Emulsion and Wetting Films Stabilized by Hydrophobically Modified Inulin Polymeric Surfactant

Abstract

Emulsion films of hydrophobically modified inulin (INUTEC SP1) polymeric surfactant, both in aqueous solution and in the presence of different electrolyte (NaCl, Na2SO4, MgSO4) concentrations have been studied. At constant disjoining pressure of 36 Pa the film thickness h w decreased with increase in electrolyte concentration until a critical value, C el,cr, was reached above which h w remained constant. This reduction in film thickness below C el,cr could be accounted for by the compression of the double layer. At a critical pressure that depends on the electrolyte type, the film jumped to a Newton Black Film (NBF) that remained very stable up to very high disjoining pressure at all electrolyte concentrations and electrolyte types studied. The polyfructose loops and tails in this NBF remain strongly hydrated and these results explain the high stability against coalescence of such INUTEC SP1 emulsions. Wetting films from INUTEC SP1 aqueous solutions on a hydrophilic quartz substrate were also studied. The results showed a dependence of film thickness on INUTEC SP1 concentration which could be accounted for by the adsorption and orientation of the polymer molecules at the solid-liquid interface. At low INUTEC SP1 concentration, the molecule adsorbs with the hydrophilic loops and tails leaving the alkylchains in solution. However at higher concentration a bilayer of INUTEC SP1 molecules could be produced by hydrophobic interaction between the alkyl chains on the backbone of the polymer and this resulted in an increase of the film thickness at high concentration. The film thickness decreased with increasing electrolyte concentration at constant INUTEC SP1 concentration till a critical value was reached above which h w remained virtually constant. The reduction of h w could be accounted for by compression of the electrical double layer in accordance with the DLVO-theory.