Physics Based Model of Ionic Polymer-Metal Composite Electromechanical and Mechanoelectrical Transduction
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Ionic polymer-metal composite (IPMC) materials have been studied for the past two decades. Both electromechanical and mechanoelectrical transduction have been reported and also quantitatively described by employing various modeling techniques. In this dissertation, a fundamental physics based model of IPMC that describes the phenomena is proposed. The same underlying equations and boundary conditions are used to calculate both voltage induced actuation and deformation induced voltage. Additionally, several more sophisticated modeling features are considered.The model incorporates conductive electrodes of IPMC - the ionic current, volumetric strain induced charge, and the electric current in the electrodes are coupled by the same set of equations and boundary conditions. While the underlying physics is the same, the electrode effect on the electromechanical and mechanoelectrical transduction is different - actuation dynamics is affected by potential gradients in the electrodes, whereas in case of the mechanoelectrical transduction, the electrodes dissipate induced voltage. The electromechanical component of the model includes mathematical formulation to describe the electrolysis current and its effect on actuation. Additionally, a new charge-force coupling is proposed in order to accurately calculate deformation in case of different IPMC geometries. The mechanoelectrical component of the model is parametrically analyzed to determine the underlying cause for the delay between induced voltage and applied deformation. It is shown that the volumetric effect of the anion charge is relevant in the mechanoelectrical transduction calculations. Experimental validation of the model is provided - three different IPMC thicknesses were used in order to ensure that the model is geometrically scalable.Fractal electrode geometry is proposed to mathematically describe the large surface area of IPMC's electrodes. Most physics-based models use very high dielectric permittivity value and adjusted diffusion constant in order to match the experimental data. While this approach allows matching the calculated and experimentally measured values, the geometric effect of the electrodes is not explicitly captured. It is shown that using the fractal geometry electrodes in calculations helps to gain insight into the electrode structure effect on both electromechanical and mechanoelectrical transduction. For instance, simulations with fractal electrodes indicate that total transported charge and thus deformation are considerably affected by the surface area. Additionally, more realistic physical constants can be used in calculations.To make the model of IPMC more applicable in system and application design, an explicit foundation of how to implement the equations is needed. Hence, the finite element method based implementation of the model with all necessary boundary conditions is presented - this is called the modeling framework of IPMC. The model's extendability and applicability are demonstrated by applying it on self-oscillating actuation calculations, 3D domains, and cylindrical geometries. Furthermore, it is shown that by using more advanced hp-FEM, the problem size can be reduced and IPMC calculations can be carried out with realistic physical constants without high computational demands.