Ionic Liquid Droplets Research Articles

Study of Wetting Behavior of BMIM+/PF6– Ionic Liquid on TiO2 (110) Surface by Molecular Dynamics Simulation

In the present work, wetting behavior of an ionic liquid droplet containing 1-methyl-3-butylimidazolium and fluorophosphate on the titanium dioxide (110) surface is studied using a molecular dynamics simulation. On the basis of the anisotropic characteristics of titanium dioxide surface, contact angles were calculated along different directions which are in agreement with experimental data. The obtained results show that a cation-rich layer is spread on the surface. Imidazolium rings of cations of ionic liquid are parallel to the titanium dioxide surface, but their orientation in the upper layer is almost vertical. Such positioning leads to the butyl-ring substituents locating at the top of the first layer to create a relatively empty space of cations while resulting in an anion-rich region. The cations and anions form a spherical shape on top of the first layer. Cross-sectional analysis of the ionic liquid reveals the circular configuration of cations and anions within the nanodroplet. The above observat...

Thermophoretic transport of ionic liquid droplets in carbon nanotubes

Thermal-gradient induced transport of ionic liquid (IL) and water droplets through a carbon nanotube (CNT) is investigated in this study using molecular dynamics simulations. Energetic analysis indicates that IL transport through a CNT is driven primarily by the fluid–solid interaction, while fluid–fluid interactions dominate in water–CNT systems. Droplet diffusion analysis via the moment scaling spectrum reveals sub-diffusive motion of the IL droplet, in contrast to the self-diffusive motion of the water droplet. The Soret coefficient and energetic analysis of the systems suggest that the CNT shows more affinity for interaction with IL than with the water droplet. Thermophoretic transport of IL is shown to be feasible, which can create new opportunities in nanofluidic applications.

Electrodeposition of Si from an Ionic Liquid Bath at Room Temperature in the Presence of Water.

The electrochemical deposition of Si has been carried out in an ionic liquid medium in the presence of water in a limited dry nitrogen environment on highly oriented pyrolytic graphite (HOPG) at room temperature. It has been found that the presence of water in ionic liquids does not affect the available effective potential window to a large extent. Silicon has been successfully deposited electrochemically in the overpotential regime in two different ionic liquids, namely, BMImTf2N and BMImPF6, in the presence of water. Although a Si thin film has been obtained from BMImTf2N; only distinguished Si crystals protected in ionic liquid droplets have been observed from BMImPF6. The most important observation of the present investigation is that the Si precursor, SiCl4, instead of undergoing hydrolysis, even in the presence of water, coexisted with ionic liquids, and elemental Si has been successfully electrodeposited.

Fabrication of ionic liquid gel beads via sequential deposition

In this paper, we demonstrate the fabrication of gel beads composed of ionic liquid (IL) and polymer. The IL droplets are kept spherical during the deposition process by placement onto chromatography paper coated with fluoropolymer. The deposition process then occurs in two steps. In the first step, the monomer is absorbed into the IL droplet. In the second step, the initiator radicals are introduced. This sequential deposition process allows polymerization to primarily occur within the liquid droplet and therefore the beads are not attached to the underlying substrate and can be easily removed.

Liquid Droplet for Motion Sensing

In this letter, inspired by the structure of a utricle/ balloon within the vestibular system as a body balance organ, a device with a droplet of ionic liquid (IL) for motion sensing is designed and fabricated. The droplet of IL serves as the inertial mass, and active carbon is used as the electrodes. The fabricated motion-sensing device with a droplet of IL ( $\sim 15~\mu \text{L}$ ) in a micro-square-groove ( $\textsf {2}~ \textsf {mm} \times \textsf {3}~ \textsf {mm} \times \textsf {5} ~ \textsf {mm}$ ) and two coaxial parallel active-carbon electrodes can successfully detect low-frequency acceleration, even without signal amplification. A voltage signal with a magnitude of millivolts is detected across the system load ${R}_{L}$ . In the frequency range of 2.5 to 11.75 Hz, the resonant frequency of the device is measured as 7.13 Hz, and the peak output voltage across ${R}_{L}$ is 10.2 mV. This motion-sensing system is promising for future stretchable electronic systems with bionic micro-fluidic sub-structures.

