Preparation and properties of polyurethane/MMT nanocomposite actuators

This study dealt with the electrostrictive response of a polyurethane (PU)/clay nanocomposite film, which was a promising candidate for a material to be used in polymer actuators. The nanocomposites were produced by using three types of montmorillonites (MMTs) such as natural MMT (Cloisite^®Na⁺), hydrophobic MMT (Cloisite^® 20A), and hydrophilic MMT (Cloisite^® 30B). The nanometer-scale silicate layers of organo-clay were completely exfoliated in PU for the cases of 1, 3 and 5 wt% PU/MMT nanocomposites as confirmed by wide X-ray diffraction (WAXD) profiles. Actuation tests indicated that the displacement of PU/MMT nanocomposite actuator was larger than pure PU actuator, caused by an increase in dielectric constant. Especially, PU/MMT nanocomposite actuator with Cloisite^® 30B had the largest displacement and it became possible to operate at low voltage.     

Actuation behavior of waterborne polyurethane/conductive filler nanocomposite electrode

This study dealt with the Maxwell stress effect of waterborne polyurethane (WPU)/conductive filler nanocomposite, which was a promising candidate for a material to be used in a dielectric elastomer actuator electrode. Conductive nanocomposites were produced by using three types of conductive filler: carbon black (CB), vapor grown carbon fiber (VGCF), and silver powder (Ag). Among them, conductive nanocomposite containing VGCF exhibited the lowest threshold concentration; and the mixture of CB and VGCF (CB/VGCF) filler had a synergistic effect to electrical conductivity. Actuation test revealed that CB/VGCF nanocomposite electrode had the largest displacement. Then it could be stated that the improvement of the displacement in CB/VGCF nanocomposite electrode originated from the increase in relative dielectric constant. In addition, a unique feature for the hysteresis of bending deformation was observed. This feature is that the prior application of an electric field significantly improves the bending speed in the successive application. Also, the effect of electrode thickness on the displacement and breakdown strength was examined.     

Temperature-responsive poly(N-isopropylacrylamide) gels containing polymeric surfactants

Poly(N-isopropylacrylamide) (PNIPA) gel containing polymer surfactant poly(2-(methacryloyloxyl)decylphosphate) (PMDP) was synthesized and was found to show rapid volume phase transition above its transition temperature. Interestingly, the phase transition temperature of the PNIPA–PMDP gel was equal to that of the PNIPA gels alone. The concentration gradient of PMDP within the PNIPA gel can be obtained by applying an electric field on the gel, similar to the gel electrophoretic technique. The PMDP-gradient PNIPA gel clearly demonstrated the prevention of skin formation and the acceleration of the phase transition rate of the PNIPA gel by PMDP. The rapid volume phase transition allows potential applications of the PNPA–PMDP gel to soft actuators and drug delivery systems. Recently we also succeeded in synthesizing cylindrical microgels (0.8 μm in diameter, 5 μm in length) by a novel strategy where template-guiding synthesis and photochemical polymerization are combined. The obtained microgels can be characterized in individual level by a laser-trapping/Raman spectroscopy. In this article we also briefly described a famous gel system containing ionic surfactant capable of electrically driven actuators although it is not PNIPA gel.