Structure and dipole moments of the two distinct solvated forms of p-nitroaniline in acetonitrile/CCl4 as studied by infrared electroabsorption spectroscopy

Structure and dipole moments of the two distinct solvated forms of p-nitroaniline (pNA) in acetonitrile/CCl4 have been studied by infrared electroabsorption spectroscopy. We measured a series of infrared electroabsorption spectra of pNA dissolved in an acetonitrile/CCl4 mixed solvent by altering the angle chi between the external electric field and the electric field vector of the incident infrared light. A singular value decomposition analysis has revealed that the observed infrared electroabsorption spectra are decomposed into two major components: the chi-dependent and chi-independent components. The decomposed spectral components as well as the infrared absorption spectrum are well explained in terms of two distinct solvated forms of pNA that exist in equilibrium in the mixed solvent. These solvated forms can be assigned to the 1:1 and 1:2 species, which have one and two acetonitrile molecule(s), respectively, associated with pNA. From a least-squares fitting analysis of the chi-dependent spectral component, it is shown that, for both the 1:1 and 1:2 species, a head-to-tail structure accounts well for the experimental results. On the other hand, the chi-independent component is likely to arise from the population change between the two solvated forms. This electric-field-induced population change of solvated forms may lead to the control of dielectric environments in solution by an external electric field.     

Superconducting properties of SmFeAsO1−x prepared under high-pressure condition

Synthetic conditions such as stoichiometries, temperature and pressure are optimized to achieve a high quality oxygen deficient SmFeAsO_0.6 superconductor. Both electric and magnetic measurements show a sharp superconducting transition at about 55 K. Several important physical parameters are deduced. The apparent superconducting gap observed in heat capacity with 2Δ_o/k_BT_c of 4.57 larger than that of previous fluorine replaced samples indicate that this superconductivity will not strongly conflict with the phonon-mediated BCS mechanism. The mean free length ?=18.8 nm and the coherent length ξ=2.3-3.3 nm show that the superconductivity is in the clean limit.     

Positive allosteric binding behavior of pyrene-appended triazole-modified thiacalix[4]arene-based fluorescent receptors

The novel heteroditopic receptors 5_a∼c have been synthesized, which bear a thiacalix[4]arene in the 1,3-alternate conformation. Two urea moieties possessing various aryl groups with either electron-donating or -withdrawing groups at their p-positions function as anion-binding sites. At the opposite side of the cavity are two pyrene-appended triazole rings, which act as cation-binding sites. The binding property of receptor 5_c was investigated by means of ¹H NMR and UV–vis spectroscopy and by fluorescence titration experiments in the presence of various transition metal cations and anions in CH₂Cl₂–DMSO (10:1, v/v) solution. Interestingly, it was found that receptor 5_c possessing two p-nitrophenyl ureido moieties, most efficiently complexes in the urea cavity or bistriazoles; the plausible allosteric effect of receptor 5_c was also investigated.     

Interfacial Interaction of Polymer/Liquid Crystal Molecules and Electrooptical Properties of their Composite Systems

Polymer/liquid crystal composite films were prepared from a solution of polymer and nematic liquid crystal (LC) by a solvent casting method. The phase-separated structure of the composite film was controlled by the solvent evaporation rate. The light-scattering profile of a poly(diisopropyl fumarate)/LC: 40/60 w/w solution during solvent evaporation exhibited a periodic structure, indicating that the phase-separated structure was formed by spinodal decomposition. The aggregation structure of the composite film was investigated with a scanning electron microscope (SEM). SEM observation of the composite film suggested the presence of periodicity and dual connectivity of polymer and LC phases. The faster the solvent was evaporated, the smaller the LC channel (domain) size in the composite film. The composite film, composed of poly(methyl methacrylate) (PMMA) and a nematic LC (E44) with a positive dielectric anisotropy, exhibited remarkable and reversible light-scattering-light-transmission switching, under the modulation of an ac electric field. The light-scattering state was dependent on such optical heterogeneities as spatial distribution of the nematic directors and/or mismatching in the refractive indices of the components. The electrooptical behavior of the composite film was strongly dependent on the LC channel (domain) size in the composite film. The transmittance increased and the rise and decay response times (τ_R and τ_D), decreased and increased, respectively, with an increase in the size of the LC channel (domain).

The electrooptical switching properties for the polymer/LC composite film should be influenced by miscibility between the polymer and the LC phases. The miscibility between both phases was evaluated from a distribution of relaxation time for interfacial polarization. The anchoring effect was also investigated by measuring the nonlinearity of the dielectric constant for the composite system.     

