Electrodiffusion Method of Near-Wall Flow Diagnostics in Microfluidic Systems

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The electrodiffusion technique has been mostly used for the near-wall flow diagnostics on large scales. A novel technique for fabrication of plastic microfluidic systems with integrated metal microelectrodes (called technique of sacrificed substrate) enables us to produce microfluidic devices with precisely shaped sensors for wall shear stress measurements. Several micrometer thick gold sensors built-in a plastic substrate exhibit good mechanical resistance and smoothness. Proper functioning of prepared chips with microsensors has been first tested in various calibration experiments (polarization curve, sensor response to polarization set-up, steady flow calibration, temperature dependence of diffusivity). Our first results obtained for separating/reattaching flow behind a backward-facing step and for gas-liquid Taylor flow in microchannels then demonstrate its applicability for the detection of near-wall flow reversal, the delimitation of flow-recirculation zones, and the determination of wall shear stress response to moving bubbles. Other applications of these sensors in microfluidics (e.g. characterization of liquid films, capillary waves, bubbles or drops) can be also envisaged