Orientational order and molecular parameters of two nematogenic mixtures from X-ray studies: confirmation of electro-optical results

This study entails the report of X-ray studies conducted on two nematogenic mixtures (code names ZLI 1221 and ZLI 1291) containing identical moieties: phenyl cyclohexane, biphenyl cyclohexane and cyclohexyl benzoate, but exhibiting different mesogenic ranges and properties. X-ray studies have been undertaken with a view to investigate the difference in the mesogenic behaviour of the said mixtures at the molecular level. The average apparent molecular length ‘l?’ and intermolecular distance ‘D’ of the two mixtures and their variations with temperature have been determined from X-ray data. The orientational order parameters ?P ₂? and ?P ₄? and their thermal variations have also been obtained. Comparison has been made with the ?P ₂? values obtained from X-ray study with those obtained from optical study. The average apparent molecular lengths of the two mixtures corroborate the findings regarding the relative molecular weights of the two samples obtained from optical and dielectric data.     

NIR photoresponse in the mixed phthalocyanine films

The structure, optical and conducting properties of thin vacuum deposited films of erbium bisphthalocyanine (Pc₂Er) and its mixtures with metal-free phthalocyanine (H₂Pc) have been studied with particular reference to the near infrared (NIR). It has been found that, in spite of intense optical absorbance over the UV/Vis/NIR domain, pure Pc₂Er films are weakly photoconductive. However, in the mixed Pc₂Er/H₂Pc films the photocurrent signal was detected in the NIR range of 1200–1500 nm, which is associated with optical activity of Pc₂Er molecules. An erratum to this article is available at .     

Analysis of the application of optical two-wavelength techniques to measurement of the Soret coefficients in ternary mixtures

We discuss the application of two-wavelength optical methods for the determination of Soret coefficient in ternary mixtures. Though the principle of such an approach was formulated in the literature earlier, we have found a significant obstacle to its implementation and suggested a way to circumvent that obstacle. The main target of our approach is the analysis of the compatibility of the matrices of contrast factors (the derivatives of refractive indices with respect to concentrations) with available light sources used for measuring the Soret effect in ternary mixtures. We report on the development of a simple mathematical approach to verify the applicability of the chosen wavelengths for laser diodes to measure transport coefficients for a certain class of ternary mixtures. The approach has been applied to a number of aqueous ternary mixtures: water–ethanol–k-ethyleneglycol, k?=?mono, di, tri, and water–t-butanol–DMSO) and light sources in the visible λ₁?=?670?nm and infrared λ₂?=?925?nm spectrum. The regions of feasibility/infeasibility of the methods have been revealed for these mixtures.     

Dielectric and electro-optic behavior of pure ferroelectric liquid crystal material and the isomeric mixtures

We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (P_S) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of P_S of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (P_S). An additional collective mode has been observed in the SmC¹ phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of P_S in the isomeric mixtures. The result has been discussed.     

HF-laser performance of CO2-laser-ignited mixtures of SF6 :H2 and of S2F10 :H2

We have used a CO₂ laser to ignite mixtures of SF₆ :H₂ and S₂F₁₀ :H₂. We observed HF lasing from these mixtures when an optical resonator was constructed around the reaction cell. The HF-lasing performance of the two mixtures was compared as a function of mixture ratio, fluorine-donor pressure, and CO₂-laser frequency. Under comparable conditions, the HF-laser output for S₂F₁₀ :H₂ mixtures was typically 5–6 times greater than that for SF₆ :H₂ mixtures. Spectral output of the HF laser was coarsely resolved to provide data about the vibrational and rotational states of the HF molecule.     

Solvent-induced optical properties of C60

Different C₆₀ aggregates, i.e. nanoparticles, clusters of nanoparticles and microcrystals in room-temperature solutions, are reported to account for the colors of fluorescence emissions centered at 440, 575 and 700 nm, respectively. And the configurations of C₆₀ aggregation created in solutions are revealed to be closely associated with the characteristic interactions between C₆₀ and solvent molecules. On this basis, aggregation behaviors and thus induced optical properties of C₆₀ have been tentatively controlled through adopting solvent mixtures.     

