Doctoral dissertation
Polyelectrolyte multilayer template assisted in-situ synthesis of inorganic nanostructures
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Abstract
Thin film nanocomposites consisting of inorganic matter embedded within a soft polymeric matrix on the nanometer scale have attracted much interest lately due to their unique properties with potential application in optoelectronics and photonics.
Polyelectrolyte multilayers formed by the layer-by-layer electrostatic assembly of oppositively charged polyions can be utilized as nanoreactors for the in-situ nanoparticle synthesis, where the surrounding polymer prevents their aggregation and thus enables a control over the inorganic-organic composite properties.
Multilayers formed from weak polyions of polyallylamine (PAH) and polyacrylic acid (PAA), possessing ion-exchangeable carboxylic groups were used to bind metal cations within the film. By subsequent wet chemical reaction process of the incorporated metal ions, pure zinc sulfide (ZnS), manganese doped zinc sulfide and silver (Ag) nanoparticles with a narrow size distribution were formed within the PEMs. The size and concentration of the inorganic nanoparticles in polyion matrix were controlled by the concentration of metal – binding carboxylic acid groups as determined by the multilayer assembly pH. Furthermore, the metal cation loading and reaction methodology could be repeatedly cycled to increase the size and volume density of the nanoparticles.
Furthermore, the polyelectrolyte multilayer films were used as templates for the ceramic (TiO2) thin film fabrication with a modified sol-gel reaction. Since the multilayer assembly is performed from polyion aqous solutions, the multilayers contain some water that after infiltration of the organometallic precursor enables in-situ reaction of hydrolysis and condensation. After calcination, nanocrystalline TiO2 thin films with thickness controllable by the number of the polyion layers in the matrix were formed.
With the in-situ synthesis approach of inorganic nanstructures in polyelectrolyte multilayer matrix, the ability of obtaining the control over the film thickness and size of the inorganic particles enabled tuning of the optical properties of as fabricated inorganic-organic composite films as well as nanocrystalline ceramic films.