(148e) A Novel Technique to Characterize the Phenomena of Crystallization and Aggregation in a Suspension Settling in a Vertical Tube

Studies of dynamic processes like crystallization, nanoparticle synthesis, and particle-particle aggregation require accurate and instantaneous measurements of particle size distribution. Existing methods, like Dynamic Light Scattering (DLS), Dynamic Image Analysis (DIA), and Laser Diffraction, measure particle size distributions in static solutions, have to be carried out periodically, and are susceptible to sampling errors. We address the need for dynamic and in-situ measurements of particle size distribution using a combination of dynamic distribution of particles using static multiple light scattering and Stokes' law for particle settling using a population balance model.

In our experimental setup, particles are allowed to settle in a vial under gravity, and the fraction of incident light transmitted through the suspension is measured along the length of the vertical cell through which the particles settle (Turbiscan LAB, Formulaction make). The data is then modelled using the population balance model, which accounts for particle growth and adsorption coupled with settling, and also the variation of solute concentration in the continuous phase. The settling velocity of the particle depends on the diameter of the particle, while the transmitted intensity is a function of the particle volume fraction and the mean particle diameter. The model equations are solved by the method of characteristics matching the transmission wave profiles. By monitoring the change in the transmission profile over time, particle size distribution in a suspension can be obtained.

We have demonstrated this technique for systems undergoing the processes of crystallization and aggregation. During crystallization, nucleation and growth of particles increase the volume fraction and mean particle diameters, which are estimated by observing the settling profiles of the suspension, and an instantaneous particle size distribution is obtained. During aggregation, the particle sizes and densities change, which again influences the settling profiles of the suspension. We have studied the formation of calcium carbonate crystals and the role of polymers in modifying the growth and/or aggregation characteristics. Independently, to study the process of aggregation, we consider the aggregation of silica particles on cellulose particles and the influence of polymers on the adsorption of silica particles on cellulose.

This versatile technique can be used to analyse complex phenomena involving particle nucleation and growth and particle-particle interactions, without removing the sample from the reservoir.