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In this work, a new model is developed by modifying the existing Maxwell-Wagner-Sillars (MWS) model to predict the gas separation properties of mixed matrix membranes (MMMs). The new modified MWS model, for the first time, provides the simultaneous exploration of the role of nanofillers/matrix interface voids and the exact geometrical shape of nanofillers in predicting the gas separation properties of MMMs. To unveil the crucial role of nanofillers/matrix interface voids by the new model, a mixed matrix membrane is considered as a three-component system composed of the polymer matrix as the continuous component, nanofillers as the dispersed component and the interface voids between the two components. Moreover, the new model elucidates the role of the exact ellipsoidal shape of nanofillers within the membrane on the gas separation of MMMs by considering the shape factor of nanofillers. The new developed modified MWS model is accurately able to predict the gas permeation of MMMs with a lower average absolute relative error (%AARE) of around 8% compared with the around 30% for conventional models such as the Maxwell model, Bruggeman model, Lewis-Nielsen model and Pal model and even compared with the modified Maxwell model (~ 24%).

In this work, a new approach is proposed to determine the thickness of interfacial voids in impermeable spherical nanoparticles-containing mixed matrix membranes (SP-MMMs) based on the gas permeation data. The interfacial void thickness, lv, between SPs and polymer matrix is firstly obtained as an adjustable parameter by fitting the modified Maxwell model to the experimental gas permeability data reported in the literature. It is shown that the value of lv parameter is independent of the nature of gas molecules and mathematically related to the strength of SP/matrix interfacial interactions. Then, for the first time in this paper, a universal relationship is established between the SPs/polymer interfacial void thickness and the interfacial interactions at the SPs/polymer interface, which is described by the Flory–Huggins interaction parameter, χ. Finally, the gas permeability of SP-MMMs is predicted using the values of lv parameter, diameter and volume fraction of SPs as well as the gas permeability of polymer matrix. Moreover, according to the obtained relationship, the interfacial void thickness in SP-polymer composites can be directly calculated for a wide range of interaction parameter values.

The existing traditional models cannot accurately predict the gas permeability of spherical nanoparticle-mixed matrix membranes (SP-MMMs) due to ignoring the physical and chemical characteristics of the SP/matrix interface. In this paper, first, a new model is derived for the prediction of thermal conductivity of SP-polymer composites according to multiple scattering theory. Then, a new theoretical model for gas permeability of SP-MMMs is developed based on the analogy with the derived model for the prediction of thermal conductivity. The significant feature of the new model is its ability to quantify the crucial role of SPs/matrix interface in gas permeability by introducing a new dense interfacial layer thickness (aint) parameter, which increases with increasing the strength of interfacial interactions. It is demonstrated that the value of aint is independent of the nature of gas molecules and mathematically correlated to the strength of SPs/matrix interfacial interactions. Finally, the gas permeability of SP-MMMs is accurately predicted by inserting the values of non-adjustable aint parameter, obtained from the correlation, diameter of SPs as well as the gas permeability of matrix into the new model, without using any adjustable parameter. Moreover, this technique can be utilized to determine the dense interfacial layer thickness in SP-polymer composites using gas permeation data.

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 reducti...

A new theoretical model was developed to predict the gas permeation behavior of mixed matrix membranes containing nanotubes (NT-MMMs). The proposed model was validated using a large number of CO2/N2 and CO2/CH4 separation data from the literature and a good agreement between the predicted and experimental data was observed. Most important, the proposed model explored the role of nanotube/matrix interface, by introducing the interfacial layer thickness parameter, lint. Moreover, an excellent correlation between the lint values and nanotube/matrix interfacial interactions, obtained from thermodynamic theories, provides a guideline to design the interface layer for fabricating the NT-MMMs with desired gas separation properties, without any need to using the adjustable parameter. Moreover, the presented procedure is a good alternative approach to expensive and tedious traditional methods to estimate the interfacial layer thickness in polymer composites.

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” (aint) and “interfacial permeation resistance” (Rint), are introduced to account for the role of nanotube/matrix interfacial interactions in the proposed model. The obtained values of aint, 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 aint and polymer–nanotube interaction parameters, χ, helped to accurately reproduce the existing experimental data from the literature without the need to re...

