Ion Gel Membranes Research Articles

Sulfonated Chitosan Gel Membrane with Confined Amine Carriers for Stable and Efficient Carbon Dioxide Capture.

Capturing carbon dioxide (CO2) from flue gases is a crucial step towards reducing CO2 emissions. Among the various carbon capture methods, facilitated transport membranes (FTMs) have emerged as a promising technology for CO2 capture owing to their high efficiency and low energy consumption in separating CO2. However, FTMs still face the challenge of losing mobile carriers due to weak interaction between the carriers and membrane matrix. Herein, we report a sulfonated chitosan (SCS) gel membrane with confined amine carriers for effective CO2 capture. In this structure, diethylenetriamine (DETA) as a CO2-mobile carrier is confined within the SCS gel membrane via electrostatic forces, which can react reversibly with CO2 and thus greatly facilitate its transport. The SCS ion gel membrane allows for the fast diffusion of amine carriers within it while blocking the diffusion of nonreactive gases, like N2. Thus, the prepared membrane exhibits exceptional CO2 separation capabilities when tested under simulated flue gas conditions with CO2 permeance of 1155 GPU and an ultra-high CO2/N2 selectivity of above 550. Moreover, the membrane retains a stable separation performance during the 170 h continuous test. The excellent CO2 separation performance demonstrates the high potential of gel membranes for CO2 capture from flue gas.

Development of an ion gel-based CO2 separation membrane composed of Pebax 1657 and a CO2-philic ionic liquid.

A tough ion gel membrane containing a CO2-philic ionic liquid, 1-ethyl-3-methylimidazolium tricyanomethanide ([Emim][C(CN)3]), was developed, and its CO2 permeation properties were evaluated under humid conditions at elevated temperatures. Pebax 1657, which is a diblock copolymer composed of a polyamide block and a polyethylene oxide block, was used as the gel network of the ion gel membrane to prepare a tough ion gel with good ionic liquid-holding properties. The polyamide block formed a semicrystalline structure in [Emim][C(CN)3] to toughen the ion gel membrane via an energy dissipation mechanism. The polyethylene oxide block exhibited good compatibility with [Emim][C(CN)3] and contributed to the retention of the ionic liquid in the ion gel. The developed ion gel membrane showed a good CO2 separation performance of 1677 barrer CO2 permeability and 37 CO2/N2 permselectivity under humid conditions of 75% relative humidity at an elevated temperature of 50 °C, which corresponds to an exhaust gas from a coal-fired power plant.

A tough double-network ion gel membrane based on poly (ionic liquid) for efficient carbon capture

Ion gel membranes show great potential for carbon capture due to their excellent solubility selectivity for CO2. However, poor mechanical properties and limited stability as well as low gas permeability limit their application. Here, we report a environmentally friendly and simple strategy for preparing double-network(DN) ion gel membranes with both high strength and excellent gas separation performance. We use a “one-pot method” that the first network(FN) and the second network(SN) with ionic liquid were mixed evenly, and the DN membrane was prepared under heating and UV light. Wherein the FN was obtained by a ring-opening reaction between O, O-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol and a trimethylolpropane triglycidyl ether. And the SN was obtained by free radical polymerisation between 1 and vinyl-3-ethylimidazole bis(trifluoromethanesulfonyl)imide and a p-divinylbenzene (DVB) crosslinker. The crosslinking density of FN and SN, the mass ratio of the FN to the SN, as well as the content and type of free ionic liquid were optimized to improve the mechanical and gas separation properties of the DN membrane. When the crosslinking groups reacted quantitatively, the tensile strength of DN membranes is 1.5 MPa and the elongation at break is 120 %. With the increase of free ILs content, the crystallinity as well as the glass transformation temperature of the DN membrane decreases and the CO2 permeability increases (PCO2:866 Barrer α (CO2/N2):31). When 1-ethyl-3-methylimidazolium dicyanamide was used, the CO2/N2 separation performance can surpass the 2008 upper bound (PCO2:464 Barrer α (CO2/N2):63). The DN membrane has better gas separation and mechanical properties than the SN membrane and shows superior combination of the permeability and selectivity. This research provides a new approach designing a tough ion gel membrane which shows great potential for practical application in carbon capture.

