Determination of Free-Volume Properties in Polymers Without Orthopositronium Components in Positron Annihilation Lifetime Spectroscopy

Abstract

Existing positron annihilation lifetime spectroscopy (PALS) uses the orthopositronium components, lifetimes, and intensities observed in molecular substrates, such as in polymers, to determine free-volume properties based on an infinitive potential spherical model originally proposed by Tao in 1972. However, in many molecular systems, positronium is either quenched or inhibited by interacting with chemical functional groups and leads to no or nearly no orthopositronium component in PALS. In this Article, a newly modified equation is developed by following the Tao’s quantum model using the positron component (not orthopositronium) of PALS. This modified equation is examined by fitting free-volume results obtained from o-Ps lifetimes with the positron lifetimes in pressure- and temperature-dependent data in polymers and calibrated with known or calculated cavity sizes in zeolite materials. A newly modified positron lifetime-free volume correlation equation is established for the determination of free volumes up to the mean radius of 5 Å in polymeric systems, where no orthopositronium component is observed in PALS.

Free-volume correlations in positron-sensitive annihilation modes in chalcogenide vitreous semiconductors: on the path from illusions towards realistic physical description

“…In this case, C converges into intrinsic defect-free bulk positron lifetime  b (e.g. experimental lifetime of positrons trapped in voids of vanishing sizes R0) and ΔR approaches the electron layer thickness for positron penetration wall region of free-volume trapping void [16][17][18][19][20][21]. It is quite understandable that both parameters are entirely defined by materials chemistry of positron trapping sites.…”

“…It was firstly fitted with void sizes in molecular and zeolite systems to reflect the case of intrinsic vacuum decay [25]. Under essential effect of chemical environment in positron-electron interaction, this  2 -R correlation can be simply parameterized in respect to the generalized master equation below with material-related parameters C and ΔR [16][17][18][19][20][21]:…”

“…(1) can be fitted to known experimental data giving a suitable form of this analytical correlation to calculate radii R(Å ) of freevolume voids responsible for positron trapping with the lifetime  2 (ns). Thus, it was shown [16] that for molecular substrates, such as polymers, the corresponding equation calibrated with known or calculated cavity sizes of some zeolites and molecular sieves can be adequately presented as:…”

“…Under this condition, the Ps annihilation lifetime  3 can be substituted by defectrelated positron lifetime  2 extracted from the same twostate trapping model, provided both positron and o-Ps are trapped before annihilation similarly [16][17][18][19][20][21]. So, this method gives a rough estimation procedure, which allows only evaluate an expected void size in solids within a sequent  3 - 2 -R correlation, the void characteristics being considerably dependent on preferential chemistry of positron trapping sites.…”

Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation

“…Also, attempts have been made to create a model using a positron component, which could be applicable when o-Ps is not formed in available free volumes [6].…”