Prediction of the mechanical characteristics of multi-walled carbon nanotube/epoxy composites using a new form of the rule of mixtures

Multi-walled carbon nanotubes (MWCNTs) were used in the low-viscosity, thermosetting polyester epoxy/amine resin LY-5052 with high temperature resistance to fabricate MWCNT/epoxy composites. Tensile tests of the specimens were carried out to obtain mechanical properties of MWCNT/epoxy composites for various weight-percents (wt.%) of MWCNTs. Experimental results show that the Young’s modulus and the tensile strength of the composites can be significantly improved by adding a small percentage of MWCNT. A new form of the rule of mixtures, including an exponential shape function, length efficiency parameter, orientation efficiency factor and a waviness parameter, is proposed for a more accurate prediction of the mechanical properties of MWCNT-reinforced epoxy composites, for both low and high wt.% ranges. In order to verify the suitability of the model, the ensuing predictions are compared to the available experimental data in the literature. Results demonstrate a good predictability of the modified form over a wide range of tests.     

Fabrication of silver nanoparticles dispersed in palm oil using laser ablation

In this study we used a laser ablation technique for preparation of silver nanoparticles. The fabrication process was carried out by ablation of a silver plate immersed in palm oil. A pulsed Nd:YAG laser at a wavelength of 1064 nm was used for ablation of the plate at different times. The palm coconut oil allowed formation of nanoparticles with very small and uniform particle size, which are dispersed very homogeneously within the solution. The obtained particle sizes for 15 and 30 minute ablation times were 2.5 and 2 nm, respectively. Stability study shows that all of the samples remained stable for a reasonable period of time.     

Morphology and Thermal Stability of Novolac Phenolic Resin/Clay Nanocomposites Prepared via Solution High‐Shear Mixing

Phenolic resin/clay composites were prepared by high‐shear mixing of clay suspended in CH₃OH solutions of Novolac resin and curing agent. Pure clay Cloisite Na⁺ and pillared clays Cloisite 10A, 30B, and Na⁺Cloisite that was pillared by 3‐hexadecyl‐1‐methylimidazolium bromide were studied. After CH₃OH evaporation, Novolac was cured at low temperatures. XRD showed that clay gallery d‐spacings decreased upon solvent evaporation and partial curing. Slight d‐spacing increases were sometimes observed from a partially cured stage to a further cured composite. Na⁺Cloisite gave the highest nanodispersion, Cloisites 10A and 30B the lowest. TGA revealed that Na⁺ clay or organoclay incorporation in partially cured and cured composites did not improve the thermal stability of Novolac.

     

The comparison of the behaviors of polymer/clay nanocomposites based on high density polyethylene and polypropylene in exposure of electron‐irradiation

The effect of irradiation on thermal and mechanical properties of high density polyethylene (HDPE) and polypropylene (PP)/clay nanocomposites in the presence of polyethylene glycol (PEG) and polypropylene glycol (PPG) for enhancing the clay dispersion into the polymer matrices is considered. The morphology studies show that clay layers satisfactorily expand in the presence of compatibilizers. The irradiation improves the mechanical properties of HDPE nanocomposites at 500 kGy, but it decreases the tensile strength of PP nanocomposites. The addition of PEG markedly ameliorates the mechanical properties of HDPE nanocomposites at 500 kGy, while this improvement is not deduced for PP nanocomposites. The thermogravimetric analysis data show that the irradiation increases the thermal stability of HDPE nanocomposites at the clay content of 5 wt% with and without compatibilizer. The thermal stability of PP nanocomposites descends with the irradiation dose, and the presence of PPG into the PP matrix intensifies this reduction. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Synthesis and characterization of clay dispersed polystyrene nanocomposite via atom transfer radical polymerization

Finely well‐defined polystyrene nanocomposites were prepared by ATRP method in bulk at 110°C using organically modified montemorillonite, cloisite 30B. The living nature of ATRP reaction was employed to in situ synthesize tailor‐made polystyrene nanocomposite with narrow molecular weight distribution and controlled molecular weight polystyrene chains. The amount of clay loading and time of swelling of clay in the monomer before polymerization were proved to have a positive effect on polymerization rate and also broadened the molecular weight destribution. The gas chromatography (GC) results showed the linear increase of Ln(M₀/M) versus time, which indicates the controlled/living polymerization in the presence of nanoclay. Another confirmation of the living nature of the polymerization was linear elevation of molecular weight against monomer conversion concluded from gel permeation chromatography (GPC) data. X‐ray diffraction analysis showed the interlayer spacing of nanoclay platelets as well as the exfoliated clay morphology in the nanocomposite samples. Transfer electron microscopy (TEM) revealed the exfoliated morphology of the in situ prepared nanocomposite as opposed to conventional solution‐blending technique which resulted in an intercalated structure. The effect of nanoclay on acceleration of polymerization was proved by GC and GPC; similarly, Fourier transform infrared spectroscopy (FTIR) was used to discuss the reasons of such a rate acceleration. A shifting in the wave number of characteristic bonds of nanoclay after polymerization mostly in the case of O H and Si O bonds, revealed the interaction between polymer chains and clay layers which resulted in an accelerated polymerization process. The living nature of polymeric chains was more elucidated by FTIR data. Atomic force microscopy (AFM) images also confirmed the proper dispersion of nanoparticles in the polymer medium. POLYM. COMPOS., 31:1829–1837, 2010. © 2010 Society of Plastics Engineers     