Mixed matrix iongel membranes containing azo-porous organic polymers: Influence of temperature, pressure and water vapour on CO2 separation

The effect of temperature, pressure, and humidity content in the gas separation performance of iongel membranes are crucial parameters that should be assessed to determine the real potential of these materials to be used in CO2 separation processes. In this work, we present a detailed study on the impact of temperature (303, 323 and 353 K), pressure (2 and 4 bar), gas composition and water vapour content (between 11 and 21% of relative humidity) on the performance of iongels containing azo-porous organic polymers (azo-POPs), for CO2/N2 and CO2/CH4 binary gas separations. The iongels combining 80 wt% of the ionic liquid (IL) [C2mim][TFSI], 20 wt% of poly(ethylene glycol) diacrylate (PEGDA) and 0.5 wt% of different azo-POPs were prepared by a solvent-free UV curing method. At the lower temperature, the pressure increase seems to have a negative impact on the CO2 permeability of the prepared mixed matrix iongel membranes (MMIMs). However, the opposite behaviour was found when the temperature increases. Moreover, the presence of humidity in the feed gas stream affects the gas separation performance of the studied iongels, since the CO2 permeability greatly increases with increasing humidity in the gas mixture, while the selectivity decreases, for both gas separations under study. In general, the high pressure and temperature, and the presence of humidity have a significant influence on the separation performance of the studied iongel membranes, due to induced alterations in their structure and overall stability.

Development of an ion gel membrane containing a CO2-philic ionic liquid in interpenetrating semi-crystalline and crosslinkable polymer networks

We developed a tough and highly CO2-permeable ion gel membrane composed of a CO2-philic ionic liquid (IL), 1-ethyl-3-methylimidazolium tetracyanoborate ([Emim][B(CN)4]), and an interpenetrating polymer network (IPN) composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and crosslinkable poly(ethyl acrylate-co-N-succinimide acrylate) (poly(EA-co-NSA)). The semi-crystalline PVDF-HFP and IL-philic poly(EA-co-NSA) networks endowed the ion gel membrane with high mechanical strength and good IL-holding properties. The high mechanical strength and good IL-holding properties achieved by the polymer networks provided the ion gel membrane with high and selective CO2 permeability under pressurized conditions at a trans-membrane pressure difference of 250 kPa. In addition, the high CO2 absorbability of [Emim][B(CN)4] provided the ion gel membrane with a CO2 permeability of more than 2500 barrer and a CO2/N2 permselectivity of approximately 20 at an elevated temperature of 80 °C. It was also demonstrated that the CO2 permeability of the IPN ion gel membrane increased with increasing IL content. The IPN ion gel membrane with an IL content of 85 wt% had a CO2 permeability of 2243 barrer and a CO2/N2 permselectivity of 43 at 30 °C. The excellent CO2 permeability and CO2/N2 permselectivity were not changed by physical aging for more than one week.

Improved CO2/N2 separation performance by relatively continuous and defect-free distribution of IL-encapsulated ZIF-67 in ion gel membranes

Metal-organic frameworks (MOFs), as a typical type of porous materials, are widely used as fillers in mixed matrix membranes (MMMs) to enhance the gas separation performance. However, non-selective interface defects are prone to appear in MMMs under high MOF loading conditions, meanwhile, the discontinuous dispersion of MOF particles in polymeric matrices makes the gas molecules diffuse along the MOF-polymer-MOF intersection path and difficult to achieve efficient molecular transfer. These factors greatly compromise the ability of MOF to enhance membrane separation performance. Herein, the [C5min][BF4] encapsulated ZIF-67 (IL@ZIF) composites were embedded into the defect-free IL/Pebax ion gel matrix to form a mixed matrix ion gel membrane without interface defects. On the basis of good interfacial compatibility, the relatively continuous and highly selective CO2 transmission channels were constructed via increasing the filler loading up to 80 wt%. In this context, the typical IL@ZIF/IL/Pebax membrane with 80 wt% IL content and 70 wt% IL@ZIF doping amount exhibits a CO2 permeability of 408.2 Barrer and CO2/N2 selectivity of 97.2, surpassing the latest upper line. This work may have high reference value in the construction and preparation of MOF-based MMMs with high performance in gas separation.

