THERMODYNAMIC MODELING OF POLYMER-SOLUTIONS WITH A MODIFIED STAVERMANEQUATION

A model describing the thermodynamic behaviour of polymer solutions is derived which explicitly accounts for the flexibility of the polymer chains. Based on computer simulations on various lattices it is shown that the flexibility of a polymer chain can be modelled by distinguish ing different polymer conformations. Here each conformation is charact erized by its corresponding number of external contact sites. The equi librium between the different conformations is then solved for any pol ymer concentration and any combination of interaction energies utilizi ng a modified Staverman equation. The model predictions are in good ag reement with the results of the computer simulations which were perfor med using the simple-sampling and the slithering-snake algorithm. Sinc e the knowledge of the distribution of the conformations of a single p olymer chain on an empty lattice is a prerequisite to perform the mode l calculations, Poisson distribution functions are fitted to the resul ts of the corresponding computer simulations. The generalization of th ese distribution functions not only facilitates the use of the new mod el but also allows to model polymers of varying chain stiffness.