Synthesis and characterization of new nematic liquid crystalline compounds-based thiophene units

Four new liquid crystalline thiophene compounds (M1?M4) with a long flexible spacer were prepared. Their structures were characterized by Fourier transform infrared and proton nuclear magnetic resonance. The mesomorphism and thermal stability were investigated with differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The photo-physical properties were evaluated using ultraviolet/visible spectroscopy and photoluminescence. M1?M4 all showed thermotropic mesogenic properties with excellent thermal stability, and exhibited nematic threaded texture, droplet texture, and Schlieren texture on heating and cooling cycles. The effect of flexible spacer and terminal groups on mesomorphic and spectroscopic property is discussed. The experimental results demonstrated that the tendency toward melting temperature (Tm) decreased, while isotropic temperature (Ti) increased with increasing the flexible spacer length. In CHCl₃ solution, these thiophene compounds displayed an intense broad absorption band peaking within 230–340 nm and a maximum fluorescent emission wavelength at 426–439 nm.     

New chiral liquid crystal materials based on menthol: Synthesis and phase behavior

To study structure-mesomorphism relationships of chiral materials based on menthol, a series of chiral compounds containing menthyl group were synthesized. Their chemical structures, formula, and the purity were characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹H NMR), and elemental analyses. The corresponding phase behavior was investigated with differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The effect of the mesogenic core, flexible spacer, and terminal groups on the mesophase formation and type was discussed. The compound 4-menthyloxyacetoxybenzoyloxy-4′- (6-bromohexyloxy)biphenyl showed the smectic A (S_A) and cholesteric phases on heating cycle, and a cubic Blue Phase, chiral smectic C (S_C^*), S_A and cholesteric phases on cooling cycle. However, the compound 4-menthyloxyacetoxybenzoyloxy-4′-(4-bromobutoxy)biphenyl showed enantiotropic S_C^*, S_A and cholesteric phases, moreover, the platelet texture of a cubic Blue Phase was also observed on cooling cycle. The methacrylate monomer with six flexible methylene units and three phenyl rings as mesogenic core only showed cholesteric phase, while the methacrylate monomer with four methylene unit and three phenyl rings showed the S_C^* and cholesteric phases. However, when the terminal methacryloyloxy groups in the monomers were substituted by thiophenylacryloyloxy groups, the corresponding monomers all show no mesophase. With increasing the rigidity of mesogenic core or decreasing the flexible methylene spacer length, the corresponding melting temperature (T_m) or isotropic temperature (T_i) increased.     

Microhardness of tetrahedrally bonded elemental and binary semiconductors

An analysis of experimental microhardness data shows that the microhardness at room temperature of the diamond, zincblende and wurtzite structure compounds follows the simple relation H = h_oa^−xT_m(1 –g_of_i) where a is the lattice parameter T_m the melting temperature, f_i the spectroscopically defined bond ionicity and h_o, x, and g_o are constants having the same values for all compounds. The close relation between microhardness and bulk modulus is discussed.     

Synthesis and Nonlinear Optical Properties of Novel Polyester Containing Nitrophenylazonitroresorcinoxy Group

A new X-type polyester (4) containing nitrophenylazonitroresorcinoxy groups as NLO chromophores, which are components of the polymer backbone was prepared. Polyester 4 is soluble in common organic solvents such as N,N-dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature (T_g) obtained from differential scanning calorimetry near 120°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength is around 5.08 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 5°C higher than T_g, and no SHG decay was observed below 125°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.     

Occurrence of Kondo-like behavior in electrical-conductivity of Al70Pd20+xMn10−x (x = 0, 1 and 2) icosahedral quasicrystals

Zero-field and in-field (at 8 T) conductivity vs temperature (σ-T), magneto-resistance (Δρ/ρ), magnetization vs temperature (M-T) and magnetization vs field (M-H) of unannealed Al₇₀Pd₂₀Mn₁₀ and annealed Al₇₀Pd₂₀Mn₁₀, Al₇₀Pd₂₁Mn₉ and Al₇₀Pd₂₂Mn₈ quasicrystalline alloys have been studied in the temperature range of 1.4-300 K. Room temperature resistivity and the low-temperature magneto-resistance show a correlation with the corresponding magnetization. The σ-T for all the studied samples shows a pair of minima and maxima. The σ-T maxima show a correlation with the total magnetization. The analysis shows that σ-T is dominated by weak-localization effects. The minima are arising due to competing inelastic scattering times τ_i (e-ph scattering in the dirty metallic limit, τ_i ∝ T⁻²) and the Kondo-type spin-flip scattering time τ_sf whereas the maxima has been attributed to ‘Kondo-maxima’, occurring due to maxima in the spin-flip rate . The magneto-resistance of these samples shows a changeover from negative to positive where the negative component shows a correlation with the magnetization of the sample. The values of parameters derived from refinement give spin-flip scattering fields, which are found to be correlated with the total sample magnetization.     

