Eur. Phys. J. E (2011) 34: 97
https://doi.org/10.1140/epje/i2011-11097-4

Regular Article

Simulated glass-forming polymer melts: Glass transition temperature and elastic constants of the glassy state

¹ Institut Charles Sadron, Université de Strasbourg, CNRS UPR 22, 23 rue du Loess, BP 84047, 67034, Strasbourg Cedex 2, France
² Institut de Mécanique des Fluides et des Solides, 2 rue Boussingault, 67000, Strasbourg, France

^* e-mail: jorg.baschnagel@ics-cnrs.unistra.fr

Received: 28 April 2011
Revised: 19 July 2011
Accepted: 28 July 2011
Published online: 23 September 2011

Abstract

By means of molecular-dynamics simulation we study a flexible and a semiflexible bead-spring model for a polymer melt on cooling through the glass transition. Results for the glass transition temperature T _g and for the elastic properties of the glassy state are presented. We find that T _g increases with chain length N and is for all N larger for the semiflexible model. The N dependence of T _g is compared to experimental results from the literature. Furthermore, we characterize the polymer glass below T _g via its elastic properties, i.e., via the Lamé coefficients λ and μ. The Lamé coefficients are determined from the fluctuation formalism which allows to split λ and μ into affine (Born term) and nonaffine (fluctuation term) contributions. We find that the fluctuation term represents a substantial correction to the Born term. Since the Born terms for λ and μ are identical, the fluctuation terms are responsible for the different temperature dependence of the Lamé coefficients. While λ decreases linearly on approaching T _g from below, the shear modulus μ displays a much stronger decrease near T _g. From the present simulation data it is not possible to decide whether μ takes a finite value at T _g, as would be expected from mode-coupling theory, or vanishes continuously, as suggested by recent work from replica theory.