Selectively erasable multilayer thin film by photoinduced disassembly

A multilayer film consisting of poly(acrylic acid) (PAA) and an azobenzene-containing surfactant (AzoTEA) was fabricated via a layer-by-layer assembly technique. The micellar structure favored by AzoTEA while in solution results in a bilayer structure when deposited on a substrate surface. This aggregation conversion behavior favors the deposition of AzoTEA and PAA in an alternating pattern to form a photoresponsive multilayer film. The molecular amphiphilicity of AzoTEA can be tuned by photoisomerization of the azobenzene moiety, which affects the aggregation behavior of AzoTEA in both films and solutions. The disassembly of AzoTEA aggregates caused by photoirradiation can induce the disassembly of the whole multilayer film. The AzoTEA-PAA multilayer films were found to be stable in pH 4 acetic acid (AcOH) solution, unless treated with UV radiation. On the basis of the different stability of multilayers with or without photoirradiation, when the multilayer films are selectively irradiated with UV light, the regions exposed to UV radiation disassembled after being immersed in pH 4 AcOH solution for 10 min but the regions not exposed to photoradiation are maintained on the substrate. Moreover, the plausible mechanism for the assembly and disassembly of these multilayer films and the confirmation of erasable films by atomic force microscopy are discussed.