Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1976"
TL;DR: In this paper, a simple theory is developed that accounts for many of the observed physical properties of micelles, both globular and rod-like, and of bilayer vesicles composed of ionic or zwitterionic amphiphiles.
Abstract: A simple theory is developed that accounts for many of the observed physical properties of micelles, both globular and rod-like, and of bilayer vesicles composed of ionic or zwitterionic amphiphiles. The main point of departure from previous theories lies in the recognition and elucidation of the role of geometric constraints in self-assembly. The linking together of thermodynamics, interaction free energies and geometry results in a general framework which permits extension to more complicated self-assembly problems.
4,563 citations
TL;DR: In this paper, the potential energy profiles for atoms adsorbed in slit-like pores, and of the enhancement of the depth of the energy well compared with that for adsorption by a single surface are presented.
Abstract: Calculations are presented of the potential energy profiles for atoms adsorbed in slit-like pores, and of the enhancement of the depth of the potential energy well compared with that for adsorption by a single surface. The vibrational frequency normal to the wall is calculated as a function of slit width and methods of analysing experimental data are suggested. A comparison is made with similar expressions for adsorption in cylindrical pores. Recently published data on the adsorption of noble gases by a series of microporous carbons is analysed and shown to be best represented in terms of slit-like pores having an average width (between the nuclei of carbon atoms) of about 0.77 nm. The width available to an adsorbed molecule is about 0.52 nm which is in quantitative agreement with the known molecular sieve properties of these carbons. A well-activated carbon has pores with a somewhat larger mean width. The calculated vibration frequencies lie in the range 5–10 × 1011 Hz. The calculated surface areas and micropore volumes are 3–4 times smaller than the “monolayer equivalent areas” and pore volumes derived from micropore adsorption of nitrogen and benzene. It is concluded, in agreement with Dubinin, that the micropore volume can be divided into ultra-micropores, consisting of 25–30 % of the total micropore volume having free widths of about 0.52 nm, together with supermicropores which are larger and are filled with adsorbed vapour only at higher relative pressures.
540 citations
TL;DR: In this article, the enthalpic pair and triplet interaction coefficients hij and hijj have been evaluated from the experimental data and compared with values which can be extracted from other published calorimetric studies.
Abstract: Heats of dilution of ethanol, n-propanol, n-butanol, t-butanol and heats of mixing of the various pairs of alcohols in aqueous solution have been measured at 25°C and concentrations of ⩽ 2 mol kg–1. The various enthalpic pair and triplet interaction coefficients hij and hijj have been evaluated from the experimental data and compared with values which can be extracted from other published calorimetric studies. All hij and hijj values are positive and show the dependence on alkyl chain length and conformation expected for a hydrophobic pair interaction. The results are discussed in terms of several models proposed for the hydrophobic interaction.
267 citations
TL;DR: In this paper, the e.s.r. spectra of phenoxyl radicals were used to determine the pKa of the radical cations, which varied from −2.0 (phenol radical cation) to −0.8 (hydroquinone radicalcation).
Abstract: Phenoxyl radicals were generated in solutions containing from 0 to 75 % sulphuric acid. The changes observed in the e.s.r. spectra over this range are shown to be due to progressive formation of phenol radical cations. In favourable cases plots of the e.s.r. parameters against acidity enabled us to determine the pKa of the radical cations, which varied from –2.0 (phenol radical cation) to –0.8 (hydroquinone radical cation). Changes in the coupling constants in going from a phenoxyl radical to the corresponding phenol radical cation are usually relatively small, but the g-values change from 2.004 4 ± 0.000 4 to 2.003 2 ± 0.000 4. The free energy changes involved in competing oxidative processes are discussed and the data support the view that the C—O group in phenoxyl resembles that in ketones.
247 citations
TL;DR: In this article, the formation of a wetting perimeter when a spherical particle touches a planar liquid surface is analyzed taking into account the line energy of this perimeter, and the minimum size of particle which can float is calculated and an accurate estimate is made for the minimum time of touching of particle and surface.