Theoretical prediction of condensed phase heat of formation of nitramines, nitrate esters, nitroaliphatics and related energetic compounds

An empirical approach is presented for calculation heats of formation of nitramines, nitrate esters, nitroaliphatics and related energetic compounds which contain at least one of the functional groups including N-NO(2), C-ONO(2) or nonaromatic C-NO(2). This approach is based on elemental composition and various structural and functional group parameters of C(a)H(b)N(c)O(d) energetic compounds. Heat of formation for 78 nitrocompounds including nitramines, nitrate esters, nitroaliphatics and the data obtained is compared with experimental data. Root mean square (rms) of deviation for 19 well known of mentioned energetic compounds are also compared with complex quantum mechanical computations which show 23.8 and 21.3 kJ/mol for new and quantum mechanical methods, respectively. Predicted condensed phase heats of formation for remainder 59 energetic molecules with complex molecular structures have a rms deviation from experiment of 42.3 kJ/mol.     

Detonation temperature of high explosives from structural parameters

A new scheme is introduced for calculating detonation temperature of different classes of high explosives. The ratio of oxygen to carbon and hydrogen to oxygen as well as specific structural parameters are the fundamental factors in the new method. An empirical new correlation is used to calculate detonation temperature of energetic compounds without considering heat contents of explosives and detonation products. Calculated detonation temperatures for both pure and explosive formulations show good agreement with respect to measured detonation temperatures and complicated computer code using BKWR and BKWS equations of state. Predicted detonation temperatures have root-mean-square (rms) percent deviation of 4.6, 14.2 and 4.6 from measured values for new method, BKWR and BKWS equations of state, respectively.     

Prevalence rate of Cryptosporidium infection in hemodialysis patients in Iran

Cryptosporidium is one of the most common causes of diarrhea in the world, which can be severe and prolonged in immunocompromised patients. We compared the prevalence rate of Cryptosporidium infection in hemodialysis patients and 2 control groups (i.e., their healthy family members and normal population). Stool specimens of 104 adult outpatient chronic hemodialysis patients, their 91 healthy family members, and 140 healthy individuals were examined for the presence of Cryptosporidium oocysts by using a modified acid-fast staining method. Twelve (11.5%) dialysis patients were infected with Cryptosporidium. This was significantly higher than 4 (4.4%), and 5 (3.6%) cases in the 2 control groups, respectively (p < 0.05). There was no significant difference between the 2 control groups. The prevalence rate of Cryptosporidium infection did not correlate with patients' sex, age, duration of dialysis, history of kidney transplantation, or history of taking immunosuppressive drugs. However, it was significantly higher in diabetics vs. nondiabetics (19.4% vs. 8.3%, respectively, p < 0.05). Our results indicate that the prevalence rate of Cryptosporidium infection is considerably higher in dialysis patients than in the general population. Moreover, dialyzed diabetic patients had the highest rate of infection. As hemodialysis patients are candidates for renal transplantation, general preventive measures against acquiring Cryptosporidium infection must be considered.     

Electrocatalytic oxidation of ascorbic acid at a 2,2′-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone modified carbon paste electrode

Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of ascorbic acid at a carbon paste electrode modified with 2,2′-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone (1,8-OBNEBHQ). The modified carbon paste electrode showed high electrocatalytic activity toward ascorbic acid; the current was enhanced significantly relative to the situation prevailing when an unmodified carbon paste electrode was used. The electrocatalytic process was highly dependent on the pH of the supporting electrolyte. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between 1,8-OBNEBHQ and carbon paste electrode were calculated as 20.2 ± 0.5 s⁻¹ and 0.47, respectively. Using differential pulse voltammetry, the calibration curves for AA were obtained over the range of 5–30 and 40–1,500 μM, respectively. The detection limit (kσ, k = 2) was 0.6 μM. With good selectivity and sensitivity, the present method provides a simple method for selective detection of ascorbic acid in biological samples.     

Gamma-gamma density and lithology tools simulation based on GEANT4 advanced low energy Compton scattering (GALECS) package

Geophysical bore-hole data represent the physical properties of rocks, such as density and formation lithology, as a function of depth in a well. Properties of rocks are obtained from gamma ray transport logs. Transport of gamma rays, from a ¹³⁷Cs point gamma source situated in a bore-hole tool, through rock media to detectors, has been simulated using a GEANT4 radiation transport code. The advanced Compton scattering concepts were used to gain better analyses about well formation. The simulation and understanding of advanced Compton scattering highly depends on how accurately the effects of Doppler broadening and Rayleigh scattering are taken into account. A Monte Carlo package that simulates the gamma-gamma well logging tools based on GEANT4 advanced low energy Compton scattering (GALECS).