| Direct imaging transmission electron microscopy at cryogenic temperature (Cryo-TEM) is in many instances the most powerful probe of microstructures of self-assembled, i.e. equilibrium, colloidal systems. It is the only technique that allows model-independent, real-space imaging at high resolution. Continuing our group's two decades devoted research with Cryo-TEM, my thesis extends the technique to new territories.; An on-the-grid deformation-and-relaxation sample preparation technique is developed that enables the time-resolved direct imaging of the recently discovered flow-induced vesicle-to-micelle transition in dilute aqueous surfactant solutions. The vesicles transform to an entangled network of thread-like micelles upon high straining rate; the process is reversible upon cessation of flow. Intermediate structures during the transition are captured by Cryo-TEM and correlated with rheological measurements. A mechanism of the transition is proposed which hinges on the alteration of electrical double layer structure by the flow-field, the alteration in turn shifting association balances between counterions and surfactant aggregates.; Systematic study of a series of viscoelastic, drag-reducing micellar solutions of cationic surfactants reveals the significant effects of counterion-surfactant ratio and counterion chemical structure, correlates solution microstructures with rheological properties, and establishes the microstructural and rheological basis of drag-reduction in these solutions.; Core-corona structures of poly(ethyleneoxide)/polybutadiene (PEO/PB) block copolymer micelles are directly resolved for the first time. Spherical micelles form at higher PEO/PB block volume ratio; cylindrical, at lower block volume ratio. Images of both shapes of micelles show a dense core and a diffuse corona. The core and corona sizes agree well with theoretical prediction from the “star” model of polymer micelles.; Interesting mixed micelle structures are observed in aqueous solutions of binary mixtures of nonionic surfactants and nonionic amphiphilic block copolymers. The evolution of the micelle structure is studied in detail as the relative proportions of surfactant and copolymers are varied. The triblock copolymer behaves differently in forming mixed micelles than its diblock counterpart; the difference stems from the difference in block architecture. |
