Water Cluster Size Research Articles

Computational Study of Hydrogen Bond Interactions in Water Cluster-Organic Molecule Complexes.

We analyzed the interactions present in complexes that acetone, azomethane, dimethylamine, dimethyl ether, methyl acetate, and oxirane form with 39 different (H2O)n clusters (n = 1-10). A random generation of configurations and a subsequent screening procedure were employed to sample representative interactions. Using quantum chemical computations, we calculated the associated binding energies, which range from -0.19 to -10.76 kcal/mol at the DLPNO-CCSD(T)/CBS level. It was found that the binding energies can be understood in terms of various factors, including the water cluster size, the nature of the organic molecule, and the type of hydrogen bond donor. We find that the most stable complexes often arise from a combination of a strong hydrogen bond plus a secondary interaction between the organic molecule and the water cluster.

Polysulfide-based redox flow batteries with long life and low levelized cost enabled by charge-reinforced ion-selective membranes

Polysulfide is one of the most promising aqueous redox chemistries for grid storage owing to its inherent safety, high energy and low cost. However, its poor cycle life resulting from polysulfide cross-over has prohibited its successful commercialization. To exploit low-cost and high-capacity polysulfide flow batteries with industrial-relevant cycling stability, we develop a charge-reinforced ion-selective membrane to retain polysulfide/iodide, restrain membrane swelling and prevent water/OH− migration. The polysulfide/polyiodide static cell demonstrates a low capacity decay rate (0.005% per day and 0.0004% per cycle) over 2.9 months (1,200 cycles) at a 100% state of charge. A flow cell containing 4.0 M KI/2.0 M K2S2 demonstrated stable cycling at 17.9 Ah l−1posolyte+negolyte over 3.1 months (500 cycles). Small-angle X-ray scattering and in-situ attenuated total reflectance–Fourier transform infrared/solid-state NMR revealed reduced water cluster size and restrained water movement in the charge-reinforced ion-selective membrane compared to commercial Nafion membrane. Techno-economic analysis shows that the developed polysulfide flow battery promises competitive levelized cost of storage for long-duration energy storage. The development of aqueous redox flow batteries (ARFBs) has been plagued by high material costs and poor operating stability. Here the authors report a membrane design to enable polysulfide-based ARFBs with minimal capacity decay over long cycles and durations as well as competitive cost-effectiveness.

Mesoscale Simulation on the Hydrated Morphologies of SPEEK Membrane

AbstractProton transport in proton exchange membrane is considered to depend on the hydrophilic domain formed by the microphase separation between hydrophobic and hydrophilic segments of the membrane. Therefore, the study of hydrated morphologies is crucial to understand proton transport. Here, the mesoscopic structure of sulfonated polyether ether ketone (SPEEK) membrane and SPEEK/polyethersulfone (PES) blend membrane is investigated by dissipative particle dynamics (DPD) simulation. The degree of sulfonation, water content, and PES content are considered to affect proton transport. Results show that the hydrophilic particles combine with water and are separated from hydrophobic particles to form clusters of different sizes. For the SPEEK membrane, with the increase in the sulfonation degree, clusters become large and begin to connect. Compared with isolated clusters at low water content, water clusters become large with increased water content. When water content λ = 16, the cluster size is the largest. The addition of PES accelerates the phase separation in the membrane and increases the size of water clusters. When SPEEK/PES = 4:6, the cluster size is the largest and provides the best proton transport pathway.

Wicking-Polarization-Induced Water Cluster Size Effect on Triboelectric Evaporation Textiles.

Sweating during exercise, physical labor, or hot weather leads to a feeling of discomfort. The stuffiness, stickiness, and heaviness brought by sweat may promote negative emotions or disease. Clothing, textiles, and wearable devices exacerbate these problems by restricting evaporation of sweat. Here, a textile that can promote and enhance sweat evaporation by coupling wicking and polarization is reported. The wicking is produced by the wettability gradient and pore size, which make the surface moisture content of the textile in contact with the skin strictly 0%. The polarization is driven by a ferroelectric-enhanced triboelectric textile. This textile degrades large-sized water clusters into small-sized water clusters or water monomers, so that the textiles have an excellent moisture evaporation rate (4.4 and 3.6 times faster than the cotton and polyester textiles, respectively). This work provides a new source of inspiration for quick-drying textiles and also finds an attractive application for triboelectric technology.

