Loosely Adsorbed Chains Expedite the Desorption of Flattened Polystyrene Chains on Flat Silicon Surface.

Abstract

Herein, the desorption of the adsorbed chains (including two regions of flattened chains and loosely adsorbed chains) was examined by monitoring the chain exchange kinetics between the adsorbed chains and the top-free chains in a bilayer system by using fluorine-labeled polystyrene (PS). The results indicated that the exchange behavior of PS-flattened chains with the top-free chains is much slower than that of PS-loose chains and has a strong molecular weight (MW) dependence. Interestingly, in the presence of loosely adsorbed chains, the desorption of flattened chains was accelerated greatly and had weaker MW dependency. We attribute the MW-dependent desorption phenomena to the average number of contact sites between polymer adsorbed chains and the substrate, which rapidly increased with increasing MW. Likewise, the desorption of loosely adsorbed chains may provide extra conformational energy to accelerate the desorption of flattened chains.