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Static measurements yield values in-between the advancing and receding contact angle depending on deposition parameters (e.g. velocity, angle, and drop size) and drop history (e.g. evaporation from time of deposition). Contact angle hysteresis is defined as θ A – θ R although the term is also used to describe the expression cos θ R – cos ...
A contact angle less than 90° (low contact angle) usually indicates that wetting of the surface is very favorable, and the fluid will spread over a large area of the surface. Contact angles greater than 90° (high contact angle) generally mean that wetting of the surface is unfavorable, so the fluid will minimize contact with the surface and ...
As with the tilt method, the difference between the advancing and receding contact angles is the contact angle hysteresis. Most researchers prefer the tilt method; the add/remove method requires that a tip or needle stay embedded in the drop which can affect the accuracy of the values, especially the receding contact angle.
An ideal solid surface is flat, rigid, perfectly smooth, and chemically homogeneous, and has zero contact angle hysteresis. Zero hysteresis implies the advancing and receding contact angles are equal. Figure 1: Contact angle for a liquid droplet on a solid surface. In other words, only one thermodynamically stable contact angle exists. When a ...
Contact angle is a measure of static hydrophobicity, and contact angle hysteresis and slide angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity. [15] When a pipette injects a liquid onto a solid, the liquid will form some contact angle.
where is the wetted perimeter (+), is the plate width, is the plate thickness, and is the contact angle between the liquid phase and the plate. In practice the contact angle is rarely measured; instead, either literature values are used or complete wetting ( θ = 0 {\displaystyle \theta =0} ) is assumed.
The receding contact angle can be measured by removing volume from the drop until dewetting occurs. The minimum possible contact angle is referred to as the receding contact angle. [3] The contact angle hysteresis is the difference between the advancing and receding contact angle. [3]
Lotus leaves have a typical contact angle of , ultra low water adhesion due to minimal contact areas, and a self cleaning property which is characterised by the Cassie-Baxter equation. [13] The microscopic architecture of the Lotus leaf means that water will not penetrate nanofolds on the surface, leaving air pockets below.