Electromechanical responses of agarose ionogels as highly soft and compliant actuators

Abstract

Ionogels have been of interest as an alternative electroactive material for soft actuator applications, as they can maintain the shape and size under ambient conditions. Herein, the physically cross-linked agarose ionogels were fabricated via a solvent casting method by using 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) as the ionic liquid. The electro-actuation responses were investigated in terms of agarose contents and electric field strengths. For the electromechanical responses, the electrostriction shows two distinct behaviors dependent on agarose contents: at the high agarose content of 12.0%v/v, the storage modulus relative response (ΔG'/G'0) was the positive value of 0.06, known as the positive electrostriction; at the low agarose contents of 4.0%v/v and 8.0%v/v, the ΔG'/G'0 were negative definite at −0.11 and −0.06, respectively. These behaviors occurred from the plasticizing [Bmim][Cl] molecules which were able to hinder the agarose intermolecular interactions. For the electro-induced bending behaviors, the AG-[Bmim][Cl] Ionogel_4.0%v/v revealed the highest deflection distance and dielectrophoresis force (Fd) due to its lower initial rigidity and the polarizations from the [Bmim][Cl], moisture, and agarose structures, respectively. Comparing with other bio-polymeric hydrogels and ionogels, the present AG-[Bmim][Cl] Ionogels are shown here to possess relatively low electrostrictive stresses but high dielectrophoresis force density; both are essential features for utilizing in soft actuator applications.