The interaction of cetyltrimethylammonium bromide and sodium dodecylbenzene sulfonate with polyvinyl alcohol. adsorption of the polymer—surfactant complexes on silica

Abstract

The interaction of cetyltrimethylammonium bromide (CTABr) and sodium dodecylbenzene sulfonate (NaDBS) with polyvinyl alcohol (PVA) (12% acetate groups, M ̄ v = 42,000 ) has been investigated using surface tension, viscosity, conductivity and cloud point measurements. The results showed that the polymer-surfactant “complex” behaves as an association polyelectrolyte. The adsorption of PVA, CTABr, NaDBS and “complexes” of CTABr + PVA and NaDBS + PVA on silica was studied in aqueous solution at low and high pH. The adsorption of PVA was higher at pH 3.6 than at pH 9.1, because at low pH there are more undissociated silanol groups which act as adsorption sites for PVA. CTA + ions are adsorbed at low pH (3.6) in a more or less vertically oriented layer. At high pH (9.1) a bilayer of CTA + ions form at the silica-solution interface. The adsorption of NaDBS was low, increasing as the pH was lowered, and the adsorption isotherms deviated from the Langmuir equation. In the presence of preadsorbed CTA + ions at high pH, the PVA adsorption increased significantly relative to the value in absence of surfactant. It is believed that the CTA + ions act as “anchors” between the dissociated -SiO − sites on the surface and PVA chains. At low pH, CTA + ions are adsorbed to a greater extent in presence of preadsorbed PVA. It is assumed that under these conditions PVA acts as the “anchor” between the undissociated SiOH groups and CTA + ions. On a silica surface with preadsorbed DBS − ions at low and high pH PVA is adsorbed to a greater extent than in the absence of DBS − ions, but to a lesser extent than in the presence of CTA + ions. The adsorption of DBS − ions on a silica surface with preadsorbed PVA at low pH is complex, especially at high PVA concentration.