POLYMER STATISTICS .1. PHASE-SEPARATION IN POLYMER-SOLUTIONS - A NEW STATISTICAL TREATMENT

A new statistical mechanics treatment of polymer systems is presented, built on the lattice model as used by Flory and Huggins, but using the pair approximation of the cluster variation method (CVM). The present paper is the first of a series, and shows how the new method compares with the most common theories in the polymer field. Phase separation diagrams are qualitatively similar to those of Flory. A noticeable difference is that our result for chi-c deviates from the value 1/2 proposed by Flory for any coordination number z. We also calculate the osmotic pressure for the polymer solution using our approximation and some comparison with Flory (F), Flory-Huggins (FH), Bawendi-Freed (BF) theories and the Monte Carlo (MC) simulations are done for the a thermal case. The qualitative agreement between our results and the FH results and the MC results supports the reliability of the present treatment.