Bicomponent Mixtures Research Articles

The Influence of Cyanoterminated Compounds on the Stability of Antiferroelectric Phase

Three bicomponent mixtures coming from the system in which antiferroelectric phase is obtained by induction as well as compound having antiferroelectric phase by itself were dopped with different cyanoterminated compounds. The influence of dopants structure on the stabilization of antiferroelectric and induced antiferroelectric phase have been tested by miscibility method in the range up to 0.2 molar fraction of dopants. Very small destabilization of antiferroelectric phase for several cyanoterminated dopants in this range is observed. Longer rigid core and longer terminal chain favour stabilization of antiferroelectric phase.

The temperature and concentration dependence of helical pitch in the mixtures of antiferroelectric compounds with the opposite helical twist sense

The temperature dependence of helical pitch for members of an homologous series of orthoconic antiferroelectric compounds (3FmHPhF) and their bicomponent mixtures (m = 3 and 5 as well as m = 3 and 7) has been measured by the method of selective light reflection. The compounds have the same chiral centre but they have different temperature dependence of the helical pitch as well as the helical twisting sense in SmC*A phase: right for member m = 3, left for m = 7, and both right and left for m = 5. For this last homologue, the change of twisting sense is connected with the appearance of the unwound structure. Concentration dependence on helical pitch was investigated in the mixtures. It was demonstrated that it is possible to obtain mixtures with desirable high pitch and also with totally unwound structure.

Absorption and Interference Sedimentation Analysis of Bi-Component Polystyrene Solutions in Analytical Ultracentrifugation

Sedimentation velocity runs were carried out using both absorption and interference detectors in an analytical ultracentrifuge for a bi-component polymer mixture and using two different data analysis programs. The concentrations of polymer were chosen between 0.11 g/L and 3.43 g/L and were kept constant for both absorption and interference detection systems so as to generate comparisons between the two apart from comparisons between the data analysis programs. The comparisons were achieved through the differential and cumulative distributions of sedimentation coefficient. Though the peak sedimentation coefficient values in both analysis programs were same, the distributions differed in peak broadness and axis interception. The amount of detected components in the mixture also differed in the analysis programs, with VelXLAI exhibiting better performance than Sedfit analysis. Similar observations were made for absorption and interference optics, except for the inability of the absorption optics to measure correctly above polymer concentration of 1 g/L.

Two-fluid pressure-driven channel flow with wall deposition and ageing effects

Two-fluid, stratified pressure-driven channel flow is studied in the limit of small viscosity ratios. Cases are considered in which the core fluid undergoes phase separation that results in the ‘precipitation’ of a distinct phase and the formation of a wall layer; these situations are common in the oil industry where ‘fouling’ deposits are formed during the flow. The thickness of this layer increases as a result of continual deposition through Stefan-like fluxes, which are related to the phase behaviour of the core fluid through a chemical equilibria model that treats the fluid as a bi-component mixture. The deposit also undergoes an ‘ageing’ process whereby its viscosity increases due to the build-up of internal structure; the latter is modelled here via a Coussot-type relation. Lubrication theory is used in the wall layer and an integral balance in the core fluid wherein inertial effects are important. By choosing appropriate semi-parabolic velocity and temperatures closures for the laminar flow in the channel core, and a closure relation for the wall layer rheology, evolution equations are derived that describe the flow dynamics. In the presence of ageing but absence of deposition, it is demonstrated how the time-varying deposit rheology alters the wave dynamics; for certain parameter ranges, these effects can give rise to the formation of steep waves and what appears to be finite-time ‘blow-up’. With both ageing and deposition, the spatio-temporal evolution of the deposit is shown together with the increase in the deposition rate with increasing temperature difference between the wall and the inlet.

Surface B-splines fitting for speeding up the simulation of adsorption processes with IAS model

The ideal adsorbed solution theory (IAS) is commonly used in process simulation for predicting multicomponent adsorption equilibrium. However, this model requires a significant computational effort which translates in time consuming simulations. A methodology using surface B-splines fitting was developed for speeding the prediction of the multicomponent equilibrium with IAS theory. As a case study, a breakthrough of an enantiomer bi-component mixture in a fixed bed was simulated and a speed-up of 57.9% was achieved while maintaining the accuracy of IAS multicomponent equilibrium prediction.

