Monte Carlo simulation of polymers in solution and bulk

The behavior of polymers in solution depends on both temperature and concentration. At least four different regions of the concentration-temperature plane exist in which the physical properties are fundamentally different. These regions are known as the dilute good solvent, theta solvent, semidilute, and concentrated regions. In this investigation, Monte Carlo simulations were performed in order to examine how properties change in going from one region to another. Two series of simulations were performed. In the first series, properties were studied as a function of concentration so that crossover from dilute, to semidilute, and then to concentrated was obtained. In the concentrated or bulk region, it was found that the second and fourth moments of the end-to-end distance were characteristic of ideal chains (without excluded volume), consistent with neutron scattering results. In the semidilute region, the concentration dependence of the mean square end-to-end distance was not in agreement with scaling theory. In the second series of simulations, the temperature was changed for an isolated chain (zero concentration limit), so that crossover from good solvent to theta solvent behavior was obtained. Over the chain length range studies (10–300), no evidence was seen for the existence of “thermal blobs.” In addition, expansion of the average internal conformation over the expected result was observed and found to be increasingly important as the temperature increases from the theta temperature.