A New Route to Prepare Hard and Anti-Scratching Coatings at Room Temperature
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Mat. Res. Soc. Symp. Proc. Vol. 576 ©1999 Materials Research Society
EXPERIMENT Materials Different polymers were used to provide the required charged polyelectrolytes for the fabrication of the multilayer nanocomposite structures. Poly(diallyldimethylammoniumchloride) (PDDA), Poly(allylamine hydrochloride) (PAH), and poly(sodium-4styrenesulfonate) (PSS) obtained from the Aldrich chemical company were used to provide cationic polyelectrolytes. A molecular dye consisting of a poly(vynilamine) backbone, with azo chromophore in the side chains (PS 119), was obtained from the Sigma chemical company and used to provide anionic polyelectrolytes. Zirconia and alumina nanocluster solutions were obtained from Alfa Aesar. All of the above-mentioned materials were used without further purification. The substrates of quartz and single crystal silicon (100) wafers were cleaned to remove any impurities prior to any deposition of films in a mixture of what is called a "piranha" solution [6], consisting of hydrogen peroxide (H202) and concentrated sulfuric acid (112 SO 4). In addition, this procedure modified the substrate surface charge. The results of this pre-treatment procedure formed negatively charged substrates. Deposition Process The self-assembly process has been commonly used to fabricate nanostructured materials. The term self-assembly means a spontaneous adsorption of molecules or particles onto a substrate [7]. There are two different self-assembly processes that are used in the fabrication of nanostructured materials. They are self-assembly methods by chemisorptions (SAMs) and by physisorption (SAMp), which are explained in details somewhere else [8-10]. The electrostatic self-assembly (ESA) technique is based on the SAMp method. The process is based on the electrostatic attraction between opposite charges, where alternating adsorption of anionic and cationic polyelectrolytes forms multilayer assemblies [6, 11-13]. The attraction between the positive and negative charges of polyelectrolytes forms strong interlayer adhesion without any activation steps. In this experiment, prior to the construction of any multilayer hard coating systems, several bilayers of PAH/PS 119 or PDDA/PSS were deposited on the substrate to promote the adhesion between the outermost surface of the substrate and the first monolayer of the hard coating film. First, the substrates were immersed in the cationic solutions, either the PAH or PDDA, producing a monolayer of positively charged films. Following the immersion, the substrates were rinsed with water and then immersed in the anionic solutions, either the PS 119 or PSS, producing a monolayer of negatively charged films. Finally, the substrates were then rinsed with water. By repeating this deposition procedure, several bilayers of polymers were deposited on the substrates providing the uppermost layer with a negatively charged surface. Both ZrO 2/PSS and Al 2 0 3/PSS hard coating films were deposited in the same manner as the above-mentioned procedures. Acidic water with a pH of 3.5 wa
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