An Atomic Force Microscopy Study on the Transition from Mushrooms to Octopus Surface “Micelles” by Changing the Solvent Quality

Atomic force microscopy (AFM) is used to study the behavior of a diblock copolymer onto a solid surface while the solvent quality is changed. In a first step, the copolymer poly(2-vinylpyridine)/polystyrene (P2VP/PS) is adsorbed onto mica from a selective solvent (the PS block is well solvated and the P2VP is not solvated). In such a case, the P2VP block adsorbs preferentially on the substrate and anchors the PS block to the surface. In a second step, the solvent quality is reduced to such an extent that the PS block is no longer solvated. This procedure allows the formation of octopus surface “micelles”. The parameters characterizing this regime are measured using AFM. In addition, a direct determination of the adsorbance is performed. It reveals that the PS blocks when immersed in good solvent do not overlap. A mushroom surface regime instead of a brush one is thus created at the surface.