Colloidal silica synthesis and evaporative assembly of Binary nanocrystal films

Open Access
Noel, Grace Helen
Area of Honors:
Chemical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Tom Mallouk, Thesis Supervisor
  • Ali Borhan, Honors Advisor
  • silica
  • nanoparticles
  • colloidal crystals
  • self-assembly
Binary crystal films of silica nanoparticles can be deposited using evaporative assembly. In this method, the energy of the system depends on the molecules’ interactions with each other, the thermodynamics of the system, as well as the kinetics of diffusion and evaporation-driven dispersion of the particles. While systems of single-sized particles have been studied and are generally understood, systems of particles of two different sizes introduce additional complexities. By changing the number ratio (ratio of the number of smaller particles to the number of the larger particles) and the evaporation rate, both the thermodynamics and kinetics of the experiment are altered and the resulting patterns change. Experiments have been conducted to form these films under different conditions in order to achieve repeatability in the crystalline patterns of the resulting films. Once the films are dried, the patterns are determined by scanning electron microscope (SEM) imaging. The results indicate that the kinetics play an important role in this method as the patterns change with both temperature and number ratio. At a lower temperature, deposition occurs more slowly, resulting in ordered crystals. Depending on the number ratio, this order can be face-centered cubic (fcc) A, fcc B, or AB2. Using this information, a map was created to illustrate the trends of the different patterns influenced by deposition temperature and number ratio. Overall, the kinetics of the evaporative assembly method compete with the thermodynamics of the system to produce repeatable film patterns at specific temperatures and number ratios.