Influences of polymer matrix melt viscosity and molecular weight on MWCNT agglomerate dispersion

In order to study the influence of melt viscosity and molecular weight on nanotube dispersion and electrical volume resistivity, three different polycarbonates (PCs) varying in molecular weight were melt compounded with 1 wt% multiwalled carbon nanotubes (MWCNTs, Baytubes^® 150 HP) using a small-scale compounder. The experiments were performed at constant melt temperature but at varying mixing speeds, thereby applying different magnitudes of shear stress. Light transmission microscopy was used to access the state of agglomerate dispersion, and electrical resistivities of the composites were measured on pressed plates. The results indicate that with increasing matrix viscosity the agglomerate dispersion gets better when using constant mixing conditions but worse considering comparable shear stress values. To study the effect of molecular weight, in a second set of experiments melt temperatures were adjusted so that all PCs had similar viscosity and mixing was performed at constant mixing speed. As investigated on two viscosity levels, the composites based on the low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices, highlighting the role of matrix infiltration into primary nanotube agglomerates as the first step of dispersion. The resistivity values of composites prepared using low viscosity matrices were lower than those of composites from high viscosity matrix.     

Safe design fatigue life of CNT loaded woven GFRP laminates under fully reversible axial fatigue: application of two-parameters Weibull distribution

ABSTRACT

In this work, constant amplitude fully reversible tension-compression (t-c) fatigue behaviour of two-phased epoxy/glass fibre and three-phased MWCNT/epoxy/glass fibre laminates modified with 0.5 and 1.0 vol.-% of MWCNTs is presented. Addition of 0.5 and 1.0 volume fraction of nanoparticles in the matrix phase increased the fatigue strength of the laminates by approximately 10% and 4%, respectively. GFRP laminates subjected to quasi-static compression and t-c fatigue were found to fail by matrix crushing and shearing contrary to matrix crushing, ply splitting and kink band failure presented by CNT modified laminates. Such mechanisms were due to additional matrix toughening imparted by the nanotubes. Two-parameters Weibull distribution was implemented for the statistical evaluation of the fatigue life data. For safety limits of the test results, S-N curves with reliability levels of 0.99, 0.5, 0.368 and 0.10 were produced using Weibull shape and scale parameters.     

PBT/Thermoplastic Elastomer Blends—Mechanical,Morphological, and Rheological Characterization

The blends of poly(butylene terephthalate) (PBT) with thermoplastic elastomer (TPE) at a blending composition of 10–30 wt.% TPE were prepared with an objective to enhance impact toughness of PBT. Two different grades of PBT were selected based on carboxyl end group and viscosity. Melting behavior, mechanical properties, morphology, and rheology of the blends were studied. At all levels of TPE, PBT showed negligible changes in its melting and crystallization temperature; however, percentage crystallinity decreased with an increase in the amount of thermoplastic elastomer. The notched as well as unnotched Izod impact strength of PBT increased with the incorporation of TPE, the increase being about 47% (unnotched) and 54% (notched) with low molecular weight PBT and 18% (unnotched) and 70% (notched) with high molecular weight PBT at 10% TPE level. The tensile strength and tensile modulus of the blends decreased steadily as the weight percent of TPE increased. Analysis of the tensile data using predicted theories indicated that at TPE levels of 30 wt.%, the blends cannot take excessive stress because the interfacial adhesion is lowered. Small angle light scattering (SALS) studies of the samples indicated the decreased rate of crystallization and, hence, an increase in spherulitic radius in the presence of TPE. The increasing incorporation of TPE in PBT/TPE blends increased the shear thinning behavior and hence eased processability.     

