Master of Science
Materials Science and Engineering
Gilchrist, James F.
There are many applications for thin films of ordered particles including membranes, microlens arrays, and structure-color coatings. Convective deposition, a process that uses evaporation-driven flow in a thin liquid film to order particles, is a relatively fast and scalable method of making such films. Recently, it was shown that using lateral vibration in the direction of coating can enhance this process. This work focuses on depositing well-ordered monolayers of a binary suspension of microspheres and nanoparticles to understand the effect of the process parameters on the final distribution of particles. In order to investigate the deposited morphology of binary suspensions, various concentrations of nanoparticles were deposited on the substrate at 50 Hz frequency and a range of vibration amplitudes. The result was for all concentrations, the deposition rate and the range of speed for monolayers tend to increase with amplitude of vibration. The overall quality of the thin films is more uniform; the stripes are rarely seen. However, areas exist where microspheres were not surrounded by nanoparticles, and this inhomogeneity increases with higher amplitude vibration. To analyze the non-uniformity of deposition, samples were imaged using confocal laser scanning microscopy and particle-level image analysis. The particle coverage, the intensity of segregation, the distribution of number of nearest neighbored particles of microsphere and local area of particles were characterized. At low amplitude, the nanoparticle coverage is higher and has small deviation over large sample areas. As expected, each microsphere on average has 6 nearest neighbored (NN) particles and a relatively uniform local area distribution for uniform, well-ordered particle coatings. On the other hand, when the coverage has many defects due to vibration, the average number of NN particles tends to decrease which can also be described by the a decrease in the distribution of local areas. Even though many localized defects are generated when vibration is imposed, the overall uniformity remains high, as indicated by a low intensity of segregation across all vibration samples. All of these parameters allow a direct connection of microstructure to the macroscopic process parameters.
Kaewpetch, Thitiporn, "Vibration-Assisted Convective Deposition of Binary Suspensions for Structured Coatings" (2017). Theses and Dissertations. 2652.