Polyacrylamide hydrogels containing bis-[4- {dimethylamine}phenyl]{4-vinyl-phenyl}methyl leucohydroxide which is so called vinyl derivative of Malachite Green have been studied as color changeable gels. The response times of the color and the volume changes of the gel were measured under 6 and 2 different stimuli, respectively. We found a way to increase their color change speed upon applied electric current (E-current), and designed a gel actuator using Nafion film as a separator between two compartments and as a cation conductor. In addition acrylamide gel swollen with Na2SO4 solution was used as a medium for increasing electric conductivity. We varied the concentration of dvMG in the gel to control the degree of color change. Furthermore, we have studied the influence of gel thickness on the color change rate. In light of the results obtained, we have proposed one device consisting of this color changeable gel.
A fast (0.8sec), large (>10%) and reversible deformation of Poly(vinyl alcohol) gel (PVA) swollen with dimethyl sulfoxide (DMSO) upon electric field was realized, and the maximum observed strain reached quite high 27% (DP2100). St-PVA gels were found to exhibit more stable and reversible deformation than at-PVA gels. Furthermore, we have studied the macroscopic structure of PVA/DMSO gels and its influence on their strain exhibition. Four differently structured PVA/DMSO gels, monolayer, circular, triple-layered and porous, were prepared. Monolayer gel exhibited the highly reproducible strain behavior. The mechanism of electric actuation of PVA/DMSO gel is proposed. Then a design of gel mechanical switch is shown, which exhibited the fast response to the electric field with a large, stable and reversible stretching deformation.
Uniaxial and biaxial mechanical tester was developed tp perform basic test for characterization of soft, low strength polymer gels. We have considered stress/strain relationship of acrylamide-based and polyacrylonitrile (PAN) fiber and sheet gels. Acrylamide-based gels were tested uniaxially, where Young's modulus estimated varies between 10 and 25 kPa. Uniaxial and biaxial tension test were performed on PAN sheets, from which Young's modulus was estimated at 6.65 Mpa, which is an extraordinarily large strength than the conventionally investigated acrylamide- based gels. Its length change in response to EtOH/H2O solution exchange proved to be not small as an actuator material, and it was observed that PAN exhibited a deformation in response to the electric field. Two types of PAN gel fibers were tested as a bundle of 50 fibers. True stress-strain data were obtained showing similar non-linear trend in both case. Statistical methods were used to assess fiber strength distribution.
In order to characterize the deformation behavior of polymer gels for actuators, spatial distribution of deformation of anionic, cationic and amphoteric gels under the electric field was measured. Amphoteric gel was found to be a promising material for inducing symmetric deformation, compared with anionic and cationic gels. It was also found that the deformation of electro-active gels was mainly attributed to interfacial phenomenon between gel-electrode. It can be concluded that by the use of as many amphoteric gel-electrode interfaces as possible will provide us with electro-active polymer gels that are fast responsive, largely deformable with symmetric deformation mode.
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