Dissertations / Theses on the topic 'Surfactants'

The first part of this thesis is concerned with thestructure-property relationships in nonionic surfactantsystems. The main aim was to investigate how the surfactantstructure influences the adsorption at interfaces andinteractions between surfactant coated interfaces.Particularly, the effect of the structure of the surfactantheadgroups was investigated. These were sugar-based headgroupwith varying size and flexibility and poly(ethylene oxide)based headgroups with or without an additional amide or estergroup. The hydrophobic part of the surfactant consisted mostlyof straight alkyl chains, except for one type of poly(ethyleneoxide) based surfactant with a dehydroabietic hydrophobe.

The main technique that was used is the surface forcetechnique, with which the forces acting between two adsorbedsurfactant layers on hydrophilic or hydrophobic surfaces can bemeasured. These forces are important for e.g. the stability ofdispersions. The hydrophilic surfaces employed were glass andmica, whereas the hydrophobic surfaces were silanized glass andhydrophobized mica. The adsorption behavior on hydrophilicsurfaces is highly dependent on the type of headgroup andsurface, whereas similar results were obtained on the two typesof hydrophobic surfaces. To better understand how the surfaceforces are affected by the surfactant structure, measurementsof adsorbed amount and theoretical mean-field latticecalculations were carried out. The results show that the sugarsurfactant layers and poly(ethylene oxide) surfactant layersgive rise to very different surface forces, but that the forcesare more similar within each group. The structure-propertyrelationships for many other physical properties have beenstudied as well. These include equilibrium and dynamicadsorption at the liquid-vapor interface, micelle size, micelledynamics, and wetting.

The second part in this thesis is about the aggregationbetween cationic polyelectrolytes and an anionic surfactant.The surface force technique was used to study the adsorption ofa low charged cationic polyelectrolyte on mica, and theaggregation between the adsorbed polyelectrolyte with theanionic surfactant. The aggregation in bulk was studied withturbidimetry, small angle neutron scattering (SANS), and smallangle x-ray scattering (SAXS). An internal hexagonal aggregatestructure was found for some of the bulk aggregates.

Keywords:nonionic surfactant, sugar surfactant,poly(ethylene oxide), amide, ester, polyelectrolyte, SDS,hydrophobic surface, glass surface, mica, adsorption,aggregation, micelle size, surface forces, wetting, dynamicsurface tension, NMR, TRFQ, SANS, SAXS, mean-field latticecalculations.

Les propriétés d’auto organisation de tensioactifs ainsi que celles de la chimie de la silice ont permis de préparer des matériaux mésoporeux organisés selon une symétrie hexagonale, cubique ou lamellaire dont la taille des pores varie de 2 à plus de 10 nm. Ils sont depuis quelques années le centre d’intérêt d’universitaires et d’industriels qui développent des recherches fondamentales et appliquées. La compréhension globale des mécanismes de synthèse et la maîtrise des propriétés structurales et texturales des matériaux mésoporeux sont nécessaires pour envisager leur utilisation dans un quelconque procédé industriel. Dans ce cadre, nous avons étudié les relations entre les propriétés physico-chimiques d’un tensioactif fluoré C7F15C2H4(OC2H4)8OH et les caractéristiques des silices mésoporeuses. Malgré l’existence d’une phase micellaire, les canaux poreux des matériaux obtenus avec ces solutions micellaires ne sont pas organisés. En revanche, l’addition de la perfluorodécaline provoque une structuration du matériau selon une symétrie hexagonale. L’utilisation de divers fluorocarbures, ayant des structures moléculaires différentes, montre que le phénomène est associé au déplacement de la courbe de point de trouble vers les hautes températures. De plus, il a été montre que la préparation de matériaux à porosité hiérarchisée à partir d'émulsions de type huile dans eau est corrélée à la température d’inversion de phase du système eau/huile/tensioactif. Enfin, les matériaux mésoporeux ont été mis à profit pour immobiliser des enzymes et les résultats montrent que les lipases physisorbées conservent une activité catalytique
The self-assembly properties of surfactants and those of silica chemistry have led to the preparation of ordered mesoporous materials with hexagonal, cubic or lamellar symmetry and with pore sizes varying from 2 to more than 10 nm. Recently, they have aroused of great deal of interest to academics and industrialists for the development of fundamental and applied research. However, their use in any industrial process needs a careful consideration of the total comprehension of the synthesis mechanism as well as the control of their structural and textural properties. In this work, the relation between the physicochemical properties of a fluorinated surfactant, C7F15C2H4(OC2H4)8OH, and the characteristics of mesoporous silica was investigated. In spite of the existence of a micellar phase, only wormlike mesoporous materials were obtained. On the other hand, the addition of the perfluorodecalin led to the organisation of the channels according to a hexagonal symmetry. The use of various fluorocarbons of different molecular structures evidenced that this phenomenon is associated to the shift of the cloud point curve towards higher temperatures. Hierarchically porous silica were also prepared from oil-in-water emulsions and their characteristics were correlated to the phase inversion temperature of the surfactant/water/oil system. Finally, the mesoporous materials were used as hosts for the physisorption of enzymes and the results showed that the catalytic activity of the immobilised lipases is preserved

This thesis deals with the synthesis and characterization ofnovel polyhydroxyl surfactants. The first part describes thesynthesis of a number of stereoisomers of a polyhydroxylsurfactant, and the second part concerns surface chemicalcharacterization.

A stereodivergent route for preparation of the hydrophilichead group was developed, featuring consecutive stereoselectivedihydroxylations of a diene. This afforded in total fourdifferent polyhydroxyl head groups. These surfactant headgroups were natural and unnatural sugar analogues, and wereused for the coupling with two different hydrophobic tailgroups.

Three of these surfactants were used to investigate thechiral discrimination in Langmuir monolayers at an air-waterinterface. The isotherms showed a remarkable difference incompressibility between surfactants of diastereomericrelationship and also a pronounced chiral discriminationbetween racemic and enantiomerically pure surfactants favoringheterochiral discrimination.

