Interaction of resorcinol-formaldehyde carbon aerogels with water: A comprehensive NMR study

Kéri, Mónika; Nyul, Dávid; László, Krisztina; Novák, Levente; Bányai, István

doi:10.1016/j.carbon.2021.12.045

Cited by 16 publications

(6 citation statements)

References 57 publications

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“…In the ideal case of long cylindrical pores in which the liquid occupies a length h while the rest of the cylinder is dry, T 2 is even independent of the saturation (which is proportional to h). Note that some studies 41,42 used an empirical parameter to describe the partial wetting conditions, but we think it is preferable, for a more straightforward interpretation, to compare the variations observed with simple physical assumptions concerning the dewetting characteristics. The evolution of the pdf of T 2 can also reflect some heterogeneity of the liquid distribution in pores.…”

Section: ■ Dynamic Relaxometrymentioning

confidence: 99%

Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media

2022

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Porous media containing voids which can be filled with gas and/or liquids are ubiquitous in our everyday life: soils, wood, bricks, concrete, sponges, and textiles. It is of major interest to identify how a liquid, pushing another fluid or transporting particles, ions, or nutriments, can penetrate or be extracted from the porous medium. High-resolution X-ray microtomography, neutron imaging, and magnetic resonance imaging are techniques allowing us to obtain, in a nondestructive way, a view of the internal processes in nontransparent porous media. Here we review the possibilities of a simple though powerful technique which provides various direct quantitative information on the liquid distribution inside the porous structure and its variations over time due to fluid transport and/or phase changes. It relies on the analysis of the details of the NMR (nuclear magnetic resonance) relaxation of the proton spins of the liquid molecules and its evolution during some process such as the imbibition, drying, or phase change of the sample. This rather cheap technique then allows us to distinguish how the liquid is distributed in the different pore sizes or pore types and how this evolves over time; since the NMR relaxation time depends on the fraction of time spent by the molecule along the solid surface, this technique can also be used to determine the specific surface of some pore classes in the material. The principles of the technique and its contribution to the physical understanding of the processes are illustrated through examples: imbibition, drying or fluid transfers in a nanoporous silica glass, large pores dispersed in a fine polymeric porous matrix, a pile of cellulose fibers partially saturated with bound water, a softwood, and a simple porous inclusion in a cement paste. We thus show the efficiency of the technique to quantify the transfers with a good temporal resolution.

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Section: ■ Dynamic Relaxometrymentioning

confidence: 99%

Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media

2022

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Section: Resultsmentioning

confidence: 99%

“…[28,73] Finally, the variation of the characteristic parameters of the relaxation domains as a function of the water content of the aerogel gives information on the hydration mechanism of the solid backbone and the filling of the nanostructured porous system by water. [47][48][49]51] The PAA was gradually hydrated, and the T 2 relaxation times of water were recorded as a function of water content. This represents the equilibrium sates of the partially hydrated PAA samples.…”

Section: Nmr Relaxometrymentioning

confidence: 99%

Mechanism of Hydration Induced Stiffening and Subsequent Plasticization of Polyamide Aerogel

Moldován

Forgács

Paul

et al. 2023

Adv Materials Inter

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The mesoporous polyamide (PA) aerogel similar in chemical structure to DuPont's Kevlar is an advanced thermal insulation material tested in airspace applications. Unfortunately, the monolithic aerogel readily absorbs humidity (from moist air), which dramatically alters its mechanical properties. The compressive strength of the PA aerogel first increases when its water content increases, but subsequently decreases following additional hydration. To provide a coherent explanation for this non-monotonic change, the aerogel is hydrated stepwise and its hydration mechanism is elucidated by multiscale experimental characterization. The molecular structure is investigated by solid-state and liquid-state nuclear magnetic resonance (NMR) spectroscopy, and the morphology by small angle neutron scattering (SANS) at each equilibrium hydration state. The physico-chemical changes in the molecular level and in the nanoscale architecture are reconstructed. The first water molecules bind into the vacancies of the intermolecular H-bonding network of the PA macromolecules, which strengthens this network and causes concerted morphological changes, leading to the macroscopic stiffening of the monolith. Additional water disrupts the original H-bonding network of the macromolecules, which causes their increased segmental motion, marking the start of the partial dissolution of the nanosized fibers of the aerogel backbone. This eventually plasticizes the monolith.

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“…As an untargeted approach, 1 H NMR spectroscopy provides access to detect all proton‐bearing compounds irrespective of their chemical characteristics, with the advantage of non‐destructive sample preparation, informative spectral patterns, simple operation, and high‐throughput acquisition 11 . Thus, 1 H NMR is widely used in metabolic profiling of complex mixtures, such as biological samples, 12,13 foods, 14–16 herbal medicine, 11,17 and environmental samples 18 . 1 H NMR has quantitative ability with high accuracy and reproducibility.…”

Section: Introductionmentioning

confidence: 99%

“…11 Thus, 1 H NMR is widely used in metabolic profiling of complex mixtures, such as biological samples, 12,13 foods, [14][15][16] herbal medicine, 11,17 and environmental samples. 18 1 H NMR has quantitative ability with high accuracy and reproducibility. However, due to the lack of shared databases of ingredients in herbal medicine, it is difficult to identify and interpret signals in related NMR spectra.…”

mentioning

confidence: 99%

Quantitative profiling of comprehensive composition in compound herbal injections: An NMR approach applied on Shenmai injection

Zhao

Xie

et al. 2022

Phytochemical Analysis

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Introduction: Compound herbal injections (CHIs) can be regarded as a significant innovation in the modernisation of herbal medicine. Therefore, improving the quality control level of CHIs has always been an active research topic in traditional herbal medicine.Objectives: In this study, Shenmai injection was used as a representative sample for investigating the ability of proton nuclear magnetic resonance ( 1 H NMR) in the quality evaluation of CHIs.Methods: A quantitative 1 H NMR method was developed to simultaneously determine the contents of total ginsenosides, polysorbate 80, and 20 primary metabolites in Shenmai injection. Multivariate statistical analysis was combined to compare differences between samples from different manufacturers.Results: It was found that the combined measurement uncertainty of each component is less than 1.61%, which demonstrates the reliability of the method. Furthermore, the components determined by this method account for up to 92.64% of the total solids, which is an unprecedented success in the analysis of Shenmai injection.In the end, the method was applied to the quality comparison of Shenmai injection from six manufacturers. The results showed that the differences among the samples from the six manufacturers were reflected in multiple types of components. Conclusion:This study fully demonstrates the superiority of the quantitative 1 H NMR method in comprehensive composition profiling of CHIs, which is conducive to improving the quality control level of Shenmai injection. Further, the present study can be used as a reference study for the research on the quality and safety of CHIs.

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Interaction of resorcinol-formaldehyde carbon aerogels with water: A comprehensive NMR study

Cited by 16 publications

References 57 publications

Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media

Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media

Mechanism of Hydration Induced Stiffening and Subsequent Plasticization of Polyamide Aerogel

Quantitative profiling of comprehensive composition in compound herbal injections: An NMR approach applied on Shenmai injection

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