Solid State Phenomena Vols. 121-123

Abstract: Compressive and tensile properties of non-twisted and twisted carbon nanotube (CNT) bundles are studied using molecular dynamics (MD) simulations. The results reveal that non-twisted CNT bundles exhibit better compressive and tensile properties than twisted CNT bundles. When the twist angle of a CNT bundle is greater than 60°, its buckling load dropped considerably due to the significant curve geometries of the surrounding single-walled carbon nanotubes (SWCNTs). Twisted CNT bundles also do not demonstrate good tensile properties. During tensile loading, the intertube distance in CNT bundle with twisting angle greater than 75° will decrease as the strain increases. This gives rise to increasing intertube van der Waals forces until the intertube distance falls below 2.0Å. At this time, the repulsive force between the SWCNTs suddenly increases causing the SWCNTs to repel one another at junction areas where they overlap. As a result, twisted CNT bundles tend to fail at these junction areas with lower failure load and strain.

Abstract: Vapor growth carbon nanofibers (CNFs), lead zirconate titanate piezoelectric (PZT) particles, as well as a combination of these two were added in an epoxy resin (EP), and their influence on the curing reaction was investigated. Moreover, the cured samples were characterised by dynamic scanning calorimetry and dynamic thermal mechanical analysis. The presence of the fillers had no significant effect of the curing reaction of the EP system and the glass transition temperature, Tg.

Abstract: This paper describes a statistical method for evaluating the surface flaw distributions responsible for the improved strength and reliability of small-scale MEMS specimens. The method uses a power-law function, which, though empirical in form, is consistent with the conventional two-parameter Weibull distribution, to approximate the flaw size distributions on specimen tensile surfaces. The parameters in the power-law function are determined from Weibull strength plots. Literature data for single-crystal silicon beam specimens covering a range of widths from mm to nm are analyzed using this method. The analysis indicates a reduction in scatter in addition to increase in strength with diminishing specimen size, and quantifies a systematic tightening in flaw distribution associated with refinement in fabrication method and the limitations of physical sizes on flaw dimensions, which is consistent with the experimental observations. Furthermore, the implications of the increased strength and reduced strength scatter to the processing techniques and structural integrity of MEMS devices are discussed.

Abstract: Nano-sized silica was pre-grafted with poly(glycidyl methacrylate) (PGMA) by solution free-radical polymerization. When these grafted silica particles were melt compounded with polypropylene (PP), reactive compatibilization effect was perceived due to the chemical bonding between the PGMA and amine functionalized PP, which led to a significant increase of tensile strength and notch impact strength of PP at rather low filler content. Accordingly, compatibility of each kind of the functionalized PP with grafted SiO2 was evaluated through investigating the mechanical properties, crystallization behavior and rheological performance of the composites. The results show that the reactive compatibilization is capable of providing stronger interfacial adhesion.

Abstract: Spherical NiO nanocrystals were obtained by thermal decomposition of the precursor obtained via a hydrothermal method using urea as precipitant and polyethylene glycol (PEG) as surfactant. The structure, morphology and magnetic properties of the products were examined by XRD, TEM, ED, IR and VSM. The results of the structure and magnetic measurements on NiO nanocrystals were discussed. The results showed that the products were nanocrystalline NiO with a diameter of 21 and 50 nm, respectively, after calcined at 300 and 500 oC. The calcined NiO nanocrystals exhibited the characteristics of weak ferromagnetism by magnetic analysis at room temperature. At low external field, the hysteresis loops exhibit low coercivity, Hc=144.7 and 200.5 Oe, for the samples calcined at 300 and 500 oC, respectively.

Abstract: Nylon 6/clay nanocomposites are comprised of nylon 6 matrix filled with montmorillonite platelets (MMT) [1, 2]. It is interest that the MMT offered exceptional reinforcing effect (such as modulus) at a low filler content[3]. Models for predicting properties of fiber composites[4-8] and their developed models[9, 10] based on the supposition of possible microstructure around the MMT platelets have been conducted with the aim of predicting the stiffening effect of the MMT in nanocomposites.

Abstract: Nanocomposites of nanosized-CaCO3/polypropylene-ethylene copolymer (PPE) and nanosized CaCO3/ PPE/ styrene-butadiene-styrene (SBS) were prepared by using two-roll mill and single screw extruder. The average particle size of nanosized CaCO3 was determined to be about 30 nm. By adding nanosized CaCO3 into PPE matrix, the toughness of the matrix improves significantly. At nanosized CaCO3 content of 12 phr (parts per hundred PPE resin by weight), the impact strength of CaCO3/PPE at room temperature reaches 61.6 KJ/m2, which is 3.02 times that of unfilled PPE matrix. In addition, the synergistic toughening effect of nanosized CaCO3 and SBS particles on PPE matrix was investigated.

Abstract: As an effective way to enhance various properties of polymer, polymer/clay nanocompoiste is being adopted since it can hybrid the properties of the two components, showing superior physical and mechanical properties. In this study, poly(ε-caprolactone) (PCL) nanocomposites using an organoclay were prepared by a solution intercalation method, and their unique internal structures and rheological properties induced by the presence of organoclay at nano level were studied using WAXD and a rotational rheometer.