Sensing solvents with ultra-sensitive porous poly(ionic liquid)   actuators
  We introduced a new concept for fabricating solvent stimulus polymer actuators with unprecedented sensitivity and accuracy. This was accomplished by integrating porous architectures and electrostatic complexation gradients in a poly(ionic liquid) membrane that bears ionic liquid species for solvent sorption. In contact with 1.5 mol% of acetone molecules in water, the actuator membrane (1 mm x 20 mm x 30 um) bent into a closed loop. While the interaction between solvents and the polymer drives the actuation, the continuous gradient in complexation degree combined with the porous architecture optimizes the actuation, giving it a high sensitivity and even the ability to discriminate butanol solvent isomers. The membrane is also capable of cooperative actuation. The design concept is easy to implement and applicable to other polyelectrolyte systems, which substantially underpins their potentials in smart and sensitive signaling microrobotics/devices. 
Qiang Zhao, Jan Heyda, Joachim Dzubiella, Karoline T\"auber, John W.C.   Dunlop and Jiayin Yuan
cond-mat.soft cond-mat.mtrl-sci