Effect of pressure on oxygen enrichment of liquid crystalline cellulose ether membranes at elevated temperature

Cholesteric liquid crystalline triheptyl cellulose (THC)/ethyl cellulose binary blend membranes were prepared and the effect of pressure on their oxygen enrichment at elevated temperature was investigated using a constant pressure-variable volume method. The oxygen enrichment increased with the increase of transmembrane pressure difference or with slight increase of the THC content in the blend membranes. The oxygen concentration through the membranes increased linearly with decreasing pressure ratio. Air was directly separated through a 17 m-thick THC/EC(1.5/98.5) membrane to prepare an oxygen-enriched air containing 39.5% oxygen at the flux of 6.99×10^–4 cm³ (STP)/s.cm² at the pressure difference of 0.43 MPa and 85 °C.     

A data base for polymer chromatography: Temperature dependence of interaction parameters in liquid adsorption chromatography

The temperature dependence of retention behaviour of polyethylene glycol (PEG) and its mono‐ and dimethyl ethers was studied on various RP columns in different mobile phases. The accessible volumes and the interaction parameters were determined from slope and intercept in a plot of the elution volumes of the oligomers of a polymer homologous series as a function of the difference of the elution volumes of consecutive oligomers. A quite different dependence of the interaction parameters was observed in the different mobile phases. While in methanol–water the interaction parameter decreases with increasing temperature, the opposite effect is observed in acetonitrile (ACN)–water. In acetone–water, the temperature dependence is almost negligible.     

Synthesis and characterization of liquid crystalline unsymmetrically substituted phthalocyanines

The synthesis of unsymmetrically substituted phthalocyanines bearing two p-tolyl-sulfonyl (tosyl)amido and six alkylthio moieties was achieved by cyclotetramerisation of two different phthalonitrile derivatives, namely 1,2-di(alkylthio)-4,5-dicyanobenzene and 4,5-dicyano-N,N′-ditosyl-o-phenylenediamine in the presence of an anhydrous metal salt and strong base. The new compounds were characterized by elemental analyses, UV/Vis, IR, NMR and mass spectra. The mesogenic properties of these new materials were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy. The mesogenic properties of these compounds were compared to that of their symmetric analogous, octaalkythia substituted phthalocyanine derivatives.     

Temperature dependence of methanol and ethanol vapor sorption in polyhedral oligomeric silsesquioxane (POSS) containing methacrylate membranes

This study aimed to determine the solubility and temperature dependence of methanol and ethanol vapor caused by the difference in the substituents of polyhedral oligomeric silsesquioxane (POSS)-containing polymethacrylate membranes and the spacer length between the backbone and POSS backbone. Vapor sorption of methanol and ethanol was measured at 25°C, 35°C, and 45°C for three kinds of POSS-containing polymer membranes, namely, poly(methacryl isobutyl POSS), poly(methacrylate isobutyl POSS), and poly(methacryl phenyl POSS). The primary structures of the three POSS-containing polymer chains were columnar. The solubility of alcohol vapor on the POSS-containing polymer membranes followed the mechanism of solid adsorption and not the general dissolution diffusion. The sorption amount at all three temperatures was related to the surface area of the cylindrical primary structure and the solid adsorption property of the alcohol molecule of the POSS substituent. The sorption amount increased because of the large surface area and adsorption property of alcohol molecules. Although a typical glassy polymer shows exothermic mixing and a rubbery polymer displays endothermic mixing, the sample with the POSS substituent of isobutyl group exhibited an unusual behavior of endothermic mixing despite being a glassy polymer.     

Kinetic analysis of coupled transport of thiocyanate ions through liquid membranes at different temperatures

Non-steady-state kinetics of coupled transport of thiocyanate ions through liquid membrane (trichloromethane), containing hexadecyl trimethyl ammonium chloride as a carrier, was examined at different temperatures. The kinetics of thiocyanate transport could be analyzed in the formalism of two, consecutive, irreversible first order reactions. The influence of temperature on the kinetic parameters (k_1d, k_2m, R_m^max, t_max, J_d^max, J_a^max) have been also investigated. The membrane entrance rate, k_1d, and the membrane exit rates, k_2m and k_2a, increase with temperature. For maximum membrane entrance and exit fluxes, J_d^max and J_a^max, the activation energies were found from the slopes of the two linear relationships: 7:75 and 8.30 kcal/mol, respectively. The values of the found activation energy indicate that the process is controlled by species difussion.     

Polarization and viscosity measurements of ferroelectric liquid crystalline monomer polymer mixtures

Measurements of spontaneous polarization, tilt angle and response time on mixtures of a ferroelectric side chain polyacrylate with a low molecular mass liquid crystal of a very similar structure are reported. From the obtained values the rotational viscosity for the ferroelectric switching process is calculated. All mixtures exhibit an Arrhenius-like temperature dependence of the rotational viscosity, the values for the polymer being three orders of magnitude higher than for the low molecular mass compound.     