Influence of the High‐Frequency Capacitive Discharge Regimes on the Parameters of the Plasma in N2/CO2/He Gas Mixtures

The optical radiation spectra and the spatial structure of a planar highfrequency capacitive discharge in N₂/CO₂/He gas mixtures have been investigated depending on the excitation frequency, discharge current, pressure, and chemical composition of the mixture.     

Studies on binary mixtures of 4-pentyloxy-4′-cyanobiphenyl with three 4, 4′-di(alkoxy)azoxybenzenes

Eighteen binary mixtures of 4-pentyloxy-4′-cyanobiphenyl (5OCB) and 4, 4′-di(alkoxy)azoxybenzenes (nOAB) with n = 5, 6, and 7 at different concentrations have been studied in detail. Over a wide concentration range, induced SmA phase was observed in all the mixtures except in one. In most of the mixtures, the refractive indices no, ne, and Δn lie between the values of pure components. The optical birefringence of the mixtures is found to decrease non-additively with concentration. The molecular polarizability anisotropy and the orientational order parameter <P₂> of the mixtures were calculated. Nature of variation of polarizability anisotropy with concentration is similar to that of Δn. In allmixtures <P₂> is more in smectic phase than in nematic phase and it also shows non-additive behaviour. Observed <P₂> values of the mixtures were compared with McMillan’s and Maier-Saupe theoretical values and good agreement is found in some mixtures. The transition temperatures obtained by fitting <P₂> data to McMillan’s theory agree with the observed values within a few degrees. Ratio of elastic constants K₃₃ and K₁₁ is determined for mixtures having nematic phase and found to diverge at T_NA transition point.     

Examination of new chiral smectics with four aromatic rings

This paper presents the results of the study of four chiral mesogens with the acronym (4X₁X₂). The investigated compounds might be of interest for use as components of multicomponent mixtures useful in technical devices. The compounds have high chemical stability. Their mesomorphic properties were tested by means of polarizing optical microscopy and differential scanning calorimetry. The helical pitch of the prepared compounds and mixtures was estimated using the selective reflection method. Their phase smectic layer structure and usefulness for formulation of multicomponent antiferroelectric mixtures were then reported.     

Theoretical and experimental study of V–I characteristics of UV pre-ionized TEA CO2 laser for variety of laser gas mixtures

Experimental and theoretical study of V–I characteristics of UV pre-ionized TEA CO₂ laser has been carried out for a variety of gas mixtures emitting different optical pulse shapes suitable for various applications. Coupled differential equations have been solved to model the pulse excitation circuit using the numerically calculated values of ionization coefficient (α), attachment coefficient (β) and drift velocity (U_d) as functions of E/N (i.e. electric field to neutral particle density ratio) for chosen gas mixture. Calculated and experimental V–I characteristics for gas mixtures (CO₂:N₂:He::1:2:3, 1:1:4, 1:1:5 and 1:0:4.7) show a good agreement. It has been shown that gas mixture has a dominant effect on the delay between pre-ionization and main discharge; thus, determining the long-term stability of discharge. The excitation pulse duration increases with increase in molecular content of gas mixture (i.e. amount of CO₂ and N₂ in gas mixture).     

The double M-effect induced by noble gases activated with negative ions

The M-effect (monochromatization-effect) is a powerful tool which can give high intensity monochromatic spectra with a certain wavelength depending on the type of used gas mixtures to generate plasma state. The effect consists in the emission of a single spectral line of plasmas ignited in certain gas mixtures. The main condition to obtain the M effect is the presence of an electropositive and an electronegative gas mixture. For example, in the case of Ne+H₂ monochrome radiation was obtained, the wavelength of Ne being 585.3 nm (1s²–2p⁵). In this paper we prove the general character of this effect, i.e. if the optical emission spectra reduced to nearly one line can be observed also in other gas mixture discharges, for example in the case of one electronegative gas and two electropositive gases. Different other mixtures, as Xe+Ne+H₂ and Xe+Ar+H₂ have been studied. In all these cases, the M-effect appeared without doubt.     

