The interfacial conformation of polypropylene glycols and foam behaviour

The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol⁻¹). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability.     

Experimental and theoretical study of the infrared spectra of BrHI- and BrDI-

Gas phase vibrational spectra of BrHI- and BrDI- have been measured from 6 to 17 microm (590-1666 cm(-1)) using tunable infrared radiation from the free electron laser for infrared experiments in order to characterize the strong hydrogen bond in these species. BrHI-.Ar and BrDI-.Ar complexes were produced and mass selected, and the depletion of their signal due to vibrational predissociation was monitored as a function of photon energy. Additionally, BrHI- and BrDI- were dissociated into HBr (DBr) and I- via resonant infrared multiphoton dissociation. The spectra show numerous transitions, which had not been observed by previous matrix studies. New ab initio calculations of the potential-energy surface and the dipole moment are presented and are used in variational ro-vibrational calculations to assign the spectral features. These calculations highlight the importance of basis set in the simulation of heavy atoms such as iodine. Further, they demonstrate extensive mode mixing between the bend and the H-atom stretch modes in BrHI- and BrDI- due to Fermi resonances. These interactions result in major deviations from simple harmonic estimates of the vibrational energies. As a result of this new analysis, previous matrix-isolation spectra assignments are reevaluated.     

Effects of phase explosion in pulsed laser deposition of nickel thin film and sub-micron droplets

Nickel (Ni) thin films were deposited on glass substrates in high vacuum and at room temperature with third-harmonic or 355-nm output from a nanosecond Nd:YAG laser. At low laser fluence of 1 J/cm², the deposition rate was about 0.0016 nm/shot which increased linearly until 4 J/cm². Above 4 J/cm², the onset of phase explosion in the ablation abruptly increased the optical emission intensity from laser-produced Ni plume as well as thin-film deposition rate by about 6×. The phase explosion also shifted the size distribution and number density of Ni droplets on its thin-film surface. On the other hand, the surface structures of the ablated Ni targets were compared between the scan-mode and the fixed-mode ablations, which may suggest that droplets observed on the thin-film surface were caused by direct laser-induced splashing of molten Ni rather than vapour-to-cluster condensation during the plume propagation.     

Two-dimensional infrared spectroscopy detected by chirped pulse upconversion

A two-dimensional (2D) infrared spectrum of Mn2(CO)10 is measured by using chirped-pulse upconversion (CPU) of the nonlinear signal field plus a reference local oscillator. By converting the spectrum to the visible, a silicon CCD camera can be used. The method offers an attractive alternative to direct IR detection due to the technological maturity of silicon and its greater intrinsic detectivity over HgCdTe. Using CPU, we acquired a rephasing 2D IR spectrum in a few seconds.     

Influence of bromoalkyloxy side chain on mesomorphic behavior in heterocyclic 7-(4-bromoalkyloxy)-3-(4′-decyloxyphenyl)-4H- 1-benzopyran-4-ones

A new homologous series of isoflavone-based ethers,7-(4-bromoalkyloxy)-3-(4’-decyloxyprienyl)-4H-1-benzopyran-4-ones were synthesized and characterized.The mesomorphic properties of all homologues were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).Enantiotropic smectic A(SmA) phase was observed for all homologues.The structure-property study was carried out by comparing the mesomorphic behavior of the homologues with those previously reported analogues.The bromine atom from the alkyloxy side chain of the benzene ring fused to the heterocyclic moiety was found to be capable of changing the mesomorphic properties.     

Anomalous temperature-dependent behaviors of electroluminescence phenomena in disordered ITO/PEDOT/PF/Ca/Al polymer light-emitting diodes

In this study we systematically investigated the anomalous Berthelot-type optical property dependence of the electroluminescence (EL) that occurs in polymer light-emitting diode (PLED) structures. Devices were operated at 0.1 and 0.5 mA over a temperature range from 300 to 20 K. Initially, the emission intensity increased as the temperature decreased, until a maximum was reached at the turning-point temperature T_t. After this, the intensity decreased with further decrease of temperature down to 20 K. A smaller reduction in intensity was exhibited by the device with 0.5 mA, a larger one exhibited by the device with 0.1 mA. The strong electron-electron scattering arising from high excitation, high microcrystalline randomization and high hopping frequency led to the corresponding dominance of the Berthelot-type process by a large T_t. It can be seen in the Arrhenius plot of the integrated EL intensity that a smaller activation energy can be expected to facilitate the redistribution of the thermal carriers, overcoming the energy barrier and the large degradation of luminescence. This results in not only better than carrier confinement, but also enhances the quantum efficiency of PLED structures requiring lower excitation.     

Slow electron velocity-map imaging photoelectron spectra of the methoxide anion

High resolution anion photodetachment spectra are presented for the methoxide anion and its fully deuterated counterpart. The spectra were obtained with slow electron velocity-map imaging. Improved electron affinities are determined for CH3O as 1.5690+/-0.0019 eV and for CD3O as 1.5546+/-0.0019 eV. The spectra resolve many features associated with spin-orbit and vibronic coupling that were not seen in previous photodetachment studies. Photoelectron angular distributions taken as a function of detachment wavelength for the ground vibronic state transitions are recorded and are consistent with the removal of a nonbonding, p-type electron localized on the oxygen atom. Several hot bands and sequence bands are observed for the first time, providing insight into the vibrational structure of the methoxide anion. The results are compared to recent calculations of the anion photoelectron spectra that incorporate bilinear coupling terms among the methoxy vibrational modes and are found to be in reasonable agreement.     

Synthesis and Simulation Study of Right Silver Bipyramids via Seed-Mediated Growth cum Selective Oxidative Etching Approach

In this study, a simple method to synthesize right silver bipyramid (AgBP) nanostructures via the seed-mediated growth cum oxidative etching approach in aqueous solution is developed. The key strategy of this method is to control the growth and etching process by careful adjustment of the reactants concentration. Ascorbic acid (AA) is used to reduce silver precursor while cetyltrimethylammonium bromide stabilizer is used to direct the preferential growth of (100) facets. The presence of Cu²⁺ and AA in the reaction mixture also enable in-situ generation of H₂O₂, leading to selective etching of (111) facets, which is crucial to the formation of anisotropic AgBPs. The structure-properties of AgBPs is systematically investigated through a series of experiments and theoretical simulations. Transmission electron microscope images and X-ray diffraction patterns of the as-synthesized AgBPs show the formation of single crystalline twined nanostructures with a relatively high yield. These results suggest the important role of the excitation of electric dipole in enhancing the electric field at the six sharp corners of AgBPs, making them especially promising for a wide range of technological applications including surface-enhanced Raman scattering with a significant enhancement factor of 1.50 × 10⁵ as demonstrated herein.