K. Jerie

Positron Annihilation in and Compressibility of Water-Alcohol Mixtures

In our recent paper we found that long lived component of lifetime spectrum τ2, which is connected with pick-off ortho-positronium annihilation and its intensity do not change monotonically with the concentration of organic components in water. The results obtained confirm the thesis of quasi-crystalline, clathrate-like structure of water-tetrahydrofuran and water-cyclohexylamine systems. The attempt of the present work was to study the structure of water-ethanol, water-n-propanol and water-isopropanol mixtures, their clathrate-likeness and stoichiometry, if any. The results of our measurements of positronium lifetime, in particular the component τ2 and the intensity I2 as well as the sound velocity data allow us to suppose that in the systems the liquid clathrate-like hydrates are formed. The stoichiometry of these structures was deduced. The results, although obtained using strongly different experimental methods, i.e., positron annihilation and acoustic measurements, are in very good agreement with the clathrate-like concept of the structure of water-organic mixtures.

Peculiarity of aqueous solutions of 2,2,2-trifluoroethanol.

Aqueous solutions of 2,2,2-trifluoroethanol appear to show a structural transition at alcohol mole fraction equal to x(TFE) = 0.05, which can be concluded from a discontinuity of the speed of sound. At the same concentration, a discontinuity was observed in the parameters of the long-living component of the positron annihilation spectrum. Moreover, the partial molar volumes of components show transition-like behavior in the range of low solute contents, which is significantly different from nonsubstituted ethanol. The peculiarities of the low concentration system correlate with minor infrared spectra changes assigned to a mode composed of the CH(2) bending and CF(3) stretching internal vibrations being sensitive to polarity of the hydration shell surrounding the solute. The majority of the spectral changes arise from a gradual shift of the equilibrium between trans ↔ gauche isomers when the composition of the solution is changing. A possible explanation for the peculiar behavior of the system is a thermodynamic equilibrium between hydrated monomers and dimers at that respective mole number.

Structure of aqueous solutions of tetraethylammonium chloride investigated by positron annihilation and ultrasonic methods

The structure of aqueous solutions of tetraethylammonium chloride was investigated using compressibility and density measurements and positron annihilation methods. The experimental results are different from those obtained earlier for systems where hydrophobic hydration dominates, although some evidences for formation of cage-like hydrates in liquid phase were observed. The results are interpreted, among others, in terms of competition among different hydrates of the tetraethylammonium cations, hydration of chloride anions, and formation of ionic pairs.

Investigation of the structure of aqueous solutions of 1,2-and 1,4-butanediol by positron annihilation and ultrasonic methods

The structure of aqueous solutions of 1,2-butanediol and 1,4-butanediol was investigated using adiabatic compressibility measurements and positron annihilation methods. In the case of 1,2-butanediol the experimental results are very similar to those obtained earlier for systems where hydrophobic hydration dominates. In both cases there are evidences for increased rigidity of the water network, which arises from the formation of hydrogen bonds between diols and water. The usefulness of both the methods applied in investigating the structure of liquid solutions was proved.

Determination of non-homogeneity in Vycor glasses by means of positron annihilation and analysis of electron microscope images

Abstract The paper presents results of measurements of heterogeneity of Vycor-type glasses, which contain pores. Concentrations and sizes of the pores affect glass quality and transmission of light. Lifetime parameters of positron annihilation in the samples have been measured. The same material was next investigated by means of electron microscopy to observe pores and measure their sizes. Comparison of the two measurements was then made; a correlation between the average lifetime for the long-life component, τ2 (as obtained from the annihilation measurement), and average cavity radii (as obtained from the analysis of electron microscope images) was found.

POSITRON ANNIHILATION IN AND COMPRESSIBILITY OF LIQUID WATER + TERT-BUTYL ALCOHOL MIXTURES

Abstract Aqueous solutions of tert-butyl alcohol (2-methyl-2-propanol) were investigated using sound velocity and positron annihilation methods. The results are interpreted in terms of changing the structure of the solution, especially the formation of clathrate-like hydrates. The annihilation method was found to be applicable for investigating the structure of aqueous solutions of nonelectrolytes; the lifetime and intensity of the long-lived component of the annihilation spectrum were found to be sensitive for structural rearrangements in liquid.

Hydrophobic-like solvation in non-aqueous solutions: Positron annihilation in and compressibility of n-hexanol in ethylene glycol, 1,2-butanediol and 1,4-butanediol

The results of positron annihilation experiments of solutions of n-hexanol in diols are compared to those of ultrasonic velocity and absorption. Variations of the annihilation parameters with composition allow the conclusion that the effect of hydrophobic solute on the original diol structure is limited. There are, however, significant similarities with the results known for aqueous systems, suggesting that clathrate-like solvates are forming in ethylene glycol, the phenomenon called here is a hydrophobic-like solvation. No evidences for it were found for the systems containing butanediols as solvents. Unfortunately, ultrasonic investigations do not confirm the formation of any specific structures, most possibly because the compressibilities of solvates are close to those of the pure components.

Positron annihilation in and compressibility of water-organic mixtures : aqueous solutions of formamide and ethylene glycol

The positron annihilation lifetime and ultrasonic velocity were measured in water+ formamide and water+ethylene glycol systems. The comparison between the concentration and temperature dependences of the results suggests that hydrophylic (substitutional) hydration plays dominating role in structuring the systems under investigation.

Influence of substituents on positron annihilation in styrene copolymers

Results of angular correlation of annihilation radiation (ACAR) and positron annihilation lifetime (PAL) measurements are presented for five styrene copolymers: poly(co-styrene-phenylmaleimide) and its three derivatives with chlorine as well as for one with the OH group substituted at the benzene ring. It occurs that the chlorine substituted at three different positions at the benzene ring poly(co-styrene-o (or-m,-p)-chlorophenylmaleimide) inhibits the formation of the positronium to different extent. The greatest effect is observed in case of the chlorine atom substituted at the benzene ring at the ortho-position towards the nitrogen atom. The two long lifetimes (τ3 and τ4) observed in the lifetime spectra are connected with the bimodal distributions of the free volume radius in the samples.

Positron Annihilation in and Compressibility of Aqueous Solutions of 1,2- and 1,6-Hexanediols

The results of positron annihilation experiments in aqueous solutions of 1,2- and 1,6-hexanediols were compared to those of ultrasonic velocity. For the former, the positron annihilation measurement shows strong hydrophobic interactions and formation of clathrate-like hydrates in solution, although their stoichiometries as well as architecture are untypical. Ultrasonic data for this system seem to be strongly influenced by a relaxation process and do not allow to conclude about formation of open-work structures in this system. For the system water + 1,6-hexanediol both the ultrasonic and annihilation methods suggest formation of labile, water-rich hydrates. They are very weak compared to those existing in the water + 1,2-hexanediol, what results from the hydrophilic hydration competing the hydrophobic one.