Conformation of a polymer chain near the solvent critical region. II. Monte Carlo simulation

Using the Monte Carlo (MC) calculations, we study the conformational behavior of a two-dimensional (2D) single flexible-chain polymer dissolved in a monoatomic solvent. It is shown that near the solvent critical region the polymer chain can contract. Such a behavior is observed if the radius of fluctuations of solvent density is smaller than the natural size of the N-unit chain with excluded volume interaction [R similar to N(v), where v approximate to 3/(d + 2) is the Flory-Edwards exponent]. On the other hand, the chain goes back to the initial swollen state when the solvent correlation length becomes larger than R. Under these conditions, the polymer chain is effectively confined in a large solvent droplet. We find that the strongly fluctuating solvent can induce significant conformational changes only if there is a rather strong attraction between polymer segments and solvent particles. In this case, the average chain size is a nontrivial function of polymer-solvent attraction: At rather weak affinity of polymer and solvent, the average chain size grows with the increase of this attraction; with further increase of affinity of polymer and solvent, the chain begins to contract. Thus, in the case of high affinity of polymer and solvent, the polymer chain can undergo the complex coil-globule-coil transition. In general, the results of the MC simulations are in reasonable agreement with those obtained from the self-consistent integral-equation calculations. (C) 1998 American Institute of Physics.