Free Volume Expansion and Nanofoaming of Supercritical Carbon Dioxide Treated Polystyrene

Abstract

Free volume of polystyrene films treated with supercritical carbon dioxide (SCCO 2) were examined by positron annihilation lifetime spectroscopy. Variation of the free volume sizes after the SCCO 2 treatment due to the release of trapped CO 2 and structural relaxation of the polymer was observed. After 500 h from the depressurization, the free volume of the treated films free from CO 2 was approximately 0.306 nm in radius and much larger than that of the untreated films of approximately 0.295 nm in radius due to the freezing of the swollen structure caused by the large solubility of CO 2.

Impact of Heating on the Structure of Perfluorinated Polymer Electrolyte Membranes: A Positron Annihilation Study

“…Following a number of successes in the past, the positron annihilation lifetime (PAL) technique has been used for sensitively probing the nanostructure of various polymers. [6][7][8][9][10] Positrons emitted from a radioactive atom (most commonly 22 Na) slow down quickly in a polymer and survive until annihilation either in the form of free positrons or as hydrogen-like positronium atoms (Ps). Depending on the spins of the electron and the positron, Ps can form as para-Ps ( p-Ps, singlet spin of the positron and the electron) or ortho-Ps (o-Ps, spin triplet).…”

Free volume, oxygen permeability, and uniaxial compression storage modulus of hydrated biphenol-based sulfonated poly(arylene ether sulfone)

“…Nanometer sized free volume holes in a polymer, whether or not hydrated, can be probed by positron annihilation lifetime (PAL) spectroscopy, as long as a reasonable fraction of the positrons form positronium (Ps), the positron-electron bound state [14][15][16][17][18]. Ps is formed by a reaction between a positron and one of the electrons, ionized and liberated from the polymer molecules by the energetic positron itself, in the terminal positron spur [19].…”

Positron Annihilation Studies of the Free Volumes in Nylon12/PVA Films Treated by Supercritical Carbon Dioxide

“…Over the past three decades, numerous polymers [1][2][3][4][5][6][7][8] including bulk materials and thin films, either amorphous or semi-crystalline polymers, have been found to be able to dissolve or swell in ScCO 2 with large density fluctuations [9][10][11]. However, very little is clearly known about the interaction between CO 2 and the polymers.…”