Assembly of Nanowires by Contact-Line Deposition
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1206-M16-45
Assembly of Nanowires by Contact Line Deposition Mei Zhang, Farag Abdelslam, Zach McDargh, Chuck Zhang, and Ben Wang High Performance Materials Institute, Florida State University; Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310, U.S.A.
ABSTRACT The post-synthetic assembly of nanowires into desired configurations presents a unique challenge. Through the use of a microscope we observed the behaviors of different nanowires during the drying of their DI water based solutions. In addition, we also viewed the resulting dried patterns on substrates by AFM and SEM. We found that nanowires are deposited and aligned along the contact line. The evaporation-induced capillary flow carries the nanowires to the contact line and their alignment there is due to self-assembly directed by solvent evaporation. Based on our observations, we developed a deposition method at the contact line and successfully assembled aligned nanowires in proper patterns on substrates.
INTRODUCTION When a drop of particle-laden liquid dries on a surface it leaves a puddle like pattern. It is demonstrated that the pattern is due to capillary flow induced by the differential evaporation rates across the drop: liquid evaporating from the edge is replenished by liquid from the interior [1]. The resulting edgeward capillary flow can carry the dispersed material to the edge. Such deposition is called contact-line deposition. Different from nanoparticles, nanowires (NWs) have anisotropic nanostructures with nanoscale diameters and a wire-like morphology. The behaviors of NWs in contact line deposition are not clear. The assembly of NWs requires techniques that are able to appropriately manipulate and direct the deposition of individual NWs. Especially challenging is directing the assembly of these structures into desired configurations using post synthetic assembly methods. Several processes have been explored [2, 3], such as assembly by molecular forces or electrostatic interactions, assembly within magnetic fields, and assembly driven by shear forces or by dielectrophoresis. The methods developed to make aligned NW arrays on a substrate involve Langmuir-Blodgett, microfluidic, assembly driven by electric fields, and optical trapping. In this work, we use NW solution to assemble NWs on substrates because many NWs can be directly processed as a solution and the concentration of nanostructures can be adjusted through dilution. We show that the NWs can be deposited on the contact-line and their alignment is along that contact-line due to NW self-assembly directed by solvent evaporation. We further show that precise control of the NW motion allows the control of the alignment of NWs and extend the range of achievable structures from single arrays to complex 2D or 3D structures.
EXPERIMENT Two types of NWs, Titanium dioxide (TiO2) NWs and Silver (Ag) NWs, were used. The gel of TiO2 NWs was produced by Novarials Technology. Aqueous dispersions of Ag NWs were purch
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