Free-volume studies in polyurethane membranes by positron annihilation spectroscopy

Abstract

The free-volume parameters in various urethane/urea membranes obtained by varying the ratio of the structural constituents, polypropylene oxide and polybutadiene, were studied by positron lifetime and Doppler broadening measurements. On bi-soft segment membranes, a correlation was found between the composition of membranes, the normalized free volume, the radii of the holes and gas permeability. However, the correlation is not clear when PU data are also considered, indicating that other features must also play an important role in the permeation mechanism.

Positron studies of the temperature-dependence of free volumes in Polydimethylsiloxane/poly(propylene oxide) urethane/urea membranes

“…In the present work, which is an extension of our previous studies (Ferreira Marques et al, 2003, 2004 polyurethane/urea membranes obtained through the introduction of two soft segments, poly(propylene oxide) and polydimethylsiloxane, were studied by PALS and Doppler broadening with the aim of establishing how the free-volume holes are influenced by phase separation and how the free volume is correlated with permeability.…”

Application of Poly (Tetraflouroethylene) Grafted with Styrene/Acrylic Acid for Proton Exchange Fuel Cell

“…But at ambient temperature the effect of uncoiling molecular chains was not obvious. So, the understudied membranes were recommended to be used onto the fuel cell at 80 o C. Positron annihilation lifetime spectroscopy is an important method for studying sub-nanometer free volumes sizes and for determination of the free volume fractions (28,29) . Increasing grafting yield and furthermore sulfonation revealed increase in the membranes free volumes.…”

The use of positron annihilation Doppler broadening spectroscopy in the characterization of radiochromic dosimetry films

“…Positron lifetime, Doppler broadening and angular correlation are the three main techniques of PAS can be used to extract basic structural features of studied samples (Schrador and Jean, 1988;Dupasquier and Mills, 1995). The PAS has been used to probe the defects and open-volumes in different types of solids (Marques-Netto et al, 2001;Abdel-Hady and Mohamed, 2002;Ferreira Marques et al, 2003;He et al, 2004;Abdel-Rahman et al, 2006a;Flounis-Mokrani, 2013). The embedded positron can preferentially be localized at various types of defects in solids and annihilate with an electron of the atoms of materials through g-ray annihilation radiation.…”