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The coarsening of a polydisperse set of N particles is studied by computer simulation. The main steps of the simulation are the following:  generation of a set of N (typically 20 000) particles according to an a priori model of the particle size distribution, and subsequent transfers of molecules from one particle to another according to predetermined growth rules. As an application, we consider the Ostwald ripening process. In this case, the exchange of molecules between small and large particles is governed by Kelvin's equation. The evolution of the average particle radius and of the size distribution is studied both in the stationary and nonstationary regimes. The typical characteristics of the stationary regime predicted by the Lifshitz−Slyozov−Wagner theory are recovered. For a more realistic initial log-normal size distribution, it was found that during an increase in average radius of about a factor of 4.3, the stationary regime was not yet attained. Results are also reported for the combined effects of Ostwald ripening and membrane resistance.

The effect of sodium dodecyl benzenesulfonate (SDBS) surfactant micelles on the Ostwald ripening was investigated by several experiments and by computer simulation. The experimental ripening rates determined by dynamic light scattering were about 2 times higher than the one predicted by the Lifshitz-Slyozov-Wagner (LSW) theory. This increase is attributed to an increase of the concentration of oil molecules in the continuous phase. The increase in solubility and hence in ripening rates is predicted by Kelvin's equation, assuming the presence of small oil droplets of the size of the micelles. A study of the solubilization kinetics of emulsion oil droplets into micellar solutions confirms that the main rate-determining mechanism for the exchange of oil between droplets and micelles is molecular diffusion through the continuous phase. Finally the combination of the simulation of Ostwald ripening in the presence of an oil sink with the experimental monitoring of the ripening of emulsions to which continuously a micellar solution is added, confirms the previous model for the transport of oil. There is also evidence that the surfactant micelles are not in local equilibrium with the oil molecules.

The Ostwald ripening rate of several alkane in water emulsions stabilized by a nonionic surfactant is determined from dynamic light scattering (DLS) measurements. With the aid of computer simulations, the intensity weighted droplet radii obtained with DLS are converted to number averages, by taking the form of the droplet size distributionwhich evolves continuously toward a stationary distributioninto account. Thereby the effect of the transition from an initial, log-normal size distribution toward its stationary form is included. Second a model is proposed to account for the effect of the finite size of the surfactant layer (surrounding each oil droplet) on the measured particle size and thus on the ripening rate. It is found that both the effect of the transition from a nonstationary regime toward the stationary Lifshitz−Slyozov−Wagner regime and the effect of the finite size of the surfactant layer influence the ripening rates significantly.

SUMMARY Among a population of 75 hospitalised Parkinsonian subjects, confusional states were observed in 46% of demented patients not receiving anticholinergic drugs and in 93% of demented patients under anticholinergic therapy. The sensitivity of demented Parkinsonians to anticholinergic drugs can be attributed to a cholinergic deficiency which has been detected in the cortex and hippocampus of Parkinsonian patients post-mortem. The observations suggest that anticholinergic medication should be avoided in Parkinsonians with intellectual impairment.