Size-Dependent Permeability Deviations from Maxwell’s
Model in Hybrid Cross-Linked Poly(ethylene glycol)/Silica Nanoparticle
Membranes
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Abstract
Currently, separation of gaseous
mixtures largely relies on energy
intensive and expensive processes, like chemical looping of amines.
This has driven research into less energy-intensive, passive methods
of performing separations such as the use of polymer membranes. Although
pure polymer membranes have demonstrated appealing separation performance,
they suffer from an inherent trade-off between permeability and selectivity,
which limits overall performance. Recent research efforts have shown
that the introduction of a secondary phase, often an inorganic species,
is added to selectively boost permeability or selectivity. However,
these hybrid organic/inorganic systems have not seen widespread
adoption because synthetic control over the size, shape, and dispersion
of the inorganic species is poor and understanding of transport in
these membranes is largely empirical. Thus, understanding and optimizing
hybrid membranes requires development of well-controlled model systems
in which size, shape, and surface chemistry of the inorganic species
are precisely controlled, leading to homogeneous membranes amenable
to careful study. Here, we report on the synthesis, characterization,
and gas transport properties of tailored hybrid membranes composed
of cross-linked poly(ethylene glycol) and silica nanoparticles. We
show excellent control of nanoparticle size, loading, and dispersibility.
We find that permeability deviations from Maxwell’s model increases
as the size of silica nanoparticle decreases and loading increases.
These size-dependent deviations from Maxwell’s model are attributed
to interfacial interactions, which scale with surface area and act
to decrease segmental chain mobility