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Contact angle measurements Contact angle of a liquid on a solid measures the wettability of the surface. Wetting describes the degree to which a liquid spreads on a solid when it comes into contact with it, one measure of wetting is the contact angle. The contact angle is important wherever the intensity of the contact between liquid and solid substances needs to be checked or assessed: coating, painting, cleaning, printing, hydrophobic or hydrophilic coating, bonding, dispersing etc. More importantly, the value of the contact angle is directly related to the free surface Energy of the material via Young's equation[1]. Hence, the contact angle is also related to the surface tension of the liquid and to the interfacial tension between the liquid and the solid. Lately, the relationship bewteen nanostrauctures on the surface and wettability has gained much interest; in this respect, the "lotus effect"[2] which appears in nature, is something that scientist are trying to imitate for practical purposes.

Contact angle measurements
Contact angle 1.jpg
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The apparatus to measure the contact angle are simple and in many cases are "home made' essentially one needs a good camera and a light to illuminate the surface from the back. Still, the equipment to measure the contact angle or "goniometers" (measure angle) are available.

Rame-Hart Goniometer

The Rame-Hart contact angle goniometer is widely used by scientist to study the interaction of liquids with the surface of semiconductors, which is a very good indication of cleanliness, surface activation, compatibility, etc.

Main article: Rame-Hart Goniometer

Method of operation

When a liquid comes into contact with a solid in a bulk, gaseous phase, according to Young’s equation, there is a relationship between the contact angle θ, the surface tension of the liquid σlg, the interfacial tension σsl between liquid and solid and the surface free energy σsg of the solid:

Young's Equation:

σsg = σsl + σlg ⋅ cosθ

θ= contact angle
σlg = surface tension of the liquid in air
σsl =interfacial tension between liquid and solid
σsg= Surface Free Energy of the solid

Contact angle of a liquid droplet on a solid in air

There are several types of surfaces depending on the contact angle value, the differents regimes Can have contac angles between 0° and the theoretical limit of 180°.

Contact Angle Wettability Type of surface
θ=0° perfect super hydrophobic
0<θ<180 highly wetting wettable
90>θ<180 low wetting not wettable
θ=180 no wetting ultrahydrophobic


In this technique, the contact angle between the droplet and the flat, horizontal surface is measured, both during preceding and receding of the droplet are measured. This contact angle depends on the surface energy, structure, cleanliness of the surface as well as the liquid droplet material.


This technique is used to measure the hydrophobicity or hydrophilicity of a surface, surface free energy, surface cleanliness, etc. through the value of the contact angle.


Optional description of materials that can be processed by technology. I think the best example of where this comes in handy would be with LPCVD describing the difference between HTO and LTO.

See also

Other related wiki pages


Further reading

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