Surface tension of pure liquid lanthanide and early actinide metals

A systematic theoretical study of the surface tension of liquid rare earth metals and early actinides is performed. An equation, based on the theoretical considerations suggested by Eyring, enables one to calculate the surface tension of elementary substances in a wide temperature range from melting to boiling points. The results of temperature-dependent surface tension calculations of a pure liquid terbium (1629–1880?K) are fitted as γ?=?845?0.1 (T???T _m) (mJ?m²), where the surface tension decreases linearly with temperature. The surface tension was also calculated, at melting points, for all the liquid rare earth metals from La to Lu and for the first six metals of the actinide series from Ac to Pu. It is observed that the lanthanides may be divided into three groups in accordance with their electronic structure. Mostly, the calculated results agree well with available experimental data.     

Synthesis and physical properties of high birefringence phenylacetylene liquid crystals containing a cyclohexyl group

We have synthesized new phenylacetylene-based liquid crystals containing a cyclohexyl or cyclohexylethyl group and evaluated their physical properties in order to develop a range of materials having high value of birefringence. The cyclohexyl-containing compounds exhibited nematic behaviour near room temperature and moderate values of δn of around 0.3. The cyclohexylethyl-containing compounds had a very wide nematic range with a high T_NI and very high values of δn of over 0.4. They also exhibited low viscosities. The order parameter was not affected by introducing either a cyclohexyl or a cyclohexylethyl group and the values of δn based on calculated polarizabilities were obtained experimentally.     

Effects of polar group incorporation on crazing of glassy polymers: Styrene–acrylonitrile copolymer and a dicyano bisphenol polycarbonate

The degree of swelling and attendant reduction in the glass transition temperature have been determined for a 70% styrene–30% acrylonitrile copolymer in a large number of organic liquids. The critical strain ?_c for crazing or cracking has been determined also in air and in each agent. Limited crazing data have been obtained also on a dicyano bisphenol polycarbonate in which the CN groups take the place of the methyl groups in bisphenol A (BPA) polycarbonate. The two resins are compared with polystyrene and BPA polycarbonate, respectively, in terms of crazing resistance, swelling, and other properties. In both systems CN incorporation raises ?_c (air) and reduces susceptibility to liquids of low solubility parameter δ; T_g and shear yield stress are raised in the polycarbonate but not in the styrene system. The volume efficiency of CN in raising ?_c (air) is greater in the polycarbonate system than the styrene system; for the rise in polymer solubility parameter, CN efficiency is apparently reversed. These changes are discussed in terms of the differences in molecular architecture of the two systems. For glassy polymers, ?_c (air) is shown to depend in semiquantitative fashion on polymer T_g, δ, and resistance to shear deformation.     

Separation of isomeric xylenes by pervaporation through cellulose ester membranes

The interaction between the isomeric xylenes and different cellulose esters was investigated using solubility parameter considerations and through measurements of swelling values. p]Hansen's three-dimensional solubility parameters δ_d, δ_p, δ_h of all the components have been calculated. These values have been used to predict the interaction between polymer and penetrant. A measure for this interaction is given by Δ, which is the distance between polymer and penetrant in the δ_d, δ_r, δ_h space. As expected, the experimental swelling values varied in inverse proportion to the calculated Δ values. p]Pervaporation characteristics of different cellulose ester membranes were determined by measuring product rates and selectivity. The differences in membrane characteristics have been explained qualitatively in terms of the solubility parameter concept.     

Interaction parameter for hydrogen-containing mixtures in the Peng—Robinson equation of state

A new correlation for the Peng—Robinson interaction parameter δ_ij of hydrogen-containing mixtures is proposed here. Values of δ_ij obtained from literature vapour—liquid equilibrium data are represented by a cubic polynomial in terms of the temperature. The correlation predicts better values than other correlations proposed in the literature for the same systems, and is applicable to wider ranges of temperature. Applications of the proposed equations to VLE are presented.     

