Positronium chemistry in porous materials

Porous materials have fascinated positron and positronium chemists for over decades. In the early 1970s it was already known that ortho-positronium (o-Ps) exhibits characteristic long lifetimes in silica gels, porous glass and zeolites. Since then, our understanding of Ps formation, diffusion and annihilation has been drastically deepened. Ps is now well recognized as a powerful porosimetric and chemical probe to study the average pore size, pore size distribution, pore connectivity and surface properties of various porous materials including thin films. In this paper, developments of Ps chemistry in porous materials undertaken in the past some 40 yr are surveyed and problems to be addressed in future are briefly discussed.     

Microstructural studies of electron beam-irradiated cellulose pulp

The effect of electron beam irradiation on the microstructure of cellulose has been investigated using positron annihilation lifetime spectroscopy (PALS) and electron paramagnetic resonance (EPR) Spectroscopy. PALS studies of irradiated cellulose samples showed that ortho-positronium (o-Ps) lifetime increases with an increase in dose up to 80 kGy and decreases at higher doses. The EPR signal of the irradiated cellulose matrix showed the presence of multiple radical sites. These results are discussed on the basis of chemical and physical changes occurring at the microscopic level in the cellulose due to irradiation.     

Positronium in solid phases of long-chain paraffins

The study of positronium intensity rise in long-chain alkanes shows two kinds of electron traps: the first, which are discharged at low temperature (≈200 K); the other, which remain populated up to the transition point to the rotator phase; e.g. in C₃₀H₆₂ they are still observed at 328 K.In the rigid phase of even-numbered alkanes o-Ps lifetime is shorter than that of odd-numbered ones, due to the difference in the width of gap between the molecular lamellae.     

Comments on the relation: positronium lifetime – free volume size parameters of the Tao–Eldrup model

The author is discussing the parameters appearing in the Tao–Eldrup (TE) model describing the ortho-positronium (o-Ps) lifetime dependence on the size of free volume in which Ps is trapped. Parameter values are not universal, applicable to all media. The Ps penetration to the bulk should depend on Ps work function; the o-Ps decay rate is strongly influenced by the contact density factor.     

Effect of compatibilizer and electron irradiation on free-volume and microhardness of syndiotactic polypropylene/clay nanocomposites

Positron annihilation lifetime spectroscopy (PALS) and microindentation methods were applied to study the modification of syndiotactic polypropylene properties (PP) due to introducing of nanoclay (4 wt%) and maleic anhydride-modified PP oligomer into the polymer matrix.The influence of electron irradiation of nanocomposites with different doses (⩽440 kGy) was also studied. It was found that the initial irradiation with 30 kGy has a considerable effect on o-Ps lifetimes and intensities. However, the studied materials do not show noticeable differences in their behavior.     

Temperature dependence of the free volume in polytetrafluoroethylene studied by positron annihilation spectroscopy

The temperature dependence of the free volume holes in pure polytetrafluoroethylene (PTFE) and doped with 25% glass have been studied in the temperature range (30–250 °C) using positron annihilation lifetime spectroscopy. The data clearly revealed the glass transition temperatures for pure and doped PTFE are 130 and 110 °C, respectively. As the temperature increases, the free volume distribution becomes positioned at larger free volume hole size. A good correlation between the electrical conductivity and the o-Ps parameters was achieved.     

Positronium interactions in organic solvents

In the present work, the chemistry of the positronium (Ps) species has been investigated in pure benzene, pyridine and their mixtures with pyridine concentrations at 4.12, 6.18 and 8.24 M, respectively, using the Doppler-broadened line-shape analysis technique. It is seen that the intensities of the para-(p-Ps) and ortho-Ps (o-Ps) in benzene and that of p-Ps in pyridine follow the Ore-model predictions while the intensity of o-Ps in pyridine is much lower than expected from this model. On the basis of these observations and of decrease in the o-Ps lifetime with increasing pyridine concentration in various organic solvents as reported in literature, it is concluded that pick-off is not the only quenching mechanism for Ps in organic solvents and pyridine is a quencher of Ps-species rather than an inhibitor. Calculations carried out considering a diffusion-controlled mechanism of Ps-quenching in pyridine via unstable (dissociative) complex/adduct formation and the bubble model show that the quenching rate is diffusion controlled and the pick-off rate is in accordance with the free-volume model. These conclusions were confirmed in the mixtures of benzene and pyridine.     

