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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Physical properties and anisotropic magnetism of EuBi 2

We report the synthesis of EuBi 2 single crystals and their magnetic and electronic properties. Plate-like crystals were grown in excess bismuth, and X-ray diffraction data confirm the previously reported tetragonal space group, I 4 1 /amd (No. 141). A Néel temperature of T N = 18.6 K was determined from the specific heat data, and corresponding anomalies occur in the magnetization and resistivity. We only observe one magnetic transition in zero magnetic field. The magnetization data above 70 K are well described by a Curie-Weiss model with a Weiss temperature of Θ CW ≈ −35 K and an effective moment near that of the expected spin-only moment of Eu 2+ (S = 7/2). Isothermal magnetization measurements reveal field-induced transitions for H||[100], including a hysteretic spin-flop centered at 10.1 T and a change in slope at 12 T and 2 K. However, while the isothermal magnetization for H||[110] displays nonlinear behavior, discrete metamagnetic transitions are not observed for H||[110] or H||[001], indicating significant magnetic anisotropy. The magnetization does not saturate by 13.5 T for any orientation. EuBi 2 is metallic and our crystals possess an in-plane residual resistivity ratio of ⍴300 K/⍴2 K ≈ 40. Single crystal neutron diffraction data reveal a large magnetic unit cell and non-trivial antiferromagnetic ordering. These results demonstrate that strong antiferromagnetic coupling drives complex magnetism in EuBi 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2022

Application of BISON to UO 2 MiniFuel fission gas release analysis

There has been a recent push to accelerate fuel qualification by developing revolutionary capabilities to reduce irradiation periods, and thereby, reduce the time required to qualify a new fuel system. One such capability is the MiniFuel irradiation capsule designed to miniaturize fuel samples and irradiate “mini” fuel samples under isothermal temperature conditions. MiniFuel allows steady-state irradiations to decouple the traditionally coupled fission rate (i.e., power) and temperature parameters to understand and generate microstructures observed in fuel operated in a commercial reactor. Furthermore, this process offers the possibility to gather in situ data as well as postirradiation or transient data such as thermal conductivity, specific heat, fission gas diffusion and release, etc. However, accelerating fuel qualification is not solely reliant on generating large amounts of data but also on developing an informed test matrix designed to rapidly generate impactful data. Additionally, this process is reliant on fuel performance codes, such as BISON, to evaluate MiniFuel irradiations using existing material models. This process pinpoints model/data gaps, identifies desired irradiation conditions, and subsequently supports model validation and development. This work describes the use of BISON to perform a number of sensitivity studies designed to understand conditions that lead to fission gas release (FGR) under steady-state isothermal irradiation conditions and temperature transient conditions. The model is applied to a UO 2 MiniFuel example and shows an overall good qualitative agreement with experimental FGR annealing tests under different temperature conditions. It also accounts well for microstructural effects on FGR. When quantitatively compared with FGR data from previously irradiated 103 MWd/kgU UO 2 discs under thermal annealing, the model shows a less satisfactory agreement with the experimental data. Finally, a UO 2 MiniFuel test matrix is proposed to help to extend the model's operational range and validate the new FGR model capabilities to higher burnups and transient conditions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Pyrolysis of high-density polyethylene: Degradation behaviors, kinetics, and product characteristics

Pyrolysis is a promising technology for converting plastic waste into valuable raw materials while offering a potential solution to the global plastic pollution crisis. In this study, the thermal pyrolysis of high-density polyethylene (HDPE) is investigated in a drop tube reactor under nearly isothermal conditions. The impact of reaction temperature and gas/volatile residence time on carbon conversion and product distribution is examined across a range of 500–900°C and 3.6–32.2s, respectively. Non-condensable gas products detected by online mass spectrometry are H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 , and C 3 H 8 . At elevated temperatures and prolonged residence time, H 2 yield reaches as high as 8.6 wt% of the initial HDPE mass due to intensified cracking reactions of C 2 –C 3 hydrocarbons and long-chain aliphatic compounds. Consequently, pyrolysis tars consist mainly of polycyclic aromatic hydrocarbons (PAHs) with 5–7 rings, accompanied by visible coke deposition within the reactor. HDPE decomposition to volatiles is an endothermic process and it is complete at a temperature between 492°C and 525°C, depending on the heating rate employed, from non-isothermal thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) measurements. The thermal degradation of HDPE pellets follows the two-dimensional nucleation growth model for conversion levels up to 0.8 with an apparent activation energy of 259–270 kJ/mol and a pre-exponential factor of 4.83 × 10 17 –1.37 × 10 19 min -1 , determined from various isoconversional methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink, along with Criado's master plots. Further, these findings provide valuable insights into optimizing process parameters and refining reactor design for pyrolysis, which can be integrated with gasification and reforming processes to enhance hydrogen production on a larger scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Deformation behavior of annealed Cu64Zr36 metallic glass via molecular dynamics simulations

