layerwas in a fluid state. Here a significant fraction of thesurfactants remained between the surfaces. Disjoining pressureisotherms were measured using a sugar based surfactant thatwere thoroughly purified and compared to the as receivedsample. Even the purified sample showed a double-layer forcealthough lower as compared to the as received, one. Asignificant difference in foam stability was also observed. / <p>NR 20140805</p>

Neste estudo foi caracterizado o processo de solubilização de solutos neutros em sistemas micelares compostos de surfactantes não iônicos da família de alcoóis secundários etoxilados com o mesmo grupo hidrofóbico e graus diferentes de etoxilação, variando de 5 a 30 subunidades de oxido de etileno. Para isso, foram utilizadas as Relações Lineares de Energias Livres de Solvatação (LSER) como modelo preditivo para a eficiência de incorporação de solutos. As análises de regressão múltipla e as validações apresentadas tiveram por base a constante de incorporação micelar KS como variável dependente e os descritores de soluto de Abraham como as variáveis independentes. A metodologia utilizada para a determinação de KS baseou-se em técnicas fotofísicas (supressão de fluorescência), medidas de solubilização (solubilização em saturação via espectrofotometria de UV-VIS) e técnicas de cromatografia líquida (Cromatografia Micelar) e gasosa (Cromatografia por Análise de Fase Vapor ou Headspace). A determinação realizada forneceu as seguintes LSERs: 15-S-5: Log KS = 0,054 - 0,227A - 1,197B - 0,600S + 0,938E + 1,854V 15-S-7: Log KS = + 0,267 + 0,435A - 1,475B - 0,831S + 1,045E + 1,805V 15-S-15: Log KS = -0,047 + 0,314A - 1,265B - 0,487S + 0,823E + 2,107V 15-S-30: Log KS = - 0,345 + 0,366A - 1,114B - 0,430S + 0,858E + 2,310V Como é típico para sistemas micelares, constatou-se que a partição dos solutos entre os agregados micelares e a fase aquosa é dominada pelas propriedades de volume molar (V) e capacidade receptora de pontes de hidrogênio ou basicidade (B) do soluto, com contribuições secundárias de dipolaridade (S) e refração molar em excesso (E) do soluto. O aumento do tamanho da cabeça hidrofílica de oligômeros de oxietileno (OE) torna a micela menos coesa, facilitando a acomodação de solutos e favorecendo também a penetração de moléculas de água de hidratação que formam pontes de hidrogênio com as unidades de OE. Isto é indicado pelas variações observadas nos coeficientes de B e V. As variações dos coeficientes de S respondem também ao tamanho da cadeia e ao grau de hidratação, o que foi verificado pelos espectros de bandas vibrônicas de fluorescência de pireno e por alterações de deslocamentos químicos de RMN-1H. Anomalias observadas para surfactante 15-S-5 provavelmente deveram-se à presença de isopropanol utilizado como aditivo para solubilizá-lo em meio aquoso. O conjunto de dados obtidos demonstra que o tamanho da cadeia de OE e da micela responde melhor ao modo do que à extensão de solubilização dos solutos analisados, uma vez que a variável KS não responde de maneira linear ao grau de etoxilação para o conjunto de detergentes estudados. / This study has characterized the solubilization of neutral solutes in micellar systems composed of nonionic surfactants belonging to the family of ethoxylated secondary alcohols with the same hydrophobic group and different degrees of ethoxylation ranging from 5 to 30 ethylene oxide units. Linear Solvation Energy Relationships (LSER) was used as a predictive model for the efficiency of incorporation of solutes. The multiple regression analysis and the validations presented were based on the micellar incorporation constant KS as the dependent variable and Abraham solute descriptors as the independent variables. The methodologies utilized to determine the KS values included photophysical techniques (fluorescence quenching), measurements of solubility at saturation (via UV-VIs spectrophotometry), micellar liquid chromatography and gas chromatography (Headspace analysis of the vapor phase above micellar solutions). This study provided the following LSERs: 15-S-5: Log KS = - 0,054 - 0,227A - 1,197B - 0,600S + 0,938E + 1,854V 15-S-7: Log KS = + 0,267 + 0,435A - 1,475B - 0,831S + 1,045E + 1,805V 15-S-15: Log KS = - 0,047 + 0,314A - 1,265B - 0,487S + 0,823E + 2,107V 15-S-30: Log KS = - 0,345 + 0,366A - 1,114B - 0,430S + 0,858E + 2,310V As typically observed for micellar systems, the partitioning of solutes between micellar aggregates and the aqueous phase is dominated by the properties of molar volume (V) and hydrogen bond basicity (B) of the solute, with secondary contributions from the dipolarity (S) and excess molar refraction (E) of the solute. The increase in the size of the hydrophilic oxyethylene (OE) headgroup decreases the cohesion of the micelle, facilitating the accommodation of solutes and also favoring the penetration of waters of hydration that hydrogen bond with the OE units. This is indicated by the changes observed in the coefficients of B and V. The changes observed for S also respond to the size of the OE chain, as reflected in the vibronic bands of the fluorescence spectra of pyrene and changes of proton chemical shifts in 1H-NMR spectra. Anomalies for the surfactant 15-S-5 were probably due to the necessity to include isopropanol as an additive to solubilize it in water. The data show that the OE chain and micelle sizes respond better to the mode than to the extent of solubilization for the solutes analyzed, since the predictor variable KS does not respond consistently to the degree of ethoxylation for the micellar systems studied.