Delayed formation and localisation of positronium in polymers at low temperatures

A theoretical model of the positron annihilation lifetime spectrum including the mechanisms of slow positronium (Ps) localisation and delayed Ps formation from a positron and a trapped electron was developed. The model was applied to two series of spectra for low-density polyethylene and high-density polyethylene (HDPE) collected at constant temperature (much below the glass temperature) as a function of measurement time. The Ps internal relaxation time and time of localisation of Ps in a free volume centre were determined. The results show that after long irradiation of the polymer a dominant fraction of positrons (unbound in Ps) annihilate from the trapped states. On the basis of parameters determined from the HDPE lifetime spectra, two S(t) curves (for sample in darkness and in light) were calculated. The predicted shapes of S(t) well agree with literature data obtained with the age–momentum correlation (AMOC) experiment. According to the new model the shapes of the para-Ps and the ortho-Ps (p-Ps) components are non-exponential. In spite of this, the multi-exponential decomposition of a polymer spectrum enables to determine correctly the value of the o-Ps lifetime, however the other parameters determined from the spectrum have no simple physical meaning.     

Interpretation of positron lifetime spectra arising from micellar solutions: Determination of the ortho-positronium diffusion coefficient in the solvent

Positron lifetime spectra arising from micellar solutions of sodium dodecylsulphate (SDS) are interpreted in terms of a classical positronium diffusion model published earlier. Unlike the generally accepted assumptions, this model results in a non-exponential ortho-positronium (o-Ps) lifetime density function. A new method is presented for the simultaneous fitting of this lifetime density function to independent lifetime spectra recorded under the same experimental conditions. Among the fit parameters D_p, the diffusion coefficient of o-Ps in the solvent (i.e. heavy water) phase is studied in detail; a detailed error analysis for D_p is also given. Provided that the mean aggregation number of SDS micelles is about 60, the published D_p values show that the diffusion coefficient of o-Ps in (heavy) water at room temperature is lower than that of small ions and molecules and the Arrhenius plot indicates a strong o-Ps localization in the solvent. The hydrodynamic radius of o-Ps is calculated from the o-Ps and micellar diffusion coefficients and from the micellar radius; it is greater than that of small ions and molecules and this can be considered as an independent indirect proof for the existence of o-Ps bubble in the (heavy) water.     

Detection of free volumes in polyaniline complexes with various acids by using positron lifetime spectroscopy

The positron lifetime spectroscopy (PLS), a non-destructive characterization method, utilizes positronium (Ps; an electron–positron bound state) as a probe and measures its lifetime in polymer free volumes. For the first time the free volumes have been estimated by PLS in polyaniline (PANI) complexes with various inorganic and organic acids. It was found that the o-Ps lifetime increases and the intensity decreases with increasing ionic radius of the counter-ions in PANI complexes. Obviously, larger counter anions result in enhanced mean size of the voids corresponding to the free volume in the bulk polymer.Electrical conductivity has been measured by conventional four-probe technique. The glass transition temperature and temperature of removal of the absorbed water have been determined by using differential scanning calorimetry. It was established fairly well correlation of the mentioned polymer parameters with the o-Ps lifetime and the free volume of PANI complexes, respectively. The greater free-volume results in a decrease of conductivity, glass transition temperature and temperature of removal of the absorbed water.     

