Positron Annilation Lifetime and Glass Transition Temperatures in CO₂Sorption Polystyrene

Abstract

Positron annihilation lifetime spectroscopy was used to measure the freevolume size and distributions as a function of temperature in polystyrene with and without 400 psi CO 2 sorption. The transition temperatures in the polystyrene with CO2 sorption obtained from ortho-positronium lifetimes were found to depend on the thermal cycles and a meta-stable state showing a negative thermal expansion coefficient was observed between 53• C and 82• C during the first heating up experiment. The observed T g in polystyrene with, and without CO2 sorption after annealing from ortho-positronium lifetimes were found to be 86• C and 91• C, which are 5 • C higher, and 10 • C lower than from the differential scanning calorimetry data, respectively. The observed free-volume variations are discussed in terms of hole expansion, creation, free-volume relaxation, plasticization, and hole filling in amorphous polymers.

Investigation on positron annihilation characteristics of CO2-exposed zeolite

“…There have been a lot of researches using many techniques that discuss the effect of plasticization caused by CO 2 on the variation of pore size (or free-volume) in membranes. Among of these techniques, the positron annihilation spectroscopy (PAS) technique is a sensitive probe for determining the average size and size distribution of pores [11][12][13][14][15].…”

Investigating the glass transition temperature at the atom-level in select model polyamides: A molecular dynamics study

“…This can manifest in a discontinuity at T g , a feature which has been demonstrated in numerous molecular dynamics [5,58] and experimental [58][59][60][61] studies. Experimentally this free volume can be measured using PALS [58,59,62] which have been shown to agree with FCV calculations through CESA. To determine if this characteristic is also apparent among these model polyamides, values of T g were extracted from a plot of FCV vs. temperature (see Figure 11).…”

Annealing Effect Reversal by Water Sorption–Desorption and Heating above the Glass Transition Temperature—Comparison of Properties

“…At room temperature the drop-off in the fractional free volume of trehalose was 1.1−1.4%, while in polymers the reported range is 2.5−10%. 20,35 Effect of Annealing on Fractional Free Volume. Annealing caused a small decrease in the o-Ps lifetime (τ 3 ) with no appreciable change in intensity (I 3 = 22%).…”

“…The measured o-Ps lifetime and intensity are respectively related to the free volume hole size and number of holes in the system. 20,21 Aging of an amorphous pharmaceutical (API or excipient) can bring about undesirable changes in properties. Heating above T g (HAT) and water sorption−desorption (WSD) are two possible strategies to reverse the aging effect.…”

“…Due to its relatively small size (1.59 Ǻ) and localization, Ps can be considered a microprobe of free volume holes. The measured o-Ps lifetime and intensity are respectively related to the free volume hole size and number of holes in the system. , …”