# Fileset [Nakamura et al. - 2024 - Spatial Dynamics of Water Molecules Confined in Deuterated Epoxies by Quasi-Elastic Neutron Scatteri.pdf](https://mdr.nims.go.jp/filesets/4b63766e-2396-4181-a6db-6c17c6cc467d/download) ## Creator [Yasuyuki Nakamura](https://orcid.org/0000-0003-0078-6413), [Taiki Tominaga](https://orcid.org/0000-0002-6782-6005), Takayuki Iwata, Koki Inoue, [Yoshihisa Fujii](https://orcid.org/0000-0001-9419-8537), Nagayasu Oshima, [Masanobu Naito](https://orcid.org/0000-0001-7198-819X) ## Rights [Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/) ## Other metadata [Spatial Dynamics of Water Molecules Confined in Deuterated Epoxies by Quasi-Elastic Neutron Scattering](https://mdr.nims.go.jp/datasets/4076d4b0-faae-47a0-a40e-acf1b0f99b80) ## Fulltext Spatial Dynamics of Water Molecules Confined in Deuterated Epoxies by Quasi-Elastic Neutron ScatteringSpatial Dynamics of Water Molecules Confined in DeuteratedEpoxies by Quasi-Elastic Neutron ScatteringYasuyuki Nakamura,* Taiki Tominaga,* Takayuki Iwata, Koki Inoue, Yoshihisa Fujii, Nagayasu Oshima,and Masanobu Naito*Cite This: Macromolecules 2024, 57, 4254−4262 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: The relationship between the water within polymermaterials and their material properties is key to expanding theirapplication scope. This study conducted quasi-elastic neutron scattering(QENS) measurements of fully carbon-deuterated epoxies to elucidatethe molecular dynamics of water confined in the nanometer-scale voids(nanovoids) of epoxies, focusing on spatial information. The QENSmeasurements of epoxies with different stoichiometries revealed that themotion space of mobile water molecules in stoichiometric epoxy wasmore than twice the average size of nanovoids in the epoxy, indicatingthe broad distribution across multiple nanovoids. In contrast, the extentsof oxirane-excess and amine-excess epoxies were close to the nanovoidsize. The spatial dynamics of water and its relationship to the chemicalstructure will help in understanding the water diffusion mechanism and designing epoxy materials with excellent water-relatedproperties, such as water resistance or transport.■ INTRODUCTIONThe relationship between the water within polymer materialsand material properties is key to expanding their applicationscope. For instance, polymer materials characterized byexcellent strength and lightweightedness can address energychallenges in transportation such as vehicles and aircraft; thus,understanding their property changes in wet environments isessential to ensure their reliability. Moreover, the watertransport properties are closely related to the water resistanceof polymer coatings for electronic devices and the separationperformance of reverse osmosis membranes. Epoxy resins arewidely used as structural materials, adhesives, and insulatingcoatings.1 The amount and rate of water absorption in epoxiesdetermine the water resistance/transport properties. Addition-ally, water-induced property changes such as swelling,2,3 glasstransition temperature (Tg),4,5 elastic modulus,6,7 adhesion,8,9and degradation4 are related to the dynamic behavior of water.Therefore, water dynamics in water-sorbed epoxy continues tobe the subject of research because of its importance in basicand applied materials science, such as the performance ofepoxy resins, composites, and carbon fiber-reinforced polymers(CFRP) in wet environments.10−13The water molecules in resins consisting of hydrophobicpolymers, such as epoxies, are located inside nanovoids in thepolymer matrix.14 The molecular-scale environment signifi-cantly impacts water dynamics and is determined by thechemical structure of the polymer. Epoxies are two-componentthermosets synthesized from oxirane and amine compounds,which serve as base resins and hardeners, respectively. Thechemical structure of an epoxy depends on its stoichiometry,i.e., the ratio of oxirane groups to NH2 groups. Astoichiometric ratio (oxirane/NH2 = 2/1) is typical; never-theless, off-stoichiometric ratios (oxirane/NH2 ≠ 2/1) are alsoutilized in practical applications for property modifications.The stoichiometry of an epoxy determines its chemicalcomposition, functional group abundance, and networkstructure; it also determines the influence of water on thewater absorption and physical property changes of theepoxy.15−17The mechanism of water diffusion and its relationship withchemical structures and the changes in material propertiesremain important challenges that are yet to be fully elucidated.There are numerous studies on the water dynamics in epoxies,including those about the diffusion constant of water andinteractions between water and these polymers. It is reportedthat these dynamics are affected by hydrogen bonds withfunctional groups in epoxy polymers, particularly oxygen-containing functional groups.18,19 Infrared (IR) spectroscopystudies indicate that 95% of the water molecules in water-Received: October 3, 2023Revised: March 8, 2024Accepted: March 13, 2024Published: April 26, 2024Articlepubs.acs.org/Macromolecules© 2024 The Authors. Published byAmerican Chemical Society4254https://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−4262This article is licensed under CC-BY 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on June 26, 2024 at 02:29:03 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yasuyuki+Nakamura"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Taiki+Tominaga"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takayuki+Iwata"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Koki+Inoue"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yoshihisa+Fujii"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Nagayasu+Oshima"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masanobu+Naito"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masanobu+Naito"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acs.macromol.3c02010&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=tgr1&ref=pdfhttps://pubs.acs.org/toc/mamobx/57/9?ref=pdfhttps://pubs.acs.org/toc/mamobx/57/9?ref=pdfhttps://pubs.acs.org/toc/mamobx/57/9?ref=pdfhttps://pubs.acs.org/toc/mamobx/57/9?ref=pdfpubs.acs.org/Macromolecules?