Abstract
Self-assembled multilayered films were prepared by alternate deposition of a strong cationic polyelectrolyte, poly(trimethylammonium ethyl methacrylate chloride) and a pH-dependant anionic polyelectrolyte, poly(acrylic acid). The layer-by-layer adsorption was followed in-situ by optical fixed-angle reflectometry and after drying by ellipsometry. A recently developed “substrate thickness method” was applied to calculate the adsorbed amount of polymer from the reflectometric signal. Surface film morphology was imaged before and after drying with atomic force microscopy (AFM). Influence of the number of adsorbed layers, concentration and type of salts on the multilayer growth was examined. The number of adsorbed layers produced a specific effect on the reflectometric signal which is linked to the refractive index of the film. Adjustment of the adsorbed amount of polyelectrolytes was done by changing sodium chloride salt concentration within a range of 10 − 3 to 10 − 1 M. AFM observations showed a significant evolution in surface morphology and a maximum of surface roughness for films built-up at 10 − 2 M. Experiments were then carried out at 10 − 3 M in either barium chloride or zinc chloride salts. In the presence of Ba 2+ and Zn 2+ ions, adsorption of 5 bilayers is completely modified and the surface morphology was smoother than the multilayers obtained using sodium chloride salt.
Highlights
Functional films with targeted properties can be produced by the layer-by-layer adsorption technique
Reflectometric measurements and atomic force microscopy (AFM) analysis were used to investigate the effect of experimental physicochemical parameters on multilayered film properties composed of a strong cationic polyelectrolyte (MADQUAT) and a weak anionic polyelectrolyte (PAA)
During the build-up of polyelectrolyte multilayers up to 24 bilayers, reflectometric output exhibits a special trend directly linked to the variation in the refractive index of the film
Summary
Functional films with targeted properties can be produced by the layer-by-layer adsorption technique. The separation performance was optimised by the controlling pH and supporting electrolyte concentration when preparing the film Encapsulation is another way to use multilayered film where the choice of the polyelectrolytes — and especially the charged chemical function — is essential in the final application [13,14]. An example of this is the release of encapsulated material, which depends mainly on the capacity of the polymer chain network to evolve when a change in pH is applied [15,16]. Physicochemical parameter adjustment was found to lead to morphological film variation
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