Positron annihilation lifetime studies of gas sorption and desorption in polyethylene and poly[1‐(trimethylsilyl)‐1‐propyne]

Abstract

ABSTRACT:The variation of free-volume parameters (lifetime, intensity, and distribution) after sorption and desorption of CO 2 and CH 4 gases in the glassy polymer poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and in the rubbery high-density polyethylene (HDPE) and low-density polyethylene (LDPE) were determined by the PAL technique. Size distributions deduced from PAL measurements reveal the presence of large free-volume holes in PTMSP with an average size of 0.725 nm 3 and intensity of 22% in addition to a free-volume hole size of 0.197 nm 3 with an intensity of 11%. In polyethylene free-volume hole sizes of 0.107 and 0.153 nm 3 with intensities of 21% and 25% could be deduced for HDPE and LDPE, respectively.

Free Volume Expansion of Poly[1-(trimethylsilyl)-1-propyne] Treated in Supercritical Carbon Dioxide As Revealed by Positron Annihilation Lifetime Spectroscopy

“…The effect of the scCO 2 treatment of the PTMSP films on the o -Ps lifetimes τ 3 and τ 4 is shown in Figure . Treating the films with pressurized CO 2 clearly induces an increase of the initial free volume, as reported for other polymers. ,,, For the present PTMSP system, both lifetimes τ 3 and τ 4 significantly increase compared to the untreated reference sample. For the scCO 2 -treated samples in the temperature range of 40−110 °C, increasing the treatment pressure has no significant effect on τ 3 and τ 4 .…”

“…These values are much larger than those reported in the literature for a similar PTMSP system treated in a CO 2 atmosphere at mild conditions. Mohsen et al observed a 7.4% increase of both lifetimes τ 3 and τ 4 for PTMSP after desorption of CO 2 at 1 bar and room temperature, thus demonstrating the large effect of pressure and temperature on the free volume expansion of scCO 2 -treated PTMSP. For other polymers like poly(ethylene naphthalate) and syndiotactic polystyrene, o -Ps lifetime increases up to ∼10% were reported after scCO 2 treatments of 6 h at 20 MPa and 100 °C and 3−10 h at 16 MPa and 40 °C, respectively.…”

“…The PALS spectra of high free volume polyacetylenes like PTMSP are typically analyzed with a four-component analysis. ,,, The third lifetime (τ 3 ) represents the channel-like holes interconnecting the larger cages which are in turn represented by the fourth lifetime (τ 4 ). The effect of the scCO 2 treatment of the PTMSP films on the o -Ps lifetimes τ 3 and τ 4 is shown in Figure .…”

“…Mohsen et al studied the free volume parameters of PTMSP after sorption and desorption of CO 2 and CH 4 gases. 34 However, the authors only reported data of PTMSP samples treated at mild conditions, i.e., 1 bar and room temperature.…”

“…Pressurized or supercritical CO 2 is known to swell and plasticize glassy polymers, leading to a depression of their T g to almost the same extent as solvents or vapors. , The effect of scCO 2 or compressed CO 2 on the physical properties, free volume, or crystal structure of several polymers has been reported, − but high free volume polyacetylenes have hardly been investigated. Mohsen et al studied the free volume parameters of PTMSP after sorption and desorption of CO 2 and CH 4 gases . However, the authors only reported data of PTMSP samples treated at mild conditions, i.e., 1 bar and room temperature.…”