Enhanced Physical and Mechanical Properties of Nitrile-Butadiene Rubber Composites with N-Cetylpyridinium Bromide-Carbon Black.

The physical and mechanical properties of nitrile-butadiene rubber (NBR) composites with N-cetylpyridinium bromide-carbon black (CPB-CB) were investigated. Addition of 5 parts per hundred rubber (phr) of CPB-CB into NBR improved the tensile strength by 124%, vulcanization rate by 41%, shore hardness by 15%, and decreased the volumetric wear by 7% compared to those of the base rubber-CB composite.

Flexible narrowband organic photodiode with high selectivity in color detection.

This study describes the design of a flexible narrowband organic photodiode (OPDs) with a novel structure. A bulk heterojunction of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) is introduced as a photoactive layer, with an optimized thickness of 160 nm, and a MoO3/Ag/MoO3 (MAM) multilayer electrode and polyimide (PI) film substrate were used. The OPD with the device architecture of PI/MAM/P3HT:PC70BM/Al showed narrowband photodiode performance in the 500-650 nm wavelength range. The maximum external quantum efficiency (EQE) of the OPD was 15.41% at 570 nm, which dropped to ∼0% outside the operation wavelength range. This narrowband detectivity originated from the cutoff of light at wavelengths below 500 nm by the PI substrate and photoreactivity of P3HT:PC70BM at wavelengths between 300 and 650 nm. Outer bending tests performed over 1000 cycles revealed that the average maximum EQE remained at ∼15%. The maximum responsivity of the OPD was calculated to be 0.07 A W-1 at 570 nm. The OPD device showed a narrow response spectrum with a full width at half maximum of 100 nm. This research suggests a new approach for the fabrication of flexible OPDs with high selectivity in color detection.

Mechanical and Tribological Properties of Polytetrafluoroethylene Composites with Carbon Fiber and Layered Silicate Fillers.

Mixtures of layered silicates (vermiculite and kaolinite) and carbon fibers were investigated as filler materials for polytetrafluoroethylene. The supramolecular structure and the tribological and mechanical properties of the resulting polymer composite materials were evaluated. The yield strength and compressive strength of the polymer increased by 55% and 60%, respectively, when a mixed filler was used, which was attributed to supramolecular reinforcement of the composites. In addition, the wear resistance increased by 850 times when using vermiculite/kaolinite fillers, which was due to protection of the surface by the formation of hard tribofilms.

Preparation and Improved Physical Characteristics of Propylene Oxide Rubber Composites.

Sealing rubbers employed in cold climates such as the Siberian Arctic must be able to withstand temperatures as low as -50 °C while still exhibiting specific relaxation, strength, tribological characteristics, and a resistance to aggressive media. Previous investigations of propylene oxide rubber (SKPO, Tg = -73 °C) modified with polytetrafluoroethylene (PTFE) have revealed that, while the rubber composite materials exhibit double the wear resistance compared to unmodified polypropylene oxide rubber, they have poor frost resistance. In the present study, we developed materials based on SKPO and ultrafine PTFE (UPTFE), which can be characterized by its smaller particle size, low molecular weight, high tribo-technical characteristics, and resistance to aggressive media. The properties of the rubber composites were evaluated using the standard methods. The structures of the materials were investigated by electron microscopy and XRD analysis. It was shown that the materials have excellent wear resistance, resistance to aggressive media, compression set, and low-temperature resistance. The addition of UPTFE is preferable to the addition of PTFE because the desired positive effects can be attained with only 0.5⁻1 parts per hundred parts of rubber (phr) UPTFE while 20 phr PTFE would be necessary.

Surfactant Effects on Structure and Mechanical Properties of Ultrahigh-Molecular-Weight Polyethylene/Layered Silicate Composites.

In this study, the reinforcement of ultrahigh-molecular-weight polyethylene (UHMWPE) with biotite was investigated. The biotite filler was mechanically activated with different dry surfactants to improve its compatibility with UHMWPE and decrease agglomeration among biotite particles. Alkyldimethylbenzylammonium chloride (ADBAC) and cetyltrimethylammonium bromide (CTAB) were selected as cationic surfactants. The tensile strength of composites containing 1 wt % of CTAB-treated biotite was increased by 30% relative to those with untreated biotite, but was unchanged with ADBAC treatment of the same biotite content. The stereochemistry of the surfactant may be critical to the composite structure and mechanical properties of the material. The stereochemistry of CTAB was preferable to that of ADBAC in enhancing mechanical properties because the stereochemistry of ADBAC impedes favorable interactions with the biotite surface during mechanical activation.

