Angle, conventionally measured through the liquid, at which a liquid/vapor interface meets a solid surface. It quantifies the wettability of the solid surface by the liquid. The contact angle is a reflection of how strongly the liquid and solid molecules interact with each other, relative to how strongly each interacts with its own kind. The contact angle is an important property of products such as non-stick pans waterproof fabrics and inks. Any given system of solid, liquid, and vapor at a given temperature and pressure has a unique value for its equilibrium contact angle. Contact angles can be measured using a contact angle goniometer. The contact angle is not limited to a liquid/vapour interface; it is equally applicable to the interface of two liquids.

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