Contact Angle: Definition, Relevance and Application Areas
A drop of liquid, placed on a solid surface, forms an angle with it called the contact angle (θ); it is therefore defined as the angle formed between the solid surface and the tangent to the drop at the point of contact with it.
Measuring the contact angle of a liquid on a solid provides information about the wetting behaviour of this combination. The desired wetting behaviour depends on the particular application.
With a contact angle of 0°, the droplet is completely spread on the solid surface. The drop forms a thin, sometimes monomolecular liquid film on the solid surface. This case is called complete wetting. With a contact angle of 180°, the drop lies spherically contracted on the surface and touches the solid only at one point. This case is called complete dewetting. In practice, the contact angle usually lies between these two extreme values. Solid surfaces on which a contact angle of less than 90° is formed are generally described as having good wettability. Higher contact angles indicate that a surface is hardly wettable or not wettable at all..
The measurement of contact angle is crucial in study of surface properties of materials and for understanding the interactions between liquids and solids; it is therefore a widely used measurement and finds application in a wide range of sectors.
Main application areas:
- Surface coatings: Measurement of the contact angle on coated materials to evaluate the quality and uniformity of the coating.
- Painting and printing industry: Evaluation of the wettability of paints, varnishes and printing inks on various substrates.
- Medical devices: Characterization of the wettability of medical implants to evaluate their biocompatibility.
- Food industry: Evaluation of the wettability of packaging materials to ensure printability and improve storage properties.
- Semiconductor industry: control of wettability on surfaces of semiconductor chips and substrates for microchip manufacturing.
- Nanotechnology: Characterizing the wettability of nanomaterials and nanoparticles to optimize their properties in various applications.
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