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 tr
eated as a thermodynamic ensemble of loops with a large polydispersity in s
ize, we are able to (a) describe the influence of the semidilute solution o
n the structure of the layer of adsorbed chains, and (b) estimate the varia
tion of the surface tension gamma of the solution as a function of the poly
merization index of the chains (N) and the monomer volume fraction in the b
ulk (Phi(b)). Concerning point a, this work provides a continuous picture f
or the variations of the static properties of the interfacial layer from th
e. dilute case (Phi(b) --> 0), to the melt case (Phi(b) --> 1). Concerning
point b, we find a law gamma(Phi(b), N) of the form (good solvent condition
s) gamma(VdW) - A Phi(b)(5/4) + B(Phi(b)(7/8)/N-1/2) In(N/Phi(b)(7/12)N*),
where gamma(VdW) accounts for van der Waals interactions and N* is a charac
teristic 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 generali
zes our recent findings on the case of molten polymer liquid.