Competitive adsorption of functionalized polymers

The adsorption and desorption of functionalized polystyrene-block-polybutadiene diblock copolymers from dilute solutions in toluene onto silicon wafers are investigated by means of null ellipsometry. The short polybutadiene block is functionalized by a reaction with 4-(3,5-dioxo-1,2,4-triazolidin-4-yl)benzoic acid. On the average there are six functional groups per chain. The polystyrene block does not adsorb on the surface. The adsorption depends on the length of the polystyrene block, and chains with short polystyrene blocks yield higher surface coverage than larger ones. When short and long chains are put together, the short chains displace the long ones in equilibrium conditions nearly completely. The desorption seems to be partial if the bulk concentration of the short chains is lower than a critical value, with the likely formation of a heterogeneous layer composed of long and short chains. At initial stages, adsorption and desorption kinetics are both controlled by a diffusive process with root t behavior. In the later stages, the desorption kinetics is roughly comparable to the adsorption kinetics only in the systems where the bulk concentration of the short chains is higher than a critical value. At lower concentrations desorption is slower than adsorption.