Investigation of the curing behaviour of carbon fibre epoxy prepreg by Dynamic Mechanical Analysis DMA

Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon fibre fabric impregnated with reactive epoxy resin. Measurements were carried out using commercially available prepreg material. For Dynamic Mechanical Analysis (DMA), a single cantilever measuring device was applied. The DMA results were refined by additional DSC measurements. The measurements were carried out with dynamic heating in the temperature range ?90 to 280 °C. The heating rates were 1 and 2 K/min, respectively. A glass transition of the uncured material (T_g0) near 1 °C, and crosslinking-induced vitrification and devitrification at the maximal glass transition temperature of the cured material (T_gmax) in the temperature range 220 to 230 °C were found. The activation energies for the glass transitions were determined using an Arrhenius plot. By detailed consideration of the influence of the frequency on the DMA data, indications for gelation were deduced.     

Structural and magnetic properties of homoleptic iron(III) complexes containing N-(8-quinolyl)-salicylaldimine [Fe(Qsal)2]+X− {X = I or (Qsal)FeCl3}

The structural properties of two homoleptic iron(III) complexes containing N-(8-quinolyl)-salicylaldimine (qsalH) are reported on the basis of two single-crystal X-ray diffraction experiments. The complexes are shown to share the general formula [Fe(qsal)₂]⁺X^? {X = I (1) or (qsal)FeCl₃ (2)} and include one new complex 2 and one previously reported complex 1 for which structural details were until now unknown. Variable-temperature magnetic susceptibility measurements on both samples indicate the nature of the spin state of the metal ion, which is low-spin for 1 and high-spin for 2. Mössbauer spectra are recorded for 1 at 293 and 5.6 K and indicate unusual temperature-dependent behaviour, which corroborates an earlier report.     

Novel Copolymers of 4-Fluorostyrene. 6. Dialkoxy Ring-Substituted 2-Phenyl-1,1-dicyanoethylenes

Novel copolymers of trisubstituted ethylene monomers, ring-substituted 2-phenyl-1,1-dicyanoethylenes, RC₆H₃CH?C(CN)₂ (where R is 2,3-(CH₃O)₂, 2,4-(CH₃O)₂, 2,5-(CH₃O)₂, 2,6-(CH₃O)₂, 3,4-(CH₃O)₂, and 3,5-(CH₃O)₂ and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is 2,6-(CH₃O)₂(2.8) > 2,5-(CH₃O)₂(2.5) > 2,3-(CH₃O)₂ (2.1) > 3,5-(CH₃O)₂ (1.8) > 3,4-(CH₃O)₂ (0.9) > 2,4-(CH₃O)₂ (0.7). High T_g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 250–400°C range with residue, which then decomposition in 400–800°C range.     

Faulknerynes A-C from a Bahamian sponge Diplastrella sp.: stereoassignment by critical application of two exciton coupled CD methods

Long-chain polyacetylene alcohols, faulknerynes A-C, along with known compounds diplynes A, C and E, were isolated from two specimens of the encrusting sponge, Diplastrella sp., collected from the surface of coral in the Bahamas. Two CD methods were critically evaluated for their suitability to terminal propargylic glycols and applied to assignment of configurations of faulkneryne A and diplyne C.     

Magnetic silyl scaffold enables efficient recycling of protecting groups

A novel organic/inorganic hybrid material comprising carboncoated cobalt nanoparticles and a poly(benzylchloride)styrene shell is the first magnetic support that complies with important requirements for immobilized reagents and scavengers, that is, stability under harsh conditions (e.g., acids), sufficient loading (up to 2 mmol g(-1)), and satisfying magnetization. The durability of the scaffold was demonstrated by immobilization of a trialkylsilane reagent, which served as a "magnetic" protecting group for a number of primary and secondary alcohols. Importantly, the scaffold could be efficiently separated, recycled, and reused after alcohol cleavage (HF·pyridine) via regeneration of the silyl chloride moiety with BCl(3).     

Detection of benzimidazole carbamates and amino metabolites in liver by surface plasmon resonance-biosensor

Two surface plasmon resonance (SPR) biosensor screening assays were developed and validated to detect 11 benzimidazole carbamate (BZT) and four amino-benzimidazole veterinary drug residues in liver tissue. The assays used polyclonal antibodies, raised in sheep, to detect BZTs and amino-benzimidazoles. A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction method was developed to isolate benzimidazole carbamate residues. Liver samples were extracted using an acetonitrile extraction method. BZTs were purified by dispersive solid phase extraction (d-SPE) using C(18) sorbent. Residues of amino-benzimidazoles were effectively cleaned-up using a simple cyclohexane defatting step. The assays were validated in accordance with the performance criteria described in 2002/657/EC. The BZT assay limit of detection was calculated to be 32 μg kg(-1), the detection capability (CCβ) was determined to be 50 μg kg(-1) and the mean recovery of analytes was in the range 77-132%. The amino-benzimidazole assay limit of detection was determined to be 41 μg kg(-1), the CCβ was determined to be 75 μg kg(-1) and analyte recovery was in the range 103-116%. Biosensor assay performance was tested by analysing liver tissue from animals treated with benzimidazole drugs and comparing the results with an ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) confirmatory method. All non-compliant samples were identified using the biosensor assays.     

Archimedean-like colloidal tilings on substrates with decagonal and tetradecagonal symmetry

Two-dimensional colloidal suspensions subjected to laser interference patterns with decagonal symmetry can form an Archimedean-like tiling phase where rows of squares and triangles order aperiodically along one direction (J. Mikhael et al., Nature 454, 501 (2008)). In experiments as well as in Monte Carlo and Brownian dynamics simulations, we identify a similar phase when the laser field possesses tetradecagonal symmetry. We characterize the structure of both Archimedean-like tilings in detail and point out how the tilings differ from each other. Furthermore, we also estimate specific particle densities where the Archimedean-like tiling phases occur. Finally, using Brownian dynamics simulations we demonstrate how phasonic distortions of the decagonal laser field influence the Archimedean-like tiling. In particular, the domain size of the tiling can be enlarged by phasonic drifts and constant gradients in the phasonic displacement. We demonstrate that the latter occurs when the interfering laser beams are not ideally adjusted.