Interphase Transport in a Salicylic Acid Emulsion

Abstract

Selected pairs of phases in the system, not in equilibrium, were brought into contact and the transport between them was evaluated from the changes in volumes with time. The results showed the rate determining factors to be the extremely slow absorption of compounds into the solid acid layer and of water into the surfactant inverse micellar solution. The former factor was referred to the protracted process of modifying the crystalline structure and the latter to the minute diffusion coefficient of the inverse micelles. In the same manner the contact between the lamellar phase liquid crystalline phase and a solid solution of the surfactant in the acid led to the formation of two inverse micellar solutions of different composition separated by a liquid crystalline layer instead of the expected aqueous liquid and one inverse micellar solution, which appeared first after significantly extended times. The equilibration was significantly retarded by the slow diffusion of acid molecules through one of the liquid layers.

Keywords:

• Emulsions
• evaporation
• liquid crystals
• phase diagrams
• skin lotions

Acknowledgements

This work was supported by the National Nature Science Foundation of China (No. 20633010 and 20773106).

Notes

Note. The compositions are marked in the diagram (Figure 9), and the density of SA (solid region) is considered as 1.440 and 1.35(I M and LC region) S is 0.946, W is 1.000. SA_s = composition at a′, Figure 8; SA_s(W)= SA solid solution in equilibrium with both water and inverse micellar solution; SA_sI = SA solid solution with maximum surfactant but no water; LX = inverse micellar solution in equilibrium with water and with SA solid solution; IM(MxW)= inverse micellar solution with maximum water content and LC = b′, Figure 8.