The effect of scattering-medium parameters on signal magnitude under acousto-optic tomography

We have experimentally studied the influence of scattering anisotropy parameter g of a medium on the magnitude of signal S (visualization parameter) at an ultrasonic frequency that is registered upon acoustooptic tomography. Aqueous solutions of mixtures of cream and skimmed milk with different ratios between them were used as scattering media. The optical properties of media (absorption coefficient μ_a and reduced scattering coefficient μ′ _S ) have been measured on a spectrophotometer (Perkin-Elmer Lambda 950 UV-VIS-NIR) using the inverse adding-doubling technique. As a result of the investigation, we have found that there is a certain correlation between the value of the scattering anisotropy parameter g of aqueous solutions of investigated mixtures and the percentage of the mixture in the aqueous solution, which ensures the required small value of extinction coefficient μ of the scattering medium. An increase in signal S has been revealed with increasing anisotropy parameter g of the medium at a invariable value of extinction coefficient μ. We have concluded that, to solve an inverse problem on the acousto-optic tomography, it is necessary to take into account possible changes in the g factor in scattering media, including biological ones.     

The dielectric relaxation study of 2(2-alkoxyethoxy)ethanol-water mixtures using time domain reflectometry

Complex permittivity spectra of 2(2-alkoxyethoxy)ethanol-water mixtures for the entire concentration range and at 25 °C have been measured using time domain reflectometry technique up to 30 GHz. The relaxation processes have been obtained by fitting the complex permittivity spectra of the binary mixtures in 2-Debye equation. In glycol ether-water mixtures except for pure water and its rich region the double relaxation times, primary process (τ₁) and secondary process (τ₂) have been observed. The primary relaxation process (τ₁) may be due to cooperative relaxation of the H-bond network of mixture constituents and the secondary relaxation process (τ₂) may be due to its flexible parts attached to the carbon chain. The intra and intermolecular hydrogen bonding of 2(2-alkoxyethoxy)ethanol in pure form as well as in binary mixtures of water have been discussed using Kirkwood correlation factor, Excess dielectric properties and the Bruggeman factor.     

Determination of C60/C70 ratios in fullerene mixtures and film characterization by scanning tunneling microscopy

Fullerene powder mixtures with different C₆₀/C₇₀ ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C₆₀/C₇₀ ratios show that C₇₀ molecules display a larger apparent diameter (0.8 nm) and corrugation than C₆₀ molecules (0.7 nm). The C₆₀/C₇₀ ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C₆₀/C₇₀ ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C₇₀ molecules and vacancies). In films prepared to have a C₆₀ coverage of less than one monolayer, stable structural units of the C₆₀(111) surface consisting of three or seven C₆₀ molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed.     

Some experiments on relaxation behind reflected shock waves in argon-molecular gas mixtures

The limitation of the applicability of plasma eaters in mixtures of argon with molecular components is shown. We were able to measuren _e andT _e in argon-hydrogen mixture behind the reflected shock wave and find a strong reduction of both parameters caused by the molecular species. Similarly, the delay of the onset of ionization in argon-hydrogen and argon-nitrogen mixtures is substantially reduced. On the other hand, the molecular component reduces the velocity of thermodynamic equilibration, as has been shown by means of time resolved optical interferometry.     

