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.