Gas Permeation Properties Research Articles

Mixed matrix membranes comprising 6FDA-based polyimide blends and UiO-66 with co-continuous structures for gas separations

Membrane gas separation is considered a highly promising alternative to conventional gas separation. Recently, mixed matrix membranes containing UiO-66 metal–organic frameworks (MOFs) have been demonstrated to achieve high gas separation performance, especially in CO2-related separation. To date, few studies have used morphological control strategies to enhance the gas transport properties of mixed matrix membranes. In this study, we fabricated mixed matrix membranes comprising porous UiO-66 nanoparticles and immiscible 6FDA-based polyimide blends with co-continuous structures. The selective location of UiO-66 nanoparticles within one polymer phase of the co-continuous polymer blend was observed. However, this co-continuous structure cannot be referred to as a double-percolative morphology since the percolative UiO-66 networks did not successfully form. The gas permeability and gas sorption properties of pure gases (H2, CO2, N2, O2, and CH4) in the dense membranes and mixed matrix membranes were measured using the constant-volume variable-pressure method and the dual-volume pressure decay method, respectively. On the basis of the solution–diffusion mechanism, the contributions of gas sorption and gas transport to the overall gas permeation properties were determined and examined. When the UiO-66 content reached 35 wt%, the CO2 permeability of the mixed matrix membranes was significantly increased from 16.5 Barrer to 104.7 Barrer (by 635 %) without scarifying the permeability selectivities of CO2/N2 (16.5 ± 1.5) and CO2/CH4 (31.7 ± 5.8). The results suggest that both the addition of porous UiO-66 nanoparticles and the co-continuous structures contributed to the strongly enhanced gas separation performance of the mixed matrix membranes.

Molecular Insight into 6FD Polyimide-Branched Poly(phenylene) Copolymers: Synthesis, Block Compatibility, and Gas Transport Study

A series of 6FDA-DABA (6FD) polyimide and branched poly(phenylene) (PP) block copolymers and homopolymers were successfully synthesized using Diels–Alder and polycondensation reactions. PP and 6FD homopolymer blends in tetrahydrofuran were immiscible. The result coincides with their large chemical dissimilarity and theoretical solubility parameter differences of 25.47 and 33.17 (MJ/m3)1/2. However, 6FD-PP block copolymer solutions were clear, and thin films were robust and creasable. Densities and fractional free volumes (FFV) (0.162–0.346) largely obeyed the rule of mixing, suggesting a “blend-like” morphology. At moderate PP block lengths, two distinct glass transition temperatures (340 and 420 °C) were evident, while large PP block lengths suppressed first-order polyimide transitions entirely. A small-angle X-ray scattering and atomic force microscopy morphological analysis revealed two distinct domains, with separation lengths increasing with the PP block length. Their gas permeation, diffusion, sorption, and separation properties were thoroughly investigated and exhibited a strong correlation with polymer chemistry, block length, and FFV. A block copolymer had an O2 permeability roughly between 6FD and PP, resulting in a 30% increase in O2/N2 selectivity. The N2/CH4 selectivities ranged from 4.2 to 0.58, suggesting that this 6FD-PP system could be efficiently tuned from highly N2-selective to CH4-selective performance. Five structural models, rule-of-mixture, Maxwell, equivalent box model, laminate, and blend, were used to predict gas transport properties. Compared with experimental data, the miscible blend model provided the best results for the 6FD-PP block copolymer system. Block copolymerization by combining highly selective polyimide and highly permeable branched poly(phenylene) provides an opportunity for gas separation tunability and improvement in selected gas pairs.

Engineering gas separation property of metal–organic framework membranes via polymer insertion

We report on a novel approach to engineering the gas permeation property of metal–organic framework (MOF) membranes via polymer infiltration. This method enables MOFs of a too large intrinsic aperture size (>0.7 nm) for membrane separation of small molecules. [Zn2(bdc)2ted]n, referred to as ZnMOF, is studied as a model system for the proof of concept. This MOF has a pore limiting diameter of 7.63 Å, which is notably larger than the kinetic diameters of the gases to be separated (2.89, 3.3, and 3.8 Å for H2, CO2, and CH4, respectively). We prepare ZnMOF membranes, followed by the insertion of polyethylene glycol (PEG) via dip coating, spin-on deposition, or drop coating. Comprehensive materials characterization is performed via a number of solid-state techniques, including nitrogen physisorption, Fourier-transform infrared spectroscopy, thermogravimetric analysis, solution-state nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The results suggest that the three deposition methods all enable the infiltration of PEG in the micropores of the ZnMOF membranes. The as-made ZnMOF membrane possesses low gas selectivity (5.19 for H2/CO2 and 3.8 for H2/CH4), owing to its large pore size. With the PEG infiltration, the ZnMOF membrane presents good selectivity of H2/CO2 (26.28) and H2/CH4 (17.6). Molecular simulations also suggest that the impregnation of PEG reduces the effective pore size of the ZnMOF structure and thus renders it a higher diffusion selectivity for gas mixtures as compared to the bare PEG or the pristine ZnMOF membranes.

