Conformational Transitions of Polymers in Critical Binary Fluids

Abstract

A mean-field theory for the coil to globule transition of polymers in critical binary fluids is presented. We show using the uniform expansion method how the density fluctuations of the solvents can bring about the collapse transition close to the critical temperature. When the size of the polymer is comparable to the correlation length of the solvent density fluctuations, we find that a polymer undergoes a partial collapse in a mixture of good solvents of slightly different quality. We calculate the blob size of a partially collapsed chain, which depends on the preferential adsorption of better solvent onto the polymer. On length scales smaller than the blob size, the chain is self-avoiding; on length scales larger than the blob size it is collapsed with R ≃ N1/3. Close to the critical temperature, the blob size of the polymer is found to depend on the nonclassical critical exponent η.