Enhanced crystallisation of isonicotinamide under strong non-uniform DC electric fields

An electric field is reported to have an influence on protein nucleation, growth and crystal quality. To prevent the electrolysis of water relatively weak electric fields are used. Stronger fields can be used in isolator solvents such as dioxane using small organic compounds that resist electrolysis. It has been found that strong inhomogeneous electric fields result in peculiar particle mobility behaviour in suspensions.1 In this contribution we build on this and investigate the effect of a strong electric field on the crystallization behaviour of small non-polar organic molecule systems from a supersaturated solution.

A crystallisation study of isonicotinamide in 1,4-dioxane in the presence and absence of a strong electrostatic field has been conducted. A potential difference of 9 kV applied between two copper electrodes at 1 cm distance immersed in a supersaturation solution promoted nucleation. In addition, isonicotinamide crystals were consistently first detected at the anode. In the presence of the field higher cloud points and smaller induction times were measured. The difference with respect to spontaneous nucleation was more pronounced at lower supersaturation ratios. Nucleation rates, quantitatively determined from nucleation probability measurements, showed a significant effect of the applied field on nucleation kinetics.

The mechanism of the enhancement of the nucleation due to the electric field is still unclear, although electromigration seems to be involved. Crystallisation induced at a specific electrode suggests that temporal and spatial control of crystallisation can be achieved by the use of electric fields.