Improvement of the well cementing technology, increasing the reliability of the annule isolation and preserving the permeability of the reservoir

The article presents measures to improve the quality of cementing the production string of high-performance wells. The relevance of the proposed technological solutions is substantiated. The results of experimental studies of the installation simulating the processes occurring during the thickening of the cement slurry under the action of gravitational forces are presented. An algorithm for creating overpressure on the wellhead during fastening of the production string is proposed. The compositions of process fluids are described, which increase the reliability of the annular space isolation and preserve the permeability of the reservoir, and provide the main data on the results of their laboratory studies. For cementing the annular space of the production string, the composition of the expanding cement slurry has been developed and the procedure for its preparation has been established. The proposed solution has low water separation and high sedimentation resistance; has adjustable rheological parameters. Cement stone is characterized by low gas permeability and high strength properties.

Improvement of the well cementing technology

The article presents measures to improve the quality of cementing the production string of high-performance wells. The relevance of the proposed technological solutions is substantiated. The results of experimental studies of the installation simulating the processes occurring during the thickening of the cement slurry under the action of gravitational forces are presented. An algorithm for creating overpressure on the wellhead during fastening of the production string is proposed. The compositions of process fluids are described, which increase the reliability of the annular space isolation and preserve the permeability of the reservoir, and provide the main data on the results of their laboratory studies. For cementing the annular space of the production string, the composition of the expanding cement slurry has been developed and the procedure for its preparation has been established. The proposed solution has low water separation and high sedimentation resistance; has adjustable rheological parameters. Cement stone is characterized by low gas permeability and high strength properties.

Gas Permeation Property of Ultra–high CO2 Permeable Composite Membranes Loaded with High Concentration of Surface–modified Nanoparticles

Highly concentrated particle composite membrane consisting of PIM–1 and surface–modified nanoparticles was developed. The gas permeation properties of the fabricated composite membranes were dependent on the molecular weight of the matrix. The maximum gas permeability of the fabricated composite membranes was 45,000 Barrer. The selectivity of the fabricated composite membranes was maintained. We have succeeded in developing an excellent separation membrane with high permeability.

Insight into the effect of biaxial compression strain on adsorption structure of bituminous coal matrix as well as gas diffusion and permeability properties by macromolecule simulation

The concentrated stress induced by mining activities leads to deformation of the coal, especially the coal matrix, which affects the production of coalbed methane (CBM). Therefore, grand canonical Monte Carlo and molecular dynamics methods were used to study the effect of biaxial compression strain on the adsorption structure of the bituminous coal matrix as well as the CH4/CO2/N2 diffusion and permeability properties based on the constructed macromolecular coal model. The results show that the dual-mode equation fits the gas adsorption isotherm and the order of influence of adsorption concentration on the model structure is N2 > CO2 > CH4. For the diffusion models, the orders of swelling rate and specific volume are CH4 > N2 > CO2, while those of the fractional free volume and pore volume are opposite. Compression (negative) strain (0.00 ∼ −0.20) reduces the bulk modulus but has a negligible effect on the shear modulus and wave velocity. Also the Poisson’s ratio of the CH4 diffusion model is smaller compared to the CO2/N2 diffusion model. The cohesive energy density (CED) order is CO2 > N2 > CH4 and its van der Waals component accounts for the major part. The mean square displacement distribution of gases successively increases in the power function and linearity with time. The self-diffusion coefficient of CH4 is larger than that of CO2/N2, which is greatly affected by strain. The (negative) interaction energy order between gas and coal matrix is CH4 > N2 > CO2, and the order of intermolecular interaction distance of gases is N2 > CO2 > CH4. Most importantly, the solubility order of gases is CO2 > CH4 > N2, and the strain has the dual effect of promoting and inhibiting the permeability of the coal matrix. The research results provide molecular-level insights into CBM recoveries in coal reservoirs with different strain degrees, with some technical value and theoretical importance.

