(6c) Effects of Temperature Cycling on Crystallization in Surfactant-Free Monodisperse Emulsions

Solution crystallization from surfactant free, monodisperse emulsions was investigated as a method from producing lactose crystals of a narrow crystal size distribution (CSD). In a monodisperse population of drops there is a maximum crystal size that depends on the initial drop size and supersaturation. Under conditions where each drop produces one crystal and the drops reach saturation a narrow crystal size distribution near this maximum size will be produced. Crystallization experiments were carried out using a microfluidic T-junction to form uniform drops followed by a plug-flow crystallizer to prevent drop coalescence. Due to the stochastic nature of primary nucleation the number of crystals per drop is not constant over the entire drop population. Isothermal monodisperse emulsion crystallization has been demonstrated to be capable of producing crystals with a coefficient of variation of crystal size as low as 14%, with 43% of drops containing a single crystal. The narrowest CSD is obtained when the fraction of drops containing only one crystal is highest.

To increase the fraction of drops containing single crystals and further narrow the CSD a temperature cycling treatment is applied to the drop population following the initial isothermal crystallization. The crystallizer temperature is first increased to dissolve small crystals then decreased to grow the remaining crystal(s). The effects of dissolution and growth temperatures, cycle times and the number of temperature cycles on the CSD and number of crystals per drop are reported. The CSD in the temperature cycled drops is compared to the CSDs obtained from isothermal monodisperse emulsion crystallization and bulk crystallization.