Interfacial Rheology and Structure of Tiled Graphene Oxide Sheets

The hydrophilic nature of graphene oxide sheets can be tailored by varying the carbon to oxygen ratio. Depending on this ratio, the particles can be deposited at either a water–air or a water–oil interface. Upon compression of thus-created Langmuir monolayers, the sheets cover the entire interface, assembling into a strong, compact layer of tiled graphene oxide sheets. With further compression, the particle layer forms wrinkles that are reversible upon expansion, resembling the behavior of an elastic membrane. In the present work, we investigate under which conditions the structure and properties of the interfacial layer are such that free-standing films can be obtained. The interfacial rheological properties of these films are investigated using both compressional experiments and shear rheometry. The role of surface rheology in potential applications of such tiled films is explored. The rheological properties are shown to be responsible for the efficiency of such layers in stabilizing water–oil emulsions. Moreover, because of the mechanical integrity, large-area monolayers can be deposited by, for example, Langmuir–Blodgett techniques using aqueous subphases. These films can be turned into transparent conductive films upon subsequent chemical reduction

Magnetomigration of Rare-Earth Ions Triggered by Concentration Gradients

Mach–Zehnder interferometry was applied to explore the effects of inhomogeneous magnetic fields on the mobility of rare-earth ions in aqueous solutions. No migration of ions was observed in a thermodynamically closed system when a homogeneous solution was subjected to a magnetic field gradient alone. However, magnetomigration could be triggered by a concentration gradient of the rare-earth ions in the solution. When a concentration gradient was introduced in the sample by solvent evaporation, consistent migration of paramagnetic Dy³⁺ ions from the bulk solution to regions with stronger magnetic fields was observed. By contrast, no movement was detected for diamagnetic Y³⁺ ions in the presence of a concentration gradient

Solvation Structure of Sodium Bis(fluorosulfonyl)imide-Glyme Solvate Ionic Liquids and Its Influence on Cycling of Na-MNC Cathodes

Electrolytes consisting of sodium bis­(fluorosulfonyl)­imide (NaFSI) dissolved in glymes (monoglyme, diglyme, and triglyme) were characterized by FT-Raman spectroscopy and ¹³C, ¹⁷O, and ²³Na NMR spectroscopy. The glyme:NaFSI molar ratio was varied from 50:1 to 1:1, and it was observed that, in the dilute electrolytes, the sodium salt is completely dissociated into solvent separated ion pairs (SSIPs). However, contact ion pairs (CIPs) and aggregates (AGGs) become the predominant species in more concentrated solutions. Some of the electrolytes with the highest concentrations can be classified as solvate ionic liquids (SILs), where all of the solvent molecules are coordinated to sodium cations. Therefore, these electrolytes are fundamentally different from more dilute electrolytes which are typically used in commercially available secondary batteries. The melting point or glass transition temperature, dynamic viscosity, density, sodium concentration, and ionic conductivity of these solvate ionic liquids are reported as well as the crystal structures of [Na­(G3)]­[FSI] and [Na­(G3)₂]­[FSI]. Galvanostatic cycling experiments were performed in coin-type cells with a Na_2/3[Mn_0.55Ni_0.30Co_0.15]­O₂ cathode to study the influence of these electrolytes on the electrochemical stability and charge/discharge behavior

Electrodeposition of Lithium from Lithium-Containing Solvate Ionic Liquids

Lithium-containing solvate ionic liquids [Li­(L)_<i>n</i>]­[X], with ligands L = 1,2-dimethoxyethane (G1, monoglyme) or 1-methoxy-2-(2-methoxyethyl)­ether (G2, diglyme) (with <i>n</i> = 1, 2 or 3) and with anions X = bis­(trifluoromethylsulfonyl)­imide (Tf₂N^–), bromide (Br^–) or iodide (I^–), were synthesized and used as electrolytes for the electrodeposition of lithium metal. Very high lithium-ion concentrations could be obtained, since the lithium ion is part of the cationic structure of the solvate ionic liquids. Without stirring, current densities up to −26 A dm^–2 at a potential of −0.5 V vs Li/Li⁺ were registered during cyclic voltammetry. The formation of a solid–electrolyte interface during electrodeposition of lithium from [Li­(G1)₂]­[Tf₂N] was studied by electrochemical quartz microbalance and Auger electron spectroscopy. SEM pictures revealed uniform and nondendritic lithium deposits

Electrochemical Film Deposition of the Zirconium Metal–Organic Framework UiO-66 and Application in a Miniaturized Sorbent Trap

Film deposition is an enabling technology for integration of novel functional materials into real-world practical applications. We report both the anodic and cathodic electrochemical film deposition of UiO-66, a prototype of highly stable, zirconium-based metal–organic frameworks, using zirconium foil as the only metal source. The fundamentally different film formation mechanisms at the cathode and anode result in a significantly different coating adhesion strength, mainly due to the formation of an oxide film serving as a bridging layer at the anode. The patterned deposition capability of the electrochemical method enables the straightforward integration of UiO-66 as a sorbent film in a miniaturized sorbent trap for online analytical sampling and concentration of dilute volatile organic compounds