Metastable phase behavior of liquids with tetrahedral symmetry

Liquids with tetrahedral symmetry exhibit well-known structural, thermophysical and dynamic anomalies that arise from a competition between high-density and low-density local coordination structures in the fluid [1,2,3]. These... [ view full abstract ]

Liquids with tetrahedral symmetry exhibit well-known structural, thermophysical and dynamic anomalies that arise from a competition between high-density and low-density local coordination structures in the fluid [1,2,3]. These structures allow such systems to form both high-density and low-density glassy phases upon rapid cooling [1]. It has been posited that these experimentally observed glass phases relax into two distinct ergodic liquids at higher temperatures that undergo a first-order liquid-liquid phase transition (LLPT) [4].  Critical fluctuations associated with the LLPT are thought to have a significant influence on the phase behavior of these substances, even at conditions far away from liquid-liquid coexistence [1,4].  Although compositional LLPTs occur in mixtures, direct experimental observation of density-driven LLPTs in pure fluids has proved to be challenging because they are typically predicted to occur at conditions where the liquids are metastable with respect to crystallization [1].  Recent computational studies of molecular fluids demonstrate metastable LLPTs are possible [5], but they have not resolved the outstanding question of how such behavior can be characterized experimentally. 

Here, we discuss results from recent computational studies [6] that suggest the possibility of designing colloidal particles to exhibit experimentally observable LLPTs. Using advanced free energy techniques, we show that a binary mixture of charged particles can form two distinct tetrahedrally structured liquids that can be brought into phase coexistence [7].   The liquids are charge-neutral phases that have identical compositions but different densities. Consequently, our calculations demonstrate that the LLPT is density-driven and isomorphic to those that have been hypothesized for pure tetrahedral substances.  We also use simulation to elucidate the connection between the system’s LLPT and its distinct structural glasses.  Finally, we discuss alternative strategies for designing colloidal systems that exhibit glass polyamorphism and LLPTs [8].

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[2] JR Errington and PG Debenedetti, Nature 409, 318-321 (2001)

[3] MS Shell, PG Debenedetti and AZ Panagiotopoulos, Physical Review E 66, 011202 (2002)

[4] PH Poole, F Sciortino, U Essmann and HE Stanley Nature 360, 324-328 (1992)

[5] JC Palmer, F Martelli, Y Liu, R Car, AZ Panagiotopoulos and PG Debenedetti, Nature 510, 385-388 (2014)

[6] E Lascaris, Phys Rev Lett, in press (2016)

[7] R Chen, E Lascaris and JC Palmer, in preparation (2016)

[8] F Smallenburg, L Filion and F Sciortino, Nature Physics 10, 653-657 (2014)