Glass Transition Behavior and Dynamic Fragility of PMMA-SAN Miscible Blend-Clay Nanocomposites

Theoretical models for gas separation prediction of mixed matrix membranes: effects of the shape factor of nanofillers and interface voids

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, a mixed matrix membrane is considered 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 newly 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%).

Drug-Smectite Clay Amorphous Solid Dispersions Processed by Hot Melt Extrusion

The aim of this study was to introduce smectite clay matrices as a drug delivery carrier for the development of amorphous solid dispersions (ASD). Indomethacin (IND) was processed with two different smectite clays, magnesium aluminium and lithium magnesium sodium silicates, using hot melt extrusion (HME) to prepare solid dispersions. Scanning electron microscopy (SEM), powdered X-ray diffraction (PXRD), and differential scanning calorimetry (DSC) were used to examine the physical form of the drug. Energy-dispersive X-ray (EDX) spectroscopy was used to investigate the drug distribution, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopic analysis was done to detect any chemical interaction between these two kinds. Both PXRD and DSC analyses showed that drug-clay solid dispersion contained IND in amorphous form. EDX analysis showed a uniform IND dispersion in the extruded powders. ATR-FTIR data presented possible drug and clay interactions via hydrogen bonding. In vitro drug dissolution studies revealed a lag time of about 2 h in the acidic media and a rapid release of IND at pH 7.4. The work demonstrates that preparation of amorphous solid dispersion using inorganic smectite clay particles can effectively increase the dissolution rate of IND.

Poly(methyl methacrylate)-Assisted Exfoliation of Graphite and Its Use in Acrylonitrile-Butadiene-Styrene Composites

One of the applications of graphene in which its scalable production is of utmost importance is the development of polymer composites. Among the techniques used to produce graphene flakes, the liquid-phase exfoliation (LPE) of graphite stands out due to its versatility and scalability. However, solvents suitable for the LPE process are generally toxic and have a high boiling point, making the processing challenging. The use of low boiling point solvents could be convenient for the processing, due to the easiness of their removal. In this study, the use of poly(methyl methacrylate) (PMMA) as a stabilizing agent is proposed for the production of graphene flakes in a low boiling point solvent, that is, acetone. The graphene dispersions produced in the mixture acetone-PMMA have higher concentration, +175 %, and contain a higher percentage of few-layer graphene flakes (<5 layers), that is, +60 %, compared to the dispersions prepared in acetone. The as-produced graphene dispersions are used to develop graphene/acrylonitrile-butadiene-styrene composites. The mechanical properties of the pristine polymer are improved, that is, +22 % in the Young's modulus, by adding 0.01 wt. % of graphene flakes. Moreover, a decrease of ≈20 % in the oxygen permeability is obtained by using 0.1 wt. % of graphene flakes filler, compared to the unloaded matrix.

Segmental Dynamics and Cooperativity Length of PMMA/SAN Miscible Blend Intercalated in Organically Modified Nanoclay

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 ( T_g). 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, ξ_CRR, 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 simulation results showed the increased segmental mobility of the PMMA/SAN chains in the presence of OMNCs, which is in agreement with the DMA and DSC results.

Influence of molecular weight on molecular dynamics and dynamic rheology of polypropylene glycol filled with silica

Molecular weight strongly influences the molecular dynamics and rheological responses of nanocomposites, which is far from being well understood. Herein molecular dynamics and rheological behaviors of hydrophilic fumed silica filled unentangled polypropylene glycol (PPG) were investigated as a function of weight averaged molecular weight (M w) of PPG and volume fraction (∅) of silica. It is shown that M w does not affect the glassy layers surrounding the nanoparticles and the segmental dynamics of the mobile PPG phase. On the other hand, the mobile PPG phase in the highly filled nanocomposites exhibits an abnormal "more fragile" to "stronger" transition with increasing M w. The reinforcement and thinning behaviors are stronger in lower-M w nanocomposites with the "more fragile" mobile PPG phase. The results suggest that reinforcement of nanocomposites affects the dynamic fragility of the mobile phase of the matrix.