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://pubs.acs.org/Macromolecules?ref=pdfhttps://pubs.acs.org/Macromolecules?ref=pdfhttps://acsopenscience.org/researchers/open-access/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/sorbed epoxies are close to polar functional groups.20 Solid-state nuclear magnetic resonance (NMR) spectra reveal theexistence of two types of water with different relaxationenergies: weakly bound and mobile water molecules andstrongly bound and immobile water molecules.21 The fractionof weakly bound and mobile water molecules has beenestimated to be 60−80%.18,22 The diffusion coefficient (Deff) isdetermined via the weight increase during water absorptionusing Fick’s law.23 This standard method has been used toelucidate the relationships between Deff and the polymerstoichiometry or chemical structure.5,16,20,24 The relationshipbetween Deff and nanovoid sizes in epoxies was previouslyinvestigated using positron annihilation lifetime spectroscopy(PALS); however, no clear effect of void size was found.25 Onthe other hand, the relationship between the free volume of thepolymer and water diffusion remains controversial.26 Some β-relaxation studies indicate that water diffusion is related topolymer chain flexibility;27,28 however, evidence at themolecular scale is lacking. Recently, molecular dynamics(MD) simulations have been extensively used for thestudy,29−31 which showed that water molecules exist in clustersin nanovoids,32−34 and identified two types of water moleculeswith different mobilities.33While the above previous investigations on water inter-actions and Deff provide information about the water dynamicsin epoxies, they lack molecular-level spatial information onmobile water molecules. The information is the size of theepoxy polymer involved in water dynamics at a time scale ofmolecular motion, and it reflects the correlation between thewater dynamics and the polymer structure. Since the spatialdynamics of mobile water should play a fundamental role inwater diffusion within polymers, quantitatively elucidating thisphenomenon is essential for revealing the water diffusionmechanism, controlling the water distribution, and further-more, manipulating changes in material properties induced bywater. Deff should indicate the spatial extent of the waterdiffusion. However, the Deff determined in conventional waterabsorption experiments is based on macroscopic observationsand is insufficient to explain molecular diffusion and thepresence of mobile and immobile water molecules. MDsimulations predict the continuous movement of watermolecules through nanovoids in epoxy, and the Deff of mobilewater determined via this route is 101−102 times larger thanthe experimental Deff obtained via the conventional meth-od.33,34 Thus, more experimental evidence is necessary tounderstand this phenomenon.Quasi-elastic neutron scattering (QENS) is the mosteffective method for experimentally obtaining molecular spatialinformation on water dynamics because it provides spatialinformation at the nanometer scale and temporal informationat the picosecond scale.35 Incoherent scattering analysis of thescattering spectrum enables the separation of mobile andimmobile water molecules, and QENS measurements canprovide the spatial information on mobile water molecules.The water dynamics obtained by observing its hydrogen atomscan be captured separately from the dynamics of polymerchains by deuterating the hydrogen atoms in the polymerbecause deuterium atoms have a neutron-incoherent scatteringcross-section 39 times smaller than that of hydrogen atoms.However, QENS studies on the diffusion of small molecules indeuterated cross-linked polymers are challenging36 because ofthe limited availability of such polymers.In this study, we applied QENS to newly synthesizedcarbon-deuterated epoxies, in which all hydrogen atoms on thecarbon atoms were deuterated to analyze the dynamics ofwater confined in the epoxy nanovoids (Figure 1). QENSmeasurements of epoxies with different stoichiometriesrevealed the diffusivity of water molecules, the ratio of mobileand immobile water, the spatial extent of mobile waterdynamics, and their dependence on stoichiometry. The spatialextent of mobile water in stoichiometric epoxy was large,spanning multiple nanovoids, whereas that in off-stoichio-metric epoxies was as narrow as a single nanovoid. The resultsindicated a relationship between the epoxy chemical structureand water dynamics and suggested the contributions offunctional groups, the epoxy network structure, and localpolymer chain mobility to the observed water dynamics.■ EXPERIMENTAL SECTIONSynthesis. C−H bisphenol A diglycidyl ether (BADGE) (h-BADGE) was synthesized from bisphenol A and epichlorohydrin. Incontrast, C-deuterated BADGE (d-BADGE) was synthesized frombisphenol A-d16 and epichlorohydrin-d5 treated with NaOH in water.The molar compositions of the monomers and oligomers weredetermined gravimetrically after fractionation by using preparative gelpermeation chromatography (GPC). C−H 4,4′-diaminodiphenyl-methane (h-DDM) was synthesized from aniline and formaldehyde,while C-deuterated DDM (d-DDM) was synthesized from aniline-d7Figure 1. Synthesis of C-deuterated epoxies (bisphenol A repeating unit number: m ≥ 0). The hydrogen atom at the ortho-position of the anilinering was omitted for clarity owing to its low incorporation ratio.Macromolecules pubs.acs.org/Macromolecules Articlehttps://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−42624255https://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig1&ref=pdfpubs.acs.org/Macromolecules?