Abstract: On the basis of the theory of capillarity, the process of formation of a wetting perimeter when a spherical particle touches a planar liquid surface is analysed taking into account the line energy of this perimeter. The minimum size of particle which can float is calculated and an accurate estimate is made for the minimum time of touching of particle and surface. The kinetic energy of collision between an air bubble and the particles is used to calculate the maximum size of particles which can remain attached for flotation. Flotation data suggest that a lower limit for the size of isolated particles which can be floated is of the order of 1 µm and a comparison of this radius with the theoretical limit gives a value of 10–4 to 10–5 dyn for the line energy of the wetting perimeter. Predictions of the flotation region in terms of particle size and contact angle using this energy do not conflict with practical findings.
232 citations
TL;DR: In this article, a model for exchange interaction taking into account the impact of the m.o.s. concept in inorganic chemistry was proposed, which is applied to the study of binuclear complexes of chromium(III).
Abstract: A model is proposed for exchange interaction taking into account the impact of the m.o. concept in inorganic chemistry. We define four principles that such a model should follow; invariance with respect to a unitary transformation between the orbital basis functions, validity of Heitler–London wavefunctions for the low lying terms, no difference in nature between direct and indirect exchange interactions, and the possible interpretation of the phenomenon by considering only the ground configuration (the coupling between ground and charge transfer configurations only leads to a small second order effect). Within this framework, we express the interaction hamiltonian as the sum of a one-electron operator coupling the magnetic orbitals in such a way that its eigenfunctions and eigenvalues are respectively the m.o.s. built from the magnetic orbitals and their energies, and a bielectronic operator. When the magnetic orbitals of similar symmetry are not orthogonal, the effect of the one electron operator on the energy differences between the low lying terms is largely predominant. The model is applied to the study of binuclear complexes of chromium(III).
228 citations
TL;DR: In this article, the authors present knowledge of these critical exponents of percolation theory and estimate theoretically the width of the critical region where the exponents β and γ should deviate from their classical values, and discuss the influence of nonclassical exponents on the molecular weight distribution function and the tail cutting effects.
Abstract: Cyclization effects lead to deviations from the classical Flory–Stockmayer theory of gelation and are taken into account by percolation theory. Nonclassical “critical exponents”β and γ should therefore occur for gel fraction G and molecular weight DPw, respectively. For example, G is predicted to vanish for p→pc as (p–pc)β with β≃ 0.4 instead of the Flory–Stockmayer prediction β= 1. Our present knowledge of these critical exponents of percolation theory is reviewed. We estimate theoretically the width of the critical region where the exponents β and γ should deviate from their classical values, and discuss the influence of nonclassical exponents on the molecular weight distribution function and the tail-cutting effects.
201 citations
TL;DR: In this article, the surface tension of aqueous electrolytes and their interfacial tension against n-dodecane was determined at 20°C. The results were discussed in terms of both electrostatic theory and dispersion force theory of interfaces.
Abstract: Surface tensions of aqueous electrolytes, and their interfacial tensions against n-dodecane, have been determined at 20°C. The salts studied were LiCl, NaCl, KCl, KBr, NaBr, KI and Na2SO4 at concentrations up to about 1 mol kg–1. For the alkali metal chlorides and Na2SO4 the surface and interfacial tension increments are similar for a given electrolyte. The corresponding increments for KBr, NaBr and KI however are found to differ considerably. The results are discussed in terms of both electrostatic theory and dispersion force theory of interfaces. With respect to the latter, it is found that if due allowance is made for the presence of an ion-free layer of water at the interface, an approximate approach in which only a single dominant interaction frequency is considered, gives results in reasonable accord with experiment.
179 citations
TL;DR: The infrared spectrum of adsorbed pyridine indicates that both goethite and phosphated Goethite have Lewis acid sites on edge faces only; neither exhibit Bronsted acidity.
Abstract: The infrared absorption spectrum of phosphate adsorbed on α-FeOOD and α-FeOOH establishes the presence of binuclear (FeO)2PO. OH groups, bridging adjacent Fe3+ ions on (100) faces of the crystals. Examination of D2O-exchanged surfaces shows the predicted three species of OD on the goethite surface, two on fluoridated goethite, and four (including POD) on phosphated goethite. The spectrum of adsorbed pyridine indicates that both goethite and phosphated goethite have Lewis acid sites on edge faces only; neither exhibit Bronsted acidity. These observations confirm a proposed model of the (100) face.
