Kinetics and mechanism of formation of quantum-sized cadmium sulphide particles in water–aerosol-OT–oil microemulsions

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Abstract
Quantum-sized cadmium sulphide particles have been prepared in water-in-oil microemulsions stabilised by Aerosol-OT. The equilibrium particle size has been varied by changing the droplet size of the parent microemulsion in which the particles are prepared. The UV–VIS spectrum of such particles is sensitive to particle size and hence the kinetics of particle growth can be readily followed using UV–VIS spectrophotometric detection. Using the stopped-flow method, particle growth has been monitored at 280 nm as a function of droplet size, temperature and the nature of the oil phase. The rates are consistent with inter-droplet exchange of solubilizates being the rate-determining step. The apparent activation enthalpies calculated for the growth process agree well with those previously found for the exchange of small ions between microemulsion droplets. To interpret the kinetics, a relatively simple model is proposed based on the rapid coagulation mechanism first proposed by Smoluchowski. In the treatment the usual diffusion-controlled rate constant is replaced with the rate constant for inter-droplet communication.

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