2. Oversaturation control

By manipulating fluids on a small scale, we can precisely and locally control the concentrations of species in solution, and thus the supersaturation of the solute to be crystallized. The choice of how to generate supersaturation (defined as the ratio between the activity of the solute in solution and its activity at equilibrium) is based, as in the case of macroscopic crystallization reactors, on the evolution of the product's solubility curve as a function of one or more physico-chemical parameters (pH, pressure, temperature, ionic strength, etc.). Three main methods are commonly used to generate supersaturation within droplets: crystallization by chemical reaction, addition of an antisolvent and thermal crystallization by temperature change or evaporation of the solution.

• In the case of reactive crystallization, two drops of solutions containing...