A spectral approach to determine location and orientation of azo dyes within surfactant aggregates

The UV–vis absorption properties of azo dyes are known to exhibit a variation with the polarity and acidity of the dye environment. The spectral properties of a series of anionic azo dyes were characterized to further probe the interaction of these dyes with two types of surfactant aggregates: (1) the spherical micelles formed in aqueous solution by alkyltrimethylammonium bromide (C_nTAB) surfactants with n = 10–16 and (2) the unilamellar vesicles spontaneously formed in water from binary mixtures of the oppositely-charged double-tailed surfactants cationic didodecyldimethylammonium bromide (DDAB) and anionic sodium dioctylsulfosuccinate (Aerosol OT or AOT). The observed dye spectra reflect the solvatochromic behavior of the dyes and suggest the location and orientation of the dye within the surfactant aggregates. Deconvolution of the overall spectra into sums of Gaussian curves more readily displays any contributions of tautomeric forms of the azo dyes resulting from intramolecular hydrogen bonding. The rich variation in UV/vis absorption properties of these anionic azo dyes supports their use as sensitive tools to explore the nanostructures of surfactant aggregates.     

Belt distance between facets of space-filling zonotopes

To every d-dimensional polytope P with centrally symmetric facets one can assign a “subway map” such that every line of this “subway” contains exactly the facets parallel to one of the ridges of P. The belt diameter of P is the maximum number of subway lines one needs to use to get from one facet to another. We prove that the belt diameter of a d-dimensional space-filling zonotope does not exceed ?log₂(4/5)d?.     

Efficient Preparative Rentes to 6,6′-Dibromo-2-2′-bipyridine and 6-Bromo-2,2′-bipyridine

The preparation of 6,6′-dibromo-2,2′-bipyridine and 6-bromo-2,2′-bipyridine are described. The dibromo compound was prepared by way of an improved cuprate synthesis resulting in a 72% yield. The monobromo species was prepared from the dibromo compound by way of metal-halogen exchange in 88% yield.     

Morphology and deformation behavior of “row-nucleated” polyoxymethylene film

Crystallization from a stressed polymer melt produces not the familiar randomly nucleated spherulitic structures, but instead a highly oriented “row-nucleated” morphology. We have crystallized films of polyoxymethylene from stressed melts; just as polyethylene, the surfaces are covered with protruding lamellar edges highly oriented in the extrusion direction. There is no evidence for the more familiar spherulitic morphology. Electron microscopy directly revealed for the first time that the row nuclei are fibers, only about 200 to 300 A in diameter, extending for distances up to 10 mU. Although comprising a negligibly small amount of total sample volume, they are of prime importance in influencing how the sample will crystallize. Their presence determines, more than any other single factor, whether the sample will crystallize spherulitically or into a row-nucleated morphology. When deformed in the extrusion direction, the twisted lamellar bundles open up to form a fishnetlike structure. Simultaneously, slip between lamellae also occurs by a mechanism similar to shearing a deck of cards; for elongations up to 50%, there is little evidence of lamellar destruction. In the transverse direction, the film is brittle and fails before 1% elongation. Voids are formed at the largest lamellar “twist points” where two or more bundles are twisted together.     

Prediction of ground pressure distribution under tracked vehicles—I. An analytical method for predicting ground pressure distribution

An analytical method for predicting the pressure distribution beneath a tracked vehicle under static conditions is presented. In the analysis, the track-suspension system which consists of the track, the suspension and the track tensioning device, is considered inits entirety. All major design parameters of the vehicle, as well as terrain characteristics, are taken into consideration. It is shown that the analytical method proposed can provide a means whereby the effects of vehicle design parameters and terrain conditions on ground pressure distribution can be assessed quantitatively.