A Hyphenated Approach Combining Pressure-Decay and In Situ FT-NIR Spectroscopy to Monitor Penetrant Sorption and Concurrent Swelling in Polymers

Abstract

A new hyphenated technique based on simultaneous in situ FT-NIR spectroscopy and pressure-decay measurements has been implemented to study sorption of low-molecular-weight compounds in polymeric membranes and the induced swelling of the matrix. The FT-NIR measurements are performed in the transmission mode and, besides sorption equilibrium and kinetics, allow also the straightforward measurement of polymer swelling. The pressure decay method is used to provide quantitative information on the concentration of penetrant sorbed in the polymer. This measurement, once combined with the photometric data, allows an accurate estimation of the molar absorptivity of the analytical peaks as well. To validate the new experimental approach, sorption of CO2 in polydimethylsiloxane at 35 °C and at pressures up to 9 bar has been investigated and the results are compared with available literature data.

Sorption of CO2, CH4 and their mixtures in Amorphous Poly(2,6-dimethyl-1,4-phenylene)oxide (PPO)

“…Our results are in excellent agreement with those from Story and Koros as expected since the sample preparation method was the same and the density of the two amorphous samples were very close (1.068 g cm -3 for our samples vs a value of 1.063 g cm -3 in the case of the samples used by Story and Koros) [7,40]. Conversely, the solubility data reported by Galizia et al [38] are systematically lower than the ones we obtained and, specifically, in the case of carbon dioxide and methane an average reduction of 20% and 76% of the solubility coefficient is observed, respectively. The reason lies in the different method of preparation of the samples that in [38] were melt at 290°C and then compression molded, thus resulting in a lower film density equal to 1.016 g cm -3 .…”

“…The concentration of the gas is evaluated from the NIST Standard Reference Database 69: NIST Chemistry WebBook [37]. The same approach has been already adopted to investigate the sorption of CO2 in polydimethylsiloxane [38]. In that case, a single polymer slab was tested while, in the present case, multiple pieces of PPO were inserted into the volume of the measuring chamber to reduce the uncertainty of the solubility measurement.…”

Weak Interactions between Poly(ether imide) and Carbon Dioxide: A Multiscale Investigation Combining Experiments, Theory, and Simulations

“…Considering first the antisymmetric stretching of CO 2 , it is known that, according to the theory of vibrational line shapes, the profile of this transition can be described by the sum of a Gaussian and a Lorentzian band shape, both centered at the peak maximum. The two-component profile is evident in systems with no molecular interactions . In the case of a collisional relaxation mechanism, this complex band shape is due to the probe dynamics, in particular to free rotation in the early stages of the relaxation process, producing the Gauss component and a faster decay at later stages, giving rise to the Lorentz band.…”

“…The two-component profile is evident in systems with no molecular interactions. 80 In the case of a collisional relaxation mechanism, this complex band shape is due to the probe dynamics, in particular to free rotation in the early stages of the relaxation process, producing the Gauss component and a faster decay at later stages, giving rise to the Lorentz band. Whenever a Gaussian component is evident, a significant free-rotation regime exists, which, in turn, indicates that the probe interrogates a poorly or noninteractive environment with a sizable free volume.…”

“…The mutual diffusivity coefficient, D 12 , in a penetrant–rubbery polymer binary system can be expressed − in terms of the so-called intra diffusion coefficient of the penetrant, D 1 , that represents the intrinsic mobility of penetrant in a binary mixture in the case of a null value of the gradients of the chemical potentials of the two components: D 12 = D 1 p = D 1 ρ p V̂ p ρ 1 true( ∂ μ 1 ∂ ρ 1 true) T , P , ρ p R T This equation holds true not only at small penetrant concentrations but also over a major portion of the concentration interval of the binary system. , In eq V̂ p is the partial mass volume of the polymer in the mixture.…”