Amorphous Glassy Research Articles

Rational Utilization of Intermolecular Interactions: Enhancing the Mechanical Properties of Amorphous Glassy Polymer through Flexible Backbones

Rational Utilization of Intermolecular Interactions: Enhancing the Mechanical Properties of Amorphous Glassy Polymer through Flexible Backbones

Modelling of fracture-involved large strain behaviors of amorphous glassy polymers via a unified physically-based constitutive model coupled with phase field method

To promote the application of amorphous glassy polymers in structural components, a reliable prediction of the deformation and the potential fracturing behaviors is in demand. This work aims to provide a simple and feasible computational method to analyze the large strain behaviors, including elasticity, viscoplasticity, and the subsequent fracture, of amorphous glassy polymers. This is achieved by incorporating a physically-based constitutive model coupled with the fracture phase field method into the commercial finite element software Abaqus/Explicit. Inside the constitutive model, shear-yielding, crazing, and disentangling are considered as the underlying mechanisms for viscoplastic deformation and damage initiation. It is noteworthy that a unified craze-initiation criterion with a clear physical meaning is proposed, distinguishing this work from the previous in the literature. Moreover, a relatively user-friendly numerical implementation is suggested by exploiting the built-in features of Abaqus/Explicit. Taking the typical amorphous glassy polymers for example, i.e., polycarbonate (PC) and poly-methyl-methacrylate (PMMA), various experiments from the literature have been simulated. The proposed approach has been validated, since an acceptable agreement between the simulated and experimental results is realized.

Physical phenomena during nanoindentation deformation of amorphous glassy polymers

We identify for visco-elasto-plastic (VEP) glassy polymers, physical phenomena during Berkovich nanoindentation, a locally imposed deformation. Live visuals via in situ nanoindentation indicate mainly sink-in during loading, with pile-up after unloading. Scanning Probe Microscopy (SPM) indicates significant volume conserving upflow below the tip, for these high ν, compliant materials, with compliance correlated high geometric fractional contact, hcΔhmΔ∼0.86−0.95. We adapt the ideal conical indentation framework to VEP Berkovich nanoindentation, to calculate the contact area and visually depict the upflow and the displacement paths, in the material. The combination of SPM and P−h data, indicates a mixed comparison with uniaxial modulus and yield stress, with conventionally defined hardness, H<3σy, and nanoindentation modulus, EN>E. By rationally removing viscoelastic (VE) effects from the loading P−h data, we find instant, zero-time hardness HL0>3σy. We apply the power law model to only the recovery onset, to estimate pure elastic recovery. We then deconvolute the VEP nanoindentation into the conventional EP (elasto-plastic) and elastic contributions, isolating the VE component. Constraint-induced sink-in, pile-up and VE recovery of the highly yielded tip-apex region, mirror the converse constrained deformation effects, governing the trends in the conventional EP EN and HL0 estimates for glassy polymers.

Analysis on shear band development under large strain torsion of amorphous glassy polymers

Unlike the shear band development of metals generally regarded as the precursor to failure, the shear banding process in amorphous glassy polymers is known to influence both the strengthening and fracturing behaviors. Complementary to the previous experimental work in the literature on the shear band development under torsion under limited cases, the finite element (FE) analysis has been conducted to investigate the general shear banding behaviors in terms of the initiation and propagation in more detail. The FE model has been established by incorporating the Boyce-Parks-Argon (BPA) constitutive model with the full-network modification via a user material subroutine in ABAQUS. A series of nondimensional quantities were used to discuss the mesh sensitivity and the effects of predefined imperfections, specimen geometry, and torsion mode. Besides, by altering the extents of the intrinsic material softening and the strain hardening, the shear banding behaviors of typical materials under typical temperature and strain rate conditions are equivalently investigated. The validity of the simulation has been qualitatively validated by directly comparing with the experimental results from the literature.

