Entropy stabilizes floppy crystals of mobile DNA-coated colloids

TL;DR

This paper reveals that vibrational entropy stabilizes floppy crystal structures in mobile DNA-coated colloids, enabling new self-assembly pathways for designing functional materials with unique properties.

Contribution

It introduces a combined theoretical and simulation approach to understand how entropy stabilizes floppy phases in mobile DNA-coated colloids, a novel mechanism in colloidal self-assembly.

Findings

Stable floppy square and CsCl crystals are found at strong binding.

Vibrational entropy and floppy modes stabilize these phases.

Entropic effects differ from conventional molecular self-assembly.

Abstract

Grafting linkers with open ends of complementary single-stranded DNA makes a flexible tool to tune interactions between colloids,which facilitates the design of complex self-assembly structures. Recently, it has been proposed to coat colloids with mobile DNA linkers, which alleviates kinetic barriers without high-density grafting, and also allows the design of valency without patches.However, the self-assembly mechanism of this novel system is poorly understood.Using a combination of theory and simulation, we obtain phase diagrams forthe system in both two and three dimensional spaces, and find stable floppy squareand CsCl crystals when the binding strength is strong, even in the infinite bindingstrength limit. We demonstrate that these floppy phases are stabilized by vibrational entropy, and "floppy" modes play an important role in stabilizing the floppy phases for the infinite binding strength limit. This special entropic effect in the self-assembly of mobile DNA-coated colloids is very different from conventional molecular self-assembly, and it offers new axis to help design novel functional materials using mobile DNA-coated colloids.