Microphase Separation in Entangled Polymeric Solutions in Extensional Flows

Recent NEMD simulations of an entangled polyethylene melt revealed that within intermediate extensional rates, entangled melts could undergo a coil-stretch transition, and exhibit bimodal configurational distributions with peaks corresponding to coiled and stretched configurations. Furthermore, it was shown that through a configurational microphase separation, the coiled molecules develop distinct domains surrounded by stretched molecules. On the other hand, various experimental studies have shown that the response of entangled polymeric melts to elongational flow fields could be very different from those of entangled solutions depending on the solvent molecule architecture. Such complexities bring up many questions about the coil-stretch transition in entangled polymeric liquids. Do entangled solutions undergo a coil-stretch transition? Do they experience any configurational or chemical microphase separation?
To address these questions, we performed a series of NEMD simulations for entangled C₁₀₀₀H₂₀₀₂ polyethylene solutions in oligomeric C₁₆H₃₂ and benzene solvents. The solutions were subject to planar elongational flows within a wide range of extension rates. The simulations revealed both similarities and differences between entangled melts and solutions that will be discussed.