Xiaodong He

Lightweight, Superelastic, and Mechanically Flexible Graphene/Polyimide Nanocomposite Foam for Strain Sensor Application.

The creation of superelastic, flexible three-dimensional (3D) graphene-based architectures is still a great challenge due to structure collapse or significant plastic deformation. Herein, we report a facile approach of transforming the mechanically fragile reduced graphene oxide (rGO) aerogel into superflexible 3D architectures by introducing water-soluble polyimide (PI). The rGO/PI nanocomposites are fabricated using strategies of freeze casting and thermal annealing. The resulting monoliths exhibit low density, excellent flexibility, superelasticity with high recovery rate, and extraordinary reversible compressibility. The synergistic effect between rGO and PI endows the elastomer with desirable electrical conductivity, remarkable compression sensitivity, and excellent durable stability. The rGO/PI nanocomposites show potential applications in multifunctional strain sensors under the deformations of compression, bending, stretching, and torsion.

Graphene Nanoribbon Aerogels Unzipped from Carbon Nanotube Sponges

Graphene nanoribbon aerogels are fabricated by directly unzipping multi-walled carbon nanotube sponges. These fascinating materials have potential applications as high performance nanocomposites and supercapacitor electrodes.

Super‐Stretchable Spring‐Like Carbon Nanotube Ropes

Spring-like carbon nanotube ropes consisting of perfectly arranged loops are fabricated by spinning single-walled nanotube films, and can sustain tensile strains as high as 285%.

Multiferroic properties of sputtered BiFeO3 thin films

A cosputtering method was used to deposit BiFeO3 thin films on Pt∕Ti∕SiO2∕Si substrates. It was confirmed as a polycrystalline film with a tetragonal crystal structure in the annealed state. Both Fe2+ and Fe3+ ions were found to coexist in the film. The leakage current density is as low as 10−3A∕cm2 at 120kV∕cm. This sputtered film shows multiferroic properties exhibiting a saturated ferroelectric loop with a large remnant polarization of 37μC∕cm2 and a saturated ferromagnetic loop with saturation magnetization of 21emu∕cm3 at room temperature.

Highly Twisted Double-Helix Carbon Nanotube Yarns

The strength and flexibility of carbon nanotubes (CNTs) allow them to be constructed into a variety of innovated architectures with fascinating properties. Here, we show that CNTs can be made into a highly twisted yarn-derived double-helix structure by a conventional twist-spinning process. The double-helix is a stable and hierarchical configuration consisting of two single-helical yarn segments, with controlled pitch and unique mechanical properties. While one of the yarn components breaks early under tension due to the highly twisted state, the second yarn produces much larger tensile strain and significantly prolongs the process until ultimate fracture. In addition, these elastic and conductive double-helix yarns show simultaneous and reversible resistance change in response to a wide range of input sources (mechanical, photo, and thermal) such as applied strains or stresses, light illumination, and environmental temperature. Our results indicate that it is possible to create higher-level, more complex architectures from CNT yarns and fabricate multifunctional nanomaterials with potential applications in many areas.

Overtwisted, Resolvable Carbon Nanotube Yarn Entanglement as Strain Sensors and Rotational Actuators

Introducing twists into carbon nanotube yarns could produce hierarchical architectures and extend their application areas. Here, we utilized such twists to produce elastic strain sensors over large strain (up to 500%) and rotation actuators with high energy density. We show that a helical nanotube yarn can be overtwisted into highly entangled, macroscopically random but locally organized structures, consisting of mostly double-helix segments intertwined together. Pulling the yarn ends completely resolved the entanglement in an elastic and reversible way, yielding large tensile strains with linear change in electrical resistance. Resolving an entangled yarn and releasing its twists could simultaneously rotate a heavy object (30u2009000 times the yarn weight) for more than 1000 cycles at high speed. The rotational actuation generated from a single entangled yarn produced energy densities up to 8.3 kJ/kg, and maintained similar capacity during repeated use. Our entangled CNT yarns represent a complex self-assembled system with applications as large-range strain sensors and robust rotational actuators.

Surface Modification of Poly(urea-formaldehyde) Microcapsules and the Effect on the Epoxy Composites Performance

The surfaces of poly(urea-formaldehyde) (PUF) were modified by γ -glycidoxypropyltrimethoxy silane (KH560) in order to improve the interfacial bonding between self-healing PUF microcapsules and epoxy matrix. The modification mechanism between PUF microcapsules and KH560 was studied. X-ray photoelectron spectra (XPS) analyses showed that the silane coupling agent molecular binds strongly to the surfaces of PUF microcapsules. Chemical bond (Si–O–C) and hydrogen bond were formed at interface by the reaction between Si–OH and the hydroxyl group of PUF microcapsules surface. The tensile and impact resistance tests revealed that strength and toughness of the composites was improved significantly. Furthermore, scanning electronic microscopy (SEM) photographs of the fractured surface confirmed that the silane coupling agent plays an important role in improving the interfacial performance between microcapsules and resin matrix.

Surface hardness enhancement in sp3-bonded carbon doped SiC nanocomposite films

The sp3-bonded carbon/SiC composite films have been produced from electron beam-physical vapor deposition of SiC materials. The hardness of such films, measured using Hysitron indentation, reaches 50GPa, which is significantly higher than the hardness of SiC (28GPa). It appears that the superhardness of the thin films is due to the formation of nanocrystalline SiC/diamondlike carbon composites.

Molecular Dynamic Simulation of Sword-Sheath Extraction Behavior in CNT Reinforced Composite

In the pull-out testing of a multi-walled carbon nanotube (MWNT) in MWNT reinforced composites, sword-sheath extraction is an observed mechanism, in which at least the outermost layer of the MWNT remains connected to its surrounding matrix whereas the inner layer(s) slide relatively. This paper presents a MD simulation to investigate the sword-sheath extraction behavior and then compare with normal debonding extraction of a whole MWNT. It is identified that the two extractions have similar pullout force-displacement behavior with sword-sheath requiring less peak forces than debonding extraction.

Study on interface behavior of 3D composites reinforced with chemically connected CNTs using molecular dynamics

In this study, we used several molecular dynamic models to simulate the pull-out process of a carbon nanotube (CNT) that is assumed to be chemically connected to a carbon fiber, and to calculate the CNTs geometry variation, displacement, energy and stress during this process. In the simulation, the CNTs elongation and necking phenomena have been noted prior to the movement of the CNTs end embedded in resin. The simulation yields a CNTs plastic constitutive model in the pull-out process. The fracture resistance capability of a chemically connected CNT is then discussed. In the simulation of shearing, the prediction of the CNTs capability of shear resistance has been conducted. Finally, by comparing the experiment result with the simulation, we predict the amido link break before the CNT pull-out in the shearing test.