Mixed matrix membranes based on ionic liquids and porous organic polymers for selective CO2 separation

The development of more efficient materials is a crucial step in the development of gas separation membranes. In this work, we combine ionic liquids (ILs) and porous organic polymers (POPs) for the first time to fabricate a new type of mixed matrix iongel membranes, which are entirely composed of organic materials. The new azo-POPs reported in this work were specifically designed due to their “CO2-philic” feature to be incorporated in iongel materials. The membranes, comprising 80 wt% of [C2mim][TFSI] IL and 20 wt% of poly(ethylene glycol) diacrylate (PEGDA) network, were prepared using a solvent-free UV curing method. The unique properties of azo-POPs within the iongel material resulted in the fabrication of dense and defect-free membranes with improved gas separation performances, in terms of both CO2 permeability (62.3–90.6 barrer) and, CO2/CH4 (9.9–12.0), CO2/H2 (6.0–12.1) and CO2/N2 (16.8–53.1) ideal selectivities, with the latter revealing to be highly dependent on the morphological properties of the azo-POPs. Furthermore, iongel characterization in terms of morphology, chemical structure and thermal properties, confirmed the potential of the novel mixed matrix iongels for CO2 separation processes.

Mixed-Matrix Ion Gel Membranes for Gas Separation

The potential of ionic liquid materials to improve membrane-based gas separation processes has been realized during the past few years, through the exploitation of diverse configurations, chemical functionalities, and properties. Nowadays, one of the most recent trends on this field is the development of mixed-matrix ion gels, an emerging family of ionic soft-solid materials, in which fillers are embedded into polymer/IL matrices. This review aims at presenting an overview on the latest developments and advances on ion gel membranes containing a third component, such as zeolites, metal organic frameworks, silica, graphene oxide, metal salts, and nanoparticles, for gas separation processes. We provide an analysis of this building system and highlight the diverse type of mixed-matrix ion gels hitherto reported, for which the impact of the different fillers on the ion gels’ overall properties is discussed in detail. The main challenges on their preparation, as well as their transport mechanism and how it can be influenced by the different fillers, are also addressed. Finally, technological aspects, perspectives, and opportunities to pursue this topic are discussed from a critical point of view.

Effects of polyimide sequence and monomer structures on CO2 permeation and mechanical properties of sulfonated polyimide/ionic liquid composite membranes

The effects of polymer structure on CO2 separation and mechanical properties of ion gel membranes composed of ionic liquids (ILs) and sulfonated polyimides (SPIs) were investigated. SPIs with different sequential distributions of ionic groups (multiblock and random) were synthesized. The multiblock copolymer exhibited higher IL uptake (∼80 wt.%) than the random copolymer, resulting in higher CO2 permeability (∼480 Barrer). The multiblock copolymer exhibited a clearer phase-separated structure than the random copolymer. However, the strain at the break of the multiblock copolymer was lower owing to the brittleness of the non-ionic phase. To improve the mechanical properties, an SPI containing fluorinated groups as a non-ionic part was also synthesized. Compared with the random SPI ion gel membranes, the multiblock SPI ion gel membranes containing fluorinated groups exhibited good CO2 permeability (∼500 Barrer) and simultaneously ductile properties with higher strain at the break due to the plasticization of the non-ionic phase, enabling a thin and tough membrane with excellent CO2 separation properties. These results indicate that the polyimide sequence in addition to the chemical structure of monomers affects CO2 permeation and mechanical properties of the sulfonated polyimide/ionic liquid composite membranes.

Poly(ethylene glycol) Diacrylate Iongel Membranes Reinforced with Nanoclays for CO2 Separation.

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to improve the mechanical properties of iongel membranes, which consists in the incorporation of montmorillonite (MMT) nanoclay, from 0.2 to 7.5 wt%, into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) network containing 60 wt% of the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][TFSI]). The iongels were prepared by a simple one-pot method using ultraviolet (UV) initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) and characterized by several techniques to assess their physico-chemical properties. The thermal stability of the iongels was influenced by the addition of higher MMT contents (>5 wt%). It was possible to improve both puncture strength and elongation at break with MMT contents up to 1 wt%. Furthermore, the highest ideal gas selectivities were achieved for iongels containing 0.5 wt% MMT, while the highest CO2 permeability was observed at 7.5 wt% MMT content, due to an increase in diffusivity. Remarkably, this strategy allowed for the preparation and gas permeation of self-standing iongel containing 80 wt% IL, which had not been possible up until now.

