Stretchy Ionogels For Soft Machines

Some engineers want to ditch hard metals and plastics and instead use flexible materials to make wearable sensors or to build robots that can deform to squeeze through tight spaces. An international research team has now demonstrated that ionogels—polymeric gels that contain an ionic liquid—could serve as transparent, stretchable conductors in such devices (ACS Appl. Mater. Interfaces 2014, DOI: 10.1021/am501130t). Zhigang Suo of Harvard University; Yong Mei Chen of Xi’an Jiaotong University, in China; and colleagues made an ionogel using acrylic acid, poly(ethylene glycol) diacrylate, and ketoglutaric acid in the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate. To test the ionogel’s properties, the team built a simple actuator based on an elastic polymer that changes shape in response to an applied voltage. The researchers stretched the polymer over a plastic frame and then attached circular sheets of ionogel to the top and bottom of the polymer. When they applied a voltage, the ionogel stretched with the polymer up to 4.6 times its original length without breaking. The sturdy ionogel could also stretch and relax for at least 1 million cycles without failing.