Conformational properties of strictly two-dimensional equilibrium polymers

Two-dimensional monodisperse linear polymer chains are known to adopt for sufficiently large chain lengths $N$ and surface fractions $\phi$ compact configurations with fractal perimeters. We show here by means of Monte Carlo simulations of reversibly connected hard disks (without branching, ring formation and chain intersection) that polydisperse self-assembled equilibrium polymers with a finite scission energy $E$ are characterized by the same universal exponents as their monodisperse peers. Consistently with a Flory-Huggins mean-field approximation, the polydispersity is characterized by a Schulz-Zimm distribution with a susceptibility exponent $\gamma=19/16$ for all not dilute systems and the average chain length $<N> \propto \exp(\delta E) \phi^{\alpha}$ thus increases with an exponent $\delta = 16/35$. Moreover, it is shown that $\alpha=3/5$ for semidilute solutions and $\alpha \approx 1$ for larger densities. The intermolecular form factor $F(q)$ reveals for sufficiently large $<N>$ a generalized Porod scattering with $F(q) \propto 1/q^{11/4}$ for intermediate wavenumbers $q$ consistently with a fractal perimeter dimension $d_s=5/4$.