Understanding the ionic activity and conductivity value differences between random copolymer electrolytes and block copolymer electrolytes of the same chemistry.

Herein, a systematic study where the macromolecular architectures of poly(styrene-block-2-vinyl pyridine) block copolymer electrolytes (BCE) are varied and their activity coefficients and ionic conductivities are compared and rationalized versus a random copolymer electrolyte (RCE) of the same repeat unit chemistry. By performing quartz crystal microbalance, ion-sorption, and ionic conductivity measurements of the thin film copolymer electrolytes, it is found that the RCE has higher ionic activity coefficients. This observation is ascribed to the fact that the ionic groups in the RCE are more spaced out, reducing the overall chain charge density. However, the ionic conductivity of the BCE is 50% higher and 17% higher after the conductivity is normalized by their ion exchange capacity values on a volumetric basis. This is attributed to the presence of percolated pathways in the BCE. To complement the experimental findings, molecular dynamics (MD) simulations showed that the BCE has larger water cluster sizes, rotational dynamics, and diffusion coefficients, which are contributing factors to the higher ionic conductivity of the BCE variant. The findings herein motivate the design of new polymer electrolyte chemistries that exploit the advantages of both RCEs and BCEs.

In English

The aim of the work is to study interaction of N-acetylneuraminic acid (NANA) with the surface of ultrafine silica (UFS) with the participation of glucose and sucrose in aqueous solution at the supramolecular level by density functional theory method (exchange-correlation functional B3LYP, basis set of 6-31G (d, p). The adsorption of N-acetylneuraminic acid, as well as individual carbohydrates (glucose and sucrose) on the hydrated surface of UFS in aqueous solution, was considered as a process of replacement of water molecules on the surface of silica by adsorbate molecules. This work considers two schemes of carbohydrate molecule influence on adsorption of N-acetylneuraminic acid. According to the first scheme the interaction of the NANA molecule occurs with the silica-monosaccharide complex, according to the second scheme, the silica cluster interacts with the NANA-monosaccharide complex, where silica binds to the complex through the carbohydrate molecule. The analysis of the calculated geometric and energy characteristics show that adsorption on the surface of silica, with hydration taken into account, is thermodynamically probable for the sucrose. The glucose molecule has a positive value (+9.8 and +2.7 kJ / mol) is an unfavorable process in terms of thermodynamics regardless of the hydrating water cluster size. The N-acetylneuraminic acid molecule has a value of -1.3 kJ / mol for the reaction with five water molecules and +0.9 kJ / mol with eight water molecules. It was found that the presence of sucrose on the silica surface in the aqueous solution weakens the hydration energy (i.e. it is easier to replace the cluster of water with the N-acetylneuraminic acid molecule from the surface of the modified adsorbent), which in turn promotes NANA adsorption on the silica surface. Therefore, scheme 1 is thermodynamically more likely than scheme 2. This indicates that there is a mutual influence of substances in a mixture of NANA with carbohydrates on the interaction with silica in comparison with the interaction of substances with silica alone.

Infrared spectra of PEHA molecule and its resistance to oxidation in water and methanol media at 298.15K: solvent cluster size dependency.

The present work investigates the infrared spectra and solvation free energies (SE) of PEHA ((E)-2-(Pyridin-2-yl) ethyl 3-(3,4-dihydroxyphenyl) acrylate) and their impact on the oxidation. The latter was examined through the ionization potential parameter (IP). These investigations were carried out by the DFT method at B3LYP/6-31G(d) for optimization and frequency calculations and corrected for BSSE. X3LYP/6-311++G(2d,2p) was employed for single-point energy calculations. Water and methanol cluster sizes were used for solvation through the explicit solvent model. Thus, the infrared spectra show that the overview frequencies of PEHA compare well with the experimental results. The intense infrared absorptions of complexes are due to the stretching of O-H bonds of solvent clusters in the range 2600-3850cm-1. The binding energy per solvent molecule of complexes was calculated and shows that water and methanol clusters mimic the liquid state as from 5 to 10 solvent molecules. The SE of PEHA increases with the increase of the cluster size of water and methanol in the direction of the limit. The latter was censured by the solvation done using the combined explicit-implicit solvent model. As for IP parameter, the results are largely above the IP limit and lower than the IP from gas phase. Thus, water and methanol media have an effect of lowering the IP of PEHA compound. Consequently, both media favour the oxidation of PEHA molecule, which facilitates its metabolism in human organism.

