# Fabrication of a High-Performance Bending Actuator Made with a PVC Gel
## 1 Introduction  
Recently, tiny but highly deformable bending actuators based on smart materials are being actively studied because they have many advantages such as being lightweight, small and simple operating mechanisms [1; 2; 3; 4; 5]. Among various smart material-based bending actuators, electroactive polymers (EAPs), which are operated by electric energy, are widely used. These electroactive polymers can be classified into two types: ionic and nonionic polymers. An ionic polymer/metal composite (IPMC) is one of the most popular ionic polymers for bending actuators. It consists of an ion-exchangeable membrane (ex, Nafion film) and electrodes. The IPMC-based bending actuators were widely studied over the past few decades, and they are still improving nowadays [6; 7; 8]. [PERSON] et al. presented a bending actuator using an IPMC with carbon for worm-like robots [7]. [PERSON] et al. proposed a new ion-exchangeable membrane (polyaniline thorium phosphate (ThP-PANI) composite) to substitute a Nafion film, which has drawbacks such as high cost, low water-retention capability and back-relaxation, and developed a bending actuator based on the IPMC with the new ionic-exchangeable membrane [8]. Poly vinyl alcohols (PVAs) are another candidate material for fabricating bending actuators. [PERSON] et al. introduced a PVA-2,2,6,6-tetramethyllyp-peridine-1-oxyl-oxidized bacterial cellulose nanofiber (TOCN)-based bending actuator [9]. [PERSON] et al. enhanced the actuation performance of a bending actuator based on PVA by improving proton conductivity and ionic-exchangeable capacity [10]. [PERSON] et al. tried to mix multi-wall carbon nanotubes (MWCNTs) with PVA to enhance the electromechanical property of PVA in order to develop a bending actuator [11]. [PERSON] et al. fabricated another type of an ionic polymer using a biopolymer (chitosan polymer) and ionic liquid, and then developed a bending actuator based on the ionic polymer [12]. [PERSON] et al. proposed a bending actuator using a post-synthetic modification of PVA and \(N^{1}\),\(N^{1}\)-diethylethane-1,2-diamine (DEEDA) (PVA-DEEDA) [13]. [PERSON] et al. developeda metal-organic framework hybrid nanoporous membrane-based bending actuator [14]. Although there are many advantages (such as light weight and low power consumption) in ionic polymers and there have been lots of attempts to enhance the performance of bending actuators based on ionic polymers, the polyelectrolyte is vulnerable to solvent evaporation, and application of the electric field is inevitably accompanied by an electrolysis reaction. On the other hand, nonionic EAP-based bending actuators, which are composed of dielectric polymers covered with stretchable electrodes on both sides, have a fast response time. [PERSON] et al. developed a bending actuator using a dielectric polymer for a soft gripper [15]. [PERSON] et al. designed a bending actuator having a minimum-energy structure based on a dielectric polymer [16]. When voltage is applied to the electrode, a dielectric material quickly expands in planar directions and compresses in the thickness direction. Because the nonionic EAPs do not need electrolyte, they are operated in air conditions. However, the nonionic EAPs require a prestretching process to maximize their deformation and they need stretchable electrodes for their operation. Among many nonionic EAPs, polyvinylidene fluoride (PVDF) is one of the most attractive and representative nonionic polymers for fabricating bending actuators. [PERSON] et al. introduced a bending actuator using prepolarized piezoelectric bimorph structure consisting of two PVDF thin films [17]. [PERSON] et al. proposed a new method to fabricate a high-performance bending actuator using an ionic liquid/PVDF blend [18]. [PERSON] et al. synthesized a PPy-PVDF multilayered electroactive polymer and fabricated a bending actuator using the PPy-PVDF multilayered polymer [19]. [PERSON] and [PERSON] enhanced the performance of the bending transducer by applying graphene quantum dots to PVDF [20].