In the present work, we investigate the isothermal annealing process of Cu 64 Zr 36 metallic glass (MG) by means of molecular dynamics (MD) simulations, and characterize the compression properties under different temperatures and compressive rates. The pair distribution functions, the bond-orientational order, and the cluster-type index method are modeled and analyzed to characterize changes in the structure. Results of the modeling and analysis reveal that the MgZn 2 -type Laves, MgCu 2 -type Laves and five-fold local symmetry structures can be formed during the isothermal holding at 950 K. Study on the compression properties shows that at a fixed strain rate, the yield strength and yield drop all increase with decreasing temperature. At a fixed temperature, however, the increase of the strain rate leads to a noticeable increase in the yield strength at 600 K, but has little effect on yield strength at 10 K. Moreover, the modeling and analysis of the structure at a temperature of 10 K and strain-rate of 5 × 10 7 s -1 demonstrate that the order-disorder transformation initiates the shear band.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Boric acid removal with polyol-functionalized polyether membranes

Poor selectivity of conventional desalination membranes for boron often necessitates multi-stage treatment trains to achieve desired boron removal for end uses such as irrigation. One approach to membrane design for improved single-pass boric acid removal is via incorporation of chelating ligands that selectively sorb boron. In this study, membranes based on epoxy-amine cross-linked poly(glycidyl glycidyl ether) (PGGE) were synthesized and functionalized with N-methyl-d-glucamine (NMDG), a polyol known to interact selectively with boron. PGGE and PGGE-NMDG membranes exhibited boron sorption isotherms that were well-described by dual mode isotherms. PGGE-NMDG sorbed 2.5 mmol B/g dry polymer from a neutral aqueous solution containing 100 mmol B/L, which was almost three times the adsorption density of a commercial boron selective resin, Amberlite IRA743. Further, the membranes were regenerated in acid without a significant loss of boron sorption capacity over four cycles. Interactions between boron and NMDG and PGGE sites (e.g., epoxides) impacted boron diffusion in both membranes. The use of ligand functionalized membranes to capture target solutes such as boron requires high loading of interacting sites to maximize uptake capacity. Establishing fundamental structure/property rules for boron selectivity could lead to new material designs with improved boron separation properties for water purification.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Evaluation of the critical behavior near ferromagnetic to paramagnetic phase transition in CrTe 1-x Se x alloys: An experimental study

For this study, we used the conventional solid-state reaction method to prepare stoichiometric samples of CrTe 1-x Se x , where 0 ≤ x ≤ 0.10, and investigated the structural and critical behavior of the prepared samples. Room temperature powder X-ray diffraction, along with Rietveld refinement, revealed the emergence of the NiAs structure with P6 3 /mmc (194) space group with increasing Se substitution. The high-temperature linear fit to inverse of the dc-susceptibility versus temperature for the mother sample resulted in an effective moment of 3.65μ B Cr with Curie-Weiss temperature near 335K, which is slightly higher than the Tc of ~332K obtained from the inflection point of magnetization versus temperature. Magnetization isotherms were employed to investigate the critical behavior of ferromagnetic CrTe 1-x Se x with 0.0 ≤ x ≤ 0.10 near their Curie temperatures (Tc). The magnetic behavior near Tc was found to follow 3D mean-field critical exponents with a second-order phase transition in all samples investigated. We fine-tuned the critical exponents (β, γ, and δ) using a combination of an iteration technique, the Kouvel-Fisher method, and modified Arrott plots. All samples follow a mean field behavior, with Tc ranging from 298 to 340K. The acquired values exhibit self-consistency, as indicated by the results from the Widom scaling relation. Furthermore, the magnetization isotherms exhibit a universal scaling behavior, providing additional credence to the calculated critical exponents.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Performance characterization of nanofiltration, reverse osmosis, and ion exchange technologies for acetic acid separation

