Layer-by-Layer (LbL) films

Layer-by-layer (LBL) assembly [1] is an easy to use method for the fabrication of multicomposite films and has kindled widespread interest in such nanohybrids [1-7]. Electrostatic interactions between anionic and cationic compounds (e. g. synthetic or natural polyions such as polyelectrolytes, DNA, proteins or even colloids) offer four major advantages:

## layer-by-layer construction due to surface charge reversal in each layer

## restriction to single layers due to repulsion between last layer and excess material

## low steric demand for interaction between oppositely charged ions

## deposition on almost any solvent accessible surface

Figure: Schematic of the film deposition process using slides and beakers. Steps 1 and 3 represent the adsorption of a polyanion and polycation, respectively, and steps 2 and 4 are washing steps. The four steps are the basic build-up sequence for the simplest film architecture, (A/B)n. The construction of more complex film architectures requires only additional beakers and a different deposition sequence. (B) Simplified molecular picture of the first two adsorption steps, depicting film deposition starting with a positively charged substrate. Counterions are omitted for clarity. The polyion conformation and layer interpenetration are an idealization of the surface charge reversal with each adsorption step. (C) Chemical structures of two typical polyions, the sodium salt of poly(styrene sulfonate) and poly(allylamine hydrochloride).