Smart magnetic ionic liquid-based Pickering emulsions stabilized by amphiphilic Fe3O4 nanoparticles: Highly efficient extraction systems for water purification

This study presents the general method to formulate magnetically responsive ionic liquid (IL)-based Pickering emulsions that are stabilized by amphiphilic Fe3O4 nanoparticles. The magnetic nanoparticle stabilizer (MN-CHOL) was synthesized using the surface-initiated ATRP method with further modification that uses a specially designed cholesteryl derivative, and characterized by FT-IR, XPS, TGA, and magnetization measurements. It is confirmed that the resulting MN-CHOL shows a stronger interfacial activity, efficiently emulsifying C4mim [PF6] and water, and resultantly forming stable Pickering emulsions without the help of any co-surfactant. Due to its super paramagnetism and high saturation magnetization, MN-CHOL attached on the IL interface enables droplets of IL to be moved very conveniently on their target for as many times by an external magnetic field without demulsification, indicating high controllability and excellent stability. The resulting Pickering emulsion is a good extraction system that efficiently separates chlorobenzene, phenol, and methyl orange from aqueous solution. Subsequently, the simple magnetic separation was applied, to produce purified water due as a result of the rapid removal of organic pollutants from contaminated water.

Electrotactic ionic liquid droplets

To our knowledge, this work describes the first example of electro-guided, self-propelled droplets composed solely of an ionic liquid (IL), namely trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These self-propelled droplets travel along an aqueous-air boundary to desired destinations within the fluidic network. Electrotactic movement of the droplets is due to asymmetric electro-stimulated release of a constituent of the IL droplet, the [P6,6,6,14]+ ion, which is a very efficient cationic surfactant, through electrochemically generated Cl− gradients. The direction and speed of movement can be controlled by switching the impressed voltage (typically 5 − 9V) ON or OFF, and by changing the polarity of the electrodes in contact with the electrolyte solution.The Cl− gradients required for droplet movement are electrochemically generated using 3D printed electrodes which are embedded within the fluidic channels. On demand creation of these Cl− gradients electrochemically allows reversible droplet movement over expended periods of time, and provides a means for precise control over the droplet trajectory.

Molecular Dynamics Simulations of the Influence of Drop Size and Surface Potential on the Contact Angle of Ionic-Liquid Droplets

In this work we have performed molecular dynamics simulations of the room temperature ionic-liquid 1-ethyl-3-methylimidazolium tetrafluoroborate on a surface with graphene structured sheets. Contact angles were calculated via polynomial-fitting of two-dimensional atomic density contours. Drop size and surface interaction were varied to assess their influences on the contact angle. At low graphene interaction potential, no change in contact angle with drop size was found. When increasing the surface interaction potential toward actual graphene, the drops deviated to fully wetting, but the spreading rate and extent became dependent on drop size. The smallest drop formed a single adsorbed layer due to its initial size and the large ratio of ions in the adsorbed layer. Larger drops wetted and formed nonuniform metastable drops upon several layers of spread liquid. These were not true equilibrium structures as when starting from a single adsorbed layer film at room temperature, the metastable layers were not r...

Controlled formation and coalescence of paramagnetic ionic liquid droplets under magnetic field in coaxial microfluidic devices

This article reports the scaling law of droplet formation of the paramagnetic ionic liquid (MIL) under magnetic field in a coaxial microfluidic device. Firstly, the effect of two phase flow rates and magnetic forces on the size of MIL droplet in a coaxial microfluidic device were studied systematically. Then, based on force analysis, a mathematical model for the prediction of the diameter of MIL droplets was developed. Furthermore, a novel method which can achieve in-situ formation and controlled coalescence of droplets was developed by using a designated magnetic field.

Novel Inverse Supported Ionic Liquid Absorbents for Acidic Gas Removal from Flue Gas

This work reports on the astonishing high capacity of inverse supported ionic liquid absorbents, hereinafter denoted as “inverse SILPs” to remove acidic gases (SO2 and CO2) from flue gas streams. These nonconventional SILPs are easily prepared in the form of flowing powder via a phase inversion technique and consist of tiny ionic liquid (IL) droplets enclosed into an ultrathin, porous solid sleeve of pyrogenic silica nanoparticles. The CO2/N2 and SO2/CO2 separation performance and regeneration efficiency of inverse SILPs developed from six different ILs and two IL/chitosan ionogels was examined via gravimetric CO2, N2 absorption isotherms and via SO2, CO2, O2 breakthrough curves from gas mixtures in fixed beds. The involved ILs varied from chemisorbing ones, composed of alkyl- or alkanol-ammonium cations and amino acid anions, to physisorbing ones including ether functionalized anions and 1-alkyl-3-methylimidazolium cations. It is noteworthy that the best performing inverse SILP consisted of a very common...

