Polyaniline-coated halloysite nanotubes: effect of para-hydroxybenzene sulfonic acid doping

This paper reports new method of preparing electrically conducting polyaniline-coated halloysite nanotube (HNT-PANI) by using para-hydroxybenzene sulfonic acid as the doping agent. The achieved DC electrical conductivity of the HNT-PANI was 9.83?×?10^?2?Scm^?1. The HNT revealed no damages by the acid doping while achieving its conductive state. The HNT-PANI exhibits polaronic transitions, existence of favorable IR peaks and Raman scattering, increased thermal stability, and desirable morphological characteristic as a result of the in situ coating. Such electronically modified tube-like clay could be useful in many applications such as conductive fillers in nanocomposites and drug delivery with the advantage of being cost effective.     

Influence of surface modification of halloysite nanotubes and its localization in PP phase on mechanical and thermal properties of PP/ABS blends

Halloysite nanotubes (HNTs) have been successfully modified using polyethyleneimine (PEI). HNTs and PEI-modified HNTs-filled 80/20 (wt/wt) polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blends and its nanocomposites in the presence of dual compatibilizer have been prepared by melt mixing technique. The refinement in matrix–droplet morphology, selective localization of PEI-modified HNTs, increase in crystallinity of PP phase, formation of β-form of PP crystals and improved dispersion of PEI-modified HNTs in PP phase has resulted in a remarkable improvement in tensile modulus, impact strength and thermal stability of PEI-modified HNTs-filled 80/20 (wt/wt) PP/ABS blends in presence of dual compatibilizer. The increase in tensile modulus, tensile strength and impact strength for PEI-modified HNTs-filled 80/20 (wt/wt) PP/ABS blends in presence of dual compatibilizer are 28.8, 26.6 and 38.5%, respectively.     

Contact resistance of multi-walled carbon nanotube/natural rubber nanocomposites with metallic ball

This paper reports on the contact resistance (R_c) between carbon filler/natural rubber (NR) nanocomposite and gold ball: three varieties of nanocomposites were prepared from carbon black (CB) and two kinds of multi-walled carbon nanotubes (MWCNTs) with different diameter. R_c of MWCNT/NR nanocomposite was remarkably less than that of CB/NR nanocomposites. The relationship between R_c of MWCNT/NR nanocomposites and applied load was expressed in the formula, R_c=C·P⁻ⁿ (P: load, C and n: constant): for the MWCNTs (diameters of 13 nm)/NR and MWCNTs (diameters of 67 nm)/ NR nanocomposites, they were expressed as R_c=1724·P^−0.6 and R_c=344·P^−0.37, respectively. The former (MWCNT, ϕ13 nm) showed higher R_c than the latter (MWCNT, ϕ67 nm) over whole region of applied load. The mechanical hardness of the former was higher (90 HsA) than that of the latter (82 HsA). Therefore, the smaller contact area between the nanocomposite and gold ball of the former resulted in higher R_c. The apparent specific contact resistivity was calculated from the observed values of R_c and contact area: 130 Ω mm² and 127 Ω mm² for the former (MWCNT, ϕ13 nm) and the latter (MWCNT, ϕ67 nm), respectively.     

Preparation and characterization of aligned carbon nanotubes/polylactic acid composite fibers

Aligned functionalized multiwalled carbon nanotubes/polylactic acid (MWNTs-PCL/PLA) composite fibers were successfully prepared by electrospinning processing. The MWNTs bonded with the polycaprolactone chains exhibited excellent uniform dispersion in PLA solution by comparing with the acid-functionalized MWNTs and amino-functionalized MWNTs. Optical microscopy was used to study the aligned degree of the fibers and to investigate the influences of the electrodes distance on the alignment and structure of the fibers, and results showed that the best quality of aligned fibers with dense structure and high aligned degree were obtained at an electrodes distance of 3 cm. Moreover, the MWNTs embedded inside the MWNTs-PCL/PLA fibers displayed well orientation along the axes of the fibers, which was demonstrated by field emission scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

The enhanced photocatalytic activity of CdS/TiO2 nanocomposites by controlling CdS dispersion on TiO2 nanotubes

CdS/TiO₂ nanocomposites were prepared via a simple wet chemical method, and characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their ability to degrade Acid Rhodamine B was investigated under visible light irradiation. The results indicate that CdS/TiO₂ nanocomposite with a mass ratio of 4:1(TiO₂:CdS) showed high photocatalytic activity and the CdS loaded on TiO₂ nanotube surface exhibited a hexagonal phase. The dispersion of CdS on TiO₂ nanotube surface had an important effect on the degradation efficiency of pollutant, which provides a strategy for practical industry application.     

An XANES study on the modification of single‐walled carbon nanotubes by nitric acid

X‐ray absorption near‐edge structure (XANES) spectroscopy has been applied to identify the modification process of single‐walled carbon nanotubes (SWCNTs) treated by nitric acid. The carboxyl groups created by the nitric acid treatment have been found to be formed on both the carbonaceous fragments and the side walls of SWCNTs. The carbonaceous fragments could be removed by a following washing treatment with sodium hydroxide. XANES spectra indicate that carbonaceous fragments are the result of the synthesis process and/or of the nitric acid treatment. Tube walls of SWCNTs are weakly oxidized by the nitric acid treatment although, after removing carbonaceous fragments, a direct oxidation process of SWCNTs is observed. Experimental data address the removal of carbonaceous fragments on SWCNTs as an efficient method for side‐wall modification of a SWCNT.     

