The Layer-by-Layer (LbL) technology uses the electrostatic pull of charged polymers (polyelectrolytes) in surfaces. If, for example, one feeds a solution of a polyanion to a positively charged surface, this solution will be adsorbed until the surface has reloaded. Then because the surface is negatively charged, the deposited polymer amount regulates itself and results in reproducible layers with nanometre thicknesses (1-5 nm). This procedure is repeated with a polycation which is adsorbed onto the polyanion in a nanometre-thick layer and the surface charge once again rendered positive. This layering procedure can be repeated as many times as required during which the most diverse charged materials, such as polyelectrolytes, proteins, DNA or nanoparticles can be combined with one another. The polymer molecules can be endowed with further functions by means of covalent bonding.
With these simple methods, flat or structurally distinctive, also colloidal surfaces can be coated and functionalised in practically infinite varieties.
The figure shows schematically the LbL basic principle of the consecutive adsorption of polyanions (blue) and polycations (green) on charged surfaces.