Effect of film processes on the chain conformations of adsorbed polymer nanolayers*

Polymer chains adsorb even onto weakly attractive solid surfaces, resulting in the formation of adsorbed polymer nanolayers (``PNs''). We report how film processing affects the chain conformations composed of PNs. 50 nm thick polystyrene (PS, Mw$=$290 kDa) thin films were prepared onto hydrogen-passivated silicon substrates by using two different processes (i.e., spin coating and dip coating). The PNs were then formed by high temperature thermal annealing and subsequent rinsing with a good solvent. We characterized the PNs using x-ray reflectivity (XR), atomic force microscopy (AFM), and sum-frequency generation spectroscopy. The XR and AFM data reveal that the homogenous PNs are composed of the two different architectures regardless of the film processing: flattened polymer chains that constitute the inner higher density region of PNs and loosely adsorbed polymer chains that form the outer bulk-like density region although adsorbed chain conformations from the two processes are different.