The Many-Body Expansion for Aqueous Systems Revisited: I. Water-Water Interactions.

We revisit the many-body expansion (MBE) for water-water interactions by examining the effects of the basis set, including those resulting from the basis set superposition error (BSSE) correction, and electron correlation on the various terms for selected sizes of water clusters up to n = 21. The analysis is performed at the second-order Møller-Plesset (MP2) perturbation theory with the family of augmented correlation consistent basis sets up to five zeta quality (aug-cc-pVxZ, x = D, T, Q, 5) for the (H2O)n, n = 7, 10, 13, 16, and 21, clusters for which we report either the complete MBE (for n = 7, 10) or the ones through the 6-body (for n = 13) and the 5-body terms (for n = 16, 21). For the n = 3 and 7 clusters, we also report the analysis at the coupled cluster with single, double, and perturbative triple replacements in order to assess the effects of a higher correlation on the magnitude and percentage of the various MBE terms. Our results suggest that the oscillatory behavior around zero found for the 5-body and larger terms is solely an artifact of the (small) size of the basis set. Indeed, all terms above the 4-body converge monotonically to practically zero upon increasing the size of the basis set toward the complete basis set (CBS) limit. In that respect, the BSSE-corrected 5-body and above terms do not exhibit the oscillatory behavior on either side of zero with the basis set observed for the BSSE-uncorrected terms. In addition, the magnitudes of the 5-body and above terms are accurately reproduced even with the smaller basis set of the series (aug-cc-pVDZ) once the BSSE correction is taken into account. The same level of theory (MP2/aug-cc-pVDZ, BSSE-corrected) also accurately reproduces the MP2/CBS values of the 3- and 4-body terms. The contribution of electron correlation to the 3- and 4-body terms is quite small so that neglecting the correlation contribution in all terms above the 3-body results in an error of the order of 0.1%. The BSSE correction to the largest 2-body term in the MBE was accurately estimated from the function a[1 + erf( - b·R)], which is proportional to the common (overlapping) area between two Gaussian distributions whose centers are separated by R with the constants a and b fitted to the calculated BSSE corrections for the individual 2-body terms of the clusters with each basis set and R is the distance between oxygen atoms. Our results demonstrate that the MBE for water-water interactions converges by the 4-body term since any finite terms above the 4-body are artifacts of the size of the basis set. The MBE can thus be safely truncated at the 4-body term when either a very large basis set is used or BSSE corrections are taken into account even with the smaller aug-cc-pVDZ basis set. We expect these findings to have important consequences in the pursuit of accurate ab initio based many-body molecular dynamics simulations for aqueous systems.

Different Average Size Evolution of Gaseous Water Cluster in an Expanding Gas Flow

Formation of pure gaseous water cluster in the supersonic gas flow from a conical nozzle was investigated by simulation. The simulation results show that average size of water cluster indicates a different size evolution along the gas flow, i.e., the average cluster size firstly increases to a maximum size and then decreases slowly, rather than keeps increasing like other gases. By further calculations of the nucleation rate and the growth rate of water cluster, it is found that the decrease of average size results from a high nucleation rate and a low size growth rate in the downstream of gas flow far away from conical nozzle throat. Formation of pure gaseous water cluster in the supersonic gas flow from a conical nozzle was investigated by simulation. The simulation results show that average size of water cluster indicates a different size evolution along the gas flow, i.e., the average cluster size firstly increases to a maximum size and then decreases slowly, rather than keeps increasing like other gases.

Molecular Dynamics Insights into the Nanoscale Structural Organization and Local Interaction of Aqueous Solutions of Ionic Liquid 1-Butyl-3-methylimidazolium Nitrate.