Electrorheological Effect and Electro‐Optical Properties of Side‐on Liquid Crystalline Polysiloxane in a Nematic Solvent

The electrorheological (ER) effect and the electro‐optical properties of a ′′side‐on′′ liquid crystalline polysiloxane (PS) are investigated. A large ER effect is observed and the response to the shear stress of neat PS in the nematic phase is shown to be affected by the shear rate. PS is also mixed with a low‐molar nematic liquid crystal (5CB) in order to improve the response behavior to the applied electric field. The rheological properties of such mixtures are highly dependent on the concentration of 5CB. The composites respond faster to the applied electric field and have improved electro‐optical properties. This study offers a new perspective on the development of liquid crystal materials for the ER effect.     

Thermo-recording in (side chain type smectic A liquid crystal polymer/nematic liquid crystal/chiral dopant/dichroic dye) composite with a low power laser

Thermo-recording in a [side chain type smectic A liquid crystal polymer (SmA-LCP)/nematic liquid crystal (N-LC)/chiral dopant/dichroic dye] composite has been realized by using 2mW of power from a He-Ne laser. The laser irradiation-induced phase transitions of smectic A (SmA) → chiral nematic (N*) → SmA formed the dominant thermo-recording mechanism in the composite. Thermo-recording in the (SmA-LCP/N-LC/chiral dopant/dichroic dye) composite exhibited a higher contrast when compared with the non-polymeric (SmA-LC)/N-LC/chiral dopant/dichroic dye composite.     

Polarization-independent refractive index tuning using gold nanoparticle-stabilized blue phase liquid crystals

Polarization-independent refractive index (RI) modulation can be achieved in blue phase (BP) liquid crystals (LCs) by applying an electric field parallel to the direction of light transmission. One of the problems limiting the achievable tuning range is the field-induced phase transition to the cholesteric phase, which is birefringent and chiral. Here we report the RI modulation capabilities of gold nanoparticle-doped BPs I and II, and we show that field-induced BP-cholesteric transition is suppressed in nanoparticle-doped BP II. Because the LC remains optically isotropic even at high applied voltages, a larger RI tuning range can be achieved.     

Hydrogel-Stiffening and Non-Cell Adhesive Properties of Amphiphilic Peptides with Central Alkylene Chains

Amphiphilic peptides bearing terminal alkyl tails form supramolecular nanofibers that are increasingly used as biomaterials with multiple functionalities. Insertion of alkylene chains in peptides can be designed as another type of amphiphilic peptide, yet the influence of the internal alkylene chains on self-assembly and biological properties remains poorly defined. Unlike the terminal alkyl tails, the internal alkylene chains can affect not only the hydrophobicity but also the flexibility and packing of the peptides. Herein, we demonstrate the supramolecular and biological effects of the central alkylene chain length inserted in a peptide. Insertion of the alkylene chain at the center of the peptide allowed for strengthened β-sheet hydrogen bonds and modulation of the packing order, and consequently the amphiphilic peptide bearing C2 alkylene chain formed a hydrogel with the highest stiffness. Interestingly, the amphiphilic peptides bearing internal alkylene chains longer than C2 showed a diminished cell-adhesive property. This study offers a novel molecular design to tune mechanical and biological properties of peptide materials.     

Activation of TiO2 photocatalyst by single-bubble sonoluminescence for water treatment

Single-bubble sonoluminescence (SBSL) continues to attract many researchers because the physics behind it remains uncertain and few applications have appeared. In this study, we propose to apply SBSL to a water-treatment technique. The SBSL flashes contain intense ultraviolet light, which activates a TiO2 photocatalyst to decompose organic compounds in water. This mechanism comes from the similar spectrum patterns between SBSL emission and TiO2 absorption. SBSL in solutions containing small amount of TiO2 powder decomposed phenol and 2,4-dinitrophenol with efficiency several times higher than those by the existing methods.     

Measurement of elastic-stiffness tensor of an anisotropic thin film by electromagnetic acoustic resonance

This paper presents a contactless methodology for determining all independent elastic-stiffness coefficients Cij of a transverse isotropic thin film: C11, C12, C13, C33, and C44. The electromagnetic-acoustic-resonance technique measures the acoustic resonance frequencies of a film-coated specimen with a high accuracy, better than 10(-5), which enables determining the film Cij with the known substrate Cij. The measurement takes two steps. First, through-thickness resonance frequencies of longitudinal and shear modes are measured to determine C33 and C44, and the film thickness. Then, remaining three coefficients are deduced from measurements of the free-vibration resonance frequencies of the layer parallelepiped specimen. Simulations and experiments with monocrystal copper and titanium confirm the reliability of the resultant film Cij within 5%, when the film thickness is more than 0.5% of the substrate.