Alumina-PEBA/ PSf Multilayer composite membranes for CO2 separation: experimental and molecular simulation studies

In this research, Polyether block amide (PEBA) containing different loadings of α-Al2O3 particles was deposited on top of the polysulfone (PSf ) supports to form PEBA 1657‒α-Al2O3/PSf multilayer composite mixed matrix membranes (MCMMMs). Multilayer Composite structure was used to overcome the sedimentation of fillers in the polymer matrix. Moreover, alpha phase of the Al2O3 particles was applied to improve the distribution of these particles at higher loadings. SEM, XRD, and FTIR tests were applied to study morphology, crystalline structure, and chemical structure of the membranes, respectively. Gas permeation properties of the membranes were also measured using three different pure gases (CO2, CH4, and N2) at the pressure of 7 bar and temperature of 25 ºC. CO2 permeance and ideal selectivity of CO2/CH4, and CO2/N2 for the optimum MCMMM with 20 wt% loading of α-Al2O3 particles were 25% (117.5 Barrer), 81.5 % (32), and 86.5% (57) higher than that of multilayer composite neat membrane (MCNM), respectively. The molecular simulation results confirmed the results of the experimental studies and approved that the α-Al2O3 particles are right candidates for improving the PEBA performance for CO2 separation.

Orientation of the microstructure of free-standing carbon hollow fiber membranes modulated by carbonization condition triggers aging-resistant properties

The aim of this study is to determine the optimal carbonization conditions for carbon hollow fiber membranes for hydrogen purification. To this end, it is a prerequisite to obtain the best permselectivity of the resultant membrane. Three different carbonization atmospheres (vacuum, helium flow, and argon flow) were examined, while their effects on the changes in the microstructure and gas permeation properties of the as-synthesized carbon membranes were elucidated using a pure gas permeation test, coupled with an array of characterizations, including Raman spectroscopy and XPS. Moreover, the issue of vacuum degree was addressed to maintain the best reproducibility of the carbon membrane. The results revealed that CHFM-HV exhibited the best separation capability for H2/CH4 of 516.90, thereby indicating distinct hydrogen purification characteristics. Such good performance was driven by the attractive synergism of the ordered microstructure and larger pore volume. Notably, the recovery of permselectivity for CHFM-HV reached 90% after four months, thus suggesting its aging resistance. Hence, the demonstrated approach is efficient for altering the microstructure of the carbon membrane, thereby strengthening the separation performance and long-term stability. Overall, it is suitable for broad applications of diverse polymer precursors and prolonged the lifespan of the as-prepared carbon membrane.

Preparation and characterization of vacuum insulation panels with hybrid composite core materials of bamboo and glass fiber

Thermal insulation materials of vacuum insulation panels (VIPs) are manufactured utilizing an efficient and cost-effective hybrid multi-level network composite core material made from natural and sustainable bamboo fiber (BF) as a raw material and glass fiber (GF) as a reinforcing agent. The morphological, textural structural, gas permeability, and tensile strength properties of the core materials, as well as the thermal insulation performance of VIP, are examined. The results showed that both the bamboo and glass fibers are uniformly dispersed in the core material and achieved a three-dimensional (3D) network structure. The inclusion of glass fiber may significantly alter the core material's structure, resulting in a considerable decrease in the thermal conductivity of VIP. VIP constructed entirely of bamboo fiber BGF0 has relatively high thermal conductivities of 12.62 mW/(m·K), which can be reduced to 4.81 mW/(m·K) while maintaining excellent aging performance by using hybrid composite core material BGF50.

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes.

A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that carbon-linking (pendant–type) units exert on a microporous structure and how this affects the gas-permeation properties of pendant–type organosilica membranes. Gas permeation results were compared with those of bridged–type organosilica membranes (C1–C8). Network pore size evaluation was conducted based on the selectivity of H2/N2 and the activation energy (Ep) of H2 permeation. Consequently, Ep (H2) was increased as the C/Si ratio increased from C1 to C8, which could have been due to the aggregation of pendant side chains that occupied the available micropore channel space and resulted in the reduced pore size. By comparison, these permeation results indicate that pendant–type organosilica membranes showed a somewhat loose network structure in comparison with bridged–type organosilica membranes by following the lower values of activation energies (Ep). Subsequently, we also evaluated the effect that fluorine doping (NH4F) exerts on pendant−type [methytriethoxysilane (MTES), propyltrimethoxysilane (PTMS)] and bridged-type [1,2–bis(triethoxysilyl)methane (BTESM) bis(triethoxysilyl)propane (BTESP)] organosilica structures with similar carbon numbers (C1 and C3). The gas-permeation properties of F–doped pendant network structures revealed values for pore size, H2/N2 selectivity, and Ep (H2) that were comparable to those of pristine organosilica membranes. This could be ascribed to the pendant side chains, which might have hindered the effectiveness of fluorine in pendant–type organosilica structures. The F–doped bridged–type organosilica (BTESM and BTESP) membranes, on the other hand, exhibited a looser network formation as the fluorine concentration increased.

