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Microfluidic screening of potassium nitrate polymorphism

P. Laval, C. Giroux, J. Leng, J.-B. Salmon — J. Crystal Growth 310 (2008) 3121

23 juillet 2007

We developed a microfluidic device for the investigation of crystallization kinetics from solution. The device allows to store hundreds of about 100 nL droplets containing a given solute and to control their temperature within 0.1°C. Upon cooling, we observe independent and mononuclear crystallization events ; crystal dissolution occurs as the temperature is raised. For potassium nitrate (KNO3) in water, these thermal cycles reveal the existence of two concomitant polymorphic forms. We measure the solubility curves of each structure for the first time and define unambiguously the metastability extent of the solution. We describe why these results essentially stem from the miniaturized scale of the crystallization reactors.

Supplementary Material - 428.5 ko

Movie showing the nucleation of three crystals in droplets upon cooling (concentration 30 g of KNO3 in 100 g of water). Yellow circles indicate the positions of the forthcoming monuclear nucleation events. In the two top droplets, stable crystals (form II) nucleate and grow rapidly. In the bottom droplet, unstable form III nucleates and its growth is less rapid. Since the PDMS device is sealed on a silicon wafer, images are taken through a stereo-microscope in a reflection mode without polarizers.

version PDF - 759.4 ko