Department of Chemistry, Bogazici University, Bebek 34342, Istanbul, Turkey*

Viscosity, glass-transition temperature, and diffusivity of polymer chains in thin films deviate from bulk due to the presence of adsorbed polymer chains on the substrate. The structure of adsorbed layers formed by linear chains has been extensively investigated and found to be composed of two layers: high density inner layer in which chains are flattened and bulk-like density outer layer in which chains adopted more tail and loop conformations. However, the role of chain architecture on the structure of the adsorbed layer is not clear.

Well-defined linear, 4-arm and 8-arm star polystyrene (PS) chains with the same total molecular weight, and 8-arm star PS with different molecular weights are used to elucidate the effect of polymer architecture on the structure of IAL by ellipsometry, X-ray reflectivity (XR) and AFM. Our results indicated that the normalized layer thickness increases as the number of arms increases and arm length decreases on both SiO_x and Si-H surfaces. Star polymers formed thicker adsorbed layers on Si-H compared to SiO_x surfaces. Adsorbed layer thickness is found to be a function of initial film thickness up to 100 nm. Annealing temperature has an impact on the equilibrium adsorbed layer thickness.