Characteristic Times of Polymer Tumbling Under Shear Flow

The tumbling dynamics of flexible chains in shear flow, analysed by Brownian Dynamics simulations, are found to be ruled by three characteristic times tau(tumb), tau(dif) and tau(lag). The average tumbling time ttumb scales with the shear rate with a robust exponent against excluded volume (EV) or hydrodynamic interactions, tau(tumb) approximate to (gamma) over dot(-2/3). The chain extensions in the flow plane decorrelate in a time tdif determined by the diffusion of the chain configuration in gradient direction, tau(dif) approximate to Y-2/D. The chain keeps memory of its configuration over a number of tumblings events given by the ratio tau(dif)/tau(tumb). While for ideal chains tau(dif)/tau(tumb) approximate to O(1), for expanded (EV) chains we find tau(dif)/tau(tumb) approximate to (gamma) over dot(0.2). Hence, EV chains tumble in a more deterministic way as (gamma) over dot is increased. As a consequence, contrary to previous assumptions, the exponential tail of the tumbling time distribution P(tau) approximate to exp(-nu tau) presents a non-Poissonian exponent. This exponent nu is found to be determined by a new characteristic time tau(lag) measuring how fast the chain in-flow elongation X responses to the drag force induced by chain fluctuations in gradient direction Y. PSCS numbers.