Free Volume Distributions in Glassy Polymer Membranes:  Comparison between Molecular Modeling and Experiments

Abstract

We compare molecular modeling results of two glassy polymer membranes and one rubbery polymer membrane with gas transport parameters and free-volume-related quantities from positronium annihilation. A simple geometric model reveals hole size distributions of asymmetric shape. Among glassy polymers, the distribution parameters show a good correlation with average hole sizes determined by positron annihilation lifetime spectroscopy. Higher permeability is measured in the glassy polymer with the higher mean value of the hole size distribution. The permselectivity of the membranes for permanent gases can be interpreted in terms of the distribution broadness via free-volume-controlled diffusion selectivity. A comparison with the rubbery polymer shows that the permeation behavior is not determined only by the free volume concentration. The thermal fluctuations of the polymer matrix play an important role for gas transport properties.

Detailed-atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials

“…A quantitative measure for the free volume contents of a polymer is the relative free volume fraction m f . This quantity was about 0.08 for the PAI models and 0.09 for the PDMS model 45) . The observed much higher constants of diffusion in the case of PDMS can be, therefore, mainly related to the described qualitative differences in the dynamic behavior of PAI and PDMS.…”

“…The MD simulations of the respective membrane/solvent systems have been performed over a period up to 5 ns at temperatures of 303 K and 353 K. Usually NVT conditions with system sizes of about 5 000 -7 000 atoms were utilized. The pcff forcefield [41][42][43][44][45] was employed in all cases.…”

“…29,30,32,33,39,[43][44][45][46] ) on solution and diffusion of small molecules in stiff-and flexible chain polymers considering the static structure and the short time dynamics of the free volume of the respective polymers and the resulting solution-and diffusion mechanisms of the small molecule penetrants.…”

Coincidence Doppler broadening spectroscopy in polyvinyl chloride after doping with Al2O3

“…Such free volume holes play a crucial role in determining a variety of properties of polymers. 13,14 By using positron annihilation spectroscopy, many studies indicate that the macroscopic properties of conducting polymers are related to the positron annihilation properties. AL-Qaradawi and Abdel-Hady 15 applied the positron annihilation lifetime (PAL) technique to investigate the behavior of the free volume in pure and doped polyvinyl chloride (PVC) as a function of lead concentration and temperature.…”

A Novel Approach to Controlling CaCO3Crystalline Assembly by Changing the Concentration of Poly(aspartic acid)

“…Understanding chain mobility is crucial for studying the transport properties of hybrid systems. 50,51 It is generally agreed that polymer chain mobility is closely related to the interaction between inorganic particles and the polymer.…”