Structure and Thermodynamics of Grafted Three-Arm Branched Polymer Layers

The conformational and thermodynamic behavior of grafted polymer layers composed of linear and three-arm branched chains, with one branch grafted to the surface and two free branches of equal length, in the good solvent regime are investigated. The molecular organization of the layers composed of branched chains with a long branch grafted to the surface and two short free branches is very similar to that of linear chains. However, as the branch grafted to the surface becomes shorter, for the same total number of segments per chain, the conformational behavior of the chains changes markedly, in particular for high surface coverages. The density of the free end segments for chains with a short grafted branch shows two maxima, one near the solvent side of the brush and the other near the grafting wall. It is found that at high surface coverages the chains organize such that the short grafted branch is very highly stretched, one of the free branches is predominantly stretched toward the solvent while the other free branch folds toward the grafting wall. The force between two parallel grafted layers is calculated as a function of the distance between the grafted walls. The interactions between grafted surfaces with branched chains are more steeply repulsive than those for linear chains. Moreover, the interdigitation and the changes in molecular organization as the layers approach each other are studied for the different chain architectures.