Engineered Deposition of Functional Coatings from Micro- and Nanoparticles using Convective Assembly

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Title: Engineered Deposition of Functional Coatings from Micro- and Nanoparticles using Convective Assembly
Author: Prevo, Brian Geoffrey
Advisors: John H. van Zanten, Committee Member
Stefan Zauscher, Committee Member
Saad Khan, Committee Member
Orlin D. Velev, Committee Chair
Abstract: The potential technological applications of micro- and nanoparticle coatings necessitate the development of rapid, inexpensive and easily controlled deposition procedures. We have developed a technique for making structured thin films from micro- and nanoparticles by dragging on a substrate a liquid meniscus at constant velocity. The advantages of this technique are improved process speed, efficiency and reduced material consumption relative to standard dip coating techniques. The governing mechanism of the deposition process was found to be convective assembly at high volume fractions. Uniform, large area coatings (square centimeters in area) can be deposited in minutes at rates approaching 100 microns per second from microliters of suspension. Operational 'phase' diagrams were constructed from coating data, relating the coating layer thickness and particle packing symmetry to the process parameters: deposition speed, particle volume fraction, and solvent evaporation rate. Varying these parameters provided the means to control and tune nanocoating structure and properties. We found the most potent parameter to be the deposition speed. The deposition process was well modeled by a simple macroscopic species balance taken around the thin film drying site. We have successfully applied this deposition technique to a wide variety of colloidal systems including: latex and silica microspheres, gold nanoparticles, ferritin proteins, and living yeast cells. Conductive coatings from metal nanoparticles exhibited tunable optical and electronic properties simply by virtue of the adjusting deposition speed. The antireflective (AR) capabilities of silica nanoparticle coatings on glass and silicon substrates can also be facilely tuned using this deposition process. These AR coatings demonstrably improved the photovoltaic efficiency of solar cells. We have also investigated the use of compressed carbon dioxide as a replacement solvent for colloidal coating deposition. We achieved rapid sedimentation of uniform, conformal nanoparticle coatings using liquid and supercritical carbon dioxide (primarily as an antisolvent). These results show potential for fabricating conformal coatings of self cleaning, technologically relevant materials by simple self-assembly techniques.
Date: 2006-05-10
Degree: PhD
Discipline: Chemical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/3681


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