Hydrogen purification for PEM fuel cells using membranes prepared by ion-exchange of Na-LTA/carbon membranes

Modified LTA membranes supported on macroporous carbon discs have been synthesized for the separation of H 2 and CO. These membranes have been prepared by hydrothermal synthesis following the secondary growth method and subsequently ion-exchanged with different alkaline cations in order to modify the zeolite pore size. Their permeation properties have been studied for the purification of a hydrogen stream (50 vol.%) containing carbon monoxide (1.25 vol.%). For this purpose, a Wicke–Kallenbach cell has been used to perform the separation experiments. Single gas permeation properties and bicomponent mixtures were carried out at three different temperatures (298 K, 398 K and 423 K). Our results indicate that even the K-LTA form would be suitable for the purification of H 2 at room temperature. The Rb- and Cs-forms exhibit the best performance, in which CO permeation is blocked at all temperatures studied. As a result, a high purity H 2 stream may be obtained by employing the Rb- and Cs-membranes derived from Na-LTA/carbon membranes.

Dye binary mixture formulation by means of derivative ratio spectra of the Kubelka-Munk function

In this study, a new method is introduced for the determination of dye concentration in fabrics dyed with bicomponent dye mixtures. The reflectance spectra of the samples dyed with different binary mixtures of dyes were recorded between 400 and 700 nm. The obtained spectra were divided by a standard spectrum of each of the components in the mixtures and the derivative spectra were calculated. The amounts of dyes were determined by measurements in suitably selected wavelengths in the acquired derivative ratio spectra. The obtained results indicate that the developed derivative ratio spectra method is more accurate than the normal Kubelka–Munk method. The proposed derivative method is simple, accurate, and suitable for quantitative analysis of samples dyed with binary mixed shades. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010

Dielectric and DSC Studies of the Bicomponent Systems with Induced Antiferroelectric Phase Comprising Cyano Terminated Compounds

Phase transitions in pure compounds with cyanoacetyloxyalkoxy groups in terminal chain (2) and second compound comprising alkanoyloxyalkoxy groups (1) and their bicomponent mixture have been studied by optical microscopy, differential scanning calorimetry (DSC) and dielectric spectroscopy. The temperatures, enthalpies of phase transitions and Cp values as a function of temperature were determined for such system by DSC method (Differential Scanning Calorimetry). Dielectric spectroscopy confirmed the presence of induced antiferroelectric phase in mixtures. The Goldstone-mode and the soft-mode relaxation process were observed for SmC* phase and also the low frequency PL and high frequency PH modes, which are typical for antiferroelectric phase.

Effect of starting powders on the sintering of nanostructured ZrO2 ceramics by colloidal processing

The effect of starting powders on the sintering of nanostructured tetragonal zirconia was evaluated. Suspensions were prepared with a concentration of 10 vol.% by mixing a bicomponent mixture of commercial powders (97 mol.% monoclinic zirconia with 3 mol.% yttria) and by dispersing commercially available tetragonal zirconia (3YTZ, Tosoh). The preparation of the slurry by bead-milling was optimized. Colloidal processing using 50 μm zirconia beads at 4000 rpm generated a fully deagglomerated suspension leading to the formation of high-density consolidated compacts (62% of the theoretical density (TD) for the bicomponent suspension). Optimum colloidal processing of the bicomponent suspension followed by the sintering of yttria and zirconia allowed us to obtain nanostructured tetragonal zirconia. Three different sintering techniques were investigated: normal sintering, two-step sintering and spark plasma sintering. The inhibition of grain growth in the bicomponent mixed powders in comparison with 3YTZ was demonstrated. The inhibition of the grain growth may have been caused by inter-diffusion of cations during the sintering.

Application of Zero-Crossing Technique in Derivatives of the Kubelka—Munk Function to the Quantitative Analysis of Bicomponent Mixtures of Dyes

In this study a new derivative method is introduced for the computation of color recipe in bicomponent mixtures of textile dyes. The reflectance spectra of the samples dyed with different binary mixtures of dyes were recorded between 400 and 700 nm. The derivative amplitudes of the Kubelka—Munk function at appropriate zero-crossing wavelengths were selected for the determination of dyes in the mixtures. The obtained results indicate that the developed zero-crossing-point derivative method is more accurate than the normal Kubelka—Munk method. The proposed derivative method is simple, accurate, and suitable for quantitative analysis of samples dyed with binary mixed shades.

Switching and characteristic dielectric parameters of a room temperature antiferroelectric liquid crystal mixture

The switching and dielectric properties of a room temperature bicomponent antiferroelectric liquid crystal mixture have been investigated as a function of temperature and frequency. Thermodynamic, optical texture, and dielectric studies carried out on the mixture show the phase sequence of Cr←(12.0 °C)→SmIA∗←(29.1 °C)→SmCA∗←(91.5 °C)→SmC∗←(92.9 °C)→SmA∗←(106.7 °C)→Iso. Spontaneous polarization (Ps), switching time (ts), and torsional bulk viscosity (γϕ) have been determined by using polarization reversal method. Dielectric spectroscopy of the mixture in the frequency range of 0.1 Hz–10 MHz reveals, eight different modes of relaxation in the paraelectric SmA∗, ferroelectric SmC∗, antiferroelectric SmCA∗ and SmIA∗ phases. Origins of these modes have been identified with the help of frequency, temperature, and bias electric field dependence of various dielectric parameters.

