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Polymers 2021, 13, 1150 crystallisation [1,25,35]. In the present work, wide-angle X-ray diffraction was carried out as described in Sec- tion 2.5 for “dry” samples of Nafion 115 membrane in its H+ (as received) and Li+ forms in order to reveal the influence of the lithiation procedure (Section 2.1) on the degree of crys- tallinity and struc◦tural characteristics. Diffraction patterns of the samples in the 2θ range range from 7 to 22 (where the most intensive peak is located) together with decomposed the difference can be attributed to the effect of side chains and ionic groups hindering samples, the measured curves were decomposed into a broad peak at 2θ ≈ 15◦ with a ◦ the measured curves were decomposed into a broad peak at 2θ ≈ 15° with a full width at full width at half-maximum (fwhm) of ≈4 (amorphous halo), and a relatively sharp ◦◦ half-maximum (fwhm) of ≈4° (amorphous halo), and a relatively sharp peak at 2θ ≈ 17° + 8 of 14 from 7 to 22° (where the most intensive peak is located) together with decomposed pro- profiles are presented in Figure 5; their characteristics are shown in Table 1. For both files are presented in Figure 5; their characteristics are shown in Table 1. For both samples, peak at 2θ ≈ 17 with fwhm of ≈2 (indexed as the (100) reflection of the hexagonal with fwhm of ≈2° (indexed as the (100) reflection of the hexagonal structure [35]). Taking structure [35]). Taking into account the significant error in the decomposition of broadened into account the significant error in the decomposition of broadened profile, the WAXD profile, the WAXD results for H Nafion are in reasonable agreement with the literature + draetsau[l1ts,2f5o,r35H–4N1]a. fiFoonr alritehinatredasNonafiabolne,acgrryesetmalleongtrwapithicthdealtiateararetuerxetdreamtae[l1y,2s5c,a3r5c–e41(o].nFlyor Rleitfh. i[a4t0e]dwNaasffiounn, cdr)y. stallographic data are extremely scarce (only Ref. [40] was found). Figure 5. Wide-angle diffraction pattern of “dry” Nafion 115 membrane before (a) and after (b) lithia- Figure 5. Wide-angle diffraction pattern of “dry” Nafion 115 membrane before (a) and after (b) tiloitnh.iation. Table 1. X-ray characteristics of “dry” Nafion 115 membrane before and after lithiation. Table 1. X-ray characteristics of “dry” Nafion 115 membrane before and after lithiation. Sample Amorphous Galo (100) Crystalline Degree, % Sample 2θ, Deg Fwhm 2θ, Deg Fwhm Crystalline Degree, % Amorphous Galo (100) Nafion 115 (H+) 2θ, Deg Fwhm 15.00 ± 0.10 4.29 2θ, Deg Fwhm 17.03 ± 0.04 2.25 29 Nafion 115 (H+) 15.00 ± 0.10 4.29 15.41 ± 0.06 5.14 17.03 ± 0.04 2.25 17.01 ± 0.03 2.27 17.01 ± 0.03 2.27 29 Nafion 115 (Li+) 20 20 Nafion 115 (Li+) 15.41 ± 0.06 5.14 As shown in Table 1, the conversion of protonated Nafion into the lithiated form bareAlys cshaonwgnedintThaebmleo1s,tthineteconnsiversciroynstoafllpinroetorenfaletecdtioNna(fi1o0n0)i.nHtootwhevliethr,iathteedmfoarxmimbuarmelyof cthaenagmedortphheomusoshtailnoteshnisfitveedcnroytsitcaelalibnlyertoeflweacrtdiolnar(g1e0r0)a.nHgloesw,ewvheirl,eththeemdaexgirmeeuomfcorfysthtael- amorphous halo shifted noticeably toward larger angles, while the degree of crystallinity linity (calculated by Equation (3)) significantly decreased as a result of lithiation. (calculated by Equation (3)) significantly decreased as a result of lithiation. The morphological features of the Nafion membrane, which contains crystalline in- The morphological features of the Nafion membrane, which contains crystalline clusions and ionic clusters along with amorphous regions, clearly influence thermal tran- inclusions and ionic clusters along with amorphous regions, clearly influence thermal sitions. It is known that crystalline regions of polymers at temperatures well below their transitions. It is known that crystalline regions of polymers at temperatures well below melting point behave similarly to chemical crosslinking [42], while electrostatic interac- their melting point behave similarly to chemical crosslinking [42], while electrostatic tions within ionic clusters act as physical crosslinking [1,43]. Limiting the segmental dy- interactions within ionic clusters act as physical crosslinking [1,43]. Limiting the segmental namics of Nafion macromolecules, all these factors are clearly manifested in its thermal dynamics of Nafion macromolecules, all these factors are clearly manifested in its thermal behaviour. As mentioned in the review of Kusoglu [1], Nafion membranes exhibit three behaviour. As mentioned in the review of Kusoglu [1], Nafion membranes exhibit three thermal transitions labelled α, β and γ, which correspond to distinct relaxation mecha- thermal transitions labelled α, β and γ, which correspond to distinct relaxation mechanisms. nisms. However, at present, even for the protonated form of Nafion, there is no consensus However, at present, even for the protonated form of Nafion, there is no consensus about about their assignment. The γ relaxation around −120 to −90 (nearly independent of water their assignment. The γ relaxation around −120 to −90 (nearly independent of water absorption and cation type) is usually attributed to short-range molecular motions of the absorption and cation type) is usually attributed to short-range molecular motions of the –CF2– backbone [1,40]; nevertheless, Corti et al. [44] reasonably reassigned this transition –CF2– backbone [1,40]; nevertheless, Corti et al. [44] reasonably reassigned this transition as the true glass transition temperature of the polymer. The β relaxation between −40 and +20 ◦C and the α relaxation between 90 and 120 ◦C (both sensitive to cation type and water content) were attributed to glass transition temperatures of the polar regions (ionic clusters) and non-polar matrix of the Nafion membrane. However, there is no consensus in the assignment of α and β relaxation to the former or latter process (see, for example,PDF Image | Li-Nafion Membrane Plasticised with Ethylene Carbonate Sulfolane
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