Onset of sliding motion in sessile drops with initially non-circular contact lines

Janardan, Nachiketa; Panchagnula, Mahesh V.

doi:10.1016/j.colsurfa.2016.03.046

Cited by 5 publications

(2 citation statements)

References 39 publications

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“…Understanding the dynamics of drops on surfaces is instrumental in designing coatings of materials for specific applications. − The motion of a drop sliding on a surface is affected, among other things, by surface topography, chemical composition of the drop, the solid surface, and the drop size. − Of special interest is the way the onset of the motion of drops on surfaces develops, the subsequent drop dynamics, ,− and the relation between the surface properties and the retention force. − In studies of drop motion, the solid interaction with the liquid is important to determine how the drop would slide across a given substrate. The interaction of the solid with the liquid can be quantified in terms of the interfacial modulus, G s , which describes the resistance of the solid’s molecules to interact with the liquid. , This parameter is associated with reorientation of the solid molecules, which, based on the Shanahan–De Gennes explanation, starts from the triple line, where the solid forms a protruding ridge.…”

Section: Introductionmentioning

confidence: 99%

Stages That Lead to Drop Depinning and Onset of Motion

et al. 2021

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In this paper, we consider drops that are subjected to a gradually increasing lateral force and follow the stages of the motion of the drops. We show that the first time a drop slides as a whole is when the receding edge of the drop is pulled by the advancing edge (the advancing edge drags the receding edge). The generality of this phenomenon includes sessile and pendant drops and spans over various chemically and topographically different cases. Because this observation is true for both pendant and sessile cases, we exclude hydrostatic pressure as its reason. Instead, we explain it in terms of the wetting adaptation and interfacial modulus, that is, the difference in the energies of the solid interface at the advancing and receding edges. At the receding edge, a slight motion exposes to the air a recently wetted solid surface whose molecules had reoriented to the liquid and will take time to reorient back to the air. This results in a high surface energy at the solid–air interface which pulls on the triple line, that is, inhibits the motion of the receding edge. On the other hand, at the advancing edge, a slight advancement does not change the nature of the solid interfacial molecules outside the drop, and the advancing side’s sliding can continue. Moreover, the solid molecules under the drop at the advancing edge take time to reorient, and hence, their configuration is not yet adapted for the liquid and therefore not adapted for retention of the advancing edge. Therefore, in sliding-drop experiments, the advancing edge moves before the receding one, typically a few times before the receding edge moves. For the same reason, the last motion of the receding edge usually happens as a result of the advancing edge pulling on it.

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Section: Introductionmentioning

confidence: 99%

Stages That Lead to Drop Depinning and Onset of Motion

et al. 2021

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“…As mentioned before, contact angle hysteresis has typically been characterized in terms of the advancing and receding angles. A mean pinning force per unit length ( ) can be related to these angles as . , We would like to examine the relationship between and a measure of the pinning force obtained from the extreme value analysis. Let us consider the case of glycerin–acrylic in Figure b to illustrate the point.…”

Section: Resultsmentioning

confidence: 99%

Shapes of Splattered Drops

2017

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Drops that impact and stick to a surface (splattered drops) commonly show noncircular triple lines. Physical or chemical defects on the surface are known to pin the triple line in this static metastable state. We report an experimental study to relate the defect distribution on a surface to the triple-line microstructure of such drops. Triple lines of an ensemble of splattered drops have been imaged on a range of surfaces varying in wetting properties. Local contact angles have been calculated, and the microscale pinning force distribution has been estimated. We propose a novel method of estimating defect strength distribution from the pinning forces, using extreme value analysis. From this analysis, we show that pinning force distributions have finite upper and lower bounds. We show that most common surfaces show both hydrophobic and hydrophilic defects, but their strength distributions are asymmetric in relation to the surface's advancing and receding angles. In addition, we show that the range of microscopic pinning forces varies linearly with macroscopic contact angle hysteresis but, surprisingly, with a nonzero intercept. We explain the intercept by drawing an analogy to static and dynamic friction.

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