Furanoate Polyesters/Polylactide/Reduced Graphene Oxide Nanocomposite Films: Thermomechanical and Gas Permeation Properties

AbstractThis work aims at preparing bioderived polymer films by blending poly(lactic) acid (PLA) and poly(dodecylene 2,5‐furandicarboxylate) (PDoF) and containing reduced graphene oxide (rGO) as a multifunctional filler in variable weight fraction (from 0.25 to 2 phr). Although the PLA/PDoF blend results as immiscible, the addition of rGO leads to smaller (from 2.6 to 1.6 µm) and more irregularly shaped PDoF domains and to a better PLA/PDoF interfacial adhesion, which suggests that rGO may act as a blend compatibilizer. Dynamic mechanical thermal analysis (DMTA) shows that rGO shifts the glass transition of PDoF (≈5°C) to higher temperatures. The addition of 10 wt% PDoF in PLA increases the strain at break (+145%), and the addition of 0.25 phr of rGO to this blend increases its tensile strength (+13%), without significantly modifying the strain at break. Finally, rGO strongly decreases the diffusivity and permeability to O2, N2, and CO2 due to an increased diffusion path for gas molecules. These results highlight the positive and sometimes synergistic role of PDoF and rGO in tuning the thermomechanical and gas permeation properties of PLA.

Investigation of the Gas Separation Properties of Polyurethane Membranes in Presence of Boehmite Nanoparticles

In this study, the effect of boehmite nanoparticles on the CO2, CH4, O2, and N2 permeability in polyurethane membranes was investigated. Boehmite nanoparticles were synthesized by the hydrothermal method using the salt of aluminum nitrate Al (NO3)3 and diethanolamine as a precipitating agent. Different temperatures (110, 160, and 200) °C and times (18–24 h) in synthesizing boehmite nanoparticles are also investigated. The characteristics of the synthesized nanoparticles were analyzed with X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), and Transmission electron microscopy (TEM). The analysis results represented that increasing the temperature to 200 °C as well as high duration time at this temperature (24 h) result in nanoparticles with high purity and high crystallinity. Polyurethane was synthesized by bulk two-step polymerization using hexamethylene diisocyanate (HMDI) and 1,4-butanediol (BDO) as hard segments and poly(tetramethylene glycol) (PTMG, 2,000 g/mol) as the soft segment. The synthesized polymer was in a molar ratio: PTMG: HMDI: BDO = 1:3:2. PU membranes and PU-boehmite nanocomposite membranes were prepared using solution casting and solvent evaporation technique. The characteristics of the synthesized nanocomposite membranes were analyzed with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), and differential scanning calorimetry (DSC). The results of characterization analyses indicated that there is a strong interaction between boehmite nanoparticles and polymer and also the appropriate distribution of boehmite nanoparticles in the prepared samples. Gas permeation properties of polyurethane—boehmite nanocomposite at different boehmite loadings (0, 5, 10, 15, and 20 wt.%) were studied for pure CO2, CH4, O2, and N2 gases at 8 bar and 30 °C. The obtained results indicated that the reduction in permeability of all gases but enhancement in CO2/N2, CO2/CH4, and O2/N2 selectivities were observed as boehmite content increases. In the membrane with 20 wt.% boehmite content, enhancement of CO2/N2 (65.33%) and CO2/CH4 (55.37%) selectivities were observed in comparison with pure polyurethane, while the CO2 permeability reduction of polyurethane–boehmite membranes was 22.08%.

Gas Permeability and Mechanical Properties of Polyurethane-Based Membranes for Blood Oxygenators.

