This award by the Biomaterials program in the Division of Materials Research to University of California Santa Barbara is to investigate the structure of polyelectrolytes of variable charge density so as to establish the relationship of the classical 'electrostatic blob' picture of weakly-charged polymers to the 'snake-like chain' (SLC) model, which appears to hold for highly-charged polymers. Additionally, this project is to broadly-establish the SLC nature of flexible polyelectrolytes. Charged, flexible polymers are ubiquitous in biology and technology, yet the basic physics underling their structure is poorly established. The investigator's recent studies indicated that these structures are best-defined as a so-called 'snake-like chain'. This project will investigate the general role of soft monomer repulsions in creating SLC structure using comb polymers that replace electrostatic repulsions with entropic repulsions between side-chains. This project will investigate these systems using low-force single-molecule elasticity measurements, and analyze them in comparison to both simulation and theory. The work described in this proposal is highly interdisciplinary, and so represents an excellent opportunity for training young scientists. To exploit this opportunity, the project plans to support graduate students and to continue investigator lab's extremely strong record of involving undergraduate researchers. Undergraduate research experiences are proven to have significant positive effects on student's nascent scientific careers, and this project has identified specific potential internship projects associated with this proposal.
Polyelectrolytes are long, string-like molecules that carry a large electrical charge. The combination of this electric charge and the floppy nature of the string-like structure itself permits polyelectrolytes to adopt a wide range of different configurations that impart technologically- and biologically-important properties. For example, polyelectrolytes are used in coating technologies (e.g. to reduce UV transmission of windows), and as water soluble-materials in diapers. In the biological arena, DNA, RNA, and many proteins can be considered polyelectrolytes whose charge affects their structure, and thus their biological functions. This proposal will use novel and powerful experimental probes to better understand the physics of individual polyelectrolytes. The information obtained will establish predictive models of polyelectrolyte configuration that, in turn, can be used to improve both technological application of polyelectrolytes, and our understanding of certain charge-based bimolecular transactions. The scientific broader impact would be a greatly improved understanding of polymer behavior, which in the long term could lead to better materials development. The educational and outreach activities included recruitment of undergraduate students from a variety of on campus programs including those enabling research activities for students from groups traditionally underrepresented in the physical sciences.
