6533b7d4fe1ef96bd1261c28

RESEARCH PRODUCT

Proof of multilayer structural organization in self-assembled polycation-polyanion molecular films

subject

description

Abstract Multilayer organization of ultrathin polycation-polyanion self-assembled films is demonstrated using two approaches. (1) Fabrication of polyion superlattices with alternation of three different polyelectrolytes in (ABCB) n fashion, which gives rise to a Bragg peak in X-ray reflectivity. The spacing d=93.4 A corresponds to the repeat unit (ABCB) n . (2) Drying-induced manipulation of the film surface at regular intervals. Normally the layer-by-layer adsorption is carried out by keeping the film wet throughout all deposition cycles. Alternatively the film surface can be manipulated by gently drying the film in a stream of nitrogen or air after the adsorption of every layer. When the films are dried at regular intervals m during the alternating deposition of a polyanion and a polycation (AB) m (e.g. m =3 for drying after deposition of every 6th layer), up to four orders of Bragg peaks are observed in X-ray reflectivity. In the case of poly(styrenesulphonate) alternated with poly(allylamine) the observed superlattice spacings d m were d 2 =104 A , d 3 =150 A and d 4 =188 A . In both cases the observation of a superlattice structure probably results from the artificially enhanced variation in electron density along the layer normal on a length scale larger than the interfacial width of adjacent layers.