Understanding Wettability in Interfacial Studies

  • Thread starter RPI_Quantum
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In summary, surface tension can affect the way a liquid droplet spreads across a solid surface. This affects the wetting angle, which is the angle between the gamma s,l and gamma l,v components of the surface tension.
  • #1
RPI_Quantum
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In interfacial studies, there is always talk of wettability. I am wondering if anyone can explain to me the significance of this concept, beyond the magnitude of the contact angle? What is the difference between interfaces with >90 deg contact angle and <90 deg contact angle that merits this distinction between wetting and non-wetting?
 
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  • #2
This answer may be completely misleading, and perhaps even wrong. Bear with me. I also apologise for my non existent latex skills, I'll try and do something about that.

If you imagine a liquid droplet on a nice flat solid surface, you can imagine that in some cases, surface tension is such that the droplet holds its shape (other than being flattened on the contact zone obviously). If this surface tension is decreased, the contact area will spread and the droplet will lose some of its shape.

For 'perfect wetting', the liquid will be spread as a thin film across the surface. In this case, the wetting angle (theta) is said to be zero.

For 'complete non-wetting', the exact opposite happens. The liquid holds itself into a spherical droplet, the contact area is minimal and the wetting angle is said to be 180 degrees.

I've got a nice little diagram here, but have no scanner so it's for my eyes only. If you imagine a semi-wetting droplet on a flat horizontal surface, there is a gamma s,l component parallel to the surface originating at the point at which the droplet boundary touches the solid surface, and a gamma l,v component tangental to the droplet at the same point. The wetting angle is that between these components. These components balance a third gamma s,v component acting the opposite direction to the first, giving rise to the Young Equation:

(gamma s,v) = (gamma s,l) + (gamma l,v)cos(theta)

I hope I've not wrecked this too much, I might try to tidy it up later.
 
  • #3
Thanks. I've used and worked with Young's equation a lot in many different courses, but I guess I needed someone else to clarify the details. It makes a lot more sense to me now conceptually.

Thanks again!
 

Related to Understanding Wettability in Interfacial Studies

1. What is wettability and why is it important in interfacial studies?

Wettability is the measure of how easily a liquid can spread on a solid surface. In interfacial studies, it is important because it affects the interactions between different phases, such as oil and water, at the interface. This can have significant implications in areas such as oil recovery, coatings, and biomaterials.

2. How is wettability measured in interfacial studies?

Wettability is typically measured using contact angle measurements, which involve measuring the angle between the liquid-solid interface and the solid surface. A high contact angle indicates low wettability, while a low contact angle indicates high wettability.

3. What factors influence wettability in interfacial studies?

Several factors can influence wettability in interfacial studies, including the chemical composition and roughness of the solid surface, the type of liquid and its surface tension, and the presence of surfactants or other additives.

4. How does wettability affect interfacial tension?

Wettability plays a crucial role in interfacial tension, which is the force that exists between two immiscible phases at their interface. A higher wettability leads to a lower interfacial tension, meaning liquids are more likely to mix and form a homogeneous solution.

5. What are some applications of understanding wettability in interfacial studies?

Understanding wettability is essential in various fields, including oil and gas extraction, pharmaceuticals, and surface coatings. In the oil and gas industry, it is used to improve oil recovery methods, while in the pharmaceutical industry, it helps with drug delivery and formulation. In surface coatings, wettability is crucial for adhesion and durability.

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