The precise manipulation of small amounts of liquids is a key-element in many scientific and technological processes involving physics, chemistry and biology. Digital microfluidics, where drops are individually controlled on open surfaces, has emerged as an alternative to the commonly used channel-based microfluidics. Current systems, such as electrowetting- and thermocapillary-based platforms, allow for adaptable droplet manipulation but they maintain the limiting need for external actuation devices (electrodes and heating elements).
An attractive option is to use light for droplet control, since optical stimulation is both remote and re-configurable, while offering high spatio-temporal resolution. This project aims at providing an inclusive digital optofluidic toolbox for on-demand droplet manipulation. An integrated investigation will be performed, going from fundamental physicochemical research on two different actuation mechanisms on liquid-liquid and liquid-solid interfaces, to the application of the acquired knowledge for new applications in chemistry. Regarding liquid-liquid systems, the host has recently discovered the chromocapillary effect and applied it for the first time to manipulate organic droplets on aqueous photosensitive surfactant solutions. A better comprehension of this partially understood effect will allow us to expand the range of digital optofluidic operations. I wish to achieve on-demand control of a large number of droplets for parallel/sequential chemical reactions using dynamic light patterns generated from a microprojector. For liquid-solid systems, I propose to explore and apply a new photothermal wetting mechanism for elementary fluidic operations (i.e. driving, scission, fusion) with water droplets on solids. It will be based on integrating thermoresponsive polymers on top of strongly adsorbing solids, where the temperature gradient generated by asymmetric irradiation will cause imbalanced capillary forces leading to drop motion.
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