Hydrogen Adsorption by δ and ε Crystalline Phases of Syndiotactic Polystyrene Aerogels

Abstract

The H2 uptake from s-PS samples exhibiting different crystalline phases and different morphologies has been studied by gravimetric measurements at 77 K in the hydrogen pressure range from 0 up to 1.7 MPa and compared with molecular simulations relative to s-PS crystals. Gravimetric experiments show that the molecular hydrogen sorption is strongly dependent on the sample morphology and is maximum for low-density polymer aerogels. However, independently of the morphology, the H2 uptake is minimum for the dense β and γ crystalline phases, intermediate for the channel-shaped nanoporous ε phase, and maximum for the cavity-shaped nanoporous δ phase. In particular, although the two nanoporous crystalline phases present essentially the same density (0.98 g/cm3), the hydrogen uptake from the δ phase is roughly double with respect to the uptake from the ε phase, both for powders and for aerogels. Infrared measurements and molecular simulations well agree with these quantitative sorption data and clearly indicate that, for both low and high pressure, the hydrogen molecules are preferentially adsorbed into the nanoporous crystalline phases. In particular, molecular simulations indicate that the maximum average hydrogen uptake is of nearly 3 molecules per cavity of the δ phase and of nearly 3.5 molecules per unit height of the channels of the ε phase.

Factors controlling the structure of syndiotactic polystyrene upon the guest exchange and guest extraction processes

“…The unit cell of nanoporous δ (δ e ) contains eight styrene monomeric units along with two identical cavities with density 0.98 g/cm 3 , whereas the density of the amorphous phase is 1.05 g/cm 3 [14,42]. These nanoporous crystalline forms were found to have the capability to absorb molecules like CO 2 and H 2 [44,45] as well as organic molecules [16,46]. Hence, these materials can be used as sensors, [47][48][49][50] molecular sieves, [46,[51][52][53], catalysts [54], etc.…”

Syndiotactic polystyrene films with a cocrystalline phase including carvacrol guest molecules

“…The thermoplastic nature of these materials allows an easy processing to products suitable for several applications, like films, membranes, and foams, as well as their recycling. As a consequence, a number of applications in the field of chemical separations, molecular sensorics, and catalysis for these inexpensive and reusable materials have been proposed.…”

Crystalline Nanoporous Materials Based on Poly(2,6‐dimethyl‐1,4‐phenylene)oxide

“…For syndiotactic polystyrene it has been shown that the sorption kinetics but also the uptake values for molecules presenting a poor solubility in the polymer amorphous phase depend on the sample morphology. In particular it has been observed that both kinetics and uptake values can be greatly increased by using aerogels instead of powder or film samples.…”