Ionic Liquids in Polyethylene Glycol Aqueous Solutions: Salting-in and Salting-out Effects

Summary. Changes of the fluid phase behaviour of polyethylene glycol (PEG) aqueous solutions – viz. critical solution temperature shifts at atmospheric pressure – were produced by the addition of different ionic liquids, namely 1-ethyl-3-methylimidazolium ethyl sulfate and 1-alkyl-3-methylimidazolium chloride (alkyl = ethyl to decyl). The addition of ionic liquids with long alkyl chains improves the solubility of PEG in water (salting-in effect), whereas the impact of short-chain ionic liquids is usually the contrary (salting-out effect). The results are interpreted taking into account the kosmotropic (water-structuring) or chaotropic (water-structure-breaking) nature of ionic liquids, as compared to other inorganic salts.     

Recent progress in the determination of solid surface tensions from contact angles

Advancing contact angles of different liquids measured on the same solid surface fall very close to a smooth curve when plotted as a function of liquid surface tension, i.e., gamma(lv)costheta versus gamma(lv). Changing the solid surface, and hence gamma(sv), shifts the curve in a regular manner. These patterns suggest that gamma(lv)costheta depends only on gamma(lv) and gamma(sv). Thus, an "equation of state for the interfacial tensions" was developed to facilitate the determination of solid surface tensions from contact angles in conjunction with Young's equation. However, a close examination of the smooth curves showed that contact angles typically show a scatter of 1-3 degrees around the curves. The existence of the deviations introduces an element of uncertainty in the determination of solid surface tensions. Establishing that (i) contact angles are exclusively a material property of the coating polymer and do not depend on experimental procedures and that (ii) contact angle measurements with a sophisticated methodology, axisymmetric drop shape analysis (ADSA), are highly reproducible guarantees that the deviations are not experimental errors and must have physical causes. The contact angles of a large number of liquids on the films of four different fluoropolymers were studied to identify the causes of the deviations. Specific molecular interactions at solid-vapor and/or solid-liquid interfaces account for the minor contact angle deviations. Such interactions take place in different ways. Adsorption of vapor of the test liquid onto the solid surface is apparently the only process that influences the solid-vapor interfacial tension (gamma(sv)). The molecular interactions taking place at the solid-liquid interface are more diverse and complicated. Parallel alignment of liquid molecules at the solid surface, reorganization of liquid molecules at the solid-liquid interface, change in the configuration of polymer chains due to contact with certain probe liquids, and intermolecular interactions between solid and liquid molecules cause the solid-liquid interfacial (gamma(sl)) tension to be different from that predicted by the equation of state, i.e., gamma(sl) is not a precise function of gamma(lv) and gamma(sv). In other words, the experimental contact angles deviate from the "ideal" contact angle pattern. Specific criteria are proposed to identify probe liquids which eliminate specific molecular interactions. Octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS) are shown to meet those criteria, and therefore are the most suitable liquids to characterize surface tensions of low energy fluoropolymer films with an accuracy of +/-0.2 mJ/m2.     

离子液体催化苯与环己烯的Friedel-Crafts烷基化反应

室温离子液体是由特定的阳离子和阴离子构成,具有独特的性质和功能。将路易斯酸型离子液体应用于苯和环己烯的烷基化反应,考察了苯与环己烯摩尔比、反应温度、反应时间对烷基化反应产物收率的影响。结果表明以制备的咪唑盐离子液体为催化剂,在反应温度80℃、反应时间1.0h、苯烯摩尔比8：1的条件下,所得环己基苯的产物收率最高,为86.75%。离子液体可重复使用,活性基本没有降低。     

Wetting in the nanoscale: a continuum mechanics approach

A continuum mechanics model has been developed to study the equilibrium shape of nanometric droplets on a planar solid substrate and how, in this scale, the contact angle depends on the drop size. The drop is modeled as a liquid volume enclosed in an inextensible membrane, subject to an isotropic tension (the surface tension) and to a field of surface forces including, in the proximity of the solid, the liquid-to-solid interactions, envisaged as a generic potential force per unit surface directed normally to the solid surface (i.e. vertically). The only conditions required to solve the problem are those of mechanical and thermodynamic equilibrium. The predictions of the model are discussed in comparison with data on nanodrops retrieved by a special AFM device for a number of different liquid–solid systems.     