170 citations
TL;DR: In this paper, a new method, similar to the method of isodynamic curves, is developed to study the electrostatic interaction between similar and dissimilar double layers under a regulated approach, where the surface potentials and charges are regulated by the association and dissociation of ionizable groups at each surface.
Abstract: The electrostatic interaction between similar and dissimilar double layers under regulated approach is considered During the interaction the surface potentials and charges are regulated by the association and dissociation of ionizable groups at each surface A new method, similar to the method of isodynamic curves, is developed to study this problem This method can provide a qualitative description of the salient features of the surface charge, the surface potential and the pressure between the surfaces as a function of separation without first having to obtain an exact solution of the problem This qualitative and the accompanying exact solution are presented in terms of the Gouy–Chapman approximation as an illustration of the role of surface regulation during interaction
142 citations
TL;DR: In this paper, a diffusion cell is described in which species diffuse through a rotating disc of filter paper and correct rotating disc hydrodynamics are established on both sides of the filter.
Abstract: The construction of a diffusion cell is described in which species diffuse through a rotating disc of filter paper. Correct rotating disc hydrodynamics are established on both sides of the filter. Liquid liquid interfaces can be established on either side of the filter and the rate at which species are transferred from one phase to the other can be measured. By extrapolation to infinite rotation speed the rate constant for the transfer reaction at the interface can be measured. Results for 11 systems are reported. The rate constant for the interfacial transfer in the downhill direction is found for each system to be approximately 10–5 m s–1. The activation parameters for two systems are also reported.
TL;DR: In this article, the authors show that the relative yields of singlets and triplets change with time as the spin correlation decays, and that the process is a coherent one resulting from the isotropic hyperfine interaction with hydrogen nuclei.
Abstract: Geminate recombination of radical ions of aromatic hydrocarbons in alkanes produces excited molecules: the relative yields of singlets and triplets change with time as the spin correlation decays. At short times ([graphic omitted] 50 ns) the process is a coherent one resulting from the isotropic hyperfine interaction with hydrogen nuclei: its rate is field-dependent and, for mobile liquids, it can be calculated exactly from e.s.r. data: deuteration will have a large effect and oscillations may be observed. At longer times, the yields became constant (but different) at high and zero field, but an additional small decay is predicted for very low fields. At still longer times, random spin relaxation will eventually make the yields independent of field. The theory is extended to cover initial production of triplet ion pairs in addition to singlets, the effect of charge transfer and recombination in viscous liquids and solids. It is applied to excited state production in radiolysis and to the radiation chemistry of pure alkanes.
TL;DR: The experimental data are in accord with the model and enable the equilibrium constants of the reactions to be obtained, and a kinetic model for the ( SCN)–2/TrpH reaction predicts a variation of the equilibrium concentration of (SCN)-2 with [H+], [trpH] and [SCN–].
Abstract: Oxidation of halide, thiocyanate, carbonate and selenite ions by hydroxyl radicals yields radicalanions which themselves oxidise amino-acids such as tryptophan and tyrosine. The free-radical product(s) of oxidation of tryptophan (TrpH) by Br–2, (SCN)–2, CO–3 and a selenite free radical have similar spectral and kinetic properties in neutral and alkaline solutions. The spectral shifts and decay kinetics of the tryptophan free-radical observed at pH ∼ 3 show that oxidation of TrpH by Br–2 and (SCN)–2 gives a radical which protonates (pKa= 4.3) and which is singly charged at pH ∼ 3. The different prototropic behaviour of the absorption of the product of oxidation of TrpH by the selenite radical suggests that in this case, more than one species is produced. The protonated free radical TrpH+ reacts with SCN– so that there is an apparent loss of reactivity of (SCN)–2 towards TrpH, especially at low pH, high [SCN–] and low [TrpH]. A kinetic model for the (SCN)–2/TrpH reaction predicts a variation of the equilibrium concentration of (SCN)–2 with [H+], [TrpH] and [SCN–]. The experimental data are in accord with the model and enable the equilibrium constants of the reactions to be obtained.
