Sensors are being developed in our group based on various sensing mechanisms for wearable sensor applications. Since many of the attributes of materials used for energy storage devices such as large surface area, fast ion and electronic transport, some of the materials developed for energy storage actually work well as sensor materials. Potentiation, capacitance-based, transistor-based, hydrogel-based, and fiber-based sensing devices are being investigated. The applications we are targeting include wearable medical sensors, environmental sensors, and gas sensors.
The sensitivity of conductive hydrogels has received increasing research attention, as it plays a critical role in determining the performance of flexible strain sensors. Traditional hydrogels, however, suffer from low gauge factors (GF) and signal hysteresis due to their inherent viscoelastic properties, which compromises their sensing capabilities. Herein, we report an MXene-based composite hydrogel (M-hydrogel) by incorporating 2D MXene nanosheets into a highly stretchable and self-healing polymer network. This M-hydrogel exhibits outstanding tensile strain sensitivity (GF of 25), remarkable stretchability (over 3400%), instantaneous self-healing, and excellent conformability to human skin. This hydrogel can be used to exploit its unique asymmetrical strain sensitivity (compressive GF of 80) coupled with viscous deformation, which enables the advanced sensing of both the direction and speed of motions applied to its surface.
The orientation of MXene has received increasing research attention as it plays a critical role in determining the performance of MXene-based assemblies. Engineering MXene into horizontal or vertical orientations can offer distinct advantages regarding high electrical conductivity/mechanical strength or efficient ion/molecule transport across layers, respectively. Herein, we report a Janus-oriented MXene fiber consisting of vertically aligned nanosheets on one side and horizontally aligned ones on the other, achieved through stepwise regulation of shear and capillary forces. This Janus MXene fiber exhibits good mechanical properties, high electrical conductivity, and strong deformation capability in response to external water stimuli. This fiber can be used to construct an event-triggered logic gate, which enables the operation of a dual-mode water immersion warning system featuring both light and Bluetooth signaling.
