In this talk, I will describe our group’s recent research on two projects. The first involves the use of evaporative assembly of multicomponent particle-particle and particle-polymer dispersions to create films with a prescribed vertical concentration profile in a one-step process. We demonstrate that evaporation rate, particle size, polymer chain length, and initial volume fraction can be used to create films with different structures, including large-on-top (e.g., large particles migrating to the top surface of the film), small-on-top, and “sandwich”-like layering. I discuss these results in terms of recent theories for stratification during evaporative drying and potential applications for antibacterial coatings. The second project focuses on the rheology and structure of polymeric hydrogels with nanoscale crystalline domains, comprised of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer gels with various ratios of L-lactide and D-lactide in the PLA blocks. These materials form associative micellar gels in water. Our systems display an unexpected maximum in the storage modulus, G’, of the hydrogels at intermediate L/D ratio. We expect the dominant contribution to the elasticity of the gels to be intermicellar bridging chains and attribute the rheology to a competition between an increase in the time for PLA endblocks to pull out of micelles as the L/D ratio is increased and PLLA crystallization occurs, and a decrease in the number of bridging chains for micelles with crystalline PLA domains, as formation of bridges may be hindered by crowded crystalline PLA domains. Collectively, our both projects demonstrate the means in which dynamic process on both the molecular scale and macroscale can be used to create complex soft materials with unexpected structure and properties.
