Optical contact angle meterBased on the wetting behavior of droplets on solid surfaces, the contact angle is quantified using optical imaging and image analysis techniques. When a droplet is placed on a solid surface, it forms a specific shape due to the effect of surface tension. By capturing side images of liquid droplets with high-resolution cameras and analyzing their contours using software, especially the shape of the liquid surface at the point of contact with the solid surface, the contact angle θ can be determined. This angle reflects the degree of wetting of the solid by the liquid and is an important parameter for measuring the surface wettability of materials.
Optical contact angle meterIt mainly consists of the following parts:
Light source: Provides uniform illumination, reduces halo interference at droplet edges, and ensures clear images.
Injection system: including automatic injection unit or differential head manual injection unit, used to slowly add liquid and form a specified volume of droplets at the needle tube port, and then transfer the droplets to the surface of the sample to be tested.
Sample stand: Used to place the sample to be tested, some sample stands have three-dimensional adjustable functions to achieve sample horizontal calibration and multi position measurement.
Video system: includes high-resolution cameras and lenses to capture images of liquid droplets on solid surfaces. The camera resolution should be at least 10 million pixels, and the lens should be equipped with a telephoto macro lens to avoid distortion, and support manual/automatic focusing.
Data processing system: Use software to analyze droplet images and calculate the contact angle of droplets. The software needs to support multiple contour analysis models, such as Young Laplace fitting, ellipse fitting, and tangent method, to meet the measurement needs of different droplet shapes.
When choosing an optical contact angle meter, the following core performance indicators should be considered:
Contact angle measurement accuracy: determines the reliability of measurement data. Attention should be paid to absolute errors (such as ± 0.1 °, ± 0.5 °) and repeatability errors (such as ≤ 0.2 °). The smaller the error, the more reliable the data.
Precision of micro injector: The stability of droplet volume will affect the measurement results of contact angle. Attention should be paid to the precision of the instrument's microsampler, such as whether it supports 0.1 μ L step size and whether the droplet is stable (without shaking or hanging).
Imaging system resolution and clarity: Camera resolution, lens performance, and lighting system collectively affect imaging quality. Ensure that the camera resolution is high enough, the lens is distortion free, and the lighting system is uniform without shadows or reflections.
Measurement methods and functions: Select the supported basic measurement methods (such as seat drop method, hanging drop method, lying drop method) and special functions (such as dynamic contact angle measurement, special sample adaptation function) according to the testing requirements.