Study of Very Low Temperature Crystallization Process in Ethylene/α-Olefin Copolymers

Summary: The crystallization behavior of Ziegler-Natta (ZN) and single site (SS) based ethylene/1-butene and ethylene/1-hexene copolymers and SS copolymer fractionated by composition and molar mass (MM) has been studied by differential scanning calorimetry. It was observed that in addition to the high temperature crystallization peak (HTCP), and for ZN copolymers in addition also to low temperature crystallization peak (LTCP), a very-low temperature crystallization peak (VLTCP) is present at temperatures in between 60–75 °C. Peak temperature of VLTCP, T_VLTCP, decreases with increasing comonomer content (C_comon) at fixed MM. If C_comon is kept approximately constant, T_VLTCP increases with increasing MM. It turns out that T_VLTCP does not depend on the type of catalyst used. The degree of crystallinity calculated from the VLTCP is independent of the chemical nature of the comonomers present, but slightly changes with C_comon. It also steeply increases with MM and levels off at MM around 50 kg/mol. It was found that the crystallinity as related to the area of the VLTCP is catalyst type dependent, and is higher for the SS catalyst used compared to the ZN catalyst.     

Thermodynamics of plasticized triblock copolymers. I. Theory

The thermodynamic theory of bulk ABA copolymers developed by Leary and Williams is extended to copolymer–solvent systems. Free energy expressions are derived for five hypothetical phase-separated morphologies and evaluated specifically for a polymer with approximately 25% of the A component. The separation temperature, T_s, at which a given morphology will be in equilibrium with a homogeneous mixture, is also evaluated. The major result is the prediction of the T_s(?S) depression, where ?s is the solvent fraction. Depression is maximized when δ_S is equidistant between δ_A and δ_B, but becomes rapidly less when δ_S is outside the δ_A–δ_B range. Morphological favoritism is independent of ?_S and δ_S (model does not apply to preferential precipitation), with a planar microstructure being favored along with microstructures containing domains of B in continuous A for the 25% A polymer.     

BEHAVIOUR OF MICELLES OF A NON-IONIC SURFACTANT IN THE PRESENCE OF CONCENTRATED ELECTROLYTES AT DIFFERENT TEMPERATURES

Micelle formation of nonylphenol polypropylene polyethylene oxide (NPE-1800) was investigated in aqueous and aqueous electrolyte solutions. The study focused on the effect of temperatures, 25, 30, 35 and 40°C and on the effect of concentrated inorganic electrolytes, NaNO₃, KCI, KNO₃, K₂SO₄ and MgCl₂.6H₂O. The Critical Micelle Concentration (CMC) was determined by surface tension measurements. On the basis of the actual CMC and its temperature dependence, the thermodynamic functions of micelle formation (δH°, δS°, δG°) were calculated.

According to the experimental results, the CMC at high electrolyte concentration increases with increasing temperature. This behaviour is attributed to the salting-in mechanism.

Viscometry supports the behaviour of NPE-1800 in concentrated electrolytes and the decrease of (η is attributed to the decrease of the solvency of the electrolytic solution.     

A computational study of surface tension determination of dense fluids as benzene,toluene, methanol,ammonia, ethylene,and carbon monoxide

In this study, the parameters of linear isotherm regularity, which called LIR equation state used to compute the surface tension of some dense fluids as benzene, toluene, methanol, ammonia, ethylene, and carbon monoxide. An expression has derived for radial distribution function (RDF) at constant temperature, g (σ), for a real fluid by the use of LIR. This expression, which is related to intermolecular interaction, can be used to describe the temperature–density dependency of RDF at constant temperature, g (σ, ρ, T). In addition, we derive an expression for surface tension of dense fluids (CO, C₆H₆, C₆H₅CH₃, CH₃OH, NH₃, and C₂H₄) using the LIR and g (σ, ρ, T). Unlike previous models, it has shown that, surface tension can obtain without employing ΔH and ΔS. Only P-V-T experimental data have been used to calculate the surface tension. Comparison of the calculated values of surface tension by LIR with the values obtained experimentally show this method is not precise. This problem has led us to try to obtain the expression for surface tension using the extended parameters A, B (A and B are the temperature-dependent parameters which noticeably are depended on attraction and repulsion). The obtained result shows that the accuracy of this method is very high and quite admissible.     

Density and surface tension of pure 1-ethyl-3-methylimidazolium l-lactate ionic liquid and its binary mixtures with water

The density and surface tension of 1-ethyl-3-methylimidazolium l-lactate ([emim][l-lactate]) ionic liquid were determined from T = (283.15 to 333.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 333.15) K. Molecular volume and standard entropies of the IL were calculated from the experimental density values. The surface properties of IL were investigated. The critical temperature and enthalpy of vaporization were also discussed. Density and surface tension have been measured over the whole composition range for {[emim][l-lactate] + water} binary systems at a temperature of 298.15 K and atmospheric pressure. Excess molar volumes V^E and the surface tension deviations δγ have been determined.     