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CAPES
O LAS é um tensoativo usado na fabricação de produtos de limpeza, sendo sua degradação no tratamento aeróbio altamente eficaz. Todavia, em ambientes anaeróbios, sua biodegradação depende de vários fatores, como a composição e concentração de alguns compostos dos esgotos. Por isso, as eficiências de degradação do LAS neste ambiente são distintas, variando de 0 a 78%. No Brasil, devido a uma carência na área do saneamento, alternativas mais baratas para o tratamento de esgoto estão sendo amplamente utilizadas. Os reatores anaeróbios do tipo UASB são um exemplo destas alternativas, devido a sua alta eficiência de remoção de matéria orgânica. Entretanto, atualmente em uma estação de tratamento de esgoto, o objetivo não é apenas a matéria orgânica de fácil degradação, mas também compostos recalcitrantes e nutrientes. Este trabalho teve como objetivo aplicar em um reator contínuo, alimentado com esgoto real, um modelo de otimização, realizado em laboratório com regime em batelada, para verificar reprodutibilidade da influência de alguns parâmetros na dinâmica de sorção/dessorção do LAS em reatores utilizados em estações de tratamento de esgoto convencionais. Foram realizados dois experimentos. O experimentoI foi o monitoramento de um reator UASB em escala de laboratório. Este reator era alimentado com esgoto de uma estação de tratamento real, ETE Mangueira. Alterações no afluente foram realizadas para proporcionar a adsorção do LAS na biomassa. O pH foi ajustado para 6. Seguindo um planejamento fatorial 2K, o reator foi operado em 4 fases alterando a concentração de óleo, entre 0 e 5 g/L e a oxigenação ou não do LAS. O experimento II foi um teste de laboratório de adsorção e de dessorção, utilizando a mesma biomassa do reator do primeiro experimento. Foram submetidas diferentes concentrações de LAS (10, 20 e 100 mg/L), e diferentes tempos de mistura. Durante o período de operação, observou-se a ocorrência de adsorção e dessorção do LAS no lodo, bem como biodegradação, quando a adsorção foi baixa; as eficiências de degradação do LAS total nas diversas fases experimentais variaram de 0 a 33%. Os homólogos C12 e C13 foram os que sofreram maior degradação durante todo período de operação, com eficiências de 42 e 57% de sua massa inicial, respectivamente, na fase com alteração apenas do pH; o C13 foi o homólogo de maior taxa de adsorção, 97% de sua massa inicial. Isto ocorreu quando a concentração de óleo foi de 5 g/L e não foi realizado aeração do LAS. No teste de adsorção, os resultados obtidos mostraram que a adsorção na biomassa seca depende da disponibilidade de LAS no líquido. No teste de dessorção o comportamento de liberação de LAS no meio aquoso foi lento. Os testes mostraram capacidade reversível da adsorção do LAS, comprovando que a dinâmica de adsorção e dessorção do LAS no reator depende da composição do meio líquido e da forma de operação do reator, e que sua indisponibilidade no meio solúvel impede a degradação. Logo, o processo de adsorção inibe a degradação do LAS em ambientes anaeróbios e os resultados obtidos no teste de otimização em laboratório foram também observados em reatores operados com esgoto real.
LAS is a surfactant used in the manufacture of cleaning products, and its degradation in the highly efficient aerobic treatment. However, in anaerobic environments, biodegradation depends on several factors, including the composition and concentration of certain compounds of sewage. Therefore, the LAS this environmental degradation efficiencies are different, ranging from 0 to 78%. In Brazil, due to a lack in the sanitation area, cheaper alternatives for the treatment of sewage are being widely used. The anaerobic reactor of the UASB type are an example of these alternatives, due to its high removal efficiency of organic matter. However, currently a sewage treatment plant, the aim is not only the organic matter degradation easily, but also nutrients and recalcitrant compounds. This study aimed to apply in a continuous reactor, fed with real wastewater, an optimization model, conducted in laboratory batch system to check reproducibility of the influence of some parameters on dynamic sorption / desorption of LAS reactors used in stations Conventional sewage treatment. Two experiments were conducted. The first was a monitoring of a UASB reactor at laboratory scale. This reactor was fed with sewage a real treatment plant, ETE hose. Changes in the influent were performed to provide the adsorption of LAS biomass. The pH was adjusted to 6. By following a factorial design 2K, the reactor was operated at four stages by changing the concentration of oil, between 0 and 5 g / L and oxygenation or not the LAS. The second experiment was a laboratory test adsorption and desorption using the same biomass from the first reactor experiment. They underwent different concentrations of LAS, 10, 20 and 100 mg / L, and different mixing times. During the operation period, it was observed the occurrence of adsorption and desorption of LAS in the sludge as well as biodegradation when adsorption was low; The degradation efficiency of the total LAS in the different experimental phases ranging from 0 to 33%. The C12 and C13 homologues have suffered the greatest degradation during the entire operating period, efficiency 42 and 57% of their initial mass, respectively, in phase with the pH change only; the C13 was the counterpart of higher adsorption rate, 97% of its initial mass. This occurred when the oil concentration was 5 g / L and aeration was not performed LAS. In the adsorption test, the results showed that adsorption of dry biomass depends on the availability of LAS in the liquid. In desorption test the LAS release behavior in aqueous media was slow. The tests showed reversible adsorption capacity of the LAS, proving that the dynamics of adsorption and desorption of LAS in the reactor depends on the composition of the liquid medium and form of reactor operation, and that their unavailability in the middle soluble prevents degradation. Therefore, the adsorption process inhibits the degradation of LAS in anaerobic environments and the results obtained in laboratory test optimization are also observed in reactors operated with real sewage.