Neste estudo foi caracterizado o processo de solubilização de solutos neutros em sistemas micelares compostos de surfactantes não iônicos da família de alcoóis secundários etoxilados com o mesmo grupo hidrofóbico e graus diferentes de etoxilação, variando de 5 a 30 subunidades de oxido de etileno. Para isso, foram utilizadas as Relações Lineares de Energias Livres de Solvatação (LSER) como modelo preditivo para a eficiência de incorporação de solutos. As análises de regressão múltipla e as validações apresentadas tiveram por base a constante de incorporação micelar KS como variável dependente e os descritores de soluto de Abraham como as variáveis independentes. A metodologia utilizada para a determinação de KS baseou-se em técnicas fotofísicas (supressão de fluorescência), medidas de solubilização (solubilização em saturação via espectrofotometria de UV-VIS) e técnicas de cromatografia líquida (Cromatografia Micelar) e gasosa (Cromatografia por Análise de Fase Vapor ou Headspace). A determinação realizada forneceu as seguintes LSERs: 15-S-5: Log KS = 0,054 - 0,227A - 1,197B - 0,600S + 0,938E + 1,854V 15-S-7: Log KS = + 0,267 + 0,435A - 1,475B - 0,831S + 1,045E + 1,805V 15-S-15: Log KS = -0,047 + 0,314A - 1,265B - 0,487S + 0,823E + 2,107V 15-S-30: Log KS = - 0,345 + 0,366A - 1,114B - 0,430S + 0,858E + 2,310V Como é típico para sistemas micelares, constatou-se que a partição dos solutos entre os agregados micelares e a fase aquosa é dominada pelas propriedades de volume molar (V) e capacidade receptora de pontes de hidrogênio ou basicidade (B) do soluto, com contribuições secundárias de dipolaridade (S) e refração molar em excesso (E) do soluto. O aumento do tamanho da cabeça hidrofílica de oligômeros de oxietileno (OE) torna a micela menos coesa, facilitando a acomodação de solutos e favorecendo também a penetração de moléculas de água de hidratação que formam pontes de hidrogênio com as unidades de OE. Isto é indicado pelas variações observadas nos coeficientes de B e V. As variações dos coeficientes de S respondem também ao tamanho da cadeia e ao grau de hidratação, o que foi verificado pelos espectros de bandas vibrônicas de fluorescência de pireno e por alterações de deslocamentos químicos de RMN-1H. Anomalias observadas para surfactante 15-S-5 provavelmente deveram-se à presença de isopropanol utilizado como aditivo para solubilizá-lo em meio aquoso. O conjunto de dados obtidos demonstra que o tamanho da cadeia de OE e da micela responde melhor ao modo do que à extensão de solubilização dos solutos analisados, uma vez que a variável KS não responde de maneira linear ao grau de etoxilação para o conjunto de detergentes estudados. / This study has characterized the solubilization of neutral solutes in micellar systems composed of nonionic surfactants belonging to the family of ethoxylated secondary alcohols with the same hydrophobic group and different degrees of ethoxylation ranging from 5 to 30 ethylene oxide units. Linear Solvation Energy Relationships (LSER) was used as a predictive model for the efficiency of incorporation of solutes. The multiple regression analysis and the validations presented were based on the micellar incorporation constant KS as the dependent variable and Abraham solute descriptors as the independent variables. The methodologies utilized to determine the KS values included photophysical techniques (fluorescence quenching), measurements of solubility at saturation (via UV-VIs spectrophotometry), micellar liquid chromatography and gas chromatography (Headspace analysis of the vapor phase above micellar solutions). This study provided the following LSERs: 15-S-5: Log KS = - 0,054 - 0,227A - 1,197B - 0,600S + 0,938E + 1,854V 15-S-7: Log KS = + 0,267 + 0,435A - 1,475B - 0,831S + 1,045E + 1,805V 15-S-15: Log KS = - 0,047 + 0,314A - 1,265B - 0,487S + 0,823E + 2,107V 15-S-30: Log KS = - 0,345 + 0,366A - 1,114B - 0,430S + 0,858E + 2,310V As typically