Electrotactic ionic liquid droplets
Francis, Wayne and Wagner, Klaudia and Beirne, Stephen and Officer, David and Wallace, Gordon and Florea, Larisa and Diamond, Dermot (2016) Electrotactic ionic liquid droplets. Sensors and Actuators B: Chemical, 239 . pp. 1069-1075. ISSN 0924-4247
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To our knowledge, this work describes the first example of electro-guided, self-propelled droplets composed solely of an ionic liquid (IL), namely trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These self-propelled droplets travel along an aqueous-air boundary to desired destinations within the fluidic network. Electrotactic movement of the droplets is due to asymmetric electro-stimulated release of a constituent of the IL droplet, the [P6,6,6,14]+ ion, which is a very efficient cationic surfactant, through electrochemically generated Cl- gradients. The direction and speed of movement can be controlled by switching the impressed voltage (typically 5 - 9V) ON or OFF, and by changing the polarity of the electrodes in contact with the electrolyte solution.
The Cl- gradients required for droplet movement are electrochemically generated using 3D printed electrodes which are embedded within the fluidic channels. On demand creation of these Cl- gradients electrochemically allows reversible droplet movement over expended periods of time, and provides a means for precise control over the droplet trajectory.
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