Contact angle measuring device

A contact angle measuring device, comprising:

• a light source,
• a container,
• a photodetector,
• a bubble generating unit,
• a test bracket, and
• a processing unit, wherein:
• the container comprises a first side wall and a second side wall that is opposite to the first side wall,
• the first side wall is made of a light-transmitting material,
• the container is filled with liquid that is transmissive to light,
• the light source is a monochromatic light source,
• monochromatic light emitted by the light source passes through the first side wall and enters an interface between the first side wall and the liquid at a total reflection angle or at an angle greater than the total reflection angle,
• the bubble generating unit is configured for generating a bubble that is in contact with an inner surface of the first side wall,
• a detection surface of the photodetector is sealed through the second side wall to contact with the liquid for detecting light intensity distribution of the monochromatic light through the liquid,
• an output of the photodetector is connected to the processing unit,
• the detection surface of the photodetector is embedded in and is flush with an inner surface of the second side wall,
• the bubble generating unit comprises a needle and an air source,
• an air inlet of the needle is in communication with the air source,
• the needle is sealed through the first side wall of the container,
• an air outlet of the needle is provided on an inner side of the first side wall, and
• the light source and the container are fixed on the test bracket.