Species Transport via Ping-Pong Droplets

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The project aims at studying the transport of dissolved/suspended species through transient liquid pores. The transient pores are formed when an aqueous droplet meets an aqueous reservoir, driven by an electric field. For large enough values of the electric field strength, a submicron-diameter liquid pore is formed, i.e. a liquid bridge connecting the droplet and the reservoir. After that, the droplet bounces back. Three classes of dissolved/suspended species will be considered: small molecules, nanoparticles and polyelectrolytes. The droplet and species dynamics will be studied using high-speed videomicroscopy and fluorescence microscopy. The focus will be on the role of the liquid pores as transient sieves. In that context, first the spatio-temporal evolution of the liquid pores will be investigated. One important goal is to identify and understand the main mechanisms of passage of the dissolved/suspended species through the liquid pores. The influence of the main control parameters (for example the voltage and the viscosity of the oil phase) will be examined, with the aim to identify especially favorable regions in the parameter space for species separation. In this context, to what extent the lifetime and diameter of the pore can be controlled will be especially studied. It is expected that particularly favorable regimes for species separation are found when the lifetime of the pore is of the same order of magnitude as characteristic timescales of the dissolved/suspended species, for example the diffusion time of small molecules of the relaxation time of polyelectrolytes. Many of these tasks will be performed in close collaboration with subprojects B2 and B4. It is expected that the exploration of transient effects will add a very promising new perspective to liquid gating technology, which so far is mainly based on quasi-stationary liquid pores.