A major obstacle to widespread implementation of bio-based fuels and chemicals is the lack of efficient and costeffective separation methods. To purify acetic acid produced by biochemical conversion of biomass via anaerobic digestion, this work employs two commonly used separation technologies: (1) ion-exchange (IX) resin and (2) pressure-driven membranes. This study tested five commercially available strong- and weak-base anion-exchange resins and five commercially available nanofiltration (NF) and reverse osmosis (RO) membranes. The pH of the feed solution significantly affected adsorption capacity. At pH 6.3, a strong-base IX resin (IRN-78) performed best (95.1% acetate removal). With strong-base IX resins, the Langmuir isotherm model fit well, whereas for weak-base IX resins, the Freundlich isotherm provided a better fit. A pseudo-second-order kinetic model fit well for both IRN-78 and IRA-67. Regarding membrane separation, RO (BW30XFR membrane) achieved the highest rejection (98.6% acetate rejection), whereas an NF membrane (NF*) achieved the best combination of permeate flux (105 L/(h∙m 2 )) and rejection (83.1% acetate rejection). For membrane performance, the experimental data were fit using the solution diffusion model. Increased pH in the feed solution lowered permeate flux but increased acetic acid rejection. Finally, then the acetic acid concentration in the feed solution increased, both permeate flux and acetic acid rejection decreased for membrane NF*.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Effect of pressure on TATB and LX-17 thermal decomposition

Thermal decomposition of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) and its formulation LX-17 is studied at pressures from 0.1 to 7 MPa for both isothermal heating at 340 K and ramped heating at 1 to 6 K min -1 . Conditions that eliminate self-heating are thoroughly explored to avoid experimental artifacts. The increase in pressure accelerates the rate of decomposition by only about 10 %, but it substantially increases the enthalpy of the reaction, presumably because of longer volatile product residence times in the heated zone. The narrowness of the decomposition profile and the acceleratory phase during isothermal pyrolysis are consistent with a multistep autocatalytic mechanism, and the lack of a significant pressure effect suggests that the autocatalytic species have low volatility. The apparent activation energy is about 210 kJ/mol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Effect of natural carbon filler on thermo-oxidative degradation of thermoplastic-based composites

Here thermo-oxidative degradation of thermoplastic-based composites filled with two types of carbon filler including bituminous (Pittsburgh No.8, P8) and sub-bituminous (Powder River Basin, PRB) coals were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. Oxidation induction time (OIT) and activation energy (AE) for coal plastic composites (CPCs), HDPE, and commercially available wood plastic composites (WPCs) were determined using isothermal and isoconversional kinetic methods. OIT values for CPC increased with coal content, indicating higher thermo-oxidative stability. AE values obtained using isothermal method were 52–116 kJ/mol for all CPC formulations, 32 kJ/mol for HDPE, and 33–114 kJ/mol for WPCs. AEs for CPCs obtained using isoconversional methods were not constant but rather dependent on the degree of degradation with CPC/ P8 coal possessing higher overall AE. Incorporating coal into HDPE increased thermo-oxidative stability of the resulting composite, indicating coal potentially acts as a natural primary and secondary antioxidant for polymer materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Effect of layer bending on montmorillonite hydration and structure from molecular simulation

