Dynamic properties of nano-confined water in an ionic liquid

The Analysis of WJ Distribution as an Extended Gaussian Function: Case Study

The double exponential WJ distribution has been shown to competently describe extreme events and critical phenomena, while the Gaussian function has celebrated rich applications in many other fields. Here we present the analysis that the WJ distribution may be properly treated as an extended Gaussian function. Based on the Taylor expansion, we propose three methods to formulate the WJ distribution in the form of Gaussian functions, with Method I and Method III being accurate and self-consistent, and elaborate the relationship among the parameters of the functions. Moreover, we derive the parameter scaling formula of the WJ distribution to express a general Gaussian function, with the work illustrated by a classical case of extreme events and critical phenomena and application to topical medical image processing to prove the effectiveness of the WJ distribution rather than the Gaussian function. Our results sturdily advocate that the WJ distribution can elegantly represent a Gaussian function of arbitrary parameters, whereas the latter usually is not able to satisfactorily describe the former except for specific parameter sets. Thus, it is conclusive that the WJ distribution offers applicability in extreme events and critical phenomena as well as processes describable by the Gaussian function, namely, implying plausibly a unifying approach to the pertinent data processing of those quite distinct areas and establishing a link between relevant extreme value theories and Gaussian processes.

Evidence of supercoolable nanoscale water clusters in an amorphous ionic liquid matrix

Nanoscale water clusters in an ionic liquid matrix, also called "water pockets," were previously found in some mixtures of water with ionic liquids containing hydrophilic anions. However, in these systems, at least partial crystallization occurs upon supercooling. In this work, we show for mixtures of 1-butyl-3-methylimidazolium dicyanamide with water that none of the components crystallizes up to a water content of 72 mol. %. The dynamics of the ionic liquid matrix is monitored from above room temperature down to the glass transition by combining depolarized dynamic light scattering with broadband dielectric and nuclear magnetic resonance spectroscopy, revealing that the matrix behaves like a common glass former and stays amorphous in the whole temperature range. Moreover, we demonstrate by a combination of Raman spectroscopy, small angle neutron scattering, and molecular dynamics simulation that, indeed, nanoscale water clusters exist in this mixture.

Nanoconfined Fluids: What Can We Expect from Them?

Nanoconfined fluids (NCFs), which are confined in nanospaces, exhibit distinctive nanoscale effects, including surface effects, small-size effects, quantum effects, and others. The continuous medium hypothesis in fluid mechanics is not valid in this context because of the comparable characteristic length of spaces and molecular mean free path, and accordingly, the classical continuum theories developed for the bulk fluids usually cannot describe the mass and energy transport of NCFs. In this Perspective, we summarize the nanoscale effects on the thermodynamics, mass transport, flow dynamics, heat transfer, phase change, and energy transport of NCFs and highlight the related representative works. The applications of NCFs in the fields of membrane separation, oil and gas production, energy harvesting and storage, and biological engineering are especially indicated. Currently, the theoretical description framework of NCFs is still missing, and it is expected that this framework can be established by adopting the classical continuum theories with the consideration of nanoscale effects.

Atomistic Insights into the Layered Microstructure and Time-Dependent Stability of [BMIM][PF6] Confined within the Meso-Slit of Carbon

Clarifying the microstructures and time-dependent stability of ionic liquids (ILs) within the confinement of the meso-slit of carbon is the first step to understand the intrinsic synergy effect between ILs and a promising mesoporous carbon electrode. In this work, we adopted molecular dynamics to systematically investigate the behavior of [BMIM][PF₆] in the 2.8 nm-wide meso-slit of carbon. The confined ILs formed a pronounced layered spatial distribution and can be divided into three distinct regions, namely, com-, sub-, and cen-layer, according to valley coordinates in the number density profiles. In the com-layer region, the imidazolium rings of ILs possess two dominant orientations, namely, "parallel" and "tilted standing". The rotation ability of all the ions is highly restrained. In the sub-layer and cen-layer regions, a part of the [BMIM] imidazolium ring has a preferred "tilted standing" orientation. The [BMIM] cations are still in a rotational restrain state and show a preferred rotation motion along the x-y plane. The hydrogen bond between [BMIM] cations and [PF₆] anions play a crucial role in determining the confined multilayered spatial distribution and distinctive orientation properties of ILs.