Control of reactions between surfactant reagents in miniemulsions. Surface nanoreactors

Emulsions may be used to speed up reactions of surface-active reagents. In this paper, a theoretical analysis of a simple catalytic reaction (A + B → P + B) is performed, where the substrate A in the presence of the catalyst B in an emulsion is converted into the product P, and both the substrate A and the catalyst B are surfactants. It was shown that, because molecules A and B are concentrated in surface layers of the emulsion, these layers act as nanoreactors ensuring a significant acceleration of the catalytic reaction within a certain range of emulsion droplet sizes. The reaction rate depends significantly on the emulsion droplet’s size and there exists an optimal droplet size at which the reaction acceleration is maximal. If the product of the reaction is not surface-active, the reaction rate can remain practically unchanged up to virtually complete substrate conversion. Besides, it was shown that the Michaelis–Menten-type dependence of the reaction rate on the substrate concentration (i.e., the increase in the rate with subsequent saturation) can be observed in the system under consideration.