CAREER: Developing the Design Rules of Charge Sequence to Inform Polymer Self-Assembly

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports theoretical and computational research and education to elucidate rules for designing polymeric materials that mimic biology. Polymers are long chain-like molecules that are made of joined molecular units called monomers. Materials made from polymers are used in a wide range of common applications from rubber bands to plastic components of automobiles to packaging materials and more. The PI is inspired by the sophisticated precision of biological systems which are made from large molecules that specifically and exclusively interact using information encoded in patterns of electrostatic charge. The PI will investigate whether polymers that self-organize can be made to behave in a similar way. The PI's group will determine how patterns of electrostatically charged monomers along a polymer molecular chain can be designed to guide the self-organization of molecular structures at the nanometer length scale. The monomer sequence of a polymer will be a tool to fit molecules together like puzzle pieces. To do this, the PI will consider polymer systems that strongly attract because they consist of chains of positive charge called polycations and chains of negative charge called polyanions. In solution, large numbers of these polycations and polyanions stick together in a dynamic, gel-like material known as a complex coacervate. This "sticking" is highly dependent on the sequence of charges along the polymer backbone, and the PI's group will establish how different patterns emerge from which polycations interact with which polyanions. This assembly motif will enable advances in a broad class of materials that demand structural precision at the nano-level, such as fuel cell membranes, functional coatings and sensors, and drug delivery vehicles. The integrated education and outreach component of this project supports broader outreach to underrepresented minority groups, along with graduate and undergraduate research training and mentorship. Outreach efforts consist of placing the computer simulation advances of the PI's group into the context of polymer sustainability and experimental collaboration. Interactive computer simulation is the centerpiece of a PI-designed activity within the St. Elmo Brady STEM Academy at the University of Illinois. This activity will introduce the lifecycle of plastics and sustainability to elementary-age students in underrepresented minorities. TECHNICAL SUMMARY This CAREER award supports theoretical and computational research and education that seeks to use sequence-designed polymers to emulate biological macromolecules. Sequence control is key to addressing a grand challenge in polymer science: design soft materials that respond to stimuli, encode information, and form complex structures. The PI's group will take cues from biopolymers that undergo specific binding due to information encoded in charge monomer sequence, and establish the design rules needed to harness charge patterning for polymer self-assembly. In this work, the PI will systematically explore how charge sequence dictates the interaction strength and specificity between oppositely-charged polyelectrolytes. Solutions of these polymers undergo associative phase separation into complex coacervates, which serve as an ideal model system for connecting charge patterning to macroscopic phase behavior and nanoscale assembly. Monte Carlo simulation and hybrid particle/field simulation methods will be used to probe: 1) local monomer placement and patterns that will control interaction strength, and 2) contour-length charge variation that can promote interaction specificity via complementary sequences. Both sequence length scales will provide the basis for using charge sequence to encode self-assembly. This research will elucidate principles of using sequence-defined polymers to drive polymer design, using simulation methods uniquely suited to addressing the disparate length scales connecting monomer-level sequence to morphological or macroscopic phenomena. The integrated education and outreach component of this project supports broader outreach to underrepresented minority groups, along with graduate and undergraduate research training and mentorship. Outreach efforts consist of placing the simulation advances of the PI's group into the context of polymer sustainability and experimental collaboration. Interactive simulation is the centerpiece of a PI-designed activity within the St. Elmo Brady STEM Academy at the University of Illinois. This activity will introduce the lifecycle of plastics and sustainability to elementary-age students in underrepresented minorities.