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asand formaldehyde-d2 treated with HCl in water. Epoxy samples weresynthesized by curing a mixture of BADGE and DDM with oxirane/NH2 molar ratios of 1/1, 2/1, or 3/1 and heating at 180 °C for 3 h.The molar number of oxirane groups in mixtures of BADGEoligomers was calculated from the molecular weight of eachcomponent and their composition ratio. The water-sorbed epoxysamples were prepared by immersing the epoxy samples intodeionized water at 65 °C until the saturation. The detailed proceduresare provided in the Supporting Information.QENS Measurements. QENS measurements were performedusing the BL02 neutron spectrometer at J-PARC MLF.37,38 Thisspectrometer has an excellent signal/noise ratio of >105 and is suitablefor collecting the scattering profiles of tiny amounts of water in epoxy.The wavelength of the incident neutron was 6.32 ± 2.07 Å. QENSexperiments with an energy resolution of 12 or 3.6 μeV wereperformed using Si(111) analyzers at 24 °C. The transition energy E(μeV) range was −0.5 < E < 1.5 or −20 < E < 100, and the scatteringvector Q (4πsin θ/λ [Å−1]) range was 0.125 < Q < 1.875. Plate-curedepoxy samples measuring 20 × 20 × 0.5 mm3 were wrapped in Nbfoil39 and then sealed into flat cells made of Al alloy (5052). Theexposure times for resolutions of 12 and 3.6 μeV were approximately3 and 7 h, respectively, at a beam power of 530 kW. The Q−E mapsof the epoxy samples, empty cells, and vanadium were obtained bysubtracting the instrumental background profiles and correcting fordetector efficiency by using a vanadium standard. The dynamicstructure factor of the samples, S(Q, E), was corrected for detectorefficiency by using a vanadium standard. The S(Q, E) of water andepoxy was obtained from Q-slices of the Q−E map at Q ∼ 1 Å−1.■ RESULTSDuring the synthesis of d-BADGE, molecules ranging fromdimers to oligomers were formed in addition to the targetcompound because the substrates reacted in a stoichiometricratio owing to the scalability of the starting materials. GPCanalysis of the reaction products confirmed the formation ofoligomers with a monomer:dimer:trimer:tetramer:>pentamermolar ratio of 55:33:10:2:2 (Figure S1). The 13C NMRspectrum of d-BADGE (Figure S2) exhibited the character-istics of C-deuterated compounds, including peak splitting byC−D spin coupling and a slight upfield shift of peaks comparedwith the spectrum of the corresponding h-BADGE. While the1H NMR spectrum of d-BADGE did not exhibit any signals ofthe compounds (Figure S3), the spectrum of d-DDM showeda proton signal at the ortho-position of the aniline ring with ano-H/o-D ratio of 16/84, indicating deuterium/proton aromaticsubstitution during the reaction (Figure S4). The structure ofd-DDM was confirmed by 13C NMR; its spectrum exhibitedpeak splitting and upfield shifts similar to those of d-BADGEand an additional singlet corresponding to the ortho-C atom ofthe aniline ring (Figure S5).During the synthesis of the epoxies, the mixing ratio ofBADGE, including oligomers and DDM, was determined byconsidering the molar ratio of oxirane and NH2 groups (Figure1). In this paper, epoxy refers to the sample or a resin material,and epoxy polymer refers to the polymer chain or chemicalstructure of epoxy. In addition to epoxy with an oxirane/NH2ratio of 2/1 (EP2), epoxies with off-stoichiometric ratios (i.e.,amine-excess oxirane/NH2 = 1/1 [EP1] and oxirane-excessoxirane/NH2 = 3/1 [EP3]) were prepared. The C-deuteratedepoxies dEP1, dEP2, and dEP3 were synthesized from d-BADGE and d-DDM. Similarly, the nondeuterated epoxieshEP1, hEP2, and hEP3 were synthesized from h-BADGE andh-DDM. hEP was used to characterize the thermal andmechanical properties of the epoxy samples.Near-infrared (NIR) spectroscopy (Figure S6) of theepoxies confirmed the consumption of oxirane in all samplesbased on the disappearance of the oxirane signal at 4525 cm−1.In hEP3 with excess oxirane compared with NH2, the absenceof the oxirane signal was attributed to the ring-openingreaction of oxirane with the OH group. In contrast to thespectra of hEP2 and hEP3, the spectrum of amine-excesshEP1 clearly exhibited NH2 and NH signals at approximately6640 and 5020 cm−1, respectively. The reasonable structures ofthe epoxy polymers deduced from the functional groupanalysis described above are shown in Figure 2.Differential scanning calorimetry (DSC) measurementsshowed that hEP2 and hEP3 had similar Tg values of 117and 115 °C, respectively, whereas the Tg of hEP1 wassignificantly lower at 84 °C (Figure S7). Dynamic mechanicalanalysis (DMA) (Figure S8) revealed different peak losstangent (tan δ) temperatures in the order hEP1 < hEP3 = (6DQENS τ0)0.5, the jump distancefor this diffusion was calculated as 2.21 Å. The DQENS ofdEP2+H2O is in the same order as the DQENS of bulk water.This indicates that the mobile water in epoxy nanovoids couldbe categorized as free water, which is only slightly affected bythe confinement effect.44 The DQENS of dEP2+H2O is close tothose of mobile water in non-cross-linked poly(methylmethacrylate)45 and poly(ethylene oxide).46 This observationcan be accounted for by considering mobile water as freewater. DQENS, in this case, is much larger than the Deff obtainedfrom conventional water absorption experiments using Fick’slaw at 65 °C (Deff = 4.13 × 10−12 m2 s−1). These resultsindicate that DQENS corresponds to the diffusion coefficient ofmobile water, whereas Deff is the average diffusion coefficient ofmobile and immobile water.The absence of the Q2 dependence in dEP1+H2O anddEP3+H2O suggests local motion, indicating that watermolecules within the epoxy network may interact with or betrapped by the epoxy polymer chains.Because the epoxy network is nearly immobile compared towater molecules as indicated by hEP+D2O QENS measure-ments, the elastic incoherent structure factor of H2O molecules(EISFW) was estimated according to eq 3, excluding theimmobile component in the dEP and extracting only the H2Ocontribution:A A AA A A AEISF( )( )WLL LdEPdEP H2OdEPdEP H2O{ }{ }=++ +++ (3)where σ is the cross section of chemical species (Table S2).The EISFW values calculated for dEP2+H2O are almostconstant over the entire range of Q. In contrast, thosecalculated for dEP1+H2O and dEP3+H2O are larger thanthose for dEP2+H2O and showed an Q dependence (Figure5). Considering the diameter of the water molecules (2.8 Å),the Q scale for molecular motion is approximately 1 Å−1. FordEP2+H2O, the equation