Fundamental Investigation of the Rate-Determining Step of CO2 Permeation through Ion Gel Membranes Containing Amino-Acid Ionic Liquid as the CO2 Carrier

The controlling factor of the CO2 permeance of an ion gel membrane containing a task-specific ionic liquid (tetraphosphonium prolinate) as the CO2 carrier was investigated. Tough double-network (DN...

Inorganic/organic double-network ion gel membrane with a high ionic liquid content for CO2 separation

To examine the potential of ion gels as materials for CO2 separation membranes, inorganic/organic double-network ion gel (DN ion gel) membranes with different ionic liquid (IL) contents were fabricated. The composition of the inorganic and organic networks was optimized to maximize the mechanical strength of the DN ion gel. The DN ion gel with an inorganic/organic network composition of 0.35 mol/mol showed the maximum mechanical strength because the inorganic and organic networks sufficiently acted as sacrificial bonds and hidden lengths, respectively. Using DN ion gel membranes with different IL contents prepared with the optimized precursor solution, the relationship between the CO2 permeability and IL content of the DN ion gel membranes was examined. The DN ion gel membrane with 95.2 wt% IL had a CO2 permeability of 1380 barrer, which was ~67% of the theoretical maximum predicted for the pure IL membrane. The CO2 permeability of the DN ion gel membrane exponentially increased with increasing IL content and approached the theoretical maximum. DN ion gels with high strength can be used to develop maximum-performance IL-based CO2 separation membranes by giving the membrane the maximum IL potential. The effect of the ionic liquid content in tough inorganic/organic double-network (DN) ion gel membrane on the CO2 permeability was investigated. By optimizing the composition of the inorganic and organic networks, the mechanical strength of the DN ion gel was significantly increased, and the DN ion gel membrane with more than 95 wt% of an ionic liquid was successfully prepared. With the increase in the ionic liquid content, the CO2 permeability of the DN ion gel membrane exponentially increased up to ~67% of the theoretical maximum CO2 permeability.

Characterization of Gel Polymer Electrolytes Based on Poly (Ionic Liquid)-Glyme Mixtures for Lithium Metal Batteries

Solid polymer electrolytes (SPE) have generated an extensive and sustained interest for its application in lithium metal batteries.[ 1 ] Compared with liquid electrolytes, solid polymer electrolytes have higher safety and thermal stability, since they can provide a physical barrier layer to prevent efficiently lithium dendrite growth and avoid thermal runaway under high temperature or impact. Despite the substantial benefits, some limitations remain to be improved, such as a low ionic conductivity at room temperature and low transference number. Several studies are being conducted to overcome these weaknesses and develop new generation of solid polymer electrolyte lithium metal batteries.[ 2 ] Most of the research on SPEs is focused on polyethylene oxide (PEO) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and its derivative. In general, PEO-based solid electrolytes have shown good dimensional stability, good safety, and can mechanically prevent dendritic growth. However, they exhibit low ionic conductivity and rather low cationic transference number (t+) of ca. 0.15. To achieve sufficient conductivity at low temperatures, polymers that are difficult to crystallize are proposed. Ionic liquids (IL) are poor crystal formers; therefore, polymers of IL are potentially good alternatives to PEO for lower temperature conductivity. An Iongel membrane based on the poly(dimethyldiallylammonium) polyDADMA-TFSI poly(ionic liquid) has gained attention in polymer metal batteries due to its favorable mechanical properties and stability against Li-metal.[ 3 ] The present study provides an insight into the properties of free-standing membranes using poly (ionic liquid)-glyme mixtures compared to typical polymer salt blends (PEO-LiTFSI) and PDADMA-LiTFSI. The benefit of tetraethylene glycol dimethyl ether (G4) is highlighted and appears to be the key component to obtain higher ionic conductivity regardless on the type of polymer used. The impact of the increase in LiG4TFSI/poly ionic liquid ratio within the electrolyte on the transference number, ionic conductivity and mechanical properties was further analyzed. For 33-66 wt% composition for PDADMAT-LiG4TFSI and PEO-LiG4TFSI membranes, a good compromise between the physicochemical and electrochemical properties was achieved.

