Theoretical consideration of contact angle hysteresis using surface-energy-minimization methods

Abstract

a b s t r a c tIn recent years, advances in coating manufacturing processes have allowed wetting characteristics of a surface to be tuned with micro/nano morphologies. Today, complex surface geometries can be created with various surface treatment methods. These advances can be implemented in phase-change heattransfer applications, such as condensation, which relies on droplet behavior on a surface. Therefore, it is important to gain a fundamental understanding of wetting characteristics of textured surfaces having different geometrical configurations. This can be accomplished by studying the behavior of a single droplet on a given surface. Drop shapes and behaviors are affected by surface energies of different interfacial surfaces and surface morphologies. Contact angle hysteresis (CAH) -which is the difference between advancing and receding angles -can be estimated by utilizing concepts of surface-energy minimization. This is essential in heat transfer applications, as parameters such as drop size and distribution in condensation heat transfer are determined by CAH. In this study, a mathematical model has been developed to estimate CAH on different surface geometries and degrees of wetting. Modeling results suggest that CAH increases with increasing degree of wetting. Further, CAH remains low at both high and low droplet contact angles, whether the surface is hydrophilic or hydrophobic.

A New Slip Length Model for Enhanced Water Flow Coupling Molecular Interaction, Pore Dimension, Wall Roughness, and Temperature

“…On the contrary, when the contact angle ranges from 90° to 180°, the contact angle will be greater due to the e ects of pore wall roughness. at is, roughness will make the hydrophilic surface more hydrophilic, and make the hydrophobic surface more hydrophobic [36][37][38][39]48]. e apparent contact angle can be expressed by the Wenzel equation [34] where is the apparent contact angle a ected by wall roughness, is a surface roughness factor that equals to the ratio of the actual area to project area.…”

“…e roughness makes the e ective contact angle smaller which results in the decrease in slip length when contact angle ranges from 0° to 90°. When the contact angle ranges from 90° to 180°, the e ective contact angle increases as the roughness increases [36][37][38][39]. For the e ects of gas lms or trapped gas on the pore wall, Ruckenstein and Rajora [23] proposed that the water could ow on the wall with gas lms, and the slip length would be larger considering gas lms [40].…”

Effects of Acoustics on Induced Droplet Shedding for Dropwise Condensation

“…When the contact angle is lower than 90°, the surface is considered hydrophilic, and if the contact angle is higher than 90°, the surface depicts hydrophobic characteristics. Engineered surfaces, those with hydrophobic and hydrophilic combined characteristics, have been studied by several researchers [16]…”

Molecular Dynamics Simulations of Sessile and Pendant Droplets Shape on Inclined and Curved Surfaces

“…They found that the advancing contact angle remained constant as independent of capillary number, while the dynamics receding contact angle decreased with increasing capillary number. Cheng et al [20] proposed a mathematical model to determine the contact angle hysteresis by employing concepts of surface-energy minimization. The model can predict contact angle hysteresis of droplets on di erent surface geometries and degrees of wetting.…”