Liquid-liquid transition in sulfur: evolution of the shear viscosity in the low- and high- density liquids.

A liquid-liquid transition (LLT) is a first-order transition separating two liquid phases of the same single-component substance with different densities. Despite the long-standing and wide interest in this phenomenon, it remains poorly understood and unambiguous experimental realizations are scarce. The present proposers reported in 2020 the experimental discovery of a LLT in compressed liquid sulphur in the range 0-2.15 GPa, 450-1040 K [1]. Moreover, we conveyed evidence for a critical point ending the LLT line, long-sought in the case of water and never observed in any other system so far. The present proposal aims at better understanding the driving mechanisms and order parameter of the LLT in sulfur by measuring the shear viscosities of the low-density and high-density liquids from 0.2 to 2.5 GPa, using the falling sphere technique in the Paris-Edinburg press.

液液相变（liquid-liquid transition, LLT）是一类一级相变，可将同一种单组分物质的两个密度不同的液态相分隔开来。尽管该现象长期以来受到广泛关注，但学界对其认知仍较为匮乏，且明确的实验实现案例寥寥无几。本研究团队于2020年报道了在0~2.15吉帕斯卡（GPa）、450~1040开尔文（K）的压缩液态硫中发现液液相变的实验结果[1]。此外，该团队还提供了实验证据，证明存在一条终结液液相变线的临界点——这一临界点是水体系中长久以来备受追寻，却迄今未在其他任何体系中观测到的关键特征。本项提案旨在通过使用巴黎-爱丁堡压机（Paris-Edinburg press）中的落球法（falling sphere technique），在0.2~2.5吉帕斯卡的压力范围内测量低密度与高密度液态硫的剪切黏度，从而进一步阐明硫中液液相变的驱动机制与序参量。