Chemotactic and electrotactic self-propelled ionic liquid droplets

TL;DRAbstract

Herein we report the chemotactic and electrotactic self-propelled movement of droplets composed solely of an ionic liquid (IL), namely trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These IL droplets move spontaneously across the liquid/air interface and are guided to specific destinations within fluidic systems along Cl- concentration gradients. 
\nThe self-propelled movement of the droplet is due to the controlled release of the [P6,6,6,14]+, a very efficient cationic surfactant, which is a constituent of the IL droplet. The rate of [P6,6,6,14]+ release depends on the solubility of the closely associated Cl- anion in the surrounding media, as the formation of free [P6,6,6,14]+ in the aqueous phase depends on the local Cl- concentration at the IL-aqueous boundary. Therefore, in Cl- gradients there is an unsymmetrical release of surfactant into the solution, which in turn results in a surface tension gradient around the droplet. This leads to Marangoni like flows which

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