Interactions, Structure, and Stability of Photoreactive Bolaform Amphiphile Multilayers

Ultrathin organic multilayer films are appealing to scientists not only because they serve as molecular level models but also because they can be transformed into superlattices through successive deposition of alternating layers of different materials. Cationic bolaform amphiphile and anionic polyelectrolyte multilayers weee self-assembled from their aqueous solutions via electrostatic attraction. The bolaform amphiphile layers are photopolymerizable by UV irradiation. The mechanical and surface electrical properties of the multilayer film weee studied by surface force measurements, and the surface topography was studied by atomic force microscopy. We observed an average increase in film thickness of 75 A with each amphiphile and polyelectrolyte double layer deposition, a molecularly smooth first anchoring amphiphile layer, and nonuniform polyelectrolyte layers with a surface roughness of 30 A. The surface roughness was preserved in the multilayer deposition process and was reduced by adding salt to the polyelectrolyte solution. Photopolymerization increases the integrity of the first anchoring layer as well as the subsequent multilayers. It took less than 5 min to dissolve a monomeric amphiphile film in chloroform, but immersion of the UV-irradiated film in chloroform for 2 h only resulted in partial removal of film materials. The multilayer film is quite fragile especially for the first few layers. Controlling of the monolayer structure by selective variation of the amphiphile chemical structure may help to optimize the photopolymerization process.