observed for micellar systems, the partitioning of solutes between micellar aggregates and the aqueous phase is dominated by the properties of molar volume (V) and hydrogen bond basicity (B) of the solute, with secondary contributions from the dipolarity (S) and excess molar refraction (E) of the solute. The increase in the size of the hydrophilic oxyethylene (OE) headgroup decreases the cohesion of the micelle, facilitating the accommodation of solutes and also favoring the penetration of waters of hydration that hydrogen bond with the OE units. This is indicated by the changes observed in the coefficients of B and V. The changes observed for S also respond to the size of the OE chain, as reflected in the vibronic bands of the fluorescence spectra of pyrene and changes of proton chemical shifts in 1H-NMR spectra. Anomalies for the surfactant 15-S-5 were probably due to the necessity to include isopropanol as an additive to solubilize it in water. The data show that the OE chain and micelle sizes respond better to the mode than to the extent of solubilization for the solutes analyzed, since the predictor variable KS does not respond consistently to the degree of ethoxylation for the micellar systems studied.

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<p>The aim of this thesis work was to investigate theadsorption of surfactants to different nonpolar interfaces.Particularly, the effects of the polar group and the nature ofthe hydrophobic interface were elucidated. The interfacialbehavior of the liquid-vapor interface was investigated bymeans of surface tension measurements. Here the effect of thepolar group and the hydrocarbon chain length was investigatedin a systematic manner. It was found that the shorter of thetwo chains examined, decyl, generated a larger surface pressurecontribution than the longer, dodecyl. Furthermore, the sugarbased surfactants behaved differently as compared to theethylene oxide based ones. The former could be modelled byassuming a hard disc behavior of the head group while thelatter displayed polymeric behavior. The influence of saltconcentration on the surface tension behavior of an ionicsurfactant, sodium dodecyl sulphate, was investigated. Theresult could be rationalized by employing the Gouy- Chapmanmodel to the polar region. Furthermore, mixtures of two sugarbased surfactants were investigated by surface tensionmeasurements and the adsorbed amount of the two components atthe interface atdifferent concentrations and fractions in thebulk were obtained by applying the Gibbs surface tensionequation. It was found that the molecule with the smaller headgroup adsorbed preferentially, and more so as the totalsurfactant concentration was increased. These findings could beexplained by considering the interactions generated by thedifferent head groups. The adsorption of sugar surfactants toan isolated hydrophobic surface was studied by means of wettingmeasurements and the behavior was similar to that at theliquid-vapor interface. Wetting isotherms were measured on twodifferent hydrophobic surfaces where the covalently attachedhydrophobic layers were in a crystalline and fluid state,respectively. The wetting results revealed that the sugarsurfactants anchored in the fluid hydrophobic layer. This had asignificant influence on the force profile. For example, at thecrystalline surface the surfactant monolayers were easilyremoved as the surface came into contact at relatively lowapplied loads. This was not the case when the hydrophobic layerwas in a fluid state. Here a significant fraction of thesurfactants remained between the surfaces. Disjoining pressureisotherms were measured using a sugar based surfactant thatwere thoroughly purified and compared to the as receivedsample. Even the purified sample showed a double-layer forcealthough lower as compared to the as received, one. Asignificant difference in foam stability was also observed.</p>