At the macroscopic scale, the condition for a liquid to spread on a solid surface is that the initial spreading parameter So should be positive. At the microscopic scale, the relevant parameter P(z) for spreading depends on the film thickness z and can be expressed as a function of the disjoining pressure ~( z ) .At molecular thicknesses, P(z) is nothing more than the usual two-dimensional film pressure. Experimental and theoretical determinations of ~( z ) and P ( z ) are available in the literature. These results are used to analyze and predict the thickness profile of films spreading on solid surfaces. It is shown that a relevant case for experiments is the "diffusive" situation, where the film grows from a nearly static macroscopic meniscus. Explicit formulas for the thickness-dependent diffusion coefficient D(z) and a discussion of characteristic film profiles are given in this case. The agreement with available experimental results is satisfactory.

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