J. Thiery’s research while affiliated with Harvard University and other places

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Publications (3)


FIG. 1. NMR profiles along sample axis at different times (time interval t) (from top to bottom) during drying for bead packings with different particle diameters: (a) 45 000 nm (time interval of 23, then 44 min), (b) 1500 nm (33 min), (c) 1000 nm (36 min), (d) 300 nm (50 min), (e) 80 nm (33 then 44 min), (f) 40 nm (28 min), (g) 12 nm (16 min), and (h) 6 nm (23 min). The first profile with some gradient in saturation is represented by a thicker line. The dotted line corresponds to the first profile after the time interval change. Note that for the sake of clarity data for 300 and 80 nm in the FRP have been smoothened. 
Drying regimes in homogeneous porous media from macro- to nanoscale
  • Article
  • Full-text available

July 2017

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298 Reads

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63 Citations

Physical Review Fluids

J. Thiery

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D. A. Weitz

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Magnetic resonance imaging visualization down to nanometric liquid films in model porous media with pore sizes from micro- to nanometers enables one to fully characterize the physical mechanisms of drying. For pore size larger than a few tens of nanometers, 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 the 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 effect of scaling of the net flow rate on the pore size observed in our tests.

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Drying kinetics of deformable and cracking nano-porous gels

December 2016

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479 Reads

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19 Citations

The European Physical Journal E

J. Thiery

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The desiccation of porous materials encompasses a wide range of technological and industrial processes and is acutely sensitive to the hierarchical structure of the porous materials resulting in complex dynamics which are challenging to unravel. Macroscopic observations of the surface and geometry of model colloidal gels during desiccation under controlled air flow highlight the role of crack formation in drying. The density of cracks and their rate of appearance depend on the initial solid fraction of the gels and their adherence to the substrate. While under certain conditions cracking leads to an increase of the drying rate, in other cases cracking allows for its conservation over an extended period of the drying process. Nevertheless, as long as the sample is saturated with water, each piece within the sample shrinks isotropically as if it were an independent drying system. By simulating the airflow around the sample and inside the crack cavities, we show the existence of a perturbation in the air velocity in the vicinity of the crack cavity whose scale depends on the aspect ratio (depth/width) of the latter. On this basis, we propose a simple model which predicts the observed drying rate variations encountered while the sample cracks; and further enables to simulate the desiccation for a designated crack density. Graphical abstract


Water transfer and crack regimes in nanocolloidal gels

April 2015

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214 Reads

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17 Citations

Physical Review E

Direct observations of the surface and shape of model nano-colloidal gels associated with measurements of the spatial distribution of water content during drying show that air starts to significantly penetrate the sample when the material stops shrinking. We show that whether the material fractures or not during desiccation, as air penetrates the porous body, the water saturation decreases but remains almost homogeneous throughout the sample. This air-invasion is at the origin of another type of fracture due to capillary effects, these results provide a new insight in the liquid dynamics at the nano-scale. PACS number(s): 47.56.+r, 68.03.Fg, 81.40.Np

Citations (3)


... The drying of a porous medium fully saturated with free water is a process which is relatively well known. For pore sizes larger than a few hundred nanometers and smaller than a few millimeters, as in the case of our cellulose fiber stacks, capillary effects dominate as long as the saturation is not too low [70] and the drying induces a transport of the liquid towards the sample surface where it evaporates. Most of the liquid is extracted during this period and the drying rate is constant. ...

Reference:

Fate of a water drop in a cellulosic material
Drying regimes in homogeneous porous media from macro- to nanoscale

Physical Review Fluids

... In contrast to silica powders or films, producing silica monoliths by drying a hydrogel formed through a sol-gel method is a complicated task. In fact, while drying, a hydrogel is exposed to capillary and adhesion forces [12][13][14]. Both forces impose enormous stresses on the silica network, eventually leading to cracking, delamination, and crumbling. ...

Drying kinetics of deformable and cracking nano-porous gels

The European Physical Journal E

... In contrast to silica powders or films, producing silica monoliths by drying a hydrogel formed through a sol-gel method is a complicated task. In fact, while drying, a hydrogel is exposed to capillary and adhesion forces [12][13][14]. Both forces impose enormous stresses on the silica network, eventually leading to cracking, delamination, and crumbling. ...

Water transfer and crack regimes in nanocolloidal gels

Physical Review E