Observation of two-step melting on a sphere

Singh, N and Sood, AK and Ganapathy, R (2022) Observation of two-step melting on a sphere. In: Proceedings of the National Academy of Sciences of the United States of America, 119 (32).

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Abstract

Melting in two-dimensional flat space is typically two-step and via the hexatic phase. How melting proceeds on a curved surface, however, is not known. Topology mandates that crystalline particle assemblies on these surfaces harbor a finite density of defects, which itself can be ordered, like the icosahedral ordering of 5-coordinated disclination defects on a sphere. Thus, melting even on a sphere, the simplest closed surface, involves the loss of both crystalline and defect order. Probing the interplay of these two forms of order, however, requires a system in which melting can be performed in situ, and this has not been achieved hitherto. Here, by tuning interparticle interactions in situ, we report an observation of an intermediate hexatic phase during the melting of colloidal crystals on a sphere. Remarkably, we observed a precipitous drop in icosahedral defect order in the hexatic phase where the shear modulus is expected to vanish. 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. Our findings have profound implications for understanding, for instance, the self-assembly and maturation dynamics of viral capsids and also phase transitions on curved surfaces.

Item Type:	Journal Article
Publication:	Proceedings of the National Academy of Sciences of the United States of America
Publisher:	National Academy of Sciences
Additional Information:	The copyright for this article belongs to the National Academy of Sciences.
Keywords:	article; colloid; melting point; phase transition; virus capsid; chemistry; freezing, Colloids; Freezing
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	30 Aug 2022 05:39
Last Modified:	30 Aug 2022 05:39
URI:	https://eprints.iisc.ac.in/id/eprint/76268

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