Characteristic Times of Polymer Tumbling Under Shear Flow

✍ Scribed by Florencio Balboa Usabiaga; Rafael Delgado-Buscalioni

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 279 KB
• Volume: 20
• Category: Article
• ISSN: 1022-1344
• DOI: 10.1002/mats.201100020

✦ Synopsis

Abstract

The tumbling dynamics of flexible chains in shear flow, analysed by Brownian Dynamics simulations, are found to be ruled by three characteristic times τ~tumb~, τ~dif~ and τ~lag~. The average tumbling time τ~tumb~ scales with the shear rate with a robust exponent against excluded volume (EV) or hydrodynamic interactions, $\tau _{{\rm tumb}} \approx {\dot {\gamma }}^{{-} 2/3} $. The chain extensions in the flow plane decorrelate in a time τ~dif~ determined by the diffusion of the chain configuration in gradient direction, $\tau _{{\rm dif}} \approx Y^{2} /D$. The chain keeps memory of its configuration over a number of tumblings events given by the ratio τ~dif~/τ~tumb~. While for ideal chains $\tau _{{\rm dif}} /\tau _{{\rm tumb}} \approx O(1)$, for expanded (EV) chains we find $\tau _{{\rm dif}} /\tau _{{\rm tumb}} \approx {\dot {\gamma }}^{0.2} $. Hence, EV chains tumble in a more deterministic way as ${\dot {\gamma }}$ is increased. As a consequence, contrary to previous assumptions, the exponential tail of the tumbling time distribution $P(\tau )\approx {\exp} ({-} \nu \tau )$ presents a non‐Poissonian exponent. This exponent ν is found to be determined by a new characteristic time τ~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.

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