INTERACTIONS, STRUCTURE, AND STABILITY OF PHOTOREACTIVE BOLAFORM AMPHIPHILE MULTILAYERS

Ultrathin organic multilayer films are appealing to scientists not onl y because they serve as molecular level models but also because they c an be transformed into superlattices through successive deposition of alternating layers of different materials. Cationic bolaform amphiphil e and anionic polyelectrolyte multilayers were self-assembled from the ir aqueous solutions via electrostatic attraction. The bolaform amphip hile layers are photopolymerizable by UV irradiation. The mechanical a nd surface electrical properties of the multilayer film were studied b y surface force measurements, and the surface topography was studied b y atomic force microscopy. We observed an average increase in film thi ckness of 75 Angstrom with each amphiphile and polyelectrolyte double layer deposition, a molecularly smooth first anchoring amphiphile laye r, and nonuniform polyelectrolyte layers with a surface roughness of 3 0 Angstrom. The surface roughness was preserved in the multilayer depo sition process and was reduced by adding salt to the polyelectrolyte s olution. Photopolymerization increases the integrity of the first anch oring layer as well as the subsequent multilayers. It took less than 5 min to dissolve a monomeric amphiphile film in chloroform, but immers ion of the UV-irradiated film in chloroform for 2 h only resulted in p artial removal of film materials. The multilayer film is quite fragile especially for the first few layers. Controlling of the monolayer str ucture by selective variation of the amphiphile chemical structure may help to optimize the photopolymerization process.