Collective dynamics in simple supercooled and polymer liquids

The Dynamic Lattice Liquid (DLL) model for molecular rearrangements in liqu ids is discussed in application to both simple supercooled liquids and poly mer melts. It is shown, that the model is able to reproduce a broad class o f various temperature dependencies of relaxation times, lying between the e xtremal cases represented by the Arrhenius relation on one and by the Vogel -Fulcher-Tamman (VFT) relation on the other hand. Rates of rearrangements a re considered as being controlled by thermal activation with activation ene rgy barriers dependent on local density. Various dependencies of the activa tion energy barriers on local density are examined. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements ope rating in a dense system under conditions of the excluded volume and contin uity of the system. The model is implemented as a simulation algorithm, which is used to descri be dynamic properties of liquids and polymer melts. Simulation results obta ined for systems representing simple liquids as well as linear polymers, mu ltiarm star polymers and microgels are presented. An analogy in the dynamic behavior between the low molecular liquids and me lts of macromolecules with complex compact architectures is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.