Application of different techniques in the determination of xanthan gum-SDS and xanthan gum-Tween 80 interaction

Polymer - surfactant aqueous systems are important for a variety of industrial applications. The properties of those systems among other depend on the interactions between them. The aim of this work was to determine interactions between anionic polymer - xanthan gum and anionic surfactant - SDS or nonionic surfactant - Tween 80. In order to get better insight into the occurrence and possible mechanism of interactions several techniques were used such as FTIR, viscometry, conductometry, tensiometry, fluorimetry as well as SEM analysis. The results obtained by the combination of all those techniques showed that xanthan gum - SDS/Tween 80 interactions existed. Structural changes of xanthan gum molecules in presence of both surfactants were obtained by viscometry and SEM. The characteristic interaction points (CAC and PSP) were determined by measuring surface tension and specific conductance of pure surfactant aqueous solutions and their mixtures with xanthan gum. The values of PSP were proportional to the polymer concentration. After overcoming electrostatic repulsion between xanthan gum and SDS, they form complexes through hydrophobic mechanism and enhance adsorption of SDS molecules at the water - air interface. Unlike SDS, Tween 80 mainly interacts with xanthan gum in the bulk creating hydrogen bonds as well as by hydrophobic interactions. The results of fluorescence measurements expressed as I-1/I-3 ratio additionally confirmed that the mechanism of interactions between xanthan gum and examined surfactants was mainly through hydrophobic interaction and by creation the hydrogen bonds with Tween 80 as through electrostatic repulsion with SDS.