The T-12 Group contributes to the Los Alamos internally funded LDRD project on polymer aging. Polymer blends (mixed with other components such as plasticizers) are used as binders for High Explosives (HE). An example is estane, which is roughly 25% polyurethane and 75% polyester. This copolymer displays microphase separation on the length scale of about 100 Angstroms. The polyurethane segments phase separate, and are believed to promote cross-linking between the soft polyester fibers, thereby giving estane its strength. One of the aims of this project is to understand theoretically the dynamics of this microphase separation, especially as the polymer ages. We have chosen to utilize as a starting point the continuum (field-theoretic) approaches pioneered by Leibler and Stillinger and developed more recently by Chandler and co-workers. We have been able to generalize these theories using notions from gauge theory. We are currently in the process of understanding this generalized theory at a level beyond the simple Gaussian approximation, using Renormalization Group ideas. We also intend to perform `MD' simulations using the energy functional obtained within our theory, in order to obtain constitutive relations at various strain-rates for estane.
People in T-12 working on this project include: