Mechanics of model semiflexible conjugated-polymer glasses

Conjugated polymers have attracted great interest recently owing to their potential use in flexible electronic circuits, including bio-implantable devices. These semiflexible polymers possess an entanglement-mesh-scale structure that is dramatically different than that of their flexible counterparts; specifically, their entangled strands are approximately one Kuhn segment (rather than >> 1 Kuhn segments) long. This difference must necessarily lead to qualitatively different mechanical properties, but since these polymers have been synthesized only recently, their mechanics have been little explored. Preparing samples suitable for mechanics experiments remains challenging, and hence much can be learned from simulations of these systems. We present the results of molecular dynamics studies of semiflexible polymers' glassy-state mechanics under a wide range of deformation protocols, for a wide range of temperatures. Our results show that although these glasses are likely to be brittle, they may be less brittle than one might expect based on traditional theories of glassy-polymer mechanics such as Kramer's expression for the craze extension ratio.