RESUMO
A new type of polymer blend, prepared by electrospinning nanofibers containing the immiscible polymers polyvinylidene fluoride (PVDF, 10 wt%) and Nafion® perfluorosulfonic acid (90 wt%), has been characterized experimentally. The internal nanofiber morphology is unique and unlike a normal blend, with individual phase-separated and randomly distributed fibrils of Nafion and PVDF (â¼2-7 nm in diameter) that are bundled together and aligned in the fiber axis direction (where the fiber diameter is â¼500 nm). This morphology is retained when fiber mats are hot-pressed into dense films. The physicochemical properties of the electrospun blended fibers are also highly unusual and unanticipated. As shown in this study, each polymer component influences the thermal and structural behavior of the other, especially in the dry state. Thus, dry composite polymer mats and membranes exhibit properties and attributes that are not observed for either pure PVDF or pure Nafion. Experimental results indicate that: (i) PVDF imparts conformational constraints on the polytetrafluoroethylene (PTFE) backbone chains of Nafion, resulting in an increased 21 helical conformation that effects Nafion's water uptake and thermal properties; and (ii) dipole-dipole interactions between PVDF polymer chains and Nafion make the ß-phase polymorph of PVDF much more stable at elevated temperatures. Such "reciprocal templating" in electrospun fibers may not be unique to Nafion and PVDF, thus the procedure represents a new method of creating nanostructured multi-component polymer materials with innovative features.
RESUMO
A prospective study of acute symptomatic viral hepatitis in childhood was started at the Department of Infectious Diseases of Padua (Italy) in 1978. During an 8-year period, 93 consecutive patients (aged 3 months to 12 years) fulfilled the diagnostic criteria, including five (5.5%) cases classified as non-A, non-B hepatitis. This figure is lower than that generally reported in adult patients, probably because of a lower exposure of children to blood and contaminated materials. Two of the five children with non-A, non-B hepatitis had received blood transfusions, while three had no history of parenteral exposure. Although the outcome of the illness was favorable in all five patients, a variety of clinical features could be observed: two children had a mild, short-lasting disease, anicteric in one case, while three had a polyphasic pattern of transaminases with delayed biochemical resolution, including one patient with deep jaundice and severe early phase features. These findings suggest that in children, as well as in adults, non-A, non-B hepatitis is probably a heterogeneous entity induced by different agents with different modes of transmission.
