NMR cryoporometry of polymers: Cross-linking, porosity and the importance of probe liquid

Rottreau, Taylor; Parkes, George E.; Schirru, Manuela; Harries, Josephine L.; Mesa, Marta Granollers; Topham, Paul D.; Evans, R. Douglas

doi:10.1016/j.colsurfa.2019.05.018

Cited by 13 publications

(8 citation statements)

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“…This indicates that spherical water droplets undergo phase transitions in hydrated CaAG of 0.3 g/g water content. The size distribution of these droplets was reconstructed from the melting curve by using the Gibbs–Thomson equations, as described in the Supporting Information. − The results are shown in Figure B. According to the SANS results, the pores of hydrated CaAG of 0.3 g/g water content are significantly larger than the original pores of the dry material.…”

Section: Resultsmentioning

confidence: 99%

“…Another important feature of the cryoporometry data is that the 1 H NMR signal intensity converges to a nonzero value at low temperature. This indicates that there is a substantial amount of water in the hydrated sample that does not freeze even at 256 K and has a long enough T 2 relaxation time to pass the relaxation filter of the pulse sequence. ,, …”

Section: Resultsmentioning

confidence: 99%

“…This indicates that there is a substantial amount of water in the hydrated sample that does not freeze even at 256 K and has a long enough T 2 relaxation time to pass the relaxation filter of the pulse sequence. 67,68,70 The melting−freezing features significantly change by the increase of the hydration level of CaAG. In the case of the wellhydrated CaAG sample of 1.4 g/g water content, the 1 H NMR signal intensity does not show hysteresis as a function of temperature (Figure 5C).…”

Section: Small-angle Neutron Scattering (Sans)mentioning

confidence: 99%

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Mechanism of Hydration and Hydration Induced Structural Changes of Calcium Alginate Aerogel

Forgács

Papp

Paul

et al. 2021

ACS Appl. Mater. Interfaces

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The most relevant properties of polysaccharide aerogels in practical applications are determined by their microstructures. Hydration has a dominant role in altering the microstructures of these hydrophilic porous materials. To understand the hydration induced structural changes of monolithic Caalginate aerogel, produced by drying fully cross-linked gels with supercritical CO 2 , the aerogel was gradually hydrated and characterized at different states of hydration by small-angle neutron scattering (SANS), liquid-state nuclear magnetic resonance (NMR) spectroscopy, and magic angle spinning (MAS) NMR spectroscopy. First, the incorporation of structural water and the formation of an extensive hydration sphere mobilize the Caalginate macromolecules and induce the rearrangement of the drystate tertiary and quaternary structures. The primary fibrils of the original aerogel backbone form hydrated fibers and fascicles, resulting in the significant increase of pore size, the smoothing of the nanostructured surface, and the increase of the fractal dimension of the matrix. Because of the formation of these new superstructures in the hydrated backbone, the stiffness and the compressive strength of the aerogel significantly increase compared to its dry-state properties. Further elevation of the water content of the aerogel results in a critical hydration state. The Ca-alginate fibers of the backbone disintegrate into well-hydrated chains, which eventually form a quasi-homogeneous hydrogel-like network. Consequently, the porous structure collapses and the welldefined solid backbone ceases to exist. Even in this hydrogel-like state, the macroscopic integrity of the Ca-alginate monolith is intact. The postulated mechanism accounts for the modification of the macroscopic properties of Ca-alginate aerogel in relation to both humid and aqueous environments.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Small-angle Neutron Scattering (Sans)mentioning

confidence: 99%

See 1 more Smart Citation

Mechanism of Hydration and Hydration Induced Structural Changes of Calcium Alginate Aerogel

Forgács

Papp

Paul

et al. 2021

ACS Appl. Mater. Interfaces

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“…All of these techniques are suitable for a wide range of polymers [18,20] and porous materials [18], including porous glass [30,31], zeolites [32], cement [33], clays [18], rock [27,34], wood [35], and biochar and other porous carbons [18,27,36,37]. In polymers, crystalline/amorphous ratios may be measured.…”

Section: Introductionmentioning

confidence: 99%

“…In polymers, crystalline/amorphous ratios may be measured. By swelling rubbers and polymers by adding liquids to them, cross-link density and nano-to micro-porous properties of the polymer may be obtained [18,20,38]. In biochar, progressive changes to the quantity and mobility of hydrocarbons, as well as changes in pore-blocking, as a function of preparation temperature, have been demonstrated [27].…”

Section: Introductionmentioning

confidence: 99%

Some Applications of a Field Programmable Gate Array Based Time-Domain Spectrometer for NMR Relaxation and NMR Cryoporometry

Webber¹

2020

Applied Sciences

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Featured Application: This compact but precision highly stable NMR time-domain relaxation spectrometer is most useful for quantitative material science measurements of both the mass and the mobility/dynamics/stiffness/viscosity/rigidity of hydrocarbons and polymers, both in the bulk and in sub-nano-meter and upward sized pores. It is highly useful for studying the properties of hydrocarbons in pores in applications such as recovered porous rock samples from oil reservoirs, and in fired biochar porous carbon samples, to give just two examples. In addition, applicable to both these fields of study is the ability to make NMR Cryoporometric measurements of pore-size distributions in porous materials, for sub-nano-to over micrometer sized pores.Abstract: NMR Relaxation (NMRR) is an extremely useful quantitative technique for material science, particularly for studying polymers and porous materials. NMR Cryoporometry (NMRC) is a powerful technique for the measurement of pore-size distributions and total porosities. This paper discusses the use, capabilities and application of a newly available compact NMR time-domain relaxation spectrometer, the Lab-Tools Mk3 NMR Relaxometer & Cryoporometer [Lab-Tools (nano-science), Ramsgate, Kent, UK (2019)]. Being Field Programmable Gate Array based means that it is unusually compact, which makes it particularly suitable for the lab bench-top, in the field and also mobile use. Its use with a variable-temperature NMR probe such as the Lab-Tools Peltier thermo-electrically cooled variable-temperature (V-T) probe is also discussed. This enables the NMRC measurement of pore-size distributions in porous materials, from sub-nano-to over 1 micron sized pores. These techniques are suitable for a wide range of porous materials and also polymers. This instrument comes with a Graphical User Interface (GUI) for control, which also enables both online and offline analysis of the measured data. This makes it is easy to use for material science studies both in the field and in university, research institute, company and even school laboratories. The Peltier cooling gives the precision temperature control and smoothness needed by NMR Cryoporometry, particularly near the probe liquid bulk melting point. Results from example NMR Relaxation and NMR Cryoporometric measurements are given.

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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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NMR cryoporometry of polymers: Cross-linking, porosity and the importance of probe liquid

Cited by 13 publications

References 48 publications

Mechanism of Hydration and Hydration Induced Structural Changes of Calcium Alginate Aerogel

Mechanism of Hydration and Hydration Induced Structural Changes of Calcium Alginate Aerogel

Some Applications of a Field Programmable Gate Array Based Time-Domain Spectrometer for NMR Relaxation and NMR Cryoporometry

Mechanism of Hydration Induced Stiffening and Subsequent Plasticization of Polyamide Aerogel

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