Theoretical approaches that accurately predict the gas permeation behavior of nanotube-containing mixed matrix membranes (nanotube-MMMs) are scarce. This is mainly due to ignoring the effects of nanotube/matrix interfacial characteristics in the existing theories. In this paper, based on the analogy of thermal conduction in polymer composites containing nanotubes, we develop a model to describe gas permeation through nanotube-MMMs. Two new parameters, "interfacial thickness" (a) and "interfacial permeation resistance" (R), are introduced to account for the role of nanotube/matrix interfacial interactions in the proposed model. The obtained values of a, independent of the nature of the permeate gas, increased by increasing both the nanotubes aspect ratio and polymer-nanotube interfacial strength. An excellent correlation between the values of a and polymer-nanotube interaction parameters, χ, helped to accurately reproduce the existing experimental data from the literature without the need to resort to any adjustable parameter. The data includes 10 sets of CO/CH permeation, 12 sets of CO/N permeation, 3 sets of CO/O permeation, and 2 sets of CO/H permeation through different nanotube-MMMs. Moreover, the average absolute relative errors between the experimental data and the predicted values of the proposed model are very small (less than 5%) in comparison with those of the existing models in the literature. To the best of our knowledge, this is the first study where such a systematic comparison between model predictions and such extensive experimental data is presented. Finally, the new way of assessing gas permeation data presented in the current work would be a simple alternative to complex approaches that are usually utilized to estimate interfacial thickness in polymer composites.
The
influence of reduction temperature on the electromechanical properties
and actuation behavior of polydimethylsiloxane (PDMS) dielectric elastomer
containing the thermally reduced graphene oxide (rGO) with different
surface chemistry has been systematically investigated. A set of rGO
nanosheets was prepared by thermal reduction of graphene oxide (GO)
at four temperatures (150, 200, 300, and 400 °C). The dielectric
permittivity, dielectric loss, and elastic modulus of PDMS composites
were increased, while the electrical breakdown strength of composites
was decreased with an increase of the reduction temperature of GO.
A thermodynamic model applied for studying the electromechanical deformation
and stability of PDMS/GO(rGO-x) dielectric elastomer
composites showed that the optimum value of the break-point was observed
in PDMS/rGO-300. It is shown for the first time that the variation
of electromechanical instability and recovery behavior are attributed
to the surface chemistry of rGOs. A critical reduction temperature
is observed at 300 °C which can be considered as proper rGO nanosheets
for electromechanical applications. By employing
an equivalent circuit on impedance spectroscopy, the interfacial polarization
is recognized as the dominant mechanism rather than the intrinsic
polarization of the matrix and nanosheets. Noteworthy, PDMS composites
containing rGO, reduced at higher temperatures, have more interfacial
polarized charges at the interface.
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