Professor, Department of Applied Molecular Chemistry, College of Industrial Technology, Nihon University, Japan

Biography: Kazutoshi Harguchi was born in 1950 in Japan. He graduated from Kyushu University in 1973 and received his PhD from Kyushu University in 1978. He joined Kawamura Institute of Chemical Research (KICR) in 1978. He worked in Liverpool University, UK as a post-doctoral fellow in 1979-1981. He became a director of KICR in 2001, and a general manager (senior director) in 2006-2014. From April 2014, he is a professor of Nihon University. He was also a visiting professor of the University of Tokyo. He was a vice president of the Society of Polymer Science, Japan during 2016-2018. His major research fields are polymer nanocomposites, smart hydrogels, hybrid nanostructures, and biomaterials. He received the Award of the Society of Fiber Science and Technology, Japan in 2003, the Award of the Society of Polymer Science, Japan in 2010, and SPSJ Award for Outstanding Achievement in Polymer Science and Technology in 2018.

Speech Title: Large retractive tensile force generation in chemo-mechanical actuators system composed of nanocomposite gels

Abstract: Transparent chemo-mechanical systems that directly transform chemical energy into mechanical energy have attracted significant attention due to their simple structures and mechanical-power-generating efficiencies. These systems are utilized in many fields such as artificial muscles, soft robots, smart valves, sensors, and drug-release technology. The most important factor in constructing an effective soft actuator is the generation of sufficiently large mechanical force and/or deformation to meet the needs of the application, preferably with excellent responsiveness, reversibility, and repeatability. However, it is difficult for polymer hydrogel actuators to satisfy all requirements.

Herein, we report a new nanocomposite hydrogel (NC gel)/stimulus system capable of generating high mechanical forces comparable to human muscle.1 That is, the large mechanical forces were generated in muscle-like isometric actuator systems composed of stimuli-responsive NC gels and aqueous NaCl solutions. NC gels with poly(N-isopropylacrylamide)-clay (PNIPA-clay) network structures exhibit high mechanical toughnesses and reversible swelling/deswelling behavior.2 NC gels constrained to constant lengths in brine generate enhanced contractive forces due to the salt-induced coil-to-globule transitions that are more than ten times larger than those induced thermally.3 A retractive tensile force (4 N/170 kPa), comparable to that of human muscle, was repeatedly generated at 20 C using an appropriately composed NC gel, and by alternating the NaCl concentration between 0 and 5 M.1 This phenomenon is attributed to the combined effects of enhanced deswelling behavior resulting from the salt-induced coil-to-globule transition of PNIPA and the high stiffness of the deswollen gel due to the NaCl-strengthened PNIPA-clay network.

References
1) K. Haraguchi, Y. Kimura, S. Shimizu, Soft Matter, 14, 927-933 (2018).
2) K. Haraguchi, Polym. J, 43, 223-241 (2011).
3) K. Haraguchi, S. Taniguchi, T. Takehisa, Chem. Phys. Chem., 6, 238-241 (2005).

Keywords: Nanocomposite gel, organic-inorganic network, stimuli-responsive, force generation