Syndiotatic Polystyrene Aerogels with β, γ, and ε Crystalline Phases

Abstract

The influence of thermal treatments and supercritical carbon dioxide extraction procedures on the crystal structure and morphology of sPS aerogels is investigated mainly by wide-angle X-ray diffraction and scanning electron microscopy. The use of supercritical CO2 extraction treatments allows the obtaining of high porosity aerogels with fibrillar morphology, not only exhibiting the nanoporous δ phase but also the dense γ and β crystalline phases. Moreover, a procedure to obtain high-porosity aerogels exhibiting the recently discovered nanoporous ε-form is described. Measurements of the sorption capacity of organic molecules from diluted aqueous solutions, for aerogels presenting different crystalline phases, clearly indicate that ε-form aerogels are the only ones suitable for detection and removal of long organic pollutants.

Absorption Kinetics of Phenol into Different Size Nanopores Present in Syndiotactic Polystyrene and Poly (p-methylstyrene)

“…[35,36] The absorption rate of solvent molecules was enhanced by a porous aerogel with a mesh structure, which was prepared by treating the sPS gel in scCO2. [37][38][39] The relationship between the size of the solvent molecule and the cavity volume of e-sPS was reported by Tsujita et al [40][41][42][43] It was shown that the cavity volume of -sPS is reduced after extracting the solvent molecules.…”

Monolithic aerogels with nanoporous crystalline phases

“…1,2 It has been shown that CO2 extraction of s-PS thermoreversible gels leads to a special class of monolithic physically crosslinked aerogels, where the crystallites that constitute the physical knots of the aerogel exhibit a nanoporous crystalline phase. [3][4][5] These nanoporous crystalline aerogels present, beside disordered amorphous mesoand macropores (typical of all aerogels), also all identical nanopores of the crystalline phases.…”

“…6 This result is due to the formation of a spherulic morphology in PPO gels rather than a fibrillar morphology as observed in s-PS gels. 3,5 However it has been shown that monolithic PPO based aerogels with nanoporous crystalline phases can easily be obtained starting from mixed PPO/s-PS gels thanks to fibrillar morphology ensured by s-PS. 6 The association of amorphous meso-and macropores and crystalline nanopores confers unique properties to this new type of material.…”

“…6 The association of amorphous meso-and macropores and crystalline nanopores confers unique properties to this new type of material. In particular sorption studies of VOC from aqueous diluted solutions 4,5,6 or from air at low vapor pressures 3 have shown that these aerogels present the fast sorption kinetics typical for aerogels (due to the high porosity and the large pore size) and a high sorption capacity characteristic (due to the sorption of the organic molecules in the host nanopores of the crystalline phase). These sorption properties as well as their good handling characteristics makes these new materials particularly suitable as a sorption medium to remove traces of pollutants from water and air.…”

Sorption of Pollutant Traces by Nanoporous Crystalline Aerogels: Visualization by a Dye

“…It has been shown recently that high porosity syndiotactic polystyrene (sPS) aerogels can be obtained by supercritical CO 2 extraction of the solvent present in the native sPS physical gels [1][2][3] or by sublimation of the solvent. [4][5] The advantage of using a supercritical extraction process to remove the solvent from the gel is the absence of surface tension and in these conditions a supercritical solution is formed between supercritical CO 2 and liquid solvent.…”