Integration of bulk and interfacial properties in a polymeric system: rubber elasticity at a polybutadiene/water interface.

Oxidation of the surface of cross-linked 1,4-polybutadiene provided a hydrophilic substrate that reconstructed against hot water to become more hydrophobic. Subsequent equilibration against water at room temperature returned its original hydrophilicity. These temperature-dependent changes in the relative concentrations of hydrophobic and hydrophilic moieties at the polymer/water interface are interpreted as arising from the entropic influence of chain extension, associated with rubber elasticity. As expected, the magnitude of this effect depended on the cross-link density of the polymer and the degree of oxidation of the surface. The reversibility of the reconstruction when the water was cycled between high and low temperature damped out only gradually over many cycles.