Conceptual models of smectite hydration include planar (flat) clay layers that undergo stepwise expansion as successive monolayers of water molecules fill the interlayer regions. However, X-ray diffraction (XRD) studies indicate the presence of interstratified hydration states, suggesting non-uniform interlayer hydration in smectites. Additionally, recent theoretical studies have shown that clay layers can adopt bent configurations over nanometer-scale lateral dimensions with minimal effect on mechanical properties. Therefore, in this study we used molecular simulations to evaluate structural properties and water adsorption isotherms for montmorillonite models composed of bent clay layers in mixed hydration states. Results are compared with models consisting of planar clay layers with interstratified hydration states (e.g. 1W–2W). The small degree of bending in these models (up to 1.5 Å of vertical displacement over a 1.3 nm lateral dimension) had little or no effect on bond lengths and angle distributions within the clay layers. Except for models that included dry states, porosities and simulated water adsorption isotherms were nearly identical for bent or flat clay layers with the same averaged layer spacing. Similar agreement was seen with Na- and Ca-exchanged clays. In conclusion, while the small bent models did not retain their configurations during unconstrained molecular dynamics simulation with flexible clay layers, we show that bent structures are stable at much larger length scales by simulating a 41.6×7.1 nm 2 system that included dehydrated and hydrated regions in the same interlayer.

58 GEOSCIENCES↗
DOE OSTI2021

Investigation of species-mass diffusion in binary-species boundary layers at high pressure using direct numerical simulations

Here, direct numerical simulations of single-species and binary-species temporal boundary layers at high pressure are performed with special attention to species-mass diffusion. The working fluids are nitrogen or a mixture of nitrogen and methane. Mean profiles and turbulent fluctuations of mass fraction show that their qualitative characteristics are different from those of streamwise velocity and temperature, due to the different boundary conditions. In a wall-parallel plane near the wall, the streamwise velocity and temperature have streaky patterns and the fields are similar. However, the mass fraction field at the same location is different from the streamwise velocity and temperature fields indicating that species-mass diffusion is not similar to the momentum and thermal diffusion. In contrast, at the centre and near the edge of the boundary layer, the mass fraction and temperature fields have almost the same pattern, indicating that the similarity between thermal and species-mass diffusion holds away from the wall. The lack of similarity near the wall is traced to the Soret effect that induces a temperature-gradient-dependent species-mass flux. As a result, a new phenomenon has been identified for a non-isothermal binary-species system – uphill diffusion, which in its classical isothermal definition can only occur for three or more species. A quadrant analysis for the turbulent mass flux reveals that near the wall the Soret effect enhances the negative contributions of the quadrants. Due to the enhancement of the negative contributions, small species-concentration fluid tends to be trapped near the wall.

42 ENGINEERING↗
DOE OSTI2024

Multistage Condensation Pathway Minimizes Hysteresis in Water Harvesting with Large-Pore Metal–Organic Frameworks

Metal-organic frameworks (MOFs) have emerged as promising materials for atmospheric water harvesting (AWH). Large-pore MOFs provide high water capacity, but their significant hysteresis between sorption and desorption makes them unsuitable for AWH. Co2Cl2(BTDD) is a noteworthy exception. This MOF has large, 2.2 nm diameter one-dimensional pores, and combines both record-high water capacity and minimal hysteresis, making it an excellent material for water capture in arid areas. Sorption reversibility in Co2Cl2(BTDD) has been attributed to continuous water uptake. However, the sharp adsorption/desorption in the isotherms supports a discontinuous first-order transition. Here we use molecular simulations to compute the water adsorption and desorption pathways and isotherms in a Co2Cl2(BTDD) model, to elucidate how does this MOF achieve reversibility despite its large pore size. The simulations reveal a multi-stage mechanism of discontinuous water uptake facilitated by spatial segregation of rows of hydrophilic metal sites bridged by ~1 nm hydrophobic ligands. The multi-stage mechanism breaks the barrier of capillary condensation into smaller, easier to surmount ones, resulting in a facile process despite the sharp density discontinuity between confined liquid and vapor. Our results explain why exchanging Co2+ for Ni2+ or Clfor F- in the MOF have minimal impact on the condensation and desorption pressures. On the other hand, we predict that a decrease in hydrophilicity of the MOF vertices would strongly increase the hysteresis. We expect that the relationships between spatial distribution of hydrophilic sites and hysteresis unraveled in this study assist the design of water harvesting materials with maximal capacity and reversibility.

