Advanced Materials Research Vols. 415-417

Abstract: Ultrafine fibers were electrospun from polyacrylonitrile (PAN)/N,N-dimethyl formamide (DMF) solution as a precursor of carbon nanofibers. The effects of solution concentration, applied voltage and flow rate on preparation and morphologies of electrospun PAN fibers were investigated. Morphologies of the green fibers, stabilized fibers and carbonized fibers were compared by scanning electron microscope (SEM). The diameter of PAN nanofibers is about 450nm and the distribution of diameter is well-proportioned. Characterization of the elements changes of fibers were performed by X-ray photoelectron spectroscopy (XPS).

Abstract: Ag, Au and Ti metal nanoparticles colloids have been prepared by pulsed laser ablation in various liquids. The particle size and morphology of the obtained nanoparticles colloids were characterized by transmission electron microscopy (TEM), the average diameter and its distribution were analyzed by Image-ProPlus software. The results showed that the Au nanoparticles were of the best characterization, the average diameter was the smallest (D=8.79 nm), and also, the distribution of particle size was the narrowest (=17.5 nm) and the morphologies were more homogeneous.

Abstract: For gelating agent in hydraulic fracturing fluid, the temperature resistance is required. To improve the temperature resistance of Guar gum (GG), it was modified by silanization. The reaction conditions were investigated, and the optimized conditions were as following: the reaction temperature of 85°C, 5: 1 molar ratio of guar gum to TMS-Cl and 4-6 h of reaction time. The viscosity of silanized guar gum (SGG) aqueous gel was greatly improved even high temperature at 80°C.

Abstract: We have successfully fabricated light emitting diodes (LEDs) based on patterned sapphire substrates (PSSs) fabricated by employing nanoimprint lithography (NIL) technique. The nano-patterns were designed as regular triangles consisting of columns, whose diameters and pitches were 100, 150, 200, 250 nm and 200, 300, 400, 500 nm, respectively. 412 nm wavelength LEDs grown by metal organic chemical vapor deposition (MOCVD) method were also demonstrated. The NIL technique and nano-etching by employing RIE were demonstrated in details. The qualities of all LEDs based on PSSs are superior compared with that non-patterned sapphire substrate LED. The experimental results showed that the light output power was increased by using the PSS structure. At a driving current of 20 mA, the light output powers of LEDs based on PSSs with 200, 300, 400 and 500 nm pitches are enhanced by 59%, 79%, 42% and 48%, compared with the conventional LEDs. These results provide promising potential to increase output powers of commercial light-emitting devices.

Abstract: A nanostructured surface layer was obtained on the surface of Zr-4 by surface mechanical attrition treatment(SMAT). The structure and the properties of the SMAT sample were analyzed by means of the optical microscope, hardness and polarization curve testing. The results show that， when processing time for 5min, the average grain sizes on the surface layer can be refined to 23nm. The average grain size by SMAT-ed for 15min is 20nm, which is the smallest. The microhardness have a significant increase, the surface roughness also increase, and the corrosion resistance reduce in 1mol H₂SO₄ solution.

Abstract: Natural fiber reinforced composites are being used as reinforcement material in composite system due to their positive environmental benefits. Added to that, natural fibers offer advantages such as low density, low cost, good toughness, high specific strength, relatively non-abrasive and wide availability. However, the low thermal stability of natural fibers is one of the major challenges to increase their use as reinforcing component. In this study, a thorough investigation has been done to compare the effect of two chemical treatment methods on the thermal stability of hemp fibers. 5wt% sodium hydroxide and 5wt% triethoxyvinylsilane was used for the treatment of hemp fibers. Fourier transform infrared spectroscopy, scanning electron microscopy and thermo gravimetric analysis were used for characterization of untreated and treated fiber. The results indicated that 24 hours alkali treatment and 3 hours silane treatment time enhanced the thermal stability of the hemp fiber. However, alkali treatment shows better improvement compared to silane treatment.

Abstract: In this paper, Silver nitrate(AgNO₃) and polyvinylpyrrolidone (PVP) acted as the silver source and dispersant respectively, the silver nanowires including a small amount of folded structure of silver nanowires, were synthesized by hydrothermal method under the polyol system combined with traces of sodium chloride. The nanowires were characterized by X-ray powder diffraction(XRD), transmission electron microscopy(TEM), selected area electron diffraction(SAED), scanning electron microscopy (SEM), energy dispersive spectrometry (EDAX) and UV-vis absorption spectroscopy to determine the chemical composition, crystal structure, morphology,and the generation mechanism of Ag nanowires was also analysed. The experimental results showed that the crystal structure of the as-prepared Ag nanowires was fcc structure with uniform width, smooth surface, the diameter about 200nm,the average length about 15μm,and the aspect ratio up to 75.The folded structure of silver nanowires synthesized were due to the straight silver nanowires were connected in an end-to-end manner, with obvious spacing between them.

Abstract: Polypropylene（PP）as the interchangeable plastic has some unique advantages and drawbacks. PP toughening by rubbery particles especially EPDM has been researched a lot. As the research progresses, more and more researchers recognize that the single rubbery particles could not solve the problem in PP. It becomes a trend and necessity that PP was toughening modified by using rigid particles. But the rigid particles could not combine with matrix resin. Before the application, it should modify rigid particles first. This article takes CaCO₃ as example modified by titanate coupling agent. Then, the modified CaCO₃ was identified by FT-IR and detected the activation degree. After that, using the modified CaCO₃ and unmodified CaCO₃ blending with PP/EPDM respectively and then compare the mechanical properties.

Abstract: The strong field enhancement of a new type of rectangle plasmonic optic nano-antenna with two protrusions in the middle gap is studied by the comparison with two another common rectangle structures using CST software. The intensity of the new type presented in the paper is about 2.5 times more than its common counterpart, up to about 60V/m in the center of antenna, and the position of peak shifts to visible region (406THz) from infrared region (382THz). Further more, the resonant magnitude in the region of corners of protrusions in the middle gap is somewhat larger than that in center region of antenna, and the resonant frequencies all are controlled in the visible range, about 410THz,the results indicate that the protrusions have a good effect on the performance of antenna. Moreover, when a glass substrate is used, the maximum of field magnitude is about 3 times lager than the same structure without substrate, up to 214 V/m, and the resonant frequency red-shifts to about 359THz, which demonstrates that the substrate plays a important role in the excitation of stronger enhancement. The type presented in the paper has a certain reference for the fabrication of high-quality optical nano-antennas and solar cells etc.

Abstract: A photoelectrochemical solar cell with a structure of modified Si nanowire anocle/K₄Fe(CN)₆+ K₃Fe(CN)₆/Pt cathode was prepared and studied. The Si nanowires were first formed by immersing n-Si chip in an etching solution of HF + AgNO₃ and Pd and Ni metals were electrolessly deposited on the surface of Si nanowires. The modified anode was characterized by a scanning electron microscope for the surface and cross section view, and by an X-ray diffractometer for the phase and structure. The properties of the photoelectrochemical solar cell were measured under standard AM 1.5 simulated sunlight (100mW/cm²). The results showed that the total photoelectron conversion efficiency of the photoelectrochemical solar cell can be slightly increased when the Si nanowire anode was deposited with Pd metal, and can be greatly increased when deposited with Ni metal.