Decrease In Free Volume Research Articles

Effect and mechanism of phenyl content on the electrical insulation properties of silicone rubber

AbstractSilicone rubber is widely used in reinforced insulation of cable accessories due to its good electrical insulation and weather resistance. With the continuous improvement of high voltage transmission grade, higher requirements are put forward for the electrical insulation performance. The effect and mechanism of phenyl content on the electrical insulation properties of silicone rubber are investigated by the method of combination of experiments and molecular simulations. The experimental results show that the properties of silicone rubber are improved with the increase of phenyl content. Among them, the silicone rubber composite with phenyl content of 20 wt% has the best comprehensive performance. Compared with vinyl silicone rubber, the dielectric constant at 50 Hz decreases from 3.50 to 2.95, and the breakdown strength increases by 38.03%, from 56.59 to 78.11 kV/mm. In addition, the tensile strength and elongation at break are 5.44 MPa and 456%, respectively. The molecular simulation results show that with the increase of phenyl content, the glass transition temperature increases, the mean square displacement decreases, and the free volume decreases, which macroscopically leads to the change of electrical properties of the silicone rubber material. This work has a certain guiding significance for improving the electrical properties of silicone rubber for cable accessories.

Strengthening effects of indentation notches on metallic glasses and their sensitivity to stress triaxiality

In this study, a metallic glass sample with an annular indentation notch was successfully constructed by a compression rod cyclic compression strategy using molecular dynamics simulation, and the mechanical behaviors of cut-notched metallic glass samples with the same stress triaxiality and notch size under triaxial compression were comparatively analyzed. It is found that the indentation notch further improves the strength and plasticity of the metallic glass, while it is insensitive to the cut-notched metallic glass with the same notch size. During triaxial compression, rejuvenation and shear softening lead to an increase in free volume, while diffusion and residual compressive stresses lead to a decrease in free volume. The stress triaxiality plays a key regulatory role in their competition and affects the final state of free volume change. This study provides a new theoretical basis and process idea for the enhancement of strength and plasticity of metallic glass.

The role of Ti in mitigating thermal expansion of silica from molecular dynamics simulations

AbstractMolecular dynamics simulations are performed to investigate the structural response of titania silicate glass to temperature. The coefficient of thermal expansion is computed for two titania silicate glasses with 0 and 10 mol% titania content, the structures of which are presented in terms of radial and angular distributions. Revealed by the different changing rates of intertetrahedra bond angles and bond lengths with respect to the Ti and Si atoms, the glass structures tend to exhibit a nonvectorized expansion process at elevated temperatures, leading to inconsistent expansion rates of the structures in different scales. While the average length of TiO and Si‐O bonds both increases with temperature, the decrease in the coefficient of thermal expansion by the addition of Ti atoms is associated with the different expansion rate of tetrahedra. Arising from the gradual decrease in atomic overlapping, decrease in free volume inside the glass with temperature is also identified.

Experimental study and numerical simulation on porosity dependent direct reducibility of high-grade iron oxide pellets in hydrogen

The transition to more environmentally friendly steel production methods has intensified research into hydrogen-based direct reduction (HyDR) of iron oxide pellets. The aim of this study is to systematically investigate the kinetics of the reduction process, the evolution of porosity and the resulting microstructural changes on the reduction behavior of high-quality pellets during HyDR of iron ore at different temperatures. A modified mathematical model is developed based on the shrinkage kernel model, taking into account both mass and heat transport in a hydrogen atmosphere. The effects of temperature, particle size and time on the reduction behavior of the pellets are investigated. The simulated results are validated and discussed by the results of a batch of iron oxide pellets consisting of ten almost spherical pellets subjected to the direct reduction process with pure hydrogen. The results show that the total energy input to the HyDR process is a complex balance of factors, including chemical reaction rates, diffusion dynamics and entropy generation. The increase in free volume and simultaneous decrease in pore diameter reflect the dynamic nature of the microstructure, which includes additional free volume and defects due to the volume discrepancies and associated stresses between the reactant and product phases. Furthermore, the data show that higher temperatures accelerate the reduction reactions, especially the transformation of wustite into metallic iron. This phase transition is characterized by a significant volume change that cannot be accommodated by elastic deformation alone, leading to the development of lattice defects such as cracks, creep pores and dislocations that serve as stress relief mechanisms. The trends for porosity change at 950 °C and 1000 °C observed in the experimental results are correct and in good agreement with the numerical and simulated results.

