Conformational Transitions of Nongrafted Polymers near an Absorbing Substrate

We have performed multicanonical chain-growth simulations of a polymer interacting with an adsorbing surface. The polymer, which is not explicitly anchored at the surface, experiences a hierarchy of phase transitions between conformations binding and nonbinding with the substrate. We discuss the phase diagram in the temperature-solubility plane and highlight the transition path through the free-energy landscape.

Figure 1

Pseudophase diagram of a polymer with 100 monomers obtained from the specific heat $C_V$ as a function of temperature $T$ and solubility parameter $s$. The white and black drawn lines indicate the ridges of the specific heat profile (see text). The dashed line separates the regions of attractive and repulsive monomer-monomer interaction.

Figure 2

Map of free-energy minima identified in the space of contact numbers $n_s$ with the substrate and $n_m$ between monomers. Also shown are exemplified paths through the free-energy landscape for different fixed solvent parameters $s$. The labels I to VII refer to the pseudophases in the case $s=1$, described in detail in the text and in Table . The lines are guides to the eye only.

Figure 3

Probability distribution $p(n_s,n_m)$ for the 100-mer in solvent with $s=1$ at $T=0.49$, where the polymer experiences the layering transition from a single to a double layer.