Functionalized diblock copolymers, polystyrene-block-polybutadiene, are adsorbed from solution onto silicon wafers. The much smaller block of polybutadiene is functionalized for adsorption, and the copolymers might be envisaged to be quite similar to end-functionalized polystyrene chains. The amount of adsorbed polymer in dilute toluene solutions and the corresponding grafting density are determined in situ by means of null ellipsometry. M e r the polymer is dried, the lateral surface structure of grafted brushes is studied in air by means of atomic force microscopy. The two techniques supplement each other in an ideal way, one revealing information on grafting density and mean film thickness and the other on lateral surface structures and topography. The grafted polymers of different molecular weights show surface grafting densities u in the range from 0.002 to 0.21 chains/nm2. Three different structural phases are observed: (i) at high surface coverage (0.21 chains/nm2) a homogeneous layer is found, (ii) at intermediate u values (0.065 chains/nm2) the formation oflaterally inhomogeneous structures (dimples) on the surface is observed, and (iii) at low values of u (0.002 chains/nm2) isolated islands of clusters of chains are observed. The dimensions of the isolated islands correspond to the radius of gyration of a polymer chain under 0 conditions. These experimental findings are in agreement with recent theoretical predictions.

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 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.

No abstract

No abstract