Effect of formation of surface complex between hydroxypropylcellulose and sodium dodecylsulfate on dispersion/flocculation of O/W-type emulsion of soybean oil

Abstract

An O/W-type emulsion of soybean oil (theta v = 0.05) was prepared in the presence of various concentrations of hydroxypropylcellulose (HPC) and sodium dodecylsulfate (SDS). The mean diameter (d) of secondary particles of the oil droplets decreased with concentrations of SDS and HPC after attaining a maximum at [SDS] = 5 mmol/dm3 and [HPC] = 10(-3) g/dl, while the relative viscosity (eta rel) of the emulsion increased with an SDS concentration after attaining a minimum around 5 mmol/dl3 when the HPC concentration was kept constant. These facts were explained in terms of the formulation of a surface complex by hydrophobic interaction between SDS and HPC adsorbed on the surface of the droplets. When the concentration of SDS is low, it bridges between the HPC segments intra- and intermolecularly on and between the particles, resulting in shrinking of the HPC surface layers as well as in bridging among the particles. Therefore, the total volume of the secondary particles effective on eta rel decreases while the d-value increases with the SDS concentration. When the concentration becomes high, binding ratio of SDS to HPC also increases and the segments are repulsive each other owing to the negative charges given by the bound SDS. As a result, the adsorption layer swells and the secondary particles are redispersed. This fact causes an increase in eta rel and a decrease in d-value with a concentration of added SDS.