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.

A mechanism of H(2) uptake, based on adsorption in the ordered cavities of nanoporous polymeric crystalline phases rather than on disordered amorphous polymeric surfaces, has been clearly established, for aerogels of syndiotactic polystyrene (s-PS) exhibiting the nanoporous δ phase. An ordered arrangement of the H(2) molecules is proven by FTIR spectra while the inclusion of H(2) is assessed by gravimetric measurements and molecular simulations.

Using the Kierlik and Rosinberg fundamental measure theory, we test the density functional theory method for determination of pore size distributions from adsorption data for porous glasses. The glasses chosen for study are model glasses prepared by a quench molecular dynamics method that mimics the experimental synthesis process and are completely characterized at the molecular level. The density functional method involves two approximations:  (a) the glasses can be regarded as made up of a distribution of nonconnected pores of simple geometry, which we refer to as the independent pore model, and (b) the adsorption isotherms for these nonconnected pores can be described by the density functional theory. Using simulated adsorption isotherm data for the glasses and adsorption isotherms for the pores of simple geometry calculated by the density functional theory, a regularization method is used to determine the pore size distribution from the adsorption data. These calculated pore size distributions, as well as the adsorption isotherms for the materials, are compared with the exact geometric pore size distributions for the material and with the simulated isotherms. Both slit-shaped and cylindrical pores are used in the density functional theory method. It is found that a unique geometry is not able to accurately describe the whole adsorption isotherm. The use of slit-shaped pores gives overall better results, although the low-pressure regime is more accurate when cylindrical pores are used; reasons for this are discussed. The pore size distributions from the density functional theory are in reasonable agreement with the geometrical ones, giving the same shape and mean pore width and similar porosities in the four materials. Since it is known that the density functional theory gives excellent results for the adsorption isotherms (approximation b above), this comparison tests the independent pore model directly.

Because this issue journal is dedicated to Gelatin, here we present a few applications of gelatin in the field of optics. Optics is the science that studies the production, propagation, interaction and detection of light. Various materials sensitive to light (photosensitive) are used for detection of light, such as photomultipliers, CCDs, crystals, two dimensional (2D) materials and more. Among the 2D materials, the most popular for several centuries has been gelatin based photographic emulsion, which records spatial distributions of light. More recently (1970), films made of Gelatin with Dichromate (DCG) and dyes have been used. We describe some characteristics and applications of these two photosensitive materials. We also describe examples where gelatin is used as a Relative Humidity (RH) sensor and in the fabrication of optical elements based on gelatin. This article is intended for researchers outside the optics community.