Growth of Large Crystals of Monodispersed Spherical Colloids in Fluidic Cells Fabricated Using Non-photolithographic Methods

This paper describes a convenient approach to the fabrication of fluidic cells to be used for crystallizing spherical colloids into three-dimensionally periodic lattices over large areas. The major component of the fluidic cell was a rectangular gasket sandwiched between two glass substrates. Here we demonstrate that these gaskets could be simply cut out of commercial Mylar films. Three non-photolithographic methods were also demonstrated to create shadow channels between the Mylar film and two glass substrates: (i) by wiping (along one single direction) both sides of the Mylar film with a piece of soft paper (Kimwipes EX-L); (ii) by coating both surfaces of the Mylar film with polymer beads whose size was smaller than those to be packed in the cell; and (iii) by patterning the surface of the bottom glass substrate with an array of gold channels using a combination of microcontact printing and selective etching. When an aqueous dispersion of monodispersed spherical colloids was injected into this packing cell, a crystalline lattice nucleated and grew from the edge(s) of the cell as a result of solvent depletion through the channels between the Mylar film and the glass substrates. The capability and feasibility of this new approach have been demonstrated by the fabrication of uniform opaline lattices of polystyrene beads and silica colloids over areas as large as several square centimeters. Because Mylar films with thicknesses in the range 20−100 μm are commercially available in large quantities and at reasonably low costs, the present approach offers a flexible tool to those who want to explore the use of large crystals of spherical colloids but have no access to clean room facilities.