Piezoluminescent devices by designing array structures.

Mechanoluminescence has attracted increasing attentions because it can convert the kinetic energy during human daily motions into light to be used in sensors and displays. However, its practical applications are still hindered by the weak brightness and limited color while under large forces. Herein, we developed novel piezoluminescent devices (PLDs) which could effectively emit visible light under low pressing forces through the stress-concentration and enhancing deformation on the basis of carefully-designed array structures. The emitting colors were also tunable by using bilayer luminescent film under different pressures. This work not only provides a new strategy to effectively harvest mechanical energy into light, but also presents a scalable, low-cost and color-tunable PLD which shows great potentials in various applications such as luminescent floors, shoes and stress-activated displays.

Stretchable and Energy-Efficient Heating Carbon Nanotube Fiber by Designing a Hierarchically Helical Structure.

Inspired by the hierarchically helical structure of classical thermal insulation material-wool, a stretchable heating carbon nanotube (CNT) fiber is created with excellent mechanical and heating properties. It can be stretched by up to 150% with high stability and reversibility, and a good thermal insulation is achieved from a large amount of formed hierarchically helical voids inside. Impressively, it exhibits ultrafast thermal response over 1000 °C s-1 , low operation voltage of several volts, and high heating stability over 5000 cycles. These hierarchically helical CNT fibers, for the first time, are demonstrated as monofilaments to produce soft and lightweight textiles at a large scale with high heating performances.

Preparation of biomimetic hierarchically helical fiber actuators from carbon nanotubes.

Mechanically responsive materials that are able to sense and respond to external stimuli have important applications in soft robotics and the formation of artificial muscles, such as intelligent electronics, prosthetic limbs, comfort-adjusting textiles and miniature actuators for microfluidics. However, previous artificial muscles based on polymer materials are insufficient in generating large actuations, fast responses, diverse deformation modes and high cycle performances. To this end, carbon nanotubes (CNTs) are proposed as promising candidates to be assembled into artificial muscles, as they are lightweight, robust and have high surface-to-volume ratios. This protocol describes a reproducible biomimetic method for preparing a family of hierarchically arranged helical fiber (HHF) actuators that are responsive to solvents and vapors. These HHFs are produced through helical assembly of CNTs into primary fibers and further twisting of the multi-ply primary fibers into a helical structure. A large number of nanoscale gaps between the CNTs and micron-scale gaps between the primary fibers ensure large volume changes and fast responses upon the infiltration of solvents and vapors (e.g., water, ethanol, acetone and dichloromethane) by capillarity. The modes of shape transformations can be modulated precisely by controlling how the CNTs are assembled into primary fibers, multi-ply primary fibers, HHFs and hierarchical springs. This protocol provides a prototype for preparing actuators with different fiber components. The overall time required for the preparation of HHF actuators is 17 h.

Nitrogen-doped hierarchical porous carbon microsphere through KOH activation for supercapacitors.

A porous carbon microsphere with moderate specific surface area and superior specific capacitance for supercapacitors is fabricated from polyphosphazene microsphere as the single heteroatoms source by the carbonization and subsequent KOH activation under N2 atmosphere. With KOH activation, X-ray photoelectron spectroscopy analysis confirms that the phosphorus of polyphosphazene microsphere totally vanishes, and the doping content of nitrogen and its population of various functionalities on porous carbon microsphere surface are tuned. Compared with non-porous carbon microsphere, the texture property of the resultant porous carbon microsphere subjected to KOH activation has been remarkably developed with the specific surface area growing from 315 to 1341 m(2) g(-1)and the pore volume turning from 0.17 to 0.69 cm(3) g(-1). Prepared with the KOH/non-porous carbon microsphere weight ratio at 1.0, the porous carbon microsphere with moderate specific surface area of 568 m(2) g(-1), exhibits intriguing electrochemical behavior in 1 M H2SO4 aqueous electrolyte, with superior specific capacitance (278 F g(-1) at 0.1 A g(-1)), good rate capability (147 F g(-1) remained at 10 A g(-1)) and robust cycling durability (No capacitance loss after 5000 cycles). The promising electrochemical performance could be ascribed to the synergy of nitrogen heteroatom functionalities and the porous morphology.