Tuning adsorption via polymer-surfactant complexation

In this thesis, we investigate multicomponent effects that occur during the co-adsorption of polymers and surfactants to the solid-liquid interface.; We examined co-adsorption from mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) with either hydroxypropyl cellulose (HPC) or hydrophobically modified hydroxyethyl cellulose (hmHEC). Co-adsorption to non-selective, hydrophobic polydimethylsiloxane (PDMS) surfaces was compared with co-adsorption to negatively charged silica surfaces that were selective for the polymers. Optical reflectometry provided the total extent of adsorption as well as the adsorption kinetics. Depending on the bulk SDS concentration, the total adsorbed mass could either be increased or decreased compared to the adsorbed mass attained from SDS-free polymer solutions. With silica surfaces, adsorption of either polymer was completely prevented, leaving the surface bare, at high SDS concentrations. On the hydrophobic PDMS surface, only SDS adsorbed when its concentration exceeded the ordinary critical micelle concentration.; The reversibility of co-adsorption with respect to changes in the solution SDS concentration was investigated for these cellulose-SDS layers. On the selective silica surface, an adsorbed layer becomes kinetically trapped in path-dependent states because SDS is electrostatically repelled from the negatively charged surface and is therefore unable to solubilize the polymer-surface contacts. On the non-selective PDMS surface, co-adsorption in the HPC/SDS system is reversible although some irreversibility persists in the hmBEC/SDS system. However, the severity of the kinetic trapping effects is greatly reduced compared with the same system on silica. The decreased kinetic trapping effects are attributed to surfactant adsorption on the hydrophobic PDMS surface. A streaming current technique was used to measure the electrokinetic thickness of kinetically trapped polymer layers on silica that were formed by co-adsorption with SDS, followed by rinsing with SDS-free polymer solution. The layer thickness was history-dependent: in spite of prolonged exposure to a constant solution polymer concentration, the adsorbed layer thickness depended on the SDS concentration that existed during the initial co-adsorption stage.; Using a combination of optical reflectometry, atomic force microscopy, and infrared spectroscopy, we examined the co-adsorption of nonionic ethoxylated surfactants, Triton X-100®, and poly(acrylic acid) (PAA) on negatively charged silica surfaces. X100 adsorbed at a maximum surface concentration above the critical micelle concentration (cmc). In the absence of surfactant, the polyelectrolyte did not adsorb to silica to any extent that is measurable by our experimental techniques. Below the cmc, the co-adsorbed mass from solutions containing both PAA and XI00 was always greater than the adsorbed mass from solutions containing only surfactant. Atomic force microscopy confirms the presence of PAA in the mixed adsorbed layer. At lower surfactant concentrations, the presence of PAA in the adsorbed layer was manifested in the form of long-range bridging adhesion between opposing surfaces. Removing surfactant by thoroughly rinsing the mixed layer left an irreversibly adsorbed, “deposited” PAA layer. Attenuated total reflection-Fourier transform infrared spectroscopy was utilized to measure the composition of the co-adsorbed layer. Adsorbed PAA was identified at all surfactant concentrations investigated with the maximum PAA surface concentration occurring at XI00 concentrations near the regime of bridging interactions identified with AFM. (Abstract shortened by UMI.)...