Multiphysics Modeling of Ionic Gel Actuators
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MULTIPHYSICS MODELING OF IONIC GEL ACTUATORS Huibiao Li1 Meie Li2 Jinxiong Zhou1,* MOE Key Laboratory for Strength and Vibration and School of Aerospace, Xi’an Jiaotong University, Xi’an 710049, P. R. China 2 State Key Laboratory for Mechanical Behavior of Materials and School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China 1
ABSTRACT When an electrocatalyst, platinum, was coated on ionic-polymer gel surfaces and was immersed into an acidic formaldehyde solution, an input dc current will produce oscillatory ac on the surfaces of the ionic-polymer-metal-composites(IPMC), which eventually causes self-oscillatory bending of the actuators. Typical IPMC actuators have a large length-to-height ratio, exhibiting large deformation during bending and relaxation processes. A multiphysics modeling of self-oscillations of IPMC actuator was carried out, incorporating the electrochemical oscillations, electrokinetics, electrostatics and nonlinear large deformation of the actuators. INTRODUCTION Ionic polymer gel actuators are soft and wet machines with diverse potential applications[1-5]. One typical example of such ionic gel actuators is known as the ionic polymer metal composite (IPMC) actuator, for review of IPMC-based artificial muscles see [4-5]. Conventional IPMC needs input of alternating current (AC) to produce oscillatory actuation, while a recently proposed idea demonstrated that, by utilizing the electrochemical reaction of platinum in HCHO solution, an input of direct current (DC) can produce self-oscillation of IMPC strip[6-9]. The physical picture behind the actuation of IMPC actuators is complex and not yet to be fully understood. A couple of factors and physical processes may affect the mechanisms behind the actuation of IPMC actuators, including migration of mobile ions, electrostatic interaction of ionic clusters, morphology of the electrode-polymer interface and large deformation of the sandwich composite structure. Following Pugal et al. [9] but avoiding the difficulties involved in modeling the actuator as a two-dimensional continuum, we describe here a tailor-made multiphysics model for such an actuator with large length-to-height ratio. Electrochemical process occurred along each cross section through the height was regarded identically as a one-dimensional process, and the mechanical deformation of the actuator was simplified as the bending of a beam. With this model, the self-oscillation of IPMC beam actuator is successfully modeled and the model can be used to predict and optimize the performance of new actuators. THEORY
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Corresponding author: [email protected]
The electrochemical model concerned with platinum in HCHO solution is described as [9,13]
θCO = k2 (1 − θCO − θOH ) − k4θCO ⋅θOH θOH = k3θCO (1 − θCO − θOH ) − k−3θOH − k4θCO ⋅θOH ψ =
(1)
(2)
1 [i − 2 FS Pt {k1 (1 − θCO − θOH ) + k4θCO ⋅ θOH }] C1
(3)
where θCO and θOH are the dimensionless adsorption coverages of intermediates CO and OH, F is
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