Partial molar volumes of organic solutes in water. VII. o- and p-Aminobenzoic acids at T = 298 K to 498 K and o-diaminobenzene atT = 298 K to 573 K and pressures up to 30 MPa

Density data for dilute aqueous solutions of two isomeric aminobenzoic acids and of o -diaminobenzene (1,2-diaminobenzene) are presented together with partial molar volumes calculated from the experimental data. The measurements were performed at temperatures from 298.15 K up to either 498.15 K (aminobenzoic acids) or 573.15 K ( o -diaminobenzene) and at either atmospheric pressure, or at pressures close to the saturated vapour pressure of water, and also at pressure p =  30 MPa. The data were obtained using either a high-temperature and high-pressure flow vibrating-tube densimeter for measurements at elevated pressures or a commercial vibrating-tube cell DMA 602HT for measurements at atmospheric pressure.     

Synthesis and structures of N,N,O-scorpionatoruthenium(II) complexes featuring “non-innocent” o-benzoquinonediimines

A series of ruthenium(II) complexes bearing redox-active o-benzoquinonediimines (o-bqdi) was synthesized and characterized. Reactions of [RuCl(bdmpza)(η⁴-cod)] (bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetato; cod = 1,5-cyclooctadiene) and 1,2-benzenediamines such as o-phenylenediamine (o-pdaH₂), 4,5-difluoro-1,2-benzenediamine (o-pdaF₂), 4,5-dichloro-1,2-benzenediamine (o-pdaCl₂), and 4,5-dimethoxy-1,2-benzenediamine (o-pda(OMe)₂) afforded [RuCl(bdmpza)(o-bqdiX₂)] (X = H, 1; X = F, 2; X = Cl, 3; X = OMe, 4).     

Thermodynamics of vaporization of some alkyladamantanes

The boiling temperature of 1,3-dimethyladamantane was measured by comparative ebulliometry over the pressure range 6  <  (p / kPa)  <  100. The temperature dependencies of saturation vapour pressure and enthalpy of vaporization, and the normal boiling temperature,T_b =  476.53 K, were derived. The enthalpy of vaporization,ΔlgHmo =  (49.21  ±  0.2)kJ · mol ^− 1, was calorimetrically measured atT =  308.15 K. The experimental and calculatedΔlgHmo values were found to agree within the error limits. Densities of the liquid phase were measured at the temperatures (293.15, 298.15, and 303.15) K. The experimental vapour pressures of 1,3-dimethyladamantane and of the previously studied 1,3,5-trimethyladamantane were extrapolated to the regions of the liquid phases from the triple to the critical temperatures.     

Thermodynamic study on the sublimation of six methylnitrobenzoic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T =  357.16 K and T =  371.16 K; 2-methyl-6-nitrobenzoic acid, between T =  355.16 K and T =  369.16 K; 3-methyl-2-nitrobenzoic acid, between T =  371.16 K and T =  385.14 K; 3-methyl-4-nitrobenzoic acid, between T =  363.21 K and T =  379.16 K; 4-methyl-3-nitrobenzoic acid, between T =  363.10 K and T =  377.18 K; 5-methyl-2-nitrobenzoic acid, between T =  355.18 K and T =  371.08 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p^o =  10⁵Pa, molar enthalpies Δ_cr^gH_m^o, entropies Δ_cr^gS_m^oand Gibbs energies Δ_cr^gG_m^oof sublimation at T =  298.15 K, were derived:     

Excess thermodynamic functions derived from densities and surface tensions of (p- or o-xylene + ethylene glycol dimethyl ether) between the temperatures (298.15 and 308.15) K

Densities (ρ) for binary systems of (p-xylene or o-xylene + ethylene glycol dimethyl ether) were measured over the full mole fraction range at the temperatures of (298.15, 303.15 and 308.15) K along with the densities of the pure components. The excess molar volumes (V^E) calculated from the density data show that the deviations from ideal behaviour in the two binary systems are negative, and they become more negative with the temperature increasing. Surface tensions (σ) of these binary systems were determined at the same temperatures (298.15, 303.15 and 308.15) K by the pendant drop method. The surface tension deviations (δσ) for p-xylene system are negative over the whole composition range, and become less negative with the temperature increasing, but for the o-xylene system, δσ are negative at high o-xylene concentration, and change to positive with the o-xylene concentration decreasing. The V^E and δσ were fitted to the Redlich–Kister polynomial equation. Surface tensions were also used to estimate surface entropy (S_σ) and surface enthalpy (H_σ).     