Determination of bicomponent dye solutions by means of zero‐crossing‐point derivative spectrophotometry

AbstractIn this study, a new spectrophotometric method was developed for the determination of some textile dyes with different types of overlapping spectra. The binary mixtures of five dyes with yellow, scarlet, red, blue, and navy blue colors were analyzed by zero‐crossing‐point first‐derivative spectrophotometry. The absorption spectra of the mixtures prepared in different ratios were recorded between 400 and 700 nm. First derivative amplitudes at appropriate zero‐crossing wavelengths were selected for the determination of dyes in the mixtures. The proposed method was successfully applied to the determination of dyes with overlapping spectra in their bicomponent mixtures. The proposed derivative method is simple, rapid, and suitable for quantitative analysis of bicomponent dye solutions. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 307–311, 2008.

Водородная связь и структура приповерхностных слоев в двухкомпонентных гетеросистемах на основе наночастиц диоксида титана

* Saratov State University E-mail: babkov@sgu.ru *Institute of Physics, NAS of Ukraine, Kiev E-mail: puchkov@iop.kiev.ua Regarding the IR spectra of the solid samples of titanium dioxide-benzophenone and titanium dioxide-4-amil-4’-cyanobiphenyl hetero-genic bicomponent mixtures measured at room temperature the presence of hydrogen bonds in the samples was revealed. The tita-nium dioxide compound was represented as nano crystalline particles embedded into corresponding sample. Using density functional the-ory method (B3LYP/6-31+G(d)) the modeling of the structures and vibrational spectra of the bezophenone, 4-amil-4’-cyanobiphenyl and water free molecules, followed by the modeling of the structures and spectra of the H-bond complexes which are formed in near surface layers of the titanium dioxide nano crystalline particles due to water, which is adsorbed on their surfaces had carried out. On the basis of analysis of the bands spectroscopic parameters (the location, inten-sity and shape) in IR spectra (measured and simulated) corre-sponded to hydroxyl, carbonyl and cyano group bonds stretches, the theoretical ground of the titanium dioxide nano crystalline particles near surface layers forming in heterogenic bicomponent systems was given. It is found that the basic role in this mechanism plays the hy-drogen bond. Водородная связь и структура приповерхностных слоев в двухкомпонентных гетеросистемах на основе наночастиц диоксида титана Л

The Induction of Antiferroelectric Phase in the Bicomponent System Comprising Cyano Compound

The phase diagrams of binary mixtures composed of two chiral three ring esters are presented. The antiferroelectric SmC* A phase was induced in bicomponent mixtures comprising esters—one with alkanoyloxyalkoxy terminal chain and another one with cyanoacetyloxyalkoxy group. Influence of the length of terminal alkanoyloxy unit in the chain on the induction of the antiferroelectric phase is presented. For longer chain homologues the induction of SmC* A is stronger.

Helical Pitch in Bicomponent Mixtures with Induced Antiferroelectric Phase

ABSTRACT The induced antiferroelectric phase in bicomponent mixtures of fluorinated compound C6F13C2H4OPhPhCOOPhCOOC*H(CH3)C6H13 and a member of homologous series of CnH2n+1COO(CH2)3OPhCOOPhPhCOOC*H(CH3)C6H13 (n = 1-7) are observed. In those systems also SmC* α phase was evidenced. The helical pitch was measured and it was found that helical pitch increases with the increase of concentration of fluorinated component in mixture. The pitch of SmC*A phase is longer than for SmC* phase. Additionally the pitch in induced SmC*A phase does not depend on temperature, while in single compounds with SmC*A phase strongly increases.

Phase diagrams and dielectric studies of binary mixtures exhibiting intermediate nematic and induced smectic phases

Investigations on the phase diagrams of two bi-component mixtures of liquid crystals are presented. Whereas in one of the bi-component systems, smectic A (SmA) phase is seen to be induced, in the other case the so-called nematic “island” has been observed. The dielectric properties of magnetically oriented sample forming nematic phase and induced smectic phase in one of the mixtures, and a nematic “island” and SmA phase in the other mixture, were measured in the frequency range from 1 Hz to 10 MHz at different temperatures. The transition temperatures obtained from the polarizing microscope and differential scanning calorimeter measurements agree well with the dielectric relaxation data.

