Water retention against drying with soft-particle suspensions in porous media

Keita, Emmanuel; Kodger, Thomas E.; Faure, Paméla; Rodts, Stéphane; Weitz, David A.; Coussot, Philippe

doi:10.1103/physreve.94.033104

Cited by 25 publications

(16 citation statements)

References 46 publications

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“…Under this assumption, after some transient stage, the drying rate would be controlled by vapor diffusion from the wet front to the free surface of the sample. This leads to a mass loss varying with the square root of time (see below), in agreement with some observations [13,15,[18][19][20].…”

Section: Introductionsupporting

confidence: 91%

Convective drying of a porous medium with a paste cover

et al. 2019

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The convective drying of a composite system made of a porous medium covered with a paste is a situation often encountered with soils, roads, building and cultural heritage materials. Here we discuss the basic mechanisms at work during the drying of model composite system made of a homogeneous paste covering a simple granular packing. We start by reviewing the rather well-known case of the convective drying of a simple granular packing (i.e. without paste cover), which serves as a reference for physical interpretations. We show that a simple model assuming homogeneous desaturation then progressive development of a dry front from the sample free surface is in agreement with observations of the internal liquid distribution variations in time. In particular, this model is able to reproduce the saturation vs time curves of various simple granular systems, which supports our understanding of physical mechanisms at work. Then we show the detailed characteristics of drying of initially saturated model composite systems (with kaolin or cellulose paste) with the help of MRI measurements providing the liquid distribution in the sample at different times during the process up to the very last stages of drying. It appears that the granular medium is unaffected (i.e. remains saturated) during an initial period during which the paste shrinks and finally forms a sufficiently rigid porous structure which will not any more shrink later on. Then the drying process is governed by capillary effects down to very low saturation. Over a wide range of saturations both media desaturate homogeneously (within each medium) at different rates which depend on the specific porous structure of the media, so as to maintain capillary equilibrium throughout the sample. During these different stages the drying rate of the whole system remains constant. For sufficiently low saturation in the paste a dry front can develop, both in the paste and the porous medium below, and the drying rate now decreases. These results show that in a drying composite system liquid extraction can occur more or less simultaneously in the different parts of the material up to the very last stages of drying. The corresponding evolution of the distributions of liquid in the different parts of the sample also provides key information for the prediction of ion or particle transport and accumulation in the different parts of a composite system.

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Section: Introductionsupporting

confidence: 91%

Convective drying of a porous medium with a paste cover

et al. 2019

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“…In detail, it was also suggested that two FRP should be considered [4,[17][18][19], associated with the continuous and the discontinuous states of the liquid network. The development of a receding dry front was observed and measured in a variety of cases such as experiments with a non-wetting liquid [20], accumulation of ions [21] or particles [22][23] below the free surface, a packing filled with a paste [10], a packing of large beads [23] etc. and in all cases the drying rate in this second regime was probed to scale as the diffusion of vapor from the wet front to the free surface.…”

Section: Introductionmentioning

confidence: 99%

Drying regimes in homogeneous porous media from macro- to nanoscale

et al. 2017

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MRI visualization down to nanometric liquid films in model porous media with pore size from micro-to nano-meter enables to fully characterize the physical mechanisms of drying. In larger pores, we identify an initial constant drying rate period, probing homogeneous desaturation, followed by a falling drying rate period. This second period is associated with the development of a gradient in saturation underneath the sample free surface that initiates the inward recession of the contact line. During this latter stage, the drying rate varies in accordance with vapor diffusion through the dry porous region; possibly affected by Knudsen effect for small pore size. However, we show that for sufficiently small pore size and/or saturation the drying rate is increasingly reduced by the Kelvin effect. Subsequently, we demonstrate that this effect governs the kinetics of evaporation in nanopores as a homogeneous desaturation occurs. Eventually, under our experimental conditions, we show that the saturation unceasingly decreases in a homogeneous manner throughout the wet regions of the medium regardless of pore size or drying regime considered. This finding suggests the existence of continuous liquid flow towards the interface of higher evaporation, down to very low saturation or very small pore size. Paradoxically, even if this net flow is unidirectional and capillary driven, it corresponds to a series of diffused local capillary equilibrations over the full height of the sample, which might explain that a simple Darcy's law model does not predict the scaling of the net flow rate on the pore size observed in our tests.

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“…The distribution of ion concentration can also be determined through their impact on the NMR relaxation time, which for example made it possible to observe the electrodissolution of metal ions (Bray et al 2016). In a similar way, the liquid distribution and deposited particle distribution in time were also obtained in the case of drying of a colloidal suspension in a porous medium (Keita et al 2013(Keita et al , 2016. These data allowed to validate a simple model assuming in that case that each particle exactly follows the liquid path until the liquid evaporates (so that the particle adsorbs to the wall), or the particle is blocked by previously accumulated particles.…”

Section: Transient Liquid Flowsmentioning

confidence: 99%

Progress in rheology and hydrodynamics allowed by NMR or MRI techniques

Coussot

2020

Exp Fluids

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We review the uses of nuclear magnetic resonance techniques for experiments with fluids. More precisely we focus on the progress of knowledge in complex flows, rheology of complex fluids, flow in porous media, colloid transport, fluid transfers in complex porous systems, which have been allowed by NMR techniques. These achievements took advantage of the versatility of NMR, which makes it possible to carry out more original measurements than the basic well-known density imaging (MRI). One may thus rely on non-destructive, non-invasive, local velocimetry, local rheometry, statistical approaches of molecular displacements or velocity, distribution of adsorbed or suspended colloids, evolution of the liquid distribution in different states, fluid transfers during drying or imbibition, etc.

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Water retention against drying with soft-particle suspensions in porous media

Cited by 25 publications

References 46 publications

Convective drying of a porous medium with a paste cover

Convective drying of a porous medium with a paste cover

Drying regimes in homogeneous porous media from macro- to nanoscale

Progress in rheology and hydrodynamics allowed by NMR or MRI techniques

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