Driven flow and pinning of molecular aggregates in a heterogeneous medium

Abstract

Aggregation and flow of polymer chains (each of length Lc) on a heterogeneous surface are studied in presence of a field E using a hybrid simulation. Effects of field, heterogeneity (i.e., the barrier concentration pb), and temperature T on aggregation and desegregation of chains with low molecular weight is found to be different from that with high molecular weight. For low Lc, at low T=0.2, the impurity barriers act as seeds for pinning the growth of molecular aggregates that lead to larger aggregates at lower pb. At high temperature (T=1.0), in contrast, larger aggregates appear at higher pb where pinning of aggregates is augmented by cluster of clustering. For large Lc, orientational ordering with a molecular bridging occurs at low pb, while a nearly isotropic network of chains anchored by the barriers emerges at higher pb. The rms displacement of chain ranges from drift-like for short chains at low barrier concentration to strongly subdiffusive for long chains at high fields. A linear response of the flow rate density j to field j∼E is observed over low to moderate fields (E⩽1.0), high temperature (T⩾1), and low barrier concentrations (pb⩽0.1). The variation of the effective linear permeability φm of polymer with the field is nonmonotonic over the range 0.0<E<1.0, with decreasing trend at higher values of E. In the low field regime (E<0.2), the monomer permeability shows a power-law decrease with chain length φm∼Lc−α, α≃0.25–0.37.