Morphology, mechanical, cross-linking, thermal, and tribological properties of nitrile and hydrogenated nitrile rubber/multi-walled carbon nanotubes composites prepared by melt compounding: The effect of acrylonitrile content and hydrogenation

The purpose of this work was to prepare nanocomposites by mixing multi-walled carbon nanotubes (MWCNT) with nitrile and hydrogenated nitrile elastomers (NBR and HNBR). Utilization of transmission electronic microscopy (TEM), scanning electron microscopy (SEM), and small- and wide-angle X-ray scattering techniques (SAXS and WAXS) for advanced morphology observation of conducting filler-reinforced nitrile and hydrogenated nitrile rubber composites is reported. Principal results were increases in hardness (maximally 97 Shore, type A), elastic modulus (maximally 981 MPa), tensile strength (maximally 27.7 MPa), elongation at break (maximally 216%), cross-link density (maximally 7.94 × 10²⁸ m⁻³), density (maximally 1.16 g cm⁻³), and tear strength (11.2 kN m⁻¹), which were clearly visible at particular acrylonitrile contents both for unhydrogenated and hydrogenated polymers due to enhanced distribution of carbon nanotubes (CNT) and their aggregated particles in the applied rubber matrix. Conclusion was that multi-walled carbon nanotubes improved the performance of nitrile and hydrogenated nitrile rubber nanocomposites prepared by melt compounding.     

Super-hydrophobicity and oleophobicity of silicone rubber modified by CF4 radio frequency plasma

Owing to excellent electric properties, silicone rubber (SIR) has been widely employed in outdoor insulator. For further improving its hydrophobicity and service life, the SIR samples are treated by CF₄ radio frequency (RF) capacitively coupled plasma. The hydrophobic and oleophobic properties are characterized by static contact angle method. The surface morphology of modified SIR is observed by atom force microscope (AFM). X-ray photoelectron spectroscopy (XPS) is used to test the variation of the functional groups on the SIR surface due to the treatment by CF₄ plasma. The results indicate that the static contact angle of SIR surface is improved from 100.7° to 150.2° via the CF₄ plasma modification, and the super-hydrophobic surface of modified SIR, which the corresponding static contact angle is 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is found that the super-hydrophobic surface ascribes to the coaction of the increase of roughness created by the ablation action and the formation of [-SiF_x(CH₃)_2−x-O-]_n (x = 1, 2) structure produced by F atoms replacement methyl groups reaction, more importantly, the formation of [-SiF₂-O-]_n structure is the major factor for super-hydrophobic surface, and it is different from the previous studies, which proposed the fluorocarbon species such as C-F, C-F₂, C-F₃, CF-CF_n, and C-CF_n, were largely introduced to the polymer surface and responsible for the formation of low surface energy.     

The influence of treatment duration on multi-walled carbon nanotubes functionalized by H2SO4/HNO3 oxidation

Variation in the nature of multi-walled carbon nanotubes (MWCNTs) subjected to different degrees of oxidation was investigated. The microstructure was determined by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) methods, and the surface chemistry was evaluated in terms of the functional groups determined by X-ray photoelectron spectroscopy (XPS) and thermal analysis-mass spectroscopy (TA-MS). In addition, TGA was used to indicate the thermal stability of the nanotubes. Results demonstrate that the graphitic structure of nanotubes oxidized with a mild mixture of H₂SO₄/HNO₃ was preserved. Decrease in the degree of crystallinity started with widening of the C(0 0 2) XRD diffraction peak, followed by this peak shifting towards lower angles. The oxygen content increased with increasing treatment time. A defect peak incorporated in deconvolution of XPS C1s spectra was helpful for detecting the generation of defect sites. The predominant surface functionalities of the nanotubes have been changed from basic to acidic groups after treatment for one day. The samples oxidized for two days had the most abundant surface -COOH and the highest oxidation resistance. The oxidation mechanism of MWCNTs in mild H₂SO₄/HNO₃ mixture was proposed, which was a successive and iterative process, including the initial attack on active sites, and next the hexagon electrophilic attack generating new defects and introducing more oxygen, and then the tubes becoming thinner and shorter.     

Carbon nanotubes growth from C2H2 and C2H4/NH3 by catalytic LCVD on supported iron–carbon nanocomposites

We report about the synthesis of carbon nanotubes by catalytic LCVD (C-LCVD), using a CW CO₂ laser and alternatively, C₂H₂/C₂H₄/NH₃ and C₂H₂/C₂H₄-containing gas mixtures. Different core–shell Fe–C nanocomposites (as synthesized and toluene extracted) were used employed as catalysts. The nanotubes grown from Fe–C residue demonstrate the lowest mean diameters. Prevalent curled and coiled morphologies are obtained for the CNTs grown in the presence of ammonia.     

Properties of thick SiO2/Si structure formed at 120 °C by use of two-step nitric acid oxidation method

Thick (i.e., ∼10 nm) SiO₂/Si structure has been formed at 121 °C by immersion of Si in relatively low concentration HNO₃ followed by that in 68 wt.% HNO₃ (i.e., two-step nitric acid (HNO₃) oxidation method of Si, NAOS) and spectroscopic properties and electrical characteristics of the NAOS SiO₂ layers are investigated. The SiO₂ thickness strongly depends on the concentration of HNO₃ aqueous solutions employed in the initial oxidation, and it becomes the largest at the HNO₃ concentration of 40 wt.%. The MOS diodes with the ∼9 nm SiO₂ layer formed by the NAOS method possess a relatively low leakage current density (e.g., 10⁻⁸ A/cm² at the forward bias of 1 V) and it is further decreased by more than one order of magnitude by post-metallization annealing (PMA) in hydrogen at 250 °C. The good leakage characteristic is attributable to atomically flat SiO₂/Si interfaces and high atomic density of 2.30-2.32 × 10²² atoms/cm³ of the NAOS SiO₂ layers. High-density interface states are present in as-prepared SiO₂ layers and they are eliminated by PMA in hydrogen.