Adsorption,Conformation,and Dynamical Properties Of Polymers On Attractive Surfaces

The adsorption of polymer on surfaces has been a hot topic in biology, physics, and chemistry, due to its universality and great potential applications in many systems, such as polymer adhesion, colloid stabilization, polymer nanocomposite materials, coating and lubrication,DNA segremation in bacteria, DNA packaging in viruses, and superhydrophobic/superhydrophilic materitial. We use Monte Carlo method to investigate the adsorption, conformation,and dynamical properties of polymers on attractive surfaces. The main results and conclusions are as follows:(1) The adsorption process of polymers on an attractive homogeneous flat surface. During the adsorption process the apparent size of the polymer parallel to the surface increases exponentially with time. The relaxation time for the apparent size reaching its equilibrium value decreases with increasing the surface attraction strength Eps, whereas the equilibrium value increases with Eps, indicating that the polymer is adsorbed faster and becomes more extended at stronger adsorption. The behavior of the polymer's asphericity parallel to surface is however different from that of the apparent size, and it is sensitive to the intra-polymer interaction. During the adsorption, the surface contacted monomer number increases monotonously with time, but the three-dimensional conformational size and shape asphericity show novel behaviors. With the increase in surface contacted monomer number, they first increase, then decrease and finally increase. Whereas the two-dimensional conformational size and shape asphericity first decrease,and then increase.(2) Coil-globule transition of adsorbed polymers on attractive surface. The effect of surface attraction strength Eps and intra-polymer attraction strength Epp on polymer phases is investigated.The coil-globule transition point is dependent on Eps, while the globule conformation is dependent on both Eps and Epp. At small Eps, the conformation of adsorbed polymer is a three-dimensional layer structure. While at large Eps, the conformation of adsorbed polymer is roughly two-dimensional at Epp = 0, and we observe a two-dimensional coil-globule transition and a layer-forming transition from two-dimensional conformation to three-dimensional layer structure. The layer-forming transition point increases with Eps. In addition, we find that the adsorption suppresses the coil-globule transition, i.e., the coil-globule transition point increases with the increase in Eps.(3) Dynamic behaviors of polymer chains adsorbed on an attractive, homogeneous surface.The translational diffusion coefficient Dxy. parallel to the surface decreases as the intra-polymer attraction strength Epp or the surface attraction strength Eps increases. The rotational relaxation time ?R increases with Eps,but the dependence of ?R on Epp is dependent on the adsorption state of the polymer. The rotational relaxation time decreases with increasing Epp for a partially adsorbed polymer but it increases with Epp for a fully adsorbed polymer. Scaling relations Dxy?N-? and ?R?N? are found for long polymers. The scaling exponent a is independent of Eps for long polymers but increases with Epp from ? = 1.06 at Epp = 0. While ? ? 2.7 is also roughly independent of Eps for the adsorbed polymer at Epp = 0, but ? increases with Eps at Epp > 0. Moreover, we find that ?always decreases with increasing Epp. Our results reveal different effects of the attractive surface on the diffusion and rotation of adsorbed polymers.(4) The adsorption process of polymers on an attractive random surface with randomly distributed attraction points. The critical adsorption site fraction decreases with the increase in surface attraction strength and intra-polymer attraction strength Epp. At large surface attraction strength the equilibrium value of the apparent size of the polymer parallel to the surface first increases, and then decreases with the adsorption site fraction. The adsorption time of polymers decreases with the increase in surface attraction strength, and increases with Epp. In addition,randomly distributed adsorption sites slow down the translational diffusion of adsorbed polymers.