The actuation performance of plasticized poly(vinyl chloride) (PVC) gel actuators in an electric field depends on their chemical composition and electrical and mechanical properties. The influence of plasticizer (dibutyl adipate) content on electromechanical behavior of PVC gels was investigated by impedance spectroscopy and space charge measurement. By plasticizing the PVC, the dielectric constant and space charge density of PVC gel were drastically increased at 1:2 w/w ratio of PVC to plasticizer. To apply the results obtained from the impedance spectroscopy and space charge measurement, electrostatic adhesive forces generated between the PVC gel and the anode were measured. The electrostatic adhesive force at the anode was also dramatically increased at the same plasticizer content. All of the results indicated a transition of electromechanical behavior of PVC gel in the electric field, which was considered to originate from the orientation of polarized plasticizer molecules and dipole rotation of PVC chains. By using the electrostatic adhesive force of PVC gel derived from the electromechanical transition, a new electroactive actuator can be developed for novel applications.
The fluorescent probe lucigenin was incorporated in poly(vinyl chloride) (PVC) gels, and laser scanning confocal microscopy (LSCM) was used to clarify the internal structures of the gels. From the two-dimensional and three-dimensional information by LSCM, we first observed the internal structure of the PVC gel at a wet status, where the PVC gels comprised a polymer-rich phase and a polymer-poor phase uniformly with a three-dimensional network structure. After an electric field was applied, an effect of the electric field resulted in the change of internal structure in the gels. The polymer-poor phase moved from the cathode to the anode and the polymer-rich phase formed linelike arrangement between electrodes due to the attraction force. On the other hand, the freeze-dried PVC gels with/without in-situ dc voltage casting were particularly fabricated to confirm above results by the field emission scanning electron microscopy (FE-SEM). It was found that many craters remained on the surface of the gel near the anode due to sublimation in freeze-drying. This phenomenon did not appear on the surface near the cathode. The results of in-situ dc voltage casting also suggested that a substantial amount of polymer-poor phase was moved and fixed at the anode. Thus, results of both LSCM and in-situ dc voltage casting corresponded to the effect of electric field on PVC gels and provided a convincing evidence for the interpretation of the deformation mechanism of PVC gel actuators by an applied electric field.
To enhance actuation performance without prestrain, an elastomeric acrylic triblock copolymer, poly(methyl methacrylate)block-poly(n-butyl acrylate)-block-poly(methyl methacrylate), was modified with two kinds of additives, oligomeric poly(n-butyl acrylate) and the plasticizer dibutyl sebacate. An actuator modified with those additives showed about 6% strain, whereas the unmodified actuator showed only 1% strain for the same applied electric field without prestrain. In addition, actuation was attained at lower critical electric field strength (625 and 1000 V mm −1 for modified and unmodified actuators, respectively). Upon increasing the amounts of the additives, the electrically induced actuation velocity and degree of deformation increased. These results are explained by the dielectric and mechanical properties of the elastomers. The dielectric constants for elastomers modified with dibutyl sebacate were larger than those for elastomers modified with oligomeric poly(n-butyl acrylate). The initial tensile stresses of both of the modified elastomers were much smaller than that of unmodified elastomer. The results provide a route to enhancing actuation performance of dielectric elastomers without prestrain.
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