We present a theoretical description of polymer adsorption from soluti
on which is based on a mean field approximation but which goes beyond
the standard ground state dominance approximation. The properties of t
he adsorbed polymer chains are described by two coupled order paramete
rs. This allows a description of the chains in terms of tails and loop
s. When the bulk solution is dilute, the adsorbed polymer layer has a
double layer structure with an inner layer dominated by loops and an o
uter layer dominated by tails. Explicit asymptotic forms are found for
the monomer concentration profile and for the crossover distance betw
een the loops and tail regions. The precise concentration profile is o
btained by a numerical solution of two coupled differential equations.
One of the surprising results is that the total polymer adsorbed amou
nt has a nonmonotonic variation with molecular weight and decreases fo
r large values of the molecular weight. The concentration profiles are
also determined when the bulk solution is semidilute or concentrated.
At any bulk concentration, the monomer concentration has a nonmonoton
ic variation with the distance to the adsorbing wall and shows a minim
um at a finite distance. This depletion effect can be significant in t
he vicinity of the crossover between dilute and semidilute solutions.
All the results are in agreement with the existing numerical solutions
of the complete mean field theory of polymer adsorption. Excluded vol
ume correlations are taken into account by constructing scaling laws f
or polymers in a good solvent both in dilute and in semidilute solutio
ns.