COMBINATION OF POLYCATION POLYANION SELF-ASSEMBLY AND LANGMUIR-BLODGETT TRANSFER FOR THE CONSTRUCTION OF SUPERLATTICE FILMS

The Langmuir-Blodgett transfer (LB) of amphiphile monolayers from the air/water interface onto solid supports is a powerful tool to create periodic lattices in many varieties, usually composed of bilayers. By self-assembly adsorption (SA) of polyelectrolytes, uniform molecular films with very exact thickness adjustment are obtained. The combination of Langmuir-Blodgett transfer and polycation/polyanion self-assembly allows a precise extension of the LB lattice, and a superlattice is formed by combination of LB and SA units. The superlattice was realized in a multicomponent film, in which additional polyelectrolyte sheets are inserted between the amphiphile headgroups. At first, Langmuir-Blodgett films of the pure lipid/polyelectrolyte complex DODAB/PVS (dimethyldioctadecylamonium bromide/poly(vinyl sulfate)) were prepared and a bilayer spacing of 4.43 nm was found. For the construction of film superlattices, sequences of polyelectrolyte layers were adsorbed between the PVS headgroups of the DODAB bilayer by the following method: After deposition of one bilayer, the wet substrate was removed from the Langmuir-Blodgett trough and PAH (poly(allylaminehydrochloride)) and PVS were adsorbed from their solutions. The resulting superlattice repeat unit consists therefore of one DODAB/ PVS bilayer and the inserted assembly of polyelectrolyte layers. Samples of 1, 3, and 5 additional polyelectrolyte layers per unit cell were prepared and investigated with small angle X-ray reflectivity. Variation of the repeat unit of superlattice results in a linear increase of the superlattice layer spacing of 0.4 nm per additionally inserted polycation/polyanion pair. Also correlation lengths and roughnesses were estimated, and a decrease of layer correlation and an increase of roughness with increasing number of polyelectrolyte layers were found. Heating the samples to 70 degrees C and slowly cooling result in a remarkable improvement of the multilayer ordering.