Osmotic swelling behavior of globules of W/O/W emulsion liquid membranes

Abstract

The osmotic swelling behavior of water-in-oil-in-water (W/O/W) type emulsion liquid membranes (ELMs) was investigated. Using an optical microscope equipped with a camera, the changes in the size of the W/O/W globules were monitored over a long period of time (up to about 4 h). The osmotic pressure gradient between the internal and external aqueous phases was induced by creating a concentration difference of d-glucose between the two aqueous phases. The results indicate that the swelling ratio, defined as the ratio of globule diameter at time t to globule diameter at t=0, decreases with the increase in ϕ W/O(0) (initial volume fraction of internal aqueous phase droplets). The swelling ratio generally increases with the increase in the concentration of surfactant present in the membrane (oil) phase. The permeation coefficient of water also increases with the increase in the surfactant concentration. With the increase in ϕ W/O(0) up to about 0.42, the permeation coefficient decreases only slightly. However, with further increase in ϕ W/O(0), a sharp reduction in the permeation coefficient occurs. The mechanism of water transfer in ELMs of the present work is reasoned to be the diffusion of hydrated surfactants.