Evaporating sessile droplet pair: Insights into contact line motion, flow transitions and emergence of universal vaporisation pattern

Abstract

We have deciphered that the vaporization rate of a pair of sessile droplets placed in a close vicinity of each other not only gets suppressed but also approached a universal pattern in the long time asymptotic limit, irrespective of substrate hydrophobicity. In a short time, these droplets exhibit a series of naturally evolving characteristics such as alteration of evaporation modes, flow transitions, asymmetric deformation, and motion of the contact line. Such dynamics are uniquely determined by the degree of pinning. In addition, we show that the enhanced hydrophobicity does not always lead to lower evaporation rate in droplets.

The shielding effect extends the lifetimes of two-dimensional sessile droplets

“…Consider the regime of most interest, Ψ R, in which the domain is large and approximately semi-circular, and the condition at the outer boundary corresponds most closely to a far-field condition. From (27), (29) and (34) we obtain Fig. 5 The quasi-semi-elliptical domain in the ζ -plane for the two-droplet problem…”

“…In practice, droplets rarely occur in isolation, and so it is important to understand how droplets evaporate in the presence of other evaporating droplets. Previous studies of the evaporation of multiple sessile droplets have employed a variety of experimental, numerical and analytical approaches [27][28][29][30][31][32][33][34][35][36][37][38]. The critical difference between the evaporation of single and of multiple droplets is the occurrence of the shielding effect, namely that the presence of other evaporating droplets increases the local vapour concentration, and so each droplet evaporates more slowly than it would in isolation.…”

Evaporation of Initially Heated Sessile Droplets and the Resultant Dried Colloidal Deposits on Substrates Held at Ambient Temperature

“…Substrate hydrophobicity is found to play an important role in deciding the mode of evaporation and the overall lifetime of the evaporating droplet . The flow mechanisms under different conditions in an evaporating droplet execute several interesting features, namely, evaporation-triggered segregation of sessile binary droplets, CRE-driven hollow rim formation at the periphery of the evaporating pure water drop on salt substrates, suppression of vaporization rate and the emergence of asymptotic universal pattern for two adjacent droplets, and interesting phenomena observed in inclined droplets . Besides, vapor bubble formation for evaporating droplets resting on superheated surfaces having varied wettability was demonstrated .…”

Contact-line deposits from multiple evaporating droplets

“…While there have been some analytical studies of mathematically analogous situations concerning clusters of microcontacts and nanobubbles (see, for example, [27,28]), analytical work on the evaporation of multiple droplets is rather limited. To a large extent this is explained by the inherent difficulty of analysing such situations, and while the evaporation of multiple droplets in various configurations has been the subject of growing recent interest, the previous studies have been predominantly numerical or experimental (see, for example, [11,[29][30][31][32][33][34][35][36]). Two notable exceptions are the recent work of Wray et al [37], who, building on the earlier work of Fabrikant [38] concerning a model for diffusion through a porous membrane, analysed the spatially non-uniform shielding that occurs in arbitrary configurations of thin droplets with circular contact lines, and that of Schofield et al [39], who used conformal-mapping techniques to analyse the analogous spatially non-uniform shielding that occurs in the closely related two-dimensional situation of a pair of evaporating ridges.…”