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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 structure of solution, especially formation of clathrate-like hydrates. The annihilation method was found to be applicable for investigating the structure of aqueous solutions of non-electrolytes. Resolution of annihilation spectrum into three components (instead of two) yield non-physical parameters, suggesting that the short-lived mechanisms of annihilation of positrons are too close to be separated.

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Abstract  

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.

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Abstract  

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.

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Abstract  

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.

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Abstract  

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.

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Abstract  

Experimental results of positron annihilation experiments in solutions of n-butanol in three diols are compared to those of ultrasonic velocity and absorption. Variations of the annihilation parameters with composition show that the effect of the hydrophobic solute on the original diol structure is rather limited and occurs only in the system where ethylene glycol is the solvent. Subtle similarities were found when compared it to the respective results for similar aqueous systems, suggesting that crystalline-like solvates are forming in ethylene glycol. However, no such evidences were found for the systems where butanediols are the solvents. Ultrasonic investigations do not confirm formation of any specific structures. This is caused, most possibly, by the fact that compressibility of solvates is close to those of the pure components and/or that of unstructured medium (regular solution).

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Abstract  

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.

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Abstract  

Positron annihilation has been applied to study samples of two crosslinked epoxy resins: onglycidyl ether of bisphenol A (Epikote 828) and polyglycidyl-ether of phenol-formaldehyde novolac (Epikote 155) cured with 4,4
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, proportional to the fractional free volume in samples. Values of
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have been estimated from the values of 3, the longest lifetime in positron lifetime spectra.I 3 corresponds to the intensity of the longest-lived component in them. Distributions of free volume radii reconstructed on the basis of PAL measurements are given for all samples. The influence of structure of both cured resin and the curing agent on the properties of the crosslinked products is clearly seen from the presented results.
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Journal of Radioanalytical and Nuclear Chemistry
Authors: A. Baranowski, M. Dębowska, K. Jerie, J. Rudzińska-Girulska, Z. Paweŀka, and R. Sikorski

Abstract  

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 ( 3 and 4) observed in the lifetime spectra are connected with the bimodal distributions of the free volume radius in the samples.

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