Microfluidic Control of Nucleation and Growth of CaCO3

A novel method for studying nucleation and growth of CaCO3 crystals in situ has been developed and tested rigorously. We demonstrate that precise flow control is essential and how this is achieved. The method has the advantage that one may study single crystals of polymorphs that are thermodynamically unstable in collections of many crystals and that one obtains precise and accurate growth rates without any extra assumptions. We also demonstrate that, at low supersaturations where 2D nucleation does not occur, we measure the growth rate constant of calcite to be 5 times larger than that reported by batch methods and 2 orders of magnitude larger than that measured by atomic force microscopy. Considering the large interest in calcite growth in, for example, geoscience, environmental science, and industry, it is important to explain the discrepancy of growth rate constants between different methods. The method presented here can easily be applied to many other minerals.