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Transient drop size distributions in a batch stirred tank were measured by a laser diffraction technique. Ita short measuring time permitted on-line analysis with minimal possible instrumental, sampling, and dispersion errors. Comparison with the previously used photographic technique showed increased sensitivity in measuring the small diameter drops. In this study, the effecta of temperature and impeller speed were investigated for a system of 1% styrene in water stabilized with 0.1 g/L poly(viny1 alcohol) (PVA) as a suspending agent. The system assumed characteristic bimodal distributions within a very short time. Further stirring only reduced the drop sizes without substantially affecting the shape of their distribution. Increasing the agitation rate caused a shift of both peake to smaller diameters since higher turbulence intensity is more effective in breaking the drops. An increase in temperature resulted in a size reduction and narrowing of the large-size peak of the distribution. Finally, the minimum time required for the system to reach steady state at different conditions was found to depend on the Weber number of the main flow. An increase of agitation rate or a decrease of interfacial tension caused a reduction of the minimum transition time, thus allowing the system to approach equilibrium much faster.

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SYNOPSISOil-containing poly(viny1 alcohol) (PVA) microcapsules in the size range of 5-20 pm were prepared by the simple coacervation of PVA followed by chemical crosslinking of the coacervated PVA membrane with glutaraldehyde. Coacervation of the aqueous polymer solution was achieved by the addition of a phase separation inducer (e.g., sodium sulfate). PVA of different grades (e.g., molecular weight and degree of hydrolysis) was utilized both as stabilizer and wall-forming material. Dispersion of the oil phase in the aqueous PVA solution was effected by a homogenizer. The effects of the various process parameters, such as the agitation speed, the type and concentration of PVA, the volume ratio of the internal oil phase to the external aqueous phase, the viscosity of the oil phase as well as the electrolyte concentration in the aqueous solution, on the stability and the size distribution of the emulsion droplets and microcapsules were experimentally investigated. It was shown that high agitation rates and low interfacial tension (e.g., high PVA concentrations) resulted in a significant reduction of the size of the emulsion droplets and microcapsules. On the other hand, as the viscosity and the amount of the dispersed oil phase increased, the capsule size increased. Finally, it was found that the concentration of the electrolyte significantly affected the stability of the (o/w) emulsion, the size and concentration of coacervated PVA colloidal aggregates, as well as the morphology of the polymer wall membrane formed by the adsorption of the polymer-rich phase to the oil/water interface.