Effect of Aromatic Rings in AESO-VDM Biopolymers on the Local Free Volume and Diffusion Properties of Polymer Matrix

In this work, the influence of aromatic rings on the local free volume of cured mixtures of acrylate epoxidized soybean oil (AESO) and vanillin dimethacrylate (VDM) was investigated. Cross-linking took place under the influence of UV light in the presence or absence of a photoinitiator. The local free volume and its homogeneity were characterized using the Positron Annihilation Lifetime Spectroscopy (PALS) technique. It was found that increasing the content of VDM, which contains aromatic rings, caused a decrease in the local free volume of the cured polymer network, with consequences for the diffusion properties of the polymer, which were tested for the case of water. Another consequence of increasing the content of VDM was a decrease in the conversion of double bonds in the finally cured samples, characterized by near-infrared spectroscopy (NIR). This finding illustrates a case where the decrease in free volume is not necessarily related to an increase in the crosslinking density of the polymer, but is a consequence of the presence of an increase in the occupied volume of aromatic rings in the volume of the polymer.

Energy Storage Performance and Dielectric Properties of Surface Fluorinated BOPP Films

Various composite films with high energy storage performance and/or dielectric strength have been fabricated. However, due to some reasons, few of them have been used in practice, and BOPP film is still regarded as the state-of-the-art capacitor dielectric film. Previous work has indicated that direct fluorination can improve the dielectric strength of BOPP films. Herein, as a continuation of previous work, the energy storage performance and basic dielectric properties of the surface fluorinated BOPP film are investigated. The charge-discharge experimental results show that the surface fluorinated BOPP sample has the maximum energy storage or release density of 5.27 or 4.43 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which is 59.8% or 44.6% higher than that of the virgin BOPP sample. The dielectric measurement results indicate that the surface fluorinated BOPP sample has slightly higher dielectric constant and dielectric loss than the virgin BOPP sample. The analyses of physicochemical characteristics reveal that the 0.75 μm thick fluorinated surface layer has a high degree of fluorination. The results of the calculation based on the three-layer dielectric model and the dielectric measurements further show that the fluorinated surface layer has high dielectric constant and loss factor, similar to non-perfluoropolymers. The enhancement of energy storage performance and dielectric strength is mainly attributed to the blocking of the fluorinated layer to electron injection from the cathode, due to a 60% reduction of the interfacial electric field and a decrease in free volume of the surface layer by the fluorination.

Laboratory Study and Molecular Dynamics Simulation of High- and Low-Temperature Properties of Polyurethane-Modified Asphalt

This study investigated the modification mechanism of polyurethane (PU) on the high- and low-temperature properties of asphalt based on experimental and molecular dynamics (MD) simulations. PU-modified asphalt was prepared using an in situ polymerization method. The high- and low-temperature properties of asphalt containing various PU contents were investigated via a series of laboratory tests. The asphalt molecular model, the PU molecular model, and the PU–asphalt mixes system were modeled using software. Based on reasonable models, the influence of PU content on the physical modulus and molecular motion of asphalt at high temperatures was researched using MD simulations. The glass transition temperature of PU-modified asphalt with different contents was obtained using software, and the free volume theory and molecular diffusion movement were used to interpret the improvement mechanism of PU content on the low-temperature performance of asphalt. The results indicate that PU effectively can improve the high- and low-temperature properties of asphalt. PU has a significant positive effect on the physical modulus of asphalt, and the effect becomes more significant with the increase of PU content. In addition, PU can form a tight structure with asphalt and increase the stability of the asphalt system. The free volume ensures the free movement of PU molecules in the asphalt, allowing PU to be dispersed homogeneously in the asphalt. However, the free volume decreases when the PU content exceeds 15% by weight, which limits the improvement of the low-temperature performance of asphalt. The results of molecular simulation can explain the enhancement mechanism of PU, providing a reference for the performance enhancement of PU-modified asphalt.

