Theory of aging, rejuvenation, and the nonequilibrium steady state in deformed polymer glasses

Kang Chen and Kenneth S. Schweizer
Phys. Rev. E 82, 041804 – Published 20 October 2010

Abstract

The nonlinear Langevin equation theory of segmental relaxation, elasticity, and mechanical response of polymer glasses is extended to describe the coupled effects of physical aging, mechanical rejuvenation, and thermal history. The key structural variable is the amplitude of density fluctuations, and segmental dynamics proceeds via stress-modified activated barrier hopping on a dynamic free-energy profile. Mechanically generated disorder (rejuvenation) is quantified by a dissipative work argument and increases the amplitude of density fluctuations, thereby speeding up relaxation beyond that induced by the landscape tilting mechanism. The theory makes testable predictions for the time evolution and nonequilibrium steady state of the alpha relaxation time, density fluctuation amplitude, elastic modulus, and other properties. Model calculations reveal a rich dependence of these quantities on preaging time, applied stress, and temperature that reflects the highly nonlinear competition between physical aging and mechanical disordering. Thermal history is “erased” in the long-time limit, although the nonequilibrium steady state is not the literal “fully rejuvenated” freshly quenched glass. The present work provides the conceptual foundation for a quantitative treatment of the nonlinear mechanical response of polymer glasses under a variety of deformation protocols.

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  • Received 19 July 2010

DOI:https://doi.org/10.1103/PhysRevE.82.041804

©2010 American Physical Society

Authors & Affiliations

Kang Chen1 and Kenneth S. Schweizer2,3,*

  • 1Center for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, Suzhou 215006, China
  • 2Department of Materials Science, University of Illinois, 1304 West Green Street, Urbana, Illinois 61801, USA
  • 3Kavli Institute of Theoretical Physics, University of California, Santa Barbara, California 93106, USA

  • *kschweiz@illinois.edu

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Issue

Vol. 82, Iss. 4 — October 2010

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