paper

Hierarchies of networked phases induced by multiple liquid-liquid critical points

arXiv:0808.3361 · doi:10.1073/pnas.0804854105

Abstract

Functionalization of nanoparticles or colloids is increasingly being used to develop customizable "atoms". Functionalization by attaching single strands of DNA allows for direct control of the binding between nanoparticles, since hybridization of double strands will only occur if the base sequences of single strands are complementary. Nanoparticles and colloids functionalized by four single strands of DNA can be thought of as designed analogs to tetrahedral network forming atoms and molecules, with a difference that the attached DNA strands allow for control of the length scale of bonding relative to the core size. We explore the behavior of an experimentally realized model for a nanoparticles functionalized by four single strands of DNA (a tetramer), and show that this single-component model exhibits a rich phase diagram with at least three critical points and four thermodynamically distinct amorphous phases. We demonstrate that the additional critical points are part of the Ising universality class, like the ordinary liquid-gas critical point. The dense phases consist of a hierarchy of interpenetrating networks, reminiscent of a woven cloth. Thus bonding specificity of DNA provides an effective route to generate new nano-networked materials with polyamorphic behavior. The concept of network interpenetration helps to explain the generation of multiple liquid phases in single-component systems, suggested to occur in some atomic and molecular network forming fluids, including water and silica.

To appear in PNAS week of Aug. 25, 2008

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