Steady Method for the Analysis of Evaporation Dynamics

Abstract

Droplet evaporation is an important phenomenon governing many man-made and natural processes. Characterizing the rate of evaporation with high accuracy has attracted the attention of numerous scientists over the past century. Traditionally, researchers have studied evaporation by observing the change in the droplet size in a given time interval. However, the transient nature coupled with the significant mass-transfer-governed gas dynamics occurring at the droplet three-phase contact line makes the classical method crude. Furthermore, the intricate balance played by the internal and external flows, evaporation kinetics, thermocapillarity, binary-mixture dynamics, curvature, and moving contact lines makes the decoupling of these processes impossible with classical transient methods. Here, we present a method to measure the rate of evaporation of spatially and temporally steady droplets. By utilizing a piezoelectric dispenser to feed microscale droplets (R ≈ 9 μm) to a larger evaporating droplet at a prescribed frequency, we can both create variable-sized droplets on any surface and study their evaporation rate by modulating the piezoelectric droplet addition frequency. Using our steady technique, we studied water evaporation of droplets having base radii ranging from 20 to 250 μm on surfaces of different functionalities (45° ≤ θ ≤ 162°, where θ is the apparent advancing contact angle). We benchmarked our technique with the classical unsteady method, showing an improvement of 140% in evaporation rate measurement accuracy. Our work not only characterizes the evaporation dynamics on functional surfaces but also provides an experimental platform to finally enable the decoupling of the complex physics governing the ubiquitous droplet evaporation process.

Scalable Slippery Omniphobic Covalently Attached Liquid Coatings for Flow Fouling Reduction

“…To characterize the surface wettability of the samples, both apparent advancing (ACA) and receding (RCA) contact angles of deionized water were measured using a microgoniometer (MCA-3, Kyowa Interface Science) at room temperature. , A piezoelectric dispenser was set 5 to 10 mm above the sample surface. The dispenser would dispense microscale droplets on the surface, allowing droplets to accumulate into a larger droplet for contact angle characterization.…”

Dynamic Defrosting on Superhydrophobic and Biphilic Surfaces

“…Article show increasing sessile droplet evaporation time with increasing apparent contact angle in ambient (moist air) conditions. [74][75][76]…”

Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

“…Many coupled factors dominate the evaporation process: heat and mass flows, thermocapillarity, substrate thermal conductivity and deformability, substrate patterning, surface curvature, and the formation of deposits. The decoupling of these processes is currently extremely difficult with current experimental and theoretical methods [8][9][10][11][12]. The situation is even more difficult when complex fluids-such as those frequently found in technological applications-are concerned because the prediction and control of the evaporation of fluid droplets becomes essential for the appropriate design of the abovementioned processes.…”