Eur. Phys. J. B 6, 233-243 (1998)
https://doi.org/10.1007/s100510050546

Langevin dynamics of the glass forming polymer melt: Fluctuations around the random phase approximation

¹ Max-Planck-Institut für Polymerforschung, Postfach 3148, 55021 Mainz, Germany
² Institute of Chemical Physics, Russian Academy of Science, 142432, Chernogolovka, Moscow region, Russia

Corresponding author: ^a vilgis@mpip-mainz.mpg.de

Received: 9 January 1998
Revised: 24 April 1998
Accepted: 2 July 1998
Published online: 15 November 1998

Abstract

In this paper the Martin-Siggia-Rose (MSR) functional integral representation is used for the study of the Langevin dynamics of a polymer melt in terms of collective variables: mass density and response field density. The resulting generating functional (GF) takes into account fluctuations around the random phase approximation (RPA) up to an arbitrary order. The set of equations for the correlation and response functions is derived. It is generally shown that for cases whenever the fluctuation-dissipation theorem (FDT) holds we arrive at equations similar to those derived by Mori-Zwanzig. The case when FDT in the glassy phase is violated is also qualitatively considered and it is shown that this results in a smearing out of the ideal glass transition. The memory kernel is specified for the ideal glass transition as a sum of all "water-melon" diagrams. For the Gaussian chain model the explicit expression for the memory kernel was obtained and discussed in a qualitative link to the mode-coupling equation.