Viscoelastic tensile constitutive framework for PVC gels

Abstract Polyvinyl chloride (PVC) gels are promising electroactive polymers because of their large actuation strains, comparatively low voltage requirements, and tunable mechanical properties through plasticization. However, their viscoelastic tensile response remains largely uncharacterized, limiting the transient and dynamic material descriptions required for multiphysics modelling of electrohydraulic systems such as the Electrohydraulic Actuator Powered by Induced Interfacial Charges (EPIC). This work develops a unified viscoelastic tensile constitutive framework for PVC gels plasticized with dibutyl adipate (DBA) by combining tensile stress relaxation and dynamic mechanical analysis (DMA). Multiobjective optimization using the dynamic non-dominated sorting genetic algorithm II (DNSGA-II) simultaneously fitted time-domain stress relaxation modulus and frequency-domain storage and loss moduli up to 35 Hz. A 5-term Prony-series was identified as the minimum investigated model order capable of representing all three responses within a 5% normalized mean absolute error criterion. Reduced 2-term and 3-term models accurately represented timedomain stress relaxation, with normalized root mean square errors below 1.60%, but did not reproduce the frequency-domain response. Power-law scaling of the Prony-series moduli with plasticizer content was consistent with similar underlying polymer network structures, while variations in relaxation time scales suggested changes in molecular mobility. The resulting framework provides the time-dependent material description required for coupled multiphysics modelling of PVC gel electrohydraulic actuators.