Selective Deposition of Two-Dimensional Colloidal Arrays on Patterned Polyelectrolyte Multilayer Templates
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Selective Deposition of Two-Dimensional Colloidal Arrays on Patterned Polyelectrolyte Multilayer Templates Haipeng Zheng, Ilsoon Lee, Michael F. Rubner, Paula T. Hammond Department of Chemical Engineering and Department of Materials Science and Engineering, The Microphotonics Center, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. ABSTRACT A new method for the patterning of colloidal particles on polymer templates is presented. A polyelectrolyte multilayer film is deposited onto a chemically patterned monolayer surface, which is further used as a functional template to direct the deposition of charged particles through electrostatic and secondary interactions. After modified by an opposite charged surfactant, the particles change their deposition selectivity from the polyelectrolyte surface to a neutral ethylene glycol monolayer surface. Based on the different selectivity, we have first demonstrated a new approach to direct two component colloidal arrays onto a patterned polyelectrolyte multilayer template. INTRODUCTION In recent years, studying on photonic crystals has been becoming an attractive topic in materials science and engineering fields. A number of methods of assembly of photonic bandgap (PBG) crystals have been investigated, such as the fabrication of two- (2D) or three- (3D) dimensional colloidal arrays[1-3] and inverse opals[4,5], the phase separation of block copolymers[6] and layer-by-layer (LBL) assembly of functional polymers and semiconductor nanoparticles[7]. Among these approaches, due to the simplicity and flexibility of operation and multiple functionalities, the assembly of spherical colloida has been extensively studied, including gravity sedimentation, electrophoretic deposition, colloidal epitaxy, convective self-assembly, physical confinement and self-assembly of particles at the air-liquid interface. In these cases, semiconducting polymers[8], metallic[9] or semiconductor nanoparticles[10] have been further introduced into these colloidal crystal templates to produce various functional photonic crystals. Utilizing surface sorting and polymer patterning, we have developed a new approach to direct colloidal particles selectively onto patterned polymer multilayer templates. In this process, we design patterned polymer surfaces with functionality on the patterned self-assembled monolayers (SAMs) using microcontact printing (µCP)[11]. The patterned polymeric thin films can be achieved by optimizing ionic strength or pH of solutions and chemical structure of polyelectrolytes. An important difference between traditional SAMs and the multilayer surfaces is that polyelectrolyte multilayers can be tuned during the LBL assembly process to vary surface charge density, density of functional groups at the surface, film thickness, and wetting properties. The polymer thin film also imparts a conformal nature that enhances adhesion, which can be used as functional templates for selective deposition of silica and polystyrene latex microspheres based on electrostatic, hydrogen bonding or
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