| Summary: | Research into the crystallisation of calcium carbonate traverses many disciplines, including chemistry, physics, biology and materials science. Control over the polymorph, hierarchical assembly, orientation, size and shape has been the focus of significant interest in developing new applications. Current synthetic techniques offer limited control over the crystallisation process and often require high temperatures and/or pressures and the use of organic additives and functionalised templates. Microfluidic systems offer superior control over reaction conditions when compared to traditional macroscale methods and hence provide an alternative approach for the synthesis of particles. Not surprisingly, the literature includes hundreds of papers reporting the microfluidic synthesis of nanomaterials. The control provided by microfluidics allows the arrest of a reaction at any particular time, which is hugely advantageous when studying the nucleation and crystallisation of such particles. Moreover, since most biochemical reactions occur in aqueous media, droplet-based microfluidic devices are excellent tools for the miniaturisation of reaction volumes and the simulation of natural or synthetic processes. In the first part of this thesis, custom built droplet-based microfluidic systems are applied to the study of the precipitation of calcium carbonate under highly controlled conditions. Reactions performed in pL-volume droplets dispersed within a continuous carrier fluid afford reproducible control over crystal polymorph, such that pure calcite, pure vaterite or a mixture of calcite and vaterite can be preferentially precipitated by varying the concentration of reagents. This contrasts with poor reaction control on the macroscale. In the second part of this thesis the early stages of the nucleation of amorphous calcium carbonate are studied in similar droplet-based formats. The precipitation of calcium carbonate is arrested at various time points, with a maximum residence time of 2 minutes, and amorphous calcium carbonate is analysed over different growth periods. Additionally, the effect of poly(styrene sulphonate) on the precipitation and growth of amorphous calcium carbonate is investigated. Results show that in the presence of polymer, calcium carbonate growth occurs by mesoscale assembly rather than by classical nucleation.
|
|---|
