Abstract: Silica nanoparticle thin films were built up from SiO2 colloid and poly（diallyldimethylammonium chloride）(PDDA) by using the electrostatic self-assembly technique.The TEM image(to see Fig.3) of a 40-bilayer thin film revealed that SiO2 nanoparticles were closely packed and that the coverage of the SiO2 nanoparticles over the thin film was uniform. The electron diffraction pattern showed that the self-assembled thin film was amorphous. The transmissivity of a glass slide coated with PDDA/SiO2 multilayers exhibited periodical oscillation as the bilayer number of the thin film was increased (to see Fig.4). The composite thin films under some bilayers were antireflection coatings. A net increment of more than 5％ in the transmissivity of a glass slide could be yielded over the same wavelength range after PDDA/SiO2 composite thin films were assembled onto both sides of the slide (to see Fig.5). Within the composite thin films,the average physical thickness of one PDDA/SiO2 bilayer was less than the average diameter of the SiO2 particles, which implied substantial overlap between the adjacent SiO2 nanoparticle layers. Although the PDDA/SiO2 multilayer thin films were prepared in the alternating layer-by-layer assembly fashion, the optical properties of the composite thin films were determined mainly by the SiO2 nanoparticles, and the composite thin films served the function of single-layer coatings.

Key words: Electrostatic self-assembly, Silica, Nanoparticle, Composite thin film, 　ptical property