Investigation On The “Pseudo-polyelectrolyte” Behaviours Of PVP-SDS Solution

The interaction between polymers and surfactants significantly contributes to the performance of the complex solution, and polymer-surfactant complexes are widely applied in pharmaceutics, paints, inks, cosmetic, daily chemicals, oil recovery and other industrial fields. Researchers have successfully synthesized a variety of nano materials by using the polymer-surfactant complex as micro- and nano- level soft templates. Therefore, the physicochemical properties and interaction mechanism of polymer-surfactant complex have been widely studied in the past few decades. The study of polymer’s impact on the self-assembly behaviors of surfactant mainly concerned about the double critical concentrations, types of the interaction force and the interaction cites, as well as some quantitative effects. On the contrary, the surfactant’s impact on the properties of non-ionic polymer received less attention. Though the binding of surfactant onto non-ionic polymer was proposed to form a “polyelectrolyte-like” complex, direct evidence was absent.In this paper, methods contain Ubbelohde viscosity, conductivity, capillary electrophoresis were used to study the “pseudo-polyelectrolyte” behaviours of PVP-SDS solution, the main results are as follows:Viscosity data of aqueous PVP-SDS solution with different PVP concentrations(cPVP) and SDS concentrations(cSDS) were examined by Ubbelohde viscometer. They gave a support to the results obtained from surface tension measurement of PVP-SDS solution, in which SDS bound-micelles associated in cluster on PVP chains and there existed double critical SDS concentrations of c1 and c2. It was also found that reduced viscosity(ηsp/cPVP) of PVP-SDS solution increased with the decrease of cPVP evidently in lower cPVP, which was different from the behavior of simple aqueous PVP solution but similar to the typical polyelectrolyte Na PAA solution. Such an abnormal phenomenon was reasonably explained as caused by SDS bound-micelles associated in cluster on PVP chains, which resulted in a unique effect on viscosity similar to the well-known “polyelectrolyte effect”. The results of mean square end-to-end distance r2 and the relative expansion value k of PVP-SDS cluster were compared with simple PVP chains. It was found that the associating process of SDS bound-micelles in cluster on PVP lead PVP chains compressing and the electrostatic repulsion between the SDS bound-micelles attributed to the coil expansion.Conductivity data of aqueous PVP-SDS solution with different cPVP and cSDS were examined by Ubbelohde viscometer. The obtained results of c1 and c2 were consistent with the results of viscosity measurement. The effects of temperature on the interaction of between PVP and SDS were studied that raising temperature would weaken the interaction. The equivalent conductance of PVP-SDS cluster solution and the square root of its concentration were found coincided with Onsager experienced equation of strong electrolyte. These phenomena were interpreted as the degree of ionic dissociation of PVP bound SDS micelles clustered on was independent from its concentration, but influenced by the molar clustering amount [Г] of SDS on PVP. With [Г] increasing, the degree of ion dissociation decreased.The effect of SDS on the charge of PVP coil was studied by capillary electrophoresis. With cSDS increasing, PVP was detected increasingly negative charged, it remained unchanged at last. The influences of the buffer ionic strength and p H on the association of PVP-SDS were also investigated. Increasing Na+ concentration and lowering the p H of the buffer will both enhance the interaction between PVP and SDS.PVP-SDS cluster was proved to be a strong dissociated “pseudo-polyanionic” structure. At the end of this paper, the interaction mechanism and structure model of PVP-SDS “pseudo-polyanionic” were discussed and summarized based on the experimental results both from this paper and previous work in our laboratory.