Novel Approach for Fabricating Highly Ordered Colloidal Crystals using Fluorinated Solvent
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1014-AA07-10
Novel Approach for Fabricating Highly Ordered Colloidal Crystals using Fluorinated Solvent Satoshi Takeda1,2 and Pierre Wiltzius1 1 University of Illinois at Urbana-Champaign, Urbana, IL, 61801 2 Asahi Glass Co., Ltd., Tokyo, Japan ABSTRACT A novel technique for fabricating highly ordered colloidal photonic crystals has been developed. In this method, a droplet of water containing polystyrene microspheres was added to the surface of a fluorinated solvent bath. Consequently, the two liquids remained separated and the colloidal particles self-assembled into close-packed structures at the interface between them. By transferring the droplet onto a glass slide, a highly ordered crystal was obtained. This technique offers a new, potentially easier, and more effective approach than currently used. We believe that it will open new ways for fabricating materials based on colloidal crystals as well as applying the colloidal photonic crystals to optical devices. . INTRODUCTION Self-assembly of colloidal crystals offers a simple and inexpensive route to threedimensional (3D) photonic crystals (PhCs) [1-6]. However, they typically contain a high density of defects such as stacking faults, vacancies and dislocations. Crystalline quality is among the most important parameters in determining the performance of colloidal crystals in optical applications. Until now, therefore, much effort has been made to improve the quality of the crystals using convenient methods. In this paper, we report a novel approach to achieving a highly ordered colloidal crystals. Our approach is shown schematically in figure 1(a). First, droplets of an aqueous suspension containing mono-dispersed negatively charged polystyrene (PS) microspheres are deposited on the surface of a fluorinated solvent (hydrochlorofluorocarbon) whose surface tension is significantly lower (16.2 mN/m) than that of water (72.8 mN/m). In addition, the solvent is immiscible with water and the density is higher than that of water. Thus, if droplets of aqueous suspension containing PS microspheres are deposited onto the solvent, they will not mix with the solvent and float on top of it, forming an interface. Interfaces between immiscible fluids have been shown to be ideal for the assembly of colloidal particles [7,8] and nanoparticles [9,10]. At the interface, the particles are highly mobile and rapidly achieve an equilibrium assembly. That is, liquid-liquid interfaces are considered to be a very useful field for the self-assembly of colloidal particles. Subsequently, the floating droplet within which the colloidal particles may be well-ordered, is transferred from the solvent surface onto a hydrophilic flat substrate by using a dip coating technique [11]. The floating droplet will move readily to the surface of an immersed hydrophilic substrate. During the deposition, the particles can be rearranged by the capillary forces at the meniscus of the colloidal solution and the substrate, leading to a more well-ordered structure.
EXPERIMENT The glass substrate was used as a
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