Percolation of co-continuous domains in tapered copolymer networks

Abstract

Inhomogeneous polymer networks with bicontinuous morphologies have shown the potential to incorporate typically incompatible material properties into a single sample, and often the desired properties depend on co-continuity of the domains. Tapered copolymers have been shown to be useful for facilitating the formation of bicontinuous morphologies, though most applications are in linear diblock copolymers. We use coarse-grained molecular dynamics simulations to study inhomogeneous co-networks formed by tapered copolymers with different strand lengths, fractions of the minority domain and gradient lengths. Cluster and fractal analyses are performed to quantify the sizes of the clusters formed by the minority domain and to characterize the threshold for domain percolation. We find that the gradient length can be tuned to widen the composition window where bicontinuous percolating structures are found, and we show that the diffusion of tracer molecules selective for one phase is enhanced as the gradient length increases. Our results show how engineering the chemistry of the constituent polymers in a crosslinked material can allow tuning the material properties.