Time-resolved spectroscopy of silver nanocubes: observation and assignment of coherently excited vibrational modes

The response of single crystal, cubic silver particles to ultrafast laser-induced heating has been examined experimentally and theoretically. The transient absorption traces display clear modulations due to coherently excited vibrational modes. Nanocube samples with edge lengths smaller than 50 nm show a single modulation, whereas samples larger than 50 nm show two vibrational modes. The results are compared to finite element calculations, where the cubes are modeled as having cubic crystal symmetry with the principal axes parallel to the sides of the particle. The action of the laser pulse is treated in two ways, first, as creating a uniform initial strain. In this case the predominant mode excited is the breathing mode. The period of this mode is in reasonable agreement with the vibrational periods measured for the smaller cubes and with the higher frequency modulation observed for the larger cubes. A nonuniform initial strain is also considered, which could arise from nonuniform heating for particles larger than the optical skin depth of the metal. In this case the predominant mode excited is a nontotally symmetric mode. The calculated periods from this analysis are in reasonable agreement with the lower frequency modulations observed for the larger samples. The results from this study show that, to within the accuracy of these measurements, the elastic constants of cubic silver nanoparticles are the same as bulk silver.     

Accelerating electrochemistry with metal nanowires

Scalable, solution-phase syntheses of metal nanowires are enabling their increased use in electrochemical processes. This review highlights recent results demonstrating how metal nanowires can exhibit better durability and higher activity than traditional metal nanoparticle electrocatalysts on carbon supports. Metal nanowires can also form interconnected two-dimensional and three-dimensional (3D) networks that eliminate the need for a carbon support, thus eliminating the detrimental effects of carbon corrosion. Porous 3D networks of nanowires can be used as flow-through electrodes with the highest specific surface areas and mass transport coefficients obtained to date, enabling dramatic increases in the productivity of electrochemical reactions. Nanowire networks are also serving as 3D current collectors that improve the capacity of batteries. The tunable surface structure and dimensions of metal nanowires offer researchers a new opportunity to create electrodes that are tailored from the atomic scale to the microscale to improve electrochemical performance.     

Ueber Schweinefett (Schmalz) und seine Verf?lschungen

Ohne Zusammenfassung     

Synthesis of platelet activating factor (paf) via a cyclic tin intermediate

Condensation of 2-0-benzylglycerol with dibutyl tin oxide gave a cyclic intermediate which was functionalized to give PAF.     

Rate of sulfonation of bead polymers of styrene crosslinked with 1,2,4- and 1,3,5-trivinylbenzene

Bead copolymers of styrene crosslinked with 1,2,4- and 1,3,5-trivinylbenzene (TVB) are sulfonated at different rates. The copolymer beads with 4% 1,3,5-TVB sulfonate more slowly than do those with 8% 1,2,4-TVB. The 8% 1,2,4-TVB crosslinked polystyrene beads sulfonate at about the same rate as do the beads prepared with 8% p-DVB crosslinkage.