Palladium and platinum recovery from bicomponent mixtures using chitosan derivatives

Chitosan has been used as a base material for the preparation of platinum and palladium sorbents. Chitosan derivatives were obtained by glutaraldehyde cross-linking (GA), by poly(ethyleneimine) grafting (PEI), and by thiourea grafting (TDC). These sorbents were tested for the recovery of platinum group metals (PGMs) in batch systems and column systems from bicomponent mixtures at the optimum pH (ca. pH 2). Sorption isotherms were determined in batch systems, considering the impact of the excess of one metal on the sorption of the second. The sorbents have a marked preference for palladium over platinum. In most cases, the total sorption capacity (taking into account both Pd and Pt sorption) was comparable to that of each metal individually, indicating that the metals compete for the same sorption sites, regardless of the type of sorbent. In fixed-bed systems, similar effects were observed, with typical profiles driven by the displacement of platinum by palladium, attributed to the greater affinity of the sorbents for palladium. The sorbents (especially GA and TDC) have a greater selectivity for Pd than for Pt, compared to PEI, which has greater sorption capacities. Metal desorption was tested using several eluants, none of which allowed the complete removal of the metals from loaded sorbent, nor the selective desorption of either. A complete separation of the metals was not obtained, but by combination of sorption and desorption conditions, a concentration of Pd of 10- to 20-fold was achieved.

Effervescent atomization under sub-sonic and choked conditions—a theoretical approach

Spray formation of a bi-component mixture under sub- and choked-flow conditions has been studied. Special attention has been drawn to the processes inside the atomizer, i.e., the expansion chamber and two orifices. The relevant processes, which include the pressure drop at the inlet orifice, nuclei formation, bubble growth inside the expansion chamber, pressure drop at the discharge orifice, the velocity slip between the bubbles and the liquid bulk, and the flow regime (sub- and choked-flow) at the discharge orifice, have been analyzed by using a one-dimensional model approach. Three different operating regions have been identified. In the 1st, when the inlet to discharge orifices' diameter ratio is small, subsonic flow is anticipated, and no noticeable slip between the bubbles and the bulk liquid is expected. As the orifices' diameter ratio increases, the slip becomes more and more significant (2nd region). When the pressure at the expansion chamber exceeds the critical pressure, the flow chokes, and the slip maximizes. Further increase results in maximum slip (3rd region). The two main roles of the expansion chamber were described: (a) to provide the required time for the bubbles to grow till one bubble touches the other, and (b) to provide the discharge orifice with a well-mixed mixture to allow dominant flashing enhanced by shear stress disintegration. Optimized operation conditions for best atomization, optimized expansion chamber volume, and optimized orifices' diameter ratio are proposed in terms of the thermodynamic properties of the mixture.

Transport with a Very Low Density Contrast in Hele–Shaw Cell and Porous Medium: Evolution of the Mixing Zone

The optimal concentration of a blue dye solution with 'tracer' properties, enabling a pollutant to be marked was determined by the use of numerical, theoretical and experimental approaches. Experimental investigations were performed on a transparent Hele–Shaw cell and the concentration distribution was analyzed using an optical technique based on dye light absorption properties. The injected optimal concentration was established thanks to a theoretical and experimental study carried out on the output signal dynamics. Using the same experimental conditions, numerical simulations were performed. The very good agreement between the data (experimental and numerical) clarified that: (i) the choice of the blue dye optimal concentration was valid and (ii) the concentration-dependent density should not be neglected in flow and transport equations even if it concerns a so-called 'tracer'. Following this remark, a theoretical aspect was developed in order to determine the analogous conditions between a Hele–Shaw cell and a porous medium for the variable density transport phenomenon. The structure of the concentration-dependent dispersion tensor used in the numerical code was obtained by homogenizing the Stokes flow of a bi-component mixture. The numerical results show that, as long as the tracer density does not exceed a certain value, it is not necessary to take into account a density contrast in terms of the dispersion tensor. The classical form of the Taylor dispersion tensor can be used successfully.

Carbon dioxide/methane gas sensor based on the permselectivity of polymeric membranes for biogas monitoring

Membrane based-sensors have been used for determining the composition of bi-component mixtures in the 0–100% range, such as oxygen/nitrogen, carbon dioxide/helium, carbon dioxide/methane, hydrogen/nitrogen, and hydrogen/methane. These sensors are suited for the low cost and low/medium precision market.The present study describes a carbon dioxide/methane sensor suitable for biogas composition monitoring. The membrane used is poly(dimethylsiloxane) (PDMS) hollow fiber. The calibration curves were obtained at three different temperatures. The results clearly show that the permeate pressure of the sensor is related to the gas mixture composition at a given temperature. The sensor enables quantitative carbon dioxide analysis in binary mixtures of carbon dioxide/methane with fast, continuous, reproducible, and long-term stable response.