ABSTRACT
Recently, various piezoresistive composites with good flexibility have been developed as sensing materials for flexible strain sensors (FSSs). External forces will be applied to strain sensors when they are used in some circumstances such as wrist bending, etc. However, conventional flexible composites may fail upon being subjected to external forces since they have low strength and are unable to protect the inner vulnerable structure of flexible sensors. In this work, the reduced graphene oxide-coated glass fabric (RGO@GF)/silicone composite is fabricated and used to make high-performance structural flexible strain sensors. The composite is not only flexible and sensitive to strain, but also exhibits the high tensile strength needed to maintain the structural integrity of the flexible strain sensor. Silicone resin and GF are employed to provide flexibility and high strength, respectively. By coating RGO on the surface of GF, the nonconductive GF becomes conductive, which renders the piezoresistive behavior and strain-sensing ability to the RGO@GF/silicone composite. The as-prepared structural flexible sensor not only possesses a good strain sensitivity with a gauge factor of around 113, which is much higher than that of typical strain sensors based on metals, but can also maintain its structural integrity until the applied external force is over 800 N, while the conventional flexible strain sensor fails upon being subjected to an external force of only 5 N. Moreover, the as-prepared structural FSS is applied to monitor wrist movement and breathing to demonstrate its applicability. Overall, the RGO@GF/silicone composite exhibits great potential as a sensing material for structural FSSs for wrist movement, etc.
ABSTRACT
Inspired by biological cilia, a highly flexible dual-mode electronic cilia (EC) sensor is fabricated from graphene-coated magnetic cilia arrays. Polydimethylsiloxane is used as a matrix to make the artificial cilia flexible while Co particles are used to endow the cilia with magnetic properties and graphene coating is employed to make the cilia conductive. The EC-based sensor shows a high sensitivity of 0.4% Pa-1 for a pressure of 0-100 Pa and a low detection limit of 0.9 Pa. The responsive behavior of the EC-based sensor is highly stable in a wide frequency range of 0.1-10 Hz up to 10 000 cycles. Meanwhile, the magnetic field sensitivity of the EC sensor is around 12.08 T-1 for a magnetic field intensity of 150-160 mT. Consequently, the EC sensor is successfully applied in blood pulse monitoring, pressure and magnetic field switching, and visualized pressure and magnetic field detection. Due to its high sensitivity, high durability and dual-mode responsiveness, the flexible EC sensor goes far beyond the capability of human skin, and is believed to have great potential in healthcare, robotics, e-skin and smart surgical tools, etc.
ABSTRACT
Latent curing systems are widely used in industrial thermosets in applications such as adhesion, coating, and composites. Despite many attempts to improve the practicality of this dormant reaction system, the majority of commercially available latent products still use particulate hardeners or liquid compounds with blocked active groups. These formulations generally lack fluidity or rapid reaction characteristics and thus are problematic in some industry applications. Here we describe a novel concept that stabilizes highly reactive benzoxazine/amine mixtures by reaction equilibrium. These new latent benzoxazine curing systems have a long storable lifetime but very short gel time at 150 °C. The reversible reaction between benzoxazine and amine is further demonstrated by FT-IR spectral measurements and rheological experiments, and it is shown that the overall characteristics of the latent system are promising for many industrial applications.
