Interfacial effects on stress distribution in model composites

Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface.     

Studies of phosphazenes. Aminolysis reactions of pentachloro(2′, 2′, 2′-triphenyl-phosphazen-1′-yl) cyclotriphosphazene,N3P3Cl5(NPPh3)

The reactions of pentachloro(2′, 2′, 2′-triphenylphosphazen-1′-yl)cyclotriphosphazene, N₃P₃Cl₅(NPPh₃), with primary and secondary amines have been investigated using diethyl ether, methyl cyanid or benzene as the solvent. The structures of the products obtained, N₃P₃Cl_5minus;nR_n(NPPh₃) [n = 1, R = NHMe, NHBu^t, NMe₂, NC₅H₁₀, NEt₂; n = 2, R = NMe₂, NC₅H₁₀, NEt₂; n = 3, R = NMe₂, NHBu^t; n = 5, R = NMe₂] are elucidated by ¹H and ³¹P NMR spectroscopy. The ? NPPh₃ substituent exerts a pronounced geminal directing influence on incoming secondary amino nucleophiles; compounds containing a ≡ PCl(NPPh₃) group are not formed at the bis and subsequent stages of chlorine replacement. The reactions that involve primary amines follow the pattern established for the analogous reactions of hexachlorocyclotriphosphazene. The effect of solvent and possible mechanism(s) are discussed.     

A high-resolution micro-gel system for analyzing small amounts of protein with a wide diversity of molecular weights

We have used a micro-gel system to analyze the proteins in extracts of amphibian neurulae. Maximum band separation and resolution was achieved by using a dissociating discontinuous buffer with gels made of a discontinuous gradient of acrylamide.     

Mass spectrometry of hop compounds—III. Mass spectra of substituted 1,3-cyclopentanediones derived from hop constituents

The mass spectra of isohumulones (IV, V), tetrahydroisocohumulones (VI, VII), tetrahydroisohumulones (VIII) neohydroisocohumulones (XI, XII) cohumulinic acid (III), lupuloxinic acid (XV), humulinone (XIV) and related compounds are described. Ions which appear to be diagnostic for particular structures are discussed.     

Solid products from thermal decomposition of polyethylene terephthalate: Investigation by CP/MAS 13C-NMR and fourier transform-IR spectroscopy

The solid reaction products from pyrolysis of polyethylene terephthalate in the presence and absence of red phosphorus were characterized by CP/MAS ¹³C-NMR, FR-IR, and MAS ³¹P-NMR spectroscopy. Over the temperature range of 300–400°C, polyethylene terephthalate was converted in a sealed vial to a highly crosslinked polymer of terephthalic acid. Pyrolysis in the presence of red phosphorus, which functions as a flame retardant by increasing the amount of char, yielded an intractible polyaromatic phosphate ester. After thermal cleavage of polyethylene terephthalate with formation of free carboxyl and vinyl ester groups, there are two competing reaction pathways. The smaller molecular weight fragments may enter the vapor phase where they undergo further degradation primarily to CO₂, CO, and acetaldehyde, as described by others. However, if volatilization of the oligomeric fragments is inhibited, an alternate reaction pathway gives rise to the formation of highly crosslinked char. Red phosphorus decreases the volatility of the oligomeric fragments by converting them to phosphates and thereby enhances char formation.     

Spectrochemical determination of lithium,sodium, potassium and rubidium in rocks and minerals using the stallwood jet

A D C, spectrochemical method using the STALLWOOD jet has been developed for the determination of Li, Na, K and Rb in silicate minerals and rocks. Samples are mixed with graphite and Cs₂CO₃ in tho ratio 2 : 1 : 1, and Cs serves as internal standard. Precision and accuracy is satisfactory.     

Fluorescence polarization assays in signal transduction discovery

Fluorescence polarization (FP) has become widely employed for high throughput screening used in pharmaceutical drug discovery. Assays of important signal transduction targets are now adapted to FP. In this review we examine assays for cyclic adenosine monophosphate, phosphodiesterases, and protein kinases and phosphatases using FP competitive immunoassays and a direct enzymatic method called IMAP.     

Amino acid analysis by micellar electrokinetic chromatography with laser-induced fluorescence detection: application to nanolitre-volume biological samples from Arabidopsis thaliana and Myzus persicae

Amino acids were derivatised with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol (NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence. The optimised MEKC background electrolyte conditions were: 40 mM sodium cholate, 5 mM beta-cyclodextrin in 20 mM aqueous borate buffer, pH 9.1, with 7% v/v acetonitrile. Using these conditions, 19 amino acids were separated within 17 min. The limits of detection were in the range of 7.6-42.2 pmol/mL and limits of quantitation from 0.05-0.14 nmol/mL. The method was systematically validated for injection volume error, migration time variation, calibration linearity, accuracy, precision, and recovery. Nanolitre volume samples of phloem sap of individual sieve element cells from the plant Arabidopsis thaliana and honeydew from the aphid Myzus persicae were directly analysed with this method. Quantitative amino acid concentrations in these two biological matrices were profiled for the first time. This method is particularly important because it allows the complete profile of the amino acids obtained from individual phloem elements, allowing cell to cell and plant to plant variation to be quantified, which to date has not been possible with Arabidopsis thaliana.     

Infrared spectroscopic studies of polystyrene emulsion polymers: Effect of oxidation during polymerization

Infrared spectroscopy was empolyed to study the nature of the structural changes which occurred through oxidation during the emulsion polymerization of styrene. Aliphatic carboxylic, amino, and phosphate emulsifiers and hydrogen peroxide and potassium persulfate initiators were empolyed for polymer preparation. In addition, a polystyrene dispersion prepared in the absence of any emulsifier or stabilizer was examined. Irrespective of the nature of the initiator–emulsifier combination employed, all of the polymer spectra revealed bands at 1705 and 1770 cm.^?1. The band at 1705 cm.^?1 was assigned in part to the carbonyl stretching mode of dimertic carboxylic acid, formed by oxidation, in the polystyrene chains. Absorption at 1770 cm.^?1, which was very weak, was tentatively attributed to the carbonyl stretching mode of the monomeric form of this acid. The structure of the acid endgroup was not established, but the results obtained suggest that it was possibly a phenylacetic acid residue or a residue with a similar structure.