FRG: Structure and Dynamics of Reversible Model Gels

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

This is a Focused-Research Group award combining synthetic, characterization, and rheological strength to the study of polymer gels. Specifically, static and dynamic light scattering and rheological measurements will be carried out on two model reversible gels to elucidate the realtion of macroscopic behavior to the underlying thermondynamics and molecular dynamics. One of the gels will comprise a water soluble telechelic polymer and a small molecule crosslinker with groups conjugate to the endsgroups of the polymer. These telechelic polymer endgroups will reversibly associate with the crosslink loci, the distributions of molecular weight of the telechelic polymer, and the functionality of the crosslinker. These will be varied to explore their effects on the structure and dynamics of the model gel. The other system will comprise an ABC triblock copolymer, with mutually incompatible A,B and C block where B, but not A and C may be swollen in water. At high temperatures the A and C blocks will be fluid, permitting the material to be formed, but at low temperatures it is anticipated that A and C will be glassy micelles, with C excluded from A micelles and vice versa. The nonergodic character of the gels will be of particular interest, and the variation of this with processing conditions will be characterized by light scattering measurements. Then viscoelastic properties of the gels will be determined and considered in terms of the structure and dynamics determined by light scattering and the known chemical characteristics imposed by the gel synthesis. Gels are an important category of "soft matter" and this multi- and inter-disciplinary approach should provide significant educational benefits to the students involved in addition to advancing our understanding.