Effect of Chain Adsorption on the Mobility of Polymer Chains*

Irreversible adsorption of polymer chains on solid substrates have a huge impact on the wetting, glass transition, aging and polymer chain mobility in thin films. In recent years the segmental mobility of the adsorbed chains and neighbouring unadsorbed chains is under discussion. We have studied the effect of polymer chain adsorption on the mobility of polymer chains in thin films for linear and star polymers. The vertical mobility of polystyrene (PS) chains was determined by probing interdiffusion between protonated PS (hPS) and deuterated PS (dPS) layers using neutron reflectivity. By varying the amount of deuterated adsorbed chains in the bottom layer for linear dPS, 4-arm star dPS and 8-arm star dPS we have determined that the mobility of polymer chains did not decrease with increasing adsorption. The apparent diffusion coefficient for 8-arm star PS was the largest even though X-ray reflectivity measurements showed that 8-arm star PS chains form adsorbed layers with the largest normalized thickness among these three polymers.