A Fluctuating Brownian Quasi-Crystal of Lithographically Pre-Assembled Colloidal Penrose Tiles
Thomas Mason, University of California, Los Angeles -- A beautiful example of a hierarchically organized multi-scale structure is Penrose's five-fold P2 quasi-crystal (QC). Kites and darts are organized locally into motifs, such as pentagonal stars. These motifs in turn are organized into a variety of superstructural patterns that become increasingly complex at larger length scales. Since self-assembly of a five-fold soft matter quasi-crystal has remained elusive, we instead create a Brownian Penrose QC in 2D through highly parallel lithographic printing and release of particles into a solution-dispersion containing a depletion agent. Using optical microscopy, we study the equilibrium fluctuations and melting of this P2 QC, thereby revealing signatures of a 'pentatic' liquid quasi-crystal (LQC5). The combination of multi-particle shape-designed fabrication, pre-assembly, and specialized release yields lithographically pre-assembled monolayers (litho-PAMs) of mobile tiles. These tiles can have sizes, shapes, and initial positions and orientations with multi-scale complexity at high densities, beyond current self- or directed-assembly methods. We envision that litho-PAMs will be useful for directly creating and studying other interesting multi-scale physical systems that would be problematic to obtain through existing assembly methods.