Segregation of chain ends to the surface of a polymer melt

Abstract

Self-consistent field theory (SCFT) is used to examine the surface of an incompressible polymer melt of freely jointed chains, each consisting of N discrete monomers connected by bonds of an arbitrary potential. As a result of entropic considerations, the end monomers tend to accumulate in a narrow region next to the surface (on the monomer scale), which causes a slight depletion of ends further into the melt (on the molecular scale). Due to the reduced configurational entropy available to polymers in the vicinity of a surface, we find an entropic contribution to the surface tension that increases with the degree of polymerization, N. While many quantities are dependent on the precise bond potential connecting the monomers, the excess of ends at the surface in the limit of infinite N, the functional form of the long-range depletion of ends, and the N dependence of the surface tension turn out to be universal.

Entropic segregation of short polymers to the surface of a polydisperse melt

“…In that case, the violation to the Silberberg treatment resulted from the finite width of the concentration profile, ξ, which increases as the polymer becomes more compressible. More recently, we [13] observed the same behaviors for the SCFT of an incompressible melt with a sharp step profile, where this time the chains a e-mail: mwmatsen@uwaterloo.ca were represented by N beads of volume ρ −1 0 connected by freely-jointed bonds of statistical length a. Here, the violation occurred because reflecting portions of a discrete chain about a plane alters the bonds that initially straddle the plane [14].…”

“…Here, we showed that A is dependent on the surface profile, which would be affected, for example, by the compressibility of the melt. We previously illustrated that it also depends on the interaction potential between bonded monomers [13]. In general, A will be affected by all microscopic details, whether it be those of a model or those of an actual system.…”

“…To obtain the surface tension, we need the grand-canonical free energy (13) where Q N is the single-chain partition function for a polymer of polymerization N , which can be evaluated by…”

“…[12] and [13]. The first step is to evaluate the field w ∞ (z) and partition function G ∞ (z) for an infinitely long polymer, which turns out to be a relatively simple numerical calculation [33].…”

Semiflexible polymers under good solvent conditions interacting with repulsive walls

“…[65] Accordingly, it is of interest to consider the effect of the chain stiffness on the end-monomer density distributions. Indeed, the enrichment of chain ends at surfaces and interfaces has been studied for a long time in polymer melts [66,67], while dilute polymer solutions have received little attention in this regard. In the upper panel of Fig.…”