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321.
Marcia Viltres Portales Ana R. Lazo Fraga Alicia M. Díaz García Osmany García-Zaldívar Aimé Peláiz Barranco Miguel A. Aguilar Frutis 《Journal of Solid State Electrochemistry》2018,22(2):471-478
The transducer of solid-state electrodes based on an epoxy-graphite composite was modified by two different methods, such as direct mixed and layer deposition of graphene (commercial and synthesized by electrochemical exfoliation of graphite). The modified electrodes were characterized by cyclic voltammetry and impedance spectroscopy. Also, scanning electron microscopy (SEM) was carried out to acquire information concerning the morphology of the composite electrode. Voltammetric measurements, in presence of [Fe(CN)6]3? as electroactive standard, determined a quasi-reversible electrochemical behavior under linear diffusion control. Electronic transference for modified and unmodified electrodes was compared. Solid-state electrode modified by inclusion of synthesized graphene showed a better electronic transference at electrode surface, due to the lower potential difference between anodic and cathodic peaks (ΔE = 125 mV) with respect to unmodified electrode (ΔE = 160 mV). Impedance spectroscopy characterization of electrode bodies in solid-state it was revealed a higher electronic conductivity and a supercapacitive behavior for the modified composites (values of intrinsic capacitances in the order of nanofarads) due to inclusions of graphite and graphene in the epoxy matrix. These inclusions were verified through SEM microscopy. The electronic conductivity and the supercapacitive character contributed both to the enhancement of electronic transference at electrode surface. 相似文献
322.
A variety of crystals containing molecules formulated generally as (ArnX)3Y-Z-Y(XArn)3 with exact or pseudo S6 symmetry have been analysed for the presence of intra- and intermolecular multiple aryl embraces composed of offset-face-to-face (OFF) and edge-to-face (EF) local motifs. Ar is phenyl or substituted phenyl; n = 1, 2 or 3; the linkage Z is linear diatomic, linear monatomic, absent (Y-Y bond), or void (Y atoms unconnected). Representative molecular systems analysed are (PhCH2)3Si-O-Si(CH2Ph)3, (PhCH2)3Sn-Sn(CH2Ph)3, (4-Me-C6H4CH2)3Ge-O-Ge(CH2C6H4-4-Me)3, [(PhS)3Fe-O-Fe(SPh)3]-, [(PhCH2)3P-Cu-P(CH2Ph)3]+ and [(Ph3P)3Ag-CN-Ag(PPh3)3]+. One characteristic intramolecular motif is a sixfold phenyl embrace (6PE) in which aryl groups fold back to the central domain of the molecule forming a rhombohedral box maintained by (EF)6. When the aryl groups are in exo positions there is an (EF)3 motif, like a tractor wheel, at each end of the molecule: [(Ph2N)3Ti-O-Ti(NPh2)3] possesses both intramolecular motifs as (EF)3-(EF)6-(EF)3. The molecules in this set are hexafaceted, and the crystal packing is generally based on intermolecular EF or OFF motifs with these faces, either from the central (EF)6 set or the end (EF)3-(EF)3 sets. Three types of subtle crystal packing isomerism occur: 1) the faces of the rhombohedral boxlike molecules slide over each other with variation of the intermolecular motifs, forming dimorphic crystals in space groups R3 or P1; 2) the faces of the tractor wheels (EF)3 slide over each other or 3) very similar molecules crystallise with the rhombohedral box or tractor wheel structures. In general the molecules considered are shape auspicious rather than shape awkward; solvent is included in a small proportion of the crystals and the crystal packing in these compounds is evidently efficient. Some principles for elaboration of these systems and the design of molecular crystal lattices are considered. 相似文献
323.
Mathematical Programming - The maximum-entropy sampling problem is a fundamental and challenging combinatorial-optimization problem, with application in spatial statistics. It asks to find a... 相似文献
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Marcia G. Oliveira Bluma G. Soares Cludia M. F. Santos Milton F. Diniz Rita C. L. Dutra 《Macromolecular rapid communications》1999,20(10):526-531
Ethylene-propylene-diene rubber (EPDM) was reacted with thioacetic acid in the presence of 2,2′-azoisobutyronitrile (AIBN), giving rise to thioacetate-modified EPDM (EPDMTA). The extent of the incorporation was studied as a function of both thioacetic acid and AIBN concentration and reaction time. The products were analyzed by FTIR spectroscopy, sulfur content, and 1H NMR spectroscopy. The hydrolysis of EPDMTA in a NaOH methanolic solution resulted in mercapto-modified EPDM (EPDMSH). The addition of 5 wt.-% of this functionalized copolymer to a sulfur-vulcanized nitrile rubber (NBR)/EPDM (70 : 30 wt.-%) blend accelerated the vulcanization process as indicated by oscillating disk rheometer analysis. In addition, an improvement of mechanical and ageing properties was also observed. 相似文献