No migration of ionic liquid under temperature gradient

Droplet migration under temperature gradient is ubiquitous throughout science and engineering. For the molecular type lubricants, the migration performance can be well described by a dynamic model based on Marangoni effects. However, no migration of ionic liquid droplet was observed under temperature gradient. The abnormal behavior may originate from a combination of ordering structure of ions in the interfaces as well as the Coulombic interactions in interior part. The finding reinforces the possibility of ionic liquid as lubricant.

Epitaxial growth of atomically flat KBr(111) films via a thin film ionic liquid in a vacuum

The NaCl-type crystal (111) polar face is electrostatically so unstable that its atomically flat (111) surface has been difficult to obtain so far. In this work, based on our preliminary results on flat KBr(111) microcrystals on an α-Al2O3(0001) substrate grown via ionic liquid droplets by vacuum deposition, we have achieved atomically flat, epitaxial KBr(111) films grown all over an α-Al2O3(0001) substrate. The key point to this success is the great improvement in the wettability of the ionic liquid on the substrate by introducing an amorphous-like “wetting layer”. Furthermore, in situ growth monitoring by means of an optical microscope with a long-distance focus lens reveals the growth process in the ionic liquid: random nucleation occurs directly on the substrate, but not in the ionic liquid, and subsequently, the nucleated KBr islands grow more rapidly in the in-plane direction rather than in the out-of-plane direction to coalesce with each other, forming a continuous KBr film over the substrate. The lateral overgrowth mechanism is proposed to explain the epitaxial growth of KBr(111) films even on the amorphous-like wetting layer/α-Al2O3(0001) substrate on the basis of a cross-sectional TEM observation.

ゲル化イオン液体によるエナジーハーベスタ応用

We propose a high power-output vibrational energy harvester based on ionic liquid. Ionic liquid enables a very large capacitance (1.0-10 µF cm-2) on the electrode at a bias voltage less than 1.9 V due to its extremely thin (∼ 1 nm) electrical double layer. By mechanical squeezing and dragging the ionic liquid droplet that was solidified with a polymer additive, between a pair of electrodes at 15 Hz, we stably obtained a current output of 22 µA cm-2 at 1.5 V.

Nanowetting of Graphene by Ionic Liquid Droplets

The behavior of nanodroplets formed by amino acid based 1-ethyl-3-methylimidazolium glycine ionic liquid on graphene sheets was studied using classic molecular dynamics. Nanodroplets of different sizes were analyzed, and the contact angle was inferred. The ion–graphene interaction energy was calculated as a function of droplets size, together with the ions arrangement at the interface. Likewise, wetting of SiO2 and graphene supported on SiO2 by ionic liquid nanodroplets was also analyzed. Graphene wetting by this ionic liquid is discussed in terms of the changes on fluid structure upon adsorption and the mechanism and strength of ion–graphene interactions.

Microfluidic room temperature ionic liquid droplet generation depending on the hydrophobicity and interfacial tension

We have characterized micro-droplet generation using water immiscible hexafluorophosphate ([PF6])- and bis(trifluoromethylsulfonyl)imide ([Tf2N])-based room temperature ionic liquids (RTILs). The interfacial tension between total 7 RTILs and phosphate buffered saline (PBS) was measured using a tensiometer for the first time. PBS is one of the most commonly used buffer solutions in cell-related researches. The measured interfacial tension ranges from 8.51 to 11.62 and from 9.56 to 13.19 for [Tf2N]- and [PF6]-based RTILs, respectively. The RTILs micro-droplets were generated in a microfluidic device. The micro-droplet size and generation frequency were determined based on continuous monitoring of light transmittance at the interface in microchannel. The size of RTIL micro-droplets was inversely proportional to the increase of PBS solution flow rate and RTILs hydrophobicity, while droplet generation frequency was proportional to those changes. The measured size of RTILs droplets ranged from 0.6 to 10.5 nl, and from 1.0 to 17.1 nl for [Tf2N]- and [PF6]-based RTILs, respectively. The measured frequency of generated RTILs droplets ranged from 2.3 to 37.2 droplet/min, and from 2.7 to 17.1 droplet/min for [Tf2N]- and [PF6]-based RTILs, respectively. The capillary numbers were calculated depending on the RTILs, and ranged from 0.51×10-3 to 1.06×10-3 and from 5.00×10-3 to 8.65×10-3, for [Tf2N]- and [PF6]-based RTILs, respectively. The interfacial tension between RTILs and PBS will contribute to developing bioprocesses using immiscible RTILs. Also, the RTILs micro-droplets will enable the high-throughput monitoring of various biological and chemical reactions using RTILs as new reaction media.