Cell patterning on photocrosslinkable polymer films with micropatternable surfaces

AbstractThe regulation of cell behavior is crucial for understanding many fundamental biological processes and designing novel medical devices. Nano/micropatterning has been developed as a means of controlling cellular properties and behaviors. Using cinnamoyl groups that have undergone photodimerization, we have prepared facile photopatterning films with adjustable surface properties for cell patterning via simple steps. Our strategy for controlling surface properties uses the decrease in free volume induced by photocrosslinking. This paper describes the surface‐patterning properties of photocrosslinkable polymer films and the cell adhesion to their micropatterned surfaces. Upon culturing cells on micropatterned surfaces, preferential cell adhesion, alignment and proliferation are observed in the unexposed regions. Additionally, diverse surface patterns of photocrosslinkable polymer films have been fabricated using various photomasks, enabling effective control of cell adhesion and alignment. The ability to regulate cellular behavior via microfabricated surfaces of photocrosslinkable polymer films enables a new and facile approach for designing scaffolds for the development of novel advanced materials, tissue engineering, and regenerative medicine.

Preparation, characterization, and mechanical-optical properties of telluro-borate glasses containing tungsten

The current work is interested in the preparation, characterization, and mechanical-optical properties of the glasses in the (75-x)B2O3–10SrO–8TeO2–7ZnO−xWO3 system, with (x = 0 (BSTZW0), 1 (BSTZW1), 5 (BSTZW2), 10 (BSTZW3), 22 (BSTZW4), 27 (BSTZW5), 34 (BSTZW6), and 40 mol% (BSTZW7). The preparation of the glasses has involved the melt-quenching route. The new glasses are characterized by different characterization techniques using densimeter, microhardness, Raman spectroscopy, UV–visible absorption and emission, and X-ray diffraction. Photoluminescence can determine the impact of substituting B2O3 with WO3 on the mechanical-optical parameters and the structure of the present glasses. The prepared samples’ X-ray patterns showed amorphous states. The density value rises from 2.88 to 4.50 g/cm3, with the amount of WO3 rising from 0 to 40 mol% as a result of the difference in molecular weight between WO3 and B2O3. The Vickers microhardness (Hv) rises as the amount of WO3 increases as a result of a decrease in free volume and the formation of covalent bonds. The elastic moduli were found to increase when the WO3 concentrations increased from 0 to 40 mol%. This increase depends on the formation of bridging oxygen atoms. The Raman bands are designed to correspond to the bonds that form the structure of the current glass and detect the insertion of WO3 content by the attribution of the new W–O–W and W–O bonds. The UV–Visible spectroscopy analysis showed no band characteristic for the reduced species of W5+ ions identified by dark blue. However, the photoluminescence spectra showed emission bands (under excitation at 300 nm) that are associated with the active centers of W4+, W5+, and W6+ ions.

High oxygen barrier materials from paper to regenerated cellulose films

AbstractA transparent, bendable, high oxygen barrier cellulose‐based film was prepared, which has far better oxygen barrier properties than conventional polyethylene, polypropylene and cellophane materials. A series of regenerated cellulose films (RCs) were prepared from filter paper lacking oxygen barrier properties under different cellulose concentrations and gelation times. It was shown that the cellulose concentration and gel time had a greater effect on the oxygen barrier properties of RCs. When the cellulose concentration was 4 wt% and the gel time was 3 h, the RCs obtained the lowest oxygen permeability coefficient (OPC) down to 2.21 × 10−17 cm3 cm cm−2 s−1 Pa−1. The films have a tensile strength of 109.5 MPa, an elongation at break of 27.3% and a light transmission rate of 89%. In further, molecular dynamics simulations showed that when the filter paper was converted to RCs, the increase in hydrogen bonding and the decrease in free volume between cellulose chains caused a decrease in the diffusion coefficient of oxygen. As a novel biobased high oxygen barrier material, the film has broad application prospect in packaging and chemical industry.

Reversible linear-compression behavior of free volume in a metallic glass

Free volume is one of the key structural concepts widely used to describe various glass phenomena. However, free volume is challenging to be rigorously defined in glass structures and directly determined by experiments. Here, we employed metallic glass as a simple glass model system and studied the structural evolution of an as-spun (hyperquenched) and another thermally annealed metallic glass with different amounts of free volume by in situ high-pressure synchrotron x-ray diffraction. Therefore, the effect of free volume on the compression behavior of metallic glasses can be clarified by comparing the two samples at identical experimental conditions. We find that a higher amount of free volume causes both lower density and bulk modulus as expected at ambient conditions. Surprisingly, during compression, the decrease of free volume has a constant rate up to $\ensuremath{\sim}30\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and appears to be mostly reversible upon decompression without obvious permanent densification after pressure release. These results suggest an elastic process in metallic glasses under pressure. Implications of these results for the structural models based on the free-volume concept are discussed. The typically assumed glass structural model with isolated domains of ``liquidlike'' (free-volume rich) region embedded in a solidlike (free-volume poor) matrix seems unlikely. Instead, a more ``homogeneous'' model over a wide range of length scales such as a nested fractal network of liquid- and solidlike regions seems more consistent with the experimental observation.

