Calculation of electric field–temperature (E,T) phase diagram of a ferroelectric liquid crystal near the SmA–SmC_α~* transition

In this work we perform a theoretical calculation in order to reconstitute the(E–T) phase diagram of a chiral smectic liquid crystal in the vicinity of the SmA–SmC_α~* transition. This reconstruction is carried out on the basis of a thermodynamic calculation of the slope of the curve joining the SmC_α~* domain and the unwound SmC~*. An empiric correction of the mean field term of Landau De-Gennes development is necessary to accomplish this reconstruction. Thereafter, an experimental validation is performed to verify our calculations.     

Optical properties,structural, and DFT studies of Pd(II) complexes with 1-phenyl-1H-tetrazol-5-thiol,X-ray crystal structure of [Pd(κ1-S-ptt)2(κ2-dppe)] complex

Seven tetrazole-thione complexes, [Pd₂(κ²-ptt)₄]( 1 ), trans-[Pd(k¹-S-ptt)₂(PPh₃)₂] ( 2 ), trans-[Pd(k¹-S-ptt)₂(SPPh₃)₂] ( 3 ), trans-[Pd(k¹-S-ptt)₂(OPPh₃)₂] ( 4 ), [Pd(k¹-N-ptt)₂(k²-dppe)] ( 5a ), [Pd(k¹-S-ptt)₂(k²-dppe)] ( 5b ), [Pd(k¹-S-ptt)₂(k²-dppeS₂)] ( 6 ), and [Pd(k¹-S-ptt)₂(k²-dppeO₂)] ( 7 ), were prepared from 1-phenyl-1H-tetrazole-5-thiol (Hptt), with substituted phosphines. These complexes were investigated by CHNS analysis; infrared (IR), nuclear magnetic resonance (NMR) (¹H and ³¹P), and ultraviolet–visible (UV–Vis) spectroscopy; and single-crystal X-ray data for 5b . In Complex 1 , the ptt⁻ ligand adopted μ²- k-N, k-S bridging mode to afford a dimeric complex, whereas in Complexes 2–4 , 6 , and 7 , the ptt⁻ was covalently coordinated via sulfur atom of the thiol group as a solo product. In contrast, in Complex 5 , the ptt⁻ ligand was bonded in a monodentate fashion through a deprotonated tetrazole ring nitrogen atom in isomer 5a or via a thiolato sulfur atom in isomer 5b . These linkage isomers were clearly shown in the ³¹P-{¹H} NMR. To explain the adoption of the ligand binding modes in Complexes 5a and 5b , geometry optimization calculations were carried out on two isomers. Very small differences of all molecular parameters were found between 5a and 5b isomers. This confirms the reason for obtaining two isomers. Also, theoretical studies are made for all compounds, and excellent agreement is obtained with experimental data. The direct band gap (Eg) values are equal to 2.88, 2.85, and 2.45 eV for Complexes 1 , 2 , and 4 , respectively, revealing a semiconductor nature. The inhibition activity of Complexes 1–3 , 5 , and 8 were evaluated versus the growth of four types of bacteria in vitro. The complexes showed a good activity compared with free ligand and a standard antibiotic.     

Cross-link network of polydimethylsiloxane via addition and condensation (RTV) mechanisms. Part I: Synthesis and thermal properties

A series of highly cross-linked polysiloxane was synthesised via hydrosilylation and condensation reaction. Structural identification using Fourier Transform Infrared (FTIR) and ¹H-NMR confirmed their chemical structures. Their thermal and, mechanical properties, and crystallinity, were analysed and related to the level of cross-link density. These systems displayed elevated thermal and hardness properties at an increased cross-link density. Furthermore, the level of crystallinity was reduced as displayed by XRD analysis. Along with this observation, the calculated fractional free volume (FFV) showed a decreasing trend leading to the ‘densification’ effect. It was envisaged that the linear polysiloxane chain segments aligned parallel to each other in a triclinic crystal system to generate a crystalline domain. The spacing between these stacking chains was found to be about 7.2 Å as measured from simulated XRD pattern.     