Applicability of a liquid membrane in enrichment and determination of nickel traces from natural waters

In this work, a bulk liquid membrane method has been applied for Ni enrichment and separation from natural waters. The carrier-mediated transport was accomplished by pyridine-2-acetaldehyde benzoylhydrazone dissolved in toluene as a complexing agent. The preconcentration was achieved through pH control of source and receiving solutions via a counterflow of protons. The main variables were optimized by using a modified simplex technique. High transport efficiencies (101.2 ± 1.8–99.7 ± 4.2%) were provided by the carrier for nickel ions in a receiving phase of 0.31 mol L⁻¹ nitric acid after 9–13 h depending on sample salinity. The precision of the method was 2.05% (without a saline matrix) and 4.04% (with 40 g L⁻¹ NaCl) at the 95% confidence level and the detection limit of the blank was 0.015 μg L⁻¹ Ni for detection by atomic absorption spectroscopy. The applicability of the method was tested on certified reference and real water samples with successful results, even for saline samples. The relative errors were −0.60% for certified reference materials and ranged from −0.39 to 2.90% and from 0.3 to 11.05% for real samples, obtained by comparison of inductively coupled plasma mass spectrometry and adsorptive cathodic stripping voltammetry measurements, respectively.     

Reinvestigation of liquid crystalline property of dimesogenic compound consisting of cholesterol and cyanobiphenyl

The dimesogenic compound consisting of cholesterol and cyanobiphenyl mesogens interlinked byω-oxyalkanoyl spacer was synthesized.The mesomorphic properties were investigated by differential scanning calorimetry(DSC),polarizing optical microscopy(POM),and X-ray diffraction(XRD).The experimental results indicated that this compound exhibited mesophase over a much wider temperature range and a new mesophase blue phase(BP).Focal conic domains(FCDs) and droplets texture to the smectic A phase(SA),oily streaks...     

Synthesis and characterization of liquid crystalline polyacrylates and non-liquid crystalline polypyrroles from bifunctional monomers

Two kinds of polymerizations of liquid-crystalline N-{{W-{4-[4-(11-acryloyloxy)undecanoxybenzoyl]biphenyleneoxy}alkyl}}pyrrole gave a side-chain liquid-crystalline polyacrylate containing pyrrole group and a non-liquid crystalline polypyrrole containing acrylate group. Liquid crystallinity was determined by DSC and optical polarizing microscope measurements. The monomers having hexyl or decyl group as the alkyl group exhibited an undefined smectic, smectic B, and smectic A phases on the heating stage. The radically polymerized polyacrylate derivatives containing the pyrrole group showed smectic A, smectic C, and undefined smectic phases on the cooling stage. On the other hand, soluble N-substituted polypyrrole derivatives containing the terminal acrylate group which were prepared by chemical oxidative polymerization by ferric chloride catalyst did not show liquid crystallinity. Structure analysis of the polypyrroles performed by ¹H and ¹³C-NMR and FT-IR spectroscopies demonstrated that the polymerization occurred at the pyrrole ring. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3877–3887, 1999     

Comparative study of liquid uptake and permeation characteristics of sulfonated cation-exchange membranes in water and methanol

Liquid permeation and uptake measurements of pure water and methanol were carried out using three commercial cation-exchange membranes: Nafion-117 (perfluorinated polyethylene with pendant ether-linked side chains terminated with sulfonated groups), MK-40 (microparticles of polystyrene–divinylbenzene with sulfonic groups randomly dispersed in a polyethylene matrix) and CR61-CZL-412 (crosslinked sulfonated copolymer of styrene–divinylbenzene). Methanol uptake by the Nafion-117 membrane was higher than that of water, in contrast, for MK-40 and CR61-CZL-412 membranes the opposite behavior is observed. Differences in the water and methanol liquid uptakes by the membranes were discussed in terms of the chemical interaction between the liquids and the polymers, and also on the size of the liquid molecules. On the other hand, the methanol permeation flow values through the membranes were higher than those of water for all the studied membranes.     

Transport and separation of carboxylic acids through bulk liquid membranes containing tributylamine

In this study, transport and separation of carboxylic acids (formic, acetic, propionic, and butyric acids) from their aqueous solutions through bulk liquid membrane (BLM) containing tributylamine (TBA) and the parameters affecting the transport were investigated. The influence of the parameters on the separation process such as the stirring of membrane phase, the stripping phase type and concentration, the feed phase type, and the feed:membrane:stripping phase ratio (F/M/S phase ratio) were examined. In the experiments, 10% (w/w) acid solutions (formic, acetic, propionic, and butyric acids) were used as the feed phase, different concentrations of NaOH solutions within the range of 0–2?N were used as the stripping phase, and 0.5?mol/lt TBA, dissolved in oleyl alcohol, was used as the membrane phase. It was determined that the stirring of the membrane phase increases the transport of acids. In the case of 2 N NaOH solution in the stripping phase and F/M/S phase ratio 1:2:1 gave the best recovery (96.75%) for butyric acid. It was observed that BLM was an effective technique for the separation of carboxylic acids from aqueous solutions.     

