Droplet on a fibre: Surface tension and geometry

The formation of the microdroplets on fibres for the MDT test offers an opportunity to carry out surface tension measurements based on the angle of contact between the resin and the fibre. Liquid microdroplets of epoxy were deposited on glass fibres, and their diameter, length and cone angle were measured. The equilibrium shape of the droplet can be derived from the principle of conservation of work and energy. If the surface tension of the polymer droplet and the specific surface energy of the polymer coated fibre are similar, then the interfacial tension is given simply by: γ_int = (1 - m)γ, where m is the gradient of a linear plot of functions of the measured parameters and γ is the liquid surface tension. The measurement of contact angles on a droplet/fibre system have been reported previously; however, our method proposes a different geometry and consequently a simpler solution to the problem, with an additional advantage of verification on the droplet equilibrium and accuracy of measurements.