# Fabrication of a High-Performance Bending Actuator Made with a PVC Gel
## 2 Experiment  
An electroactive PVC gel was fabricated using poly vinyl chloride (PVC), tetrahydrofuran (THF) as a solvent, and dibutyl adipate (DBA) as the plasticizer. The process for fabrication of the electroactive PVC gel is shown in Figure 1. First, we poured PVC powder and DBA (Sigma-Aldrich, St. Louis, MO, USA) plasticizer into the THF (Sigma-Aldrich, St. Louis, MO, USA) solvent, and then stirred the solution (we call it PVC-DBA solution) for 4 h to fully dissolve the PVC and the DBA in the THF solvent. To obtain flat, transparent PVC gel, we poured the fully dissolved PVC-DBA solution into a Teflon dish; then we dried the solution for 72 h at room temperature. To evaporate the THF fully in the solution, we put the solution into a vacuum oven for 24 h. Finally, we obtained a transparent, electroactive, physically crosslinked and flat PVC gel, 1 mm thick. Two electrodes were attached, one on each side of the PVC gel, to fabricate a transparent bending actuator, as shown in Figure 2a, where the PVC gel, PVC chains and dipoles in the PVC gel are colored aquamarine, white and red, respectively. Figure 2b shows the fabricated bending actuator, and Figure 2c,d show the voltage-off and -on states (respectively) of the proposed actuator. When we applied voltage input to the proposed actuator, the dipoles (DBA plasticizer) rotated and reoriented, then moved toward the anode, dragging the PVC chains. Thus, the PVC gel was deformed toward the anode, as shown in Figure 2d. In the voltage-off state, electric field-induced deformation does not occur because the dipoles are randomly distributed in the PVC gel. Figure 1: Process for fabrication of the electroactive PVC (poly vinyl chloride) gel. As we mentioned before, the performance of the PVC gel-based bending actuator is closely related not only to the plasticizer content but also to the molecular weight of the PVC. When the PVC gel is fabricated using a high-molecular-weight PVC resin, it can contain more plasticizer than a low-molecular-weight PVC-based gel. Furthermore, because a high-molecular-weight PVC gel has more entanglement and more physical crosslinking than a lower-molecular-weight PVC gel, the density of the PVC chains in the high-molecular-weight PVC gel is higher than in a PVC gel based on low-molecular-weight PVC. Under voltage input, the PVC chains and the plasticizer move toward the anode. At that time, the plasticizers in the high-molecular-weight PVC gel can accelerate the movement of PVC chains toward an anode. Because there are many more PVC chains near an anode in the high-molecular-weight PVC gel than in the lower-molecular-weight PVC gel, more PVC chains can be influenced by applied electric field [27]. For these reasons, we expect that the molecular weight of the PVC will affect the deformation of the PVC gel-based bending actuator and its response time. To investigate the molecular weight effect of the PVC gel-based bending actuator, we prepared three commercial PVCs (PVC\({}_{\rm L}\): Wako; PVCM: Sigma-Aldrich; and PVCH: Scientific Polymer), with molecular weights of 116,000, 239,000 and 282,000, respectively. Furthermore, to observe the plasticizer effect, we fabricated PVC gels with different weight ratios of PVC resin to DBA plasticizer: 1:0, 13, 1:5, 1:7, 1:9, 1:11 and 1:13 denoted as PVC0 (PVC film), PVC3, PVC5, PVC7, PVC9, PVC11 and PVC13, respectively. In this preparation, for PVCL, we could only obtain PVCL3 and PVCL5 because the PVCL has low entanglement, low physical crosslinking, and a small crystalline region. If the ratio of PVCL to plasticizer was more than 1:5, we could not obtain a PVC gel. Hence, we prepared 17 PVC gels as shown in Table 1 (PVC\({}_{\rm L}\)0, PVCL3, PVCL5, PVCM0, PVCM3, PVCM5, PVCM7, PVCM9, PVCM11, PVCM13, PVCH0, PVCH3, PVCH5, PVCH7, PVCH9, PVCH11 and PVCH13).