Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry
We use 2H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that t...
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Frontiers Media S.A.
2024-03-01
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| Series: | Frontiers in Soft Matter |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/frsfm.2024.1379816/full |
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| author | Christoph Säckel Regine von Klitzing Renée Siegel Jürgen Senker Michael Vogel |
| author_facet | Christoph Säckel Regine von Klitzing Renée Siegel Jürgen Senker Michael Vogel |
| author_sort | Christoph Säckel |
| collection | DOAJ |
| description | We use 2H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that the 2H spin-lattice (T1) and, in particular, spin-spin (T2) relaxation times abruptly decrease when heating through the LCST, indicating that the polymer collapse causes an emergence of a water fraction with strongly reduced mobility. To quantify the dynamics of this slow water fraction, we exploit the fact that 2H field-cycling relaxometry allows us to measure the spectral density of the water reorientation in a broad frequency range. We find that the slow water fraction is characterised by a broad logarithmic Gaussian distribution of correlation times (σLG = 2.3), which is centred about τLG ≈ 10–9 s near the LCST. Hence, the common assumption of a Debye spectral density does not apply. We argue that a minor water fraction, which is located inside the pNIPAM globules and shows dynamics governed by the disordered polymer matrix, accompanies a major water fraction with bulk-like dynamics above the LCST. The former fraction amounts to about 0.4 water molecules per NIPAM monomer. Several findings indicate fast exchange between these bound and free water fractions on the T1 and T2 time scales. |
| first_indexed | 2024-04-24T21:43:42Z |
| format | Article |
| id | doaj.art-75b731fc3a464e50a508ad5089606a3c |
| institution | Directory Open Access Journal |
| issn | 2813-0499 |
| language | English |
| last_indexed | 2024-04-24T21:43:42Z |
| publishDate | 2024-03-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Soft Matter |
| spelling | doaj.art-75b731fc3a464e50a508ad5089606a3c2024-03-21T04:23:49ZengFrontiers Media S.A.Frontiers in Soft Matter2813-04992024-03-01410.3389/frsfm.2024.13798161379816Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometryChristoph Säckel0Regine von Klitzing1Renée Siegel2Jürgen Senker3Michael Vogel4Institute for Condensed Matter Physics, Technische Universität Darmstadt, Darmstadt, GermanyInstitute for Condensed Matter Physics, Technische Universität Darmstadt, Darmstadt, GermanyInorganic Chemistry III and Northern Bavarian NMR Centre, University of Bayreuth, Bayreuth, GermanyInorganic Chemistry III and Northern Bavarian NMR Centre, University of Bayreuth, Bayreuth, GermanyInstitute for Condensed Matter Physics, Technische Universität Darmstadt, Darmstadt, GermanyWe use 2H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that the 2H spin-lattice (T1) and, in particular, spin-spin (T2) relaxation times abruptly decrease when heating through the LCST, indicating that the polymer collapse causes an emergence of a water fraction with strongly reduced mobility. To quantify the dynamics of this slow water fraction, we exploit the fact that 2H field-cycling relaxometry allows us to measure the spectral density of the water reorientation in a broad frequency range. We find that the slow water fraction is characterised by a broad logarithmic Gaussian distribution of correlation times (σLG = 2.3), which is centred about τLG ≈ 10–9 s near the LCST. Hence, the common assumption of a Debye spectral density does not apply. We argue that a minor water fraction, which is located inside the pNIPAM globules and shows dynamics governed by the disordered polymer matrix, accompanies a major water fraction with bulk-like dynamics above the LCST. The former fraction amounts to about 0.4 water molecules per NIPAM monomer. Several findings indicate fast exchange between these bound and free water fractions on the T1 and T2 time scales.https://www.frontiersin.org/articles/10.3389/frsfm.2024.1379816/fullwaterpoly (N-isopropyl acrylamide)NMRfield cycling NMRmolecular dynamics |
| spellingShingle | Christoph Säckel Regine von Klitzing Renée Siegel Jürgen Senker Michael Vogel Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry Frontiers in Soft Matter water poly (N-isopropyl acrylamide) NMR field cycling NMR molecular dynamics |
| title | Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry |
| title_full | Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry |
| title_fullStr | Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry |
| title_full_unstemmed | Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry |
| title_short | Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry |
| title_sort | water dynamics in solutions of linear poly n isopropyl acrylamide studied by 2h nmr field cycling relaxometry |
| topic | water poly (N-isopropyl acrylamide) NMR field cycling NMR molecular dynamics |
| url | https://www.frontiersin.org/articles/10.3389/frsfm.2024.1379816/full |
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