The effect of nanoconfinement on the segmental dynamics of a poly(methyl methacrylate) (PMMA)/poly(styrene-ran-acrylonitrile) (SAN) miscible blend, intercalated into the interlayer spacing of the organically modified nanoclay (OMNC), was investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) methods. We reported an unusual phenomenon in which the weak interfacial interactions between the polymer chains and OMNCs was responsible for increase in segmental mobility at the glass-transition temperature (Tg). Remarkably, we found a positive correlation between dynamic fragility and thermodynamic fragility, in which both fragilities decreased under nanoconfinement. The cooperative length of segmental motions, or length of cooperatively rearranging regions, ξCRR, decreased from 2.64 nm for the PMMA/SAN blend to 1.86 nm for the PMMA/SAN/OMNC nanocomposite. The segmental mobility of the PMMA/SAN/OMNC model was also studied using the molecular dynamics simulations. The simul...

The effect of graphene oxide (GO) nanosheets on the CO2/CH4 separation performance of a rubbery (poly(dimethylsiloxane), PDMS) as well as a glassy (polyetherimide, PEI) polymer is studied. Interfacial interactions between the nanosheets and both polymers are revealed by FTIR and SEM. The results of gas permeation through the membranes demonstrate that GO nanosheets enhance CO2/CH4 diffusivityselectivity of PEI and CO2/CH4 solubility-selectivities of the PEI and PDMS polymers, while diminish CO2/CH4 diffusivity-selectivity of PDMS. Furthermore, the possibility of overcoming the common tradeoff between CO2 permeability and CO2/CH4 selectivity of rubbery and glassy polymers by incorporating very low amounts of graphene oxide nanosheets is addressed. In other words, at 0.25 wt % GO loading, the PEI membrane shows simultaneous enhancement of CO2 permeability (16%) and CO2/CH4 selectivity (59%). Also, for the PDMS membrane simultaneous enhancement of CO2 permeability (29%) and CO2/CH4 selectivity (112%) is occurred at 0.5 wt % GO loading. Finally, the capability of the well known Nielsen model to predict the gas permeability behavior of the nanocomposites is investigated.

The influence of nanoconfinement on segmental relaxation behavior of poly(methyl methacrylate) and poly(styrene-ran-acrylonitrile) miscible blend and its nanocomposites with spherical and layered nanoparticles have been investigated. Dynamic mechanical analysis was employed to examine the effect of geometry of nanoparticles on the temperature dependence and relaxation function breadth of segmental dynamics (α-relaxation) in the glass transition region. The maxima of the loss modulus curves were used to fit to the Vogel–Fulcher–Tamman equation to describe the temperature dependence of the characteristic relaxation times. Furthermore, the T g-normalized semi-logarithmic Arrhenius plots (fragility plots) were exploited to indicate the changes in cooperative segmental motions across the glass transition. The master curves for relaxation modulus were also constructed for each sample as a function of time using the time–temperature superposition principle. The investigated nanocomposites showed a narrower segmental dispersion in the glass transition region compared to the neat systems. The relaxation modulus master curves were fitted by the Kohlrausch–Williams–Watts (KWW) function. It was observed that the distribution parameter of segmental relaxation time increased with addition of nanoparticles which was correlated with a decrease in fragility index. In addition, the increase of the KWW distribution parameter (β KWW) for spherical silica nanocomposites was less than that for nanocomposites prepared with layered silicates (organoclay).

An investigation of the segmental dynamics and glass transition behavior of a miscible polymer blend composed of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) and its melt intercalated nanocomposite by dynamic mechanical analysis is presented. The principle goal was to address the effect of intercalation on local molecular structure and dynamics. The results showed that the intercalation of polymer chains in the galleries of organoclay (Cloisite 30B) led to a lower temperature dependence of the relaxation time (fragility) and activation energy of α-relaxation. Moreover, calculation of the distribution of the segmental dispersion showed a narrower dispersion in the glass transition region so that the Kohlrausch-Williams-Watts (KWW) distribution parameter (βKWW) increased from 0.21 for neat PMMA to 0.34 for the 50/50 PMMA/SAN blend nanocomposite containing 3 wt% organoclay. Furthermore, the relaxation behavior of the blends showed a negative deviation from mixture law prediction...