Because of their outstanding electrical and mechanical properties, graphene strain sensors have attracted extensive attention for electronic applications in virtual reality, robotics, medical diagnostics, and healthcare. Although several strain sensors based on graphene have been reported, the stretchability and sensitivity of these sensors remain limited, and also there is a pressing need to develop a practical fabrication process. This paper reports the fabrication and characterization of new types of graphene strain sensors based on stretchable yarns. Highly stretchable, sensitive, and wearable sensors are realized by a layer-by-layer assembly method that is simple, low-cost, scalable, and solution-processable. Because of the yarn structures, these sensors exhibit high stretchability (up to 150%) and versatility, and can detect both large- and small-scale human motions. For this study, wearable electronics are fabricated with implanted sensors that can monitor diverse human motions, including joint movement, phonation, swallowing, and breathing.

With the growth of the wearable electronics industry, structural modifications of sensing materials have been widely attempted to improve the sensitivity of sensors. Herein, we demonstrate patterned graphene strain sensors, which can monitor small-scale motions by using the simple, scalable, and solution-processable method. The electrical properties of the sensors are easily tuned via repetition of the layer-by-layer assembly, leading to increment of thickness of the conducting layers. In contrast to nonpatterned sensors, the patterned sensors show enhanced sensitivity and the ability to distinguish subtle motions, such as similar phonations and 81 beats per minute of pulse rate.

Graphene-based carbon nanostructures with nanometer dimensions have been of great interest due to the existence of a bandgap. So far, well-ordered edge structure and uniformly synthesized graphene quantum dots (GQDs) with a hexagonal single-crystalline structure have not been directly observed owing to the limited precision of current synthesis approaches. Herein, we report on a novel approach not just for the synthesis of the size-controlled single-crystalline GQDs with hexagonal shape but also for a new discovery on constructing 2D and 3D graphene single crystal structures from d-glucose via catalytic solution chemistry. With size-controlled single-crystalline GQDs, we elucidated the crucial role of edge states on luminescence from the correlation between their crystalline size and exciton lifetime. Furthermore, blue-emissive single-crystalline GQDs were used as an emitter on light-emitting diodes and exhibit stable deep-blue emission regardless of the voltage and doping level.

We have studied the effect of thermally reduced graphene oxide (TRG) on the properties of polypropylene/ maleic anhydride-graf t-ethylene−vinyl acetate (PP/EVA-g-MA) blends. In blends without TRG, EVA-g-MA was dispersed as droplets in PP. At low TRG content, the sheets located in the EVA-g-MA phase. At 5 wt %, the morphology was cocontinuous and the domain sizes of EVA-g-MA were small, while TRG sheets were randomly distributed in the blend. The electrical percolation threshold was between 3 and 5 wt %. Melt rheological analysis revealed that PP/EVA-g-MA/ TRG nanocomposites exhibited a viscous behavior of up to 3 wt % but showed a solidlike behavior at 5 wt %. The addition of TRG into PP/EVA-g-MA blend up to 3 wt % enhanced the tensile strength and modulus of PP/EVA-g-MA blend, while not adversely affecting its impact strength. PP/EVA-g-MA/TRG nanocomposites exhibited higher electrical and thermal conductivities compared to PP or PP/EVA-g-MA blends.