Tuning of scleroglucan adsorption on carbonate surfaces via grafting alkyl side chains of different lengths: a theoretical and experimental study.

Abstract

The semi-flexible polysaccharide scleroglucan (Sclg) is a well-known viscosity modifier and its highly hydrophilic nature limits its utilization as a polymeric surfactant of high efficiency. Grafting hydrophobic alkyl moieties onto the chain backbone provides a convenient means to reduce the hydrophilicity of Sclg. Herein, by using a self-consistent field theory (SCFT) that considers both the semi-flexibility of the Sclg main chain and the presence of grafted alkyl chains, we study the influences of the grafted alkyl moieties with different lengths (C6, C10 or C18) on the adsorption behaviors of the resultant polymeric surfactants on a carbonate surface. The extended SCFT well predicts the experimentally observed side alkyl-length-, salt- and temperature-enhanced surface excess of the modified Sclgs. The accumulation profiles of the main chains of different modified Sclgs are nearly superimposable under each solution condition. However, increasing the alkyl-length enhances the accumulation of the adsorbed side-chain segments on the surfaces. Polymer/surface entropic repulsion forces and side-chain/surface interactions govern the adsorption behaviors in regions near the surface, while the adsorption behaviors far away from the surface are controlled by the side chain/side chain interactions. On the basis of conformation profiles of the directly adsorbed chains, a model depicting the effects of the alkyl-length on the adsorbed chain conformations is proposed. These combined theoretical/experimental results enable production of advanced bio-polymeric surfactants with wide tunability and high performance.