Events
Self-Assembly of Functional Polymers
May 9, 2013 at 3pm/36-428
Bradley Olsen
Department of Chemical Engineering, Massachusetts Institute of Technology
Abstract:
Block copolymer self-assembly represents an elegant, low-cost technique for the fabrication of complex new soft materials. Critical for many of the applications for such materials is incorporating polymers with a given optical, electronic, or biological functionality into the nanostructured material. In contrast to traditional polymers which have Gaussian coil chain shapes, functional systems often have highly anisotropic shapes and specific interactions that can lead to extremely rich self-assembly behavior.
In organic electronics, significant effort has been dedicated towards elucidating the thermodynamics of self-assembly in semiconducting polymer systems which tend to take on extended chain conformations due to the conjugated backbones present in the polymers. Over the past decade, a great deal of knowledge has emerged about the effects of chain rigidity on thermodynamic aspects of self-assembly in these systems, driving forward the capability of these block copolymer systems. However, our knowledge of kinetic effects in self-assembly continues to lag, necessitating fundamental studies of dynamics to compliment thermodynamics. Through a combination of scaling theories, molecular dynamics simulation, and experiments we have explored diffusion and molecular relaxation in these systems, hinting at dynamic design rules in organic electronic materials.
The use of self-assembled ionic templates provides an alternative method to control structures in optoelectronic materials using block copolymers processed under aqueous conditions. Reversible addition-fragmentation chain transfer (RAFT) polymerization is employed to synthesize diblock copolymers with one neutral thermoresponsive and one polycationic block and the pH-dependent complexation between fluorescent proteins or biomimetic J-aggregating chromophores and the polycationic block is demonstrated. Spin casting is used to prepare nanostructured films from the protein-block copolymer and chromophore-block copolymer coacervates. After film formation, the lower critical solution temperature (LCST) of the thermoresponsive block allows the nanomaterial to be effectively immobilized in aqueous environments at physiological temperatures, enabling use of the materials for biomolecule immobilization and controlled release. The local block copolymer environment is shown to have significant effect on the J-aggregate formation process and morphology.
Bio:
Professor Olsen earned his S.B. from MIT in June 2003. He earned a Ph.D. in Chemical Engineering in December 2007 at UC Berkeley advised by Prof. Rachel Segalman. His research developed the first universal phase diagram for rod-coil block copolymers, an emerging category of polymers with importance for producing self-assembled nanomateirals in biotechnology and organic electronics. He was a NIH and Beckman Institute Postdoctoral Fellow with Profs. David Tirrell, Julia Kornfield, and Zhen-Gang Wang at Caltech, where he applied protein biosynthesis to the design of physically associating telechelic protein hydrogels applied as injectable biomaterials.
His current research interests are broadly clustered in the areas of soft condensed matter physics and macromolecular physics, including liquid crystals, biomaterials, colloids, and polymers. He is particularly interested in how biosynthesis can be used as a natural green chemistry for the preparation of designer polymeric materials, how controlled polymerization through biology can give us unique materials that provide insight into polymer physics, and the unique physics of self-assembly in complex protein nanostructures for biotechnology and energy applications.
