Surface Free-Energy of Solid Paraffin Wax

Abstract

As part of a programme of research on the surface free-energy of solids, we have lately been working on paraffin wax. The method used is the one proposed by Bergren1 and consists in measuring the rates of elongation or contraction of thin filaments of different lengths hanging under their own weights. The change in length results from two opposing forces: one which tends to shorten the filament so that its surface free-energy is decreased, and the other tending to lengthen the filament because of its weight. A critical filament-length, l0, is determined at which the elongation of the upper part of the filament is equal to the contraction of the lower part, so that the length remains constant. Assuming that the solid near the melting point behaves as a viscous liquid, that is, the rate of deformation is proportional to the applied stress, the surface free-energy of the solid can be calculated from the critical length l0 using the equation: where γ is surface free-energy, ρ is density of solid at temperature of experiment, g is acceleration due to gravity, and r is radius of wire.