Interface influenced phase transitions of alkylcyanobiphenyl liquid crystals A calorimetric study

Abstract

Using an AC-calorimetry technique, we report measurements of the heat capacity and the phase shift between the applied heating power and the resulting thermal oscillations on the thermotropic liquid crystal series of alkylcyanobiphenyl (nCB) above the tricritical point. Specifically, we studied the first order phase transition smectic A to isotropic as a function of substrate, under atmospheric pressure. Different combinations of sapphire, Kapton type 200H polyimide film and air, are used to vary systematically the interfaces encountered by a liquid crystal. The calorimeter uses a sapphire disk, 10 mm in diameter and 0·13 mm thick, above which the samples are placed. A second sapphire disk, or a disk-shaped Kapton film, are used to sandwich the liquid crystal. Air interface samples are droplets allowed to spread naturally on the chosen substrate. The chosen geometry is such that interface effects appear to be maximized. Striking features found in the heat capacity and the phase shift studies with 10CB and 12CB will be presented for the different interfaces.     

Isolation by Means of Preparative Reversed-Phase Liquid Chromatography of Epimeric Alcohols Formed Upon Reduction of Pregnenolone and Progesterone

Abstract

A method is described which permits complete separation on a preparatory scale of the 20R and 20S epimeric alcohols obtained from lithium aluminium hydride and sodium borohydride reduction of pregnenolone and progesterone, respectively. The retention behaviour and resolution obtained on chromatography of the epimers on C-18 bonded phase material and elution with different acetonitrile/water and methanol/water mobile phases were studied. The order of retention is in both cases in accordance with ¹H-NMR chemical shift data which indicate a stable conformation with a more exposed 20-OH group in the 20S (=20α) epimer. Deviations from the elution order expected for true reversed-phase retention mechanisms were found on elution with mobile phase systems of reduced water content.     

Poly(N-vinyl-2-pyrrolidone) and 1-Octyl-2-pyrrolidinone Modified Ionic Microemulsions

The influence of the nonionic polymer poly(N-vinyl-2-pyrrolidone) (PVP) in comparison to the surfactant 1-octyl-2-pyrrolidinone (OP) on the phase behavior of the system SDS/pentanol/xylene/water was studied. In both modified systems a strong increase in the water solubilization capacity was found, accompanied by a change in the spontaneous curvature toward zero. In the polymer-modified system an isotropic phase channel is formed with increasing polymer content that connects the L1 and the L2 phase. The lamellar liquid crystalline phase is destabilized in both cases. In the L1 phase the adsorption of PVP at the surface of the microemulsion droplets and the formation of a cluster-like structure is proven by several methods like ¹³C NMR T₁ relaxation time measurments, zeta potential measurements, and rheology. In the L2 phase a modification of the interface of the inverse droplets is detected by a shift in the percolation boundary (conductivity) and ¹³C NMR T₁ relaxation measurements. The formation of a cluster-like structure can be assumed on the basis of our rheological measurements.     

Acoustic Nonlinearity Parameter of Liquid Alkanes as a Function of Temperature,Chain Length and Isomerism

Abstract

The acoustic nonlinearity parameter B/A along with intermediate quantities such as the pressure derivative of sound speed and the phase shift were measured in 8 linear alkanes and a series of four isomers of hexane. The influences of temperature and chain length on these quantities were revealed. It was found that the phase shift parameter is more sensitive to molecular structure and temperature than B/A and that the pressure derivative of sound speed.     

Optimization of A Reverse Phase Ion-Pair Chromatographic Separation for Drugs of Forensic Interest Part I - Variables Effecting Capacity Factors

Abstract

A study is presented employing approximately 50 drugs of forensic interest to determine the effect of stationary phase, water-methanol ratio, alkyl length and concentration of counter-ion and basicity of the compound chromatographed on capacity factors utilizing a reverse phase ion-pair separation. Microbondapak-C18, Microbendapak-Alkyl Phenyl and Microbondapak-CN are the columns examined. The mobile phases used contain water, methanol, acetic acid and an alkylsulfonate salt. Horvath's solvophobic theory is a useful model for explaining many of the chromatographic trends.     

New Device for Adding Polar Modifiers to Carbon Dioxide Mobile Phase for Supercritical Fluid Chromatography

Abstract

Adding additional components to supercritical carbon dioxide in supercritical fluid chromatography can extend or significantly alter the fluid solvating properties. Polar samples which are difficult to be analyzed with pure supercritical CO₂ because of their high polarity can be separated by adding polar modifiers to supercritical CO₂. In this paper, a new mixing device using a teflon high capacity filter for adding polar modifiers to carbon dioxide mobile phase is introduced. This new mixing device could keep the amount of modifier in the mobile phase constant for a much longer time than a saturator column. The amount of water or methanol dissolved in supercritical CO₂ was measured by amperometric microsensor which is made of thin film of perfluorosulfonate ionomer(PFSI).     

