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

Ning Wu

ningwu@mines.edu

Although atomic quasicrystals are predominantly intermetallic alloys, quasicrystalline structures have also been found in self-assembled soft materials including metal-organic frameworks, nanoparticles, micelles, and polymers. The length scales of these building blocks, however, range from 0.5 nm to 50 nm, which are smaller than the diffraction limit of visible light. As a result, it is extremely challenging to observe their formation directly. Recent experiments and simulations by the PIs demonstrated the first two-dimensional (2D) dodecagonal quasicrystals assembled by single-component microspheres under AC electric fields, which creates an opportunity to answer fundamental questions in quasicrystal formation, i.e., how does the long-range but aperiodic order emerge and evolve and what stabilizes low and high temperature quasicrystals, through optical characterization in both real space and real time.

Grand Challenge: Not applicable

This research offers an excellent opportunity to search for physical principles that unify the formation of soft-matter quasicrystals over a broad range of length scales. It is novel in several aspects. First, although numerous computational works suggest that quasicrystals can be formed via different types of colloidal interactions, experimental realization is extremely difficult. In contrast, our method relies on simple electric-field induced interactions, which are omnipresent in dielectric and metallic particle suspensions. Supported by our preliminary results, our work can lead to a general strategy to make 2D colloidal quasicrystals of different materials. Second, assembling quasicrystals from colloidal microspheres will allow us to directly observe, by using optical microscopy, the nucleation and growth of quasicrystals. Such an ability to probe quasicrystal nucleation, growth, stability, and phason dynamics by soft matter in real space and real time has not been achieved before. In particular, the proposed work will allow experimental determination of the role of phason modes in quasicrystal dynamics and stability, for which there are currently hypotheses and most observations are from simulation. Third, our proposed rare-event path-sampling simulations of quasicrystal nucleation, which do not rely on selecting pre-formed seeds as in prior works, can provide an unbiased quantitative determination of the nucleation mechanism and structure of the critical nuclei.

Xingrui Zhu