A finite deformation formulation for amorphous glassy polymers under moderate and impact strain rates: Application to adhesive films

This work describes a novel finite strain hypo-elastic formulation for amorphous thermoset polymers working in the glassy regime. The constitutive formulation is able to describe time and pressure-dependent behaviour under loading rates ranging from quasi-static to impact-type loading conditions and to account for thermo-mechanical coupling effects. A non-linear pressure dependent potential function is introduced to capture the non-associative visco-plastic potential flow for volumetric plastic strain control. The formulation also incorporates an internal state or deformation resistance variable to enable the description of the polymer hardening — softening behaviour, as well as a novel relation for the dissipative fraction of the plastic work in terms of the equivalent accumulated plastic strain. The constitutive model is formulated within a finite strain kinematics framework, and full details of its numerical implementation into the finite element method using a fully implicit Euler Backward algorithm are given. Model calibration is carried out for three different thermosetting resins (PR520 and RTM6 Epoxies, and MMA adhesives).To illustrate the model capabilities, two case studies are investigated: (i) the de-formation behaviour of epoxy under moderate and impact-type loading conditions under isothermal and fully adiabatic conditions, and (ii) the fracture behaviour of adhesive layers used to bond stiff metallic substrates. Results on RTM6 epoxy show that at, e.g., 60% true strain, 48.5% of the rate of plastic work is dissipative, and that the corresponding predicted increase in temperature due to the locally dissipated heat is consistent with published calorimetry data on a similar thermoset polymer. It was also found that, by coupling the proposed constitutive model with a cohesive zone model, it was possible to predict accurately the effect of an MMA adhesive layer thickness and pressure-dependency on the growth of an interfacial crack between the MMA adhesive and the metallic substrates. The proposed model should constitute a generic phenomenological formulation for the mechanical behaviour prediction of a wide range of thermoset polymers under confined and quasi-adiabatic conditions such as in composites and adhesive joints.

Effects of loading rate on void growth in amorphous glassy polymers

Initiation, growth, and coalescence of microscopic voids are precursors to failure in amorphous glassy polymers. Hence, void growth analysis is important for understanding the failure in these polymers. Under quasi-static conditions, void growth in polymers is well understood; however, a similar analysis under dynamic conditions is not available in the literature. In the present work, we analyse the effect of loading rate on the void growth behaviour using large deformation finite element simulations. An axisymmetric unit cell model of a spherical void is considered for the analysis. The void is subjected to a range of strain rates (10−3s−1 to 105s−1). Remote triaxialities equivalent to uniaxial loading, biaxial loading, and higher triaxiality conditions are considered. Remote mean stresses, which are important from the perspective of void growth, have been characterized as a function of void size, strain rate, and triaxiality. Results show that the critical mean stresses required for unstable void growth increase with increasing triaxiality. Higher loading rates further amplify the critical mean stresses, and the amplification depends upon the material rate sensitivity of polymers. The void growth mechanism does not change because of material rate-sensitivity. During void growth, inertia effects are found to be significant after a strain rate of 103s−1. It is found that inertia increases with increasing triaxiality and increasing void size. It stabilizes the void growth and makes them expand in a more spherical shape, even at low triaxialities.

A physically-based constitutive model for amorphous glassy polymers in large deformations

A physically-based constitutive model for predicting the mechanical response of amorphous glassy polymers at room temperature and low strain rates was established within the frame of thermodynamics and kinematics. In our previous work (Lan et al., 2022b), the concepts of permanent entanglement (PE) and dynamic entanglement (DE) were utilized to reproduce the complicated behavior of amorphous glassy polymers from quasi-static to dynamic loading at temperatures from below to near the glass transition temperature. PE formed by the coiling of macromolecular chains is relatively stable and contributes to the yield and unloading behavior. DE formed by the weak interaction between monomers of adjacent segments is unstable and contributes to the macroscopic yield peak and strain hardening. However, due to including many parameters, the model is not easy to apply in practice. In this work, by ignoring the influence of temperature, the previous model (Lan et al., 2022b) was simplified. Taking polycarbonate (PC) and polystyrene (PS) as examples, the simplified model focused on the macroscopic mechanical behavior under simple compression and cyclic simple compression, analyzed the effects of mesh and specimen size on the evolution of shear bands under plane strain compression, and compared the obvious differences in localized deformation of these two types of amorphous polymers under plane strain compression. In addition, the forging process of PC at room temperature was simulated. By comparing the predictions with the experiments, it is demonstrated that the simplified model can reproduce the macroscopic mechanical response of amorphous polymers under simple compression, cyclic simple compression, plane strain compression and forging.

