Crossover of a polymer chain from bulk to surface states

Using exact enumeration, conformational properties of a surface-interacting long flexible polymer chain are determined in a two-dimensional poor solve nt where the possibility of collapse in bulk exists. A model of a self-attr acting self-avoiding walk (SASAW) on a square lattice is considered and up to 28 steps in series were evaluated. A new state having the conformation o f a surface attached globule in between the adsorbed and desorbed collapsed phases is found. The fact that this state may not represent a new thermody namic phase is emphasised. The phase diagram is drawn showing the region of existence of the four phases: (i) desorbed expanded, (ii) desorbed collaps ed, (iii) adsorbed expanded, and (iv) surface attached globule. The uncerta inities in locating the phase boundaries particularly in the vicinity of mu lticritical point is mentioned.