Synthesis of novel and regioselectively mesogen-incorporated thermotropic liquid crystals from cellulose derivatives

Regioselectively mesogen-incorporated cellulose derivatives, in which the hydroxy group at C-6 is displaced by a bulky and rigid mesogenic group such as {4-[(4-methoxyphenoxy)carbonyl]phenoxy}acetate or [(4′-cyanobiphenyl-4-yl)oxy]acetate, and the C-2 and C-3 groups are displaced by octanoyl or lauroyl groups, were synthesized. Thermogravimetric and differential scanning calorimetric analyses of the final products, along with polarized optical microscopic observations, revealed that the obtained cellulose derivatives have a thermotropic liquid-crystalline nature and transition from the mesomorphic to the isotropic phase over a wide range of temperatures. These derivatives could be considered to be main-chain liquid-crystalline cellulosic polymers.     

Temperature dependence of the electronic factor in the nonadiabatic electron transfer at metal and semiconductor electrodes

The temperature dependence of the electronic contribution to the nonadiabatic electron transfer rate constant (k_ET) at metal electrodes is discussed. It is found in these calculations that this contribution is proportional to the absolute temperature T. A simple interpretation is given. We also consider the nonadiabatic rate constant for electron transfer at a semiconductor electrode. Under conditions for the maximum rate constant, the electronic contribution is also estimated to be proportional to T, but for different reasons than in the case of metals (Boltzmann statistics and transfer at the conduction band edge for the semiconductor versus Fermi–Dirac statistics and transfer at the Fermi level, which is far from the band edge, of the metal).     

Preparation and properties of surface modified ceramic membranes. Part II. Gas and liquid permeabilities of 5 nm alumina membranes modified by a monolayer of bound polydimethylsiloxane (PDMS) silicone oil

A new way to prepare hydrophobic membranes is reported. Polydimethylsiloxane oil (and any other silicone oil molecules) was grafted onto a porous alumina membrane (or any hydroxylated ceramic or glass) by heating, to 180°C, producing a covalently grafted monolayer of silicone oil, chemically and thermally stable, unaffected by organic solvents but susceptible to alkali attack (as is the silicone oil itself). The membrane is totally impermeable to pure water, and organic solvents may be extracted from water mixtures by pervaporation. Very high permeation fluxes were obtained, suggesting possible use of these silicone/ceramic membranes in extraction of volatile organic compounds (VOCs). This simple modification can be applied to macroporous membranes increasing hydrophobicity without pore blocking.     

The dependence of the properties of liquid crystals on the film thickness and surface quality of capillary columns

Summary Glass capillary columns were prepared from non-deactivated and deactivated glass and coated with (2-methyl-4-[trans-4-n-propyl-cyclohexylcarbonyloxy]-benzoic acid-[4-n-heptyloxy-phenylester]) as the liqud phase, in different film thicknesses. The columns were tested using substances of different structures and polarities. It was verified that the capacity factors, retention indices and selectivity significantly depend on the thickness of the liquid crystalline stationary phase film and the quality of the tube, particularly in the case of columns with thin films. Trasition temperatures (melting and clearing point) of the liquid crystal are also dependent on these two factors.Dedicated to Professor J. F. K. Huber on the occasion of the his 60th birthday.     

The first normal stress difference and viscosity in shear of liquid crystalline solutions of hydroxypropylcellulose: new experimental data and theory

The constitutive equations for liquid crystalline polymers recently proposed by one of us [1] are applied here to interpret the behaviour of the shear viscosity η and the first normal stress difference N₁() measured for liquid crystalline (LC) solutions of hydroxypropylcellulose in acetic acid. N₁( ) is observed to change from positive to negative and again to positive, as the shear rate increases, at lower concentrations, in the LC phase. The -values at which N₁ changes sign depend on the molecular mass (degree of polymerization) and on the concentration. η shows a small Newtonian plateau at low shear rates and a strong shear-thinning at higher values of . The rate of decrease of η in this region shows an “hesitation” similar to one previously observed in LC solutions of poly-γ-benzyl-L-glutamate PBLG. All these observations can be rationalized within the frame-work of Martins' theory. The expressions for N₁() and η derived from this theory fit very well (quantitatively) to the experimental data and some fundamental viscoelastic parameters of the system under study are thereby obtained for the first time.     

Polymerization and viscoelastic behavior of networks from a dual‐curing,liquid crystalline monomer

The network formation and viscoelastic behavior of a liquid crystalline monomer, whose structure includes both acrylate and acetylene reactive groups, have been studied. By combining both photo and thermal polymerization, the networks can be formed in two separate steps, with the initial photopolymerization dominated by acrylate crosslinking and subsequent thermal polymerization dominated by acetylene crosslinking. In addition, the monomer exhibits a liquid crystalline phase. Photopolymerization while in the liquid crystal phase locks in the molecular ordering. Dynamic mechanical analysis shows that networks formed from the liquid crystalline phase have lower crosslink densities and narrower distributions of molecular weights between crosslinks when compared to networks formed from the isotropic phase (and at higher polymerization temperatures). After thermal postcure at 250°C, the networks formed from the isotropic monomer have a 23% higher dynamic mechanical storage modulus (in the glassy state) than the networks formed from the liquid crystalline monomer. The thermally postcured networks have unusually high glass‐transition temperatures, which exceed 300°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1183–1190, 1999