75,003 research outputs found
Preparation and characterization of polyamide 6-montmorillonite nanocomposites by in-situ polymerization
No full textOn polyamide 6-montmorillonite nanocomposites obtained by in-situ polymerization
No full textNanocomposites based on polyamide 6 (PA6) and montmorillonite-type (MMT) commercial clays, either unmodified or organically modified, have been prepared by in-situ polymerization of e-caprolactam (CL). The above materials have been characterized in detail by a number of experimental techniques, including transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The formation of nanostructured systems has been checked not only for the common used w-aminoacid-modified clay, but also for other types of organoclays. In general, a correlation has been found between nanoscopic swelling of the clay in molten CL, measured by X-ray diffraction, and level of clay dispersion in PA6. Specifically, with the most swellable clays, completely exfoliated nanocomposites have been obtained. However, also layered silicates modified by compatibilizers having carboxy groups, because of the active role of the latter in CL polymerization, turned out to form delaminated nanocomposites despite their low degree of swelling in CL monomer. Both molecular mass and crystallinity of the polyamide matrix have been found to be strongly influenced by the presence of specific layered silicates. In particular, some characterization techniques (WAXD, FTIR) have evidenced a close relationship between the MMT used and PA6 crystal structure. Namely, PA6 gamma form is promoted by the clay with compatibilizer bearing the carboxy group which is able to induce the polymer to be tethered on the silicate layers, thus provoking conditions of restricted mobility to occur
Bubbles with constant mean curvature, and almost constant mean curvature, in the hyperbolic space
No full textGiven a constant , let be the family of round spheres of radius
{artanh}(k^{-1}) in the hyperbolic space , so that any
sphere in has mean curvature . We prove a crucial nondegeneracy result
involving the manifold . As an application, we provide sufficient conditions
on a prescribed function on , which ensure the existence
of a -curve, parametrized by , of embedded
spheres in having mean curvature at each
point
Preparation and characterization of nanocomposites based on polyamide 6 and clay by in-situ polymerization
No full textInfluence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites
No full textInfluence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites
No full textThe Benefits of Being Economics Professor A (and not Z)
No full textAlphabetic name ordering on multi-authored academic papers, which is the convention in the economics discipline and various other disciplines, is to the advantage of people whose last name initials are placed early in the alphabet. As it turns out, Professor A, who has been a first author more often than Professor Z, will have published more articles and experienced afaster growth rate over the course of her career as a result of reputation and visibility. Moreover, authors know that name ordering matters and indeed take ordering seriously: Several characteristics of an author group composition determine the decision to deviate from the default alphabetic name order to a significant extent.performance measurement, incentives, economists, name ordering
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