Eur. Phys. J. E (2011) 34: 130
https://doi.org/10.1140/epje/i2011-11130-8

Conformational dynamics and internal friction in homopolymer globules: equilibrium vs. non-equilibrium simulations

¹ Physik Department, Technische Universität München, James-Franck-Straße, 85748, Garching, Germany
² Department of Materials Science and Engineering, Massachusetts Institute of Technology, MA 02139-4307, Cambridge, USA
³ Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany

^* e-mail: einert@ph.tum.de
^** e-mail: rnetz@physik.fu-berlin.de

Received: 24 February 2011
Accepted: 3 November 2011
Published online: 14 December 2011

Abstract

We study the conformational dynamics within homopolymer globules by solvent-implicit Brownian dynamics simulations. A strong dependence of the internal chain dynamics on the Lennard-Jones cohesion strength and the globule size N _G is observed. We find two distinct dynamical regimes: a liquid-like regime (for < with fast internal dynamics and a solid-like regime (for > with slow internal dynamics. The cohesion strength of this freezing transition depends on N _G . Equilibrium simulations, where we investigate the diffusional chain dynamics within the globule, are compared with non-equilibrium simulations, where we unfold the globule by pulling the chain ends with prescribed velocity (encompassing low enough velocities so that the linear-response, viscous regime is reached). From both simulation protocols we derive the internal viscosity within the globule. In the liquid-like regime the internal friction increases continuously with and scales extensive in N _G . This suggests an internal friction scenario where the entire chain (or an extensive fraction thereof) takes part in conformational reorganization of the globular structure.