Stimuli-Responsive Polymer-Clay Nanocomposites under Electric Fields

The Soft and High Actuation Response of Graphene Oxide/Gelatin Soft Gel

The high actuation response of soft gel from a graphene oxide/gelatin composite was prepared as an alternative material in soft robotics applications. Graphene oxide (GO) was selected as the electroresponsive (ER) particle. GO was synthesized by modifying Hummer's method at various ratios of graphite (GP) to potassium permanganate (KMnO₄). To study the effect of ER particles on electromechanical properties, GO was blended with gelatin hydrogel (GEL) at various concentrations. The electrical properties of the ER particles (GO and GP) and matrix (GEL) were measured. The capacitance (C), resistance (R), and dielectric constant of the GO/GEL composite were lower than those of the GO particles but higher than those of the GEL and GP/GEL composite at the given number of particles. The effects of external electric field strength and the distance between electrodes on the degree of bending and the dielectrophoresis force (F_d) were investigated. When the external electric field was applied, the composite bent toward electrode, because the electric field polarized the functional group of polymer molecules. Under applied 400 V/mm, the GO/GEL composite (5% w/w) showed the highest deflection angle (θ = 82.88°) and dielectrophoresis force (7.36 N). From the results, we conclude that the GO/GEL composite can be an alternative candidate material for electromechanical actuator applications.

Preparation of Cellulose/Laponite Composite Particles and Their Enhanced Electrorheological Responses

Cellulose, as a natural polymer with an abundant source, has been widely used in many fields including the electric field responsive medium that we are interested in. In this work, cellulose micron particles were applied as an electrorheological (ER) material. Because of the low ER effect of the raw cellulose, a composite particle of cellulose and Laponite was prepared via a dissolution–regeneration process. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to observe the morphologies and structures of the composite particles, which were different from pristine cellulose and Laponite, respectively. The ER performances of raw cellulose and the prepared composite were measured by an Anton Paar rotational rheometer. It was found that the ER properties of the composite were more superior to those of raw cellulose due to the flake-like shapes of the composite particles with rough surface. Moreover, the sedimentation stability of composite improves drastically, which means better suspension stability.

Structural, thermal and mechanical properties of polymer nanocomposites based on organosoluble polyimide with naphthyl pendent group and layered double hydroxide

In this study, a soluble aromatic polyimide (PI) with naphthyl pendent group was initially synthesized by the reaction of pyromellitic dianhydride (PMDA) with 5-methyl- N,N-bis(4-nitrophenyl)naphthalen-1-amine. Then, via co-precipitation reaction of zinc nitrate hexahydrate and chromium nitrate nonahydrate, Zn/Cr-layered double hydroxide (LDH) was synthesized using hydrothermal techniques. Finally, different novel nanocomposites (NCs) based on PI and Zn/Cr-LDH (1, 2, 4 wt%) were produced through in situ polymerization. The resulting materials were characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetry analysis (TGA), field emission scanning electron microscopy, transmission electron microscopy, and mechanical testing. According to the TGA results, the prepared NCs showed high thermal stability at higher temperature due to the good dispersion and homogeneity of Zn/Cr-LDH in polymeric matrix. Consequently, the mechanical properties of the synthesized NCs were enhanced by the incorporation of 2 wt% Zn/Cr-LDH in the polymer matrix.