The effect of annealing polycarbonate at 125 °C (≈T g − 20 K) for aging times up to almost 2000 h has been investigated by differential scanning calorimetry, and the kinetics of the enthalpy relaxation process are compared with the effects of aging at the same temperature on the creep response and on the yield behavior. The enthalpy relaxation is analyzed by the peak shift method, and the following kinetic parameters are obtained:  nonlinearity parameter x = 0.46 ± 0.02; apparent activation energy Δh* = 1160 kJ mol-1; nonexponentiality parameter β is in the range 0.456 < β < 0.6. The similarities and/or differences between these results and others quoted in the literature are discussed. The creep response is analyzed by the commonly accepted procedure of horizontal and vertical shifting of deflection vs log(creep time) curves, and a shift rate of μ = 0.87 is obtained, with an excellent master curve. It is shown that a similar shift rate for enthalpy relaxation can be defined, and a value of μH = 0.49 is found. The difference between these two shift rates suggests that the time scales for the aging process are different when probed by the two techniques of creep and enthalpy relaxation. Similarly, it is found that the yield stress of annealed samples depends on log(aging time) in quite a different way from its dependence on log(strain rate), and it is argued that this provides further support for the contention that the time scales and rates of physical aging will be different when probed by different techniques.

Gas separation membranes are one of the lowest energy technologies available for the separation of carbon dioxide from flue gas. Key to handling the immense scale of this separation is maximised membrane permeability at sufficient selectivity for CO2 over N2. For the first time it is revealed that metals can be post-synthetically exchanged in MOFs to drastically enhance gas transport performance in membranes. Ti-exchanged UiO-66 MOFs have been found to triple the gas permeability without a loss in selectivity due to several effects that include increased affinity for CO2 and stronger interactions between the polymer matrix and the Ti-MOFs. As a result, it is also shown that MOFs optimized in previous works for batch-wise adsorption applications can be applied to membranes, which have lower demands on material quantities. These membranes exhibit exceptional CO2 permeability enhancement of as much as 153% when compared to the non-exchanged UiO-66 mixed-matrix controls, which places them well above the Robeson upper bound at just a 5 wt.% loading. The fact that maximum permeability enhancement occurs at such low loadings, significantly less than the optimum for other MMMs, is a major advantage in large-scale application due to the more attainable quantities of MOF needed.

Despite the exceptional separation performance of modern glassy mixed matrix membranes, these materials are not being utilized to improve the performance of existing membrane technologies. Nano-sized additives can greatly enhance separation performance, and have recently been used to overcome age-related performance loss of high performance MMMs. However nano-additives also compromise the structural integrity of films and little is known on how physical aging affects their mechanical properties over time. A solution for both physical aging and mechanical instability is required before these high performance materials can be utilised in industrial membrane applications. Here, we examine physical aging in mixed matrix membranes through mechanical properties and single gas permeation measurements using three glassy polymers, Matrimid® 5218, poly-1-trimethylsilyl-1-propyne (PTMSP), and a Polymer of Intrinsic Microporosity (PIM-1); and a range of nano-scale additives; Silica, PAF-1, UiO-66, and Ti5UiO-66, each previously shown to enhance gas separation performance. We find polymer-additive interactions strongly influence local physical aging and play a key role in determining the overall material properties of glassy nanocomposite films. Strong interface interactions can slow physical aging, and may not correlate to reinforced or age-stable films. Whereas traditionally 'incompatible' nanocomposites exhibit mechanical properties that can improve over time and even outperform their native polymers.Tuning polymer-additive interactions is vital to achieving the physical aging, mechanical stability, and permselectivity requirements of advanced mixed matrix membrane technologies and reducing the enormous global energy cost of separation processes.

Membranes are particularly attractive for lowering the energy intensity of separations as they eliminate phase changes. While many tantalizing polymers are known, limitations in selectivity and stability slightly preclude further development. Mixed-matrix membranes may address these shortcomings. Key to their realization is the intimate mixing between the polymer and the additive to eliminate nonselective transport, improve selectivity, and resist physical aging. Polymers of intrinsic microporosity (PIMs) have inherently promising gas transport properties. Here, we show that porous additives can improve transport and resist aging in PIM-1. We develop a simple, low-cost, and scalable hyper-cross-linked polymer (poly-dichloroxylene, pDCX), which was hydroxylated to form an intimate mixture with the polar PIM-1. Solvent variation allowed control of physical aging rates and improved selectivity for smaller gases. This detailed study has allowed many interactions within mixed matrix membranes to be directly elucidated and presents a practical means to stabilize porous polymers for separation applications.

Membrane separation is a promising technology for extracting temperature-sensitive organic molecules from solvents. However, a lack of membrane materials that are permeable toward organic solvents yet highly selective curtails large-scale membrane applications. To overcome the trade-off between flux and selectivity, additional molecular transportation pathways are constructed in ultrathin polyamide membranes using highly hydrostable metal organic frameworks with diverse functional surface architectures. Additional passageways enhance water permeance by 84% (15.4 L m h bar) with nearly 100% rose bengal rejection and 97.6% azithromycin rejection, while showing excellent separation performance in ethyl acetate, ketones, and alcohols. These unique composite membranes remain stable in both aqueous and organic solvent environments. This immediately finds application in the purification of aqueous mixtures containing organic soluble compounds, such as antibiotics, during pharmaceutical manufacturing.

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Post-synthetic exchange (PSE) and defect engineering have emerged as powerful techniques for tuning the properties and introducing novel functionality to metal organic frameworks (MOFs). Growing evidence suggests that each technique plays a key role in the mechanism of the other: linker coordination chemistry is pivotal to defective frameworks, while defect sites can help initiate PSE. Here, the intersection of these approaches is explored by exchanging an MOF with linkers already present within the framework. Post-synthetic annealing (PSA) modifies an MOF’s properties by redistributing the framework’s mixture of bound linker/modulator species. Using changes to the polymer-additive interactions in poly-1-trimethylsilyl-1-propyne nanocomposites observed through aging, we demonstrate that PSA causes one linker species to preferentially accumulate on the MOF’s crystal surface. Reaction conditions are shown to affect molecular composition of the resulting annealed UiO-66 MOFs, a finding explained through established reaction constants. This work simultaneously reveals intricacies of post-synthetic modification chemistry and presents a facile means of tuning MOFs and MOF nanocomposites.

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