Positronium formation and thermostimulated luminescence: A common nature and combined application to studies of organic systems

Abstract

Polymeric membrane materials with highly developed intrinsic microporosity for gas separation are studied. The porosity can be essentially improved by filling the polymer with nonorganic components (zeolites). This porosity, herein referred to as artificially induced, turned out, in some cases, to be higher than that of the con stituent components. The reasons for this effect are not always clear. To gain additional insights into the nature of this effect, an experimental study is suggested with the use of a combination of two methods related by being based on track processes: positron annihilation lifetime spectroscopy PALS and thermostimulated luminescence (TSL). The present paper summarizes and discusses both recently published results and completely new data.

Specifics of positron studies of microheterogeneous systems as applied to new polymeric sorbents

“…At a low temperature, the positronium formation rate and the integrated (over wavelength) TSL intensity [14,15] depend on the buildup of weakly bound electrons (track electrons) and are prone to optical quenching (bleaching). These results are another piece of evidence for the spur mechanism of positronium formation [16,17].In [18][19][20], we showed the effectiveness of the combined use of the room temperature PALS and low temperature TSL methods for investigation of some new membrane materials including materials with a heterogeneous structure. The following logic was adopted.…”

“…without spe cial measurements, using the PALS and TSL data alone. Moreover, the studies [18][19][20] showed the TSL technique to be more responsive to a change in the character of porosity and specific surface area that leads to alteration of the functional properties of membrane materials and sorbents. This brings up the question of what is the minimal concentration of pores determinable by the positron technique.…”

“…In [18][19][20], we showed the effectiveness of the combined use of the room temperature PALS and low temperature TSL methods for investigation of some new membrane materials including materials with a heterogeneous structure. The following logic was adopted.…”

“…In our case, the shape of the TSL emission curve is characterized by the relative intensity of its high temperature (above 200-250 K) component (so called α parameter) [18]. In [18][19][20][21][22], the correlation of PALS data on the pore size (effective radius), oxygen permeability P(O 2 ), and α was illus trated by data for a number of polymer and composite membrane materials. The results confirm the idea [23][24][25] that there is a relation between permeability, free volume, and local stiffness (local stresses, steric hindrances) in the polymer matrix.…”