Physical characterization of multiple emulsions formulated with a green solvent and different HLB block copolymers

This paper reports a physical characterization of multiple emulsions formulated with a green solvent (2-ethylhexyl lactate) and different HLB amphiphilic block copolymers (Atlas™ G-5000 and Atlox™ 4912), as emulsifiers. 15 wt% 2-ethylhexyl lactate emulsions stabilized by a 1:1 mass ratio of both copolymers were prepared with different copolymer concentrations in one single emulsification step, using a rotor-stator emulsification device. Multiple emulsions were characterized by means of electrolytic conductivity measurements, viscosity, optical microscopy, laser diffraction and multiple light scattering techniques. W/O/W emulsions were obtained in all cases, regardless of the copolymer composition used. All emulsions showed Newtonian behaviour and relatively low viscosity values (2–2.6 times the viscosity of water at 20 °C). Viscosity hardly increased with the overall copolymer concentration. The mean Sauter diameter of O/W globules increased with copolymer concentration, while the evolution of the volumetric mean diameter depended on the occurrence of some recoalescence. The onset of different simultaneous destabilization mechanisms was detected by multiple light scattering. Even though creaming was the predominant destabilization mechanism, a separated layer of oil phase due to coalescence was also observed in most cases after a long aging time. The destabilization kinetics was slowed down by increasing the total copolymer concentration when both types of copolymers were used.