Surfactants comprise one of the largest volume commodity chemicals in the world and have multifarious uses from pharmaceuticals, agrochemicals, food, fuel and lubricant additives, paints and inks as well as detergents and cleaning agents. The ability to control surfactants once they are in solution is of great importance not only for scientific reasons but also because of environmental and economic interest. To this end, surfactants sensitive to changes in pH, temperature, C02, light and redox have already been developed. This thesis investigates a new class of surfactants designed to be magnetically active, whereby the composition and physico-chemical properties of a system may be perturbed simply by the switching "on" and "off" of a magnetic switch and with no significant energy input. The thesis demonstrates that these new magneto-responsive surfactants behave like conventional surfactants but are now bifunctional allowing for new magnetic approaches where previously magnetic nanoparticles have been employed. For example, the magnetic properties makes it easier to round up and remove the surfactant from a system once it has been added. By developing the first nanoparticle-free magnetic emulsions the potential for further applications in environmental clean ups (e.g. oil spills), water treatment or drug delivery have been demonstrated. In addition to this, the combination of surfactant adsorption and intrinsic magnetism has allowed for the control and manipulation of biomolecules without the need for magnetic nanoparticles. This work explores both the fundamental properties of these novel surfactants and also takes significant steps to optimize the surfactants for potential applications.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 249-264).
This thesis focuses on two research areas that are particularly relevant to the practical application of surfactant science: (1) the micellization of multicomponent surfactant mixtures, and (2) the micellization of pH-sensitive (or amphoteric) surfactants. Surfactant formulations of practical utility typically consist of many surfactant components. In many practical applications, pH-sensitive surfactants are added as a secondary surfactant because they enhance performance properties, including solubility, foaming, and mildness to the skin or to the eyes. In addition, pH-sensitive surfactants may be used eectively in novel applications where pH variations can be utilized to control self-assembly, including controlled drug release, targeted gene delivery, and the fabrication of nanoscale materials for optics, electronics, and sensors. First, a molecular-thermodynamic (MT) theory was developed to account for counterion binding to mixed micelles composed of ionic-nonionic and ionic-zwitterionic binary surfactant mixtures. The theory successfully predicted the degree of counterion binding ([beta]) of monovalent and multivalent ions to mixed micelles as a function of the micelle composition ([alpha]).
(cont.) The theory was also found to be consistent with the concept of critical counterion binding. An inection in the [beta vs. [alpha] curve was correlated to a micelle shape transition. Second, the MT theory was generalized to include pH eects in order to model the micellization of pH-sensitive surfactants. The theory was validated by comparing predictions of critical micelle concentrations (cmc's), micelle aggregation numbers, and micellar titration behavior to experimental data for alkyldimethylamine oxide surfactants, which are cationic in the protonated state (at low pH) and zwitterionic in the deprotonated state (at high pH). The MT theory qualitatively reproduced the minimum in the cmc and the maximum in the micelle aggregation number, which are both observed experimentally at intermediate pH values, resulting from the synergy between the two forms of the pH-sensitive surfactant in the micelle. This self-synergy, which was previously attributed by other researchers to the formation ofsurfactant-surfactant hydrogen bonds in the micelle, was rationalized instead in terms of electrostatic interactions operating between surfactants and bound counterions in the micelle. Very good quantitative agreement was obtained for the predicted cmc's in solutions containing no added salt.
(cont.) In particular, the experimentally observed maximum in the cmc, which originated from changes in the solution ionic strength, was reproduced by the MT theory but not by the empirical regular solution theory (RST). Micellar titration data were also examined in terms of the relative values of the micellar deprotonation equilibrium parameter (pK). The pK was related to the derivative of the electrostatic contribution to the free energy of micellization ( gelec) with respect to . The molecular model of gelec predicted pK > 0 in the limit of micelles composed entirely of the deprotonated form of the pH-sensitive surfactant, consistent with the experimental data. Third, a theory based on RST was developed to model the titration behavior of micelles containing a pH-sensitive surfactant and an arbitrary number of conventional surfactants. The conventional surfactants were successfully modeled as a single eective surfactant, thus considerably simplifying the theoretical analysis of multicomponent surfactant mixtures. The RST description was validated using experimental micellar titration data for single surfactant systems (obtained from the literature) and for binary surfactant mixtures (measured as part of this thesis).
(cont.) Experimental uncertainties in the micellar titration data were examined, and a new method was introduced to account for these uncertainties by using a weighted regression analysis. Fourth, a MT theory was developed to model the micellization of mixtures containing an arbitrary number of conventional surfactants. The maximum micelle radius was examined theoretically for a ternary surfactant mixture. Due to the limited availability of experimental data, only the predicted cmc's were compared with the experimental cmc's. Good agreement was obtained for the predicted cmc's, which were comparable to, and sometimes better than, the cmc's determined using RST. The MT theory was also used to model a commercial nonionic surfactant (Genapol UD-079), which was modeled as a mixture of 16 surfactant components. The predicted cmc agreed remarkably well with the experimental cmc. The monomer concentration was predicted to increase signicantly above the cmc. In addition, the monomer and the micelle compositions were predicted to vary signicantly with surfactant concentration. These composition variations were rationalized in terms of competing steric and entropic eects and a micelle shape transition near the cmc.
(cont.) Finally, the MT theory was further generalized to model the micellization behavior of mixtures of a pH-sensitive surfactant and an arbitrary number of conventional surfactants. Predicted values of the solution pH of mixtures of a pH-sensitive surfactant and an ionic surfactant, as well as of the cmc's of mixtures of two pH-sensitive surfactants, compared favorably with the experimental values. The MT theory was also validated using micellar titration data for varying compositions of mixed micelles containing dodecyldimethylamine oxide (C12DAO) and a cationic, nonionic, or anionic surfactant. The MT theory accurately modeled the titration behavior of C12DAO mixed with the nonionic surfactant. However, C12DAO appeared to interact more favorably with the anionic and the cationic surfactants than waspredicted by the MT theory. The MT theories presented in this thesis represent the rst molecular-based models of the micellization behavior of the following systems: (1) pH-sensitive surfactants, (2) mixtures of three or more conventional surfactants, and (3) mixtures of pH-sensitive surfactants and conventional surfactants. The MT theories resulted in qualitative and quantitative predictions of the micellization properties for a variety of surfactant systems.
(cont.) A simpler theory based on RST was also developed to model titrations of micelles containing pH-sensitive and conventional surfactants. In addition, this thesis resulted in the rst experimental study of the eect of micelle composition on the titration behavior of mixed micelles containing a pH-sensitive surfactant and a conventional surfactant. The resulting MT theories have provided fundamental, physical insight, and they may also decrease the need for the costly and time-consuming process associated with "trial-and-error" surfactant formulation.
by Arthur Clayton Goldsipe.
Ph.D.

For any solvent to find global application in the chemical industry, methods by which its physical-chemical properties might be manipulated (with respect to e.g. polarity, surface tension, wettability and viscosity) are often required. One way to achieve this Is through the use of surfactants. To this end, surfactant behavior in a variety of unconventional solvent systems (polar hydrocarbons, fluorocarbons and liquid CO2) has been investigated with respect to aggregation, microemulsion formation and nanoparticle stabilization. Both commercial and custom-designed, in-house synthesized surfactant systems have been investigated.

With regard to CO2-based processing and handling technologies, research into optimising COrphilic surfactant design is especially important. Here, surfactant structure design is focused on anionic surfactant analogues of Aerosol-OT (sodium bis (2-ethylhexyl) sulfosuccinate). The surfactants were systematically synthesised with modification centred on four strategies including (1) alkyl chain type (2) introduction of a third chain (3) counterion type and (4) surfactant template. The work presented in this thesis has aimed to investigate the relationship between the architecture and the properties (aggregate formation and interfacial activity) of AOT analogue in water and water-in-C02 (wlc) microemulsion. The surfactants have been investigated by a range of techniques including high-pressure phase behaviour, small-angle neutron scattering (SANS) and air-water (alw) surface tension measurements. The results show fluorination is a crucial factor influencing AOT surfactant analogue compatibility with CO2• The presence of fluorine in the surfactant chemical structure gives rise to an optimum interfacial packing density needed to promote favourable interactions with CO2• On the other hand, CO2- philicity of hydrocarbon surfactants can be enhanced by introducing a third chain as well as terminal methyl groups. However, despite low cost and being environmentally friendly, a major limitation of these hydrocarbon surfactants is inability to disperse water in the CO2 continuous phase. The results also highlight the challenges in controlling the CO2-philicity of hydrocarbon surfactants by changing bulky tetrapropylammonium (TPA) counterion and hydroxyaluminium disoap headgroup. It has now been established that both modifications are detrimental to CO2 compatibility. Here, a novel hybrid surfactant, with one F-chain and another H-chain, was synthesised where attention has been paid to minimizing the fluorine content while retaining' an acceptable level of COrphilicity. The work has advanced the understanding of how CO2-philicity of AOT analogues can be enhanced in CO2. The results obtained are beneficial for expanding CO2 industrial applications and realising its potential using the most economic and efficient CO2- philic surfactants.

