Crossover behavior in dilute polymer solutions: Square-well chains

Monte Carlo simulations for model polymer chains composed of hard spheres w ith square-well attractions were performed to find a precise relation betwe en the parameters of a crossover theory and the parameters of the square-we ll chain. For sufficiently large bond lengths, there was a direct relation between the effective parameters of the crossover theory and the second- an d third-virial coefficients of the square-well atoms. For the systems under study, the theta temperature is close to the Boyle temperature of the disc onnected monomers, is mainly dependent on the details of the monomer-monome r interactions, and is only weakly dependent on the bond length of the chai n. Above the theta temperature, the crossover theory is in good agreement w ith the simulation data. Near the theta point, the main effect of tricritic al corrections is a shift in the critical amplitudes. Other effects are ext remely small. The simulation data are consistent with the tricritical cross over theory. However, more precise data are needed to quantitatively test t he tricritical crossover theory. (C) 1999 American Institute of Physics. [S 0021-9606(99)50536-9].