TL;DR: In this article, the authors describe the kinetics of activated chemisorption by plots of the time t against the reciprocal of the rate of adsorption Z=(dq/dt) −1.
Abstract: The kinetics of activated chemisorption are described by plots of the time t against the reciprocal of the rate of adsorption Z=(dq/dt)–1. The parameter t0 of the Elovich equation q=(1/b) ln ab+(1/b) ln (t+t0) where a, b and t0 are constants is estimated from the plot of t against Z. The plot of q against log(t+t0) is convex towards the q axis at low t indicating that the Elovich equation is not obeyed in that range. The “combined model” of Aharoni and Tompkins predicts a curvature in the wrong direction and is inapplicable without modification.
TL;DR: The differences between the one-electron reduction potentials at pH 7 (E17) of a quinone couple (Q/Q–), and seventeen nitroimidazole couples (S/S–) were estimated, by measuring the equilibrium constant Kc of the reaction S–+ Q ⇌ S + Q–.
Abstract: The differences between the one-electron reduction potentials at pH 7 (E17) of a quinone couple (Q/Q–), and seventeen nitroimidazole couples (S/S–) were estimated for S = substituted 2-, 4-, and 5-nitroimidazoles, by measuring the equilibrium constant Kc of the reaction S–+ Q ⇌ S + Q–. The radical-ions S– and Q– were generated by pulse radiolysis, and their concentrations measured spectrophotometrically after the equilibrium was attained (typically 1–50 µs after the pulse). Estimated values of E17(S/S–) range from –243 mV for S = 5-formyl-1-methyl-2-nitroimidazole; –398 mV for 1-(2-hydroxyethyl)-2-nitroimidazole; –486 mV for 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole to ⩽–527 mV for 4-nitroimidazole (all ± 10 mV). In the absence of other factors, 2-nitroimidazoles have more positive E17 values than the 5-nitro-analogues, and 4-nitroimidazoles are still weaker oxidants. Substitution with electron-withdrawing groups in the side chain can increase E17 by amounts greater than the difference between 2- and 5-nitroimidazoles. These values are based on E17(Q/Q–)=–244 ± 7 mV for duroquinone, and –375 ± 8 mV for 9,10-anthraquinone-2-sulphonate. These reference potentials were determined by measuring Kc for one-electron transfer equilibria between the quinones and 1,1′-dibenzyl-4,4′-bipyridylium ion (BV2+), assuming E17(BV2+/BV+)=–354 ± 6 mV. The usefulness of viologens as redox indicators in this type of study is discussed.
TL;DR: In this article, a quasi-thermodynamic transition from supercooled fluid to amorphous solid at a density slightly greater than the equilibrium freezing density has been investigated for the hard-sphere fluid.
Abstract: Equations of state and transport data for the hard-sphere fluid suggest a quasi-thermodynamic transition from supercooled fluid to amorphous solid at a density slightly greater than the equilibrium freezing density This has been substantiated with a lengthy MD computation in which the density was increased very gradually from a low density fluid state to almost close-packing The amorphous close-packed density of 500 spheres with periodic boundary is found to be ρaσ3= 1217 ± 0004 A glass transition occurs in the density region ρgσ3= 100 ± 001; a (diffuse) thermodynamic transition of the third-order is indicated
TL;DR: In this article, the HeI vacuum ultraviolet photoelectron spectrum of the methyl radical produced by pyrolysis of azomethane has been investigated and three ionization potentials corresponding to the formation of the 1A′1, 3E′ and 1E′ ionic states were observed with vertical ionisation potentials of 984, 1476 and 1610 eV respectively, with the aid of both ab initio and semi-empirical molecular orbital calculations.
