Adsorption of polymer -surfactant complexes onto solid surfaces

The adsorption of polyvinylpyrollidone/sodium dodecyl sulfate (PVP/SDS) and polyvinylpyrollidone/sodium octyl sulfate (PVP/SOS) complex solutions onto alumina were studied. PVP's of 10, 40, and 360 Kilodalton (Kda) molecular weights were used in preparing the complex solutions. Nominal concentrations of 0.1%, 0.2%, and 0.3% PVP were used to prepare the complex solutions which had an SDS and SOS content ranging from 2 mM to 14 mM, in 2 mM increments. In all cases, it was found that an increase in molecular weight resulted in an increase in the amount of complex solution adsorbed. The adsorption reached saturation at an SDS and SOS concentration of 10--12 mM. A fluorescence spectrum of the complex containing SDS was also studied. Pyrene was used as the fluorescence probe. Three regions were observed. The first, R1, represents the equilibrium distribution of SDS in solution. The second, R2, represents the onset and the formation of SDS micelles as well as the saturation of the PVP/SDS associates. The third, R3, represents the free SDS molecules in equilibrium with PVP/SDS associates. The pyrene probe was found to exhibit a less hydrophobic environment in the SDS/PVP complex than that experienced in the SDS micelles alone. A study of the effect of the molecular weight (10Kda, 40Kda, and 360Kda) and concentration (0.1% and 0.2%) of PVP on the development of the critical micelle concentration (cmc) of the surfactant, SDS, was done using conductance and surface tension measurements. The results obtained indicate that two types of micelles are formed. The cmc was determined for both types. For the first micelle type, the cmc was at 3.1 mM of SDS, and for the second type, the cmc was in the region of 9.5 to 11.2 mM SDS.