Zaragoza, Alberto↗
DOE OSTI2022

Insights into Controls of Mineralogy and Pore Structure on the Density of Methane Adsorption Phase in Shales under Supercritical Conditions

With gradually increasing enhancing population and industrialization, exploitation of shale gas is enhancing in the world to satisfy the growing demand for energy worldwide. To exploit shale gas efficiently, accurate assessment of shale gas in place (GIP) is necessary for determining production strategies. Unlike free and dissolved gas, adsorbed gas contributes to the shale GIP up to 85% due to the well-developed surface area and micropores. Measured excess adsorption of methane (up to over 95% of subsurface shale gas) is often corrected to absolute adsorption to obtain the actual amount of adsorption under supercritical (or geological) conditions. During the correction, adsorption phase density (APD) is critical. However, the APD of subsurface shale gas and the effects of shale properties (e.g., mineralogy and pore structure) on APD remain poorly understood. A series of high-pressure methane adsorption isotherms (HPMAI) on Caney Shales were collected and analyzed in conjunction with other United States and Chinese shales from the literature at 35–125 °C and up to 15 MPa. Here, a three-layer Ono–Kondo (OK3) model is utilized to derive the temperature- and pressure-dependent APD coupling low-pressure nitrogen adsorption isotherms (LPNAI) and HPMAI. X-ray diffraction and organic geochemistry are combined to reveal the mineralogy. Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and Horvath–Kawazoe analyses via LPNAI are used to investigate the pore structures. Results show that APD increases with organic matter (OM) proxied by total organic carbon and decreases with clay minerals and the sum of quartz and feldspar. OM dramatically contributes to the APD as multiple-layer adsorption exists, and the APD for OM could be 1.4–8.5 times that for clay minerals. Other inorganic minerals contribute less to APD. The properties and constitution of the surface area instead of the volume fraction contribute to the APD in shales. APD does not show an obvious correlation with micropore volume, likely related to the ratio of micropore volume to the total pore volume. Here, we provide a significant and comprehensive study of petrological factors that impact the APD of subsurface shale gas, which will improve the estimation of supercritical adsorption and shale GIP under reservoir conditions. Also, the findings in this work can provide applications for subsurface carbon dioxide adsorption and storage.

58 GEOSCIENCES↗
DOE OSTI2024

Downstream Separation of Formic Acid with Anion-Exchange Resin from Electrocatalytic Carbon Dioxide (CO 2 ) Conversion: Adsorption, Kinetics, and Equilibrium Modeling

The electrocatalytic carbon dioxide reduction reaction (CO 2 RR) that produces liquid formic acid (FA) is one potential route to minimize the CO 2 concentration in the atmosphere by utilizing CO 2 as a feedstock. However, one of the main disadvantages of this route is the high energy demand required for purification through conventional distillation. This method of purification has been shown to result in a large carbon footprint in life-cycle analysis (LCA). Therefore, finding an alternative purification technique that can integrate with an electrochemical CO 2 RR process with the potential to lower the carbon footprint would be of great interest. Under the experimental conditions of the CO 2 RR, FA remains in its basic form as the formate anion in the catholyte. Anion exchange resins with their basic properties can separate the formate anion from the catholyte mixture as an alternative to energy intensive distillation. In this work, three anion exchange resins with increasing basicity order: Amberlite IRA-96 < Amberlite IRA-910 < Ambersep 900 are tested to separate FA in the presence of aqueous solution of potassium bicarbonate catholyte with varying levels of resin and FA. Kinetics and equilibrium studies data for the FA adsorption are interpreted using several kinetics and isotherm models. The kinetics data fit well with a pseudo-first-order model at high initial FA concentrations and a pseudo-second-order model at low initial FA concentrations. The experimental data can be best explained with the Freundlich isotherm model. The fitted results show that strongly basic Ambersep 900 is more effective at separating FA, with a maximum adsorption capacity of 336.7 mg/g compared to Amberlite IRA-96 (275.2 mg/g) and Amberlite IRA-910 (209.2 mg/g) in neutral water. However, weakly basic Amberlite IRA-96 (110.8 mg/g) can separate FA more efficiently from potassium bicarbonate catholyte than Amberlite IRA-910 (99.9 mg/g) and Ambersep 900 (40.0 mg/g). As a result, competitive adsorption occurs in the presence of potassium bicarbonate catholyte, but the formic acid adsorption capacity is still sufficient for adequate separation.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2024

