Real-space and Real-time Study of Two-dimensional Colloidal Quasicrystals

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Quasicrystals are structures that lie between crystalline and disordered phases. They exhibit some properties similar to those of crystals, but they do not have the periodic structure of crystals. Quasicrystals can interact with light in unique ways and exhibit rich optical properties that are not manifested in crystals or in completely disordered materials. Although atomic quasicrystals are predominantly metallic alloys, synthetic quasicrystals have also been found in soft materials made from nanoparticles, micelles, and polymers. However, both natural and synthetic quasicrystals are built from units that are too small to be directly observed by optical microscopy. As a result, it has proven challenging to fully understand the formation and stability of quasicrystals. The goal of this project is to build two-dimensional quasicrystals from single-component microparticles that are large enough to observe with optical microscopy. The assembly of the microparticles into quasicrystals will be driven using applied alternating current electric fields. The formation of the Microparticles will be observed in detail and the experiments will be compared with numerical simulations to understand the dynamics of quasicrystal formation. Results of the project will address fundamental questions about quasicrystal formation, such as how the long-range but non-periodic order emerges and evolves and what stabilizes low and high temperature quasicrystals. The research will be integrated with a variety of educational and outreach efforts, including an activity to encourage participation of children with dyslexia in science and engineering. The objective of this project is to assemble two-dimensional dodecagonal quasicrystals from particles whose sizes are comparable to the wavelengths of visible light. Owing to the size of the particles, the dynamic formation of quasicrystals can be observed directly with optical microscopy. This provides a tool to address fundamental issues related to quasicrystal formation from soft matter. Large high-quality two-dimensional quasicrystals will be assembled from colloidal microspheres of different materials by combining externally applied fields with geometric confinement. The coordinates of all particles will be visualized as a function of time, the underlying driving forces that stabilize colloidal quasicrystals will be determined, and nucleation and growth mechanisms will be identified. Complementary Monte Carlo and Brownian Dynamics simulations will be performed in parallel to interpret experimental observations. Finally, the photonic properties of the assembled quasicrystals in both visible and near-infrared light spectra will be measured. This project will offer an opportunity to search for physical principles that unify the formation of soft-matter quasicrystals over a broad range of length scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.