The structure of gel-emulsions in a water/ nonionic surfactant/oil system

Abstract

Gel formation in an oil-rich region was studied in water/nonionic surfactant/oil systems. The gel consists of an aqueous micellar solution phase and excess oil phase. It is necessary that the surfactant is hydrophilic enough to produce gels in an oil-rich region. This result is opposite to that of gels in a water-rich region; a surfactant must be lipophilic to form the gel. The structures of both types of gels were determined by VEM (video enhanced microscopy). Gels in water-rich regions are W/O type whereas those in oil-rich regions are O/W type concentrated emulsions. The shape of droplets is not spherical but polyhedral because the volume fraction of the internal phase exceeds the limiting value of close packing of undistorted spheres. The effect of temperature on the stability of the O/W gel (in an oil-rich region) was also investigated in a water/R 12EO 8/ hexadecane system by VEM. With an increase in temperature, the coalescence of droplets in the gel is started at a temperature about 25–30°C lower than HLB temperature. It is considered that this phenomenon is related to the stability of ordinary O/W type emulsions in nonionic surfactant systems.