Capillary bridges between two spherical bodies

A method was developed for measuring the capillary forces arising from micr oscopic pendular liquid bridges. Results are described for perfectly wettin g bridges between spheres of equal and unequal radii. A comparison with the theoretical values calculated from a numerical integration of the Laplace- Young equation demonstrated the accuracy of the method. It also showed that existing criteria for gravitational distortion are too restrictive and tha t the influence of the disjoining pressure is negligible. The Derjaguin app roximation for spheres of unequal size was shown to be relatively accurate for small bridge volumes and for separation distances excluding those at cl ose-contact and near-rupture, which correspond to maxima in the filling ang le. Closed-form approximations were developed in order to conveniently calc ulate the capillary forces between equal and unequal spheres as a function of the separation distance and For a given bridge volume and contact angle. A closed-form approximation was also developed to calculate the rupture di stance for liquid bridges between spheres of unequal sizes.