Flow-Induced Crystallization: Unravelling the Effects of Shear Rate and Strain

We have used large scale nonequilibrium molecular dynamics simulations to separate the effects or shear rate (gamma) and strain (gamma) in postshear crystallization or polymers. Here we show the strain plays a major role in flow-induced crystallization (FIC) and a critical strain, with a clear correlation to the rheology and molecular structure, must be applied to observe enhanced crystallization. Although the amount of crystallinity initially increases with gamma, our simulations appear to be consistent with experimental observations of an upper limit gamma(c), above which the effect is reversed, and show it is at the reciprocal of the stress relaxation time. We reveal the structural origins of this phenomenon and show the shear rate does not affect the crystallization rate in post shear crystallization of a model polymer with 162 monomers.