EISFW(Q) = Pm × (3j1(QRS)/(QRS))2 + 1 − Pm, where Pm is the ratio of mobile hydrogenatoms (0 ≤ Pm ≤ 1), RS is the radius of the space in whichmobile hydrogen atoms move, and j1 is the first-order Besselfunction, was used for fitting assuming the dynamics ofconfined water in a restricted space.47 For dEP1+H2O anddEP3+H2O, the equation EISFW(Q) = Pm × exp(−1/3 ×Q2RB2) + 1 − Pm, where RB is the average amplitude distanceof the fluctuations, was employed assuming simple fluctua-tions.48−50 The fitting parameters are summarized in Table 2.Figure 4. Q2 dependence of Γ for the dEP+H2O series.Figure 5. EISF profiles of the dEP+H2O series.Table 2. Fitting Parameters from the EISF Analysis and theRatio of Mobile Water MoleculesadEP1+H2O dEP2+H2O dEP3+H2OPm 0.426 (2 × 10−4) 0.532 (7 × 10−5) 0.360 (3 × 10−4)RB (Å) 3.14 (0.002) 3.74 (0.07)RS (Å) 15.3 (0.08)aStandard errors are shown in parentheses.Macromolecules pubs.acs.org/Macromolecules Articlehttps://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−42624258https://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig5&ref=pdfpubs.acs.org/Macromolecules?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asRB (3.14 or 3.74 Å) reflects the radius of the local motionspace, which is 4−5 times smaller than RS (15.3 Å) fordEP2+H2O, indicating the space involved in the time scale ofjump-diffusion. The spatial size comparison of RS and RB andthe average void size RPALS is summarized in Figure 6. The Pmof dEP2+H2O indicates approximately 1.3∼1.5 times as manyhighly mobile hydrogen atoms, which originates from mobilewater molecules, with a relaxation time scale of subnano-seconds compared with that of dEP1+H2O and dEP3+H2O.The remaining hydrogen atoms are less mobile, with relaxationtimes longer than subnanoseconds, and are represented by thedelta function in the S(Q, E) profiles. And thus, Pm indicatesthe proportion of mobile water molecules within the entirewater molecules in epoxy.The S(Q,E) profiles of the hEP+D2O series were similar tothose of all wet epoxies (Figure S11). Because the spectrarepresent the dynamics of hydrogen atoms in the polymerchains, these results indicate that there are similar polymerchain dynamics regardless of the stoichiometry. In addition,90−95% of the hydrogen atoms are immobile, which indicate arigid polymer chain at the experimental temperature below theglass transition temperature. From these results, the ratio ofhydrogen atoms with high mobility in hEP3+D2O wascalculated as 5.4%, half those in hEP1+D2O and hEP2+D2O(Table S3). This finding implies that stoichiometry determinesthe fraction of mobile polymer chain segments and that theepoxy chains have a lower flexibility in hEP3+D2O than inother samples.■ DISCUSSIONIn all epoxy samples examined, the majority of the watermolecules exhibited restricted dynamics. On the other hand,the proportion and the spatial extent of mobile watermolecules exhibited significant differences of approximately1.5-fold and 4-fold, respectively, indicating the influence of theepoxy polymer structure and the environment of watermolecules on the dynamics (Table 2). The ratios of mobilewater molecules in dEP2+H2O were 53%, which is consistentwith the reported amount of mobile water,18,22 whereas theydecreased to 43 and 36% in dEP1+H2O and dEP3+H2O. Thehydrogen atoms of the mobile water molecules in dEP1+H2Oand dEP3+H2O were predominantly associated with localmotion over a small motion space, indicating the dynamics ofthese molecules inside the nanovoids in the epoxy polymernetwork. By contrast, the mobile water in dEP2+H2Oexhibited a large motion space that could be described bythe jump-diffusion model, indicating the diffusive nature ofthese molecules in dEP2+H2O.The mobile/immobile water molecule ratio depends on thenumber of hydrogen-bond interactions between the watermolecules and the epoxy polymer. The remaining unreactedNH group in EP1 plays a significant role in hydrogen bonding.The structural feature of EP3 is the presence of numerous estercross-links formed via the reaction between −OH groups andoxiranes (Table S4). The phenol ether in the epoxy polymerforms an intramolecular hydrogen bond with the neighboring−OH group. However, the formation of ester cross-linksresults in the formation of phenol ether without intramolecularhydrogen bonds (Figure 2). The abundance of immobile waterin dEP3+H2O suggests that phenol ether has sufficient abilityto bind water molecules via hydrogen bonds (Table S4).The spatial extent of water dynamics in dEP1+H2O anddEP3+H2O analyzed by EISF (Figure 5, RB = 3.14−3.74 Å) isclose to the average void size obtained by PALS (Figure S9,RPALS ∼ 2.6 Å) (Figure 6). Such results support the dynamicsof water molecules within a single nanovoid in wet epoxies, asindicated by the Q2 dependence of Γ (Figure 4). The waterdynamics in dEP2+H2O was fitted using the jump-diffusionmodel with a jump distance of 2.21 Å, plausibly indicatingpositional translation within a nanovoid. By contrast, thespatial extent of mobile water in dEP2+H2O determined byEISF was RS = 15.3 Å, more than twice the average voiddiameter determined by PALS.Because mobile water molecules are not strongly bound byhydrogen bonds to the polymer chain, the different spatialextents of their dynamics can be ascribed to other structuralfactors. The voids in polymer resins with nonporous structuresare separated by a polymer matrix (i.e., polymer chains).Therefore, the diffusion of small molecules in a void over alarge spatial extent is only allowed via the transientinterconnection of nanovoids through the dynamic localmotion of polymer chains or, in other words, the transientgap of the polymer matrix between nanovoids (Figure 7).47,48QENS analysis of the hEP+D2O series demonstrated thatchain motion in the epoxy polymer was more pronounced inhEP1+D2O and hEP2+D2O than in hEP3+D2O (Figure S11).However, considering the existence of numerous non-cross-linked polymer chains in hEP1, as evidenced by its low cross-linking density and low Tg (Table 1), the fraction of mobileepoxy polymer chains in hEP1 may be overestimated. Therestricted