Rheological properties and structures of cationic surfactants and fatty alcohol emulsions: effect of surfactant chain length and concentration

Rheological and optical propel ties of cetyltrimethylammonium chloride (CTA C)/fatty alcohol (FA), behenyltrimethylammonium chloride (BTAC)/FA and CTAC / FA/hydroxyethyl cellulose (HEC) emulsions have been studied with particul ar emphases on the effects of FA content, the difference in the chain lengt h of the hydrophobic groups between CTAC and BTAC, and the addition of a wa ter soluble polymer, HEC. The effects of the FA content are to accelerate t he structure development during the aging period and to increase the storag e modulus, the yield stress, and the zero-shear-rate viscosity in the three emulsion systems investigated. At a low FA content of 2% w/w, lamellar and vesicular aggregates and isolated multilamellar vesicles can be observed i n the CTAC/FA and BTAC/FA emulsions, respectively. At a high FA content of 6% w/w or with an excess of FA present, networklike structures and sunflowe r-like structures form, respectively, instead, inducing a higher entangleme nt storage modulus and a higher yield stress relative to those emulsions wi th a low FA content. The effect of adding HEC to the CTAC/ FA emulsion is t o reduce the entanglement storage modulus and the yield stress, consistent with the optical observation that the presence of the polymer disrupts the formations of lamella and vesicular aggregates and network structures.