LINE TENSION MEASUREMENTS - AN APPLICATION OF THE QUADRILATERAL RELATION TO A LIQUID LENS SYSTEM

The quadrilateral relation derived in a previous paper(1) is a general ization of the classical Neumann relation; it can be derived either fr om the minimum principle of free energy(1) or from the generalized the ory of capillarity of Boruvka and Neumann.(2) We demonstrate that such a quadrilateral relation can be applied to line tension measurements. The experimental design involves the measurement of two contact angle s and the diameter of a liquid lens system. As an example, the line te nsion of the three-phase contact line formed by dodecane, water, and a ir is found to be (-1.29 +/- 0.21) x 10(-6) J/m at the 95% confidence level, which is in the same order of magnitude as those obtained throu gh drop-size dependence of contact angle measurements(3,4) but with th e opposite sign. The negative line tension observed is found to be ind ependent of the diameter of the three-phase contact line ranging from 1 to 7 mm, which conforms with the theoretical assumption of the formu lation of the quadrilateral relation.(1) The methodology presented in this paper is believed to be simple and efficient.