Transient Elastomers with High Dielectric Permittivity for Actuators, Sensors, and Beyond

Enhancing Dielectric Properties of (CaCu3Ti4O12 NWs-Graphene)/PVDF Ternary Oriented Composites by Hot Stretching

Using high-dielectric inorganic ceramics as fillers can effectively increase the dielectric constant of polymer-based composites. However, a high percentage of fillers will inevitably lead to a decrease in the mechanical toughness of the composite materials. By introducing high aspect ratio copper calcium titanate (CaCu3Ti4O12) nanowires (CCTO NWs) and graphene as fillers, the ternary poly(vinylidene fluoride) (PVDF)-based composites (CCTO NWs-graphene)/PVDF with a significant one-dimensional orientation structure were prepared by hot stretching. CCTO NWs and graphene are arranged in a directional manner to form a large number of microcapacitor structures, which significantly improves the dielectric constant of the composites. When the ratio of CCTO NWs and graphene is 0.2 and 0.02, the oriented composites have the highest dielectric constant, which is 19.3% higher than the random composites, respectively. Numerical simulations reveal that the introduction of graphene and the construction of the one-dimensional oriented microstructure have a positive effect on improving the dielectric properties of the composites. This study provides a strategy to improve the dielectric properties of composite materials by structural design without changing the filler content, which has broad application prospects in the field of electronic devices.

10× continuous optical zoom imaging using Alvarez lenses actuated by dielectric elastomers

Optical zoom is an essential function for many imaging systems including consumer electronics, biomedical microscopes, telescopes, and projectors. However, most optical zoom imaging systems have discrete zoom rates or narrow zoom ranges. In this work, a continuous optical zoom imaging system with a wide zoom range is proposed. It consists of a solid lens, two Alvarez lenses, and a camera with an objective. Each Alvarez lens is composed of two cubic phase plates, which have inverted freeform surfaces concerning each other. The movement of the cubic phase masks perpendicular to the optical axis is realized by the actuation of the dielectric elastomer. By applying actuation voltages to the dielectric elastomer, cubic phase masks are moved laterally and then the focal lengths of the two Alvarez lenses are changed. By adjusting the focal lengths of these two Alvarez lenses, the optical magnification is tuned. The proposed continuous optical zoom imaging system is built and the validity is verified by the experiments. The experimental results demonstrate that the zoom ratio is up to 10×, i.e., the magnification continuously changes from 1.58× to 15.80× when the lateral displacements of the cubic phase masks are about 1.0 mm. The rise and fall response times are 150 ms and 210 ms, respectively. The imaging resolution can reach 114 lp/mm during the optical zoom process. The proposed continuous optical imaging system is expected to be used in the fields of microscopy, biomedicine, virtual reality, etc.

Thioether-Containing Zirconium(Alkoxy)Siloxanes: Synthesis and Study of Dielectric and Mechanical Properties of Silica-Filled Polydimethylsiloxane Compositions Cured by Them

A number of thioether-containing zirconium siloxanes, differing in their composition and metal atom shielding degree with a siloxy substituent, were synthesized and characterized. Synthesis of such compounds made it possible to evaluate the effect of sulfur atoms' presence in the cured compositions on their dielectric properties, as well as to evaluate their curing ability and influence on mechanical characteristics compared to the sulfur-free analogs obtained earlier. Studying a wide range of compositions differing in their content and ratio of metallosiloxane and silica components revealed that such systems are still typical dielectrics. At the same time, the introduction of thioether groups can provide increased dielectric constant and conductivity in comparison with previously obtained sulfur-free similar compositions in the <102 Hz frequency range (dielectric constant up to ~10-30 at frequency range 1-10 Hz). As before, the dielectric parameters increase is directly determined by the silica component proportion in the cured material. It is also shown that varying sulfur-containing zirconium siloxanes structure and functionality and its combination with previously obtained sulfur-free analogs, along with varying the functionality and rubber chain length, can be an effective tool for changing the dielectric and mechanical material parameters in a wide range (tensile strength 0.5-7 Mpa, elastic deformation 2-300%), which determine the prospects for the use of such cured systems as dielectric elastomers for various purposes.