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.

Adsorption on solid surfaces from solution is a fundamental property of a surfactant. It might even be the most important aspect of surfactant behavior, since it influences many applications, such as cleaning, detergency, dispersion, separation, flotation, and lubrication. Consequently, fundamental investigations of surfactant adsorption are relevant to many areas.

The main aim of this thesis has been to elucidate the adsorption properties, primarily on the solid/water interface, of a particular class of polyhydroxyl based surfactants: the alkyl glucosides. By the use of ellipsometry, the equilibrium and kinetic aspects of adsorption on titanium dioxide with respect to structural effects has been studied. Furthermore, the effects of small amounts of cationic surfactant additives on the adsorption on silica have been investigated. The results have been compared with similar studies for other nonionic surfactants.

We have found that the surfactant structure has a strong effect on the adsorption properties. An increase in the surfactant chain length increases the cooperativity of the system. An increase in the head group polymerization decreases the cooperativity and the plateau adsorbed amount at equilibrium. The effect of surfactant structure on the adsorption kinetics depends on the concentration relative to the cmc, while the there is a decrease in the rate of desorption with increasing hydrophobic chain length independent of the concentration. The adsorption/desorption process is concluded to be diffusion driven, as suggested by the model used. When comparing these results with studies on ethylene oxide based surfactants, we conclude that the two types of surfactants exhibit similar trends on surfaces onto which they adsorb.

Adsorption from binary surfactant solutions is even more interesting than adsorption from single surfactant solutions, since it brings us one step closer to the systems used in applications. In addition, adsorption from a mixture can be very different from adsorption from any of the single surfactants in the mixture. Alkyl glucosides alone do not adsorb on silica, but addition of small amounts of a cationic surfactant to the alkyl glucoside solution allows for adsorption on silica. A comparison between the adsorption and bulk properties has shown that mixed micellization explains most, but not all, effects of the coadsorption properties. Changing the pH in the mixed systems reveals that a surfactant with a pH-dependent charge and the ability to adapt its charge to the environment, e.g. a surface, enhances the adsorbed amount over a wider range of pH values than a purely cationic surfactant.

It is well known that alkyl glucosides and ethylene oxides adsorb differently on different types of hydrophilic surfaces. As a consequence, replacing ethylene oxides with alkyl glucosides might not be all straight-forward; however, we have shown that the effect of the surface can be eliminated by the use of a cosurfactant.

In this thesis technical nonionic surfactants are studied using multivariate techniques. The surfactants studied were alkyl ethoxylates (AEOs) and alkyl polyglucosides (APGs). The aquatic toxicity of the surfactants towards two organisms, a shrimp and a rotifer, was examined. The specified effect was lethality, LC50, as indicated by immobilisation. In a comparative study, the LC50 values obtained were used to develop two different types of model. In the log P model the toxicity was correlated to log P alone, while in the multivariate model several physicochemical variables, including log P, were correlated to the toxicity. The multivariate model gave smaller prediction errors than the log P model. Further, the change in reactivity when a surfactant mixture was added to dissolving pulp under alkaline conditions was studied, using the amount of residual cellulose as a measure of the reactivity. Ten AEO/APG mixtures were tested, and the mixture with greatest potential was studied in more detail. An optimum in the amount of added surfactant was found that seems to coincide, according to surface tension measurements, with the CMC.

A large number of commercial and some novel Brunel synthesised surfactants have been studied with a view to their potential usefulness for enhanced oil recovery (EOR) application. Ethoxylated phenols and their sulphonated derivatives were given especially high priority. The surfactants were well-characterised in order to understand their EOR potential. High pressure liquid chromatography, mass spectrometry, Raman spectrometry, nuclear magnetic resonance spectrometry and other quantitative techniques were used. Aspects of their behaviour (as single components and as blends with co-surfactants and co-solvents) which have been considered in terms of: (i) phase behaviour with brine and hydrocarbons (ii) adsorption onto various oxide surfaces (iii) interfacial properties such as surface tension, wetting, contact angles and viscosity (iv) stability Three different blends using sulphonated surfactants which: (i) produce a microeinulsion which is stable to high salinity brines over a large temperature range (ii) exhibit low adsorption onto reservoir rock (iii) interfacial tension as low as 10-2mNm-1 have been subsequently optimised. Core flooding tests carried out under reservoir conditions produced an additional 20% of the original-oil-in-place.

The binary surfactant system nona (ethylene glycol) mono-( 11 -oxa- 14,18.22,26-tetramethylheptacosylether) in heavy water has been investigated using deuterium nuclear magnetic resonance, optical polarising microscopy and small angle scattering techniques. The phase diagram has been established and the phases encountered exist for the most part from 24 to 60% surfactant by weight. Above and below these concentrations exist isotropic and lamellar phases respectively. The phase diagram features three main phases, a hexagonal phase of circular rods, a lamellar phase and an intermediate phase. The length of the alkyl chain is shown to be the most important factor in stabilising intermediate phases in preference to the bicontinuous cubic phases usually encountered between hexagonal and lamellar phases in shorter chain homologues. A nematic phase has also been observed in the water penetration scan. The intermediate phase is extensive, ranging from 32 to 60% surfactant by weight and is about 5°C wide. It has a body centred tetragonal mesh structure, comprised of layers of surfactant with regularly spaced holes which are also correlated between the layers, the hole of one layer overlapping the intersection of the layer below. As the concentration is decreased, from 60% to 30% (surfactant by weight) this correlation relaxes. The actual form of the aggregate appears to be elliptical rods (ellipticity - 1.7) joined four by four to form the basis of the mesh structure. A simplified version of the model based on circular rods joined by cube junction regions has been used to quantitatively investigate this phase. The results from this crude model produce results very close to those anticipated and produces results to within 2% of those generated using a more sophisticated model. This system is unusual in that the nature of the interaction between aggregates appears to be dominated by a single interaction - 'headgroup overlap force. This arises from the repulsive pressure experienced by the headgroups penetrating from the aggregate interface and also between headgroups on the same aggregate.