Ionic conductivity of BaF2 crystals

By fitting theoretically calculated to experimentally found lg σT ÷ 1/T dependencies (σ conductivity) there were obtained: the free formation enthalpy of anti-Frenkel defects g_AF = 1.81 eV − 7.85 kT, and the mobilities v_V and v_i of F⁻ ion vacancies and interstitials: v_VT = 240 exp (−0.59 eV/kT) cm² K/Vs, v_iT = (4080 + 610) exp (−0.79 eV/kT) cm² K/Vs. The free association enthalpies were reestimated for complexes consisting of single foreign cations (Na⁺, K⁺, Y³⁺, La³⁺, Tm³⁺, Yb³⁺) and the corresponding charge-compensating defects. At the melting point of BaF₂ at least 5.7 per cent of the F⁻ ions are disordered.     

Nuclear Spin-Lattice Relaxation in the Linear Chain Metal,NbSe3

Abstract

The nuclear spin-lattice relaxation time T ₁ of ⁹³Nb in NbSe₃ has been observed as a function of frequency v _N in the range 6-40 MHz at 4.2 K and of temperature T in the range 1.3-77 K at 10 MHz. [T ₁ T]^?1 is found to be proportional to 1/√ν corresponding to characteristic divergence of spin correlation function in 1-D system. Below ~10 MHz, a break down of the divergence is observed. The important features of the T dependence observed are a sharp minimum at ~45 K and an asymptotical approach to the metallic relation, T ₁ T= const, with decreasing T down to helium temperature. This [T ₁ T]^?1 minimum is explained by the destruction of the Fermi surface due to the CDW gap formation. The re-increase of [T ₁ T]^?1 below the CDW transition may suggest a partial recovery of the destructed Fermi surface.     

The annealing of alkaline-earth metal polymetaphosphate powders (I). Crystallisation and sintering processes

Amorphous barium, strontium, calcium and magnesium polymetaphosphate powders (MP₂O₆)_n, n = 20 were prepared by dehydration of the corresponding polymetaphosphate hydrate precipitates. These powders were annealed by different continuous and isothermal heat treatments over the temperature range 450° to 700 °C, the glass transition temperatures T_g to above (T_g + 120) °C. The morphologies at different degrees of crystallisation were studied by scanning electron microscopy. For the main crystallisation process (ten to sixty-seventy percent crystallisation), the powder particles retained their original pea-pod form; then after seventy percent crystallisation, these crystallised particles sintered laterally to lozenge-shaped twin-hexagonal crystals of lengths 0.5 to 3 μm. Differential thermal analysis confirmed that a markedly exothermic crystallisation process (overall enthalpy changes from about 30 to 45 kJ mol⁻¹) was occurring within the powder particles. Crystallisation rates varied from < 0.005 min⁻¹ at temperatures near T_g to > 0.5 min⁻¹ at higher temperatures; the activation energies for this process varied from 360 to 560 kJ mol⁻¹. The completely annealed crystals were studied by scanning electron microscopy, X-ray diffraction and further differential thermal analysis to 1000 °C. The X-ray diffraction d value patterns, the fusion temperatures and the enthalpies of fusion were all in close agreement with the literature values for the corresponding beta alkaline-earth metal polymetaphosphates prepared by melt crystallisation.     

