Investigating the Nucleation Kinetics of Calcium Carbonate Using a Zero-Water-Loss Microfluidic Chip

Characterization of nucleation processes is essential to the development of strategies to control crystallization in many industrial, atmospheric, biological, and geological environments. An effective route to studying nucleation processes is the use of large numbers of small, identical volumes, where these minimize the effects of impurities that can dominate in bulk solution and allow the stochastic nature of nucleation to be considered. Here, we present a multilayered microfluidic device for nucleation studies that can be used to carry out 10 »000 simultaneous reactions in identical microcavities, and 500 of them are used for investigating nucleation kinetics. Unlike droplet-based systems, no surfactants are required, and the presence of an integrated water reservoir prevents water loss, allowing studies to be performed for long durations. This device was used to study the nucleation of calcium carbonate in the presence and absence of magnesium ions. Two distinct nucleation rates of 286 cm^-3 s^-1 and 12.6 cm^-3 s^-1 were observed in the absence of magnesium, where the rapid rate likely derives from microcavities containing impurities. The nucleation rate was then significantly reduced in the presence of magnesium ions, and the profile was more complex. This device is therefore an ideal platform for studying slow nucleation processes in surfactant-free environments.