Modelling and characterization of the unzipping dynamics of dielectric fluid actuators

Dielectric Fluid Actuators (DFAs) are variable capacitors that contract as a result of electrostatic forces acting on a compliant multilayer structure composed of a polymer film and an insulating liquid. Differences in the dielectric time constants of the liquid and polymeric layers lead to charge retention at their interface, causing a decay in Maxwell stress that ultimately leads to a relaxation of the actuator stroke in the presence of a constant applied voltage. In this work, we introduce a new physics-based continuum framework that extends electrostatic force modelling from fixed parallel-plate capacitors to actuator-level modelling, by coupling continuum electrical dynamics with a lumped mechanical model of the DFA. The DFA is represented as a continuum of infinitesimal variable capacitors, each modelled using simple RC elements. The framework is experimentally validated on a simple multi-layer open-pouch DFA, and on an established layout of hydraulically amplified self-healing electrostatic actuator. Even with a simplified description of the material electrical response (e.g., constant resistivities) and lumped deformation mechanics, the framework captures the relevant trends in unzipping dynamics with respect to geometry and operating conditions (applied voltage and external forces). The proposed framework lays the foundations for electro-mechanical dynamic continuum modelling of DFAs.