Fabrication of Multilayer Films Using a Spinning Process
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Fabrication of Multilayer Films Using a Spinning Process Jinhan Cho, Kookheon Char, Jong-Dal Hong1, Ki-Bong Lee2 School of Chemical Engineering, Seoul National University, San 56-1, Shinlim-dong, Kwanak-gu, Seoul 151-742, Korea 1 Department of Chemistry, University of Inchon, Dowha-dong, Namgu, Inchon 402-749, Korea 2 Department of Physics, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784, Kyoungbuk, Korea ABSTRACT We introduce a method to build up organic/organic and organic/inorganic multilayer films composed of cationic poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) or inorganic cadmium sulfide (CdS) nanoparticles using a spinning process. Since the deposition of each layer is made at a high spinning speed, the adsorption time for the formation of a homogeneous thin layer takes only 8 to 15 seconds. The adsorbed film thickness per bilayer can be easily controlled from about 5Å to 40Å by varying the spinning speed (Ω) and the mole concentration of polyelectrolytes. We also demonstrated with X-ray reflectivity that the alternating organic/inorganic ultrathin films fabricated by the spin SA process retain highly ordered internal structure in comparison with those prepared by the conventional SA process.
INTRODUCTION Ultrathin multilayer films have attracted much interest for their wide applications such as sensors, integrated optics, friction reducing coating, biological surface, light-emitting devices (LED), or surface orientation layers [1,2]. Most of these applications require preparation of stable and well-organized films with fast fabrication processes. Several years ago, Decher et al.[3] presented the layer-by-layer self-assembly (SA) method to fabricate multilayer thin films consisting of anionic and cationic polymer layers. This layer-by-layer self-assembly method is principally based on the self-diffusion process in which charged polyelectrolyte chains are adsorbed onto an oppositely charged surface due to the electrostatic attraction. As a result, the adsorption time, proper control of pH, polyelectrolyte concentration and amount of added ionic salt should be considered in order to increase the surface coverage of a polymer layer adsorbing onto a substrate. In addition, without thorough washing using a flow of pure solvent after the adsorption of a polyelectrolyte layer, the weakly adsorbed polyelectrolyte chains significantly increase the surface roughness of the multilayer films, yielding poor film quality. Consequently, optimum conditions for both adsorption and careful washing steps are required in order to prepare well-defined multilayer films. In present study, we report a fabrication of multilayer films using a spinning process as an alternative to fabricate well-organized multilayer films in a very short process time. Poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were, for example, used as a cationic and an anionic polymer, respectively. Inorganic cadmium sulfide (CdS) nanopar
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