No abstract

No abstract

No abstract

Mesoporous manganese dioxide was successfully synthesized by alkene oxidation with permanganate in soft template medium. Four linear and three cyclic alkenes have been used as reactants to show their impact on the MnO 2 particles microstructure (specially the pore volume), on their agglomeration, and hence on their electrochemical performances as positive electrode materials in supercapacitors. The reaction proceeds via an intermediate product step, a manganate(V) cyclic diester, capable of producing aggregates. Aggregate macromolecular characteristics, such as intrinsic viscosity [η], molecular weight M, aggregation number N, and radius R, depend on the alkene employed. The role of CTAP as phase-transfer agent and as templating agent for MnO 2 synthesis when associated with alkene is also confirmed. This first study allowed the proposition of a structure for the aggregates (called model B in the text). The electrochemical performances of the manganese oxides were subsequently determined with aqueous, environmentally friendly K 2 SO 4 electrolyte. Suitable performances, in terms of high specific capacitances (>150 F•g −1 ) are provided by oxides prepared by employing bulky cyclic or long-chain linear alkenes. Asymmetric devices AC∥MnO 2 with one of the mesoporous manganese oxide as the positive electrode, obtained from the oxidation of 1-octadecene, and activated carbon (AC) as the negative electrode yield suitable energy density of 18.2 Wh•kg −1 and a power density of 0.2 kW•kg −1 for electrochemical capacitor purposes. Finally, this particular device, cycled under galvanostatic regimes, shows a high-capacitance retention (81.2% after 10000 cycles). Therefore, this particular soft template method is suitable for the preparation of supercapacitor electrodes.

No abstract

The aqueous solution properties and the micellar structure of two short-chain nonionic surfactants containing a hydrocarbon tail, 1,2-hexanediol (HD), and a perfluorinated tail, 3,3,4,4,5,5,6,6,6-nonafluoro-1,2-hexanediol (PFHD), have been compared by using various techniques such as pyrene fluorescence spectroscopy, vapor pressure osmometry, tensiometry, and dye solubilization. The aggregational behavior of both systems in aqueous medium has been evidenced by the polarity decrease of the pyrene microenvironment with increasing surfactant concentration. The binding coefficient of pyrene with the aggregates was calculated by application of the phase-separation model to the pyrene fluorescence results. The aggregation numbers of the HD (N H) and PFHD (N PF) micelles have been evaluated by application of the phase-separation and the mass-action law models to the osmotic coefficients measurements. The N H value (26 ± 8), which is in good accordance with previous experimental results (30 ± 10), is higher than N PF (15 ± 1). Both compounds exhibit surface-active properties with a maximum surface tension lowering of 42 and 57 mN m-1 for HD and its perfluorinated homologous compound, respectively. Their solubilizing power toward Orange OT was compared. Critical micelle concentrations (CMCs) have been determined in the temperature range 20−50 °C (30−50 °C for PFHD insoluble below 30 °C), and thermodynamic parameters such as standard enthalpy and entropy changes for micellization have been calculated.

No abstract

No abstract