STATICS AND DYNAMICS OF A POLYMER-CHAIN ADSORBED ON A SURFACE - MONTE-CARLO SIMULATION USING THE BOND-FLUCTUATION MODEL

A polymer chain under good solvent condition near a short-range attrac tive impenetrable wall (xy plane) is investigated by dynamic Monte Car lo simulation using the bond-fluctuation model. For the statics, the a dsorption transition is clearly observed and the adsorption transition temperature, T(a) for this model is determined. Chain conformation, s egment orientation, fraction of segment adsorbed, chain dimensions, an d layer thickness as a function of temperature and. distance away from the wall are studied and discussed. Our results for the scaling behav ior of the radii of gyration and fraction of segment adsorbed confirm previous analytical theories and static simulation results. We also ob tain an estimate for the critical exponent which is consistent with pr evious static simulations of self-avoiding walks. Furthermore, our dat a on specific heat show another peak, apart from the one at T(a), at a temperature T2 distinctively below T(a), suggesting a second transiti on. As for the dynamics, both the time autocorrelation function and th e time dependence of the mean square displacement of the center of mas s of the chain are studied. We find that the time autocorrelation func tion in the adsorbed state can be fitted to a stretched exponential fo rm-and the relaxation time starts to diverge for temperatures below T2 . The diffusion coefficients for motions parallel (D(z)) and perpendic ular(D(perpendicular-to)) to the z axis are also extracted. D(z) shows a sharp drop as the temperature is lowered below the adsorption trans ition temperature while D(perpendicular-to) remains constant until aro und T2 at which it decreases abruptly. Furthermore we also observe tha t the lateral diffusion (D(perpendicular-to)) crosses over from a Rous e behavior (D(perpendicular-to) is similar to N-1) to a D(perpendicula r-to) is similar to N-2 behavior for temperatures below T2. These resu lts are discussed in terms of the appropriate scaling theories.