Sorption, Transport, and Structural Evidence for Enhanced Free Volume in Poly(4-methyl-2-pentyne)/Fumed Silica Nanocomposite Membranes

Abstract

In contrast to the performance of traditional filled polymer systems, penetrant permeability coefficients in high-free-volume, glassy poly(4-methyl-2-pentyne) (PMP) increase systematically and substantially with increasing concentration of nonporous, nanoscale fumed silica (FS). For instance, the permeability of PMP containing 40 wt % FS to methane is 2.3 times higher than that of the unfilled polymer. Gas and vapor uptake in the PMP/FS nanocomposites is essentially unaffected by the presence of up to 40 wt % FS, while penetrant diffusion coefficients increase regularly with increasing filler content. This increase in diffusivity is responsible for elevated permeability in the PMP/FS nanocomposites. The addition of FS to PMP augments the permeability of large penetrants more than that of small gases, consistent with a reduction in diffusivity selectivity. Consequently, vapor selectivity in the nanocomposites increases with increasing FS concentration. Activation energies of permeation in PMP decrease with increasing FS content, suggesting that penetrant diffusive jumps require less energy at higher filler concentrations. Positron annihilation lifetime spectroscopy (PALS) reveals that FS subtly increases the free volume in PMP available for molecular transport. The accessible free volume measured by PALS correlates favorably with relative penetrant permeability in the nanocomposites. Transmission electron microscopy confirms that the FS nanoparticles are relatively well dispersed in PMP.

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

“…Journal of Membrane Science 550 (2018) 198-207 related to (1) disruption of the chain packing of the polymer, (2) porosity introduced by MOF particles [34] and (3) increase in the polymer free volume [56][57][58]. The characterization of the MMM shows that in our case the MOF distribution is quite even throughout the membrane with good adhesion between the MOF filler and the polymer.…”

Polycarbonate/Polypropylene-Graft-Maleic Anhydride and Nano-Zeolite-Based Nanocomposite Membrane: Mechanical and Gas Separation Performance

“…Generally, gas permeability is affected by nanofiller distribution and matrix/nanofiller alignment [31,32]. The permeability and permselectivity of PC/PPMA-based nanocomposite membrane as a function of filler concentration is given in Table 3.…”

Polymer nanocomposites

“…15 This will have implications on the underlying construct of a glass transition. 16 With regard to the nanoparticle, the spatial distribution of the particle center of mass will depend on volume fraction, particle size distribution, and particle shape (sphere, rod, plate). For extended spheroids (rods and plates), excluded volume interactions between particles will lead to local orientation correlations, as well as the possibility of fractal association leading to percolation behavior and interpenetrating polymer-nanoparticle rich regions.…”