Surface adsorption and collapse transition of a linear polymer chain in three dimensions

A phase diagram for a surface-interacting long flexible polymer chain in a poor solvent where the possibility of collapse exists is calculated using an exact enumeration method. A model of a self-attracting self-avoiding walk on a simple cubic lattice was considered and up to 16 steps in series were evaluated. The phase diagram indicates that while the boundary between the expanded and collapsed phases is straight in the bulk, it exhibits a bend in the surface resulting in two adsorbed collapsed phases separated by an adsorbed expanded phase. This is attributed to competition between the entropic fluctuations and effects due to monomer-monomer attraction.