Nanoemulsions with extremely small droplet sizes (<100 nm) have shown several advantages over conventional emulsions. However, almost all nanoemulsions in usage are liquids that restrict their use in many soft materials. The aim of this thesis is to understand the formation and long-term stability of viscoelastic nanogels developed from liquid nanoemulsions. At first, gelation in 40 wt% canola oil-in-water nanoemulsions were investigated as a function of emulsifier type (anionic sodium dodecyl sulfate (SDS) or nonionic Tween 20) and concentration. Three different regimes of colloidal interactions were observed as a function of SDS concentration. 1) At low SDS concentration (0.5 – 2 times CMC) the counterion shell layer increased the effective volume fraction of the dispersed phase (eff) close to the random jamming, resulting in repulsive gelation. 2) At SDS concentration between 5 – 15 times CMC, micelle induced depletion attractions led to extensive droplet aggregation and gelation. 3) At very high SDS concentration, however, oscillatory structural forces (OSF) due to layered-structuring of excess micelles in the interdroplet regions led to loss of gelation. In repulsive gelation, reduction in droplet size coupled with the electrical double layer resulted in a linear increase of Gʹ. On the contrary, attractive nanoemulsions showed rapid increase in gel strength below a critical droplet radius, and was explained by transformation of OSF into depletion attraction. No gelation was seen in Tween 20 nanoemulsions, due to lack of repulsive interactions and weak depletion attraction. Next the influence of the dispersed phase volume fraction () on repulsive nanoemulsion gelation was investigated and the Gʹ values were modeled using empirical scaling law developed by Mason et al. (1995). It was found that an initial liquid regime transformed into glassy phase at a eff = g ~ 0.58, where droplets are entrapped in a cage of neighbouring droplets due to crowding. It was followed by jamming transition at a critical volume fraction (j), where droplet deformation led to large increase in elasticity. The model predicted j = 0.7, which is close to the predictions for repulsive polydispersed emulsions found in the literature. In the final phase long-term stability of the nanogels was evaluated until 90 days, during which the nanogels remained stable to creaming and coalescence. However, repulsive nanogels showed a significant decrease in Gʹ and the gels converted into flowable liquids over time. For attractive nanogels decrease in Gʹ was much less, although given enough time they would also transformed into weak gels. It was hypothesized that surface active compounds generated due to lipid oxidation altered interfacial charge cloud leading to loss of gel strength for repulsive nanogels. For attractive nanogels slippery bonds in the aggregates permitted rotational and translational diffusion of nanodroplets on the surface of each other leading to network compactness and a decrease in gel strength with time. Overall, it was concluded that it is possible to form nanogels from canola oil nanoemulsions using ionic emulsifiers. The gel strength and stability of the nanogels depends on emulsifier concentration, droplet size,  and the chemical stability of the oil used. More investigation is needed in order to improve the long-term stability of the nanogels. The nanogels possess high potential for use in low-fat foods, pharmaceuticals, and cosmetic products.

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Within a colloidal dispersion, the presence of negatively adsorbing material can produce a variety of effects on the dispersion properties and interactions. With increasing concentration, the negatively adsorbing material induces both depletion and structural forces on the dispersion, which can dramatically affect both colloidal stability and near-contact hydrodynamics. This project focused on expanding our understanding of the effects of such negatively adsorbing materials on both equilibrium and dynamic interactions between particles. The effects of charged, hard spheres (silica nanoparticle) on the hydrodynamic drag force a particle experiences as it approaches a flat plate were measured experimentally using colloid probe atomic force microscopy (CP-AFM). Deviation was found between the measured drag force and predictions for the drag force in a simple, Newtonian fluid. The measured drag force was always smaller than the predicted drag force as the particle approached contact with the plate. An effective viscosity, that approached the dispersing fluid viscosity at contact and the bulk viscosity at large separations, was determined for the system. This effective viscosity displayed similar characteristics to those predicted theoretically by Bhattacharya and Blawzdziewicz (J. Chem. Phys. 2008, 128, 214704.). The effects of both anionic and cationic micelles on the depletion and structural forces in a colloidal dispersion were studied both experimentally (with CP-AFM) and theoretically. The depletion and structural forces between a microparticle and a flat plate were measured and compared with the depletion force predicted by the force-balance model of Walz and Sharma (J. Colloid Interface Sci. 1994, 168, 485-496.). Consistent with previous work, the measured depletion force for both micelles was smaller in magnitude than that predicted by the Walz and Sharma model for hard, charged spheres. It is theorized that rearrangement of the micelle surfaces charges or physical deformation of the micelles may be responsible for the observed result. An effective surface potential for the micelles is proposed as a correction to the Walz and Sharma model. Finally, the stability of colloidal dispersions was studied macroscopically in solutions of ionic micelles. The colloidal dispersions displayed clear flocculation behavior in both cationic and anionic micelles. This flocculation behavior was compared with energy profiles determined from CP-AFM experiments between a single particle and a flat plate. A simple phase diagram was proposed for predicting the stability of colloidal dispersions based solely on the depth of the depletion energy well and the height of the repulsive energy barrier. / Ph. D.