The effect of chain length of bonded organic phases in reversed phase high performance liquid chromatography

Summary Bonded hydrocarbon phases have been prepared by the reaction of organotrichlorosilanes with silica (Lichrosorb Si-100, 10 m, Merck) using conditions for maximum coverage. Alkyl phases, CH₃ (CH₂)_n-With n=7, 10, 12, 14, 17 and 20 and arylakyl phases, Ph (CH₂)_n—with n=0,2,4,6 were investigated. In reverse phase chromatography using water/methanol phases a linear relationship was between the capacity ratios k and the amount of coverage, independent of chain length. The selectivity, however, depends on the chain length of the bonded phase and molecular structure of the solute, whereas for halogenated benzene derivatives the selectivity is constant, and changing the mobile phase composition shows only a minor effect. The selectivity of 4,4-dibromodiphenyl in relation to the benzene derivatives is strongly influenced by the chain length and solvent composition. The utilization of chemically bonded organic long chain phases with maximum coverage makes it possible to reduce the water content in the water/methanol phase increasing the efficiency and loading capacity. The extent of maximum coverage was slightly dependent on the chain length and showed only a 10% decrease from n-octyl-to heneicosyl phase. Treatment of the bonded organic phase with TMCS was not effective with long chain materials, but further reaction occurred with bonded phenyl phase, which could be shown by IR-analysis.     

Investigation of Miscibility of Linseed Oil Epoxy with Poly(vinyl alcohol)

Blending of two polymers in solution is a simple and cost effective technique to improve upon the physical and mechanical properties of the component polymers. Maximum synergism in the properties of the two polymers occurs when they are thermodynamically miscible. Poly(vinyl alcohol) (PVA) yields tough, flexible and water sensitive films. Linseed oil epoxy(LOE), a product from sustainable resource, used as a plasticizer and corrosion resistant coating, does not produce free standing film. A blend of PVA with LOE may yield films of good toughness and flexibility, and low water absorption if the two components are miscible with each other. Blends of PVA with LOE were prepared in weight ratios 80/20, 60/40, 40/60 and 20/80 through solution method by mixing in dimethyl sulphoxide. In the first instance, the miscibility the two components were investigated using the techniques of viscosity and ultrasonic measurements. The study revealed that the two components showed miscibility up to below 60 wt% PVA in the blend as at the composition LOE: PVA 40/60, phase inversion occurs. Above this composition, immiscibility is indicated; differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) delineates the above behavior in the solid phase.     

Degradation of organic compounds on TiO<Subscript>2</Subscript> photocatalysts prepared by a hydrothermal method in the presence of NH<Subscript>4</Subscript>F

TiO₂ photocatalysts were synthesized by a hydrothermal method from tetraisopropyl orthotitanate (TPOT) in the presence of NH₄F with different NH₄F/Ti molar ratios (0, 0.25, and 1). The formation of a well-crystallized anatase phase of TiO₂ and the suppression of phase transition to rutile were observed, even at high calcination temperature, owing to the effects of NH₄F. The TiO₂ synthesized hydrothermally with NH₄F exhibited absorption with a shift to the longer wavelengths of the visible-light region. The hydrothermally synthesized TiO₂ with a moderate amount of NH₄F exhibited high photocatalytic activity for the degradation of alcohol diluted in water under both UV-light and visible-light irradiations.     

Design of Binary Solvent Systems for Separation of Protected Oligo-Peptides in Silica Gel Liquid Chromatography

Abstract

In order to adjust the binary mobile phase for the separation of protected oligo-peptides, a systematic investigation of the retention behaviour on silica gel columns was carried out using seven peptide derivatives. Quantitative correlation between the capacity ratios of solvent systems using various concentrations of the stronger eluent was determined. The strengths and selectivities of fourteen binary systems were discussed on the basis of their retention indices. The design of equi-eluotropic binary systems containing these stronger components is presented.     

不同锌铝比水滑石的合成及其吸附脱除水中邻苯二甲酸性能

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射(XRD)、扫描电镜(SEM)、热重(TG)、氮气吸脱附及电感耦合等离子体质谱(ICP-MS)等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时(6),随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。     

不同锌铝比水滑石的合成及吸附脱除水中邻苯二甲酸性能的研究

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射（XRD）、扫描电镜（SEM）、热重（TG）、氮气吸脱附及电感耦合等离子体质谱（ICP-MS）等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时（>6）,随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。     

REACTION OF 5,5-DIPHENYL-2-THIOHYDANTOIN WITH 1,4-DIBROMOBUTANE. THE CRYSTAL AND MOLECULAR STRUCTURE OF 2,3,4,5-TETRAHYDRO-7,7-DIPHENYLIMIDAZO-[2,1-b]-THIAZEPINE-8(7H)-ONE

