Interphase Structures and Dynamics near Nanofiller Surfaces in Polymer Solutions

We report the in situ structures and dynamics of hydrogenated polybutadiene (PB) chains bound to carbon black nanoparticle surfaces in polymer solutions composed of deuterated PB and deuterated toluene using small-angle neutron scattering and neutron spin-echo techniques together with molecular dynamics (MD) simulations. The experimental results showed that the swollen bound polymer chains exhibit the collective dynamics (the so-called breathing mode) at polymer concentrations (c) below and above the overlap polymer concentration (c) (i.e., 0.61 < c/c∗ < 1.83), where the concentration profiles of the bound polymer remained unchanged with the different c values. Interestingly, the collective dynamics slowed down by a factor of 2 compared to that in pure d-toluene when the chain lengths of the bound polymer and matrix polymer were equal. However, when the free polymer chains were longer than the bound polymer chains, the decrease in collective dynamics was not as significant. MD simulations were performed to explore the interfacial event as a whole. As a result, we found that the matrix polymer chains, whose length is equal to that of the bound polymer, can be accommodated in the bound polymer layer effectively and are "strangulated" by the bound polymer chains, while the longer matrix polymer chains only partly penetrate into the bound chains and the diffusion behavior was hardly affected compared to that in bulk.