Thermodynamic study on the sublimation of 1,2-diphenylethane and of 3-phenylpropiolic acid

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline compounds: 1,2-diphenylethane (bibenzyl), between T =  289.16 K and T =  303.20 K, and of 3-phenylpropiolic acid between T =  329.15 K and T =  343.15 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental range were derived by the Clausius–Clapeyron equation. From these results the standard, p^o =  10⁵Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T =  298.15 K, were calculated:     

Column packings for high-performance liquid chromatography and positron annihilation lifetime spectroscopy

Positron annihilation measurements as a function of temperature and the length of bonded alkyl groups have been carried out on silica gel samples. Silica gel samples were bare and bonded with alkyl group from C1 up to C18. The diameters of pores were deduced from the lifetime of trapped ortho-positronium (o-Ps), and it was found that o-Ps lifetime provides reasonable information on the pore sizes for both bare and alkyl bonded silica gels.     

Phase transitions on (liquid + liquid) equilibria for (water + 1-methylnaphthalene + light aromatic hydrocarbon) ternary systems at T = (563, 573, and 583) K

Phase transitions for (water + 1-methylnaphthalene + light aromatic hydrocarbon) ternary systems are observed at their (liquid + liquid) equilibria at T = (563, 573, and 583) K and (8.6 to 25.0) MPa. The phase transition pressures at T = (563, 573, and 583) K were measured for the five species of light aromatic hydrocarbons, o-, m-, p-xylenes, ethylbenzene, and mesitylene. The measurements of the phase transition pressures were carried out by changing the feed mole fraction of water and 1-methylnaphthalene in water free, respectively. Effects of the feed mole fraction of water on the phase transition pressures are very small. Increasing the feed mole fraction of 1-methylnaphthalene results in decreasing the phase transition pressures at constant temperature. The slopes depending on the feed mole fraction for 1-methylnaphthalene at the phase transition pressures are decreased with increasing temperature for (water + 1-methylnaphthalene + p-xylene), (water + 1-methylnaphthalene + o-xylene), and (water + 1-methylnaphthalene + mesitylene) systems. For xylene isomers, the highest and lowest of the phase transition pressures are obtained in the case of p- and o-xylenes, respectively. The phase transition pressures for ethylbenzene are lower than those in the case of p-xylene. The similar phase transition pressures are given for p-xylene and mesitylene.     

Equilibrium solubility of sodium 2-naphthalenesulfonate in binary (sodium chloride + water), (sodium sulfate + water), and (ethanol + water) solvent mixtures at temperatures from (278.15 to 323.15) K

The equilibrium solubility of sodium 2-naphthalenesulfonate in binary (sodium chloride + water), (sodium sulfate + water), and (ethanol + water) solvent mixtures was measured at elevated temperatures from (278.15 to 323.15) K using a steady-state method. With increasing temperatures, the solubility increases in aqueous solvent mixtures. The results of these results were regressed by a modified Apelblat equation. The dissolution entropy and enthalpy determined using the method of the least-squares and the change of Gibbs free energy calculated with the values of Δ_diffS^o and Δ_diffH^o at T = 278.15 K.     

Thermodynamic study of the sublimation of crystalline tris(1,1,1-trifluoro-2,4-pentanedionate)ruthenium(III) and tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)ruthenium(III)

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of two crystalline ruthenium complexes: tris(1,1,1-trifluoro-2,4-pentanedionate)ruthenium(III) {Ru(tfacac)₃}, between T =  350.20 K and T =  369.17 K and tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)ruthenium(III) {Ru(hfacac)₃} between T =  299.15 K and T =  313.14 K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. By using an estimated value for the heat capacity differences between the gas and the crystal phases the standard, p^o =  10⁵Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T =  298.15 K, were derived: