The interaction between polymer and surfactant: The composition of the complex between polyvinylpyrrolidone and sodium alkyl sulfate as revealed by surface tension, dialysis, and solubilization

Abstract

Abstract The interaction between polyvinylpyrrolidone (PVP) and sodium alkyl sulfate (RSO 4 Na) in 0.1 N NaCl solution has been studied by surface tension, dialysis equilibrium, and solubilization. Two transition points were clearly found on the surface tension vs. concentration curves of RSO 4 Na in the presence of PVP. The first transition point is considered as the concentration at which the adsorption of RSO 4 Na on PVP begins, and the second transition point is considered as that at which the adsorption of RSO 4 Na on PVP is complete. This reasoning was confirmed from the results of dialysis equilibrium and solubilization. The weight ratio of PVP to sodium dodecyl sulfate (R 42 SO 4 Na) consumed for the complete adsorption was constant, i.e. , 1: 2.3 regardless of the amount of PVP in solution. The concentration of RSO 4 Na above which the adsorption of RSO 4 Na on PVP begins was about 40% lower than the respective critical micelle concentration (CMC). The relationship between the logarithm of the CMC's or of the concentration of RSO 4 Na at first transition points and the hydrocarbon chain length of RSO 4 Na was linear. The slope of the first transition point vs. the hydrocarbon chain length agreed with that of the CMC, that is, the free energy of transferring a CH 2 from aqueous solution to the aggregate (complex) or to the micelle is in both cases 1.1 kT . It can be deduced from these results that RSO 4 Na molecules adsorbed on PVP seem to contact each other and not to be uniformly distributed on the PVP molecules right from the initial stages of adsorption.