Control of Persistent Nonequilibrium Adsorbed Polymer Layer Structure by Transient Exposure to Surfactants

By adsorbing polymers in the form of polymer/surfactant complexes, it is possible to control the nonequilibrium structure of adsorbed polymer layers. At moderate NaCl concentrations, the extent of poly(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide) triblock copolymer adsorption to silica surfaces is increased by a sequential sodium dodecyl sulfate (SDS) complex coadsorption procedure, when compared to the extent of adsorption in the absence of surfactant. The complex adsorption procedure entails polymer/surfactant complex formation and coadsorption at high SDS concentrations, followed by SDS dilution and eventually complete SDS removal, while maintaining a constant polymer concentration in solution. The amount of polymer that remains adsorbed after the complex adsorption procedure is nearly 40% greater than the amount that ordinarily adsorbs for the same polymer concentration in the absence of surfactant. We use independent atomic force microscopy and streaming current techniques to measure the polymer layer thicknesses. Both techniques indicate that polymer layers that were produced by the complex adsorption procedure followed by thorough rinsing in surfactant-free polymer solutions are significantly denser than the ordinary layers produced by adsorption in the absence of surfactant. Layers produced by complex adsorption contain more mass per unit area but are only approximately 70% as thick as the ordinary layers. The differences between the two adsorption procedures persist even during continued bathing of the layers in identical surfactant-free polymer solutions for 6 h. Polymer/surfactant complex adsorption thereby provides a tool for guiding adsorbed polymer layers into persistent nonequilibrium structures that might not be accessible by ordinary adsorption procedures.