Hongbing Jia

Electronic currents and the formation of nanopores in porous anodic alumina

The formation processes of barrier anodic alumina (BAA) and porous anodic alumina (PAA) are discussed in detail. The anodizing current J(T) within the oxide includes ionic current j(ion) and electronic current j(e) during the anodizing process. The j(ion) is used to form an oxide and the j(e) is used to give rise to oxygen gas or sparking. The j(e) results from the impurity centers within the oxide. For a given electrolyte, the j(e) is dependent on the impurity centers and independent of the J(T). The formation of nanopores can be ascribed to the oxygen evolution within the oxide. Oxygen gas will begin to be released at the critical thickness d(c). The manner of the development of PAA is in accordance with that of BAA. The differences between PAA and BAA are the magnitude of j(e) or the continuity of oxygen evolution. There are two competitive reactions, i.e. oxide growth (2Al3 + 3O2- --> Al2O3) and oxygen evolution (2O2- --> O2 up arrow + 4e). The former keeps the wall of the channel lengthened, the latter keeps the channel open. By controlling the release rate of oxygen gas under different pressures, the shape of the channels can be adjusted. The present results may open up some opportunities for fabricating special templates.

Centrifugal purification of chemically modified single-walled carbon nanotubes

Abstract A wet chemistry procedure which couples chemical functionalization and a dispersion—centrifugation cycle was applied to the dissolution and purification of as-prepared electric-arc produced single-walled carbon nanotubes (SWNTs). It is validated that K2S2O8 treatment generates hydrophilic groups such as carboxyl and hydroxyl on the surfaces of varying carbons, whereas such treatment also causes no severe destruction on the structure of SWNTs. Amidation of the K2S2O8-treated and mixed acids shortened SWNTs leads them largely soluble in tetrahydrofuran (THF) or other organic solvents. The soluble sample was fractionated via a dispersion—centrifugation cycle and highly pure and well-separated SWNTs were successfully obtained in the middle fractions. The purity of the centrifugally fractionated samples is qualitatively estimated with Raman spectroscopy, scanning electron microscope (SEM), and atomic force microscopy (AFM). Quantitative optical absorption spectroscopy and thermogravimetric analysis show that about 60% nanotubes in the starting material are transferred into liquid phase and the carbonaceous purity reaches as high as 129% of a reference sample R2, an ‘impurity-free’ fragment of soot directly from the arc chamber.

Polyvinyl pyrrolidone modified graphene oxide for improving the mechanical, thermal conductivity and solvent resistance properties of natural rubber

Polyvinyl pyrrolidone (PVP) was applied to modify graphene oxide (GO) to obtain PVP modified GO (PGO). The PGO/natural rubber (NR) nanocomposites were fabricated by mixing a PGO aqueous dispersion with NR latex, followed by coagulation and vulcanization. The structure of PGO was characterized using atomic force microscopy, solid state 13C NMR, Fourier transform infrared spectroscopy, Raman spectra and X-ray photoelectron spectroscopy. The interaction between GO and PVP molecules as well as the effects of PGO on the mechanical properties, thermal conductivity and solvent resistance properties of the NR matrix were thoroughly studied. The results revealed that PVP molecules might interact with GO via hydrogen bonds. With the addition of PGO, the tensile strength, tear strength and thermal conductivity as well as solvent resistance of the PGO/NR nanocomposites increased. The PGO/NR nanocomposite with 5 phr (parts per hundred rubber) PGO had an 81%, 159%, 30% increase in tensile strength, tear strength, thermal conductivity and a 46% decrease in solvent uptake, respectively, compared with pristine NR.

Highly Stretchable, Ultrasensitive, and Wearable Strain Sensors Based on Facilely Prepared Reduced Graphene Oxide Woven Fabrics in an Ethanol Flame

The recent booming development of wearable electronics urgently calls for high-performance flexible strain sensors. To date, it is still a challenge to manufacture flexible strain sensors with superb sensitivity and a large workable strain range simultaneously. Herein, a facile, quick, cost-effective, and scalable strategy is adopted to fabricate novel strain sensors based on reduced graphene oxide woven fabrics (GWF). By pyrolyzing commercial cotton bandages coated with graphene oxide (GO) sheets in an ethanol flame, the reduction of GO and the pyrolysis of the cotton bandage template can be synchronously completed in tens of seconds. Due to the unique hierarchical structure of the GWF, the strain sensor based on GWF exhibits large stretchability (57% strain) with high sensitivity, inconspicuous drift, and durability. The GWF strain sensor is successfully used to monitor full-range (both subtle and vigorous) human activities or physical vibrational signals of the local environment. The present work offers an effective strategy to rapidly prepare low-cost flexible strain sensors with potential applications in the fields of wearable electronics, artificial intelligence devices, and so forth.

Synergistic effects of hybridization of carbon black and carbon nanotubes on the mechanical properties and thermal conductivity of a rubber blend system

Abstract The effects of hybridization of multi-walled carbon nanotubes (MWCNTs) with carbon black (CB) and the structure-property relationships of nanocomposites based on hydrogenated nitrile-butadiene rubber/hydrogenated carboxylated nitrile-butadiene rubber blends were extensively studied. MWCNTs used in this work were modified through acid treatment to improve the dispersion of MWCNTs in the rubber matrix and the surface interaction between MWCNTs and matrix. Synergistic interaction between CB and MWCNTs increased the tensile modulus and tear strength of nanocomposites. The effect of MWCNTs on the transport properties invoked an increment in the thermal conductivity of the nanocomposites. A combination of 10 phr (parts per hundred rubber) MWCNTs with 40 phr CB dramatically increased the modulus at 100% elongation, tear strength, and thermal conductivity of the nanocomposite by 66%, 28%, and 36%, respectively, compared with those of nanocomposite filled with 40 phr CB.

Effect of Melting Conditions on Crystallization Behavior of Poly(trimethylene terephthalate)

Abstract The effect of melting conditions on the crystallization kinetics of poly(trimethylene terephthalate)(PTT) was presented by means of depolarized light intensity (DLI) technique. The kinetics of PTT crystallization from melt depends on melting conditions and primarily upon the temperature of the melt. Higher melt temperature or longer time of melting may cause a reduction of crystallization rates at the melt temperature range from 506 to 531 K. Crystallization mechanism of PTT crystallizing from various melting conditions has been discussed according to Avrami kinetics parameters and morphology study. The reduction of the rate may result from two reasons: 1) the decrease of regularity such as residual nuclei in the PTT melt which lead to a reduction in the number of heterogeneous nuclei in the crystallization process; 2) the decreased spherulitic growth rate of PTT with higher melt temperature or longer residence time for melting