Collective dynamics in simple supercooled and polymer liquids

The Dynamic Lattice Liquid (DLL) model for molecular rearrangements in liquids is discussed in application to both simple supercooled liquids and polymer melts. It is shown, that the model is able to reproduce a broad class of various temperature dependencies of relaxation times, lying between the extremal cases represented by the Arrhenius relation on one and by the Vogel-Fulcher-Tamman (VFT) relation on the other hand. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements operating in a dense system under conditions of the excluded volume and continuity of the system. The model is implemented as a simulation algorithm, which is used to describe dynamic properties of liquids and polymer melts. Simulation results obtained for systems representing simple liquids as well as linear polymers, multiarm star polymers and microgels are presented. An analogy in the dynamic behavior between the low molecular liquids and melts of macromolecules with complex compact architectures is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.