Controlling and Imaging Multi-Component Dispersed-Phase Nanoemulsions

Oil-in-water nanoemulsions are aqueous dispersions of oil droplets having radii a < 100 nm and serve as interesting model systems for studying basic colloidal science. The nature of such small droplet sizes gives rise to a new range of physical properties that are potentially beneficial to a wide range of industries. In this dissertation, methods of controlling droplet sizes and morphologies through manipulation of dispersed-phase components are presented. An evaporative ripening technique is developed in which one of the components in a multi-component dispersed-phase nanoemulsion is evaporated out of the system to create nanoemulsion droplet sizes approaching the micellar scale. Foundational groundwork is then provided for cryogenic transmission electron microscopy (CTEM) of oil-in-water nanoemulsions; expansion of water upon freezing may cause nanoinclusions to appear in nanoemulsion droplets depending on the phase of ice and oil type. Finally, a method of controlling coalescence using oppositely charged surfactants is presented and extended to produce anisotropic emulsions and nanoemulsions using multiple immiscible liquids

Controlling and Imaging Multi-Component Dispersed-Phase Nanoemulsions

Oil-in-water nanoemulsions are aqueous dispersions of oil droplets having radii a < 100 nm and serve as interesting model systems for studying basic colloidal science. The nature of such small droplet sizes gives rise to a new range of physical properties that are potentially beneficial to a wide range of industries. In this dissertation, methods of controlling droplet sizes and morphologies through manipulation of dispersed-phase components are presented. An evaporative ripening technique is developed in which one of the components in a multi-component dispersed-phase nanoemulsion is evaporated out of the system to create nanoemulsion droplet sizes approaching the micellar scale. Foundational groundwork is then provided for cryogenic transmission electron microscopy (CTEM) of oil-in-water nanoemulsions; expansion of water upon freezing may cause nanoinclusions to appear in nanoemulsion droplets depending on the phase of ice and oil type. Finally, a method of controlling coalescence using oppositely charged surfactants is presented and extended to produce anisotropic emulsions and nanoemulsions using multiple immiscible liquids

Time-Dependent Nanoemulsion Droplet Size Reduction By Evaporative Ripening

To overcome limitations of flow-induced rupturing and obtain nanodroplet sizes approaching the micellar scale, we make oil-in-water nanoemulsions having a dispersed phase that contains lower- and higher-molecular-weight oils. After nanoemulsion formation by extreme flow-induced droplet rupturing, the nanodroplets become even smaller as molecules of the lower-molecular-weight oil migrate out of the droplets into the aqueous continuous phase and are removed by evaporation while stirring. We control the degree of reduction primarily through the volume fraction of higher-molecular-weight oil originally present in the dispersed phase. We study the droplet size reduction rate using time-dependent dynamic light scattering. This method is useful for making nanodroplets containing extremely viscous high-molecular-weight liquids that would be difficult to emulsify otherwise. Additionally, we recover the evaporated lower-molecular-weight oil by distillation and reuse it in subsequent emulsification, thus demonstrating an environmentally friendly method for mass-producing extremely small nanodroplets

Hierarchical Self-Assembly of Amphiphilic Semiconducting Polymers into Isolated, Bundled, and Branched Nanofibers

Herein, we report a high-yield click synthesis and self-assembly of conjugated amphiphilic block copolymers of polythiophene (PHT) and polyethylene glycol (PEG) and their superstructures. A series of different length PHT_<i>m</i>-<i>b</i>-PEG_<i>n</i> with well-defined relative block lengths was synthesized by a click-coupling reaction and self-assembled into uniform and stably suspended nanofibers in selective solvents. The length of nanofibers was controllable by varying the relative block lengths while keeping other dimensions and optical properties unaffected for a broad range of <i>f</i>_PHT (0.41 to 0.82), which indicates that the packing of PHT dominates the self-assembly of PHT_<i>m</i>-<i>b</i>-PEG_<i>n</i>. Furthermore, superstructures of bundled and branched nanofibers were fabricated through the self-assembly of PHT_<i>m</i>-<i>b</i>-PEG_<i>n</i> and preformed PHT nanofibers. The shape, length, and density of the hierarchical assembly structures can be controlled by varying the solvent quality, polymer lengths, and block copolymer/homopolymer ratio. This work demonstrates that complex superstructures of organic semiconductors can be fabricated through the bottom-up approach using preformed nanofibers as building blocks