The liquid-liquid extraction of biomolecules using a reverse micellar system has been studied in literature as a simple and easily scalable purification method that can be used in fermentation industry. The recovery of proteins from the reverse micellar phase has shown a low efficiency (less than 20%) making the technique unfavorable in industrial practice. In addition, the modeling is often complicated due to the complex interactions among surfactants, cosurfactants, electrolytes and charged biomolecules. Thus, this work was aimed to examine the solubilization behavior of lysozyme into four different reverse micellar systems, in order to better understand the extraction mechanism. The water uptake and the concentration of lysozyme obtained in the organic phase were measured. The recovery of lysozyme from the reverse micellar phase was attempted using a second aqueous phase with pH and ion strength adjustments, a conventional method used in literature. The best extraction was obtained with aerosol-OT, but low recoveries were obtained with all three anionic and one cationic surfactants tested. During these experiments, the formation of a white precipitate at the aqueous-organic interface was observed, and this observation provided the basis for an understanding of the extraction mechanism and a proposal of a novel separation method.
A novel purification method is proposed to extract lysozyme from an aqueous solution using surfactants and recover it as a solid. In this method, the surfactant is directly added to the aqueous solution containing lysozyme, instead of using a liquid-liquid extraction mechanism. Upon contact, the lysozyme forms an insoluble lysozyme-ligand complex. The insoluble compound was then dissolved in acetone, and the surfactant-free lysozyme was recovered as a solid. An overall recovery efficiency of up to 70% was obtained, and the lysozyme was found to retain its original enzymatic activity. A simple mathematical model is suggested to describe the formation of lysozyme-surfactant complex. The model was also used to better understand, the extraction mechanism of lysozyme into a reverse micellar phase.

This thesis is concerned with the interactions of oils with surfactants. The understanding of these interactions is important for a number of practical applications which include perfume delivery in fabric softeners. Both non-ionic surfactants, of the general formula H( CH2)n( OCH2CH2)m-OH, and lome surfactants, of the general formula CnH2n+lW(CH3)3Br were used in the study. Oils of varying polarity were investigated from non-polar alkane oils to moderately polar perfume oils.Initially, the work of adhesions of the perfume oils with water were studied to establish where these oils 'fitted-in' to a range of oils of varying polarity. It was found that the three perfume oils studied (linalool, cineole and eugenol) all exhibited adhesion properties which were fairly typical of moderately polar oils. In order to obtain the enthalpies and entropies of adhesion of the perfume oils with water the surface tensions and interfacial tensions with water were measured as a function of temperature. The enthalpy of adhesion for linalool with water is consistent with values obtained for the enthalpy of hydration of the hydroxyl group.The co-surfactant nature of the perfume oils was investigated by tension measurements of their adsorption to the heptane-water interface. Linalool and eugenol show reasonably high surface activity at this interface and could therefore be expected to act as cosurfactants in systems that contain conventional surfactants.The phase behaviour of the CgE5 + water + octane micro emulsion system was investigated to determine the effect of adding different concentrations of perfume oil on the size, shape and position of the three phase region. It was found that linalool reduces the size of this three phase region and also reduces the temperature at which the three phase region occurs. Although not conclusive, this behaviour suggests the system is approaching a triclitical point.It is of interest also to understand the adsorption of oils at planar surfactant mono layers and then attempt to relate the adsorption data to bulk phase solubilisation of the oils in micelles. The adsorption at a planar interface was attained by measuring the surface pressure of the oil at different activities. The surface concentration of the oils was then calculated from the Gibbs adsorption equation. By measuring these surface pressures as a function of activities at various temperatures, it was possible to derive the adsorption enthalpies and entropies with use of a form of the Van't Hoff equation. It was found that alkane adsorption increases with decreasing alkane chain length and the isotherms show a greater curvature upwards for the shorter chain length alkanes suggesting that the adsorption becomes more favourable as more alkane is added to the mixed alkane/surfactant film.Headspace analysis was employed to measure the solubilisation of oils in bulk surfactant solutions. The results obtained with this technique were preliminary although early indications suggest that more alkane oil is solubilised in bulk aggregates with curved monolayers than is adsorbed at planar monolayer interfaces. However, solubilisation of oil in bulk solutions may either be in the curved monolayer or they could form a 'core' of oil inside the aggregate.

The adsorption and aggregation properties of twenty seven anionic hydrocarbon surfactants have been studied in aqueous systems. They are single-chain sulfonates with sodium or TAA counterions (where TAA = tetraalkylammonium, i.e. tetrapropylammonium), and di-chain sulfosuccinates with sodium counterions. The novel surfactants introduced possess branched tail structures which differ by the extent and position of branching. All surfactants were synthesised and purified to investigate the relationships between surfactant structure and performance. The aim of this project is to fundamentally improve our understanding of controlling surface tension, and consequently use this to improve the performance of hydrocarbon surfactants to achieve low surface energies. First, by evaluating the surface coverage of various effective surfactants, a new general property to account for low aqueous surface tension regardless of surfactant type is introduced. Where it is shown that all super-effective surfactants pack effciently at air-water interfaces to generate dense surface coverages. With this general property in mind, the adsorption and aggregation properties of novel surfactants are studied through tensiometry and small-angle neutron scattering (SANS). By making small systematic variations in the surfactant structure, general structure-property relationships of effective hydrocarbon surfactants have been distinguished. The branching position, extent, and chain length are all shown to be both highly sensitive, and critical to generate low surface energies. The structural characteristics of effective hydrocarbon surfactants are encapsulated in a new index to assess potential surfactant performance, based on the molecular structure of the tail alone, H-Gamma. Novel approaches to improve packing effciency at the surface have been explored, leading to the lowest surface tensions for single-chain, di-chain and mixed hydrocarbon surfactant systems. For example, replacing carbon in the surfactant tail chain-tip with silicon leads to an increased molecular volume, greater packing effciency and thus, lower surface tension. The ability to further improve packing effciency by choice of surfactant counterion is demonstrated. By systematically changing the identity of the head group for various tail structures, the TPA (tetrapropylammonium) counterion is shown to be an effective alternative for all hydrocarbon surfactants. Furthermore, mixing linear and branched surfactants help to generate dense surface coverages, as spaces within the monolayer are effectively filled, generating lower surface energies than either constituent surfactant. The research presented here highlights structural characteristics of effective hydrocarbon surfactants, outlines design principles, developing our understanding and ability to control, surface tension.

