Structural Engineering and Optimization of Zwitterionic Salts for Expeditious Discovery of Thermoresponsive Materials.

Yen-Ho Chu,Chien-Yuan Chen,Jin-Syuan Chen

doi:10.3390/molecules27010257

Yen-Ho Chu, Chien-Yuan Chen + Show 1 more

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https://doi.org/10.3390/molecules27010257

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Abstract

This work reported the discovery of N-triflimide (NTf)-based zwitter-ionic liquids (ZILs) that exhibit UCST-type phase transitions in water, and their further structural optimization in fine-tuning polarity to ultimately afford newfangled thermosensitive materials carrying attractive and biocompatible Tc values that clearly demonstrated the true value of the tunability of ZIL structure. This research established that with non-aromatic, acyclic ZILs as small-molecule thermoresponsive materials, their mixing and de-mixing with water triggered by temperatures are entirely reversible.

Highlights

Thermoresponsive ionic liquids (TILs) belong to the class of stimuli-responsive, smart materials [1,2] that change properties with temperatures in their environment, and can be chemically devised to respond reversibly to external temperature changes [3,4,5]
It is envisioned that designing zwitter-ionic liquid (ZIL)-water systems showing thermoresponsive behavior should be highly attractive for applications involved in extraction and separation, since the ion pairs of zwitter-ionic liquids (ZILs) are fixed covalently even after adding other charged components [3,4]
UCST behavior; that is, IL 1 is immiscible with water at room temperature, but forms homogeneous solution at temperatures above 72 ◦ C [6]

Summary

Introduction

Thermoresponsive ionic liquids (TILs) belong to the class of stimuli-responsive, smart materials [1,2] that change properties with temperatures in their environment, and can be chemically devised to respond reversibly to external temperature changes [3,4,5]. These TILs display a miscibility gap in their temperature-composition phase diagram and, depending on whether the gap is found at high or low temperatures, an upper or lower critical solution temperature occurs (UCST or LCST), respectively. Both UCST and LCST systems are two typical phase behaviors of thermoresponsive materials with solvents [5]. In LCST systems, two immiscible solutions homogeneously mix upon cooling These TIL-water systems, have the potential to detract their properties as a result of unwanted ion pair formation through ion exchange after being mixed with other ions. It is envisioned that designing zwitter-ionic liquid (ZIL)-water systems showing thermoresponsive behavior should be highly attractive for applications involved in extraction and separation, since the ion pairs of ZILs are fixed covalently even after adding other charged components [3,4]

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