# Fabrication of a High-Performance Bending Actuator Made with a PVC Gel
## 3 Results and Discussion
Considering the dielectric/mechanical properties of the proposed PVC gel, we selected PVC\({}_{\rm L}\)5, PVC\({}_{\rm M}\)9 and PVC\({}_{\rm H}\)11 gels. We inserted the following work in the reference section. We conducted an experiment to investigate the dynamic mechanical properties of those three PVC gels (PVC\({}_{\rm L}\)5, PVC\({}_{\rm M}\)9 and PVC\({}_{\rm H}\)11) using a TA Instruments RSA-G2 dynamic mechanical analyzer. Specimens of the three PVC gels were prepared with dimensions of 10 mm (W) \(\times\) 50 mm (H) \(\times\) 0.2 mm (T). In this experiment, we obtained the dynamic mechanical properties of the PVC gels in the time domain and frequency domain. In the case of the time domain, the PVC gels were strained 10 times (2% at  
Figure 8: Experimental results for the leakage current 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. 1 Hz, sinusoidal), and then the PVC gels were strained with 2% at 1-50 Hz (sinusoidal) in the frequency domain. Figure 9a shows the result of the dynamic mechanical analysis in the time domain. The points are the average of the modulus, and the error bars show the standard deviation. The average storage moduli of the PVC15, PVCM9 and PVCH11 gels were 13.866, 13.923 and 14.366 kPa, respectively. Although the three PVC gels had different plasticizer contents, there was no significant discrepancy in the storage modulus. Figure 9b shows the result of the dynamic mechanical analysis (DMA) in the frequency domain. As with the time domain result, there was no significant discrepancy among the three PVC gel samples in the low-frequency range (1-10 Hz), but the moduli of the PVC gels dramatically increased above 10 Hz and their rates of increase were distinct. In particular, the modulus of the PVCH11 gel, which had the longest PVC chains among the three samples, showed a remarkable increase. The maximum modulus of the PVCH11 gel reached 299 kPa, while the moduli of PVCL5 and PVCM9 were 66 and 145 kPa, respectively. It seems that the modulus of the PVC gel is proportional to the PVC chain length. We found that the valid frequency range of all three PVC gel samples was about 20 Hz. We fabricated three bending actuators based on the PVC15, PVCM9 and PVCH11 gels, and then quantitatively evaluated their actuation performance in terms of response times and deformation angles. To measure these, we designed an experimental environment using a graph paper and a digital camera (1 V3, Nikon, Tokyo, Japan), as shown in Figure 10. To measure the bending angle of the actuator, we installed a wall behind the bending actuator and attached the graph paper to the wall. When we applied a voltage to a PVC gel-based bending actuator, the bending deformation occurred rapidly. At that time, we recorded the bending angle (\(\theta\)) using the camera (120 fps) and saved it to memory. After that, the time it took for the bending angle of the proposed actuator to increase by 10\({}^{\circ}\) was calculated through image processing. Figure 11 shows the measured bending angles of the three transparent actuators over time. The maximum bending angle of the PVC15 gel-based actuator was only about 50\({}^{\circ}\), and its elapsed time was 11 s. On the other hand, the maximum bending angle of the PVCM9- and PVCH11-based bending actuators was 180\({}^{\circ}\). However, the elapsed time of the PVCH11 gel-based bending actuator (3.154 s) was much faster than that of the PVCM9 gel-based bending actuator (194.79 s). The transparencies of the PVCM9 and PVCH11 gels were measured using UV-vis spectroscopy. As a result, the PVCH11 gel was found to have transparency >92% at 550 nm (Figure 12). From this result, the PVCH11 gel-based bending actuator, which had the largest bending angle and the quickest response time, was selected as the most transparent and highly deformable bending actuator.