The term “wettability” refers to the ability of a material to absorb a liquid or become hydrated by a liquid. The wetting or wettability of a material, or a surface, is represented by its contact angle, which is defined as the angle formed between a liquid droplet on a solid surface and the horizontal plane. This angle is a measure of how wet or dry a surface is.
Generally, the lower the contact angle, the colder a surface is to liquid, and the higher the contact angle, the hotter the surface is to liquid. The contact angle is affected by many factors like surface roughness, surface chemistry and surface energy. For example, smooth surfaces, such as Teflon, tend to have lower contact angles than rougher surfaces, like sand paper.
Wetting or wettability is important in many applications such as lubrication and coating, as well as in biomedical applications. In order to properly lubricate a surface, the surface must be wet enough to incorporate the lubricant and spread it evenly over the surface. Similarly, when painting a surface, the surface must be wettable enough to hold the paint. In biomedical applications, wettability is an important factor in tissue engineering and drug delivery. Tissues must be wet enough to ensure good adhesion of cells to the scaffold materials, while drug delivery systems must be wettable enough to allow for proper absorption of the drug.
The wetting or wettability of a surface is usually characterized using the contact angle. The contact angle is usually measured using the sessile droplet method, where a droplet of liquid is placed on a solid surface and the angle of contact between the droplet and the surface is measured. There are also experimental methods such as the dynamic contact angle method, which is used to measure the wettability of a surface under dynamic conditions.
Generally, wettability is categorized as follows: superhydrophobic, hydrophobic, oleophilic, hydrophilic and oleophobic. Superhydrophobic surfaces are those with extremely high contact angles, typically greater than 150°. These surfaces are usually comprised of hydrophobic materials, such as a Teflon-like coating, which repel water and prevent it from wetting the surface. Hydrophobic surfaces have high contact angles, around 100° or higher, while oleophilic surfaces have low contact angles, around 5° to 90°. Hydrophilic surfaces attract water and have contact angles lower than 5°, while oleophobic surfaces repel oil and have contact angles higher than 90°.
In conclusion, wettability, or the ability of a surface to absorb a liquid or become hydrated by a liquid, is determined by its contact angle, which is affected by factors such as surface roughness, chemistry and energy. Wettability is important in many applications, including lubrication, coatings, tissue engineering, and drug delivery.
