2019 Volume 18 Issue 2 Pages 105-107
Bottlebrush polymer (BBP) absorbed on a negatively charged ceramics surface creates a low friction surface. However, the effect of the contact pressure on friction force of the surface covered by BBP is still unknown due to the difficulty in in-situ observation of the friction interface. Moreover, conventional coarse-grained molecular dynamics simulation is difficult to be directly compared to experimental data because the conventional coarse-grained model cannot consider chemical specificity of monomers. Herein, we developed a coarse-grained molecular dynamics friction simulator which can consider chemical specificity. Then, we performed friction simulation between substrates covered by BBP in water. We showed that the friction coefficient rapidly increased at contact pressure of 16 MPa, when we increased the contact pressure. We found that a sufficient coordination of water to the side chain of BBP facilitated slip between substrates under low pressure (< 16 MPa), leading to a low friction coefficient. On the other hand, under high pressure (> 16 MPa), the number of side chain of BBP contacts with the BBP on the counter surface increased because water beads were squeezed out from the side chain of BBP. Therefore, the main chain of BBP was strongly stretched to the sliding direction, which induced shear between substrate and BBP. We found that the shear under high pressure caused a high friction coefficient.
