Zeta potential and effective diameter of n-tetradecane emulsions in n-propanol solutions and in the presence of lysozyme

Abstract

Zeta potentials and effective diameters of the emulsions were studied using a ZetaPlus instrument (Brookhaven Co.). The emulsions were prepared by dissolving 0.1 ml of n-tetradecane in n-propanol and then deionized water or lysozyme solution was added to obtain the emulsion. The effective diameters and zeta potentials were determined after 5, 15, 30, 60, 120 min, and 1 and 2 days after preparation. Both types of emulsions, in the presence and absence of the lysozyme, were stable over the time period studied. An increase in the effective droplet diameter was observed in the presence of lysozyme in 1 M n-propanol solutions and at pH 4 and 6.8 (natural). The higher the concentration of propanol, the higher the effective diameter of the microdroplets. In the absence of lysozyme the zeta potentials were negative at the various alcohol concentrations and pHs studied. However, in the presence of lysozyme, and at pH 4 and 6.6, positive zeta potentials were found. As the sign of the zeta potential is not important for the stability of the emulsion, but rather its absolute value, the reversal in sign did not affect the effective diameter of the microdroplets. Possible mechanisms for the zeta potential changes and interfacial interactions are discussed.