Actuation performances and microscopic mechanism of a stimuli-responsive artificial muscle based on the chelation of sodium alginate with CaI2·4H2O

Abstract

Abstract With the popularization of energy conservation and environmental protection, a stimuli-responsive artificial muscle (SRAM) prepared by green process of the chelation of sodium alginate (SA) with calcium iodide tetrahydrate (CaI2·4H2O), provides new ideas and prospects for the development and application of smart artificial muscles. In this paper, actuation performances including force density (Fρ , mN/g), working life (τ, s), rise time (τ r, s) and response speed (V F, mN/g·s) of the SRAM with different concentrations of CaI2·4H2O was researched through the test platform of electrically bending force. Furthermore, the microscopic mechanism on mechanical and electrochemical characteristics of the SRAM was analyzed and verified comprehensively by microstructure, energy dispersive spectroscopy, ion channel, infrared spectroscopy and diffraction of x-rays. The experimental results were demonstrated that when the concentration of CaI2·4H2O was within the range of 1.5 g l−1–2.0 g l−1, the SRAM achieved optimal modification, where at 1.5 g l−1 CaI2·4H2O, its specific capacitance and τ were both the maximum values of 93.7 mF g−1 and 1080 s, but internal resistance was the minimum of 3.09 Ω; at 2.0 g l−1 CaI2·4H2O, the Fρ, V F, elastic modulus, yield strength and ion channel of the SRAM reached the largest values of 22.807 mN g−1, 0.1046 mN g−1·s, 20 MPa, 0.18091 MPa and 60.2%, respectively, but τ r obtained the lest of 98 s. Because after being chelated by CaI2·4H2O, the α-L-guluronic blocks in SA molecular chains coagulated with Ca2+ ions, making the synergy between molecular chains of the SRAM stronger, thus forming a three-dimensional ‘egg box’ network structure of polymeric hydrogel.