1,720,969 research outputs found
Crystalline Nanoporous Materials based on Poly(2,6-dimethyl-1,4-phenylene)oxide
No full textDifferent types of crystalline nanoporous materials (powders, films, aerogels) based on poly(2,6-dimethyl-1,4-phenylene)oxide can be easily obtained depending on the preparation procedures. The nanoporous nature of the crystalline phase confers to these materials peculiar transport properties which make them particularly interesting for a potential use as a sorption medium to remove traces of pollutants from water and air or for membrane based gas separation processes.
Different aspects relative to the structure and the transport properties of these new polymeric materials are described
Monolithic Polymeric Aerogels with Organically Modified Clays and Graphite Oxide Nanofillers
No full textSummary In this contribution the preparation of composite syndiotactic polystyrene (s-PS) monolithic aerogels with nanofillers such as organically modified montmorillonite (OMMT) and graphene oxide (GO) is described. In these aerogels the crystallites that constitute the physical knots exhibit a nanoporous-crystalline form. The aerogels preparation procedure allows the inclusion of also large amount of nanofillers, without aggregation, at least up to a content of 20 wt.%. This allows to improve mechanical and electrical properties of the nanoporous-crystalline aerogels of s-PS, which are particularly suitable to remove selectively traces of pollutants from water and air. Composite aerogels exhibiting large nanofiller content, can be also used as masterbatches for polymer composites
High porosity polyethylene aerogels
Full text linkMonolithic aerogels of high molecular weight polyethylene (Mw= 3x106- 6x106 g/mol) have been prepared by solvent extraction with supercritical carbon dioxide from thermoreversible gels prepared in decalin. These low density and highly porous aerogels present an apparent porosity up to 90%. The aerogel morphology observed by scanning electron microscopy (SEM) is characterized by spherulitic structures being interconnected by fibers. X-ray diffraction experiments show that PE aerogels are highly crystalline with a degree of crystallinity of c.a. 80% and PE chains being packed into the typical orthorombic unit cell. Combined SEM and N2 sorption investigations show that PE aerogels are essentially macroporous with a small amount of mesopores. The oil-sorption performance of polyethylene aerogels has been also evaluated in this study in order to assess a possible use of these materials for oil spillage recovery and results show that aerogel macropores allow a very fast sorption kinetics with a 100% oil weight uptake obtained in less than 1 minute
Basified Graphene Oxide and PPO Composite Aerogel with Basified Graphene Oxide for Henry Reaction in Solvent-Free Conditions: A Green Approach
No full text[Image: see text] Novel basified graphene oxide and high-porosity monolithic composite aerogels of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) containing basified graphene oxide (b-eGO) have been prepared as recoverable and reusable catalysts for the Henry reaction in solvent-free conditions at room temperature. The results showed that, although b-eGO was able to promote the reaction, it suffered from reduced stability. On the other hand, PPO/b-eGO aerogels were able to efficiently promote the Henry reaction in solvent-free conditions. The product could be obtained pure without a purification step, and the catalyst was stable for over 15 months and could be easily recycled without losing catalytic efficiency. The stereochemical outcome was further investigated in the presence of PPO/b-eGO. Despite its negligible influence on diastereoselectivity, better efficiency and a sensible reduction of reaction time were observed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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