Abstract: The cavitation of block copolymer micellar thin films was studied by atomic force microscopy(AFM). The results demonstrate that the formation of this structure is strongly dependent on the number of the hydrogenous ion of the used acids, i.e. unitary, binary or other acids. Only using unitary acids can we obtain the cavitated structure. We explained the possible mechanism of the formation of this structure. It was considered that when unitary acids(HCl, HNO₃ or HAc) were used, they could enter into the P4VP domains and P4VP would be protonated, the swelling occurred and this made the volume of the P4VP domain increasing and then the thin shells of glassing polystyrene that confined the P4VP domains would be ruptured. When binary or other multiacids were used, the two or more hydrogenous ions can protonize the adjacent P4VP domains. So the ionic cross-linking between the P4VP and the multiacid efficiently inhibited the volume expansion of P4VP domains, the cavitated structure did not appear. Using selected solvent vapor or unitary acids we can obtain the cavitated structure, but whether the essence of two methods is the same or not needs to be proved further by experiment.

Key words: Atomic force microscopy(AFM), Block copolymer micelles, Cavitated structure