Abstract: The HeI vacuum ultraviolet photoelectron spectrum of the methyl radical produced by pyrolysis of azomethane has been investigated Three ionization potentials, corresponding to the formation of the 1A′1, 3E′ and 1E′ ionic states, have been observed with vertical ionization potentials of 984, 1476 and 1610 eV respectively The observed band positions have been interpreted with the aid of both ab initio and semiempirical molecular orbital calculationsThe band associated with the first ionization potential is the only one for which vibrational structure could be resolved This has been investigated in both CH3 and CD3 using Hel and NeI radiation From the Franck–Condon envelope of this band and the observed shifts on deuteration, it is concluded that the methyl radical is essentially planar in its ground electronic state The factors which control the values of the out-of-plane deformation frequencies in the ground state of CH3 and CH+3 are discussed in detail Jahn–Teller splitting has been detected in the band associated with the second ionization potential of CH3
TL;DR: In this paper, the rates and extents of hydrogen sorption by platinised tungsten trioxide and molybdenum trioxide have been measured between 273 and 363 K and between 3 and 101 kN m-2.
Abstract: The rates and extents of hydrogen sorption by platinised tungsten trioxide and molybdenum trioxide have been measured between 273 and 363 K and between 3 and 101 kN m–2. Maximum diffusion coefficients for hydrogen spilling-over from platinum to the trioxide supports have been estimated. X-Ray diffraction, differential thermal analysis and thermogravimetric analysis, e.s.r. and i.r. spectroscopy indicate that the products of this spillover are hydrogen bronzes of tungsten and molybdenum. These may be represented as HxWO3, where x has a maximum value of 0.46, and HxMoO3, where x has a maximum value of 1.63. The latter violates the ranges of composition previously accepted for bronzes. The chemical and thermal stability of these bronzes is discussed in terms of their structures.
TL;DR: In this article, permittivity, refractive index, molecular dipole moment, dielectric relaxation parameters and molecular Kerr constant are reported for the nematogen 4,4-n-heptyl-cyanobiphenyl (HCB) in the nematic phase, in the pure isotropic phase and in benzene solutions.
Abstract: The permittivity, refractive index, molecular dipole moment, dielectric relaxation parameters and molecular Kerr constant are reported for the nematogen 4,4-n-heptyl-cyanobiphenyl (HCB) in the nematic phase, in the pure isotropic phase and in benzene solutions. The anisotropy of molecular polarizability is less than in benzene. Kirkwood–Bordewijk g-factors show significant dipole antiparallelism in the isotropic and nematic phases: in the latter it is much larger parallel to the director axis than perpendicular to it. The two major (orthogonal) component activation enthalpy and entropy terms for dipole reorientation (Bauer) in the nematic phase (including benzene solutions) are compared with those in the isotropic media: in the pure nematic ΔHB(‖)= 60 ± 8 kJ mol–1; ΔHB(⊥)= 6 ± 2 kJ mol–1. The current theoretical representations of the nematic phase are examined using the experimental data. The occurrence of pre-transitional molecular interaction in benzene solutions (above 3 mol dm–3) and in the pure isotropic phase can be detected.
TL;DR: In this article, the free energies of transfer from water to dichloroethanes have been calculated and have been split into single-ion values through the assumption that ΔGt°(Ph4P+, Ph4As+)=ΔGtµ(P4BÕ−ε) for each ion.
Abstract: The solubility of 27 1:1 electrolytes in 1,2-dichloroethane and 25 1:1 electrolytes in 1,1-dichloroethane has been determined. Combination of the solubility values with association constants, and correction for activity coefficients by the extended Debye–Huckel theory, yields standard free energies of solution of the ionic species (M++ X–). From like data in water, free energies of transfer from water to the dichloroethanes have been calculated and have been split into single-ion values through the assumption that ΔGt°(Ph4P+, Ph4As+)=ΔGt°(Ph4B–). It is shown that the free energy of anions (Cl–, Br–, I– and ClO4–) in the dichloroethanes is much higher in value than in water and in dipolar approtic solvents (DMSO, DMF and MeCN). The free energy of most cations (Na+, K+, Rb+, Cs+, Me4N+, Et4N+, Pr4N+ and Bu4N+) is also higher in value in the dichloroethanes than in the dipolar approtic solvents. Both anions and cations are invariably higher in free energy by ∼1 kcal mol–1 in 1,1-dichloroethane than in 1,2-dichloroethane. It is concluded that the (Ph4P+, Ph4As+)=(Ph4B–) assumption yields single-ion free energies of transfer to or from the dichloroethanes that are chemically reasonable.
