Adsorption of anionic surfactant Na-dodecylsulphate (SDS) at the polyvinylpyrrolidone (PVP)-modified Na-montmorillonite surface

Abstract

An enhanced adsorption of Na-dodecylsulphate (SDS) at Namontmorillonite is observed through a specific binding to an adsorbed layer of nonionic polyvinylpyrrolidone (PVP) polymer. These results are supported by electrokinetic measurements and the fluorescence pyrene probe method. At high PVP loadings, a negative electrophoretic mobility increase and the fluorescence detection of PVP/SDS aggregates confirm that a PVP coiled structure promotes the interactions with anionic SDS molecules outside the range of electrostatic repulsion forces arising from the negatively charged montmorillonite surface.

Polyvinylpyrrolidone Adsorption on Na-Montmorillonite. Effect of the Polymer Interfacial Conformation on the Colloidal Behavior and Binding of Chemicals

“…Taking 0.92 nm as the crystallographic basal spacing of sodium montmorillonite, an expansion of the interlayer space by 1.5 nm is calculated between the montmorillonite layers, which can be related to the collapse of the adsorbed PVP structure after the drying step. This may represent a mean thickness of interpenetrating buckled polymer chains of a bimolecular layer size because the molecular thickness of the PVP monomer is 0.56 nm (18,19,23,27).…”

“…Thus, the binding of SDS at the PVP-loaded montmorillonite can a priori be used to measure the adsorbed PVP extent at the sodium montmorillonite surface. Indeed, the interaction of SDS with the bare sodium montmorillonite is negligible (24,63) due to the electrostatic anion exclusion at the negatively charged basal plates (64) that make up at least 95% of the total surface area (14). Evidence for a SDS adsorption at the edge surface has only been provided by microelectrophoresis (24).…”

“…Other methods have also been used to confirm more qualitatively the extent of SDS binding and the aggregate structure of the SDS/PVP complex at PVP loadings higher than 0.30 g PVP/g. Thus, the specific binding of SDS, an organic anion, can be detected by an increase of the negative electrophoretic mobility of the PVPloaded montmorillonite (24,27). On the other hand, the hydrophobic nature of the SDS/PVP complex (24,27) has also been investigated by the fluorescence pyrene technique.…”

“…This result implies that the adsorbed PVP structure at a low PVP loading is not accessible to an SDS binding. The binding sites are in the anion exclusion volume at the surface as discussed elsewhere (24). They can also be blocked through direct contact with the montmorillonite surface.…”

“…Adsorption behavior at negatively charged clay minerals shows that the adsorption is driven by the nonionic character of PVP, a much higher adsorbed amount being found than in the case of anionic polycarboxylic derivates (14,26,(40)(41)(42). In the case of adsorption on sodium montmorillonite, a swelling smectite, X-ray diffraction studies of dry samples have shown that the collapsed structure of the polymer is intercalated between montmorillonite plates, forming a quasi-crystalline structure (18,19,23). It must be noted that such materials have been recently investigated (20,21), such as polymer layer silicate (PLS) nanocomposite (43).…”