Mixed ionic and electronic conductivity in the quaternary V2O5–Na2O–ZnO–P2O5 glass system

The melt quenching method was adopted to synthesize glasses with the formula xV2O5–(0.4-x) Na2O–0.35ZnO–0.25P2O5 (x = 0.05, 0.1, 0.15, 0.2, and 0.25). X-ray diffraction patterns for the x = 0.05 sample showed the complete amorphous structure, whereas other composites revealed the development of nanocrystallites over the amorphous glassy networks. DSC measurement showed that glass transition temperature reduced as V2O5 concentration rose, and values were consistent with modified CBH model theoretical (fitting) data. DC conductivity for x = 0.05 and 0.1 composites followed an Arrhenius-type relation and linearity against the reciprocal of temperature, revealing ionic conductivity. On the contrary, the electronic or small polaron hopping mechanism was responsible for DC conductivity for all other composites. AC conductivity mechanism was described by the modified correlated barrier hopping model, and ideal glass transition temperatures were predicted (361 °C (x = 0.05) to 412 °C (x = 0.25)). It was observed that with rising V2O5 content (x), there was blockage of ionic pathways of Na+ ions, causing the ionic conductivity to decline and the electronic or small polaronic conductivity to enhance, as the radius of small polaron reduces. AC conductivity scaling property established that the time-temperature superposition principle and the BNN relation did not hold for the systems.

Coupled thermo‐viscoplastic fracture model for ductile‐brittle failure of amorphous glassy polymers with phase‐field approach

AbstractAmorphous glassy polymers have an extensive use in the industrial sectors including micro‐electronics, medical industry and aerospace, therefore their design and usage have become a significant task nowadays. The fracture response of these polymers may vary from ductile to brittle depending on several factors such as entanglement density, temperature level and external loading rate. The ductile response is driven by diffuse shear zones exhibiting volume–preserving inelastic deformations while the brittle response is manifested by very small crack‐like defects composed of a sequence of fibrillar bridges separated by micro‐voids, thereby connotating void formation consisting of nucleation and propagation steps. The presents study is focused on the description of shear yielding and crazing phenomenon in terms of their respective evolution equations. In addition, an extension towards the modelling of the fracture is employed via the crack phase–field approach, considering ductile and brittle failure simultaneously. This is provided by the novel failure criterion that features a critical amount of plastic strain and void volume fraction. Since the proposed approach unitedly models the macroscopic crack initiation and propagation for ductile or brittle failure, it is asserted to be more physically grounded compared to present models in the literature. Constitutive formulations for shear yielding, crazing, and void volume fraction are derived with their specific forms starting with the local and conductive component of the dissipation inequality. The performance of model is evaluated after developing the local and global Newton–type update algorithms for the dissipative internal and primary field variables, respectively and it has been analysed by fitting of several experimental data of homogeneous and inhomogeneous tests. The findings reveal the remarkable temperature dependency on the type of failure as well as the interaction between loading rate and temperature change owing to dissipative heating in the solid.

A mean-field shear transformation zone theory for amorphous polymers

The complex nonlinear constitutive behavior of amorphous polymers has been extensively investigated in numerous experiments, displaying a strong dependence on the thermal history and loading path. Theoretical models have been proposed to conjoin the underlying mechanisms to certain aspects of mechanical features, such as yielding, strain hardening, physical aging, and the Bauschinger effect. However, an urgent need for theoretical understanding capable of fulfilling the comprehensive predictions of the featured constitutive behaviors of amorphous polymers is to be addressed. In this paper, we develop a micromechanical mean-field shear transformation zone (STZ) model to systematically describe the stress responses of amorphous polymers. The dynamics of STZ is affected by the nonequilibrium structural state described by effective temperature and also related to the anisotropic internal structure induced by the microscopical deformation. Our model exhibits the ability to fully capture the behaviors of amorphous polymers in constant rate/switch rate loading, creep, relaxation, and loading-unloading-reloading cycles. The model is further verified by reproducing the Bauschinger effect in experiments, which remains a challenge to other widely used models. Our results show that the deformation-induced material polarization, in the form of an anisotropic distribution of STZs, is the governing mechanism of the Bauschinger effect. This work establishes a comprehensive relationship between the microscopic mechanisms and the constitutive behaviors of deforming amorphous polymers, which advances the fundamental understanding of complex mechanical behaviors in amorphous glassy polymers.

