EQUATION OF STATE AND STRESS TENSOR IN INHOMOGENEOUS COMPRESSIBLE COPOLYMER MELTS - DYNAMIC MEAN-FIELD DENSITY-FUNCTIONAL APPROACH

We have derived an expression for the global stress in inhomogeneous c omplex copolymer liquids. We apply the principle of virtual work to th e free energy as defined in the dynamic mean-field density functional method. This method automatically provides the full stress tensor (dev iatoric and isotropic parts) and hence an equation of state for inhomo geneous compressible copolymer melts. The excluded volume interactions and cohesive interactions between chains have been explicitly taken i nto account. Therefore the expressions for the stress and thermodynami c pressure have a wide range of validity. The connectivity of the chai ns is automatically accounted for and the fret. energy adapts very wel l to changes in the molecule properties. In the limiting case of homog eneous systems it simplifies to known results. In order to study rheol ogical properties of copolymer melts and npT-ensemble simulations, the pressure and stress components have to be calculated at any given mom ent in time. We show how the pressure and stress can be numerically ev aluated during simulations using a Green propagator algorithm, instead of having to calculate the time dependent configuration distribution function explicitly from a Smoluchowski equation. We provide illustrat ive numerical results that indicate how the pressure changes during mi crophase separation. (C) 1998 American Institute of Physics.