Effect of chemical activity jumps on the viscoelastic behavior of an epoxy resin: Physical aging response in carbon dioxide pressure jumps

We report the results from tensile creep tests performed on an epoxy resin in the presence of carbon dioxide at different pressures (Pco₂) and at a constant temperature below the glass‐transition temperature. Time‐Pco₂ superposition was applied to the data to account for the plasticization effect because of the interaction between the carbon dioxide molecules and the polymer. In addition, physical aging of the epoxy films was investigated with sequential creep tests after carbon dioxide pressure down‐jumps at constant temperature and after temperature down‐jumps at constant carbon dioxide pressure. The isothermal pressure down‐jump experiments showed physical aging responses similar to the isobaric temperature down‐jump experiments. However, the aging rate for the CO₂ jump was slightly lower than that for the temperature‐jump (T‐jump) experiments, and the retardation time for the Pco₂‐jump experiments was up to 6.3 times longer than for the T‐jump conditions. The results are discussed in terms of classical physical aging and structural recovery frameworks, and speculation about the differences in the energy landscape resulting from the Pco₂‐jump and T‐jump experiments is also made. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2050–2064, 2002     

Surface tension of tin and its alloys with lead

The temperature and concentration dependencies of the surface tension of high-purity tin and its alloys with lead were investigated in an ultrahigh vacuum by the large-drop method. It was shown that the tin surface-tension polytherm obeyed the equation σ(T) = 570.0 ? 0.08(T ? T _m). Lead was found to possess high surface activity in the range of its low concentrations in tin. Estimate was made for the limiting lead surface activity in tin-based alloys. Our conclusions about lead surface activity in alloys with tin are consistent with the literature data obtained by the modern electron-spectrometric methods for the surface compositions of the alloys studied.     

The liquid–gas interface of oxygen–nitrogen solutions: 1. Surface tension

The capillary method of surface tension measurement has been used to measure the surface tension of oxygen–nitrogen solutions in the temperature range from 80 to 132 K. At temperatures below the nitrogen critical temperature (T_c = 126.2 K) the capillary constant and the surface tension of solutions are smaller than their additive values and vary linearly with the temperature. Experimental data are compared with the results of calculating the surface tension by the theories of Pinnes and Rowlinson.     

Epr Spectroscopy of Adsorbed Spin-Labeled Peptides: Immobilization of Trichogin on the Titanium Oxide

The TOAC-spin-labeled peptide Trichogin GA IV adsorbed on the TiO₂ surface is studied. It is shown that the continuous wave (CW) electron paramagnetic resonance (EPR) spectrum does not depend on temperature in a wide range of 77–300 K. A pulsed EPR method of electron spin echo (ESE) utilizing a two-pulse sequence (π/2-τ-π) is used to study temperature dependence of the phase relaxation time, T_F. The T_F values are found to change from 750 ns to 100 ns in the interval of 77–300 K. The pulsed electronelectron double resonance (PELDOR) measurements utilizing the pulse sequence((π/2)_A,-T-π_B,-(τ-T)-π_A) show that the space distribution of spin labels on the surface remains uniform irrespective of the temperature, and provide the fractal dimension of the surface of 2.7±0.1. The obtained results testify that EPR pulse experiments can be used to study adsorbed spin-labeled molecules at room temperatures, i.e. not only at cryogenic temperatures.     

Correlation of the prigogine-flory theory with isothermal compressibility data. I. Systems with quasi-spherical molecules

The isothermal compressibilities K_T for cyclohexane + benzene, cyclohexane + toluene and benzene + toluene systems at 25, 35, 45 and 60°C have been used to test the Prigogine-Flory theory using Van der Waals and Lennard-Jones energy potentials. Flory's energy parameter X ₁₂ was calculated for these systems at the four temperatures. From X ₁₂ for the equimolar mixture, the following excess functions were calculated: (?V^E/?_p)_T which is related to K _T ^E , the heat of mixing H ^E , and the excess volume V ^E . The theory and any of the two potentials give (?V^E/?_p)_T which fit the experimental data, but H ^E and V ^E , calculated using the same X ₁₂ parameter, depart appreciably from the experimental data even though they agree in sign and have the essential features of the excess functions. The departure is apparent in both magnitude (in particular for the cyclohexane + benzene, and cyclohexane + toluene systems) and in the temperature dependence. The conclusion is that the X ₁₂ parameter does not predict the thermodynamic properties of these systems and the Lennard-Jones potential, involving a more complicated expression, does not contribute any improvement over the Van der Waals potential.     