Content: Surfactants of different ionic nature are used in virtually all steps of leather production. In processes like soaking, degreasing and wool washing, tremendous amounts of surfactants are applied and to a great extent discharged into the tannery effluent. In order to improve the sustainability of leather processing, there is a constant search for more efficient, environmentally friendly emulsifiers, which give superior results already in smaller usage amounts. By introduction of propylene oxide based lipophilic linkers between the hydrophilic head and hydrophobic tail, the wetting and emulsion capability of a surfactant can be increased significantly. The resulting surfactants, so called extended surfactants, are generally more hydrophobic and have an extended tail, which reaches further into the oil face without scarifying the water solubility, what would be the results when increasing the alkyl chain. Thus, the use of lipophilic linker changes the emulsion on a structural level. Extended surfactants have been found to be superior in various applications, including textile laundry or tertiary oil recovery. In the present work, the efficiency of various types of non-ionic and anionic extended surfactants is demonstrated in various stages of leather making. Model surfactants with lipophilic linkers are compared to their analogues without linker molecules. In many processes, significantly improved surfactant efficiencies are found making this group of molecules an interesting topic for further exploitation. Take-Away: Significantly improved surfactant efficiency for more sustainable leather processing

Nous presentons l'etude experimentale de l'etalement spontanee de gouttes de solutions de tensioactifs sur des substrats solides. Nous utilisons des tensioactifs non-ioniques du type c 1 2e n et le superspreader. Les premiers, dans ethylene et diethylene glycol, s'etalent sur des disques de silicium et le superspreader, en solutions aqueuses, sur des boites de petri hydrophyles. Les parametres d'etude sont d'une part la concentration du tensioactif dans les solutions et d'autre part l'humidite relative ambiante. Nous trouvons que, pour toutes les concentrations et a faible humidite ( 30%), les etalements des solutions de tensioactifs du type c 1 2e n sont normaux, c'est-a-dire, l'evolution temporelle du rayon de la goutte suit une loi du type t 1 / 1 0. Pour des taux d'humidite superieure au 30% et des concentrations moyennes, on observe des instabilites de la ligne de contact dues a l'effet marangoni. Les etalements des solutions aqueuses du superspreader montrent des caracteristiques similaires mais l'apparition des instabilites ne depends pas du taux d'humidite ambiante. Nous effectuons une etude systematique des instabilites et nous proposons une explication de l'apparition des phenomenes observes basee sur l'influence de la mobilite des tensioactifs sur les substrats solides et la generation des gradients de tension de surface qui controlent l'etalement.

Demonstrou-se pela primeira vez que é possível determinar surfactantes e água em formulações de Sabonetes Líquidos (SL) e Shampoos (SH), direta e simultaneamente pela técnica de infravermelho por transformada de Fourier (FTIR) acoplada à uma cela de reflectância total atenuada (ATR). Tradicionalmente, a principal aplicação do infravermelho médio (2,50 - 15,0 µm) é a identificação de compostos orgânicos. O desenvolvimento de novos acessórios, principalmente de ATR, os avanços na área de microinformática e de métodos quimiométricos, vem viabilizando as análises quantitativas rápidas com excelentes resultados mesmo em meio aquoso. A determinação simultânea de surfactantes em formulações por FTIR-ATR é investigada em detalhes nesta tese. Dentre os surfactantes utilizados, o Lauril Éter Sulfato de Sódio (LESS) e a Cocoamidopropil Betaína (CAPB) são comuns em ambas as formulações, sendo a Coco Dietanolamida (CDEA) empregada em shampoo e o Alquilpoliglicosídeo (APG) em sabonete líquido. Espectros de absorbância de amostras padrão e de verificação foram adquiridos na região do infravermelho médio (800-1600 e 1900-3000 cm-I). Para a regressão de mínimos quadrados clássicos (CLSR), selecionou-se 200 números de onda, enquanto que para a regressão de mínimos quadrados inversos (ILSR), apenas 10. Nas regressões de componentes principais (PCR) e de mínimos quadrados parciais (PLSRI e PLSR2), utilizaram-se de 300 à 1100 números de onda. Dois conjuntos de amostras padrão foram preparados, o primeiro, contendo 27 misturas padrão, foi estudado somente pelos métodos CLSR e ILSR, enquanto que o segundo conjunto, contendo 48 amostras padrão, foi avaliado por todos os métodos mencionados acima. A seleção das regiões de quantificação favoreceu números de onda dos componentes minoritários CAPB, APG e CDEA e resultados satisfatórios foram encontrados para 18 amostras de shampoo e sabonete líquido. Interferentes como NaCl e perfume foram incluídos no segundo conjunto e os métodos PCR e PLSR proporcionaram melhores resultados. Os erros relativos (RSEP%) para água (correspondendo a 84-88% do produto) e LESS (6-10%) não excederam 1%; para CAPB (<3%) e CDEA (<2%), o RSEP% situou-se entre de 2-4% e para APG (<3%), não excedeu 5%. Avaliações do processo de normalização, repetibilidade, vulnerabilidade a interferentes (perfumes), redução no número de padrões de calibração foram conduzidos, encontrando-se resultados satisfatórios para todos os casos, com erro relativo inferior à 5,0%. Um dispositivo simples para injeção direta da amostras no acessório de ATR foi construído, permitindo aumentar a freqüência analítica de 20 para 60 análises por hora.
It is demonstrated for the first time that the principal constituents of a shampoo as well as of a liquid soap -three surfactants and water- can be determined directly, simultaneously and quickly in undiluted samples by Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy in the middle infrared region, despite the broad absorption bands ofthe solvent. The main application of the middle infrared (2,50 - 15,0 µm) was the identification of organic compounds. The development of new accessories, such as ATR, and the advance of computers and chemometrics, extended the technique to quantitative analysis, with excellent results. The simultaneous determination of surfactants in shampoos and liquid soap formulations by FTIRA TR is investigated in detail in this thesis. Two of the surfactants, sodium lauryl ether sulfate (LESS) and cocoamidopropyl betaine (CAPB) are common to both formulations; alkylpolyglucoside (APG) is the third surfactant of the liquid soap and cocodiethanolamide (CDEA), the corresponding ingredient of the shampoo. Absorbance data of the undiluted verification samples and calibration standards was collected in the middle infrared region of the spectrum (800-1600 and 1900-3000 cm-1). Five methods of multivariate quantification were compared: Classical Least Squares Regression (CLSR), where absorbance data measured at 200 wavenumbers was processed, Inverse Least Squares Regression (ILSR), were data at 10 selected wavenumbers was analyzed, Principal Components Regression (PCR), and Partial Least Squares Regression, which has two different approaches, PLSR1 and PLSR2. Two sets of standard samples were prepared for the method calibration. The first one, consisting of 27 standard mixtures, was evaluated by the CLSR and ILSR methods; a second set, with 48 standards, was evaluated by all the methods mentioned above. Potential interfering, such as NaCI and perfume, were inc\\uded in this second set. By favoring wavenumbers where absorption bands of the minor components (CAPB in both formulations, APG in the liquid soap and CDEA in the shampoo) are more intense, good results were obtained for 18 simulated samples of shampoo and 18 samples of liquid soap. For the second set, PCR and PLSR methods were most favorable; relative errors (RSEP%) for water (major component, 84-88%) and LESS (6-10%) did not exceed 1%; for CAPB (<3%) and CDEA(<2%), RSEP% of 2-4% were observed, and for APG(<3%), 5% was not exceeded. Tests for repeatability, normalization performance evaluation, effect of interferents presented favorable results. A simple device for direct sample injection was designed and evaluated. It permitted an increase ofthe analytical frequency from 20 to 60 samples per hour.

