EXPERIMENTS ON WETTING ON THE SCALE OF NANOMETERS - INFLUENCE OF THE SURFACE-ENERGY

Via ellipsometry, the time-dependent profiles of liquid droplets spreading completely on plane solid substrates are measured in the range 0200. Two different surfaces are used, a high-energy surface (wettable by water) and a low-energy surface (Langmuir-Blodgett layer of a double-bond-terminated fatty acid), respectively. We have observed that the shape of spreading droplets of the same fluid (polydimethylsiloxane) are quite different on these two surfaces: On the low-energy surface, the spreading occurs by the macroscopic lateral spreading of essentially one monolayer, away from the central part of the drop. On the contrary, for the high-energy surface, spreading occurs by the macroscopic lateral spreading of several monolayers in a kind of hierarchical process. Nevertheless, in both cases there is a signature of molecular structuring in the fluid flow at the center of the drop. © 1990 The American Physical Society.