Spreading of polymeric liquids at a microscopic scale

The spreading of polymeric liquids on solid substrates has been a very lively subject of research both by experimentalists and theoreticians. It has been observed that some drops, which spread on solids may form a precursor film of molecular thickness with possible accompanying layers, with a radius growing as a square root of time in the early stages after deposition. These results have been obtained for several polymeric liquids on top of bare or grafted oxidized silicone wafers. The first theoretical model describing this phenomenon was developed by de Gennes and Cazabat. In this original paper the spreading is described as a competition between the driving force, which is due to the wall attraction and the friction between layers of liquid, and the solid. Assuming the essentially viscous nature of the friction forces, the authors were able to recover most of the experimental observations mentioned before. However, the friction parameters have to be introduced at a macroscopic scale and are questionable at a microscopic point of view. It is the aim of this paper to give a review of the experimental observations completed, case by case, by microscopic simulations, giving a more detailed understanding of the rich variety of these phenomena.