Thermo- and Photocatalytic Activation of CO2 in Ionic Liquids Nanodomains

Ionic liquids (ILs) are considered to be potential material devices for CO₂ capturing and conversion to energy-adducts. They form a cage (confined-space) around the catalyst providing an ionic nano-container environment which serves as physical-chemical barrier that selectively controls the diffusion of reactants, intermediates, and products to the catalytic active sites via their hydrophobicity and contact ion pairs. Hence, the electronic properties of the catalysts in ILs can be tuned by the proper choice of the IL-cations and anions that strongly influence the residence time/diffusion of the reactants, intermediates, and products in the nano-environment. On the other hand, ILs provide driving force towards photocatalytic redox process to increase the CO₂ photoreduction. By combining ILs with the semiconductor, unique solid semiconductor-liquid commodities are generated that can lower the CO₂ activation energy barrier by modulating the electronic properties of the semiconductor surface. This mini-review provides a brief overview of the recent advances in IL assisted thermal conversion of CO₂ to hydrocarbons, formic acid, methanol, dimethyl carbonate, and cyclic carbonates as well as its photo-conversion to solar fuels.     

Solvent effectiveness factor: A new correlation to study the influence of solvent,temperature, and stirring rate on synthesis yield of Ionic Liquids

The main objective of this study is to investigate the effect of solvent, temperature, and stirring on synthesis yield of Ionic Liquids (ILs). A representative Ionic Liquid [BMIM][BF₄] is prepared using seven different solvents and their influence on percentage yield is explained using a new correlation; solvent effectiveness factor (SEF). The SEF of solvent is governed by nature of solvent, operating temperature and stirring rate. Acetone has the highest SEF 1.275 and affords maximum IL yield 88.11% while toluene has the least SEF 0.674 and produces minimum IL 63.21%. When synthesis temperature is increased from 50 to 80 °C, synthesis yield is substantially increased from 76.7 to 93.08% because rise in temperature increases the SEF from 1.234 to 1.333, mainly due to the decrease in solvent viscosity. Similarly, when stirring rate is increased from 80 to 200 RPM, IL yield slightly increased from 87.37 to 91.35% due to addition of mechanical energy in the reaction mixture which in turn reduced solvent viscosity and increased SEF from 1.278 to 1.297.     

New regularities and an equation of state for liquids

Three regularities have been introduced for liquids (T < T_C and ρ > ρ_C) based on average potential energy. The experimental data have been used to show the validity of the regularities. First, there exists near-linearity relation between and ρ for all isotherms of a liquid, where P_i and ρ are internal pressure and density, respectively. Second, changes linearly with ρ for each isotherm of any liquid, where Z and V_m are compressibility factor and molar volume, respectively. Third, a new regularity using the definition of bulk modulus and our new equation of state between reduced bulk modulus and density has been introduced, that is versus ρ must be linear for all isotherms of a liquid where B_r is the reduced bulk modulus.

A new equation of state has been also derived. The density of some liquids in the extensive ranges of temperature and pressure has been calculated using the new equation of state. The densities calculated from this equation agree with experiment to better than 0.3%. The new equation of state can predict internal pressure, thermal expansion coefficient, and isothermal compressibility of liquids within experimental error.     

Infrared spectra of superconducting La2−xSrxCuO4 and YBa2Cu3O7−δ

Abstract

Abstract Infrared spectra of La_2?xSr_xCuO₄ and YBa₂Cu₃O_7?δ are discussed, specially with respect to the disappearance of the high-frequency (～650 cm) band of the superconducting compositions at 300K. Some of the bands persist at 300K eventhough the materials are fairly conducting. YBa₂Cu₃O_7?δ does not show evidence in the far IR spectrum for the presence of an optical gap.     

Structural Quantum Effects In Hydrogeneous Liquids And Glasses: Part I Review Of Early Methods And Experiments

The atomic or molecular structure of simple liquids may be studied experimentally through radiation scattering experiments. Normally, these experiments involve either beams of E-M radiation or of thermal neutrons, and frequently the samples included both hydrogenated and deuterated liquids. In order to interpret such data it has been assumed (frequently) that the liquid structure was unchanged when the H/D composition was changed. Similar comments apply to hydrogeneous glasses. As the quality of the data and of model calculations improved with passing years, limits to these assumptions were discovered. Part I of this review will cover both the background material and the research which led to an understanding of this field, and also determined the magnitude and shape of the observable effects. Subsequent research from the 90s onwards will be reviewed in Part II.