Physical characterisation of the geometry and microfluidic flow within microreactors
We have investigated the physical properties of glass microreactors. These devices contain a network of micron-sized channels and have application in chemical synthesis. To perform chemical reactions in a micro reactor one requires an understanding of the microfluidics involved and this has been studied here. A 3D profiling method has been developed to determine the internal micro reactor channel dimensions to an accuracy of a few microns. This technique is based on optical imaging of a dye filled channel network. Its advantages over existing profiling techniques include that it is rapid, non-destructive and capable of profiling the covered interior channels. A model has been developed to predict the voltage- (electroosmotic) and pressure-driven flows of different solvent systems in micro reactor channels with known geometries, from measured electrical currents and driving voltages applied to the electrodes situated in each reservoir. The model was validated usmg extensive experimental measurements of these variables for chips of different channel dimensions, to a level of experimental uncertainty of approximately 20 %. The model provides a useful quantitative tool, which enables the design of channel network dimensions required to achieve a desired set of flow characteristics prior to fabrication. In the final investigation, we set out to understand the effects of voltage-driven mobilisation of charged and uncharged dye species and colloidal particles in a micro reactor channel. Using absorbance-imaging to monitor the dye front velocities it was possible to determine: (1) a channel surface-solvent interface zeta potential and hence, characterise the flow properties of the solvent system and (2) calculate the diffusion coefficient for the charged dye species in the solvent. For the colloid sample with a Gaussian particle size distribution, a range of different velocities and mobilities were observed.