Partial Collapse and Reswelling of a Polymer in the Critical Demixing Region of Good Solvents

Using small-angle neutron scattering, we explored the conformational behavior of a polymer in a mixture of good solvents near their critical demixing temperature T{sub c}. Experiments at full and zero average neutron contrast were used to study the correlation length of concentration fluctuations {zeta} and the radius of gyration R{sub g} of individual polymer coils as a function of temperature T. The results confirm a theoretically predicted partial collapse followed by reswelling of polymer coils to the original dimensions as T {yields} T{sub c}. Reswelling begins when {zeta} becomes comparable to the R{sub g} of the polymer.