Conformation of a polymer chain near the solvent critical region. 1. The integral equation theory

摘要

Using the polymer reference interaction site model (PRISM) approximation and hybrid self-consistent MC/RISM method which combines the traditional Monte Carlo (MC) simulation with the numerical solution of the site-site Ornstein-Zernike-type (RISM) integral equation, we study solvent-mediated interactions and the conformational behavior of a single flexible-chain polymer immersed in a monoatomic solvent. The PRISM theory and the self-consistent MC/RISM method predict that in the vicinity of the solvent critical point there is an effective intrachain attraction between monomeric units of the chain. However, the strongly fluctuating 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 microstructure of the chain is modulated as a result of the competition between the intrachain short-range excluded volume repulsion and the nonlocal solvent-mediated attraction. For the dilute polymer solution without polymer-solvent attraction, the MC/RISM calculations show that the flexible polymer chain shrinks when approaching the critical point of the solvent. In this case, under the action of indirect intrachain attraction, long chain can take a specific winding conformation, with the fractal structure which is rather close to the globular structure. (C) 1998 American Institute of Physics. [References: 48]