Antioxidant and Antiulcer property of different solvent extracts of Cassia tora Linn.

Aim: The fundamental objective and goal of the current research is to determine the effectiveness of Cassia tora in the treatment of gastric ulcers in order to produce an anti-ulcer medication of natural origin. Method: The plant material was successively extracted by the Soxhlet extraction technique with chloroform, methanol, butanol and water. The antioxidant activity of the plant extracts and the standard drugs were based on consideration of the radical scavenging influence of the stable "1,1-diphenyl-2-picrylhydrazyl" (DPPH) free radical action and hydrogen peroxide process. Two models, and non-steroidal anti-inflammatory induced ulcer and pyloric ligation, were analysed for methanolic extract of Cassia tora for its antiulcer activity. Results: Among all the extract, the percent of DPPH inhibition at 200 μg mL-1 for MECT extracts (Cassia tora methanolic extract) was 58.67±1.95. The overall scavenging potential for the H2O2 process was 68.23±0.19 at 200 μg mL-1 by MECT extract. Hence MECT extract was undertaken for the antiulcer property. Compared with control, there was a significant (p&lt;0.05) decrease in free acidity, gastric volume, and total acidity in the extract-treated classes and ranitidine (standard). The Cassia tora methanolic extract demonstrated significant (p&lt;0.05) inhibition activity, i.e. 59.42 and 69.59 percent at 500 mg mL-1 with the PL (Pylorus ligation) and NSAID (Non-steroidal anti-inflammatory drugs) process respectively. Conclusion: The findings of present study provide the scientific evidence to Cassia tora as a strong antiulcer and antioxidant agent.

Photoresponsive Polymer Films with Directly Micropatternable Surfaces Based on the Change in Free Volume by Photo‐Crosslinking

AbstractPhotoresponsive polymers, whose structures or properties change when exposed to ultraviolet (UV) light, have been studied for the fabrication of micro‐ and nano‐devices for various applications. Herein, photoresponsive polymer films are investigated with directly micropatternable surfaces formed by only UV exposure without the development process using solvents. The photoresponsive polymer films are designed based on the decrease in free volume induced by the photodimerization of cinnamoyl groups. The photoresponsive polymers are synthesized by copolymerizing a monomer with photodimerizable groups and a poly(dimethylsiloxane) macromonomer. Micropatterns are easily formed on the film surfaces by only UV exposure using photomasks. The micropatterns are achieved due to the decrease in the film thickness with a decrease in the free volume induced by photo‐crosslinking. Using a decrease in free volume by photo‐crosslinking leads to wide practical applications with simple processes and low costs.

Mechanically Strong, Thermally Stable Gas Barrier Polyimide Membranes Derived from Carbon Nanotube-Based Nanofluids.

Gas barrier membranes with impressive moisture permeability are highly demanded in air or nature gas dehumidification. We report a novel approach using polyetheramine oligomers covalently grafted on the carbon nanotubes (CNTs) to engineer liquid-like CNT nanofluids (CNT NFs), which are incorporated into a polyimide matrix to enhance the gas barrier and moisture permeation properties. Benefiting from the featured liquid-like characteristic of CNT NFs, a strong interfacial compatibility between CNTs and the polyimide matrix is achieved, and thus, the resulting membranes exhibit high heat resistance and desirable mechanical strength as well as remarkable fracture toughness, beneficially to withstanding creep, impact, and stress fatigue in separation applications. Positron annihilation lifetime spectroscopy measurements indicate a significant decrease in fractional free volume within the resulting membranes, leading to greatly enhanced gas barrier properties while almost showing full retention of moisture permeability compared to that of the pristine membrane. For membranes with 10 wt % CNT NFs, the gas transmission rates, respectively, decrease 99.9% for CH4, 94.4% for CO2, 99.2% for N2, and 97.9% for O2 compared with that of the pristine membrane. Most importantly, with the increasing amount of CNT NFs, the hybrid membranes demonstrate a simultaneous increase of barrier performance and permselectivity for H2O/CH4, H2O/N2, H2O/CO2, and H2O/O2. All these results make these membranes potential candidates for high-pressure natural gas or hyperthermal air dehydration.