Adsorption Equilibrium, Kinetics, and Column Breakthrough Data of Acetic Acid, Butyric Acid, and Lactic Acid on IRN-78 Ion-exchange Resin at Initial pH ~3 – 7 and Temperature 25 – 55 °C

This work presents systematic aqueous-phase adsorption equilibrium, kinetics, and column breakthrough measurements with three key biointermediates that are common compounds in many bioprocesses. Adsorption equilibrium experiments were carried out with acetic acid, butyric acid, and lactic acid on a commercial ion-exchange resin, Amberlite IRN-78, at wide ranges of acid concentration (8-500 mmol/L), initial pH (similar to 3-7), and temperature (25-55 degrees C), simulating the effluent characteristics from different fermenter operations. The kinetics and column breakthrough experiments were conducted at an initial pH of 6 and a concentration of 200 mmol/L. The equilibrium study shows a higher loading at the initial pH < pK(a) and a lower loading at the initial pH > pK(a). Overall removal varies between 16 and 99% depending on the initial pH, temperature, and organic acid concentration and type. The study further indicates monolayer adsorption at the equilibrium pH > 10 and multilayer adsorption at the equilibrium pH < 6. The thermodynamic modeling of adsorption isotherm data was carried out using Langmuir and Freundlich isotherms. IRN-78 presents fast adsorption kinetics as the maximum loading was attained in <= 10 min and nearly the same breakthrough time for all three organic acids involved in this study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Self-Assembly of Partially Charged Diblock Copolymer-Homopolymer Ternary Blends

Ternary blends comprising of a diblock copolymer and the corresponding homopolymers provide ready access to a variety of morphologies, but the impact of charge on their phase behavior has not been studied extensively. Here, three partially charged ternary blends consisting of symmetric poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)] (POEGMA#), polystyrene (PS), and POEGMA#-PS with different charge fractions were prepared, where # denotes the mole fraction of charged monomers in the POEGMA chain. Here, the phase behavior was systematically studied using small-angle X-ray scattering (SAXS), and isothermal phase diagrams at 120 °C were constructed. The resulting isothermal planes contain a wide lamellar (LAM) phase window with a slight deviation from symmetry for ion-containing ternary blends, due to the homopolymer size difference. Given the absence of any significant change in the phase diagrams as the charge fraction increases, the role of charge is primarily to increase the segregation strength in the ternary system, as in the case of partially charged diblock polymers. In addition, examination of the increase in domain size along the volumetrically symmetric isopleth reveals a “dry-brush” like swelling behavior of homopolymers in all three blends, presumably due to the space-filling nature of the oligomeric ethylene glycol side chains on POEGMA.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Exponential Water Uptake in Ionomer Membranes Results from Polymer Plasticization

Water content is the most influential factor in the performance of ion-exchange membranes (IEMs), controlling their mechanical rigidity, ionic conductivity, and degradation rates. Membranes absorb water exponentially at high water activity (a w ), making that region of the sorption isotherm the most influential on membrane properties. Plasticization of the polymer by water has been proposed to cause this exponential uptake at high a w . However, an integrated microscopic picture of the structure, thermodynamic, and mechanical properties of IEMs as a function of a w has remained elusive. In this work, we use large-scale molecular simulations validated with experimental measurements to compute the sorption isotherms, Young’s modulus, polymer dynamics, and structure of IEMs. The simulations unveil that the exponential increase in water uptake (WU) coincides in all cases with the glass to rubber transition of the membrane, as measured through its Young’s modulus and segmental polymer dynamics. Functionalization of the polymer with alkyl groups further contributes to its plasticization, increasing the WU at a given a w and ion-exchange capacity (IEC). The alkyl chains act synergistically with water to plasticize the polymer matrix and allow water penetration in the membrane. The simulations reveal that the width of the water channels depends on the ratio λ of water to ions in the polymer but is independent of its IEC. We conclude that differences in the polymer matrix–not the water channels–are responsible for the distinct uptake response of IEMs to the thermodynamic driving force of water activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