A density functional study of adsorption of oligomers on weakly attractive surfaces modified with grafted chains is presented. The chain molecules are modeled as freely jointed tangent spheres. The segments interact via Lennard-Jones (12-6) potentials. Two types of substrates are considered - a neutral surface and the Lennard-Jones (9,3) surface. The mechanism of adsorption is discussed. Depending on the system characteristics, the primary, secondary and ternary adsorption is found. The effects of selected factors on adsorption and separation of mixtures are analyzed. (C) 2011 Elsevier Inc. All rights reserved.