The umbrella term for these innovative applications is ICL—ionic and capacitive laminate, which identifies a class of soft ionically conductive laminates that have the best qualities of an electromechanical actuator and a flexible energy-storage unit. A group of researchers at the University of Tartu Institute of Technology introduced the term in their publication.
Of course, the term itself is not the main knowledge gained from the research. They introduce how the incorporation of textile enables scaling up the manufacturing process. Friedrich Kaasik, PhD student of engineering and technology at the University of Tartu, said that researching mass production possibilities is important to insure that the actuators get exactly the same characteristics. “The currently available manufacturing methods could not be easily automated, they are relatively complex, which reflects in their poor repeatability, and often rely on prohibitively expensive materials. This way, every piece can act differently,” he added.
Help from the Embroidery Frame
Regarding the potential applications, a practical ICL manufacturing process must be reproducible and scalable, and preferably should not rely on prohibitively costly materials. To date, any method used has had its advantages and disadvantages, but now Kaasik and his colleagues report on an improved process that is not limited to laboratory-scale batches and can produce ICLs in a quantity and size suitable for industrial manufacturing.
They used a thin inelastic electrically nonconductive reinforcement grid, which was tautened to form an appropriate level of support, a thin woven fiberglass mesh as the reinforcement grid and an embroidery frame as the support.
“Instead of using fabric electrodes, we have formed an ICL with a fabric-incorporated separator: the newly-developed ICL is formed layer-by-layer on the sides of a fibrous woven substrate. The fibrous substrate is under tension in a fixed position that prevents the swelling of the material in the axial direction during production, thus providing a pathway to fabricate ICL actuators using a continuous process,” Kaasik explained.
He added that the presence of a non-stretchable reinforcement layer offers a significant benefit in comparison with the previous Direct Assembly Process (DAP) fabrication technique (it involved spray-coating the electrodes on a free-standing cast membrane), as the extensive swelling of the membrane during the application of the subsequent electrode layers can result in a mechanical failure of the membrane.
The new fabrication procedure allows to produce electroactive laminates with outstanding uniformity in thickness and areal capacitance (standard deviations at 95% confidence interval are 9.2% and 9.4%, respectively) and with a lifetime of more than ten thousand cycles.
In conclusion, Kaasik said that the research shows this method has a prospect of being developed into an industrial process involving roll-to-roll processing, which in turn opens up new possibilities for fabricating textile-incorporated ICLs for applications, including actuators, sensors and energy-storage units.
One of them also works at the Institute of Chemistry (University of Tartu) and another at the Center for Micro-BioRobotics, Istituto Italiano di Tecnologia in Pontedera, Italy.
Kaasik, F., Must, I., Baranova, I., Põldsalu, I., Lust, E., Johanson, U., Punning, A. & Aabloo, A. (2017) Scalable fabrication of ionic and capacitive laminate actuators for soft robotics. Sensors and Actuators B: Chemical Volume 246, pages 154–163. http://dx.doi.org/10.1016/j.snb.2017.02.065
This article was funded by the European Regional Development Fund through Estonian Research Council.