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The effect of surfactant type and temperature on the kinetics of the formation of platinum nanoparticles in water-in-oil microemulsions by chemical reduction of PtCl₆²⁻ were examined with time-resolved UV–vis absorption spectroscopy. The surfactants used were poly(ethylene glycol)monododecyl ethers (C₁₂E₄, C₁₂E₅, C₁₂E₆), sodium bis(2-ethylhexyl)sulphosuccinate (AOT), and mixtures of the alcohol ethoxylates and AOT. The oil domain was n-heptane. The microemulsion droplet size was measured by a dynamic light scattering technique (photon correlation spectroscopy) and the final platinum particle size was determined by transmission electron microscopy. The reaction rate for platinum particle formation was approximately the same in microemulsions based on either of the alcohol ethoxylates but considerably lower for microemulsions based on AOT. In microemulsions based on mixtures of an alcohol …