Influence of Anion Structure on Thermal, Mechanical and CO2 Solubility Properties of UV-Cross-Linked Poly(ethylene glycol) Diacrylate Iongels.

Iongel-based CO2 separation membranes were prepared by fast (< 1 min) UV-initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of different ionic liquids (ILs) with the [C2mim]+ cation and anions such as [TFSI]−, [FSI]−, [C(CN)3]− and [B(CN)4]−. The four ILs were completely miscible with the non-ionic PEGDA network. Transparent and free-standing iongels containing between 60 and 90 %wt of IL were obtained and characterized by diverse techniques (FTIR, TGA, DSC, DMTA, SEM, CO2 solubility and pure gas permeability). The thermal and mechanical stability of the iongels, as well as CO2 solubility, were found to be strictly dependent on the IL content and the anion’s nature. The TGA results indicated that the iongels mostly follow the thermal profile of the respective neat ILs. The DMTA analysis revealed that the iongels based on fluorinated anions have higher storage modulus than those of cyano-functionalized anions. Conversely, the PEGDA–C(CN)3 iongels presented the highest CO2 solubility values ranging from 72 to 80 mmol/g. Single CO2 permeabilities of 583 ± 29 Barrer and ideal CO2/N2 selectivities of 66 ± 3 were obtained with the PEGDA–70 C(CN)3 iongel membrane. This work demonstrates that the combination of PEGDA with high contents of the best performing ILs is a promising and simple strategy, opening up new possibilities in the design of high-performance iongel membranes for CO2 separation.

The effect of Poly(Ethylene oxide) cross-linking structure on the mechanical properties and CO2 separation performance of an ion gel membrane

Ionic liquid gels of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide plasticizing a cross-linked poly(ethylene oxide) are high performance CO2 separation membranes. Here, the effect of polymer cross-link density on the ionic liquid stability, on the mechanical properties of the resulting films, and on the gas separation properties were studied. Cross-link density was modified by changing the chain length of ethoxylated diacrylate and triacrylate monomers, and by incorporating small amounts of short, multifunctional acrylate monomers. Without the ionic liquid acting as permanent plasticizer, higher cross-link density is associated with higher yield strength but lower strain at break, as expected. In a plasticized network, however, the loss in flexibility is not accompanied by higher yield strength, leaving ion gels made from highly cross-linked network more fragile than those having longer, more flexible chains. Lowering cross-link density also allowed more ionic liquids to be incorporated as a phase stable gel and led to better CO2 separation performance.

Role of Cation Structure in CO2 Separation by Ionic Liquid/Sulfonated Polyimide Composite Membrane.

The development of suitable separation technologies for the separation of carbon dioxide is a pressing technological requirement. The application of ion gel membranes for this purpose continues to stimulate a great deal of research, and in this study we focus on the chemical structure of the ionic liquid component in the ion gel, and its interactions with the sulfonated polyimide polymer. Whilst such membranes are known to give promising carbon dioxide separation properties together with mechanical strength and thin-film-processability, we further elaborate on how changing the cation of the ionic liquid from a typical imidazolium cation to a protic variant effects the physicochemical, thermal, and structural properties of the membranes, and how these changes further influence the carbon dioxide separation properties. We compare and contrast our findings with our earlier study on protic and aprotic ammonium-based ionic liquids, and highlight that for CO2 absorption behavior in the imidazolium systems, the importance of directionality of interactions (ion pairs exhibit a large energy stabilization only for a specific geometrical arrangement of cation and anion, e.g., hydrogen bonding rather than Coulombic interaction) between cation and anion applies not only to the protic system, but also to the nominally aprotic cation. Finally, we demonstrate that the phase separation behavior in the ion gels is an important factor in determining the carbon dioxide separation behavior.

