Two-Dimensional Ordering of Ionic Liquids Confined by Layered Silicate Plates via Molecular Dynamics Simulation

Abstract

Recent experiments and computer simulation studies on nano-confined ionic liquids(ILs) has shifted the focus from perpendicular to lateral distribution, the understanding of which is crucial for ILs performance in the field of energy storage system and tribology. In this article, the structure of 1-ethyl-3-methylimidazolium Bromide, [Emim][Br], confined by hydroxyl group functionalized surface of kaolinite plates has been studied by molecular dynamics simulation. Depending on the degree of confinement, ILs anion can pack into a 2D ordered structure with square symmetry, coexisted liquid/solid phase or liquid-like structure. The ordered structure arises from surface-induced ionic orientational preference and the driving force from confinement that supports the formation of 2D planar structure. The flexible H-bond formed between Br and surface hydroxyl group at fixed d-spacing results in the liquid-like ordering that breaks down the electrostatic network in ILs. The influence of water addition varies when confining plates are treated differently, namely forming large H-bonding network and small isolated oligomers, for relaxed and fixed d-spacing, respectively. This work reveals additional information about the relative importance of factors like packing constrains, interaction within ILs and selective attraction in determining the structure and dynamics of confined ILs.

Preparation and Comparative Stability of a Kaolinite-Tetrabutylphosphonium Bromide Intercalation Compound for Heat and Solvent Treatments

“…The TG curve of Kaol-TBPBr showed a mass loss at 300–400 °C, while the TG curve of Kaol-TBABr showed a mass loss at 200–300 °C. It is well-known that organophosphonium salts exhibit much higher thermal stability than the corresponding organoammonium salts, − for which the following three reasons have been proposed: first, the P–C bonds in organophosphonium salts are more covalent than the N–C bonds in organoammonium salts; second, the empty d orbitals of the central phosphorus atoms contribute to a greater increase in bond strength between the phosphorus cations and counter anions in organophosphonium salts while no d orbital is available for nitrogen atoms in organoammonium salts; ,− and third, less volatile species such as polyphosphate, phosphine, and phosphine oxide-based compounds are formed upon thermal decomposition of organoammonium salts. ,,− As regards the decomposition mechanisms, some reactions for the decomposition of intercalated organophosphonium and organoammonium ions in the interlayer spaces of montmorillonite have been proposed by Vaia and co-workers. , The central phosphorus atoms of organophosphonium ions were less affected by the decomposition reactions than the central nitrogen atoms in organoammonium ions, due to the larger steric tolerance of central phosphorus atoms than central nitrogen, leading to higher thermal stability of intercalated organophosphonium ions . Thus, these could explain the higher thermal stability of TBPBr between the layers of kaolinite.…”

Clay Minerals—Ionic Liquids, Nanoarchitectures, and Applications

“…Methoxy‐kaolinite was also used as a precursor to intercalate bulky ammonium derivatives such as benzylalkylammonium chlorides . A molecular dynamics study on the interface between imidazolium‐based ILs and kaolinite was recently performed, relating the degree of confinement to the type of packing, going from ordered to liquid‐like structures . Terahertz time‐domain spectroscopy was demonstrated to afford useful information on the structural configurations of an imidazolium IL intercalated in kaolinite and in halloysite, indicating different configurations in the two intercalates …”

Expansion of orderly stacked metakaolinite layers and order destruction using a kaolinite-tetraphenylphosphonium chloride intercalation compound

“…Although metakaolinite can be obtained aer grinding of kaolinite and/or its intercalation compounds and subsequent heat treatment, the grinding for approximately 15 min is more facile; no disappearance of the diffraction line of pristine kaolinite was observed upon mechanochemical grinding using a planetary mill for 6 h. 13,14 Additionally, diffraction lines due to expanded kaolinite layers in the intercalation compounds appeared upon the milling for 2-6 h. 13,14 The intercalated carbonaceous material derived from acrylamide thermal polymerization at 620 C partially suppressed the conversion of kaolinite into metakaolinite, because of the hydrogen bond formation between the C]O groups of the carbonaceous material and the interlayer hydroxy groups of kaolinite. 17 By contrast, the weak interaction of TPhPCl and the interlayer hydroxyls of kaolinite, which is similar to those of kaolinite-organic salt intercalation compounds, 25,27,40,41 is thus likely to facilitate the conversion of kaolinite into metakaolinite, as can be concluded from the following results; (1) the XRD pattern of the present metakaolinite shows no diffraction lines attributed to kaolinite (Fig. 1e), whereas pristine kaolinite heated at 540 C showed kaolinite diffraction lines; 17 (2) the 27 Al MAS NMR spectrum of the present metakaolinite (Fig.…”