Effect of montmorillonite content and the type of its modifier on the thermal properties and flammability of polyimideamide nanocomposite fibers

The effects of montmorillonite (MMT) content (1, 3, 5%) and the type of its modifiers on the thermal properties and flammability of PIA nanocomposite fibers have been assessed. Sodium montmorrilonite was modified with aminododecane acid and octadecylamine. Samples of PIA nanocomposite containing commercial MMT: Nanomer PGW from Nanocor were also included in the comparative analysis. It has been found that the glass transition temperature (T _g) of the fibers under investigation depends on the type of MMT’s modifier. On the other hand this parameter does not affect the thermal stability of fibers defined with T ₅ and T ₅₀ indicators since the thermal decomposition of modifiers takes place at lower temperatures.     

Molecular versus tissue liquids: an atomic length?

For the monatomic classical liquids like Ar, Kr and Xe, it has long been known that near the triple point, the product of surface tension σ and isothermal compressibility K_T , having dimensions of length, is less than 1?Å. More recently, a similar result has been established from experimental data on some 20 organic liquids. The purpose of this article is to raise a possibly interesting question with experimentalists working on complex molecular liquids as well as biological cell assemblies. Thus, we first draw attention to measurements of the compressibility of some 25 proteins in water. Can complementary measurements of surface tension be carried out on at least some of these systems? And is the product σK_T a length of order of an Å or so? Second, we note existing measurements of surface tension σ on five embryonic tissues and ask essentially the same question as to whether or not the product σK_T is of atomic dimensions. Finally, via a biopsy of a tumour which might provide material to yield an approximately spherical aggregate of the cancerous cells, is σK_T measurable and if so, is this product dependent on the presence of the tumour?     

Properties of argon liquid-vapor interface

The short-wave cutoff boundary of the capillary wave spectrum is established. Effective thickness L _b of the “bare” density profile in the interfacial layer is calculated according to experimental data on the ellipticity ratio of reflected light. The free parameters of the extended van der Waals theory of capillarity are determined. The positions of the equimolecular dividing surface and tension surface are calculated, as well as the temperature dependence of the Tolman parameter.     

The correctional kinetic equation for the peak temperature in the differential thermal analysis

The peak temperature (T _p) and different temperature (ΔT) are the basic information in the differential thermal analysis (DTA). Considering the kinetic relation and the heat equilibrium in DTA, a correctional differential kinetic equation (containing T _p and ΔT parameter) is proposed. In the dehydration reaction of CaC₂O₄·H₂O, the activation energy calculated from the new equation showed some smaller than that from Kissinger equation, but some bigger than that from Piloyan equation.     

On the applicability of Young–Laplace equation for nanoscale liquid drops

Debates continue on the applicability of the Young–Laplace equation for droplets, vapor bubbles and gas bubbles in nanoscale. It is more meaningful to find the error range of the Young–Laplace equation in nanoscale instead of making the judgement of its applicability. To do this, for seven liquid argon drops (containing 800, 1000, 1200, 1400, 1600, 1800, or 2000 particles, respectively) at T = 78 K we determined the radius of surface of tension R_s and the corresponding surface tension γ_s by molecular dynamics simulation based on the expressions of R_s and γ_s in terms of the pressure distribution for droplets. Compared with the two-phase pressure difference directly obtained by MD simulation, the results show that the absolute values of relative error of two-phase pressure difference given by the Young–Laplace equation are between 0.0008 and 0.027, and the surface tension of the argon droplet increases with increasing radius of surface of tension, which supports that the Tolman length of Lennard-Jones droplets is positive and that Lennard-Jones vapor bubbles is negative. Besides, the logic error in the deduction of the expressions of the radius and the surface tension of surface of tension, and in terms of the pressure distribution for liquid drops in a certain literature is corrected.