chain mobility in off-stoichiometric epoxies agreeswith the report that the activation energy of β-relaxation ishigher for off-stoichiometric epoxies than for stoichiometricones.51 Although the reason for this restriction is unclear, itmay be related to network-structure characteristics, such as thelow cross-linking density and remaining NH groups in hEP1and numerous ester cross-links in hEP3. Restriction of thechain mobility limits the interconnection of voids and inducesthe dynamics of mobile water in these voids. By contrast, thelarger fraction of the mobile polymer chain in hEP2 indicatesthe interconnection of voids, which induces a broad watermolecule displacement over multiple nanovoids (Figure 7a−c).The extent of chain mobility observed by QENS andcorrelated with the motion space of mobile water moleculesdid not correspond to the degree of segmental chain motionexpected from Tg of the epoxies.The spatial dynamics information provides insights into therelationship among the chemical structure, water diffusion, andproperty changes induced by water. A recent simulation studyposited that the difference between the macroscopic waterdiffusion in epoxies from the theoretical expectation arisesfrom the heterogeneity of water distribution and diffusivity.34Our experiments clearly revealed that the microscopic waterdiffusion varies depending on the stoichiometry. TheFigure 6. Comparison of the nanovoid radius determined by PALS(RPALS in green) and motion space radius of mobile water moleculedetermined by QENS (RS in red and RB in blue).Macromolecules pubs.acs.org/Macromolecules Articlehttps://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−42624259https://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig6&ref=pdfpubs.acs.org/Macromolecules?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asinterrelationship between water dynamics and polymer chaindynamics is possibly one of the factors contributing to theheterogeneity.Nanoscale water mobility offers proposals for the changes inTg and other properties of epoxy induced by water absorption.Table 1 shows the effect of stoichiometry and chemicalstructures on the magnitude of water-induced Tg change in EP.The water dynamics in dEP2+H2O is characterized by amobile water ratio that is larger than those of dEP1+H2O anddEP3+H2O and a broader spatial range than these. Therefore,the stoichiometric epoxy (EP2) structure, in which watermolecules move in a large space within the time scale ofmolecular motion, may mitigate the Tg change. In other words,it can be presumed that the epoxy structure with localizedwater mobility within voids is susceptible to water-induced Tgchange. Although there have been reports of Tg and propertychanges observed in water-sorbed epoxies,4,5,15,16 there is a lackof systematic studies that take into account the variation instoichiometry and chemical structure. Such experimentalstudies would contribute to the evaluation of the proposedmodel.■ CONCLUSIONSThe dynamics of water confined in the nanovoids of dEP+H2O epoxies with different stoichiometries were analyzed viaQENS measurements. Analysis of the QENS spectra providedquantitative information about the ratio and motion space ofhighly mobile water molecules. The comparison of QENSspectra of dEP+H2O and hEP+D2O revealed that thedynamics of water molecules and polymer chains have differenttime scales. The lower abundance of mobile water molecules inamine-excess dEP1+H2O and oxirane-excess dEP3+H2O thanin stoichiometric dEP2+H2O suggested the importance of theamine and phenol ether chemical structures. The motion spaceof mobile water molecules was much larger in stoichiometricepoxy than in off-stoichiometric ratio epoxies. It was related tothe local mobility of the epoxy polymer chain. Consequently,the behavior of water in a single nanovoid is assumed for off-stoichiometric dEP1+H2O and dEP3+H2O to understandtheir water dynamics. On the other hand, for stoichiometricdEP2+H2O, mobile water molecules move through multiplenanovoids over a time scale of molecular motion; therefore, thewater dynamics over a large spatial extent must be consideredin conjunction with the local chain motion of epoxy polymers.The insights gained regarding the relationship between thespatial dynamics of water and the epoxy polymer structure arenot limited to the series of epoxies with differentstoichiometries but can be applied to other epoxies andpolymer networks to explain the characteristics of waterdynamic behavior. This study can also contribute to thesimulation of water dynamics. That is, the experimentalinformation provides guidance for the scale of polymer chainlength and interpretation of water dynamic behavior, whichhelps the understanding of the mechanism. The dynamicsinformation pertains to the mechanisms of diffusion of waterwithin the polymer and their relationship with materialproperties. These insights would contribute to the futuredevelopment of high-performance epoxy materials with watersuppression, resistance, or transporting properties.■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010.Detailed information on the materials, instrumentalanalysis, synthetic procedures, water absorption experi-ment, and PALS; GPC, NMR, IR, DSC, DMA, PALS,and QENS experiments; and tables (PDF)■ AUTHOR INFORMATIONCorresponding AuthorsYasuyuki Nakamura − Research Center for Macromoleculesand Biomaterials, National Institute for Materials Science,Tsukuba 305-0047, Japan; orcid.org/0000-0003-0078-6413; Email: NAKAMURA.Yasuyuki@nims.go.jpTaiki Tominaga − Neutron Science and Technology Center,Comprehensive Research Organization for Science andSociety (CROSS), Tokai 319-1106, Japan; orcid.org/0000-0002-6782-6005; Email: t_tominaga@cross.or.jpMasanobu Naito − Research Center for Macromolecules andBiomaterials, National Institute for Materials Science,Tsukuba 305-0047, Japan; Department of AdvancedMaterial Science, Graduate School of Frontier Sciences, TheUniversity of Tokyo, Kashiwa 277-0882, Japan;Figure 7. Schematic illustration of plausible water dynamics in relation to epoxy polymer (dEP) chain dynamics. The green region indicatesnanovoids in the epoxy polymer, the blue and red arrows indicate the motions of water molecules, and the green arrows indicate the motion ofpolymer chains. (a) and (c) show individual nanovoids separated by the epoxy polymer and (b) shows temporarily interconnected voids owing tothe dynamic motion of epoxy polymers. Some deuterium atoms in the epoxy polymer were omitted for clarity.Macromolecules pubs.acs.org/Macromolecules Articlehttps://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−42624260https://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?goto=supporting-infohttps://pubs.acs.org/doi/suppl/10.1021/acs.macromol.3c02010/suppl_file/ma3c02010_si_001.pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yasuyuki+Nakamura"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-0078-6413https://orcid.org/0000-0003-0078-6413mailto:NAKAMURA.Yasuyuki@nims.go.