Abstract

The reaction of 5,5-diphenyl-2-thiohydantoin (1) (DPTH) or its potassium salt (DPTH-K) with 1,4-dibromobutane gave two isomeric bicyclic products: 2,3,4,5-tetrahydro-7,7-diphenylimidazo-[2,1-b]-thiazepine-8(7H)-one (6) and 2,3,4,5-tetrahydro-8,8-diphenylimidazo-[2,1-b]-thiazepine-7(8)-one (7) in different ratios depending on the reaction conditions: [DPTH-K, EtOH, N-ethylpiperdine; phase transfer catalytical conditions: DPTH-K, Et₃N, benzene/water or DPTH acetone/K₂CO₃]. Compound (6) crystallizes in the space group P2₁/c with a = 10.4624(2), b = 8.3643(1), c = 18.4371(3) Å β = 96.3(1)°. The 7-membered thiazepine ring in (6) adopts a disordered chain conformation. The discussion of some physico-chemical properties and some factors showing the influence on the yield and ratios of isomeric compounds [(2), (3)], [(4), (5)] and [(6), (7)], obtained in the alkylation of DTPH (1) with dibromoalkanes, has been carried out.     

Influence of Physicochemical Parameters of Some Ring-Substituted Phenol Derivatives on Their Retention on a Porous Graphitized Carbon Column

Abstract

The retention characteristics of 29 phenol derivatives were determined on a porous graphitized carbon column in unbuffered acetonitrile—water and methanol—water eluent mixtures at various organic phase concentrations. Each phenol derivative showed symmetric peaks in each eluent without buffers. Good linear correlations were found between the log k' value and the organic mobile phase concentration in the eluent. Principal component analysis indicated that methanol and acetonitrile expose different selectivities. Stepwise regression analysis proved that the retention of ring—substituted phenol derivatives is mainly governed by the sterical parameters, electron-withdrawing power and hydrogen donor capacity of substituents. According to the results of Free-Wilson analysis, the substituents with large steric parameters, strong electron-withdrawing power and hydrogen donor capacity have the highest impact on the retention. The lipophilicity of phenol derivatives did not affect significantly the retention, although the eluents were typical reversed-phase eluents.     

Preparation of KHSO4/SiO2 Nanocomposites and Their Physical Properties

A series of SiO₂/KHSO₄ nanocomposites with various SiO₂/salt ratios was prepared where the active compound was added before gelation. The sol was prepared by mixing of these hydrogen salts, TEOS (tetraethyl orthosilicate) and water. After gelation and heat treatment (heating slowly to 200–220°C under vacuum), the samples were characterized by X-ray diffraction, Differential Scanning Calorimetry (DSC), IR spectroscopy, Scanning Electron Microscopy (SEM), and High Resolution Transition Electron Microscopy (HR TEM). DSC measurements showed phase transition temperature shifts that depended on the SiO₂/salt ratio. The properties of the nanocomposite samples were compared with the bulk materials. The shift in the phase transitions to lower temperatures was attributed to the particle size effect.     

Determination of Tetracycline and Related Compounds by High-Performance Liquid Chromatography

Abstract

An isocratic high-performance liquid chromatography method for the determination of tetracycline and its related compounds is described. The method uses a reverse phase (C₁₈) column, a modified acetonitrile/water mobile phase, and banzoic acid as the internal standard. Elution of all compounds of interest is complete within seven minutes. Results are presented for thirteen commercial capsule formulations and are compared with results by microbiological assay and thin-layer chromatographic methods.     

Alkyl chain order in a lamellar lyotropic liquid crystal with varying surface charge density

Abstract

The alkyl chain order in the lamellar liquid-crystalline phase formed in the octylamine/octylammonium chloride/water system has been investigated by ²H N.M.R. at constant mole ratio water/amphiphile and varying charge of the lamellae. The results are correlated to the dimensions of the aggregate obtained from X-ray low angle diffraction measurements.     

First order transitions to a lyotropic biaxial nematic

Abstract

The phase diagram of the sodium dodecylsulphate/decanol/water system is studied by²H NMR spectroscopy in the range between the calamitic nematic (N⁺ _C) and discotic nematic (N^? _D) phases. In this narrow range a nematic biaxial phase (N_BX) is observed. The phase transitions between the nematic phases are all of first order. The shape of the surfactant aggregates in the nematic phases varies with composition and temperature.     

Polysiloxane dizwitterionomers. III. Water sorption

The interaction of water with the various polysiloxane dizwitterionomers and the model compound 4,7-diazaheptyl-4,7-di(3-propane-sulfonate) heptamethyltrisiloxane was studied. The model compound is soluble in water but the polymers swell inhomogeneously when soaked in water. The initial sorption kinetics of these zwitterionomers indicate similar mechanisms of water uptake which is independent of ion concentration (D = 4.7 × 10^?7 cm²/sec). The sorption isotherms reveal the high sorptive capacity of these ionomers. Furthermore, the linear relationship between the water uptake and the concentration of ions over a large relative humidity range (0.22 ≤ P/P₀ ≤ 0.93) allowed us to treat each phase separately. It has been found that most of the absorbed water molecules are immobilized in the ionic domains. Their concentration in this phase is nearly identical to the sorptive capacity of the model compound.