Efficient spectral response of locally uncertain linear systems

It is difficult to model any real dynamical system with fully deterministic characteristics and yet, capture its behavior reasonably. Randomness arises from many sources, such as uncertain material properties, assumptions involved in structural modeling, and the stochastic nature of input forces. Thus, the random vibration analysis of systems with uncertain parameters is a crucial component of structural design and optimization procedures. In this paper, a new method is presented for fast spectral analysis of locally uncertain systems subjected to random inputs based on the response of one such system (called the nominal system). Unlike other methods, such as modal expansion methods, the proposed method is applicable to general uncertainties in the damping and stiffness matrices with the sole restriction that the system remains stable with probability one. Moreover, the proposed method yields exact responses for the perturbed systems and its accuracy is not affected by the size or magnitude of the uncertainties. However, the degree of locality of the uncertainty dictates the observed gains in computational efficiency when using the proposed method. When the uncertainty is extremely localized, one can expect gains in computational efficiency of two to three orders of magnitude while only modest gains of 2–3 times are observed when half the model is uncertain. Two numerical examples are presented to illustrate the accuracy and gains in computational efficiency of the proposed method.     

Evaluation of the effect of Ultra Rice® EDTA supplementation on the soluble iron,visual acceptance and vitamin A stability of commercial milled rice blends

The addition of NaFeEDTA at only 5% of total iron to ferric pyrophosphate‐fortified Ultra Rice^® increased the in vitro soluble iron ten‐fold. Ultra Rice^® formulated with NaFeEDTA at 2–7% of total iron, or with Na₂EDTA·2H₂O at 0.5× the total iron equivalents, increased the soluble iron seven‐ to thirty‐fold. The colour of the batches was acceptable through 20 weeks at 21 °C, but colour stability needs to be evaluated under authentic storage conditions. Although only 34–46% of the initial vitamin A remained after extrusion, 18‐week storage at 30 °C/70% relative humidity, and simulated cooking, there were indications that losses could be decreased by raising the pH (to ~5) and/or using a better protected vitamin A ingredient. The enhancement of soluble iron afforded by low‐level NaFeEDTA or Na₂EDTA·2H₂O supplementation suggests that this fortification strategy may merit further study as a means of increasing absorbable iron in Ultra Rice^®.     

Misinformed About the Affordable Care Act? Leveraging Certainty to Assess the Prevalence of Misperceptions

According to some recent research, Americans hold a great deal of misinformation about important political issues. However, such investigations treat incorrect answers to quiz questions measuring knowledge as evidence of misinformation. This study instead defines misperceptions as incorrect answers that respondents are confident are correct. Two surveys of representative samples of American adults on the Affordable Care Act reveal that most people were uncertain about the provisions in the law. Confidently held incorrect beliefs were far less common than incorrect answers. Misperceptions were most prevalent on aspects of the law on which elites prominently and persistently made incorrect claims. Furthermore, although Americans appear to have learned about the law between 2010 and 2012, misperceptions on many provisions of the law persisted.     

Voltage assisted control of spin-transfer nano-oscillators

The spin-transfer nano-oscillator(STNO) has recently acquired a huge amount of research interest, due to its promising easy tunability along with the miniature size. The output frequency control of an STNO through magnetic field and current has been examined almost to its full extent; however, there are issues that still need to be addressed. Here, we propose a novel way of voltage control of the output frequency of an STNO, and alongside reducing its power requirement.     

Intermetallic growth between lead-free solders and palladium

Intermetallic growth between Pd and the lead-free solders Sn-Ag and Sn-Ag-Cu has been studied. Diffusion couples were prepared by reflowing the solders on Pd and then aging the couples at 156°C, 175°C, 195°C, and 210°C. At the higher temperatures of 175°C, 195°C, and 210°C, PdSn₄ made up most of the layer that grew between the solders and the Pd, although small regions of second phases were always found in the PdSn₄ matrix, and it was sometimes possible to identify discontinuous regions of PdSn₃ next to the Pd. The thickness of the intermetallic layer increased with the square root of time, consistent with diffusion-controlled growth. In couples annealed at 156°C, the morphology of the PdSn₃ phase and growth kinetics differed depending on the composition of the solder.