Chemical flooding, or surfactant flooding, is a well known EOR technique which has been used worldwide for decades. For this method to be economically feasible, it is crucial to minimize the loss of surfactant to the reservoir. Currently the industry is considering combining chemical flooding with the newer technique of low salinity waterflooding which also has proved to be an efficient method for increasing oil recovery from reservoirs. In this study the adsorption of the anionic surfactant Aerosol OT onto kaolinite has been investigated by the indirect method of measuring surface tension.The adsorption studies were conducted under four different salinities, categorized by ionic strength and ionic composition. The experiments were performed with and without calcium to study the effect of ionic composition. The ionic strength of the solutions were 0,6 and 0,2. The results reveal that adsorption of Aerosol OT does occur onto kaolinite, and that reducing the ionic strength of the solution also reduces adsorption. The presence of divalent cations was found to promote adsorption. The method which was utilized for this study was considered to have limited accuracy and thus more experiments would be preferred to confirm the results. The tendencies of adsorption are however in agreement with the theories of similar studies and should be considered to be valid.

Orientador: Rosiane Lopes da Cunha
Texto em português e inglês
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: As nano partículas possuem grande potencial para a liberação controlada de bioativos, porém ainda são pouco exploradas na área de alimentos. Neste trabalho foi estudada a formação de nanopartículas a partir da autoagregação de surfactantes, associação surfactante-polissacarídeo e complexação eletrostática entre diferentes polissacarídeos, no caso, quitosana e gelana. A compreensão das interações moleculares responsáveis pela formação das partículas e o conhecimento das variáveis que afetam sua formação permitem predizer e controlar suas propriedades. Tais interações dependem fortemente das características de cada macromolécula, como flexibilidade, estado conformacional e densidade de cargas que são diretamente afetadas pelas condições físico-químicas do meio como pH, força iônica e temperatura. Por isso, este trabalho foi dividido em três etapas. (I) Inicialmente foi avaliado o comportamento em solução dos polissacarídeos utilizados posteriormente para a formação de complexos. Os efeitos do pH e da temperatura nas características reológicas e no estado conformacional de soluções puras de gelana e quitosana foram estudados. A agregação da gelana foi mais sensível às alterações do meio que a quitosana. (II) Na segunda etapa, nanopartículas foram formadas por autoassociação de polissorbatos na presença de quitosana. A influência do comprimento da cauda hidrofóbica do surfactante e do pH do meio nas propriedades das partículas foi estudada por espalhamento de luz, reologia, condutivimetria e microscopia de luz polarizada. O tamanho e estrutura das partículas formadas pelo surfactante de menor cadeia hidrofóbica foram mais favoráveis à associação com a quitosana. O pH do meio (3,0 ou 6,7) não influenciou de maneira significativa as características das partículas. O efeito da concentração de quitosana na estrutura e tamanho de partículas foi analisado. Maiores concentrações levaram a viscosidades mais elevadas, impedindo a agregação das micelas e formando partículas menores. (III) No terceiro estudo, nanopartículas foram obtidas pela complexação eletrostática de gelana e quitosana. Os efeitos da razão de concentração de cada polissacarídeo, do tempo de estocagem a 25 °C e da presença de um surfactante nãoiônico (polissorbato) no tamanho, carga e quantidade de partículas formadas foram avaliados. Devido à menor densidade de carga e flexibilidade da gelana, maior quantidade deste polissacarídeo foi necessária para obtenção de partículas neutras. De forma geral, as partículas apresentaram aumento de tamanho ao longo das primeiras 100 horas após o preparo e não foram observadas mudanças significativas das propriedades das partículas devido à adição de surfactante. O método de preparo das amostras também foi estudado. Partículas preparadas pela mistura das soluções de polissacarídeos em dois passos foram consideravelmente maiores que as preparadas pela mistura em uma única etapa. Este trabalho confirmou a possibilidade de formação de nanopartículas promissoras para a encapsulação de bioativos em alimentos a partir da associação de biopolímeros e surfactantes, cujas propriedades poderiam ser moduladas em função da composição e condições de processo
Abstract: Nanoparticles are promising vehicles for bioactive delivery, but their potential has not been fully explored by the food industry. This work studied the formation of nanoparticles by self-assembly of surfactants, polysaccharide-surfactant association, and electrostatic complexes formed by different polysaccharides, especially chitosan and gellan gum. The knowledge of molecular interactions and the variables that affect particle formation allows predicting and controlling the properties of nanoparticles. These interactions depend on the characteristics of each macromolecule such as conformation, charge density and flexibility, which are affected by the physicol-chemical properties of the solution, such as pH, ionic strength and temperature. This work was divided in three parts: (I) Firstly it was studied the behaviour of each polysaccharide alone. The influence of the pH and temperature on the rheological properties and structural conformation of the pure gellan and chitosan samples was determined. Gellan aggregation was more strongly affected by such variables than chitosan. (II) In the second part, nanoparticles were obtained by polysorbate-chitosan association. The effect of the length of surfactant tail and the solution pH on the particle properties was studied by dynamic light scattering, rheological and conductivity measurements and polarizing microscopy. The size and structure of nanoparticles composed by the shorter surfactant were more appropriated to chitosan assembly. The pH (6.7 or 3.0) did not affect significantly the particle properties. The effects of chitosan concentration on particle structure and size were studied. Greater chitosan concentration led to smaller particles due to the increase in viscosity values which prevented micelles aggregation. (III) In the third study nanoparticles were produced by electrostatic complexation of chitosan and gellan gum. Particle size, charge density, stability and complexes number were evaluated as a function of polysaccharide concentration, chitosan:gellan ratio and the presence of a non-ionic surfactant. Due to the stiffness and low charge density of gellan gum, a greater amount of such polysaccharide was necessary to obtain neutral particles. Overall particles showed an increase in size during 100 hours of storage at 25 °C, but no significant changes on particle properties were observed due to surfactant addition. The methodology of particle preparation was also evaluated. Particles prepared by 2 mixing steps were markedly larger than those prepared by mixing polysaccharides in a single step (all together). This work showed that it is possible to produce nanoparticles with promising application on bioactive delivery by biopolymer-surfactant association, since their properties could be modulated as a function of composition and process conditions
Doutorado
Engenharia de Alimentos
Doutor em Engenharia de Alimentos