Synthesis, Crystal Structure and ab initio Studies of Cyclohexyl N-Phenylcarbamate

Abstract  

Cyclohexyl N-phenylcarbamate, C₁₃H₁₇NO₂ (I), which is a useful target for biotransformations by fungi, has been synthesized and the structure has been solved by X-ray diffraction. The crystals are triclinic, space group P [`1] \bar{1} , with a = 5.2581 (2) ?, b = 9.5080 (3) ?, c = 12.6165 (4) ?, α = 70.544 (2)°, β = 89.075 (2)°, γ = 80.447 (2)°, M _r = 219.28, V = 585.96 (3) ?³, Z = 2 and R = 0.065. In the title compound the phenyl ring makes a dihedral angle of 30.68(7)° with the carbamate group The molecules are linked into infinite chains via N–H···O hydrogen bonds along the a axis. These hydrogen-bonded chains are further linked by weaker C–H···π interactions. Quantum-mechanical ab initio calculations for the free molecule reproduce well the observed bond lengths and valency angles but show that the crystal packing might be responsible for the rotation of the phenyl ring out of the carbamate plane in the solid state conformation.     

PVC membrane sensor based on periodate—Cetylpyridinium ion pair for the potentiometric determination of periodate

A new plasticized membrane sensor has been proposed for the determination of periodate based on periodate-cetylpyridinium ion pair complex. The electrode shows a linear, reproducible and stable potentiometric response with anionic Nernstian slope of 58.1 ± 0.5 mV/decade over a wide range of concentrations 10⁻⁵–10⁻² M and a detection limit of 2.0 × 10⁻⁶ M of IO₄⁻. The membrane exhibits a fast response time of 30–40 s which is independent of pH in the range 2.0–9.0. The selectivity coefficients indicate excellent selectivity for periodate over a large number of anions, e.g. iodide, bromide, chloride, iodate, bromate, nitrate, sulfate, phosphate, thiocyanate, chromate, thiosulfate, sulfite, perchlorate, citrate, acetate, oxalate, and nitrate. The prepared sensor has been successfully used for the determination of periodate (IO₄⁻) and iodate (IO₃⁻) ions with an average recovery of 99.84 ± 0.34% and 98.22 ± 0.43%, respectively. It is also applied to the determination of hydrazine compounds and aminophenol derivatives with an average recovery of 98.66 ± 0.53% and 98.40 ± 0.56%, respectively. Also, the proposed sensor was used for the determination of potassium iodate in iodized table salt and hydrazine in steam boiler feed water and p-aminophenol. The results obtained are in good agreement with those obtained by standard methods.     

A comparative study of lithium and sodium salts in PAN-based ion conducting polymer electrolytes

The conducting polymer electrolyte films consisting of polyacrylonitrile (PAN) as the host polymer, lithium triflate (LiCF₃SO₃) and sodium triflate (NaCF₃SO₃) as inorganic salts were prepared by the solution-cast technique. The pure PAN film was prepared as a reference. The ionic conductivity for the films is characterized using impedance spectroscopy. The room temperature conductivity for the PAN + 26 wt.% LiCF₃SO₃ film and the PAN + 24 wt.% NaCF₃SO₃ film is 3.04 × 10⁻⁴ S cm⁻¹ and 7.13 × 10⁻⁴ S cm⁻¹, respectively. XRD studies show that the complexation that has occurred in the PAN containing salt films and complexes formed are amorphous. The FTIR spectra results confirmed the complexation has taken place between the salt and the polymer. These results correspond with surface morphology images obtained from SEM analysis. The conductivity–temperature dependence of the highest conducting film from PAN + LiCF₃SO₃ and PAN + NaCF₃SO₃ systems follows Arrhenius equation in the temperature range of 303 to 353 K. The PAN containing 24 wt.% LiCF₃SO₃ film has a higher ionic conductivity and lower activation energy compared to the PAN containing 26 wt.%LiCF₃SO₃ film. These results can be explained based on the Lewis acidity of the alkali ions, i.e., the interaction between Li⁺ ion and the nitrogen atom of PAN is stronger than that of Na⁺ ion.     

Novel co-extruded electrolyte–anode hollow fibres for solid oxide fuel cells

Novel CGO/NiO–CGO dual-layer hollow fibres (HFs) have been fabricated in a single-step co-extrusion and co-sintering process. LSCF–CGO cathodes layers were then deposited onto the dual-layer HFs to construct micro-tubular SOFCs. The NiO in the micro-tubular HF–SOFCs was reduced at 550 °C using hydrogen gas to form Ni anodes. Scanning electron microscope images showed that the dual-layer HFs have porous anodes and dense electrolyte layers. Preliminary measurements with a HF–SOFC fed with H₂ and atmospheric oxygen, produced maximum power densities of 420 W m⁻² and 800 W m⁻² at 450 °C and 550 °C, respectively.     

Properties of certain semigroups and their potential as platforms for cryptosystems

In this paper, we study some properties of semigroups with presentation 〈a,b ; a ^p =b ^r ,a ^q =b ^s 〉. We will also study their potential as platforms for the Diffie-Hellman key exchange protocol.