Considering the growing number of applications of the aqueous ionic liquids (ILs), atomistic molecular dynamics (MD) simulations were used to probe the effect of water molar fraction, xw, ranging from 0.00 to 0.90, on the nanoscale local structure of 1-butyl-3-methylimidazolium nitrate, [bmim][NO3], IL. The results prove that, with water addition, the cation-anion, cation-cation, and anion-anion structural correlations are weakened, while strong anion-water and unconventional cation-water hydrogen bonds are formed in the solutions. Water molecules were detected as bridges between nitrate anions, and the water cluster size distribution at different xw's was investigated. Simulation shows a similar pattern of probability densities for water and anion around the acidic hydrogen atoms of the reference cation ring, while both species move away from the cation butyl chain. Increasing the water concentration to xw = 0.90 causes decreasing of the local arrangement of the nearest-neighboring cations, because of the weakening of cation-cation π-π stacking. In addition, this dilution reduces the probability of the in-plane cation-anion conformation, disrupts both the polar ionic network and nonpolar domains, and diminishes the nanoaggregation of the cation butyl chains compared to those of the neat IL. These results can rationalize the origins of the fluidity enhancements and transport property trends upon adding water to the imidazolium-based ILs. The current study proposes a deep atomistic-level insight into the complex coupling between water concentration, microscopic structure, and local interactions of aqueous imidazolium-based ILs with hydrophilic anions.

Tracing Local Nanostructure of the Aqueous Solutions of the Biocompatible [Cho][Gly] Ionic Liquid: Importance of Hydrogen Bond Attraction between Like-Charged Ions.

The neat and aqueous solutions of the cholinium glycinate ionic liquid (IL), [Cho][Gly], at different water mole fractions, xws, are studied by molecular dynamics simulations. The changes in the local nanostructure of systems with composition have been determined by calculation of various structural distribution functions. Hydrogen bond (H-bond) attractions determine the major relative orientations of the oppositely and like charged nearest neighbors. The cation-anion H-bonds mainly form between the hydrogen of the hydroxyl or methyl groups of the cation and the carboxylate oxygen of the anion. A preferred (antiparallel) arrangement between adjacent [Cho]+ cations is due to the effective H-bond between the hydroxyl oxygen and the methyl hydrogen sites that promotes the like-charge cluster formation. Adding water decreases the occurrence probability of the [Cho]+···[Gly]-···[Cho]+ bridge structure in the aqueous solutions due to the formation of the [Gly]-···HOH···[Gly]- structure via H-bonding. Observed density trend versus xw is interpreted based on an interstice model and investigating the water cluster size distribution. Finally, the effect of xw on the infrared (IR) vibrational spectra were studied and blue and red shifts were observed for the stretching and bending vibrational modes of the hydroxyl group of [Cho]+, respectively. Current findings will improve the efficient engineering design and task-specific applications of aqueous solutions of bio-ILs consist of [Cho]+ and amino acid anions.

Geochemical controls on wettability alteration at pore-scale during low salinity water flooding in sandstone using X-ray micro computed tomography

We performed a pore-scale multiphase flow experiment on a sandstone core sample. We imaged the core sample at initial oil saturation, residual oil saturations after high salinity and low salinity water flooding. Moreover, we examined fluid occupancy maps and water cluster size distribution at pore-scale before and after low salinity waterflooding. Furthermore, we performed a geochemical study to relate physicochemical process at sub-pore scale to account for in-situ wettability alteration at pore-scale.Micro-CT imaging shows that low salinity waterfloodng yielded 5% of residual oil saturation reduction after high salinity water flooding. Fluid occupancy maps within pore network show water film propagation at pore surface during low salinity water flooding, suggesting the oil film detachment from pore surfaces due to in-situ wettability alteration. Micro-CT imaging analysis also shows that the large size water cluster (greater than 107 µm3) occupies 87.7% of water volume after high salinity water flooding, whereas the same size water cluster occupies 89.6% pore volume after low salinity water flooding, implying that water clusters coalesce into each other to transport in pore network during low salinity water flooding in line with fluid occupancy maps. Geochemical modelling predicts a pH increase (from 7 to 8.9) during low salinity water flooding largely due to ankerite and albite dissolution. This study sheds light on the significance of geochemical controls over wettability alteration at pore-scale through water film propagation.

Atlas of putative minima and low-lying energy networks of water clusters n = 3-25.