TL;DR: In this paper, the adsorption, desorption and surface structural chemistry of CO on Pt(110) have been studied by low energy electron diffraction, Auger spectroscopy, work function measurement, and flash DESORption.
Abstract: The adsorption, desorption, and surface structural chemistry of CO on Pt(110) have been studied by low energy electron diffraction, Auger spectroscopy, work function measurement, and flash desorption. Chemisorption induces a (1 × 2)→(1 × 1) change of periodicity in the clean reconstructed surface; the adsorption rate follows precursor state kinetics. It is shown that the diffraction and desorption data are consistent with the presence of two physically distinct kinds of CO in the adsorption layer. These species, denoted αCO and βCO, have adsorption energies of ∼105 and ∼129 kJ mol–1 respectively. βCO predominates under all conditions, and at high coverages ordering of the β state takes place with the formation of a structure which belongs to the space group plgl. The structure of this ordered phase is examined in some detail, and a bonding model for CO on Pt(110) is proposed. This model is shown to be consistent with the presence of the observed α and β states, the facile (1 × 2)→(1 × 1) transformation of the Pt surface, and the formation of the plgl phase at high coverage.
TL;DR: In this article, it was shown that at temperatures above 650 K cupric ions are reduced to some extent to cuprous ions, and that Lewis sites are also formed upon degassing.
Abstract: In CuY zeolites degassed at temperatures above 650 K cupric ions are reduced to some extent to cuprous ions.Evidence for this process of auto-reduction was taken from the decrease in weight of the sample, and the detection of a desorbing gas in a volumetric system. The latter was identified as oxygen. U.v. reflectance spectroscopy showed directly the decrease of the Cu2+ species upon outgassing and their increase after oxygen adsorption. Excitation spectra showed the presence of Cu+ ions after high temperature degassing. Infrared spectroscopic techniques showed that Lewis sites are also formed upon degassing. A mechanism is proposed that accounts for the observations.
TL;DR: In this article, a previously described model for exchange interaction is applied to the study of antiferromagnetic coupling in binuclear oxo-bridged iron (III) complexes.
Abstract: A previously described model for exchange interaction is applied to the study of antiferromagnetic coupling in binuclear oxo-bridged iron (III) complexes The energies of the magnetic orbitals (singly occupied d orbitals of each transition ion, partially delocalized towards the ligands surrounding this ion), and of the mos built from these magnetic orbitals are calculated, using the Angular Overlap Model The wavefunctions associated with the low lying terms are expressed in the form of HL functions and the relative energies of these terms are calculated from a one electron matrix, which couples the magnetic orbitals in such a way that its eigenfunctions an eigenvalues are the mos and their energies An interpretation of the relative magnitudes of antiferromagnetic coupling in FeIII—O—FeIII and CrIII—O—CrIII dimers is proposed
TL;DR: In this article, three different paramagnetic species were identified: OI−OII−CO−III, OII−OIII and OIII according to the reaction: O3−3+ CO → O2−latt.
Abstract: Oxygen absorbed on TiO2 when subjected to u.v. irradiation gives rise to three different paramagnetic species. The first species, A, has been identified as O–2(g1= 2.021, g2= 2.009 and g3= 2.001 and C1≈C2≈ 0 Oe, C3= 77 Oe for 17O hyperfine spliting), the second species, C, as O–3(g1= 2.014, g2= 2.009 and g3= 2.003, no detected hyperfine lines due to 17O) and the third, B, as O3–3(g∥= 2.008 and g⊥= 2.001, no detectable hyperfine lines due to 17O). The latter species reacts readily with CO at 77 K and gives rise to species D, identified as OI–OII–CO–III according to the reaction: O3–3+ CO → O2–latt.+ O—O—CO– where the two directly bonded oxygen atoms originate from the absorbed molecular oxygen. The e.p.r. parameters of species D are : g1= 2.0465, g2= 2.006, g3= 2.001, C1≃ 6 Oe ± 0.5C2≈C3≈ 4 Oe ± 0.5 for 13C hyperfine interaction, CI1≈CI2≈ 0 and CI3= 104 Oe, CII1C≈II2 0 and CII3≃ 42.5 Oe and CIII1≈CIII2≈CIII3≈ 0 for 17O hyperfine splitting constants of the three oxygen nuclei. It is mainly the characterization of species, D, which enables us to postulate the nature of species, B.
