Swelling determination of W/O/W emulsion liquid membranes

Based on the definition of swelling in emulsion liquid membrane (ELM) process, the concepts of apparent swelling and actual swelling are proposed to illustrate the relationship between the emulsion swelling (the osmotic swelling and entrainment swelling) and the membrane breakage, focussing on the effect of the volume change caused by emulsion swelling and membrane breakage on the experimental results. Theoretical analyses indicate that "zero" or "negative" swelling may occur under certain experimental conditions. A bi-tracer method is further proposed and then used to measure the osmotic, entrainment swelling and the membrane breakage simultaneously, only requiring some initial operation conditions and measurements of concentrations of both tracers in the external and internal phases. It has been experimentally proved that this new method is highly applicable in ELM process and provides a useful tool to specify the effects of membrane breakage, osmotic swelling and entrainment swelling in the same experiment. "Negative" swelling may occur under certain operating conditions, particularly when the electrolyte concentration in the external phase is higher than that in the internal phase. The experimental results also indicate that the effect of membrane breakage on the measurement of emulsion swelling should not be neglected to avoid measurement error. Polymeric surfactant LMA is superior to other commercial surfactants as it imparts high membrane stability and small emulsion swelling. (C) 2002 Elsevier Science B.V. All rights reserved.