Cornell University

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Uncovering hidden structural order in dense colloidal liquids in flat-space and melting of colloidal crystals on a sphere

The conventional wisdom is that liquids and glasses are completely disordered and lack any non-trivial structure. By using colloidal suspensions as a model system to probe the structure and dynamics of liquids and glasses at the single-particle level, I will present experimental findings that upend this view and reveal that the structural order in these systems is unusually rich. Using a recently introduced four-point correlation function, we will show that colloidal liquids have a highly non-trivial structure comprising alternating layers with icosahedral and dodecahedral order that grows with supercooling and governs dynamics. 

The latter part of the presentation addresses the problem of melting colloidal crystals on the surface of a sphere. Unlike the established two-step process in 2D flat-space melting, the mechanism on curved surfaces remains unknown. The inherent topology of curved surfaces introduces defects, such as icosahedral ordering of disclination defects on a sphere. Through in-situ tuning of interparticle interactions, we unveil the emergence of an intermediate hexatic phase during colloidal crystal melting on a sphere. Furthermore, unlike in flat-space, where disorder can fundamentally alter the nature of the melting process, on the sphere, we observed the signature characteristics of ideal melting.  

 

1. Navneet Singh et al., Intermediate-range order governs dynamics in dense colloidal liquids, Proceedings of the National Academy of Sciences, 120, no. 19 (2023): e2300923120. https://doi.org/10.1073/pnas.2300923120 

2. Navneet Singh et al., Observation of two-step melting on a sphere, Proceedings of the National Academy of Sciences, 119.32 (2022): e2206470119. https://doi.org/10.1073/pnas.220647011

Hosted by Itai Cohen. Please email kicnano@cornell.edu for Zoom details. 

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