We report a database consisting of the putative minima and ∼3.2 × 106 local minima lying within 5 kcal/mol from the putative minima for water clusters of sizes n = 3-25 using an improved version of the Monte Carlo temperature basin paving (MCTBP) global optimization procedure in conjunction with the ab initio based, flexible, polarizable Thole-Type Model (TTM2.1-F, version 2.1) interaction potential for water. Several of the low-lying structures, as well as low-lying penta-coordinated water networks obtained with the TTM2.1-F potential, were further refined at the Møller-Plesset second order perturbation (MP2)/aug-cc-pVTZ level of theory. In total, we have identified 3 138 303 networks corresponding to local minima of the clusters n = 3-25, whose Cartesian coordinates and relative energies can be obtained from the webpage https://sites.uw.edu/wdbase/. Networks containing penta-coordinated water molecules start to appear at n = 11 and, quite surprisingly, are energetically close (within 1-3 kcal/mol) to the putative minima, a fact that has been confirmed from the MP2 calculations. This large database of water cluster minima spanning quite dissimilar hydrogen bonding networks is expected to influence the development and assessment of the accuracy of interaction potentials for water as well as lower scaling electronic structure methods (such as different density functionals). Furthermore, it can also be used in conjunction with data science approaches (including but not limited to neural networks and machine and deep learning) to understand the properties of water, nature's most important substance.

Charge delocalization effects on Nafion structure and water /proton dynamics in hydrated environments

In this work, using molecular dynamics simulations, we examine the effect of atomic charge delocalization on the pendant side chain of Nafion membrane on the structural and dynamical properties in various hydrated environments. The sulfur-sulfur radial distribution functions suggest that the sulfonate groups of the pendant side chain have closer geometric proximity with an increase in charge delocalization. However, the interactions of the sulfonate groups with water molecules/hydronium ions show a slight change with the charge delocalization. The average water cluster size decreases significantly with charge delocalization, though the diffusion coefficients of water molecules (at medium and higher water concentration) increase initially and then decreases slightly with excessive charge delocalization. The diffusion coefficients of hydronium ions do not follow any particular trend with charge delocalization. A complex interplay between sulfur-sulfur, sulfur-water/hydronium interactions, and water cluster distribution plays an essential role in the magnitude of the diffusion coefficient of water molecules and hydronium ions.

Structural effects on water molecules on the low index planes of Pt modified with alkyl amines and the correlation with the activity of the oxygen reduction reaction

Our previous study shows that the activity of the cathodic reaction (oxygen reduction reaction: ORR) of fuel cells is increased markedly by the adsorption of alkyl amines on a well-defined Pt(111) electrode. On Pt(100) and Pt(110) electrodes, however, the adsorption of alkyl amines deactivates the ORR significantly. We have studied the possible factors of the activation and deactivation by infrared (IR) reflection absorption spectroscopy. An IR band of icelike water is found on all the electrodes after the modification with alkyl amines. The band of the icelike water on Pt(111) is located at a higher wavenumber than those on Pt(100) and Pt(110). These findings indicate that the cluster size of icelike water on Pt(111) is smaller than those on Pt(100) and Pt(110). The cluster size of the ice correlates with the ORR activity on Pt electrodes.

Investigation and modelling of the water transport properties in unfilled EPDM elastomers

The water sorption properties (i.e. diffusivity and solubility) of three unfilled vulcanized EPDMs were investigated in wet atmosphere (typically between 0 and 95% RH) and in pure distilled water (denoted as 100% RH) at 70 °C with an IGAsorp dynamic sorption analyzer. In the 0–0.5 activity range, all EPDMs obey to the usual Fick and Henry's laws. In contrast, at activities higher than 0.5, the water sorption behavior of all EPDMs deviates from these two laws because of the formation of water clusters. Park's equation was used for simulating accurately the sorption isotherms and thus, accessing Henry's constant and the average size of water clusters. In wet atmospheres, clusters would be composed of about 8 ± 4 molecules corresponding approximately to the size of free volume holes. In contrast, in pure distilled water, clusters consist in a much larger number of water molecules (between 55 and 71) presumably because of an exacerbated swelling of EPDM samples. Thus, immersion in water solution is more drastic than exposure to fully saturated wet atmosphere. The impact of the EPDM formulation (nature and content of crosslinking agent) on these experimental results is clearly of the second order of magnitude.

Water Clusters in Lignite and Desorption Energy Calculation by Density Functional Theory.

