Enhanced viscoelastic effect of mesoscopic fillers in phase separation

Here we report the significant enhancement effect of mesoscopic fillers in viscoelastic phase separation of dynamic asymmetric polymer blends. Mesoscopic fillers with their size much larger than the dimensions of the polymer chains, from nanometres to microns, are preferentially immersed into the slow dynamic phase and phase interface due to the entanglement with polymer chains. For sufficiently high volume fraction and fine dispersion, mesoscopic fillers conduce to the pronounced slowing down of the phase separation process, and result in refined structures with sharply decreased characteristic length scales. The pinning of the phase separation is attributed to the dramatic increase of dynamic asymmetry from the entanglement of polymer chains with mesoscopic fillers. The principal difference between mesoscopic fillers in classic and viscoelastic phase separation is whether there exists a filler enforced elastic-force balance condition. This suggests a general physical scenario of entanglement selection of the polymer chains under stress.