The production of medical devices follows strict guidelines where bio- and hemocompatibility, mechanical strength, and tear resistance are important features. Segmented polyurethanes (PUs) are an important class of polymers that fulfill many of these requirements, thus justifying the investigation of novel derivatives with enhanced properties, such as modulated carbon dioxide and oxygen permeability. In this work, three segmented polyurethane-based membranes, containing blocks of hard segments (HSs) dispersed in a matrix of soft segment (SS) blocks, were prepared by reacting a PU prepolymer (PUR) with tris(hydroxymethyl)aminomethane (TRIS), Congo red (CR) and methyl-β-cyclodextrin (MBCD), rendering PU/TRIS, PU/CR and PU/MBCD membranes. The pure (control) PU membrane exhibited the highest degree of phase segregation between HSs and SSs followed by PU/TRIS and PU/MBCD membranes, and the PU/CR membrane displayed the highest degree of mixing. Pure PU and PU/CR membranes exhibited the highest and lowest values of Young’s modulus, tangent moduli and ultimate tensile strength, respectively, suggesting that the introduction of CR increases molecular mobility, thus reducing stiffness. The CO2 permeability was highest for the PU/CR membrane, 347 Barrer, and lowest for the pure PU membrane, 278 Barrer, suggesting that a higher degree of mixing between HSs and SSs leads to higher CO2 permeation rates. The permeability of O2 was similar for all membranes, but ca. 10-fold lower than the CO2 permeability.

Construction of selective gas permeation channels in polymeric membranes using nanocage tuned ionic liquid/MIL-53 (Al) filler nanoparticles for effective CO2 separation

Polymeric membranes with metal-organic frameworks (MOFs) holds great potential for gas separation. However, finely tailoring the adhesion between MOFs and polymer matrices is crucial in reducing the membranes defective structure. The partial inorganic structure of MOFs limits the interaction with the polymer matrix, which tends to agglomerate on the membranes. Herein, an interfacial strategy is reported by post-synthetic functionalization of MIL-53 (Al) with ionic liquids (ILs) to construct IL@MIL-53 (Al) composite to improve interfacial interaction among filler and polysulfone (PSf) matrices. At 2 wt% of IL@MIL-53 (Al), the composite membranes tensile strength and % elongation were enhanced by about 66.13 and 97.40% compared to the neat PSf membrane. The intimate contact between IL@MIL-53 (Al) and PSf matrices renders uniform dispersion evident from morphological studies. The gas permeation properties were evaluated for carbondioxide (CO2), nitrogen (N2), methane (CH4) gases. At 2 wt% of MIIL-53 (Al) nanofiller, the CO2 permeance was found to be 37.56 ± 0.63 GPU which was significantly higher than the neat PSf membrane. Besides, the CO2 permeance of the PSf/2% IL@MIL-53 (Al) membrane was noted to be 34.23 ± 0.68 GPU, whereas the CO2/CH4 and CO2/N2 selectivities were 48.64 and 49.19% higher than the neat membrane. As the pressure increased from 2 to 10 bar, the CO2, N2, and CH4 gas permeances in composite PSf membranes were decreased, whereas the CO2/N2 and CO2/CH4 selectivities were observed to be increased. The introduction of ILs into the MOFs pores will tune pore size with the enhanced adsorption selectivity due to its high CO2 solubility and affinity of ILs. ILs functionalization on the cores of the MIL-53 (Al) structure is an effective strategy, which opens up the selection to a broad range of fillers in the aspect of commercialization.

Effect of Polyurethane Substrate Morphology on Gas Permeation Properties of Poly(dimethyl siloxane) Block Copolymer/Polyurethane Layered Membranes

Effect of Polyurethane Substrate Morphology on Gas Permeation Properties of Poly(dimethyl siloxane) Block Copolymer/Polyurethane Layered Membranes

Preparation of semi-alicyclic homo- and blended polyimide membranes using alicyclic dianhydrides with kink structures and their gas separation properties

Aromatic polyimides are promising membrane materials for gas separation due to their excellent gas separation properties. Herein, two soluble semi-alicyclic polyimides were synthesized via a one-step thermal imidization process with two semi-alicyclic dianhydrides possessing kink structures: bicyclo[2,2,2] oct-7ene-2,3,5,6-tetracarboxylic dianhydride (BCDA) and 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA), and a flexible aromatic diamine: 4,4′-Oxydianiline (ODA). Their homo- and blended membranes were prepared in various mixing ratios (100/0, 75/25, 50/50, 25/75, and 0/100) and their gas permeation properties were investigated for five gases (H2, CO2, O2, N2, and CH4) and selectivity for five gas pairs (H2/CH4, H2/N2, CO2/CH4, CO2/N2, and O2/N2). The homopolyimides (BCDA-ODA, DOCDA-ODA) exhibited amorphous structure without crystallinity and good solubilities in the casting solvents. BCDA-ODA showed larger d-spacing/FFV values, higher gas diffusivities/gas solubilities than DOCDA-ODA, resulted in higher gas permeabilities and lower gas selectivity, which were remarkably affected by feed temperature. Also, the gas permeability and selectivity of the blended membranes were dependent upon the BCDA/DOCDA mole ratio. The good gas separation performances of homo- and blended membranes were observed for H2/CH4, H2/N2, CO2/CH4, and O2/N2, which are comparable to those of commercial membrane materials such as P84®, PSF, CA, Matrimid®, etc.