TL;DR: In this paper, a number of iodine compounds are studied as solids, in particular some iodine-oxygen and iodine-chlorine compounds and the tri-iodide ion.
Abstract: A number of iodine compounds are studied as solids, in particular some iodine-oxygen and iodine-chlorine compounds and the tri-iodide ion. The chlorine 2p electron binding energy for I2Cl6 can be resolved into two peaks of intensity ratio 2:1 corresponding to terminal and bridging chlorine atoms. The iodine 3d electron binding energy for the tri-iodide ion may be resolved into peaks corresponding to different iodine atoms. The experimental results are compared with CNDO calculations, using both a 5s, 5p(sp model) and a 5s, 5p and 5d(spd model) basis set, in the framework of the ground and relaxation potential models (GPM and RPM). The CNDO calculations (spd model) give good agreement with previously published charges for xenon compounds, and the spd model, but not the sp model, is found to give good agreement with the experimental results for iodine compounds. The RPM model is found to be an improvement over the GPM model. The overall bond orders obtained with the spd model charges and charges based on Pauling electronegativities are compared for the isoelectronic series SiO4–4, PO3–4, SO2–4, ClO–4, and the trends found to be in the opposite directions. For ClO–4, Pauling charges give particularly poor agreement with experiment.
TL;DR: In this paper, the order parameter S is > 0.36 in the one-phase nematic region in the phase diagram and is equal to 0.37 through the two-phase region.
Abstract: Wide-line n.m.r. has been used to obtain the order parameter, S, as a function of temperature, for nematic p-methoxybenzylidine-p-n-butylaniline (MBBA) containing solutes of differing size and shape. These consisted of : (i) anisotropic molecules, capable of correlating their orientations with MBBA molecules, viz n-hexane, n-hexadecane and trans-decalin, and (ii) isomers of more isotropic shape, apparently incapable of orientational correlation, viz 2,2-dimethylbutane, 2,2,4,4,6,8,8-heptamethylnonane, and cis-decalin. With the same mole fraction, x2, of anisotropic solute, there is the same lowering of S while the lowering with the isotropic solutes increases with solute size. The parameter S is > 0.36 in the one-phase nematic region in the phase diagram and is equal to 0.36 along both the (T, x2)N line where the isotropic phase first appears on heating and the (T, x2)I line where the nematic phase appears on cooling, i.e., S= 0.36 through the two-phase region. For all systems, S is a single function of the ratio T/TN. Phase diagrams have been obtained for 21 MBBA + solute systems. Solutes include the anisotropic, orientation-correlating normal alkanes, n= 6, 8, 12, 16, 20, 24 and trans-decalin and a variety of more isotropic, non-correlating solutes : the highly branched alkane isomers of Cn, n= 6, 8, 12 and 16; cycloalkanes; cis-decalin; SnX4, where X = methyl, butyl, octyl and lauryl; Pb(butyl)4 and dimethylsiloxane oligomers. Identical (T, x2) phase diagrams are obtained for all n-alkane solutes, their effect on the nematic-isotropic transition being independent of their molecular dimensions. This implies that the molecular cross-sectional area is the relevant factor for these anisotropic solutes. For the isotropic solutes, in contrast, there is a strong dependence on solute size of the (T, x2)N and (T, x2)I lines. Values of the slopes of TN and TI against solute mole fraction are corrected to infinite solute dilution. The results are compared with predictions of lattice model, virial expansion and other theories. They are also used to give the difference of solute activity coefficients in the nematic and isotropic MBBA(γN∞2/γI∞2– 1). This quantity is independent of size for the normal alkane solutes but increases rapidly for the branched alkanes and other isotropic solutes.