Preparation and characterization of nitrogen-incorporated SnO2 films

Nitrogen-incorporated SnO₂ thin films have been grown on Si(100) and quartz substrates by reactive sputtering of a Sn target in gas mixtures of N₂–O₂. The structure of the nitrogen-incorporated SnO₂ thin films was studied by X-ray diffraction, and the changes in the chemical bonds and atomic binding states of the nitrogen-incorporated SnO₂ thin films were analyzed by X-ray photoelectron spectroscopy. It was found that the binding energy of Sn 3d and O 1s shifts 0.65 eV and 0.35 eV, respectively, toward the lower-energy side after nitrogen was incorporated into the SnO₂ thin films as a comparison with that of pure SnO₂ film. The indirect optical band gap gradually decreases from 3.42 eV to 3.23 eV, i.e. from the UV to the edge of the visible-light range, with increasing nitrogen flux content in the N₂–O₂ gas mixtures. PACS 81.15.Cd; 78.20.-e; 68.37.Xy; 81.05.Je     

Measurement of the Soret,diffusion, and thermal diffusion coefficients of three binary organic benchmark mixtures and of ethanol–water mixtures using a beam deflection technique

We have measured the Soret (S _T ), diffusion (D), and thermal diffusion (D _T ) coefficients of three binary mixtures of dodecane (DD), isobutylbenzene (IB) and 1,2,3,4-tetrahydronaphthalene (TH) for a concentration of 50 wt% at a temperature of 25°C by means of an optical beam deflection cell. This relevant experimental technique was still missing from a recent benchmark campaign for the measurement of the Soret effect. The measured coefficients agree to within a few percent (10% for S _T , D of TH/IB) with the proposed benchmark values. A detailed analysis of the measurement process of the beam deflection cell, which allows for an elegant extension to include temperature gradients within the windows, is given, and improved benchmark values are suggested. In addition, ethanol–water mixtures have been investigated very carefully over a broad concentration and temperature range. Comparison with data of Kolodner and Wiegand gives a generally good agreement with some systematic deviations. Contrary to theoretical predictions, we have not been able to identify a second sign change of S _T at high ethanol concentrations.     

The ZnHg excimer: Optical and kinetic properties

The optical and collisional properties of the ZnHg excimer have been examined by optically pumping the Zn (4¹S₀→ 4³P₁) resonance line in Zn-Hg vapor mixtures. The stimulated emission cross-section determined for ZnHg¹ (2.3 × 10^?19 cm²) and the excimer's low rate of quenching by Hg (5.5 × 10^?15 cm³ s^?1) make it attractive for future energy-storage laser research.     

Thermal diffusion in binary mixtures containing molecular gases. III. The temperature dependence of αT

A recent expression for the thermal diffusion factor α_T for binary atom-molecule mixtures, which includes a full range of inelastic collisional contributions [McCourt, F. R. W., 2003, Molec. Phys., 101, 2181] has been utilized to calculate its temperature dependence for equimolar N₂-He, Ne, Ar mixtures and for an equimolar CO₂-Ar mixture. Accurate classical trajectory values for the effective cross-sections entering into the expression for α_T, obtained for the most reliable potential energy surfaces available, have been employed in the calculations. Good agreement has been attained with experiment for all four binary mixtures, including the decrease of α_T with increase in temperature observed for CO₂-Ar mixtures, heretofore considered to be anomalous.     

Gas Density Distributions and Reduced Field Strenghts of the Positive Column of Low Pressure XeCl* Glow Discharges

Interferometric measurements of radial gas density distributions have been performed on the cylindrical positive column of DC low pressure glow discharges (LPGD) in pure Xe and Xe/Cl₂ gas mixtures. Absolute gas temperatures have been measured by thermocouples. In the mixtures, the gas temperature is several hundred Kelvin above the temperature in pure Xe. Additionally, the radial distribution of the gas density in the mixtures cannot be described by Bessel profiles, which would result from Schottky's diffusion theory. Combined with field strength measurements, radial profiles of E/N (electric field strength/neutral density) have been determined. Results of this work will be useful for model developments of LPGD in rare-gas/Cl₂ mixtures but also for the general understanding of the positive column in attaching gases.