Wetting of the container wall as a critical-point phenomenon

• Published in: Journal of colloid and interface science 1984-03, Vol.98 (1), p.223-228
• Main Authors: Ross, Sydney, Kornbrekke, Ralph E.
• Format: Article
• Language: English
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(84)90498-3

A direct and convenient way to measure contact angles of a liquid—vapor or liquid—liquid interface against glass is by means of a photomicrograph of the meniscus inside a cylindrical tube. This method may be used when two requirements are duly met: that the astigmatic distortion of the optical system, caused by the tube acting as a cylindrical lens, be counteracted; and that the deviation of the meniscus from a spherical surface be negligible. The conditions to achieve these goals are defined in this paper; when they are observed, the contact angle may be determined readily from the spherical curvature of the meniscus, by finding its center and radius R . The contact angle is given by cosθ = rR , where r is the radius of the tube. By using this procedure we may disregard any obscuration of the image that sometimes occurs close to the wall by internal reflections.