Comparison of the Mechanical Properties of a Conjugated Polymer Deposited Using Spin Coating, Interfacial Spreading, Solution Shearing, and Spray Coating.

The mechanical properties of π-conjugated (semiconducting) polymers are a key determinant of the stability and manufacturability of devices envisioned for applications in energy and healthcare. These properties─including modulus, extensibility, toughness, and strength─are influenced by the morphology of the solid film, which depends on the method of processing. To date, the majority of work done on the mechanical properties of semiconducting polymers has been performed on films deposited by spin coating, a process not amenable to the manufacturing of large-area films. Here, we compare the mechanical properties of thin films of regioregular poly(3-heptylthiophene) (P3HpT) produced by three scalable deposition processes─interfacial spreading, solution shearing, and spray coating─and spin coating (as a reference). Our results lead to four principal conclusions. (1) Spray-coated films have poor mechanical robustness due to defects and inhomogeneous thickness. (2) Sheared films show the highest modulus, strength, and toughness, likely resulting from a decrease in free volume. (3) Interfacially spread films show a lower modulus but greater fracture strain than spin-coated films. (4) The trends observed in the tensile behavior of films cast using different deposition processes held true for both P3HpT and poly(3-butylthiophene) (P3BT), an analogue with a higher glass transition temperature. Grazing incidence X-ray diffraction and ultraviolet-visible spectroscopy reveal many notable differences in the solid structures of P3HpT films generated by all four processes. While these morphological differences provide possible explanations for differences in the electronic properties (hole mobility), we find that the mechanical properties of the film are dominated by the free volume and surface topography. In field-effect transistors, spread films had mobilities more than 1 magnitude greater than any other films, likely due to a relatively high proportion of edge-on texturing and long coherence length in the crystalline domains. Overall, spread films offer the best combination of deformability and charge-transport properties.

Unravelling the origin of in-cage vibrations in a La50Al15Ni35 metallic glass

The structural origin of β-relaxation is still an open issue in glassy materials. Focusing on the as-cast and annealed La50Al15Ni35 metallic glasses (MGs), we demonstrate that the local vibration of Ni atoms contributes more to the β-relaxation in both samples through synchrotron X-ray measurements and theoretical calculations. It is found that besides the free volume decreases, the chemical constitution around mobile Ni atoms in Ni-centered polyhedra tends to transform from Al-free to Al/Ni-containing after annealing, which suppress the local vibration of central Ni atoms, thus leading to the unpronounced β-relaxation event. Moreover, we observe that the atomic mobility of Ni atoms more depends on their local polyhedral geometry and chemical constitution than the content of surrounding free volume. Our work paves a way to better understand the origin of β-relaxation in MGs and other glassy materials from their local atomic environments.

Enhanced DC breakdown strength of epoxy nanocomposites at elevated temperature and its mechanisms

Breakdown of epoxy composites is easy to be triggered as the temperature is elevated. In order to improve the DC breakdown strength of epoxy composites at elevated temperature and explore the DC breakdown mechanism, functional nano-titania (TiO2) particles were incorporated into the epoxy matrix with different filler loadings, molecular chain dynamic characteristics were analyzed by dielectric relaxation spectrum analysis, free volumes of epoxy nanocomposites were evaluated by thermal expansion dilatometer, and DC breakdown strengths of samples were tested at 413 K. Results indicate that DC breakdown strength first increases and then decreases with nanoparticle filler loadings, and a 10.89% improvement of DC breakdown strength is found compared to pristine epoxy resin. The breakdown strength of epoxy resin at elevated temperature is determined by the expansion properties of free volume in the interfacial region between the epoxy matrix and nanoparticles. When incorporating a small amount of nanoparticles, free volume is difficult to expand due to the strong interactions between molecular chains and nanoparticles, the fraction of free volume decreases, and long molecular chains of epoxy are hard to move, and thus DC breakdown strength increases. While further adding nanoparticles, interfacial regions of nanoparticles overlap and free volumes are likely to expand by thermal stimulation in the overlap region, which accelerate molecular chain dynamics and improve free volume fraction, and DC breakdown strength increases. It can be found that DC breakdown strength at an elevated temperature can be enhanced by tailoring free volume through incorporating proper content of functional nanoparticles.

