Unraveling the role of phenyl groups on the packing process of polystyrene chains bound to a solid surface*

In response to the growing demand for precisely controllable nanotechnologies, emerging polymer-based materials are transitioning to nanometer scales while maintaining outstanding performance. Enabling further advancements in polymer-based technologies may hinge on a deeper understanding of a buried solid-polymer melt interface, which governs both their structural stability and properties. In this talk, we focus on revealing substrate-induced, short-range nanostructures of polymer melts strongly bound ("flattened chains") to solid surfaces. Atactic polystyrene (aPS) flattened chains prepared on silicon substrates were used as a rational model. Following an established solvent rinsing method, the final thicknesses of the aPS flattened layers measured about 2 nm. In-situ grazing incidence small-angle X-ray scattering measurements were conducted to study how amorphous aPS chains are arranged and packed in the lateral direction. In addition, atomistic molecular dynamics simulations were performed to complement the experimental results and further characterize the experimentally unobservable local chain conformations of aPS backbone and phenyl groups. The integrated results delineate the role of pi-pi interactions in the flattening process of bound polymer chains.