Driven flow and pinning of molecular aggregates in a heterogeneous medium

Aggregation and flow of polymer chains (each of length L-c) on a heterogene ous surface are studied in presence of a field E using a hybrid simulation. Effects of field, heterogeneity (i.e., the barrier concentration p(b)), an d temperature T on aggregation and desegregation of chains with low molecul ar weight is found to be different from that with high molecular weight. Fo r low L-c, at low T = 0.2, the impurity barriers act as seeds for pinning t he growth of molecular aggregates that lead to larger aggregates at lower p (b). At high temperature (T = 1.0), in contrast, larger aggregates appear a t higher p(b) where pinning of aggregates is augmented by cluster of cluste ring. For large L-c, orientational ordering with a molecular bridging occur s at low p(b), while a nearly isotropic network of chains anchored by the b arriers emerges at higher p(b). The rms displacement of chain ranges from d rift-like for short chains at low barrier concentration to strongly subdiff usive for long chains at high fields. A linear response of the flow rate de nsity j to field j similar to E is observed over low to moderate fields (E less than or equal to 1.0), high temperature (T greater than or equal to 1) , and low barrier concentrations (p(b) less than or equal to 0.1). The vari ation of the effective linear permeability phi(m) of polymer with the field is nonmonotonic over the range 0.0 < E < 1.0, with decreasing trend at hig her values of E. In the low field regime (E < 0.2), the monomer permeabilit y shows a power-law decrease with chain length phi(m) similar to L-c(-alpha ), alpha similar or equal to 0.25-0.37. (C) 2000 American Institute of Phys ics. [S0021-9606(00)50222-0].