Impact of compression molding conditions on the thermal and mechanical properties of polyethylene

Compression molding is a current technique in polymer processing. Despite numerous studies, effect of molding pressure on physical properties has surprisingly not been fully investigated. In this study, the thermal and mechanical behavior of the compression‐molded polyethylene were thus explored to better grasp the relationship between processing parameters and ensuing properties. The effect of the molding temperature, pressure, cooling rate, and temperature profile on the tensile and flexural moduli as well as melting point of polyethylene was studied. We conclude that higher tensile and flexural moduli are obtained by increasing pressure and molding temperature, as well as decreasing the cooling rate. Our results were corroborated by X‐ray diffraction and differential scanning calorimetry measurements. Moreover, the use of a temperature gradient with different temperatures for the upper and bottom plates of the mold leads to asymmetric samples whose tensile and flexural moduli are improved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46176.     

Imbibition by polygonal spreading on microdecorated surfaces

Micropatterned surfaces have been studied extensively as model systems to understand influences of topographic or chemical heterogeneities on wetting phenomena. Such surfaces yield specific wetting or hydrodynamic effects, for example, ultrahydrophobic surfaces, 'fakir' droplets, tunable electrowetting, slip in the presence of surface heterogeneities and so on. In addition, chemical patterns allow control of the locus, size and shape of droplets by pinning the contact lines at predetermined locations. Applications include the design of 'self-cleaning' surfaces and hydrophilic spots to automate the deposition of probes on DNA chips. Here, we discuss wetting on topographically patterned but chemically homogeneous surfaces and demonstrate mechanisms of shape selection during imbibition of the texture. We obtain different deterministic final shapes of the spreading droplets, including octagons, squares, hexagons and circles. The shape selection depends on the topographic features and the liquid through its equilibrium contact angle. Considerations of the dynamics provide a 'shape' diagram that summarizes our observations and suggest rules for a designer's tool box.     

Cross-platform comparison of Caenorhabditis elegans tissue extraction strategies for comprehensive metabolome coverage

The nematode Caenorhabditis elegans is widely used as a model organism in many areas of the life sciences. Metabolite profiling (metabolomics/metabonomics) is a powerful means of assigning phenotypes to experimentally perturbed C. elegans samples (e.g., mutants, RNAi, or chemical treatments). Tissue extraction is a key step, and high-quality and reproducible extractions are essential to the success of metabolomics studies. We have performed an extensive comparison of different tissue extraction techniques with C. elegans, comparing two different solvent systems (chloroform/methanol and aqueous methanol) and six different tissue disruption techniques (including manual grinding in a cooled mortar, homogenization, and various grinding media in both reciprocating and orbital tissue mills). All twelve combinations were then compared by GC/MS, (1)H NMR spectroscopy, and UPLC-MS, and the results were evaluated by both overall multivariate clustering approaches as well as distributions over individual metabolites/metabolite features of coefficient of variation and yield. The choice of solvent had more influence than the disruption method used, although the homogenizer results were clearly outliers. Overall, we concluded that bead-beating with 80% methanol solution was a good trade-off, although it is important to note that the definition of the apparent "best" method depended on which analytical platform was used to evaluate the results.     

Chemical transformation of Au-tipped CdS nanorods into AuS/Cd core/shell particles by electron beam irradiation

We demonstrate that electron irradiation of colloidal CdS nanorods carrying Au domains causes their evolution into AuS/Cd core/shell nanoparticles as a result of a concurrent chemical and morphological transformation. The shrinkage of the CdS nanorods and the growth of the Cd shell around the Au tips are imaged in real time, while the displacement of S atoms from the CdS nanorod to the Au domains is evidenced by high-sensitivity energy-dispersive X-ray (EDX) spectroscopy. The various nanodomains display different susceptibility to the irradiation, which results in nanoconfigurations that are very different from those obtained after thermal annealing. Such physical manipulations of colloidal nanocrystals can be exploited as a tool to access novel nanocrystal heterostructures.     

Influence of Mechanical Surface Treatment on High-Temperature Oxidation of Pure Titanium

The excellent combination of light-weight and good mechanical properties makes titanium alloys attractive for compressor section components in gas turbine engines (temperature between 250 and 600 °C). However, above 600 °C, the formation of an unprotective oxide layer facilitates the oxygen diffusion into the alloy. In this experimental study, pure titanium was treated with mechanical surface treatment to promote better protection against oxidation at high temperature. Shot-peened and laser-shock peened specimens were compared to untreated samples in terms of oxidation behavior at high temperature. We used thermal gravimetric analysis to oxidize the samples at 700 °C for 100 h. Subsequently, XRD, optical microscopy, SEM/EDS, NRA, micro-Raman spectroscopy, and micro-hardness were used to characterize the oxide scale and the alpha-case layer formed during the high-temperature exposure. The shot-peened samples oxidized less (?45%) than the untreated and laser-shock peened samples. This behavior was attributed to the formation of a continuous nitride layer between oxide and metal.     

Epileptiform activity induced by low Mg2+ in cultured rat hippocampal slices

Organotypic cultured slices of the rat hippocampus undergo synaptic reorganization. Besides the establishment of reciprocal connections between area CA1 and the dentate gyrus (DG), collateral excitatory connections between granule cells are formed which are similar to those appearing in several epilepsy models and in the DG from patients with temporal lobe epilepsy. We studied the characteristics of epileptiform activity induced by low Mg2+ perfusion in cultured hippocampal slices using extra- and intracellular recordings. With low Mg2+ perfusion synchronous seizure like events (SLEs) were readily observed in the DG and areas CA3 and CA1. Also, the isolated DG was able to display seizure like activity. Intracellular recordings revealed long lasting depolarization shifts in granule cells of the DG and pyramidal cells of areas CA3 and CA1. The SLEs, lasting 2-3 s, could be recorded for at least 3 h in areas CA1 and CA3. However, approximately an hour after perfusion with low Mg2+, the epileptiform activity disappeared in the DG and responses to single pulse hilar stimulation progressively deteriorated. These responses returned to control values 1 week after reincubating the cultures. Interestingly, no deterioration of stimulus induced responses was observed in the isolated DG after exposure to low Mg2+.