Exfoliated clay nanocomposites of renewable long-chain aliphatic polyamide through in-situ polymerization

The current study was performed to synthesize a series of renewable polyamide 614/organoclay nanocomposites (PAC) with the improved structural, mechanical, and thermal properties via in-situ polymerization. The uniform dispersion and exfoliation of clay into the PA614 matrix, particularly at a lower loading of organoclay (less than 3%), confirmed via structural analyses (XRD, SEM, and TEM). Furthermore, the mechanical tests revealed remarkable improvement; namely, the tensile strength and storage modulus increased by 27% and 30%, respectively, in the sample contained 2% organoclay. Similarly, the TGA results showed a slight improvement in the thermal stability of the nanocomposite samples. Altogether, these improvements confirmed excellent compatibility between nanofiller and matrix and the organoclay homogenous dispersion into the PA matrix achieved by employing in-situ polymerization. Furthermore, all the samples illustrated a shear-thinning behavior over frequency attributed to the lack of time for the polymer chain to respond to the applied oscillation. Finally, the crystallinity of the samples diminished upon increasing the filler's content, which could be due to the decrease of free volume resulting from the presence of organoclay. To sum up, the current investigation supported the benefit of employing in-situ polymerization to synthesize renewable PA614/clay nanocomposites with enhanced physio-mechanical properties, which could be appropriate candidates for engineering applications.

Fabrication of radiation crosslinked and MWCNT reinforced ethylene acrylic elastomer nanocomposites: Evaluation of mechanical, dynamic mechanical, thermal and dielectric properties

Abstract The electron beam (EB) crosslinked and MWCNT reinforced ethylene acrylic elastomer (AEM) nanocomposites have been developed with varying the EB dose (50–250 kGy) and MWCNT loading level (0–8 parts per hundred gram of rubber (phr)) for various applications. The crosslink density and gel fraction significantly increase with increase in EB dose and MWCNT loading which ensures the radiation sensitizing effects of MWCNT. The chain scission to crosslink density has been check by using Flory–Rehner relationship at room temperature and the decrease in slope of the plots again confirms the predominance of crosslinking over chain scission at higher EB dose. The dispersion patterns of the MWCNT phase in bulk AEM matrix have been analyzed by using FESEM technique. Uniformly dispersed MWCNT with closely spaced network structures has been found in the FESEM photomicrographs at 4 phr loading level. The tensile strength and tensile modulus are extensively increased with increasing EB dose and up to 6 phr of MWCNT loading which ensures the reinforcing nature of MWCNT. Increase in tensile modulus (M100) and storage modulus (E ') with increase in EB dose and MWCNT indicates the absorption of applied load due to decrease in free volume of the systems. Increase in decomposition temperature with MWCNT loading of the nanocomposites has been confirmed from the thermal analysis. The significant increase in dielectric permittivity (eʹ) on increasing the MWCNT loading is mostly due to the increase accumulation of charge particles at the interface as well as increase in polarizable dipoles. The improvement in AC conductivity (σac) of these nanocomposites is mostly due to the easy electron tunnelling and hopping transport processes executed through the constructed networks by MWCNT in the bulk as well as interface.

Characterization and gas transport properties of UV-irradiated polydimethylsiloxane (PDMS)-containing polyimide copolymer membranes

The influence of UV irradiation on gas permeation properties of random segmented poly (imide-siloxane) (PIS) copolymer films was investigated. Random segmented copolymers were synthesized via ester-acid imidization from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) in a 7:3 M ratio with 2,4-diamino mesitylene (DAM) and varying amounts of a diamine terminated polydimethylsiloxane (PDMS) oligomer (Mn = 3000 g/mol). Solvent cast films of these copolymers were UV-irradiated on both sides in air at 365 nm, which induced crosslinking and photooxidation. Pure-gas permeabilities of H2, O2, N2, CH4, and CO2 were measured with upstream pressures ranging from 2 to 18 atm at 35 °C. Gas permeability coefficients of a series of PIS copolymers decreased, and selectivity of all gas pairs increased after UV irradiation due to a decrease in free volume by UV crosslinking and photooxidation.