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Taiki+Tominaga"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-6782-6005https://orcid.org/0000-0002-6782-6005mailto:t_tominaga@cross.or.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masanobu+Naito"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0001-7198-819Xhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?fig=fig7&ref=pdfpubs.acs.org/Macromolecules?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asorcid.org/0000-0001-7198-819X;Email: NAITO.Masanobu@nims.go.jpAuthorsTakayuki Iwata − Department of Advanced Material Science,Graduate School of Frontier Sciences, The University ofTokyo, Kashiwa 277-0882, JapanKoki Inoue − Department of Chemistry for Materials,Graduate School of Engineering, Mie University, Tsu 514-8507, JapanYoshihisa Fujii − Department of Chemistry for Materials,Graduate School of Engineering, Mie University, Tsu 514-8507, Japan; orcid.org/0000-0001-9419-8537Nagayasu Oshima − Research Institute for Measurement andAnalytical Instrumentation, National Institute of AdvancedIndustrial Science and Technology, Tsukuba 305-8568,JapanComplete contact information is available at:https://pubs.acs.org/10.1021/acs.macromol.3c02010NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSThis study was based on the results obtained from a project(JPNP14014) commissioned by the New Energy andIndustrial Technology Development Organization (NEDO).The QENS experiments using BL02 (DNA) at the Materialsand Life Science Experimental Facility (MLF) of J-PARC wereperformed under Proposal Nos. 2019B0311 and 2019I0002.This work is partially supported by the Japan Society for thePromotion of Science KAKENHI Grand No. 23K04845(Y.N.).■ REFERENCES(1) Chemistry and Technology of Epoxy Resins; Ellis, B., Ed.; SpringerNetherlands: Dordrecht, 1993.(2) Xiao, G. Z.; Shanahan, M. E. R. Swelling of DGEBA/DDAEpoxy Resin during Hygrothermal Ageing. Polymer 1998, 39, 3253−3260.(3) Xiao, G. Z.; Shanahan, M. E. R. Irreversible Effects ofHygrothermal Aging on DGEBA/DDA Epoxy Resin. J. Appl. Polym.Sci. 1998, 69, 363−369.(4) DeNev̀e, B.; Shanahan, M. E. R. Water Absorption by an EpoxyResin and Its Effect on the Mechanical Properties and Infra-RedSpectra. Polymer 1993, 34, 5099−5105.(5) Nogueira, P.; Ramírez, C.; Torres, A.; Abad, M. J.; Cano, J.;López, J.; López-Bueno, I.; Barral, L. Effect of Water Sorption on theStructure and Mechanical Properties of an Epoxy Resin System. J.Appl. Polym. Sci. 2001, 80, 71−80.(6) Cui, T.; Verberne, P.; Meguid, S. A. Characterization andAtomistic Modeling of the Effect of Water Absorption on theMechanical Properties of Thermoset Polymers. Acta Mech 2018, 229,745−761.(7) Masoumi, S.; Valipour, H. Effects of Moisture Exposure on theCrosslinked Epoxy System: An Atomistic Study. Modelling Simul.Mater. Sci. Eng. 2016, 24, No. 035011.(8) Ogata, S.; Takahashi, Y. Moisture-Induced Reduction ofAdhesion Strength between Surface Oxidized Al and Epoxy Resin:Dynamics Simulation with Electronic Structure Calculation. J. Phys.Chem. C 2016, 120, 13630−13637.(9) Tam, L.; Lau, D. Moisture Effect on the Mechanical andInterfacial Properties of Epoxy-Bonded Material System: An Atom-istic and Experimental Investigation. Polymer 2015, 57, 132−142.(10) Vukovic,́ F.; Walsh, T. R. Moisture Ingress at the MolecularScale in Hygrothermal Aging of Fiber−Epoxy Interfaces. ACS Appl.Mater. Interfaces 2020, 12, 55278−55289.(11) Uthaman, A.; Xian, G.; Thomas, S.; Wang, Y.; Zheng, Q.; Liu,X. Durability of an Epoxy Resin and Its Carbon Fiber- ReinforcedPolymer Composite upon Immersion in Water, Acidic, and AlkalineSolutions. Polymers 2020, 12, 614.(12) Carey, M. S.; Sokol, M.; Palmese, G. R.; Barsoum, M. W. WaterTransport and Thermomechanical Properties of Ti3C2Tz MXeneEpoxy Nanocomposites. ACS Appl. Mater. Interfaces 2019, 11,39143−39149.(13) Lin, K.; Wang, Z. Multiscale Mechanics and MolecularDynamics Simulations of the Durability of Fiber-Reinforced PolymerComposites. Commun. Mater. 2023, 4, 66.(14) Wijmans, J. G.; Baker, R. W. The Solution-Diffusion Model: AReview. J. Membr. Sci. 1995, 107, 1−21.(15) Wu, T. H.; Foyet, A.; Kodentsov, A.; van der Ven, L. G. J.; vanBenthem, R. A. T. M.; de With, G. Wet Adhesion of Epoxy−AmineCoatings on 2024-T3 Aluminum Alloy. Mater. Chem. Phys. 2014, 145,342−349.(16) Frank, K.; Wiggins, J. Effect of Stoichiometry and CurePrescription on Fluid Ingress in Epoxy Networks. J. Appl. Polym. Sci.2013, 130, 264−276.(17) Grave, C.; McEwan, I.; Pethrick, R. A. Influence ofStoichiometric Ratio on Water Absorption in Epoxy Resins. J. Appl.Polym. Sci. 1998, 69, 2369−2376.(18) Wong, T. C.; Broutman, L. J. Water in Epoxy Resins Part IIDiffusion Mechanism. Polym. Eng. Sci. 1985, 25, 529−534.(19) Moy, P.; Karasz, F. Epoxy-Water Interactions. Polym. Eng. Sci.1980, 20, 315−319.(20) Mijovic,́ J.; Zhang, H. Local Dynamics and Molecular Origin ofPolymer Network−Water Interactions as Studied by BroadbandDielectric Relaxation Spectroscopy, FTIR, and Molecular Simulations.Macromolecules 2003, 36, 1279−1288.(21) Zhou, J.; Lucas, J. P. Hygrothermal Effects of Epoxy Resin. PartI: The Nature of Water in Epoxy. Polymer 1999, 40, 5505−5512.