Influence of surfactants on the structure of the adsorption layer in the system: Carboxymethylcellulose/alumina

The influence of surfactants: anionic SDS, nonionic Triton-100 and their mixture (SDS/TX-100) on the structure of the adsorption layer in the system: carboxymethylcellulose (CMC)/alumina (Al2O3) was measured. The surface charge density of alumina and its zeta potential were determined in the presence of the CMC macromolecules and the surfactant particles. In order to gain more information about the structure of adsorption layer the amount of CMC adsorption in the presence of surfactants as well as the thickness of the CMC adsorption layer were determined. It was proved that in the presence of surfactants mixture (SDS/TX-100) the amount of adsorption of CMC is the highest and the obtained adsorption layer is the thickest. On the other hand, when Triton X-100 is added to the measured system the polysaccharide conformation is closely packed. The amount of adsorption is large but the thickness of the adsorption layer is relatively low. In the presence of SDS macromolecules of CMC form conformation expanded towards the bulk solution. Such a conformation is characterized by the smaller amount of adsorption of polymer but the larger thickness of the adsorption layer.

Research highlights
► The presence of SDS, Triton X-100 and their mixture causes the decrease of the surface charge density of Al2O3 and also the shift of pHpzc point to lower pH values. The main reason for that is the presence of the negatively charged groups not linked with the surface but present in the compact surface layer of Al2O3
► The presence of CMC and surfactants causes the decrease of the zeta potential of Al2O3. This phenomenon comes from two effects a shift of the slipping plane towards the bulk solution by an adsorbing polymer or a polymer–surfactant complex and the presence of negatively charged groups in the diffused part of electric double layer.
► The addition of surfactants (SDS, Triton X-100 and their mixture) to the adsorption system strongly influences the amount of adsorption of carboxymethylcellulose on Al2O3 surface. The smallest values were observed in the presence of SDS, larger in the presence of Triton X-100 and the largest in the presence of SDS/Triton X-100.
► When Triton X-100 is added to the system: CMC/Al2O3 polymer conformation is full of closely packed macromolecules. The amount of adsorption is large but thickness of adsorption layer is small.
► In the presence of SDS macromolecules of CMC form conformation expanded towards the bulk solution. Such a conformation results in small amount of adsorption and large thickness of adsorption layer.