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 _C. Experiments at full and zero average neutron contrast were used to study the correlation length of concentration fluctuations ξ and the radius of gyration R _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→T _C. Reswelling begins when ξ becomes comparable to the R _g of the polymer.