Molecular Dynamics of Polymyrcene: Rheology and Broadband Dielectric Spectroscopy on a Stockmayer Type A Polymer

Molecular dynamics of polymyrcene (PM) covering a wide range of molecular weights from 6.7 × 103 ≤ Mw ≤ 3.47 × 105 g/mol (weight-average molecular weight Mw) with a molar mass dispersity Đ ≤ 1.16 were investigated by oscillatory shear rheology and broadband dielectric spectroscopy. The analysis of the zero-shear viscosity (η0) versus molecular weight in a double-logarithmic plot reveals a scaling exponent of ∼1.2 below the critical molecular weight and ∼3.7 above a critical molecular weight of Mc ≅ 4.4 × 104 g/mol. However, at molecular weights greater than the reptation molecular weight Mr, a molecular weight substantially larger than the entanglement molecular weight Me, the zero shear viscosity scaling decreases. A scaling of η0 ∝ M3.0, which might be attributed to a pure tube-reptation behavior, was found. The exponent of 1.2 is attributed to a Rouse-like dynamic and is interpreted in terms of PM’s bottlebrush-like nature arising from tightly packed C6/C8 pendant groups. Dielectric spectroscopy measurements revealed two relaxation processes typical for fully amorphous glassy polymers: The first is a segmental mode process, with a dynamic glass transition process (α), due to the segmental motions and the second one is a local relaxation process in the glassy state (β). Additionally, above the glass transition temperature at low frequency, another relaxation process was observed, which appears to be the normal mode process (n) due to the fluctuation of the end-to-end vector. This polymer is assigned to be a new Stockmayer type A polymer, whose normal mode relaxation is strongly dependent on its molecular weight. These findings allow for the rare possibility to explore the global dynamics of PM by using both oscillatory shear rheology and broadband dielectric spectroscopy methods over a wide range of temperatures to investigate molecular dynamics using the time–temperature superposition principle.

Fatigue life prediction for amorphous glassy polymers based on cumulative evolution of micro-defects

This study is focused on the fatigue life prediction model of the amorphous glassy polymers by alternating different parameters on the experimental results. The mechanism of fatigue failure was investigated through scanning electron microscopy. Respected to the different temperature conditions different regions of fracture were observed consisting of the thermal and mechanical zones. The proposed model is based on the cumulative evolution of micro-defects up to the rupture. In this regard, different constant parameters depending on the material, temperature, and frequency were considered. According to the results, the model showed a good ability to predict the fatigue life of the polymers.

Ductile–brittle failure of amorphous glassy polymers: A phase-field approach

Optimal use and design of amorphous glassy polymers in goods have become a significant task in the key industrial sectors ranging from micro-electronics to aerospace and medical industry. Depending on the microstructure, temperature level and the external loading rate to which these polymers are subjected, the fracture response may change from ductile to brittle or vice versa. While the ductile response is manifested by diffuse shear zones exhibiting volume-preserving inelastic deformations, the brittle response is revealed by very small crack-like defects containing a sequence of fibrillar bridges and elongated micro-voids, thereby resembling the void formation consisting of nucleation and growth stages. Their formation is driven by tensile straining followed by volumetric inelastic deformations. The present study is concerned with the description of shear yielding and crazing in terms of their respective evolution equations. Besides, an extension towards the modeling of the fracture is employed via the crack phase-field approach, accounting for ductile and brittle failure concomitantly. This is granted by the novel failure criterion that features a critical amount of plastic strain and void volume fraction. Such a modality simultaneously models the macroscopic crack initiation and growth leading to ductile or brittle fracture, as such purports to be more physically grounded compared to extant models in the literature. The predictive performance of the proposed model has been demonstrated by fitting of various extant experimental data of homogeneous and inhomogeneous tests in relation to initial boundary value problems.

A thermodynamically-based constitutive theory for amorphous glassy polymers at finite deformations

