Imbibition and dewetting of silica colloidal crystals: An NMR relaxometry study

Gallego-Gómez, Francisco; Cadar, Calin; López, Cefe; Ardelean, I.

doi:10.1016/j.jcis.2019.11.050

Cited by 11 publications

(11 citation statements)

References 49 publications

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“…In the NMR relaxometry of porous materials it is routinely considered that the pores are saturated with the filling liquid and the observed transverse relaxation rate of confined molecules is a weighted average between the bulk relaxation rate and the surface relaxation rate of molecules confined inside a thin layer of few molecular diameters, uniformly covering the internal surface of the pores [ 16 , 28 ]. However, there are many situations when the pores are only partially saturated with the liquid.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…However, there are many situations when the pores are only partially saturated with the liquid. In that case, the relaxation rate depends on the pore filling and the liquid distribution on the pore surface [ 16 , 28 , 29 , 30 ]. Assuming that the confined molecules wet the surface of the pores, the relaxation rate can be expressed as a weighted average between the relaxation rate of the remaining bulk-like liquid and the surface relaxation rate.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

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The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations

Ardelean

2021

Molecules

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Nuclear Magnetic Resonance (NMR) relaxometry is a valuable tool for investigating cement-based materials. It allows monitoring of pore evolution and water consumption even during the hydration process. The approach relies on the proportionality between the relaxation time and the pore size. Note, however, that this approach inherently assumes that the pores are saturated with water during the hydration process. In the present work, this assumption is eliminated, and the pore evolution is discussed on a more general basis. The new approach is implemented here to extract information on surface evolution of capillary pores in a simple cement paste and a cement paste containing calcium nitrate as accelerator. The experiments revealed an increase of the pore surface even during the dormant stage for both samples with a faster evolution in the presence of the accelerator. Moreover, water consumption arises from the beginning of the hydration process for the sample containing the accelerator while no water is consumed during dormant stage in the case of simple cement paste. It was also observed that the pore volume fractal dimension is higher in the case of cement paste containing the accelerator.

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Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Theoretical Backgroundmentioning

confidence: 99%

The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations

Ardelean

2021

Molecules

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“…Their specific relaxation times and volumes, given by the maxima and areas of the respective distribution peaks for each SD, will be referred to as T 2 void , T 2 micro , and A void , A micro . While the slow mode is studied in detail elsewhere (in the context of void imbibition and drainage of particulate packings), we focus here on the characterization of the Stöber microporosity via the fast mode. Note that, actually, a third, smaller peak systematically appeared at very short times (∼0.1 ms), which may be an artifact of the ILT; however, this peak could also correspond to tightly bound water molecules (e.g., structural water or water confined in very narrow micropores)this residual contribution is not considered here.…”

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confidence: 99%

Microporosity Quantification via NMR Relaxometry

et al. 2019

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Micropores and their interplay with liquids are critical in many solid systems but challenging to investigate, often requiring complex and indirect techniques to even be detected. Here we perform low-field 1 H NMR transverse relaxometry on submicron Stöber silica spheres to directly detect micropore water. Colloidal crystals with a well-defined spheres configuration are used to facilitate unambiguous distinction of the interparticle voids water and enable straightforward micropore volume quantification. We evidence significant microporosity (~16% of the sphere volume) with high water-accessibility and monitor the drying of the micropore water, which exhibits high resilience, evaporating only after complete voids drainage. Progressive microporosity closure by thermal annealing above 600 ºC is shown, until complete removal at 900 ºC. Increasing hydrophobicity of the micropore walls is observed, although it barely affected the water access. Our results prove the capability of NMR relaxometry to quantitatively investigate complex microporosity and the behavior of water confined therein.

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“…If the exchange between the microenvironments is relatively slow on the time scale of the relaxometric experiments (ca. 1 ms), multiple relaxation domains are observed. , In contrast, only one relaxation domain is observed in the case of fast exchange, even for water molecules located in different microenvironments in the hydrated porous solid. Detailed considerations on the characteristic relaxation time ( T 2 ) of such a domain are given in the Supporting Information.…”

Section: Resultsmentioning

confidence: 96%

“…The mechanisms of the interactions between highly hydrophilic porous networks and water are still far from being fully understood. − Recently, we interpreted the mechanical properties of partially wetted model polysaccharide aerogel networks by using a decomposition concept; that is, the dry aerogel network was described on the basis of a micromechanical model, while hydrated aerogel fibrils were assumed to form a new phase with hyperelastic behavior . Although being successful in quantifying the mechanical response of the aerogels to hydration, such an approach offers only a phenomenological treatment.…”

Section: Introductionmentioning

confidence: 99%

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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Imbibition and dewetting of silica colloidal crystals: An NMR relaxometry study

Cited by 11 publications

References 49 publications

The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations

The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations

Microporosity Quantification via NMR Relaxometry

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

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