On the Phase Transition Behaviour of Binary Systems: Various Non-Nematic Solutes in Nematic Solvent (EBBA)

Phase transition behaviour of the systems of EBBA with methyl alcohol (MeOH), 1.2-dibromo-ethylene (DBE), o-xylene, m-xylene, and p-xylene has been studied. The phase diagrams for each system have been determined by the polarizing microscope. The slopes, β_n and B_i, of the nematic and the isotropic phase boundary lines in each system have been qualitatively described by the molecular field treatment proposed by Humphries. The order parameters for both cis-and trans-DBE in EBBA have been obtained from analyses of ¹H-NMR spectra. In the nematic phase, they decrease with increase in temperature. In the nematic/isotropic coexisting phase (N/I phase), the order parameter for CIS-DBE is almost independent of temperature. The proton spin-lattice relaxation times (T₁) in the MeOH/EBBA system have been measured by a pulse NM R technique. Little temperature dependence of T¹ has been found in the N/1 phase region.c     

The double phosphates MIMIIPO4 (MI – Na,K; MII – Mg,Mn, Co,Ni, Zn) – synthesis from chloride melts and characterization

The particularities of the chemical interaction in systems M^IPO₃‐M^IIO(or Mn₂O₃)‐M^ICl (M^I – Na, K; M^II – Mg, Co, Ni, Zn) have been investigated at the temperature 1073 K and molar ratios P/M^x = 1 or 2 and M^ICl/(M^IPO₃ + M^IIO(or Mn₂O₃)) = 30. The conditions of formation of complex phosphates M^ІM^IIPO₄ and Na₄Ni₃(PO₄)₂P₂O₇ have been found. Influences of the nature of alkali and bivalent metals on the products composition were discussed. The advantages of chloride melts using (synthesis time reduction and temperature reducing) for preparing of complex phosphates were shown. The synthesized compounds have been characterized using the powder X‐ray diffraction, Fourier transform infrared and diffuse reflectance spectroscopies.     

Synthesis and Properties of Novel Nonlinear Optical Polyester Containing Cyanovinylnitroresorcinoxy Group

Novel X-type polyester 5 containing 4-(2’-carbomethoxy-2’-cyano)vinyl-6-nitroresorcinoxy group as nonlinear optical (NLO) chromophore, which constitutes parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polyester 5 shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 116°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at the 1064 nm fundamental wavelength is 4.25 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 4°C higher than glass-transition temperature (T_g), and no significant SHG decay is observed below 120°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.     

Plastic Deformation of Cesium Iodide Single Crystals at High Temperatures

The plastic deformation of CsI crystals of three crystallographic orientations 〈100〉. 〈110〉. and 〈111〉 at temperatures from 423 to 773 K (0.5 to 0.86T_m) and strain rates from 2 × 10⁻³ to 10⁻⁵ s⁻¹ is studied. Four-stage stres-strain curves were found, three stages being more and more distinct with an increase in temperature up to 623 K above which stage III prevails. For all the temperatures, strain rates and oreintations studied the superplasticity features (jerky flow, deformation localization, active dynamical recovery etc.) were observed. The thermal activatoin analysis has shown that the rate of high temperature deformation of CsI is controlled by dislocation climb limited in its turn by mobility of cation vacancies (quasiviscous creep).     

The thermal expansion of microcracks and grain boundaries in crystals (I). A new mechanism of crack formation

Apart from known reasons for crack formation it may be effected by the spontaneous microcrack wall heating. This heating takes place because of crack widening and formation of relatively free surfaces (crack walls). These surfaces must have the effective temperature that is well above the temperature in the bulk of crystals, as it has been shown earlier by the author. Simple equations for the thermal expansion of microcracks had been suggested. It has been shown that at the temperature above of 0.9T_m (T_m is the melting point) for the pure metals the spontaneous, without external stresses, crack formation takes place that may cause creep and superplasticity proceeding by the diffusion mechanism. At T_m the spontaneous cracking results in the crystal crushing to the microcrystallites, that is the spontaneous cracking may be considered to be the melting mechanism. From this point of view the intensive thermal expansion of liquids in temperature range from T_m to the critical temperature involves mainly the enlargement of microcrystallite gaps. By using this supposition simple equations for thermal expansion of liquids have been proposed.     

Synthesis and Nonlinear Optical Properties of Novel Polyurethane Containing Cyanovinylnitroresorcinoxy Group

Novel X-type polyurethane 5 containing 4-(2′-carbomethoxy-2′-cyano)vinyl-6-nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stabilities up to 260°C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry near 108°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064 nm fundamental wavelength is 9.83 × 10^?9 esu. Polymer 5 exhibits a high thermal stability even at 2°C higher than T_g, and no significant SHG decay is observed below 110°C, which is acceptable for nonlinear optical device applications.     