Enhancement of Emission Lifetime of CNT Emitters by Coating ZnO on the CNT Surface.

Carbon nanotubes (CNTs) have been investigated as field-emission sources owing to their high electrical conductivity and high aspect ratio. However, practical applications demand that the emission lifetime of CNTs be further improved. Since ZnO demonstrates impressive electrical and thermal conductivity, when coated on the surface of CNTs, it can allow the CNT field emitters to endure high electrical stress and high temperature. Moreover, ZnO nanostructures protect the CNT emitters from being bombarded by high-energy ions, which are accelerated by the high electric field. From the result of emission lifetime measurements at the emission current density of 100 mA/cm2, we found that the emission lifetime was increased by more than a factor of 2 when ZnO had been coated onto the CNT emitters. The observation registers as an important contribution to the practical application of CNT emitters with long-term emission stability, as well as with high emission currents. In this work, we elucidate the detailed mechanism of long-term stability that can be achieved by coating ZnO nanostructures on the surface of CNTs.

Giant enhancement of the Raman response due to one-dimensional ZnO nanostructures.

We observed giant enhancement of the Raman intensity from 4-Mpy molecules adsorbed on semiconducting one-dimensional ZnO nanostructures, nanowires and nanocones, without involving any noble metals. Interestingly, the enhancement is strongly dependent on the geometry of ZnO nanostructures and can mainly be explained by the cavity-like structural resonance of the electric field. Our results can be applied to systematically create hot spots for Raman signal enhancement using one-dimensional semiconducting nanomaterials.

Superior field emissions from boron-doped nanocrystalline diamond compared to boron-doped microcrystalline diamond.

Boron-doped microcrystalline diamond (BMD) and nanocrystalline diamond (BND) thin films were grown on Si substrates by microwave-assisted chemical vapor deposition, and their field emission properties were evaluated. BND exhibited a lower turn-on field and higher field enhancement factor than BMD. Furthermore, in a long-term emission stability test, BND showed only a 4% increase in the current density after 12 h of emission, whereas the current density of BMD decreased by - 59%. These results indicate that BND is a more stable and viable current emitter than BMD.

Direct observation of enhanced cathodoluminescence emissions from ZnO nanocones compared with ZnO nanowire arrays.

We report, for the first time, direct observation of enhanced cathodoluminescence (CL) emissions from ZnO nanocones (NCs) compared with ZnO nanowires (NWs). For direct and unambiguous comparison of CL emissions from NWs and nanocones, periodic arrays of ZnO NW were converted to nanocone arrays by our unique HCl [aq] etching technique, enabling us to compare the CL emissions from original NWs and final nanocones at the same location. CL measurements on NW and nanocone arrays reveal that emission intensity of the nanocone at ∼ 387 nm is over two times larger than that of NW arrays. The enhancement of CL emission from nanocones has been confirmed by finite-difference time-domain simulation of enhanced light extraction from ZnO nanocones compared to ZnO NWs. The enhanced CL from nanocones is attributed to its sharp morphology, resulting in more chances of photons to be extracted at the interface between ZnO and air.

Formation of ZnO nanocones using wet chemical etching of ZnO nanorods in an aqueous solution of HCl.

In this report, a simple wet chemical etching of ZnO nanorods to fabricate large area ZnO nanocones is demonstrated. The cone-like morphology formation utilizes anisotropic etching rate on the different crystal planes of ZnO nanorods in an aqueous solution of HCl (HCl [aq]). To form ZnO nanocones, single crystalline ZnO nanorods with a flat hexagonal shape are synthesized on p-Si(100) using hydrothermal method at 90 degrees C and then, are immersed in HCl [aq]. Electron microscopy reveals that the HCl [aq] treatment of ZnO nanorods significantly etched sidewalls of nanorods, resulting in the cone-like morphology formation. The nanocone formation is the most noticeable when the etching occurred in HCl [aq] with a pH of 2.5-3.0 for 5 min etching time. Geometrical analysis using the electron microscopy reveals that the sidewall of a ZnO nanocone have formed a plane indexed as (0-111) after the etching process.