Ionic-polymer metal composites (IPMCs) are a subset of ionic electroactive polymers (EAPs). They produce an actuation response based on the electrically induced flux of mobile ions through a parent-polymer matrix. This response is a result of the accumulation of cations and anions on opposing sides of the matrix and is directly related to the size disparity between the two types of ions. These factors impose a differential expansion across the matrix, which generates the macroscopic bending that is observed. It is well known that the motion of these EAPs is highly nonlinear and time dependent, making for a process that is difficult to model. A simplistic approach to modeling the physics behind this phenomenon and correlating that to experimental results is outlined, herein. This new methodology enables a comprehensive analysis of the boundary conditions (BCs) needed to be considered in order to accurately characterize the IPMC actuation response. The subsequent series of equations developed, which depict the ionic motion under these BCs, is presented. Empirical data for model analysis was acquired from IPMCs created using poly(ethylene oxide) (PEO), a well-known, biodegradable, solid-polymer electrolyte infused with lithium perchlorate, as the ionic salt. Experimental results fitted with this new model returned a favorable average adjusted-R2, goodness-of-fit, of 0.987, 0.994, and 0.992 when PEO films were tested under varying conditions, including: ionic concentration, applied voltage, and testing temperature, respectively.
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.
Poly(ethylene oxide) (PEO) has been widely studied as a solid-polymer electrolyte where both the cations and
anions can move inside of it under an applied electric field. The motion of these charge carriers in the PEO results in the
accumulation of ions close to the electrodes. The inherent size difference between the types of ions causes an unequal
volume change between the two sides which translates to an observed mechanical bending. This is similar to
electroactive polymers made from conducting polymers. Typically, PEO has a slow response. Some efforts have been
given to develop PEO-based polymer blends to improve their performance. In this work, a fundamental study on the
electromechanical response is conducted: the time dependence of the electromechanical response is characterized for
PEO under different electric fields. Based on the results, a new methodology to monitor the electromechanical response
is introduced. The method is based on the frequency dependence of the samples’ dielectric properties. To improve the
electromechanical response, the PEO is embedded with piezoelectric nanocrystalline cellulose (NCC). NCC is a biomass
derivative that is biodegradable, renewable, and inexpensive. The dielectric, mechanical, and electromechanical
properties of the NCC-PEO composites are characterized. It is found that the mechanical and electromechanical
properties of the PEO are significantly improved with adding NCC. For example, the composites with 1.5 vol.% of NCC
exhibit an electromechanical strain and elastic modulus that is 33.4% and 20.1% higher, respectively, than for PEO
without NCC. However, the electromechanical response decreases when the NCC content is high.