Multilayered clay films: Atomic force microscopy study and modeling

Self-assembled natural and synthetic clay- polymer films have been prepared by sequential adsorption of poly(diallyldimethylammonium chloride) (PDDA) and clay particles onto mica. The influence of pH, polymer concentration, and clay particle size on the building and roughness of mono- and multicycle depositions was investigated. The monocyclic deposition gives a submonolayer of clay particles. The thickness of the films increases linearly with the number of cycles in the deposition process, thus giving an average increase of thickness per cycles which depends on clay particle size and PDDA concentration. The film roughness is affected by the same parameters and increases with particle size of the clay and PDDA concentration. Optimal conditions for the deposition of smooth multilayer films consist of the combined use of a 0.05-0.5% (w/w) aqueous solution of PDDA and a 0.05% (w/w) clay suspension at pH = 9-10. The film formation was modeled assuming a deposition of homogeneous layers partially covering the surface. The model indicates that Laponite films are characterized by significantly higher surface coverages than natural clay films.