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

Zaneta Wojnarowska,Beibei Yao,Marian Paluch,Anne Mcgrogan,Malgorzata Swadzba-Kwasny,Shannon Mclaughlin,Shinian Cheng,Yoan Delavoux

doi:10.1038/s41467-022-29021-0

Abstract

Liquid−liquid transition (LLT) between two disordered phases of single-component material remains one of the most intriguing physical phenomena. Here, we report a first-order LLT in a series of ionic liquids containing trihexyl(tetradecyl)phosphonium cation [P666,14]+ and anions of different sizes and shapes, providing an insight into the structure-property relationships governing LLT. In addition to calorimetric proof of LLT, we report that ion dynamics exhibit anomalous behavior during the LLT, i.e., the conductivity relaxation times (τσ) are dramatically elongated, and their distribution becomes broader. This peculiar behavior is induced by isobaric cooling and isothermal compression, with the τσ(TLL,PLL) constant for a given system. The latter observation proves that LLT, in analogy to liquid-glass transition, has an isochronal character. Finally, the magnitude of discontinuity in a specific volume at LLT was estimated using the Clausius-Clapeyron equation.

Highlights

Liquid−liquid transition (LLT) between two disordered phases of single-component material remains one of the most intriguing physical phenomena
Aprotic ionic liquids (AILs)—a class of glass-formers composed solely of ions[25], give a unique opportunity to investigate the universality of LLT
By monitoring the relaxation dynamics of selected AILs under high-pressure conditions, we addressed the long-standing questions regarding the effect of compression on LLT and density fluctuations at TLL

Summary

Introduction

Liquid−liquid transition (LLT) between two disordered phases of single-component material remains one of the most intriguing physical phenomena. These findings lead to conclusion that the prominent peak observed in DSC thermograms of [P666,14][TFSI], [P666,14][TCM], and at lower temperature range for [P666,14] [SCN], and [P666,14][BH4] indicates the liquid–liquid phase transition (LLT).

Results

Conclusion