Colloidal and bulk block polymer nanostructured materials fabricated via solvent- or polymerization-induced structural transitions have been used in a host of applications ranging from biomedical to energy technologies. In both methods, the resulting nanostructure forms due to a change in the initial environment by either changing the solvent quality or the compatibility between polymers during polymerization. The work presented here will discuss two methods, solvent- and polymerization-induced structural transitions, which our group has recently utilized to create nanostructured materials. The first part of the talk will focus around creating physically crosslinked hydrogels using amphiphilic triblock copolymers that will rapidly self-assemble when injected into water. For example, the final state (micelles, microgels, and hydrogels) for a poly(styrene)-poly(ethylene oxide)-poly(styrene) (SOS) sample depends on the initial concentration of the polymer solution before quickly injecting into water. In the dilute regime we produce micelles. Near c* and in the semi-dilute regime, we see microgels. In the concentrated regime, the SOS polymer forms a hydrogel. The second part of the presentation will focus on how in situ polymer grafting drives interesting and controllable morphology transitions. In our approach, we are able to induce a lamellar-to-hexagonally-packed cylinder transition via the polymerization of styrene, which initially acts as a neutral solvent for the lamellar-forming diblock copolymer, poly(styrene)-block-poly(butadiene) (PS-PBD). Furthermore, in situ small-angle X-ray scattering (SAXS) experiments during the polymerization process reveal a complex phase path in which the gyroid phase is an intermediate morphology between the lamellar and hexagonally-packed cylinder phases. The underlying theme of the presentation will highlight how polymer chain architecture, and kinetic and chemical processes can be utilized to create nanostructured materials.
Prof. Robert Hickey is currently an Assistant Professor in the Department of Materials Science and Engineering at The Pennsylvania State University. He received his B.S. in Chemistry at Widener University (2007) and doctorate in Chemistry at the University of Pennsylvania (2013). At Penn, he worked in the laboratory of Prof. So-Jung Park and researched how to control the morphology and materials properties of colloidal aggregates composed of inorganic nanoparticles and amphiphilic diblock copolymers. The summer after graduate school, Prof. Hickey conducted research related to his Ph.D. work at Ewha Womans University in Seoul, South Korea. As a postdoctoral researcher, he worked in the labs of Profs. Frank Bates and Tim Lodge at the University of Minnesota. At Minnesota, his research focused on fundamentally understanding the self-assembly and phase behavior of ternary polymer blends, as well as on applying these principles to ternary polymer electrolyte systems in which intricate relationships exist between morphology and Li+ ion diffusion.