Sessile drop technique

About: Sessile drop technique is a research topic. Over the lifetime, 2827 publications have been published within this topic receiving 68943 citations.

Wetting behavior of nanodroplets: The limits of Young's rule validity

Abstract: We study the contact angle of polymer melt sessile droplets on a flat structureless substrate subject to long-range van der Waals forces when the droplet size is diminished. For this purpose, droplets containing 4096 to 512 monomers for chains of length N = 32 are carefully equilibrated at 80% of the Θ-temperature using a coarse-grained bead spring model of flexible polymers in a Monte Carlo computer experiment. The spherically averaged density profile of these droplets, both in the z-direction perpendicular to the substrate surface and in the radial direction, is obtained. At weak adhesion we find that the contact angle grows steadily with the decrease of drop size so that below a critical size these drops dewet the surface. This suggests a strong contribution of a positive line tension κ in the determination of the equilibrium drop shape. At much stronger adhesion, however, the contact angle does not change with drop size, indicating κ ≈ 0. In general, our simulational results outline the limits of validity of Young's relation for the contact angle of sessile nanodroplets and support the more general Gretz rule which takes into account the role of line tension in the balance of surface forces.

Substrate constraint modifies the Rayleigh spectrum of vibrating sessile drops.

Abstract: In this work, we study the resonance behavior of mechanically oscillated, sessile water drops. By mechanically oscillating sessile drops vertically and within prescribed ranges of frequencies and amplitudes, a rich collection of resonance modes are observed and their dynamics subsequently investigated. We first present our method of identifying each mode uniquely, through association with spherical harmonics and according to their geometric patterns. Next, we compare our measured resonance frequencies of drops to theoretical predictions using both the classical theory of Lord Rayleigh and Lamb for free, oscillating drops, and a prediction by Bostwick and Steen that explicitly considers the effect of the solid substrate on drop dynamics. Finally, we report observations and analysis of drop mode mixing, or the simultaneous coexistence of multiple mode shapes within the resonating sessile drop driven by one sinusoidal signal of a single frequency. The dynamic response of a deformable liquid drop constrained by the substrate it is in contact with is of interest in a number of applications, such as drop atomization and ink jet printing, switchable electronically controlled capillary adhesion, optical microlens devices, as well as digital microfluidic applications where control of droplet motion is induced by means of a harmonically driven substrate.