Application of Protic Ionic Liquids to CO2 Separation in a Sulfonated Polyimide-Derived Ion Gel Membrane

It is of great interest to determine whether a relatively easily prepared and inexpensive protic ionic liquid (PIL) could be used in place of an aprotic ionic liquid (AIL) in a composite membrane for CO2 separation. We prepared mechanically reliable sulfonated polyimide (SPI) composite membranes with a PIL, [N124][NTf2] (N,N,N-butylethylmethylammonium bis(trifluoromethylsulfonyl)amide) by a solution casting method, and their mechanical, thermal, and gas separation (CO2 and N2) properties were compared with those of membranes incorporating an isomeric AIL, [N1123][NTf2] ([N1123]+, N,N,N,N-ethyldimethylpropylammonium). We discussed the influence of the presence or absence of active protons in the ILs on CO2 separation characteristics and the applicability of the PIL to a CO2 separation membrane. The SPI/PIL membrane exhibited a slightly lower selectivity, but higher permeability, than the SPI/AIL membrane. It is supposed that these differences originate from the difference in membrane structure and CO2 inte...

Poly(ionic liquid) iongel membranes for all solid-state rechargeable sodium battery

Sodium-ion is seen as one of the most promising alternative technologies to the current lithium-ion batteries. Sodium is cheap and widely available in comparison to lithium, however new electrode and polymer electrolyte materials need to be found to improve the performance and security of sodium batteries. In this work, we show a new iongel electrolyte with excellent properties for an all solid-state rechargeable sodium batteries. This iongel membrane is based on the poly(dimethyldiallylammonium) polyDADMA-TFSI poly(ionic liquid), N-Propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) and sodium bis (fluorosulfonyl)imide (NaFSI) the salt. PolyDADMA-TFSI can incorporate up to 50 wt% of C3mpyrFSI ionic liquid content in a self-standing membrane with high ionic conductivity. The increasing the NaFSI concentration in this electrolyte was beneficial for the sodium transference number but detrimental for the ionic conductivity of the membranes. The addition of alumina nanoparticles further improved the membrane mechanical robustness without affecting significantly the ionic conductivity. The iongel membranes presented a wide electrochemical window of 5 V thereby supporting sodium electrochemistry as demonstrated by excellent symmetric sodium cell cycling at 70 ᵒC for 60 cycles. Finally, the electrochemical performance of the optimum composition iongel was evaluated in sodium all solid-state battery using a sodium metal anode and NaFePO4 as the cathode material. The cells show good capacity retention with high coulombic efficiency (>97%) at C rates between C/20 and C/5 achieving 110 mAhg−1 at C/20.

Toluene vapor removal using an inorganic/organic double-network ion gel membrane

ABSTRACTTough gel membrane composed of a large amount of an ionic liquid and an inorganic/organic composite double-network (inorganic/organic DN ion gel membrane) was examined to remove toluene vapor from toluene vapor/N2 mixed gas. The DN ion gel membrane with 80 wt% of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide showed higher toluene vapor permeability (more than 30,000 barrer) and toluene vapor/N2 permselectivity (690) than the supported ionic liquid membrane. The toluene vapor permeability and toluene vapor/N2 permselectivity were maintained under pressurized condition. It was confirmed that the toluene vapor permeation was limited by intramembrane diffusion of the dissolved toluene vapor.

Phosphonium-Based Poly(ionic liquid)/Ionic Liquid Ion Gel Membranes: Influence of Structure and Ionic Liquid Loading on Ion Conductivity and Light Gas Separation Performance

The influence of free IL structure and loading level in phosphonium-based poly(ionic liquid)/ionic liquid (PIL/IL) ion gel composite membranes was studied with regards to their ion conductivity and light gas separation performance. The resulting series of ion gels demonstrated ion conductivity values of 10–7–10–5 S/cm at 25 °C and 10–5–10–3 S/cm at 110 °C. It was found that shorter alkyl chain lengths on the phosphonium cation of the IL resulted in increased thermal stability of the ionic conductivity for the resulting PIL/IL membrane materials with negligible changes in ionic conductivity performance at temperatures up to 110 °C. Further, an increase of free IL loading resulted in an increase in overall ion conductivity and membrane mechanical stability. Similar structure/composition/function relationships were observed for the light gas separation performance of these phosphonium-based PIL/IL ion gel membranes. However, the resulting performance is lower than PIL/IL ion gel membranes based on imidazoliu...