Effect of Copolymer Sequence on Mechanical Properties of Simulated Polymer Nanoparticle Composites

We simulate a simple nanocomposite consisting of a single spherical nanoparticle surrounded by coarse-grained polymer chains. The polymers are composed of two different monomer types, with different interaction strengths with the nanoparticle. We examine the effect of copolymer sequence and monomer-nanoparticle interaction strength on structure (using the monomer-nanoparticle radial distribution function), relaxation times (using the end-to-end and bond vector autocorrelation functions), and dynamic moduli (using the stress autocorrelation function). We measure these properties as a function of distance from the nanoparticle surface and find significant effects of copolymer sequence on the range and magnitude of the interphase of slowed dynamics and increased modulus surrounding the nanoparticle. Our work is motivated by design questions surrounding tire tread compounds, composed primarily of styrene-butadiene rubber copolymer (with potentially controllable block structure) and reinforced with carbon black and/or silica nanoparticles, though here we focus on the basic physical trends present in greatly simplified and uncrosslinked systems.