Assembly of colloidal particles via site-specific functionalizations
Colloidal and nanocolloidal particles are used as the building blocks for more complex materials and devices. These range from traditional materials like thin films, coatings and ceramics, to applicable devices such as circuits, sensors, photonic crystals and colloidal crystals. The two major challenges that exist when processing a suspension of colloids are controlling the stability of the particles in the system and promoting accurate particle self-assembly. Traditionally, stabilization is accomplished through the passivation of particles with dispersant molecules, which allows for the synthesis of simple structures such as films and uniformly ordered colloidal crystals. However, passivation often prevents downstream bottom-up assembly processes.
Current assembly methods go beyond simple colloidal crystal packed structures to produce close-packed and isotropic structures. These simple and new assembly structures are limited by photolithography, functionalizing chemistries, and the fact that they are made up of the same material. The work described in this thesis created simple, localized and nanoscale charge distributions on the surfaces of individual colloidal particles using the technique of particle lithography. The size and effectiveness of the nanoscale charge region was enhanced with changes in the particle suspension conditions and characterized through imaging with field emission scanning electron microscopy and confocal microscopy. In addition, a method called the salting out - quenching - fusing technique was developed to produce a high yield formation of in-suspension colloidal homo and hetero doublets. Lithographically defined templates were employed to self-assemble more complex and anisotropic colloidal aggregates without the use of dispersants. A model was also developed that relates the aggregation times of these colloidal particles to their size and concentration in the assembly suspension, which provides realistic predictions about the experimental times required for colloidal particle assembly.