(22) Diamant, Y.; Marom, G.; Broutman, L. J. The Effect ofNetwork Structure on Moisture Absorption of Epoxy Resins. J. Appl.Polym. Sci. 1981, 26, 3015−3025.(23) Lee, M. C.; Peppas, N. A. Water Transport in Epoxy Resins.Prog. Polym. Sci. 1993, 18, 947−961.(24) Li, L.; Yu, Y.; Wu, Q.; Zhan, G.; Li, S. Effect of ChemicalStructure on the Water Sorption of Amine-Cured Epoxy Resins.Corros. Sci. 2009, 51, 3000−3006.(25) Soles, C.; Chang, F. T.; Gidley, D. W.; Yee. Contributions ofthe Nanovoid Structure to the Kinetics of Moisture Transport inEpoxy Resins. J. Polym. Sci., Part B: Polym. Phys. 2000, 38, 776−791.(26) Kwisnek, L.; Kaushik, M.; Hoyle, C. E.; Nazarenko, S. FreeVolume, Transport, and Physical Properties of n-Alkyl DerivatizedThiol−Ene Networks: Chain Length Effect. Macromolecules 2010, 43,3859−3867.(27) Soles, C. L.; Yee, A. F. A Discussion of the MolecularMechanisms of Moisture Transport in Epoxy Resins. J. Polym. Sci.,Part B: Polym. Phys. 2000, 38, 792−802.(28) Gerard, J. F.; Galy, J.; Pascault, J. P.; Cukierman, S.; Halary, J.L. Viscoelastic Response of Model Epoxy Networks in the GlassTransition Region. Polym. Eng. Sci. 1991, 31, 615−621.(29) Shundo, A.; Yamamoto, S.; Tanaka, K. Network Formation andPhysical Properties of Epoxy Resins for Future Practical Applications.JACS Au 2022, 2, 1522−1542.(30) Karuth, A.; Alesadi, A.; Vashisth, A.; Xia, W.; Rasulev, B.Reactive Molecular Dynamics Study of Hygrothermal Degradation ofCrosslinked Epoxy Polymers. ACS Appl. Polym. Mater. 2022, 4,4411−4423.(31) Guha, R. D.; Idolor, O.; Grace, L. An Atomistic SimulationStudy Investigating the Effect of Varying Network Structure andPolarity in a Moisture Contaminated Epoxy Network. Comput. Mater.Sci. 2020, 179, No. 109683.Macromolecules pubs.acs.org/Macromolecules Articlehttps://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−42624261https://orcid.org/0000-0001-7198-819Xmailto:NAITO.Masanobu@nims.go.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takayuki+Iwata"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Koki+Inoue"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yoshihisa+Fujii"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0001-9419-8537https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Nagayasu+Oshima"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.macromol.3c02010?ref=pdfhttps://doi.org/10.1016/S0032-3861(97)10060-Xhttps://doi.org/10.1016/S0032-3861(97)10060-Xhttps://doi.org/10.1002/(SICI)1097-4628(19980711)69:2<363::AID-APP18>3.0.CO;2-Xhttps://doi.org/10.1002/(SICI)1097-4628(19980711)69:2<363::AID-APP18>3.0.CO;2-Xhttps://doi.org/10.1016/0032-3861(93)90254-8https://doi.org/10.1016/0032-3861(93)90254-8https://doi.org/10.1016/0032-3861(93)90254-8https://doi.org/10.1002/1097-4628(20010404)80:1<71::AID-APP1077>3.0.CO;2-Hhttps://doi.org/10.1002/1097-4628(20010404)80:1<71::AID-APP1077>3.0.CO;2-Hhttps://doi.org/10.1007/s00707-017-1997-yhttps://doi.org/10.1007/s00707-017-1997-yhttps://doi.org/10.1007/s00707-017-1997-yhttps://doi.org/10.1088/0965-0393/24/3/035011https://doi.org/10.1088/0965-0393/24/3/035011https://doi.org/10.1021/acs.jpcc.6b04754?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcc.6b04754?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcc.6b04754?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.polymer.2014.12.026https://doi.org/10.1016/j.polymer.2014.12.026https://doi.org/10.1016/j.polymer.2014.12.026https://doi.org/10.1021/acsami.0c17027?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.0c17027?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.3390/polym12030614https://doi.org/10.3390/polym12030614https://doi.org/10.3390/polym12030614https://doi.org/10.1021/acsami.9b11448?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.9b11448?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.9b11448?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1038/s43246-023-00391-2https://doi.org/10.1038/s43246-023-00391-2https://doi.org/10.1038/s43246-023-00391-2https://doi.org/10.1016/0376-7388(95)00102-Ihttps://doi.org/10.1016/0376-7388(95)00102-Ihttps://doi.org/10.1016/j.matchemphys.2014.02.022https://doi.org/10.1016/j.matchemphys.2014.02.022https://doi.org/10.1002/app.39140https://doi.org/10.1002/app.39140https://doi.org/10.1002/(SICI)1097-4628(19980919)69:12<2369::AID-APP8>3.0.CO;2-6https://doi.org/10.1002/(SICI)1097-4628(19980919)69:12<2369::AID-APP8>3.0.CO;2-6https://doi.org/10.1002/pen.760250904https://doi.org/10.1002/pen.760250904https://doi.org/10.1002/pen.760200417https://doi.org/10.1021/ma021568q?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ma021568q?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ma021568q?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/S0032-3861(98)00790-3https://doi.org/10.1016/S0032-3861(98)00790-3https://doi.org/10.1002/app.1981.070260917https://doi.org/10.1002/app.1981.070260917https://doi.org/10.1016/0079-6700(93)90022-5https://doi.org/10.1016/j.corsci.2009.08.029https://doi.org/10.1016/j.corsci.2009.08.029https://doi.org/10.1002/(SICI)1099-0488(20000301)38:5<776::AID-POLB15>3.0.CO;2-Ahttps://doi.org/10.1002/(SICI)1099-0488(20000301)38:5<776::AID-POLB15>3.0.CO;2-Ahttps://doi.org/10.1002/(SICI)1099-0488(20000301)38:5<776::AID-POLB15>3.0.CO;2-Ahttps://doi.org/10.1021/ma1001113?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ma1001113?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ma1001113?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1002/(SICI)1099-0488(20000301)38:5<792::AID-POLB16>3.0.CO;2-Hhttps://doi.org/10.1002/(SICI)1099-0488(20000301)38:5<792::AID-POLB16>3.0.CO;2-Hhttps://doi.org/10.1002/pen.760310813https://doi.org/10.1002/pen.760310813https://doi.org/10.1021/jacsau.2c00120?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/jacsau.2c00120?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsapm.2c00383?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsapm.2c00383?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.commatsci.2020.109683https://doi.org/10.1016/j.commatsci.2020.109683https://doi.org/10.1016/j.commatsci.2020.109683pubs.acs.org/Macromolecules?