# Fabrication of a High-Performance Bending Actuator Made with a PVC Gel
## 3 Results and Discussion
From Figure 5, we found that the increase of plasticizer in a PVC gel makes the PVC gel soften, and higher molecular weight leads to increased stiffness of the PVC gel. That is, these are two major factors (the weight ratio of PVC to DBA plasticizer and the molecular weight of PVC resin) for adjusting the stiffness of the PVC gel. The dielectric property is also an important factor in the proposed bending actuator because the proposed actuator has electrically induced actuation behavior. The dielectric constant of a PVC gel was investigated by changing the molecular weight of the PVC resin and the amount of the plasticizer. An SI-1260 impedance/gain-phase analyzer connected with a 1296 dielectric interface (Solartrron Analytical Co., Fambborough, UK) was used for the dielectric constant. The input frequency is swept from 1 Hz to 10\({}^{6}\) Hz with 10 points/decade under 2 V input voltage. Figure 6 shows the results of dielectric constants of the prepared PVC gels as a function of input frequency. The dielectric constants are increased in the low-frequency range (1-20 Hz). It can be considered that, in a nonionic PVC gel physically crosslinked with plasticizer, DBA molecules are charged and polarized under the electric field, and then the polarized DBA easily facilitates the free dipole reorientation of the PVC chain in the PVC gel network [28]. This dipole reorientation of a PVC gel makes its dielectric constant high. In the high-frequency range (20 Hz-10\({}^{6}\) Hz), the dielectric constants of the PVC gels were almost saturated because the dipoles stop rotation. Figure 4: Mechanical property of the pure PVC films. Figure 5: _Cont._  
Figure 5: Experimental results for the mechanical properties of the PVC gels: different molecular weights of PVC with the weight ratio of PVC to DBA plasticizer of (**a**) 1:3, (**b**) 1:5, (**c**) 1:7, (**d**) 1:9, (**e**) 1:11, and (**f**) 1:13. Figure 6: _Cont._  
We plotted the dielectric constants of the prepared PVC gels at 1 Hz (Figure 7). As shown in Figure 7, as the amount of plasticizer increases, the number of dipoles increases, and as a result, the dielectric constant also increases. Furthermore, the dielectric constant is proportional to the molecular weight of the PVC resin (Figure 6). It means that the use of PVC resin with high molecular weight makes entanglement, physical crosslinking and crystallization regions in a PVC gel increase. The leakage current is another important factor in electrically induced actuation of the proposed bending actuator. The leakage current of the prepared PVC gels was measured by a potentiostat/galvanostat (Bio-logic Science Instruments, SP300) in applied electric fields of 500 V/mm at room temperature. Figure 8 shows the results of the prepared samples' leakage currents. It seems that the leakage current in the PVC gel is proportional to the contents of the plasticizer and is inversely proportional to the molecular weight of the PVC. However, there are little differences in leakage currents from the prepared PVC gel samples. As we mentioned before, we prepared three PVC gel groups (PVC\({}_{\text{L}}\)-based gel, PVC\({}_{\text{M}}\)-based gel and PVC\({}_{\text{H}}\)-based gel). In each group, we need to select the best mixing ratio of PVC and a plasticizer using two important properties (dielectric and mechanical properties). The increase of a plasticizer makes a PVC gel soft and it makes its dielectric constant high. Although the increase of the dielectric constant can improve the performance of the PVC gel, the increase of the compliance can disturb the precise movement of the PVC gel-based bending actuator. Thus, we can say that there  
Figure 6: Experimental results for the dielectric constant of the PVC gels: different molecular weights of PVC with the weight ratio of PVC to DBA plasticizer of (**a**) 1:3, (**b**) 1:5, (**c**) 1:7, (**d**) 1:9, (**e**) 1:11, and (**f**) 1:13. Figure 7: Dielectric constants of the PVC gels at 1 Hz. is a trade-off relationship between the dielectric constant of a PVC gel and its stiffness.