We present a scaling description of adsorbed polymer layers in the presence of a semidilute
solution. Within a very simple model where the layer is treated as a thermodynamic ensemble of loops
with a large polydispersity in size, we are able to (a) describe the influence of the semidilute solution on
the structure of the layer of adsorbed chains, and (b) estimate the variation of the surface tension γ of
the solution as a function of the polymerization index of the chains (N) and the monomer volume fraction
in the bulk (Φb). Concerning point a, this work provides a continuous picture for the variations of the
static properties of the interfacial layer from the dilute case (Φb → 0), to the melt case (Φb → 1). Concerning
point b, we find a law γ(Φb, N) of the form (good solvent conditions) γVdW − AΦb
5/4 + B(Φb
7/8/N
1/2) ln(N/Φb
7/12
N*), where γVdW accounts for van der Waals interactions and N* is a characteristic index of
polymerization of the polymer under consideration (A and B are calculated within numerical coefficients
of order unity). This law is in good quantitative agreement with experimental measurements and
generalizes our recent findings on the case of molten polymer liquid. (Aubouy; Manghi; Raphaël. Phys.
Rev. Lett.
2000, 84, 4858.)