Contact angle: When the liquid droplet reaches the liquid equilibrium on the surface of the solid, at the three-phase junction of gas, liquid and solid, the angle between the gas-liquid interface and the liquid-solid interface is called the contact angle, and the contact angle is represented by θ. Called the contact angle, the Chinese alias of the contact angle is also called the wetting angle and the water droplet angle.

Contact angle characteristics:

If θ<90°, the solid is hydrophilic, that is, the liquid can wet the solid, and the smaller the angle, the better the wettability; if θ>90°, the solid is lyophobic, that is, the liquid does not wet the solid, Moves easily on surfaces and cannot enter capillaries.

From this, the size of the contact angle can predict the following wetting situations:

1) When θ=0, complete wetting;
2) When θ<90°, partial wetting or wetting;
3) When θ=90°, it is the boundary line of wetting or not;
4) When θ>90°, no wetting;
5) When θ=180°, no wetting at all.
Wettability problems are closely related to mining flotation, oil extraction, textile printing and dyeing, pesticide processing, photosensitive film production, paint formulations, and waterproofing, washing, etc.

The meaning of the contact angle:

Contact angle plays a very important role when the strength of the contact between liquid and solid needs to be checked and evaluated, such as adhesion, dispersion, hydrophilic/hydrophobic materials, printing, coloring, cleaning, etc.

Contact angle measuring method:

There are usually two types of contact angle testing methods: one is the profile image analysis method; the other is the weighing method. The latter is usually called a wetting balance or a penetration method contact angle meter, but it is the most widely used and the measured value is most directly related to Accurate is the profile image analysis method.

The principle of the shape image analysis method: drop the droplet on the surface of the solid sample, obtain the shape image of the droplet through the microscope head and the camera, and then use the contact angle measuring instrument software to fit and analyze the value of the contact angle.

Application fields of contact angle measuring instrument: