Wormlike polystyrene brushes in thin films

Mono- and multilayer films were prepared on mica by solution casting of a high molecular weight polymacromonomer, i.e., a polymethacrylate of about 1000 repeating units each of which was substituted by a polystyrene chain with a molecular weight of about 5000 Da. The films were studied by tapping scanning force microscopy. The material showed a remarkable preference for forming well-defined monolayers of a thickness of 6.5 +/- 0.2 nm consistent with the hard core diameter of the collapsed cylindrical brush molecules. When the films were probed with high normal force, the single molecules were observed to organize in a dense nematic-like packing as expected for inherently stiff molecules. In order to minimize the surface area, the polymacromonomers form hairpins, i.e., rather tight folds parallel to the surface. The orientational order was shown to be highest in a monolayer, S = 0.74, and to decrease for layers at a larger distance from the flat substrate to a value S = 0.65.