Transition Mechanism from the Metastable Two-Dimensional Gel to the Stable Three-Dimensional Crystal of Imidazolium-Based Ionic Liquids

Abstract

One important quest for making high quality materials with amphiphiles is to understand how a disordered self-assembly changes to a stable crystalline state. Herein, we addressed the basic question by investigating the phase transition mechanism of imidazolium-based ionic liquid (IL) [C 16 mim]Br, using time-resolved small-and wide-angle X-ray scattering (SAXS-WAXS), differential scanning calorimetry, and Fourier transform infrared spectroscopy techniques. Totally, a hexagonal phase, two lamellar-gel phases, and three lamellar-crystalline phases were observed, showing the special polymorphism of the system. It was demonstrated that at low concentrations the two-dimensional gel phase (L β1 ) transforms into the most stable lamellar-crystal phase (L c3 ) through two intermediate crystalline phases L c1 and L c2 . At high concentrations, the L β1 phase changes to a condensed lamellar gel phase (L β2 ) before changing to L c2 and eventually to L c3 . Comparative studies using [C 16 mim]Cl and [C 16 mim]NO 3 unveiled that the interactions between the counterions and the headgroups of the IL, as well as the dehydration process, govern the nucleation process of L c3 and thus the formation of the crystal. The in-depth investigation on the transition mechanism and the phase polymorphism in the present work advances our understanding of the crystallization of amphiphilic ionic liquids in dispersions and would promote future applications.

Efficient and Selective Dissolution of Li from Lithium-Ion Battery LiFePO4 Cathode by Natural Deep Eutectic Solvents

“…However, many other DESs are not so green and even not eutectic. , Particularly, Chen and Yu for the first time propose a new concept as low-melting mixture solvents (LoMMSs) for extending DESs; it is because the evidence of phase diagram for DESs is difficult and time-consuming. Compared with ionic liquids (ILs), DESs own the merits of easy synthesis and high atomic efficiency; both ILs and DESs are highly tunable and applied in many areas. ,− This research provides valuable guidance for the development of a green, mild, natural, and efficient process for achieving sustainable recovery of spent LFP-based LIBs.…”

A Novel Strategy for the Characterization of Self-Assembled Structures Using the Static Solid-State Phosphorus Nuclear Magnetic Resonance Technique

“…By employing amphiphilic ionic surfactants, [C 16 mim]Cl and [C 16 mim]­Br, as model systems, we demonstrated the identification of three types of self-assembled structures through their distinct 31 P NMR signals. The new method is relatively easy to access and inexpensive compared with other techniques such as SAXS, WAXS, , small-angle neutron scattering (SANS), , freeze-fracture electron microscopy, − and cryo-electron microscopy. , For the microscopic methods, samples need to be frozen quickly to make replicas for examination, while for the spectroscopic 31 P NMR, SAXS, and SANS methods, samples can be examined as they are. For the new NMR method, the data can be used straightforwardly to characterize the self-assembly structures, which is more convenient than SAXS and SANS.…”