TL;DR: In this article, ammonium mordenite has been studied in aqueous solution over a pH range of 4-7 at 25°C and values of the thermodynamic equilibrium constant Ka and the standard free energy of exchange ΔG⊖ were calculated for reversible systems.
Abstract: Ion exchange of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ in ammonium mordenite has been studied in aqueous solution over a pH range of 4–7 at 25°C. Values of the thermodynamic equilibrium constant Ka and the standard free energy of exchange ΔG⊖ were calculated for reversible systems. In no case at 25°C did the degree of exchange of metal ions exceed 50%, and pH and anion were found to have no significant effect on the equilibria. A thermodynamic affinity sequence of Mn2+ > Cu2+ > Co2+∼ Zn2+ > Ni2+ was established and thermodynamic affinities of the zeolite for pairs of metal ions were calculated using the triangle rule. Selectivity quotients indicated that mordenite would preferentially remove manganese(II) or copper(II) from a binary solution mixture of one of these ions with cobalt(II), nickel(II) or zinc(II).
TL;DR: In this paper, surface pressure (II) against area (A) isotherms are measured as a function of temperature for insoluble monolayers of 1,2-distearoyl-sn-glycero-3-phosphorylcholine spread at the n-heptane/aqueous sodium chloride interface.
Abstract: Using compression techniques, surface pressure (II) against area (A) isotherms are measured as a function of temperature for insoluble monolayers of 1,2-distearoyl-sn-glycero-3-phosphorylcholine spread at the n-heptane/aqueous sodium chloride interface. Problems of spreading are resolved and accurate results at moderate and high II are presented. The results show an almost first order phase change which is very temperature sensitive. Various forms of the Clapeyron analysis are applied to the data to calculate the heats of the phase change and to assess variations arising from the choice of a close-packed area. These heats vary with temperature but not with salt concentration or pH over the range studied. Results on 1,2-dioleoyl-sn-glycero-3-phosphorylcholine show no such phase changes.
TL;DR: In this paper, the diffusion of the reactant through the pores was investigated and the influence of several parameters on the reducibility of Cu2+ has been investigated: the degree of cation exchange, the presence of Cu 2+ complexing ligands, the procedure of sample preparation and degassing.
Abstract: The uptake of hydrogen and oxygen by (Cu, Na)–Y zeolites has been followed kinetically in a volumetric system. The temperature region investigated was between 273 and 773 K. The influence of several parameters on the reducibility of Cu2+ has been investigated: the degree of cation exchange, the presence of Cu2+ complexing ligands, the procedure of sample preparation and degassing.The formation of Cu+ ions is determined mainly by the mobility of Cu2+ ions in the zeolite. The preparational and degassing procedure has a drastic influence on the reducibility of the Cu2+ species. The rate of formation of Cu° is determined by the diffusion of the reactant through the pores.Cu+ ions and small Cu° clusters are reoxidized reversibly, the mobility of Cu+ ions determining the rate of the process. The reoxidation of Cu° external to the zeolite consists of a homothetic attack of oxygen on the Cu° particles.
TL;DR: In this article, the second-order rate constants for the reaction OH + NO2+M→ HNO3(+M) have been determined, using flash photolysis to generate OH radicals and time-resolved resonance absorption to observe the rate of their removal.
Abstract: The kinetics of the reaction OH + NO2(+M)→ HNO3(+M) have been studied, using flash photolysis to generate OH radicals and time-resolved resonance absorption to observe the rate of their removal. Effective second-order rate constants, k1=(–d ln [OH]/dt)/[NO2], have been determined for the ranges: 220 ⩽T⩽ 550 K and 3.2 × 1017⩽[M]⩽ 1.6 × 1019 molecule cm–3. In this range of [M] the kinetics are in the changeover region between third- and second-order, but values of limiting low and high pressure rate constants have been found using an interpolation procedure due to Troe. Most of the experiments have been carried out with M = N2 but results have also been obtained with M = He, Ar, O2 and SF6.