The interaction between polymer and surfactant: The effect of temperature and added salt on the interaction between polyvinylpyrrolidone and sodium dodecyl sulfate

Abstract

The effect of temperature and added salt on the interaction between polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS) has been studied by surface tension and solubilization. Applying the phase separation theory to the complex formation of SDS with PVP, the heat of complex formation of SDS with PVP ( ΔHc) in 0.10 N NaCl solution was calculated from the temperature dependence of the concentration of SDS at the first transition point which appeared clearly on the surface tension or the solubilization vs concentration curve of SDS in the presence of PVP. ΔH c was less exothermic than the heat of micellization ( ΔH m ) up to 60°C. The relationship between the logarithm of the first transition point and the logarithm of the concentration of counter ion was linear. The slope of the first transition point vs concentration of counter ion agreed with that of the CMC, viz., K g = 0.52. From the discussion of the results, it was found that the differences between the CMC and the concentration of SDS at the first transition point, as well as those between ΔH m and ΔH c , can be understood from the surface charge density and the free volume of SDS in the absence and in the presence of PVP; the concentration of SDS at the first transition point may be lower than the CMC due to the interaction between the polar group of SDS molecules contacting each other on PVP and that of the PVP molecule.