Heptatic liquid quasi-crystals by colloidal lithographic pre-assembly

Area of Science:

• Soft Matter Physics
• Crystallography
• Materials Science

Background:

• Quasi-crystals (QCs) exhibit symmetries not found in traditional crystals.
• Understanding phase transitions in complex particle assemblies is crucial.
• Brownian dynamics in confined or dense systems present unique challenges.

Purpose of the Study:

• To investigate the emergence of a heptatic liquid quasi-crystal (LQC) phase from pre-assembled lithographic seven-fold QCs.
• To analyze the heterogeneous dynamics and structural hierarchy within the LQC phase.
• To explore novel methods for analyzing complex particle assemblies.

Main Methods:

• Fabrication of seven-fold QCs using lithographically pre-assembled monolayers (litho-PAMs) with three rhombic tile shapes.
• High-resolution optical microscopy for spatio-temporal particle tracking of Brownian fluctuations.
• Development of an edge-proximity tessellation method for analyzing nearest neighbors in dense systems.

Main Results:

• Identification of a fluctuating heptatic LQC phase at high tile area fractions.
• Observation of heterogeneous dynamics and multi-length scale order, indicating hierarchical motif structures.
• Demonstration of collective motif rotations, analogous to phason-flips, leading to gradual order loss.

Conclusions:

• The heptatic LQC phase emerges from dense colloidal quasi-crystals and displays complex dynamics.
• Hierarchical structures and collective dynamics are key features of this LQC phase.
• Edge-proximity tessellation is a promising tool for studying phase transitions in geometrically complex systems.