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Measuring contact angles for pendant drops is much more complicated than for sessile drops due to the inherent unstable nature of inverted drops. This complexity is further amplified when one attempts to incline the surface. Experimental apparatus to measure pendant drop contact angles on inclined substrates has been developed recently. [20]
Thus, the contact angle is used as an inverse measure of wettability. [7] [8] 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.
Wettability is a measure of how well a liquid spreads and how complete the contact of the liquid is across the surface of a solid interface. A small contact angle indicates good wettability, while a large contact angle indicates poor wettability. The critical surface tension is the highest liquid surface tension that can completely wet a ...
This type of measurement is referred to as a static contact angle measurement. [3] The contact angle is affected not only by the surface chemistry but also by the surface roughness. The Young equation, which is the basis for the contact angle, assumes a homogeneous surface with no surface roughness.
The most common way to measure surface energy is through contact angle experiments. [1] In this method, the contact angle of the surface is measured with several liquids, usually water and diiodomethane. Based on the contact angle results and knowing the surface tension of the liquids, the surface energy can be calculated. In practice, this ...
Contact angles are important as they quantify a surface's wettability, the nature of solid-fluid intermolecular interactions. [2] Cassie's law is reserved for when a liquid completely covers both smooth and rough heterogeneous surfaces. [3] Cassie-Baxter state.
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 ...
In a contact angle measurement, the angle between the droplet and solid surface indicates the wettability of the surface. In surface science , an instrument called a contact angle goniometer or tensiometer measures the static contact angle , advancing and receding contact angles, and sometimes surface tension.