Collapse of one polymer coil in a mixture of solvents

Abstract We discuss the size of a polymer chain P dissolved in a mixture of two solvents A and B, which are both good solvents of P, but which are close to a consolute critical point Tc. As shown earlier by one of us preferential adsorption effects become very important in this situation, and upset the classical picture : in a certain region near the AB critical point, the chain is predicted to collapse(1). There is one complication however : when the polymer concentration inside the coil increases, the AB critical point inside the coil shifts and preferential adsorption is reduced. We conclude that, upon decreasing the temperature T (with the bulk A/B concentration fixed at the critical value) ***he P chain must collapse first at a certain temperature T*, but must return to its ideal dimensions when T reaches Tc. Similar conclusions should hold for gels ***ollen by a mixture of two solvents.