Tuesday, 30 August 2011
Tuesday, 9 August 2011
The influence of hydrogen bonding on the physical properties of ionic liquids
Koichi Fumino, Tim Peppel, Monika Geppert-Rybczyńska, Dzmitry H. Zaitsau, Jochen K. Lehmann, Sergey P. Verevkin, Martin Köckerling and Ralf Ludwig
Phys. Chem. Chem. Phys., 2011, Advance Article
Potential applications of ionic liquids depend on the properties of this class of liquid material. To a large extent the structure and properties of these Coulomb systems are determined by the intermolecular interactions among anions and cations. In particular the subtle balance between Coulomb forces, hydrogen bonds and dispersion forces is of great importance for the understanding of ionic liquids. The purpose of the present paper is to answer three questions: Do hydrogen bonds exist in these Coulomb fluids? To what extent do hydrogen bonds contribute to the overall interaction between anions and cations? And finally, are hydrogen bonds important for the physical properties of ionic liquids? All these questions are addressed by using a suitable combination of experimental and theoretical methods including newly synthesized imidazolium-based ionic liquids, far infrared spectroscopy, terahertz spectroscopy, DFT calculations, differential scanning calorimetry (DSC), viscometry and quartz-crystal-microbalance measurements. The key statement is that although ionic liquids consist solely of anions and cations and Coulomb forces are the dominating interaction, local and directional interaction such as hydrogen bonding has significant influence on the structure and properties of ionic liquids. This is demonstrated for the case of melting points, viscosities and enthalpies of vaporization. As a consequence, a variety of important properties can be tuned towards a larger working temperature range, finally expanding the range of potential applications.
Friday, 5 August 2011
Identification and Quantification of Polymorphism in the Pharmaceutical Compound Diclofenac Acid by Terahertz Spectroscopy and Solid-State Density Functional Theory
Matthew D. King, William D. Buchanan, and Timothy M. Korter*
Department of Chemistry, Syracuse University, 1-014 Center for Science and Technology, Syracuse, New York 13244-4100, United States
Polymorph detection and quantification in crystalline materials is a principle interest of the pharmaceutical industry. Terahertz (THz) spectroscopy can be used for such analytical applications since this technique is sensitive to the intermolecular interactions of molecules in the solid state. Understanding the fundamental nature of the lattice vibrational motions leading to absorptions in THz spectra is challenging, but may be achieved through computational approaches. In this study, the THz spectra of two diclofenac acid polymorphs were obtained by THz spectroscopy, and the vibrational characters of the observed absorptions were analyzed using solid-state density functional theory (DFT). The results demonstrate the quantitative capacity of THz spectroscopy and the reliability and utility of solid-state DFT in the calculation of low-frequency vibrational motions.
Monday, 1 August 2011
Tunable resonance enhancement of multi-layer terahertz metamaterials fabricated by parallel laser micro-lens array lithography on flexible substrates
Z. C. Chen, N. R. Han, Z. Y. Pan, Y. D. Gong, T. C. Chong, and M. H. Hong
Optical Materials Express, Vol. 1, Issue 2, pp. 151-157 (2011) doi:10.1364/OME.1.000151
Large-area split ring resonators (SRRs) array is fabricated by laser micro-lens array (MLA) lithography on flexible Polyethylene Naphthalate (PEN) substrates. Multi-layer metamaterials are formed by stacking and bonding several layers of the laser fabricated metamaterials together. The resonance of the multi-layer metamaterials is enhanced significantly as compared to the single-layer metamaterials. The roll-off value of the half-wavelength resonant dip, which reflects the strength of resonance, increases significantly from 4.9 to 11.2 as the layer number increases from 1 to 5. A logarithm relationship between the amplitude of the resonant dip and the layer number is also studied, which indicates a flexible method to tune the strength of resonance by changing the layer number. The multi-layer metamaterials with the enhanced resonance can be used to make narrow band terahertz filters.
“The samples are characterized by a Terahertz Time Domain Spectroscopy (THz-TDS,
TPS3000, Teraview Inc.) in transmission mode at a normal incidence. The electric field of the
incident terahertz wave is aligned parallel to the gap-bearing side of the SRRs as illustrated in
Fig. 1 (B). All the transmission spectra of the samples with different layer numbers are
normalized against the reference transmission spectrum of Nitrogen gas environment ”