Stabilization of water-in-octane nano-emulsion. II Enhanced by amphiphilic graft copolymers based on poly (higher α-olefin)- graft-poly(ethylene glycol)

Abstract

Previously water-in-octane nano-emulsions were prepared by mixed surfactant systems. In this paper, a series of amphiphilic graft copolymers, namely poly (higher α-olefin- co- para-methylstyrene)- graft-poly(ethylene glycol) and poly (higher α-olefin- co-acrylic acid)- graft-poly(ethylene glycol), were used as additives to enhance the stability of these nano-emulsions. Although the amphiphilic graft copolymers did not impact the average diameter of the water droplets in these emulsions to a major extent, the stability of these emulsions were enhanced significantly by the interaction between surfactants and amphiphilic graft copolymers. Amphiphilic graft copolymers’ stabilizing capability depends on their chain structure and composition. In a proper range of poly(ethylene glycol) content, e.g. 6.0–34.0 wt.%, the higher the poly(ethylene glycol) content, the higher the stabilizing capability of these amphiphilic graft copolymers. However, when amphiphilic graft copolymers contained too much poly(ethylene glycol), e.g. 64.8 wt.%, their stabilizing capability dropped because of insufficient amphiphilic character. Furthermore, when amphiphilic graft copolymers had the same content of poly(ethylene glycol), their stabilizing capability increased as the carbon number of higher α-olefin increased. The most stable water-in-octane nano-emulsion could be stored for 86 days at 25 °C. At elevated temperature, e.g. 40 °C, this emulsion could be stored for 8 days. Under the influence of a centrifugal force, this emulsion could still exist for 210 min at the rotational speed of 15,000 rpm.