Modeling of the time-dependent strain response of electroactive NCC-PEO and PVDF composites

Ionic electroactive polymers have been widely studied, wherein the electrically induced ionic motion generates an actuation response. The electromechanical bending observed in these polymers is due to the size difference between two types of ions which results in an unequal expansion and contraction between the two sides. Nanocrystalline cellulose (NCC) is a biodegradable, renewable, and inexpensive biomass derivative. Poly(ethylene oxide) (PEO) is also biodegradable and a well-known solid-state electrolyte capable of having both cations and anions diffuse through its matrix under an applied electric field. In this study, NCC is mixed with the PEO to make 0-3 composites with increased Young's modulus and improved actuation performance. Experimental results showed that the time-dependent strain response for these composites followed an Arrhenius behavior. Using the Stokes-Einstein model, the flux of the ions within in the polymer matrix were defined as charged, spherical particles moving through a viscous medium with low Reynold's number. This new approach makes it possible to calculate parameters that may otherwise have been difficult or impossible to obtain. In this work, calculations for these properties, such as: apparent ionic diffusion coefficient, ionic velocity, and the dynamic viscosity of the matrix material are analyzed and presented. For example, the parameters for PEO-NCC composites doped with 5.0 wt.% lithium were calculated to be 3.58e-10 cm²/s, 102 nm/s, and 275 Poise, respectively. Electroactive polyvinylidene fluoride films were also synthesized for comparison and refinement of the introduced model.