Flow-induced phase phenomena in an entangled polyethylene/benzene solution under uniaxial elongational flow

Abstract

Flow-induced phenomena in entangled solutions of linear, monodisperse C\(_{1000}\)H\(_{2002}\) polyethylene dissolved in benzene were simulated under steady-state and startup uniaxial elongational flow via nonequilibrium molecular dynamics at a concentration of \(13.5c^*\) of the coil-overlap concentration, \(c^*\). The simulations revealed that the solution exhibited a chemical phase separation of the polymer and solvent components when subjected to uniaxial extensional flow at extension rates faster than the inverse Rouse time of the solution, followed by flow-induced crystallization of the polymer-rich phase into fibrillar structures of roughly 50 Å in diameter. The polymer phase was generated by the migration of the polymer chains into locally concentrated domains due to the favorable energetics of the stretched polymer chains, which simultaneously resulted in the expulsion of the less energetically favorable solvent molecules, thus producing a configurationally-based flow-induced demixing effect of polymer and solvent.