Autostratification in Drying Colloidal Dispersions: Effect of Particle Interactions

Atmuri, Anand K; Bhatia, Surita R.; Routh, Alexander F.

doi:10.1021/la2039762

Cited by 64 publications

(78 citation statements)

References 18 publications

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“…Using the extended RZ model, Atmuri et al studied the effects of inter-particle interactions amongst the same species (i.e., the particles of the same size) on the particle distribution during drying of the suspension. [17]. They also investigated suspensions containing particles of the same size but some of them are neutral while the others are charged.…”

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confidence: 99%

“…Their work demonstrated the effects of high particle concentrations and the associated jamming that prevents the particles to stratify.From the reported studies we now understand that stratifying phenomena in a drying suspension containing a bidisperse mixture of neutral particles depend on several factors including the evaporation rate of the solvent, the initial volume fractions of the particles, the particle size ratio, and the interactions between the particles. [17,19,[22][23][24] The ZJD model predicts that for the initial volume fractions only that of the smaller particles matters.[23] However, in previous simulations [15-17, 19, 22, 24] and theory[23] the solvent was treated as an implicit, uniform viscous background. Very recently, Sear and Warren used the Asakura-Oosawa model to study the drift of a large particle in a solute (i.e., small particle) gradient, [27,28] taking into account the contribution from the solvent back-flow to the pressure gradient, and showed that the analyses of Fortini et al and the ZJD model based on an implicit solvent overestimate the drift velocity of large particles roughly by a factor of α 2 .…”

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Stratification in Drying Films Containing Bidisperse Mixtures of Nanoparticles

2018

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Large scale molecular dynamics simulations for bidisperse nanoparticle suspensions with an explicit solvent are used to investigate the effects of evaporation rates and volume fractions on the nanoparticle distribution during drying. Our results show that "small-on-top" stratification can occur when Pe ϕ ≳ c with c ∼ 1, where Pe is the Péclet number and ϕ is the volume fraction of the smaller particles. This threshold of Pe ϕ for "small-on-top" is larger by a factor of ∼α than the prediction of the model treating solvent as an implicit viscous background, where α is the size ratio between the large and small particles. Our simulations further show that when the evaporation rate of the solvent is reduced, the "small-on-top" stratification can be enhanced, which is not predicted by existing theories. This unexpected behavior is explained with thermophoresis associated with a positive gradient of solvent density caused by evaporative cooling at the liquid/vapor interface. For ultrafast evaporation the gradient is large and drives the nanoparticles toward the liquid/vapor interface. This phoretic effect is stronger for larger nanoparticles, and consequently the "small-on-top" stratification becomes more distinct when the evaporation rate is slower (but not too slow such that a uniform distribution of nanoparticles in the drying film is produced), as thermophoresis that favors larger particles on the top is mitigated. A similar effect can lead to "large-on-top" stratification for Pe ϕ above the threshold when Pe is large but ϕ is small. Our results reveal the importance of including the solvent explicitly when modeling evaporation-induced particle separation and organization and point to the important role of density gradients brought about by ultrafast evaporation.

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Stratification in Drying Films Containing Bidisperse Mixtures of Nanoparticles

2018

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“…1. 21 Investigated by DLS and zeta potential, the clay solutions in this study was suitable for the preparation of nacre-like composites. 18 Then, by this separation method, the average size of most clay nanoparticles was found to be 31 nm and a small quantity of them had a mean diameter of 279 nm.…”

Section: Dispersion Of Clay Aqueous Solutionsmentioning

confidence: 93%

“…The crosshead speed was set at 1 mm min 21 . The zeta potentials of the nanoparticles and aqueous clay solutions were measured using Malvern Zetasizer 3000HSA (Malvern Instruments, UK).…”

Section: Characterizationsmentioning

confidence: 99%

Supramolecular ionic strength-modulating microstructures and properties of nacre-like biomimetic nanocomposites containing high loading clay

Zhu

Chang

et al. 2012

RSC Adv.

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In this study, we prepare thick nacre-like polymer clay nanocomposite films by a simple solution casting method. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. The water-soluble poly(vinyl alcohol) (PVA) was chosen as an organic binder to connect each smectic clay sheet in the form of a nacre-like microstructure. The polymer-clay composite is in the form of a membrane in which the clay sheets are like stacked bricks. In addition, when applying normal stress larger than the yield stress-about 40 MPa-white shear bands develop at strains larger than 10%, much like the conditions where crazing of organic PVA is suppressed by inorganic fillers of clay sheets. Their corresponding microstructure and mechanical properties are studied using wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques and a tensile testing machine and are discussed in detail.

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“…On the theoretical side, Atmuri et al developed a diffusive model that explicitly took into account the self-interaction between particles of the same type, but the cross-interaction is absent. [47] …”

Section: Adv Mater 2017 29 1703769mentioning

confidence: 99%

Structure Formation in Soft‐Matter Solutions Induced by Solvent Evaporation

et al. 2017

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etc., and the interplay between different processes determines the final structure of the dried materials.Here, we report recent advances of selfassembled structures induced by uniform evaporation, examples including drying in a thin-film geometry or evaporating a spherical droplet on a superhydrophobic surface. [4] In these situations, the structure formation takes place in the direction of the evaporation. This excludes the case where lateral flow is induced by nonuniform drying. The lateral flow is important in explaining the coffee-ring effect, where excellent reviews exist in literature. [5,6] After introducing the general procedure in experiments, we explain the physical mechanisms responsible for the structure formation in solvent evaporation. We then discuss recent advances based on single-and binarycomponent solutions, with a special emphasis on the theoretical approaches. Drying of Single-Component SolutionsA general experiment starts with spin-coating a thin-film solution on a substrate, then the sample is left to dry. In the first step, it is important that the spin-cast film is uniform. [7,8] In the second step, the evaporation flux, i.e., the mass removed from the liquid phase to the vapor phase in unit time from unit surface area needs to be controlled precisely. Even for the pure solvent evaporation, the process is complex and involves the diffusion of solvent molecules in both the liquid and vapor phases, and external flow in the vapor phase to prevent saturation. The evaporation flux can be computed using the Hertz-Knudsen equation that is based on the thermodynamics variables [9][10][11] or solving the diffusion equation in the vapor phase using suitable boundary conditions. [12][13][14] The solvent evaporation drives the free surface to recede toward the substrate, resulting in an accumulation of the solutes at the surface. Two competing processes determine the spatial distribution of the solutes. One is the Brownian motion, which is characterized by the diffusion constant D of the solutes. The other is the evaporation, characterized by the rate v ev at which the free surface recedes. Two timescales are related to these two processes: the diffusion time τ D =  2 /D, where  is a characteristic length and the evaporation time τ ev = /v ev . To quantify the relative importance between the diffusion and the evaporation, one can define a dimensionless number called film formation Peclet number: [15]

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Autostratification in Drying Colloidal Dispersions: Effect of Particle Interactions

Cited by 64 publications

References 18 publications

Stratification in Drying Films Containing Bidisperse Mixtures of Nanoparticles

Stratification in Drying Films Containing Bidisperse Mixtures of Nanoparticles

Supramolecular ionic strength-modulating microstructures and properties of nacre-like biomimetic nanocomposites containing high loading clay

Structure Formation in Soft‐Matter Solutions Induced by Solvent Evaporation

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