INTERFEROMETRIC STUDY OF TRANSITION FROM WEAK TO STRONG PENETRATION OF A POLYMER-SOLUTION INTO A POROUS SILICA BEAD

The concentration equilibrium of polymer molecules with a porous mediu m was studied using a Jamin interferometer and digital image analysis. A porous silica bead was immersed into a solution of the polymer in a solvent isorefractive with silica. The concentration of the polymer i n the porous medium was measured as the concentration in the exterior solution was changed in a wide range from dilute to semidilute. For al l the chain dimensions studied, the partition coefficient increased to a value close to unity, as the exterior solution became semidilute, a result in agreement with theoretical predictions of the weak-to-stron g penetration transition. The transition was, however, found to be mor e diffuse than predicted. The difference can be partly ascribed to a d istribution in the effective pore diameter of the network-structured p orous medium.