BS in Materials Engineering
Materials Engineering Department
Synthetic opals were synthesized by creating polymethyl methacrylate (PMMA) nanospheres in order to determine which conditions would create the best iridescent samples. The factors affecting the iridescence were nanosphere concentration, stir rate, and processing temperature. PMMA solutions were made by adding 17 mg of granular azobis to a solution of 16 mL of distilled water with 3 mL of methyl methacrylate (MMA). The solution was stirred at different rates, slow and fast, and different temperatures, 70 °C and 90 °C, under a constant flow of nitrogen gas for 40 minutes until the polymerization reaction was complete. Glass substrates were prepared by being cleaned with isopropyl alcohol for 10 minutes before being soaked in distilled water for 5 minutes. The glass was then suspended in a diluted solution consisting of 20 mL of distilled water and different concentrations of the PMMA nanosphere solution, 50, 100, and 150 μL. The samples were dried at 50 °C for 36 hours to evaporate the solution and grow a thin film of self-assembled PMMA nanospheres on the glass substrates. Light spectrometery was used to determine the maximum absorbance wavelength of light when light was being transmitted perpendicular or at an angle to the samples. The Bragg equation was used to estimate to the size of the PMMA spheres from the wavelength of maximum absorbance. To verify the size of the nanospheres, samples were sputtered in gold and examined using the scanning electron microscope (SEM) and measured using the imaging software ImageJ. Nanosphere diameters ranged from 290 nm to 370 nm. Using a nanosphere concentration of 150 µL, a fast stir rate, and a processing temperature of 90 °C produced the most consistently iridescent samples.