Electrophoretic flow of interacting polymer chains: Effects of temperature, polymer concentration, and porosity


GM Foo
RB Pandey

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Using a Monte Carlo simulation in three dimensions, we studied the variation of the root-mean-square (rms) displacement (R-rms) of polymer chains with time and the rates of their mass transfer (j) as a function of biased field (B), polymer concentration (p), chain length (L-c), porosity (p(s)), and temperature (T). In homogeneous/annealed system, the rms displacement of the chains shows a drift-like behavior, R-rms similar to t, in the asymptotic time regime preceded by a subdiffusive power-law (R-rms similar to t(k), with k < 1/2) at high p. The subdiffusive regime expands on increasing L-c and p but reduces on increasing T or B. In quenched porous media, the drift-like behavior of R-rms persists at low barrier concentration (p(b)) and high T. However, at high p(b) and/or low T, chains relax into a subdrift and/or subdiffusive behavior especially with high p or long L-c. Flow of chains is measured via an effective permeability (sigma) using a linear response assumption. In annealed system, sigma increases monotonically with B at high T and low p but varies nonmonotonically at low T, high p and high L-c. We find that sigma decays with L-c, sigma similar to L-c(-alpha), where alpha depends on B, p and T with a typical value alpha similar or equal to 0.43-0.64 for p = 0.1-0.3 at B = 0.5. Further, sigma decays with p, sigma similar to - Cp with a decay rate C sensitive to T and B. In quenched porous media, even at low p(b) and high T, sigma varies nonmonotonically with bias, i.e., the increase of sigma is followed by decay on increasing the bias beyond a characteristic value (B-c). This characteristic bias seems to decrease logarithmically with barrier concentration, B-c similar to - kappa lnp(b). The pre-factor kappa depends on the chain length, kappa approximate to 0.35 for shorter chains (L-c = 20, 40) and approximate to 0.15 for longer chains (L-c = 60). Scaling dependence of sigma on L-c similar to that in annealed system is also observed in porous media with different values of exponent alpha. The current density shows a nonlinear power-law response, j similar to B-delta, with a nonuniversal exponent delta approximate to 1.10-1.39 at high temperatures and low barrier concentrations.

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