Studies of oil-in-water emulsion stability in the presence of new dicephalic saccharide-derived surfactants

Abstract

New nonionic surfactants, N-alkyl-[ N, N-bis(3-lactobionylamido)propyl] amine ( N-alkyl: C 12H 25, C 16H 33, C 18H 38) and a gemini surfactant containing cetyl chain were investigated as stabilizers for n-tetradecane/ethanol (0.5 or 1 M) emulsions. These are nontoxic substances and could be applied for pharmaceutical or dairy emulsion preparation. The dynamic light scattering technique was applied for determination of the average effective diameter and zeta potential of the droplets as a function of time up to two days. These parameters were determined subsequently on the same sample without any mixing of it. Depending on the surfactant concentration (10 −6, 10 −5 and 10 −4 M) and the emulsion pH, an increase or decrease in the droplet size was observed relative to the emulsion in the alcohol solution alone. It seems that the dynamic light scattering technique is a useful one for tracking changes in droplet size distribution in the emulsion systems. Some of the emulsions were more stable in the surfactant presence. However, in some other cases the surfactants destabilized emulsion. The zeta potentials in 10 −5 and 10 −4 M surfactant solutions were positive at pH natural (5–8) and acidic (pH 4) while at pH 11 they were negative. The isoelectric point of the emulsion droplets occurred in pH range 8–10, depending on the kind and concentration of the surfactant. It indicated that H + and OH − ions were potential determining via adsorbed on the oil surface the surfactant molecules. In surfactant-free emulsion, the zeta potentials of n-tetradecane droplets were negative in pH range 4–11. It was concluded that hydrogen bondings between surfactant/alcohol and alcohol/water polar groups played an essential role in the emulsion stabilization (the extended DLVO theory).