A New Scaling Theory of Semiflexible Polymer Phases Near Attracting Surfaces

Abstract

The finite chain backbone stiffness in polymers gives rise to a number of novel behaviors described on short length scales. We analyze the semiflexible polymer phases near surfaces using a new scaling theory, incorporating the surface attraction in terms of its range and depth. It is found that the phase diagram includes five different phases: desorbed, weakly- adsorbed with both isotropic and nematic-type distribution of polymer segments inside the potential well, strongly-adsorbed states with the isotropic and nematic-type distribution. We draw conclusions on the orders of the transitions between the phases. The stiffness of polymer chain backbone means the presence of an orientation "memory" be- tween segments along the chain. A rigid rod is the very stiff polymer, for which the persistence length is much larger than the total contour length. This polymer can not be crumpled without breakage. On the other hand a very flexible chain can be crumpled practically on any length scales. It can be crumpled as a whole (as in so-called globule-to-coil transition iii and in the ideal limit it can be crumpled on smaller and smaller length scales (down to the microscopic scales of chain diameter order), carrying a self-similar or fractal structure. For the intermediate cases of semiflexible chain, which are probably the most interesting for applications including biophysical problems, the persistence length is much smaller than the total polymer contour length, so it can be crumpled as a whole in a similar way as a flexible chain. In general, we can treat a semiflexible polymer chain as a flexible one, when we are interested in the universal macroscopic polymer properties measured over the scales of whole macromolecule dimensions. But on the scales smaller than the persistence length the semiflexible structure can be con- sidered as an array of rigid rods interconnected at a fixed angle. (Naturally, the semiflexible wormlike chain can be viewed as the continuous limit of the discrete model iii.) Therefore, on these scales already, semiflexible polymer can not be crumpled without breakage and its properties are essentially different from those of flexible polymer. A wide class of synthetic and