Fracture behavior in nylon 6 fibers

A reaction rate model of fracture in polymer fibers is described. This model assumes that bond rupture is governed by absolute reaction rate theory with a stress-aided activation energy. It is demonstrated that the key in obtaining good agreement between the model and experiment lies in taking proper account of the variation of stress on the tie-chain molecules. The more taut chains rupture first, and the load is redistributed among the remaining unruptured tie chains. The effect of varying the temperature both in the model and in experiments on fracture in fibers is explored. Good agreement between predictions of the model and experiment is possible only with an undeterstanding of the distribution in stress on the tie chains. The distribution in stress on the chains was experimentally determined by monitoring the kinetics of bond rupture with electron paramagnetic resonance (EPR) spectroscopy. Temperature is found to have two effects on macroscopic strength. (1) The thermal energy aids the atomic stress in breaking the atomic bonds; as a consequence the rate of bond rupture of a family of bonds under a given molecular stress is increased. In this respect temperature might be viewed as decreasing the “strength” of a bond. (2) Temperature also serves to “loosen” the molecular structure and in this way modify the distribution in stress on the tie chains. To explain bond rupture and macroscopic fracture behavior quantitatively, account must be taken of both effects.     

μSR studies of the vortex lattice in high‐Tc and other superconductors

We review some of the assumptions made in the use of muon spin rotation in superconductors: i.e. that the muons are implanted at random positions in the flux lattice, remain static after implantation and do not appreciably affect the properties of the surrounding superconductor; also that the flux lines are straight and static, and that the observed muon rotation frequency spectrum reflects the microscopic distribution of field values. We shall show how evidence for and against the truth of these assumptions in particular cases may be obtained from the μSR results themselves or by comparison with other measurements, and how this in turn may lead to deeper understanding of flux line structure and motion in superconductors. This revised version was published online in August 2006 with corrections to the Cover Date.     

A rapid procedure for obtaining hydrodynamic voltammetry plots for electrochemical detectors in high-pressure liquid chromatography systems

The construction of relatively simple and inexpensive apparatus for the determination of the operating conditions for electrochemical detectors in high-pressure liquid chromatography systems is described. A procedure has been developed for the characterization of electrochemically active compounds.     

3-Hydroxy-1,4-diphenyl-7-oxabicyclo[4.1.0]hept-3-ene-2,5-dione. A microbial product from streptomyces species (AAA566)

The epoxyenedione 1a has been isolated from a strain $\text{Streptomyces}$ and its structure has been established by nmr spectroscopy and by its conversion to 2,5-diphenyl-3,4-dihydroxyphenol. Selective hetero J-resolved nmr spectroscopy played a pivotal role in the structure elucidation.     

Phase inversion sulfonated polysulfone membranes

The use of two nonsolvents serving as a cosolvent system, replacing the traditional volatile solvent plus less volatile nonsolvent system, in the formation of asymmetric phase inversion membranes was investigated. Specifically, asymmetric membranes of sulfonated polysulfone were cast from a cosolvent system consisting of tetrahydrofuran and formamide. The nonsolvents and the proportions in which they are mixed to produce the cosolvent system, as well as the gelation medium isopropyl alcohol, were selected based on the three-component solubility parameter concept of Hansen. The structure of each membrane was evaluated using scanning electron microscopy; the performance was evaluated for use in pressure-driven membrane separation processes. The membranes were found to be dependent on the composition of the original casting solution and the composition of the nascent membrane at the instant of gelation. These ideas are clearly represented through the use of a triangular polymer solubility diagram.