Effect of nanoscale roughness on adhesion between glassy silica and polyimides: A molecular dynamics study

The effect of nanoscale roughness on the adhesion between glassy silica and polyimides is examined by molecular dynamics simulation. Different silica surfaces, with varying degrees of roughness, were generated by cleaving bulk structures with a predefined surface and a desired average roughness, with different roughness periods and hydroxylation densities in an effort to study the influence of these surface characteristics on adhesion at the silica−polyimide interface. The calculated results reveal that average roughness R_a is the primary controlling factor within the considered conditions. Further, an energy decomposition analysis of the pulling process suggests that hydrogen bonding contributes to the adhesion on all the rough surfaces, while the Coulombic energy contribution becomes significant at higher R_a. From a structural analysis of the vacant volume and surface area, it is shown that the periodicity of roughness provides a rather interesting trend for the adhesion energy. Adhesion can increase with a reduction in period due to the corresponding surface area expansion; however, if vacant volumes exist at the interface, the level of adhesion can decrease. Competition between two opposing tendencies leads to the maximum adhesion, and hence, both R_a and period are key parameters to control the adhesion in nanoscale roughness.