MERCURY SPREADING ON SILVER FILMS - INTERFACE CHARACTERISTICS

We have studied the spreading of a liquid Hg drop on a Ag film. Geomet rical characteristics of the propagating Hg spot front, its roughness and hull exponents have been investigated. The mechanism of Hg spot fr ont formation has been analysed by optical microscopy, transmission el ectron microscopy, scanning electron microscopy and X-ray diffraction. We found that at short scales (up to about 20 mu m) the roughness exp onent of the Hg steady state interface is alpha approximate to 1 which is characteristic for self-similar objects. We also studied the hull exponent nu at these scales and found that nu = 1.3-1.7. We suggest th at on these scales a selfsimilar interface is generated by the process of invasion percolation. The invasion of Hg through the grain boundar ies, which is observed at a high magnification, might be the origin of the roughening of the front interface. On larger scales the roughness saturates and the corresponding exponents are alpha = 0 and nu = 1.