Cationic and zwitterionic polymerizable surfactants bearing tri- and tetraethyleneglycol spacer groups between the polymerizable moiety and the surfactant structure were prepared and polymerized. Monomers and polymers were investigated with respect to their aggregation behavior in aqueous systems and compared to analogous monomers and polymers lacking spacer groups. In the case of the monomeric surfactants, the spacer groups depress both the Kraffttemperature and the critical micelle concentration. the area occupied per molecule at the air-water interface is substantially enlarged by the spacers, whereas the depression of surface tension is nearly constant. Although the monomers with and without spacers are true surfactants, all the polymers are water-insoluble, but form monomolecular layers at the air-water interface. In analogy to the monomer behavior, the incorporation of the spacer groups increases the area occupied per repeat unit at the air-water interface substantially, but hardly affects the surface activity.

This thesis consists of a collection of studies on surfactant adsorption at different interfaces. Particularly, this dissertation focuses on adsorption processes occurring at buried interfaces (solid-liquid and liquid-liquid). Because of complexity in the sample environment, the study of buried interfaces is experimentally challenging. Neutron reflectivity enables the study of adsorption processes at interfaces at atomic length scale. Furthermore, neutrons can be transmitted through solid substrates, permitting the analysis of buried interfaces. The technique was used to describe adsorption processes both qualitatively and quantitatively, delivering information regarding structure of adsorbed layers and adsorbed amount. Different investigations were carried out during the PhD and the results are grouped into two main sections. Investigations at the solid-liquid interface are presented in the first section. Chapter 3 provides an example of structural study of complex multi-layers at the silicon-water interface; a surfactant adsorption study at the technologically relevant metal-oil interface is presented in Chapter 4. The second section discusses a series of neutron reflectivity experiments at the important oil-water interface. The structural study of a series of non-ionic dodecanol ethoxylate surfactants is discussed in Chapter 6. The structure of a lipid monolayer as model for a biological membrane is reported in Chapter 7. Chapter 8 is a comparative study of fatty acid-alkylated azacrown ether co-adsorption at the air-water and oil-water interface. These mixtures are used for metal ion extraction processes. This was the first analysis of a surfactant mixture at the oil-water interface using neutron reflectivity. Some of the studies reported here are the first of their kind and the advances affect different technologically and biologically relevant areas. As a result of this PhD project a number of follow-up studies have been planned and several neutron reflectivity experiments will be performed in the future to further explore these interesting areas of science.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2005.
Includes bibliographical references.
In this thesis, a new class of nonionic, photoresponsive surfactants consisting of a polar di(ethylene oxide) head group attached to an alkyl spacer of between two and eight methylene groups, coupled through an ether linkage to an azobenzene moiety, were synthesized and developed. Structural changes associated with the interconversion of the azobenzene group between its cis and trans forms as mediated by the wavelength of an irradiating light source, cause changes in the surface tension, critical micellization concentrations (CMC), and self-assembly behavior. Differences in saturated surface tensions (at concentrations above their CMCs) were as high as 14.4 mN/m under radiation of different wavelengths. This large and reversible change in saturated surface tensions in response of different illumination conditions made these new surfactants have potential applications in the pumping and control of flow in microfluidic devices, and in the microchemical analysis of complex fluids, flow cytometry, rapid DNA screening. The interfacial properties of these new surfactants have been investigated through surface tension measurements and neutron reflection experiments under both UV and visible light. From surface tension measurements, the surface excess and therefore average molecular areas can be obtained through Gibbs equation; while through measuring neutron reflectivities at different Q range, the interfacial conformations of these surfactants can be determined within the resolution of several angstroms. It was found that the interfacial conformations of these surfactants are very sensitive to the length of the spacer and conformation of azobenzene group. Depending on the different lengths of spacer and conformations of azobenzene groups (trans or cis),
(cont.) surfactants can take either regular conformation or loop conformation, in which the spacer between the polar head and the intermediate polar group forms a loop anchored at both ends in the interfacial plane. This explained the observed large change in saturated surface tensions under different wavelengths radiation. The self-assembly behavior of these surfactants in bulk phase has been studied experimentally through the static and dynamic light scattering, small angle neutron scattering, and cryo-TEM techniques under both UV and visible light. At high enough concentrations, trans surfactants form the vesicles; while cis surfactants self-assemble into bicontinuous phase. This transition indicated the significance of the sign of Gaussian rigidity in surfactant self-assembly. Through varying the azobenzene conformation by radiation of different wavelengths, the sign of the Gaussian rigidity can be controlled, and therefore, there self-assembly behavior can be controlled by light too.
by Tiangang Shang.
Ph.D.

Methods for the analysis of surfactants and proteins by Capillary Electrophoresis (CE) were investigated. Several modifications of the system to achieve detection and separation of these analytes were examined. These modifications included buffer additives, sample additives and surface treatment and modification of the fused silica capillary. For the analysis of anionic surfactants, the addition of an anionic IN absorbing compound to the buffer was investigated to achieve indirect detection of the non-absorbing surfactants. The effect on detection sensitivity and separation efficiency of the absorbing ion was examined. These parameters were affected by differences in the electrophoretic mobilities of the analytes in comparison to the absorbing ion. The use of organic modifiers was also investigated to minimize micelle formation of the surfactants which leads to zone spreading. For the analysis of serum and urine proteins, the use of high pH buffers was investigated to minimize solute/capillary surface interactions and achieve separation. At high pH's the proteins are negatively charged; therefore, they should be repelled by the negatively charged fused silica surface. To improve reproducibility of migration times of the proteins the addition of polyvinyl alcohol to the sample was also investigated. The polyvinyl alcohol improved reproducibility by reversibly covering the active sites on the capillary surface to minimize protein interactions. Migration time reproducibility was also improved by optimizing the capillary cleaning procedure. Lastly, the addition of methyl cellulose to the buffer to work as a dynamic molecular sieving medium was investigated to improve resolution. Analyte/ capillary surface interactions are a major limitation in CE especially for the analyses of proteins. The use of coated capillaries to eliminate these interactions has been widely investigated. However, reproducibility and degree of surface deactivation with these coating can be poor. In this work hydrothennal treatment of the fused silica capillary surface prior to deactivation was examined. Hydrothennal treatment was used to produce a homogenous surface prior to coating which leads to the production of more highly deactivated, reproducible columns. The effects of the treatment were studied by coating the surface with a silane and examining the influence of the coating on electroosmotic flow and analyte adsorption.
Ph. D.