Iron-Chloranilate Intercalation Compounds: Synthesis,Crystal Structures,and Thermal Properties

Abstract

Hydrogen bond supported new iron-chloranilate assemblies, {(Hpy)[Fe(CA)₂(H₂O)₂](H₂O)}_n (py = pyridine, H₂CA = chloranilic acid, C₆H₂O₄Cl₂) (1), and [(phz)₂[Fe(CA)₂(H₂O)₂](H₂O)₂]_n (phz = phenazine, C₁₂H₈N₂) (2) have been synthesized and characterized. Compound 2 crystallizes in the monoclinic, space group C2/m (#12), with a= 29.135(6) Å, b= 16.886(6) Å, c = 15.017(5) Å, ß = 165.907(1)°, V= 1798(2) ų, Z = 2. In both the compounds two chloranilate dianions and two water molecules are coordinated to the iron ion making anionic monomers [Fe(CA)₂(H₂O)₂]^?, which are the building blocks of the compounds. The coordination environment around the iron ion in the building block is a distorted octahedron, where two water molecules sit on the trans position to each other. [Fe(CA)₂(H₂O)₂]^? anions form common layer structures, supported by hydrogen bonds. Hpy⁺ are intercalated in between the layers of 1 by electrostatic and hydrogen bonding interactions and phz are intercalated in that of 2 by electrostatic interactions. DSC traces of 1 show anomaly at 174 K, indicating phase transition in the compound.     

Structures of the Triclinic and the Monoclinic Modification of Divascan®

Trielinic modification: C₁₂N₄O₃H₁₆. Mr = 264.26, triclinic P 1 , a = 7.702(3), b = 9.420(11),c = 10.893(8) A, α = 73.37(8), β = 82.22(5), γ = 66.30(6)°, V = 638(1) A³, Z = 2, D_m = 1.360 Mg m⁻³, D_x = 1.362 Mg m⁻³, λ(MoK_α) = 0,71062 A, μ = 0.1084 mm⁻¹, F(000) = 280, T = 296 K, final R = 0.0742, wR = 0.0758 for 1842 reflections. Monoclinic modification: C₁₂N₄O₃H₁₆·, 3/2H₂O, M_r = 291.28, monoclinic P 2₁,/c, α = 14.075(5), b = 12.631(6), c = 16.234(5) A, β = 99.25(3)°, V = 2849(1) A³,Z = 8, D_m = 1.338 Mg m⁻³, D_m = 1.359 Mg m⁻³, λ(MoK_α) = 0.71062 A, μ = 0.1134 mm⁻¹, F(000) = 1240, T = 296 K, final R = 0.0557, wR = 0.0691 for 1266 reflections. Comparison of the two independent Divascan® molecules of the monoclinic modification with the one of the triclinic modification demonstrates good agreement of related bond distances and angles in the molecules. Disorder of the hydroxyl groups of one Divascan® molecule of the monoclinic modification is announced by high vibration parameters of the related oxygen atom and a very short C O distance, which is not adequate to a real C O bond length.     

Octahedral Copper(II) Carboxylates with 1,10-Phenanthroline: Synthesis,Structural Characterization,DNA-Binding and Anti-Fungal Properties

Two mono-nuclear axially distorted octahedral copper(II) complexes have been prepared and characterized via FT-IR, UV–Visible, elctrochemical, electron spin resonance and powder and single crystal XRD techniques. The complexes consist of a phenanthroline and two carboxylate ligands each bonded in bidentate fashion. Carboxylates are ortho-nitro-2-phenyl acetate (L1) and para-chloro-2-phenyl acetate (L2). Structural study showed that both complexes possess Jahn–Teller distorted octahedral geometry. The bulk purity was assessed from the matching experimental and simulated powder XRD spectra. The results of spectroscopic techniques are consistent with each other. ESR data revealed single electron occupancy of d_x² ? _y² orbital with ²B_1g as ground state typical of tetragonally distorted octahedral geometry. Electrochemical solution study showed diffusion controlled electron transfer processes with diffusion co-efficient values of 10.323?×?10^–8 cm²s^–1 and 0.972?×?10^–8 cm²s^–1 for 1 and 2. Complexes exhibited excellent DNA-binding activity studied via UV–Visible spectroscopy, cyclic voltammetry, florescence spectroscopy and viscometry yielding K_b values of 1.871?×?10⁴ M^–1 (1) and 1.577?×?10⁴ M^–1 (2), 0.38?×?10⁴ M^–1 (1) and 6.39?×?10⁴ M^–1 (2) and 2.1?×?10⁶ M^–1 (1) and 2.0?×?0⁶ M^–1 (2), respectively, for the first three techniques. Complexes possess good antifungal activity against three fungal strains.

