ARTICLE Received 19 Mar 2013 | Accepted 1 Jul 2013 | Published 30 Jul 2013 Fast low-voltage electroactive actuators using nanostructured polymer electrolytes Onnuri Kim 1 , Tae Joo Shin 2 & Moon Jeong Park 1,3 Electroactive actuators have received enormous interest for a variety of biomimetic techno- logies ranging from robotics and microsensors to artificial muscles. Major challenges towards practically viable actuators are the achievement of large electromechanical deformation, fast switching response, low operating voltage and durable operation. Here we report a new electroactive actuator composed of self-assembled sulphonated block copolymers and ionic liquids. The new actuator demonstrated improvements in actuation properties over other polymer actuators reported earlier, large generated strain (up to 4%) without any signs of back relaxation. In particular, the millimetre-scale displacements obtained for the actuators, with rapid response (o1s) at sub-1-V conditions over 13,500 cycles in air, have not been previously reported in the literature. The key to success stems from the evolution of the unique hexagonal structure of the polymer layer with domain size gradients beneath the cathode during actuation, which promotes the bending motion of the actuators. DOI: 10.1038/ncomms3208 1 Division of Advanced Materials Science (WCU), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea. 2 Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea. 3 Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea. Correspondence and requests for materials should be addressed to M.J.P. (email: moonpark@postech.edu). NATURE COMMUNICATIONS | 4:2208 | DOI: 10.1038/ncomms3208 | www.nature.com/naturecommunications 1 & 2013 Macmillan Publishers Limited. All rights reserved.