Abstract Some gender scholars who have studied Western welfare regimes have argued that dominant cultural assumptions about women (ideational forces) should be examined in order to understand the development of these regimes. On the other hand, gender scholars working on Iran’s social policy argue that religious assumptions and institutions have shaped the position of women in Iran’s welfare regime. However, none of these researchers have thoroughly and explicitly examined the role of ideas in the development of Iran’s social policy. In contrast, this thesis studies the role of ideational forces in the formation of the only Iranian social assistance program designed exclusively for women, Empowering Women Without Guardians (EWWG). It also examines the connection of these forces to non-ideational factors in order to further elucidate their impact on policymaking. As argued, multiple cultural assumptions influence policymaking on women’s issues in Iran. Traditional cultural assumptions reinforce and legitimize the unequal position of women in society, whereas reformist and secularist ideas assume that men and women are equal. As claimed, the interaction of these assumptions with institutional and structural forces empowers some of these ideas over others at different stages of policymaking regarding the formation of EWWG: Iran’s laws (institutional forces) have reinforced previously dominant traditional assumptions about women (ideational forces) in the problem stream; in contrast, reformist interpretations of structural factors challenged previously prevailing traditional ideas and resulted in the adoption of a policy, which is more consistent with reformist and secularist ideas. The relative power of these assumptions helps explain both policy continuity and change in Iran’s context of policymaking on women’s issues.

Understanding and controlling the forces between colloidal particles in solution, along with the resulting stability of a dispersion of such particles, continues to be at topic of great interest. Although most laboratory studies focus on model systems in which the number of system species is kept to a minimum, real colloidal systems can be much more complex, consisting of multiple components that can vary greatly in size, charge, shape, etc. This dissertation focused on a topic that has received very little prior study, namely synergistic effects that can arise in mixed colloidal systems in which the resulting force and stability of the system cannot be predicted using results obtained in more idealized systems consisting of fewer components. Two specific systems were studied. The first was a ternary system of particles in which micron-sized particles were in a dispersion containing both nanoparticles and submicron particles. It was shown through both computation modeling and direct force measurements that the nanoparticles can create attractive forces between the micron and submicron particles such that a halo of submicron particles is formed. This halo results in long range forces between the microparticles that cannot be predicted from measurements in systems containing only nanoparticles or only submicron particles. In addition, the forces can be large enough to alter the stability of a dispersion of these microparticles. The second system consisted of microparticles in a solution containing nanoparticles and a polyelectrolyte, specifically poly(acrylic) acid. Again, through modeling and experimentation, it was found that complexation of the nanoparticles and polyelectrolyte molecules led to depletion and structural forces between the microparticles that were substantially greater than the sum of the forces measured in systems of only nanoparticles or only polyelectrolyte. It was also found that these greater forces could lead to destabilization of a dispersion of microparticles that was stable when only nanoparticles or only polyelectrolyte was present. While these results clearly demonstrate the difficulty associated with predicting forces and stability in mixed colloidal systems, they also indicate that such systems offer new and interesting opportunities for controlling stability that clearly warrant additional study. / Ph. D.