[SY-O8] Molecular Dynamics Simulation Study on Friction of Bottlebrush Polymer with a Cationic Anchor Block Adsorbed on Substrate
In recent years, concentrated polymer brush (CPB), which is constructed by grafting polymer chains onto a substrate with high density, has been developed. CPB has attracted much attention for application to low friction materials as artificial joints because of its high wear resistance and biocompatibility. However, the graft of polymer chains onto substrate is complicated and takes much cost. As an alternative method analogous to CPB, bottlebrush polymer (BBP) known as macromolecules with polymeric side chains is candidate for low friction materials. Previous studies have revealed that BBPs with a cationic anchor block adsorbed on a negatively charged surface swell, which produces low friction force. However, the detail of friction mechanism of BBP is not clear. Furthermore, the effects of sliding speed and side chain length on friction properties are also unknown because the in-situ observation of the sliding interface is difficult. Thus, computational simulation is required. Herein, to reveal the mechanism during friction of BBP consisting of a cationic anchor block, we developed a coarse-grained molecular dynamics code which can consider chemical specificity of each monomer, and performed friction simulation in water solvent. The low friction coefficient was observed at the low load, but friction coefficient was increased at high load. We found that, at low load, water beads which coordinate to the side chain of BBP suppressed contact between BBPs on the counter surfaces, because side chains of BBP prefer to interact with the water beads. This swelling state of BBP facilitates shear between the opposite substrates. With high load, water beads were removed from the sliding interface, which reduces the number of water beads around BBP. Therefore, the contact between BBPs on a counter surface leads to high friction coefficient. The effects of side chain length and sliding speed on the friction properties will be discussed on the day.