CONFORMATION OF A POLYMER-CHAIN NEAR THE SOLVENT CRITICAL REGION - 1 - THE INTEGRAL-EQUATION THEORY

Using the polymer reference interaction site model (PRISM) approximati on and hybrid self-consistent MC/RISM method which combines the tradit ional Monte Carlo (MC) simulation with the numerical solution of the s ite-site Ornstein-Zernike-type (RISM) integral equation, we study solv ent-mediated interactions and the conformational behavior of a single flexible-chain polymer immersed in a monoatomic solvent. The PRISM the ory and the self-consistent MC/RISM method predict that in the vicinit y of the solvent critical point there is an effective intrachain attra ction between monomeric units of the chain. However, the strongly fluc tuating solvent can induce significant conformational changes only if there is rather strong attraction between polymer segments and solvent particles. At such conditions, the collapse transition of long chains is possible near the solvent critical point. The equilibrium microstr ucture of the chain is modulated as a result of the competition betwee n the intrachain short-range excluded volume repulsion and the nonloca l solvent-mediated attraction. For the dilute polymer solution without polymer-solvent attraction, the MC/RISM calculations show that the fl exible polymer chain shrinks when approaching the critical point of th e solvent. In this case, under the action of indirect intrachain attra ction, long chain can take a specific winding conformation, with the f ractal structure which is rather close to the globular structure. (C) 1998 American Institute of Physics.