The interaction of water and hydrophilic sites with hydroxyl, carboxyl, and multiple oxygen-containing functional groups (OFGs) in lignite molecules was studied by density functional theory. The adsorption of water molecules on the lignite surface initially resulted in the formation of hydrogen bond-driven stable rings by three to four water molecules, followed by the formation of three-dimensional water clusters like a ″patchwork″. Aqueous layer thickness obtained from the water cluster size was 0.4–0.6 nm, which was consistent with the experimental data. Thus, pore-filling water beyond this range was less affected by the OFGs on the surface. Calculation of the adsorption energy predicts that the water clusters were primarily formed in the hydrophilic sites with three OFGs (site 1, including a carbonyl group, an alcoholic hydroxyl group and an etheroxy group in tetrahydropyran), then in COOH, and in O–H. For isolated hydroxyl groups, the interaction between the hydroxyl group and water molecules was weaker than that between the water molecules. When the water cluster was located at the hydrophilic sites with two or more OFGs, the adsorption energy of lignite–water interaction was higher than that of water–water interaction. Investigating the thermodynamics of the adsorption process at a molecular scale will help in understanding both drying and resorption process of dried lignite during industrial production.

Thermodynamic of solvation, solute – Solvent electron transfer and ionization potential of BSCAPE molecule and its UV–vis spectra in aqueous solution

The molecular system 2-Phenylethyl (2E)-3-(1-benzenesulfonyl-4,5-dihydroxyphenyl) acrylate (BSCAPE) is a phenolic acid that covers a large spectrum of biological properties. The investigations of solvation and oxidation processes of BSCAPE molecule by computational means were the challenge of this present work. Water was required for solvation throughout the work. The explicit H2O were sequentially added to form the complexes BSCAPE(H2O)n=0-11. The discrete – continuum model was at the heart of this work. DFT and TD-DFT both associated to the continuum model SMD were required. Hence, the structures, the solvation energies, the energies of solute – solvent electron transfer (SSET), the ionisation potential (IP), and the UV–vis spectra were studied. It comes out that, the structure of the CAPE part included in BSCAPE agrees well with the available experimental values of CAPE but with a minor influence due to the presence of benzensulfonyl group. The enthalpy and free energy of solvation increase linearly with nH2O. The global reactivity indexes were assessed to appreciate the oxidation of BSCAPE. The latter quality was strongly assessed by the enthalpy and free energy of SSET and IP. The SSET potential increase with nH2O and the size of water clusters. The values 723.16 and 711.62 kJ/mol were found for enthalpy and free energy of IP respectively. Then in aqueous solution, the results fall down and upon addition of nH2O, they approach gas phase value for 11H2O and still are not stabilized. Therefore, the resistance to oxidation starts to raise at this level. Elsewhere, the UV–vis spectra of BSCAPE present four important peaks about 279.3, 234.8, 208.4 and 199.4 nm in gaseous state. The excitation shifts to the red as the number of H2O increase. Their oscillator strengths also increase with solvation.

Relationship between Transport Phenomena and Characteristics of the Cluster Structure

Using a statistical approach, we have estimated the size of water clusters and the number of free molecules participating in transport phenomena. The sizes of clusters and the number of molecules in them, as well as the number of free water molecules and their mean free paths, have been determined using experimental data on the temperature dependence of viscosity and density of water. It has been concluded that a temperature of 36.6°C is a special point in the range of 0–100°C. At temperatures higher than this value, the binding energy of a molecule with a cluster decreases abruptly, while the concentration of free molecules sharply increases. Quantitative data have been compared with the parameters of the superplastic state of titanium. As an example, we consider metabolism in functioning of erythrocytes of blood in an adult human.

Effects of Side Chain Length on the Structure, Oxygen Transport and Thermal Conductivity for Perfluorosulfonic Acid Membrane: Molecular Dynamics Simulation

Many researches have indicated that the side chain length of perfluorosulfonic acid (PFSA) polymers had nonnegligible effects on PFSA membrane properties. However, the effects have not been completely revealed yet. This paper uses molecular dynamics simulation to explore the effects of side chain length on the structure, oxygen transport and thermal conductivity of PFSA membrane. In PFSA membrane with longer side chains, the maximum size of water clusters is larger, while the connectivity of water clusters is poorer and size distribution of water clusters is more heterogenous. And the structural characteristics have a strong effect on the diffusion and solubility coefficient of oxygen molecules. The diffusion of oxygen molecules may be hindered due to the existence of small pores in PFSA membrane with longer side chains even at high water content, leading to a lower diffusion coefficient. In addition, with the increment of water content λ, the solubility coefficient of oxygen molecules in PFSA membrane with shorter side chains decreases more quickly at λ < 12, resulting in a most obvious difference of solubility coefficients for different side chain lengths when λ is about 12. Moreover, the thermal conductivity of PFSA membrane with shorter side chains is higher.