Simulation study on effect of polymer entanglement on the strain hardening

The effect of the molecular entanglement on the elongational viscosity was investigated by Brownian dynamics simulation in 2-dimension. The polymer wa s represented by freely-rotated bead-rod model. The entanglement constraint was assumed by a repulsive interaction between bonds in the chain and rand omly located obstacles. Under an elongational flow, affine deformation was applied to spatial distribution of the obstacles. Varying lifetime and dens ity of the obstacles, we investigated these effect on elongational viscosit y. We found that (i) linear viscosity increases with increasing density whi le it is independent of the lifetime, that (ii) critical strain rate at whi ch the strain hardening begins is independent of both the lifetime and the density, that (iii) the longer lifetime gives the stronger strain hardening , and that (iv) when the density becomes higher than entanglement threshold of the chain, the strain hardening is discontinuously enlarged.