Conformational Changes of a Single Semiflexible Macromolecule Near an Adsorbing Surface: A Monte Carlo Simulation

摘要

The properties of a single semiflexible chain tethered to a planar surface with a long-ranged attractive potential are studied by means of Monte Carlo simulations. We employ the bond fluctuation lattice model and the Wang—Landau sampling technique. We present the diagram of states for semiflexible chains consisting of N = 64 and 128 monomer units as a function of temperature T and strength of the adsorption potential, ε_w, and also compare this with the diagram of states for flexible chains of these two lengths. The diagram of states consists of the regions of a coil, liquid globule, solid isotropic globule, adsorbed coil, and quasi-two-dimensional solid globule with nematic bond order (or quasi-two-dimensional isotropic crystal in the ease of a flexible chain). The diagram of states for the flexible case agrees with a result for the same model and a short-ranged attraction to the wall for small values of the attraction strength. For larger values, the transition to the two-dimensional behavior is more gradual in the long-ranged attractive potential. For the range of chain stiffness that we studied, the low-temperature phase in the bulk is an isotropic globule (i.e., a globule without bond order). At the attractive surface, a nematic-type bond order is induced upon adsorption, leading to ordered structures, which can be considered a precursor to the crystalline lamellae forming in real polymers. Other than that, the diagram of states in general is not changed by introducing stiffness of the chains.