Observations of a novel case of capillary-induced phase separations (CIPS), which we judge to be of considerable practical significance, is reported. A long-range attractive force was observed between mica in mixed aqueous semidilute solutions of dextran and poly(ethylene oxide). The result was found to be similar to reported CIPS in liquid mixtures, and the origin of the long-range Linear force can be related to the formation of a capillary condensate with a polymer composition different from the mixed polymer bulk solution.