At present, most optical materials are in solid states, and once fabricated their functions are fixed. Applying external electric fields to assemble metallic particles and metallodielectric particles into different configurations is an approach to realize tunable optical materials. This thesis reports how metallic particles and Janus particles can be self-assembled by an alternating current (AC) electric field with different range of frequencies. The experimental results show that under a wide range of frequencies, Janus particles can form into chain structures while metallic core-shell particles can only form chain structures under a narrow range of frequencies. The fundamental theories indicate that the formed chain structures by those two kinds of particles are mainly due to the dielectrophoresis force and/or induced-charge electrophoretic phenomena.
Micro-sized core-shell gold/silica particles used in the experiment are synthesized by chemical methods based on Duff’s protocol, and the Janus particles are made by coating dielectric polystyrene latex microsphere using microfabrication techniques. The optical properties of polystyrene particles monolayer, half gold coated monolayer, and assembled chain structures are measured by Fourier transform infrared (FTIR) spectroscopy.
The specific line features appeared in the FTIR spectrum were also discussed.
The formed chain structures in this work, and the unique FTIR characteristics promise dynamically tunable optical materials by changing the size and the shape of particles, and the parameters of the external electric field (intensity and frequency). More sophisticated structures are possible by introducing the complexity in the electric field pattern. In addition to the possible tunable optical materials, the manipulation and assembly of metallodielectric particles and metallic particles may have application in the field of microfluidic devices and liquid-borne microcircuits.
- Professor Yongmin Liu (Advisor)
- Professor Yung Joon Jung
- Professor Hui Fang