Nonionic Hydrophilic Surfaces: Adsorption and Interactions

An overview is given of recent studies of nonionic, hydrophilic surfaces formed by the adsorption of surfactants or surface active polymers. Hydrophobic surfaces can be easily hydrophilized by the adsorption of nonionic surfactants or block copolymers containing hydrophobic chain segments; the cooperative interaction between the hydrocarbon moieties contributes more to the free energy of adsorption than the interaction with the hydro- phobic surface. Hydrophilic layers are also readily formed on hydrophilic surfaces provided specific interaction between the hydrophilic end groups and the surface creates a sufficiently hydrophobic surface so that a second layer can be formed through cooperative interaction. The temperature dependence of the interaction forces between layers of surfactants can be closely correlated with their phase equilibria with water. In order to prevent protein adsorption the surface should be neither charged nor hydrophobic; it is shown that, accordingly, protein adsorption is extremely low on polyethylene oxide-covered surfaces