Horizontal drying fronts during solvent evaporation from latex films

Routh, Alexander F.; Russel, William B.

doi:10.1002/aic.690440916

Cited by 254 publications

(272 citation statements)

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“…Previous work has provided a robust description of the film formation processes during lateral drying [3, 4,9,12,13]. The general observation is that drying fronts sweep across the liquid film, starting from the edge and progressing toward the middle.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Therefore the deposition of a uniform liquid colloidal film leads to a final solid film that has homogeneous composition, thickness and microstructure. Relatively homogeneous films can also be obtained through mechanisms where there is a moving liquid-solid boundary, and there is a flow of liquid phase near this boundary [8,9].(b) Coffee-ring: this process has also been extensively studied [1, 2]. In this situation a macroscopic flow throughout the liquid carries nearly all the particles to the fixed edges of the film, where they pack into a dense rim.…”

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confidence: 99%

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Drying Dip-Coated Colloidal Films

Cabane

Sztucki

et al. 2011

Langmuir

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We present the results from a Small Angle X-ray Scattering (SAXS) study of lateral drying in thin films. The films, initially 10 µm thick, are cast by dip-coating a mica sheet in an aqueous silica dispersion (particle radius 8 nm, volume fraction φs = 0.14). During evaporation, a drying front sweeps across the film. An X-ray beam is focused on a selected spot of the film, and SAXS patterns are recorded at regular time intervals. As the film evaporates, SAXS spectra measure the ordering of particles, their volume fraction, the film thickness and the water content, and a video camera images the solid regions of the film, recognized through their scattering of light. We find that the colloidal dispersion is first concentrated to φs = 0.3, where the silica particles form a gel with repulsive interactions. Then the particles aggregate until they form a cohesive wet solid at φs = 0.68 ± 0.02. Further evaporation from the wet solid leads to evacuation of water from pores of the film, but leaves a residual water fraction φw = 0.16. The whole drying process is completed within three minutes. An important finding is that, in any spot (away from boundaries), the number of particles is conserved throughout this drying process, leading to the formation of a homogeneous deposit. This implies that no flow of particles occurs in our films during drying, a behavior distinct to that encountered in the iconic coffee-stain drying. It is argued that this type of evolution is associated with the formation of a transition region that propagates ahead of the drying front. In this region the gradient of osmotic pressure balances the drag force exerted on the particles by capillary flow toward the liquid-solid front. INTRODUCTIONCoatings are often made through deposition of liquid colloidal dispersions. Common examples are paints, anticorrosion coatings and ceramic coatings. In most cases, the dispersion is applied as a liquid film, and it changes into a solid film as a result of solvent evaporation. A variety of deposition patterns can be obtained, depending on the evaporation profile over the liquid film and on the flows taking place inside the deposit during drying [1][2][3][4][5][6][7]. The two extreme situations are as follows:(a) Homogeneous film formation: in the simplest case, there is no lateral flow through the liquid film, and all volatile components are evaporated locally. The number of particles at each point of the film is conserved throughout the drying process. Therefore the deposition of a uniform liquid colloidal film leads to a final solid film that has homogeneous composition, thickness and microstructure. Relatively homogeneous films can also be obtained through mechanisms where there is a moving liquid-solid boundary, and there is a flow of liquid phase near this boundary [8,9].(b) Coffee-ring: this process has also been extensively studied [1, 2]. In this situation a macroscopic flow throughout the liquid carries nearly all the particles to the fixed edges of the film, where they pack into a dense rim. At the end o...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Drying Dip-Coated Colloidal Films

Cabane

Sztucki

et al. 2011

Langmuir

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“…Within the liquid region, pressure is due to surface tension, and the magnitude of this pressure is much lower than that generated by flow through the solid region [2]. Hence a boundary condition p(0) = 0 is appropriate.…”

Section: Theorymentioning

confidence: 99%

“…Colloidal dispersions, such as those used in the production of paints, ceramics, or photonic crystals, typically dry directionally [1,2]. During directional drying a film dries first at its edge, leaving a slowly shrinking liquid area.…”

Section: Introductionmentioning

confidence: 99%

Solidification and Ordering during Directional Drying of a Colloidal Dispersion

2010

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During drying, colloidal dispersions undergo processes such as solidification, cracking, and the draining of interstitial pores. Here we show that the solidification of polystyrene and silica dispersions, during directional drying, occurs in two separate stages. These correspond to the initial ordering, and subsequent aggregation, of the colloidal particles. Transitions between these stages are observed as changes in transparency and color that propagate as distinct fronts along the drying layer. The dynamics of these fronts are shown to arise from a balance between compressive capillary forces, and the electrostatic and van der Waals forces described by DLVO theory. This suggests a simple method by which the maximum inter-particle repulsion between particles can be measured through the optical inspection of the dynamics of a drying dispersion, under a microscope.

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Drying Structure

Okubo¹

2016

Encyclopedia of Biocolloid and Biointerface Science 2V Set

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Horizontal drying fronts during solvent evaporation from latex films

Cited by 254 publications

References 16 publications

Drying Dip-Coated Colloidal Films

Drying Dip-Coated Colloidal Films

Solidification and Ordering during Directional Drying of a Colloidal Dispersion

Drying Structure

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