Morphology of a droplet deposited on a strip and triangular groove

Abstract

The behavior of a droplet deposited on solid surfaces, one in the shape of a narrow strip and the other in the shape of a groove of triangular cross-section, was studied. Surface/interface energy of the droplet on the surfaces was calculated. In addition, Laplace pressure and linear size of the droplet were determined. Unexpected dependence of the shape of the droplet placed on the triangular groove on its volume, that is, the jumpwise change in the droplet shape taking place on increasing of its volume, was revealed. This change was found to show some features of a second-order phase transition.

Morphological Transitions of Droplets Wetting a Series of Triangular Grooves

“…However, even for a very simple geometry, when the droplet is deposited into a deep single wedge so its contact lines are not pinned, the necking instability can be observed if the droplet surface is long enough. Thus, in the system studied, which satisfies the canthotaxis condition, the occurrence of the Rayleigh−Plateau instability involving transformation of the droplet shape from filament-like to bulge, as reported for a droplet sitting on a single groove, 16 can be expected.…”

“…The abrupt change in the droplet morphology at the V C is reversible and, because of a jumpwise change in the thermodynamical parameters of the system, it resembles a phase transition. 16 Exploration of new areas of morphological transitions is particularly interesting because of potential use in the microfluidal systems. This study was aimed at examination of the possibility of similar morphological transitions of the droplet deposited on several grooves without flat separators.…”

“…Gau et al were the first to observe that a droplet settled on linear inhomogeneities can show the morphological wetting transitions. Many authors have been interested in spontaneous and reversible change in shape of a droplet deposited, for example, on substrates with striped surface domain, ,,− between two posts or parallel fibers, − and also in triangular or rectangular grooves. ,,, They have been mainly concerned with an attempt at description of behavior of a droplet settled on a single linear inhomogeneity. The droplet behavior on surfaces with 1D geometric patterns, made of a few linear inhomogeneities, has not been studied in detail yet.…”

“…As shown in ref , the shape of the droplet settled on a single triangular groove of the dihedral angle α = 90° and at the contact angle θ Y = 75° depends in a complex way on the droplet volume: (1) The droplet of the volume at which the linear size of the droplet is smaller than the width of the groove assumes the shape of a part of a spherical cap. (2) With increasing volume of the droplet, its shape changes up to a certain critical volume ( V C ).…”

Shape Evolution of Droplets Growing on Linear Microgrooves

“…We will show rigorously that the crucial condition is the the initial number of grooves the equilibrated droplet occupies immediately after deposition. The emergence of different morphologies of droplets growing on a linear groove pattern is closely related to the mechanical bistability between elongated and localized liquid shapes on the plane chemical stripe. , Although the possibility to find different droplet morphologies on substrates with microgrooves has been already mentioned in refs , , , the implications of the morphological bistability on the shape evolution of slowly growing droplets has been largely overlooked.…”