Surface-wetting characterization using contact-angle measurements

Abstract

Wetting, the process of water interacting with a surface, is critical in our everyday lives and in many biological and technological systems. The contact angle is the angle at the interface where water, air and solid meet, and its value is a measure of how likely the surface is to be wetted by the water. Low contact-angle values demonstrate a tendency of the water to spread and adhere to the surface, whereas high contact-angle values show the surface's tendency to repel water. The most common method for surface-wetting characterization is sessile-drop goniometry, due to its simplicity. The method determines the contact angle from the shape of the droplet and can be applied to a wide variety of materials, from biological surfaces to polymers, metals, ceramics, minerals and so on. The apparent simplicity of the method is misleading, however, and obtaining meaningful results requires minimization of random and systematic errors. This article provides a protocol for performing reliable and reproducible measurements of the advancing contact angle (ACA) and the receding contact angle (RCA) by slowly increasing and reducing the volume of a probe drop, respectively. One pair of ACA and RCA measurements takes ~15-20 min to complete, whereas the whole protocol with repeat measurements may take ~1-2 h. This protocol focuses on using water as a probe liquid, and advice is given on how it can be modified for the use of other probe liquids.

Mapping micrometer-scale wetting properties of superhydrophobic surfaces

“…Conventionally, the forces required to remove the droplets are inferred indirectly from the advancing and arXiv:1909.04253v1 [cond-mat.soft] 10 Sep 2019 receding contact angles θ adv, rec [12,13,28]. For example, the friction force F fric required to move the droplet laterally is given by the Furmidge's relation F fric = πγr∆ cos θ = πγr(cos θ rec − cos θ adv ), (1) where r is the droplet's base radius, γ is the surface tension, and ∆ cos θ = cos θ rec − cos θ adv is the contact angle hysteresis [6,7,29].…”

Cu–MoS2 Superhydrophobic Coating by Composite Electrodeposition

“…Results from these measurements are presented in the Supplementary Materials, Table S1. From these results, the best samples were further analyzed, measuring θ A and θ R with the sessile drop-needle in drop technique (Dataphysics Contact Angle System OCA, Filderstadt, Germany) equipment, following the procedure detailed in [31]. The advancing and receding contact angle were calculated using the Young-Laplace fitting method, calculating the contact angle 20 times while the volume of the droplet was first increased and then decreased in four different spots in the center of the sample to avoid border effects.…”

Steerable Droplet Bouncing for Precise Materials Transportation

“…[29] By introducing anisotropic microstructures, guided self-propelled leaping of droplet is realized on the superhydrophobic surface. [5,22,[30][31][32] However, due to the complexity in the interaction between the droplet and the solid, [33][34][35][36][37][38] the precise control of the lateral droplet movement, both in the direction and the quantity, remains a great challenge.Recently, the development of the surface wettability provides an efficient way to control the liquid behaviors. [5,22,[30][31][32] However, due to the complexity in the interaction between the droplet and the solid, [33][34][35][36][37][38] the precise control of the lateral droplet movement, both in the direction and the quantity, remains a great challenge.…”

“…[22] The dominating factor for the droplet directional movement is to induce the asymmetric forces to the droplet. [5,22,[30][31][32] However, due to the complexity in the interaction between the droplet and the solid, [33][34][35][36][37][38] the precise control of the lateral droplet movement, both in the direction and the quantity, remains a great challenge.Recently, the development of the surface wettability provides an efficient way to control the liquid behaviors. [19,39,40] Through rational design of the surface wettability pattern, we report a facile method to realize the directional transportation of rebounding droplets with precise controllability.…”

“…[22] The dominating factor for the droplet directional movement is to induce the asymmetric forces to the droplet. [5,22,[30][31][32] However, due to the complexity in the interaction between the droplet and the solid, [33][34][35][36][37][38] the precise control of the lateral droplet movement, both in the direction and the quantity, remains a great challenge.…”