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We discuss the influence of few-walled carbon nanotubes (FWCNTs) treated with nitric acid and/or sulfuric acid on field emission characteristics. FWCNTs/tetraethyl orthosilicate (TEOS) thin film field emitters were fabricated by a spray method using FWCNTs/TEOS sol one-component solution onto indium tin oxide (ITO) glass. After thermal curing, they were found tightly adhered to the ITO glass, and after an activation process by a taping method, numerous FWCNTs were aligned preferentially in the vertical direction. Pristine FWCNT/TEOS-based field emitters revealed higher current density, lower turn-on field, and a higher field enhancement factor than the oxidized FWCNTs-based field emitters. However, the unstable dispersion of pristine FWCNT in TEOS/N,N-dimethylformamide solution was not applicable to the field emitter fabrication using a spray method. Although the field emitter of nitric acid-treated FWCNT showed slightly lower field emission characteristics, this could be improved by the introduction of metal nanoparticles or resistive layer coating. Thus, we can conclude that our spray method using nitric acid-treated FWCNT could be useful for fabricating a field emitter and offers several advantages compared to previously reported techniques such as chemical vapor deposition and screen printing.

Polyvinylidene fluoride (PVDF)/multiwalled carbon nanotube (MWCNT) composites were prepared by using twin screw extruder at various (0–5 wt %) MWCNT loadings. Field Emission Scanning Electron Microscope (FESEM) micrographs showed a relatively good dispersion and random distribution of MWCNT in PVDF matrix. The physical and dielectric properties increased gradually with the increase in MWCNT content but the thermal stability decreased. The DSC result revealed the increase in crystallinity of the PVDF matrix. Wide angle X-Ray diffraction (WAXD) result showed a large shoulder at 2θ of 20.78° with increasing in MWCNT content. The experimental percolation threshold for the surface resistance of PVDF/MWCNT composites were estimated and clearly observed at 4 wt % of MWCNT loading. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

PLA biodegradable composites reinforced with various silk fibroin powder contents (0, 1, 3, 5 and 7 wt.-%) were prepared by solution processing technique using CH 2 Cl 2 as solvent. After that the composites and virgin PLA were foamed by using supercritical CO 2 . The influence of silk contents on PLA/silk fibroin powder composite foams were investigated by using SEM, XRD and DSC. Compared with PLA foam, the composite foams exhibited a reduction in cell size and increase in cell density at high silk content. With an increase in saturation temperature and pressure, the cell size was increasing and both the cell density and foam density were decreased simultaneously.

A method for evaluating bulk sensitive structural characteristics of unpurified, as-purified, and acid treated single walled carbon nanotubes (SWNTs) was described in the present study. The optical spectra of SWNT solutions were well resolved after prolonged sonication and they were correlated to the diameter and the distribution of nanotubes. The acid-treated SWNTs were similar to as-purified SWNTs in terms of catalyst residue, radial breathing mode (RBM) in the Raman spectra, and the first band gap energy of semiconducting tubes in the optical spectra. The solution phase optical spectra were more sensitive to changes in the small diameter and metallic tubes after the acid treatment than were the RBM spectra.

Poly(ethylene terephthalate) (PET)/multiwalled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in the PET matrix, functionalized MWCNTs having acid groups (acid-MWCNTs) and acetic groups (acetic-MWCNTs) on their surfaces were used. The functional groups were confirmed by infrared spectrometry. Scanning electron microscopy showed that acetic-MWCNTs had a better dispersion in the PET matrix than pristine MWCNTs and acid-MWCNTs. A reaction between PET and acetic-MWCNTs was confirmed by a shift of the Raman G band to a higher frequency and an increase of the complex viscosity in the rheological properties. The composites containing functionalized MWCNTs showed a large increase in their tensile strengths and moduli. The values of the strengths and moduli of the PET/acetic-MWCNT composites were higher than those of the PET/acid-MWCNT composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Poly(ethylene terephthalate) (PET)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by in situ polymerization. Light scattering measurement suggested that there is significant change in molecular weight arising from gel formation by chemical crosslinking during polymerization. The thermal decomposition temperatures of the composites measured at 5 wt % weight loss were 5–10°C higher than that of PET. There is no significant change in other thermal properties. Scanning electron microscopy observations suggest that there is obvious phase separation in PET/POSS composites, composites containing 1 wt % of disilanolisobutyl and trisilanolisobytyl-POSS show fine dispersions of POSS (30–40 nm in diameter), which arise from strong interfacial interactions between POSS and PET during polymerization. The viscosity of the composites increased with the addition of POSS. The observation of a plateau region of composites containing 1 wt % of POSS in the plot of log G′ vs. log G″ indicates strong interfacial interactions between POSS and PET. Sixty-three percent and 41% increase in tensile strength and 300 and 380% increase in modulus were achieved in the composites containing 1 wt % of disilanol- and trisilanol-POSS, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The present result indicates that the steady-state fluorescence behavior of E7/NOA-65 polymer disperse liquid crystal films prepared by a photoinitiated-polymerization induced phase separation method plays a significant role in understanding electro-photophysical response and hysteresis on varying applied electric fields. The fluorescence technique is sensitive to molecular alignment of LC molecules in the polymer matrix and it also provides useful quantitative information on the rise time, the threshold voltage and the driving voltage of a PDLC system.

