Wetting dynamics of the edge of a spreading drop

We report the first explicit measurements on the profile of a spreading edge of nonvolatile liquid, in support of the theory of Hervet and de Gennes on a one-dimensional thin spreading edge. From the laser light interference patterns, the meniscus shape of the edge was reconstructed and the advancing dynamic contact angle was measured. The meniscus shape and the contact angle are in good agreement with their theory. The meniscus shape obtained at several different capillary numbers can be collapsed into one dimensionless curve, using their scaling laws.