Effect of Substrate on the Mechanical Response and Adhesion of PEGylated Surfaces: Insights from All-Atom Simulations

Responsive surfaces show potential for many applications; however, the molecular mechanisms of their responsive behavior are often dependent on the nature and properties of the substrate and this dependence is not fully understood. We present a molecular dynamics study on the mechanical response of poly(ethylene glycol) (PEG) grafted on substrates of varying flexibility in "dry" conditions. Our in silico surface loading tests show that when PEG is grafted onto a hard substrate (silica), there is a significant reduction in adhesion to a solid surface, owing to augmented steric repulsions at the interface. However, when the same chains are tethered onto a soft substrate (polyester), interfacial adhesion is strengthened. We find that the deformable substrate allows significant rearrangement of the subsurface and grafted segments during loading. Asperities along the rough soft surface also provide free volume for the tethered chains to occupy, enabling them to carpet the surface and increasing the density at the interface. Our results explain the molecular basis of the mechanical response of PEG when grafted onto hard and soft substrates and provide a rationale for surface protection using PEG.