The gas permeability properties of poly(vinyltrimethylsilane) treated by low‐temperature plasma

AbstractThe results of one‐sided treatment of polyvinyltrimethylsilane (PVTMS) films using low‐temperature air plasma are presented. The treatment was carried out at 25°C in air at a pressure in the reaction chamber of 10–25 Pa and a processing time of 10–60 s. The surface of the plasma‐treated PVTMS films was analyzed by X‐ray photoelectron spectroscopy and atomic force microscopy and the contact angle values determined. The effect of the plasma conditions, such as the treatment time and the pressure in the reactor chamber, on the transport properties of the modified membrane for He, O2, N2, CO2, and CH4 were investigated in detail. The permeability of all plasma‐treated PVTMS films for the studied gases except for He was found to decrease depending on the modification conditions, leading to an increase in selectivity for such pairs as He/CH4, CO2/CH4, and O2/N2. The selectivity of the modified PVTMS achieved a maximum value when the films were treated with plasma for 20–40 s at a chamber pressure of 15–20 Pa. The effective diffusion coefficients of the studied gases were obtained experimentally. It was shown that the volumetric diffusion of gases, particularly O2 and N2, in PVTMS before as after plasma treatment is described by the classical diffusion equations. The theoretical approaches to the influence of boundary conditions on selective gas transfer through polymeric membrane are considered. To estimate the prospects for the long‐term use of membranes based on modified PVTMS, the stability of the parameters gas permeability and selectivity of the modified samples was investigated over 9 months. It was shown that the modification of PVTMS by the method of low‐temperature plasma in air is a promising method for expanding the spectrum of membrane processes based on existing commercial membranes.

Cometary dust analogues for physics experiments

ABSTRACT The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This ‘CoPhyLab dust’ is planned to be mixed with water and CO2 ice and placed under cometary conditions in vacuum chambers to study the physical processes taking place on the nuclei of comets. In order to develop this dust analogue, we mixed two components representative for the non-volatile materials present in cometary nuclei. We chose silica dust as a representative for the mineral phase and charcoal for the organic phase, which also acts as a darkening agent. In this paper, we provide an overview of known cometary analogues before presenting measurements of eight physical properties of different mixtures of the two materials and a comparison of these measurements with known cometary values. The physical properties of interest are particle size, density, gas permeability, spectrophotometry, and mechanical, thermal, and electrical properties. We found that the analogue dust that matches the highest number of physical properties of cometary materials consists of a mixture of either 60 per cent/40 per cent or 70 per cent/30 per cent of silica dust/charcoal by mass. These best-fit dust analogue will be used in future CoPhyLab experiments.

Enhanced Dielectric Strength and Capacitive Energy Density of Cyclic Polystyrene Films.

The maximum capacitive energy stored in polymeric dielectric capacitors, which are ubiquitous in high-power-density devices, is dictated by the dielectric breakdown strength of the dielectric polymer. The fundamental mechanisms of the dielectric breakdown, however, remain unclear. Based on a simple free-volume model of the polymer fluid state, we hypothesized that the free ends of linear polymer chains might act as “defect” sites, at which the dielectric breakdown can initiate. Thus, the dielectric breakdown strength of cyclic polymers should exhibit enhanced stability in comparison to that of their linear counterparts having the same composition and similar molar mass. This hypothesis is supported by the ∼50% enhancement in the dielectric breakdown strength and ∼80% enhancement in capacitive energy density of cyclic polystyrene melt films in comparison to corresponding linear polystyrene control films. Furthermore, we observed that cyclic polymers exhibit a denser packing density than the linear chain melts, an effect that is consistent with and could account for the observed property changes. Our work demonstrates that polymer topology can significantly influence the capacitive properties of polymer films, and correspondingly, we can expect polymer topology to influence the gas permeability, shear modulus, and other properties of thin films dependent on film density.