Use of microemulsions as liquid membranes. Improved kinetics of solute transfer at interfaces

Abstract

When the volume fraction occupied by the dispersed phase of a microemulsion is small, the microglobules making up this dispersed phase can be viewed as mobile carriers permitting the transport of substances which are either insoluble or very poorly soluble in the continuous phase. In this paper water-in-oil microemulsions composed of decane, water, tetraethyleneglycol dodecylether (TEGDE) and hexan-1-ol are used as liquid membranes and the microglobules are shown to transport alkali-metal picrates between two aqueous phases. The effect of changing the initial picrate concentration in the source compartment has been investigated and the resulting flux can be adequately described by a classical model of facilitated transport (fast transfer and ‘chemical reaction’ coupled with slow diffusion), as has been observed previously for the transport of lipophilic substances by oil-in-water microemulsions.

The presence of dicyclohexano-18-crown-6 (DC18C6) in the liquid membrane brings about an increase in the flux of alkali-metal picrates. At optimum conditions, the transport of K⁺ picrate by the microemulsion alone is 5.1 times faster than with DC18C6 in pure decane, but it is 12.6 times faster when DC18C6 is added to the microemulsion. Although drastically reduced, selectivity for ion transport still exists in the latter situation.