STRUCTURE AND THERMODYNAMICS OF GRAFTED 3-ARM BRANCHED POLYMER LAYERS

The conformational and thermodynamic behavior of grafted polymer layer s composed of linear and three-arm branched chains, with one branch gr afted to the surface and two free branches of equal length, in the goo d solvent regime are investigated. The molecular organization of the l ayers composed of branched chains with a long branch grafted to the su rface and two short free branches is very similar to that of linear ch ains. However, as the branch grafted to-the surface becomes shorter, f or the same total number of segments per chain, the conformational beh avior of the chains changes markedly, in particular for high surface c overages. The density of the free end segments for chains with a short grafted branch shows two maxima, one near the solvent side of the bru sh and the other near the grafting wall. It is found that at high surf ace coverages the chains organize such that the short grafted branch i s very highly stretched, one of the free branches is predominantly str etched toward the solvent while the other free branch folds toward the grafting wall. The force between two parallel grafted layers is calcu lated as a function of the distance between the grafted walls. The int eractions between grafted surfaces with branched chains are more steep ly repulsive than those for linear chains. Moreover, the interdigitati on and the changes in molecular organization as the layers approach ea ch other are studied for the different chain architectures.