Interaction between Hydrophilic Surfaces in Triblock Copolymer Solution

We report on the interactions between fused quartz surfaces immersed in solutions of low molecular weight nonionic homopolymers and triblock copolymers. The polymers studied were a poly(ethylene oxide) (PEO) homopolymer and a triblock copolymer of the type poly(ethylene oxide)−poly(tetrahydrofuran)−poly(ethylene oxide). The surface force measurements were performed by the interfacial gauge technique. In water, a strong repulsive force was observed at short surface separations. This force has its origin in electrosteric interactions imposed by formation of a gel layer on silica. This interaction was totally suppressed when small amounts of polymers were adsorbed or when water was substituted for ethanol. Adsorbed polymers induce a long-range steric repulsion. However, in solutions containing homopolymers, when the distance between the surfaces decreases below 3 nm, the repulsive interaction levels off. Here the force remains more or less constant with decreasing surface-to-surface distance. Adsorbed polyme...