Graphic Abstract

     

Facile preparation of graphene-based chitosan films: Enhanced thermal,mechanical and antibacterial properties

Chitosan is considered a model polymer because of its excellent biocompatibility, biodegradability, antibacterial property and metal binding ability. Despite the favorable properties, the poor mechanical strength and the loss of structural integrity limits the applications of chitosan. Graphene's intrinsic low weight with excellent thermal stability makes it an ideal filler for reinforcing polymers. In this work, we prepared graphene oxide (GO) via Hummer's method and simplified Hummer's method using graphite powder and graphite flakes as starting materials, respectively. The GO obtained using Hummer's method and simplified Hummer's method had a small area of less than 50 μm² and a large area of about 7000 μm², respectively. The small area GO and large area GO were reduced by sodium hydroxide, in which the reduced GO (rGO) with small area and large area were incorporated into a chitosan matrix, respectively, using a simplistic drop-casting technique to produce a thin film. Glass transition temperature (T_g) and mechanical strength of chitosan/large area rGO at concentrations of 0.3, 0.6 and 0.9 wt.% of GO were found to be better than chitosan/small area rGO. We also investigated the T_g and mechanical strength between chitosan/small area GO and chitosan/small area rGO, where we discovered that the former had better thermal and tensile properties. By comparing the T_g and mechanical strength of chitosan/small area GO against chitosan/large area GO, we found that the latter displayed superior thermal and tensile properties. Antibacterial tests were performed on the graphene-based chitosan composites and their ability to act as bactericide was manifested in the retardation of the growth of Pseudomonas aeruginosa. These composite materials with excellent thermal, tensile and antimicrobial properties find real-life applications in the physical, chemical, mechanical, electrical and bioengineering fields.     

Emissionselektronenmikroskopische Untersuchungen am Zweistoffsystem Niob-Eisen

Results from emission electron microscope investigations of thermal and mechanical behaviour of the Laves-phase NbFe₂ and of two-phase areas in the binary system Nb Fe are presented. The melting process of NbFe₂ samples with included μ-phase NbFe was observed in the emission microscope and supported the existence of a eutectic between both intermetallic compounds. The Laves-phase NbFe₂ was deformed plastically by a microhardness tester and also homogenously by a compressive device during electron microscope observations. Both yield stress and microhardness of NbFe₂ were measured as a function of temperature up to 1550 K. The relation between a critical temperature T₀ of the hardness-temperature curve and the melting temperature T_m was T₀/T_m = 0,64, in good agreement with results from other Laves-phases. During the heating of NbFe₂ samples a niobium oxide decoration structure appeared at residual air pressures from 1 · 10⁻⁶ torr to some 10⁻⁴ torr. The observed density of decoration points amounted to (1…5) · 10⁸ cm⁻². A discussion shows the possibility of a connection between decoration points and dislocations emerging from the crystal.     

The Crystal Structures of Bis(2-amino-5-methylpyridinium) Tetrabromometallate(II): Intermolecular Interactions in (C<Subscript>6</Subscript>H<Subscript>9</Subscript>N<Subscript>2</Subscript>)<Subscript>2</Subscript>[MBr<Subscript>4</Subscript>]; M = Cd and Co

Abstract The crystallization and structures of a triclinic (henceforth T) (C₆H₉N₂)₂[CdBr₄] and a monoclinic (henceforth M) of (C₆H₉N₂)₂[CoBr₄] are reported. The crystal packing of both solids is analyzed and compared: both contain parallel chains of cations and stacks of anions. In both T and M, each [MBr₄]²⁻ is hydrogen bonded non-symmetrically to surrounding cations in a ladder chains that run along b axis, with planar cations in both structures falling in parallel to the planes to anions. In T the cation chains are further involved in classical π···π stacking, while in M the cation chains show less significant stacking, with longer repeat distance. Index Abstract Extensive N–H···Br hydrogen bonds link both anions and cations into chains of the ladder type parallel to the crystallographic b axis. The crystal structures of bis(2-amino-5-methylpyridinium) tetrabromometallate(II): Intermolecular interactions in (C6H9N2)2[MBr4]; M = Cd and Co Rawhi Al-Far and Basem Fares Ali