First-Order Liquid–Liquid Transition without Density Discontinuity in Molten Sodium Acetate Trihydrate and Its Influence on Crystallization

Abstract

Liquid–liquid transition (LLT) refers to the phase transition among thermodynamically distinct liquid states with identical composition in analogy to the polymorphic transition in solid. The growing awareness of its significance to understanding the nature of liquid also provokes curiosity about its potential impact on crystallization. Here, we report a first-order liquid–liquid transition above liquidus temperature in the melt of sodium acetate trihydrate using nuclear magnetic resonance, differential scanning calorimetry, and high-precision density measurements, which show negligible change in density associated with the observed LLT. Further, the kinetics and products of crystallization are significantly influenced by LLT, providing a new way for the controlling crystallization pathway and realizing crystal polymorph selection.

Pressure-induced liquid-liquid transition in a family of ionic materials

“…These small variations in the specific volume can be easily overlooked in direct V(T,P) measurements and reveal that density is not the dominant order parameter governing the LLT in ILs. This is in agreement with the experimental data recorded for sodium acetate trihydrate (CH 3 COONa•3H 2 O) where a first-order LLT without density discontinuity was identified 19 . Moreover, LLTs without density change were suggested to take place in several metallic glass-formers 44 .…”

“…Nevertheless, the LLT in these systems remains controversial since it occurs in the supercooled state capable of cold crystallization 18 . The theoretical and experimental observations show that a first-order LLT can occur without a noticeable density change, making this phenomenon even more puzzling 19 . Furthermore, magnetic field can affect the local structure and lead to another liquid phase 20 .…”

Glass-forming ability correlated with the liquid-liquid transition in Pd42.5Ni42.5P15 alloy

“…As T increases from 8 to 20 K (i.e., Tiso decreases from 1055 to 1043 K), the incubation time decreases rapidly from 240 s to 30 s. The inset shows the plot of log(Tiso / ) versus log(T), which can be well fitted with a linear function, indicating a power-law relation of iso / ( ) m TT   with m = 2.1. Similar power-law was also observed in the LLTs in La50Al35Ni15 liquid [22] and molten sodium acetate trihydrate [30].…”

Pressure-induced liquid-liquid transition in a family of ionic materials

“…This is in agreement with the experimental data recorded for sodium acetate trihydrate (CH3COONa•3H2O) where a first-order LLT without density discontinuity was identified. 17 Moreover, LLTs without density change were suggested to take place in several metallic glass-formers. 34 In summary, our findings provide experimental support for the hypothesis that the LLT occurs in ion-containing systems.…”

“…16 The theoretical permits and experimental observations that a first-order LLT can take place without a noticeable density change make this phenomenon even more puzzling. 17 At the same time, nothing is known about the effect of molecular packing on LLT, except for a…”