From argon to polystyrene: Strategies in model refinement and data‐fitting for phase equilibria

Abstract

AbstractLong‐range density or concentration fluctuations in the critical region of phase changes are directly tractable in modern “universal” models (Ising, Potts, percolation). Real polymers are apt to display “non‐universal” phase transitions depending on their detailed individual structures. Here mean field model can be refined in steps to portray critical fluctuations of individual systems through an approach via pseudo‐phase equilibria. Comparison between the “bridging theory” for semi‐dilute polymer solutions, originated by Koningsveld et al. (1974), and the model for the condensation of argon vapour by Gibbs, Pavlin and Yang (1983) reveals some common ingredients for a general but adaptable meanfield methodology. The mathematical mechanisms behind quasi‐linear “cross‐over” behaviour of phase loci and of plots for critical exponents are discussed.