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as(32) Mijovic,́ J.; Zhang, H. Molecular Dynamics Simulation Study ofMotions and Interactions of Water in a Polymer Network. J. Phys.Chem. B 2004, 108, 2557−2563.(33) Pandiyan, S.; Krajniak, J.; Samaey, G.; Roose, D.; Nies, E. AMolecular Dynamics Study of Water Transport inside an EpoxyPolymer Matrix. Comput. Mater. Sci. 2015, 106, 29−37.(34) Yamamoto, S.; Kuwahara, R.; Tanaka, K. Dynamic Behaviour ofWater Molecules in Heterogeneous Free Space Formed in an EpoxyResin. Soft Matter 2021, 17, 6073−6080.(35) Bée, M. Quasielastic Neutron Scattering; Adam Hilger: Bristol,1988.(36) Shudo, Y.; Izumi, A.; Hagita, K.; Yamada, T.; Shibata, K.;Shibayama, M. Diffusion Behavior of Methanol Molecules Confinedin Cross-Linked Phenolic Resins Studied Using Neutron Scatteringand Molecular Dynamics Simulations. Macromolecules 2018, 51,6334−6343.(37) Kawakita, Y.; Matsuura, M.; Tominaga, T.; Yamada, T.;Tamatsukuri, H.; Nakagawa, H.; Ohuchi, K. Recent Progress on DNAToF Backscattering Spectrometer in MLF. J-PARC. EPJ. Web Conf.2022, 272, No. 02002.(38) Shibata, K.; Takahashi, N.; Kawakita, Y.; Matsuura, M.;Yamada, T.; Tominaga, T.; Kambara, W.; Kobayashi, M.; Inamura, Y.;Nakatani, T.; Nakajima, K.; Arai, M.; The Performance of TOF nearBackscattering Spectrometer DNA in MLF, J-PARC; In Proceedings ofthe 2nd International Symposium on Science at J-PARC; JPS ConferenceProceedings; Journal of the Physical Society of Japan, 2015, Vol. 8.(39) Tominaga, T.; Sahara, M.; Kawakita, Y.; Nakagawa, H.;Yamada, T. Evaluation of Sample Cell Materials for AqueousSolutions Used in Quasi-Elastic Neutron Scattering Measurements.J. Appl. Crystallogr. 2021, 54, 1631−1640.(40) Hayward, D.; Hollins, E.; Johncock, P.; McEwan, I.; Pethrick,R. A.; Pollock, E. A. The Cure and Diffusion of Water in HalogenContaining Epoxy/Amine Thermosets. Polymer 1997, 38, 1151−1168.(41) Vanlandingham, M. R.; Eduljee, R. F.; Gillespie, J. W., Jr.Moisture Diffusion in Epoxy Systems. J. Appl. Polym. Sci. 1999, 71,787−798.(42) Meyer, F.; Sanz, G.; Eceiza, A.; Mondragon, I.; Mijovic,́ J. TheEffect of Stoichiometry and Thermal History during Cure onStructure and Properties of Epoxy Networks. Polymer 1995, 36,1407−1414.(43) Popineau, S.; Rondeau-Mouro, C.; Sulpice-Gaillet, C.;Shanahan, M. E. R. Free/Bound Water Absorption in an EpoxyAdhesive. Polymer 2005, 46, 10733−10740.(44) Yamada, T.; Takahashi, N.; Tominaga, T.; Takata, S.; Seto, H.Dynamical Behavior of Hydration Water Molecules betweenPhospholipid Membranes. J. Phys. Chem. B 2017, 121, 8322−8329.(45) Fujii, Y.; Tominaga, T.; Murakami, D.; Tanaka, M.; Seto, H.Local Dynamics of the Hydration Water and Poly(MethylMethacrylate) Chains in PMMA Networks. Front. Chem. 2021, 9,No. 728738.(46) Tominaga, T.; Hishida, M.; Murakami, D.; Fujii, Y.; Tanaka,M.; Seto, H. Experimental Evidence of Slow Mode Water in theVicinity of Poly(Ethylene Oxide) at Physiological Temperature. J.Phys. Chem. B 2022, 126, 1758−1767.(47) Mark, T. F.,A Practical Guide to Quasi-Elastic Neutron Scattering;Royal Society of Chemistry: Croydon, 2020.(48) Noferini, D.; Faraone, A.; Rossi, M.; Mamontov, E.; Fratini, E.;Baglioni, P. Disentangling Polymer Network and Hydration WaterDynamics in Polyhydroxyethyl Methacrylate Physical and ChemicalHydrogels. J. Phys. Chem. C 2019, 123, 19183−19194.(49) Geise, G. M.; Paul, D. R.; Freeman, B. D. Fundamental Waterand Salt Transport Properties of Polymeric Materials. Prog. Polym. Sci.2014, 39, 1−42.(50) Freeman, B. D. Basis of Permeability/Selectivity TradeoffRelations in Polymeric Gas Separation Membranes. Macromolecules1999, 32, 375−380.(51) Won, Y.; Galy, J.; Gérard, J.-F.; Pascault, J.-P.; Bellenger, V.;Verdu, J. Internal Antiplasticization in Copolymer and TerpolyrnerNetworks Based on Diepoxides. Diamines and Monoamines. Polymer1990, 31, 1787−1792.Macromolecules pubs.acs.org/Macromolecules Articlehttps://doi.org/10.1021/acs.macromol.3c02010Macromolecules 2024, 57, 4254−42624262https://doi.org/10.1021/jp036181j?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/jp036181j?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.commatsci.2015.04.032https://doi.org/10.1016/j.commatsci.2015.04.032https://doi.org/10.1016/j.commatsci.2015.04.032https://doi.org/10.1039/D1SM00529Dhttps://doi.org/10.1039/D1SM00529Dhttps://doi.org/10.1039/D1SM00529Dhttps://doi.org/10.1021/acs.macromol.8b00535?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.macromol.8b00535?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.macromol.8b00535?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1051/epjconf/202227202002https://doi.org/10.1051/epjconf/202227202002https://doi.org/10.1107/S1600576721009687https://doi.org/10.1107/S1600576721009687https://doi.org/10.1016/S0032-3861(96)00614-3https://doi.org/10.1016/S0032-3861(96)00614-3https://doi.org/10.1002/(SICI)1097-4628(19990131)71:5<787::AID-APP12>3.0.CO;2-Ahttps://doi.org/10.1016/0032-3861(95)95918-Qhttps://doi.org/10.1016/0032-3861(95)95918-Qhttps://doi.org/10.1016/0032-3861(95)95918-Qhttps://doi.org/10.1016/j.polymer.2005.09.008https://doi.org/10.1016/j.polymer.2005.09.008https://doi.org/10.1021/acs.jpcb.7b01276?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcb.7b01276?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.3389/fchem.2021.728738https://doi.org/10.3389/fchem.2021.728738https://doi.org/10.1021/acs.jpcb.1c09044?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcb.1c09044?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcc.9b04212?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcc.9b04212?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcc.9b04212?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.progpolymsci.2013.07.001https://doi.org/10.1016/j.progpolymsci.2013.07.001https://doi.org/10.1021/ma9814548?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ma9814548?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/0032-3861(90)90203-Bhttps://doi.org/10.1016/0032-3861(90)90203-Bpubs.acs.org/Macromolecules?ref=pdfhttps://doi.org/10.1021/acs.macromol.3c02010?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as