Droplet wetting transitions on inclined substrates in the presence of external shear and substrate permeability

Espín, Leonardo; Kumar, Satish

doi:10.1103/physrevfluids.2.014004

Cited by 21 publications

(34 citation statements)

References 38 publications

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“…This argument is also supported by the images obtained from droplet motion and the presence or the lack of a measureable droplet residue on the surface (see the droplet detachment videos in the Supporting Information). As can be seen in the bottom-right image in Figure , a Wenzel droplet breaks up into smaller droplets as it moves over the surface, the so-called pearling effect as explained in ref .…”

Section: Resultssupporting

confidence: 93%

Droplet Mobility on Hydrophobic Fibrous Coatings Comprising Orthogonal Fibers

2018

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Water droplet mobility on a hydrophobic surface cannot be guaranteed even when the droplet exhibits a high contact angle (CA) with the surface. In fact, droplet mobility on a surface, especially a fibrous surface, has remained an unsolved empirical problem. This paper is a combined experimental-computational study focused on droplet mobility on a fibrous surface. Electrospun polystyrene (PS) coatings were used in this work for their ability to exhibit high CAs simultaneously with low droplet mobility. To simplify this otherwise complicated problem and better isolate droplet-fiber interactions, the orientation of the fibers in the coatings was limited to the x and y directions. As the earth gravity was not strong enough to mobilize small droplets on PS coatings, experiments were conducted using ferrofluid droplets, and a magnet was used to make them move on the surface. Experimentally validated numerical simulations were used to enhance our understanding of the forces acting on a droplet before moving on the surface. Effects of Young-Laplace CA and fiber-fiber spacing on droplet mobility were investigated. In particular, it was found that droplet mobility depends strongly on the balance of forces exerted on the droplet by the fibers on the receding and advancing sides.

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Section: Resultssupporting

confidence: 93%

Droplet Mobility on Hydrophobic Fibrous Coatings Comprising Orthogonal Fibers

2018

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“…However, previous studies (e.g. Krechetnikov 2010;Espín & Kumar 2017) have demonstrated that the lubrication approximation can work beyond the strictly small-slope limits. Furthermore, we emphasise only qualitative comparisons with the experiments, instead of quantitative ones.…”

Section: Theorymentioning

confidence: 96%

Droplet breakup in a stagnation-point flow

et al. 2020

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“…Apart from this assumption, no other restrictions are placed on the droplet shape. Whereas previous studies often assume that the droplet shape is a spherical cap, − the advantage of our model is that it can readily be extended to much more general situations (e.g., droplets on inclined surfaces) where the spherical-cap assumption is no longer valid. ,, Second, although real surfaces contain a distribution of topographical features of varying size, shape, and location, we focus here on the presence of a single topographical defect. This approach allows us to gain insight into how individual topographical features influence droplet dynamics, and provides a rational basis for understanding more complex situations where multiple defects are present.…”

Section: Introductionmentioning

confidence: 99%

Drying of Droplets of Colloidal Suspensions on Rough Substrates

2017

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In many technological applications, excess solvent must be removed from liquid droplets to deposit solutes onto substrates. Often, the substrates on which the droplets rest may possess some roughness, either intended or unintended. Motivated by these observations, we present a lubrication-theory-based model to study the drying of droplets of colloidal suspensions on a substrate containing a topographical defect. The model consists of a system of one-dimensional partial differential equations accounting for the shape of the droplet and depth-averaged concentration of colloidal particles. A precursor film and disjoining pressure are used to describe the contact-line region, and evaporation is included using the well-known one-sided model. Finite-difference solutions reveal that when colloidal particles are absent, the droplet contact line can pin to a defect for a significant portion of the drying time due to a balance between capillary-pressure gradients and disjoining-pressure gradients. The time-evolution of the droplet radius and contact angle exhibits the constant-radius and constant-contact-angle stages that have been observed in prior experiments. When colloidal particles are present and the defect is absent, the model predicts that particles will be deposited near the center of the droplet in a cone-like pattern. However, when a defect is present, pinning of the contact-line accelerates droplet solidification, leading to particle deposition near the droplet edge in a coffee-ring pattern. These predictions are consistent with prior experimental observations, and illustrate the critical role contact-line pinning plays in controlling the dynamics of drying droplets.

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Droplet wetting transitions on inclined substrates in the presence of external shear and substrate permeability

Cited by 21 publications

References 38 publications

Droplet Mobility on Hydrophobic Fibrous Coatings Comprising Orthogonal Fibers

Droplet Mobility on Hydrophobic Fibrous Coatings Comprising Orthogonal Fibers

Droplet breakup in a stagnation-point flow

Drying of Droplets of Colloidal Suspensions on Rough Substrates

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