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 altering the solvent quality or the compatibility between polymers during polymerization. The work presented here discusses two techniques, solvent- and polymerization-induced structural transitions, which our group has recently utilized to create nanostructured materials. The first part of the talk focuses on creating physically crosslinked hydrogels using amphiphilic triblock copolymers that will rapidly self-assemble when injected into water. We have developed a universal and quantitative method for fabricating and controlling physically crosslinked hydrogels exhibiting hierarchical ordering and photonic band gap properties using a solvent-non-solvent rapid-injection process. The second part of the presentation describes 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). Furthermore, in situ small-angle X-ray scattering (SAXS) experiments during the polymerization process reveal a complex phase path in which the hexagonally-perforated lamellae is an intermediate morphology between the lamellar and hexagonally-packed cylinder phases. The work presented here highlights how polymer chain architecture, and kinetic and chemical processes can be utilized to create nanostructured materials.
Prof. Robert J. Hickey is currently an Assistant Professor in the Department of Materials Science and Engineering at The Pennsylvania State University. He received his B.S. and Ph.D. in Chemistry at Widener University (2007) and the University of Pennsylvania (2013), respectively. 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. 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. The Hickey group investigates chemical and self-assembly methods for creating nanostructured polymeric materials. Robert was the recipient of the Air Force Office of Scientific Research Young Investigator Prize in 2018.