Olympic Gels: Concatenation and Swelling

Abstract

Concatenation and equilibrium swelling of Olympic gels, which are composed of entangled cyclic polymers, is studied by Monte Carlo Simulations. The average number of concatenated molecules per cyclic polymers, $f_n$, is found to depend on the degree of polymerization, $N$, and polymer volume fraction at network preparation, $ϕ_0$, as $f_n ~ ϕ_0^{ν/(3ν-1)}N$ with scaling exponent $ν = 0.588$. In contrast to chemically cross-linked polymer networks, we observe that Olympic gels made of longer cyclic chains exhibit a smaller equilibrium swelling degree, $Q ~ N^{-0.28} ϕ_0^{-0.72}$, at the same polymer volume fraction $ϕ_0$. This observation is explained by a desinterspersion process of overlapping non-concatenated rings upon swelling, which is tested directly by analyzing the change in overlap of the molecules upon swelling.