In this work, a fully thermomechanical coupling constitutive theory is developed for amorphous glassy polymers to explain and predict their complex temperature- and rate-related nonlinear behavior during finite deformations. The foundation for the theory is the original kinematic and thermodynamic framework derived by Bouvard et al. (2013), in which internal state variables with clear physical significance are applied to describe the deformation mechanism of polymers. In contrast to the viewpoint of Bouvard et al. (2013), in the proposed model, we further divide the entanglements into two kinds of molecular microstructures, “permanent entanglements” and “dynamic entanglements”, and describe how their evolution during deformation is regarded as the internal mechanism for the material's macroscopic mechanical properties. Further, a series of new constitutive equations related to “dynamic entanglements” are proposed, which account for the strain softening caused by the dissociation of “dynamic entanglements”, reflect the influence of temperature on the dissociation rate of “dynamic entanglements” and include the effect of rate-dependent glass transition temperature (θg) on the microstructure. The equations related to “permanent entanglements” are also illustrated, which are improved based on the the work of Ames et al. (2009). The predictive capacity of the proposed thermomechanical coupling constitutive theory has been numerically realized by writing a user subroutine for finite element program. Taking polycarbonate (PC) as an example, the simulations are compared with experimental results for compression, shear, tension, and creep at different temperatures and strain rates. It is demonstrated that our proposed constitutive model with a more detailed physical meaning can well reproduce nonlinearity before yield, yield peak, strain softening, hardening and unloading behavior for amorphous glassy polymers under different stress states.

Shear band development under simple shear and the intrinsicality of strain softening of amorphous glassy polymers

The development of shear bands that induced by localized strain inhomogeneity is a characteristic deformation mechanism and determines ductility of amorphous glassy polymers. To investigate the essence of intrinsic strain softening and its influence on shear band evolution under shearing and reverse shearing, a full-network constitutive model based on the micro-mechanism is implemented into the material point method and finite element method respectively. The results show that the shear band nucleates and propagates in forward shearing, and gradually fades until disappears in following reverse shearing when the specimen regains its original geometry. As reverse shearing proceeds or there is a second forward shearing, the homogeneous plastic deformation occurs preferentially in the previously deformed band but it doesn't display any shear band like the initial forward shearing. It means the glassy polymers undergoing plastic deformation cannot be recovered by reverse straining. In further shearing, new shear bands tend to be initiated outside the existing band and then propagates to merge with the previous band. The initiation and propagation of shear band along the shearing direction is caused by the intrinsic strain softening, independent of loading histories and boundary conditions. The widening of shear band is related to the strain hardening. • Origin of intrinsic strain softening lies in the saturation of plastic shear strain. • Amount of intrinsic strain softening keeps fixed. • Glassy polymers undergoing plasticity cannot be recovered by reverse straining. • Full-network model can capture the shear band evolution under reverse shearing.

Preparation and Characterization of Stable Amorphous Glassy Solution of BCS II and IV Drugs.

The focus of the present investigation was to develop amorphous glassy solutions (AGSs) of BCS Class II and IV drugs using sucrose acetate isobutyrate (SAIB). The drugs studied were rifaximin (RFX), dasatinib (DST), aripiprazole (APZ), dolutegravir (DLT), cyclosporine (CYS), itraconazole (ITZ), tacrolimus (TAC), sirolimus (SRL), aprepitant (APT), and carbamazepine (CBZ). AGSs were prepared by dissolving known quantity of the drug in the SAIB at 120 (TAC and APZ), 140 (CYS) or 150 oC (RFX, DST, DLT, ITZ, SRL, APT, and CBZ). They were characterized visually and by NIR, NIR hyperspectroscopy (NIR-H), and XRPD. Stability were determined by exposing open vials to 40 oC/75% RH for a week. AGSs behave like a glassy solid at room temperature and liquified above 60 oC. The solubility of APT, DLT, SRL, APZ, RFX, CBZ, TAC and CYS in SAIB was 0.4±0.0, 1.7±0.4, 1.9±0.0, 21.6±2.6, 36.4±0.9, 76.5±4.0, 115.1±2.3, and 239.0±12.6 mg/g, respectively. NIR, NIR-H, and XRPD data indicated the amorphous nature of the AGSs. Furthermore, AGSs were stable against devitrification on exposure to high temperature and humidity. In summary, SAIB can be employed to develop stable AGSs of poorly soluble drugs to increase dissolution, and oral bioavailability with the addition of hydrophilic excipients.