We have extensively characterized the fluorescence behavior of unsaturated polyester (UP) resin in the absence and presence of a 1,3-bis-(1-pyrenyl)propane (BPP) fluorescent probe at various dynamic and isothermal cure histories by means of a steady-state fluorescence technique using a front-face illumination equipment. In addition, we explored the effect of the fluorescence intensity on the relaxation of the fluorescent probe in the UP resin by resting the dynamically and isothermally cured resin at ambient temperature and pressure for 24 h. The monomer fluorescence intensity, which has two characteristic peaks at 376 and 396 nm, changed noticeably depending on the cure temperature and time and provided important information with respect to the molecular and photophysical responses upon curing. The result of the fluorescence study indicates that the increased local viscosity and restricted molecular mobility of the UP resin surrounding the BPP probe after curing are both responsible for the enhancement of the monomer fluorescence intensity. Our results also demonstrate that once the BPP probe has enough time to rearrange and become isolated prior to fluorescence, a sufficient amount of fluorescence is emitted. Therefore, we note that the fluorescence behavior of this UP resin system is influenced strongly by the relaxation process of the fluorescent probe in the resin as well as process used to cure the resin.

This paper proposes two important models useful for describing heat transfer and temperature profiles in single and modular self-wiping co-rotating twin-screw extruders. One model predicts heat transfer coefficients. Calculations of the barrel and screw heat transfer coefficients are made for various modules in different diameter extruders. We compare the values of the heat transfer coefficients from the model with those from literature. The second model predicts the axial screw temperature profile when the barrel, but not the screw, is heated, Example calculations of the cup mixing and screw temperature profiles are also made for different diameter extruders.

Extensive experimental studies of a starved flow modular tangential screw extruder are described. Die pressures and fill factor profiles along the screw axis are measured and used to determine screw characteristic curves Q vs. AP/L for individual screw elements of varying designs in a Leistritz twin screw extruder. Superior pumping characteristics of matched as opposed to staggered elements is found. The experimental screw characteristic curves are compared with the results of mathematical simulations of the flow. Agreement is generally good.

A model for flow in a Farrel Continuous Mixer based upon cylindrical coordinate hydrodynamic lubrication theory is presented. Pressure and flux fields over the rotor surface are calculated. The pumping characteristics of the various sections of the machine rotors were calculated. Generally Farrel Continuous Mixers are operated under starved conditions. Calculations are presented for continuous mixers operating under starved conditions. Pressure and fill factor profiles are determined. Fill factors are predicted to be increased by increasing throughput, increasing exit gate pressure and reducing screw speed.

Multi-walled carbon nanotubes (MWCNTs) filled polypropylene (PP) composites were prepared by a corotating intermeshing twin screw extruder. To improve the dispersion of MWCNTs, the surface of MWCNT was modified with 1,10-diaminodecane, and maleic anhydride grafted polypropylene (MA-g-PP) was used as a compatibilizer. Micrographs of well dispersed functionalized MWCNTs (diamine-MWCNT) were observed due to the reaction between MA-g-PP and diamine-MWCNT in PP/MA-g-PP/diamine-MWCNTs composites. The different behaviors in crystallization and melting temperatures of PP/MA-g-PP/diamine-MWCNTs composite were observed compared to PP and PP/neat-MWCNT. Especially, the decomposition temperature of the composite was increased by 50°C compared to PP. PP/MA-g-PP/diamine-MWCNTs composite showed the highest complex viscosity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009