Precipitation of calcium surfactants. Part 2

Abstract

The kinetics of precipitation of calcium dodecyl and tetradecyl sulphate have been studied by stopped-flow spectrophotometry. Mie theory of light scattering was used to convert the absorbance, measured at two wavelengths, to degree of reaction and chronomal analysis indicated two possible rate-determining growth mechanisms. In the early stages of precipitation, diffusion in bulk solution was the rate-limiting process, whereas, in the later stages, it is more likely to be 1st order polynuclear growth. However, the approximations involved in the analysis lead to an underestimate of the total amount of precipitate expected being accounted for by this technique. Conductance was also applied to the precipitation of calcium dodecyl sulphate and analysis of the data agreed with the kinetic interpretation obtained from stopped-flow. In this case, > 85 % of the expected mass of precipitate was detected.