Effects of cold rolling on the tensile response of glassy polymers: Experiments and modeling

Cold rolling can significantly affect the mechanical response of amorphous glassy polymers. Traditionally, uniaxial compression tests are commonly used to evaluate the mechanical response of oriented polymers. In contrast, the tensile response of predeformed polymers is still not well characterized since the specimens typically do not exhibit a homogenous deformation in the subsequent reloading process. To address this limitation, in this work we first perform cold rolling on poly(ethylene terephthalate)-glycol (PETG), an amorphous glassy polymer, followed by a subsequent reloading test in uniaxial tension mode. Based on the digital image correlation technique, we are able to extract the stress–strain relationship of rolled specimens. The influence of rolling ratio and direction on stress response is then obtained, which shows a significant increase of hardening response for specimens rolled in the length direction while much less pronounced strain hardening for polymers rolled in the width direction. The yield strength and strain softening also depend on the rolling conditions. We then apply a viscoplastic model to predict the above experiments. The results show that the model can capture the hardening response of cold rolled specimens, while it fails to describe the yield strength. This indicates that the constitutive model needs to be improved for the future study. Overall, our work can deepen the fundamental understanding on the effects of cold rolling on mechanical properties of amorphous glassy polymers.

Advantage of graft architecture with a flexible main chain for implantation of ductile nature into brittle amorphous acrylic glass

Toughness enhancement of amorphous glassy polymers is required to expand the application range of thermoplastic polymers. This report describes the implantation of ductile nature into poly(methyl methacrylate) (PMMA) resins utilizing a graft architecture with a flexible polyester main chain, which was synthesized via atom transfer radical polymerization (ATRP) with a graft-from approach using a polyester macroinitiator bearing multiple bromo side groups. A comparison with a PMMA homopolymer and a blend PMMA containing a plasticizer revealed that the graft-type PMMA showed much higher elongation without sacrificing the modulus. The ductile nature of the graft-type PMMA was analyzed according to X-ray scattering, scanning electron microscopy observation, and rheological measurement. In the last section, effects of the length of both main chain and graft chain on the tensile properties were investigated.

Effect of varying phosphate content on the structure and properties of sol-gel derived SiO2-CaO-P2O5 bio-glass

In this work, biocompatible glass (bioglass) particles were prepared by low temperature, acid catalysed sol-gel method. The effect of varying phosphate (P2O5) content (10, 15 and 20 mol %) in the sol-gel derived glass composition were studied. The sol-gel derived bioglass particles were compacted into cylindrical pellets via hydraulic press machine and sintered at 600°C for 3 hours. The bioglass particulates were analysed by x-ray fluorescence (XRF), Fourier Transformed Infrared (FTIR), X-Ray Diffraction (XRD) and nitrogen gas adsorption. Meanwhile, the sintered bioglass pellets were analysed by FTIR, XRD and FESEM-EDX. Furthermore, in vitro bioactivity analysis was performed by immersion in simulated body fluid (SBF) for 14 days. Bioglass particulates with high glassy phase, high surface area and high porosities were obtained for all compositions. Increasing of phosphate content to 20 mol% particularly reduced the porous characteristics of the bioglass particulates. Furthermore, leads to higher bridging oxygen (BO) atoms, higher amorphous silicate networks, lower glass crystallinity and higher number of phosphate crystallites within the amorphous glassy matrix. Increased to 20 mol% of phosphate also reduced the ability of the bioglass surface to induce carbonated apatite formation when immersed in simulated body fluid (SBF) solution.

Recent Progress on Polymers of Intrinsic Microporosity and Thermally Modified Analogue Materials for Membrane‐Based Fluid Separations

Solution‐processable amorphous glassy polymers of intrinsic microporosity (PIMs) are promising microporous organic materials for membrane‐based gas and liquid separations due to their high surface area and internal free volume, thermal and chemical stability, and excellent separation performance. This review provides an overview of the most recent developments in the design and transport properties of novel ladder PIM materials, polyimides of intrinsic microporosity (PIM–PIs), functionalized PIMs and PIM–PIs, PIM‐derived thermally rearranged (TR), and carbon molecular sieve (CMS) membrane materials as well as PIM‐based thin film composite membranes for a wide range of energy‐intensive gas and liquid separations. In less than two decades, PIMs have significantly lifted the performance upper bounds in H2/N2, H2/CH4, O2/N2, CO2/N2, and CO2/CH4separations. However, PIMs are still limited by their insufficient gas‐pair selectivity to be considered as promising materials for challenging industrial separations such as olefin/paraffin separations. An optimum pore size distribution is required to further improve the selectivity of a PIM for a given application. Specific attention is given to the potential use of PIM‐based CMS membranes for energy‐intensive CO2/CH4, N2/CH4, C2H4/C2H6, and C3H6/C3H8separations, and thin film composite membranes containing PIM motifs for liquid separations.