Droplet motion on chemically heterogeneous substrates with mass transfer. I. Two-dimensional dynamics

Groves, Danny; Savva, Nikos

doi:10.1103/physrevfluids.6.123601

Cited by 4 publications

(7 citation statements)

References 64 publications

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“…The excess surface energy is dissipated through capillary waves during the rapid jump (see figure 4c, f,i). It should be noted that similar effects of bifurcation diagrams have also been reported in a recent contribution on sessile droplets (Groves & Savva 2021). In general, our simulation accurately reproduces the CAH and complex contact line dynamics predicted by the theory.…”

Section: Contact Line Dynamicssupporting

confidence: 87%

Width effect on contact angle hysteresis in a patterned heterogeneous microchannel

Chang

Huang

et al. 2022

J. Fluid Mech.

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The width effect on contact angle hysteresis in a microchannel with patterned heterogeneous surfaces is systematically investigated. In the model, identical defects periodically appear on the background surface. To this end, a droplet's evaporation and condensation processes inside the microchannel are studied by theoretical analysis and numerical simulation based on a diffuse-interface lattice Boltzmann method. The microchannel width effect on the system's equilibrium properties is studied. The results demonstrate that the number of equilibrium configurations increases linearly with the microchannel width ( $b$ ), and has a quadratic relationship with the cosine of the reference contact angle and the heterogeneity strength ( $\varepsilon$ ). The average most stable contact angle is independent of $b$ and is always equal to the contact angle predicted by the Cassie–Baxter equation. For contact angle hysteresis ( $H$ ), when the microchannels are narrow and wide, there are individual-effect-dominated hysteresis (IDH) and collective-effect-dominated hysteresis (CDH), respectively. The IDH and CDH are hysteresis modes corresponding to the jumping behaviour of contact lines affected by individual defects and two neighbouring defects, respectively. Based on the graphical force balance approach, we establish a scaling law to quantify the connection between $H$ , $b$ and $\varepsilon$ . Specifically, in the IDH mode, $H\sim b \varepsilon ^2$ , while in the CDH mode, $H$ increases linearly with $\varepsilon$ but nonlinearly with $b$ .

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Section: Contact Line Dynamicssupporting

confidence: 87%

Width effect on contact angle hysteresis in a patterned heterogeneous microchannel

Chang

Huang

et al. 2022

J. Fluid Mech.

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“…Although the outcomes of a 2D model cannot be straightforwardly scrutinized by experiments, the combined analytical and computational work we have undertaken made looking into the complex bifurcation structure of the dynamics possible; gaining further insights into how hysteresis-like effects and transients to periodic motion occur by following the topological changes that take place as the nature and stability of droplet equilibria evolve with changing the droplet area. Importantly, the outcomes of this work are to be combined with the recent developments presented by Savva et al on 3D droplet motion over chemically heterogeneous surfaces [63], to offer a novel extension to the fully 3D geometry, which is the subject of the second part of the present study [47].…”

Section: Discussionmentioning

confidence: 94%

“…taken to be some characteristic contact angle; in the case of substrates with localized features α s corresponds to the contact angle in the defect-free region of the substrate. The lengthscale L = V /(2α s ) is a measure of the characteristic size of the droplet and is associated with its cross-sectional area, denoted by V to be consistent with the notation for the 3D volume in Part II of the present investigation [47]. Under Eq.…”

Section: Problem Formulationmentioning

confidence: 96%

“…The discussion here is limited to the two-dimensional (2D) geometry primarily to highlight, in qualitative terms, the interesting interplay between surface heterogeneities and mass transfer, deferring the arguably more realistic threedimensional (3D) setting to the following paper [47]. We also seek to extend related works in 2D on homogeneous surfaces, e.g.…”

Section: Introductionmentioning

confidence: 99%

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Droplet motion on chemically heterogeneous substrates with mass transfer. I. Two-dimensional dynamics

Groves,

Savva

2020

Preprint

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We consider the dynamics of thin two-dimensional viscous droplets on chemically heterogeneous surfaces moving under the combined effects of slip, mass transfer and capillarity. The resulting longwave evolution equation for the droplet thickness is treated analytically via the method of matched asymptotic expansions in the limit of slow mass transfer rates, quasi-static dynamics and vanishingly small slip lengths to deduce a lower-dimensional system of integrodifferential equations for the two moving fronts. We demonstrate that the predictions of the deduced system agree excellently with simulations of the full model for a number of representative cases within the domain of applicability of the analysis. Specifically, we focus on situations where the mass of the drop changes periodically to highlight a number of interesting features of the dynamics, which include stick-slip, hysteresislike effects, as well as the possibility for the droplet to alternate between the constant-radius and constant-angle stages which have been previously reported in related works. These features of the dynamics are further scrutinized by investigating how the bifurcation structure of droplet equilibria evolves as the mass of the droplet varies.

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“…Typical references are refs. [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85]. A brief summary of these works for l d ∼ l p is as follows.…”

Section: Introductionmentioning

confidence: 99%

Wetting Effect on Patterned Substrates

Wang

Nestler

2023

Advanced Materials

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A droplet deposited on a solid substrate leads to the wetting phenomenon. A natural observation is the lotus effect, known for its superhydrophobicity. This special feature is engendered by the structured microstructure of the lotus leaf, namely, surface heterogeneity, as explained by the quintessential Cassie-Wenzel theory (CWT). In this work, recent designs of functional substrates are overviewed based on the CWT via manipulating the contact area between the liquid and the solid substrate as well as the intrinsic Young's contact angle. Moreover, the limitation of the CWT is discussed. When the droplet size is comparable to the surface heterogeneity, anisotropic wetting morphology often appears, which is beyond the scope of the Cassie-Wenzel work. In this case, several recent studies addressing the anisotropic wetting effect on chemically and mechanically patterned substrates are elucidated. Surface designs for anisotropic wetting morphologies are summarized with respect to the shape and the arrangement of the surface heterogeneity, the droplet volume, the deposition position of the droplet, as well as the mean curvature of the surface heterogeneity. A thermodynamic interpretation for the wetting effect and the corresponding open questions are presented at the end.

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Droplet motion on chemically heterogeneous substrates with mass transfer. I. Two-dimensional dynamics

Cited by 4 publications

References 64 publications

Width effect on contact angle hysteresis in a patterned heterogeneous microchannel

Width effect on contact angle hysteresis in a patterned heterogeneous microchannel

Droplet motion on chemically heterogeneous substrates with mass transfer. I. Two-dimensional dynamics

Wetting Effect on Patterned Substrates

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