Preconcentration and determination of lead and cadmium levels in blood samples of adolescent workers consuming smokeless tobacco products in Pakistan

The present study was aimed to evaluate the cadmium (Cd) and lead (Pb) levels in the blood samples of adolescent boys, chewing different smokeless tobacco (SLT) products in Pakistan. For comparative purpose, boys of the same age group (12-15years), not consumed any SLT products were selected as referents. To determine trace levels of Cd and Pb in blood samples, a preconcentration method, vortex-assisted liquid-liquid microextraction (VLLME) has been developed, prior to analysis by flame atomic absorption spectrometry. The hydrophobic chelates of Cd and Pb with ammonium pyrrolidinedithiocarbamate were extracted into the fine droplets of ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate, while nonionic surfactant, Triton X-114 was used as a dispersing medium. The main factors affecting the recoveries of Cd and Pb, such as concentration of APDC, centrifugation time, volume of IL and TX-114, were investigated in detail. It was also observed that adolescent boys who consumed different SLT products have 2- to 3-fold higher levels of Cd and Pb in their blood samples as compared to referent boys (p < 0.001).

Mirrorless dye doped ionic liquid lasers.

The study of electromagnetic waves propagation in periodically structured dielectrics and the linear and nonlinear optical phenomena in disordered systems doped with gain media represent one of the most challenging and exciting scientific areas of the past decade. Lasing and Random Lasers (RL) are fascinating examples of topics that synergize multiple scattering of light and optical amplification and lately have been the subject of intense theoretical and experimental studies. In this manuscript we demonstrate laser action in a new category of materials, namely dye doped ionic liquids. Ionic liquids prove to be perfect candidates for building, as shown, a series of exotic boundaryless or confined compact laser systems. Lasing is presented in standard wedge cells, freely suspended ionic liquid films and droplets. The optical emission properties are investigated in terms of spectral analysis, below and above lasing energy threshold behavior, emission efficiency, far field spatial laser modes intensity profiling, temporal emission behavior etc. As demonstrated, these materials can be employed as optimal near future replacements of conventional flammable solvents in already available dye laser instruments.

J2220106 凝着力計測によるイオン液体硬化過程の評価

Ionic liquid (IL) is a kind of molten salt, which has negligible vapor pressure. Therefore IL can be utilized as a support for soft materials for observation under vacuum by electron microscopy. However, it has been concerned that IL may harden by electron irradiation during the electron microscopy observation. The purpose of this study is to reveal the relations between process of IL hardening, irradiation conditions of electron beam (acceleration voltage, irradiation density) and parameter of IL such as volume of IL. Adhesion force generally has strong correlation with surface tension, which is proportional to the adhesion force. To estimate the degree of hardening, adhesion force of an individual droplet of IL was measured in scanning electron microscope (SEM) equipped with nanomanipulator. Experimental data show that the adhesion force increases for several tens minutes, and then rapidly decreases. Correlating this result with SEM images taken simultaneously, we constructed a model. At the process of a model, Surface region of IL droplet hardens rapidly and forms solid film due to high energy electron irradiation. Film gradually increases its thickness by hardening of IL near the solid/liquid interface. Simutaeously, liquid phase of IL at inner region of the droplet also hardened slowly due to electrons penetrating to inside of droplet.

Self-propelled chemotactic ionic liquid droplets.

Herein we report the chemotactic behaviour of self-propelled droplets composed solely of the ionic liquid trihexyl(tetradecyl)phosphonium chloride ([P(6,6,6,14)][Cl]). These droplets spontaneously move along an aqueous-air boundary in the direction of chloride gradients to specific destinations due to asymmetric release of [P(6,6,6,14)](+) cationic surfactant from the droplet into the aqueous phase.

비전도성 매질 내 이온성 액체 액적의 충전 현상

이온성 액체는 상온에서 액체로 존재하는 이온성염으로 최근 청정 공정에 사용될 수 있는 용매, 전해질, 촉매로써 주목받고있다. 본 연구에서는 비전도성 매질 내 액적의 접촉 충전 현상을 이용하여 여섯 가지 서로 다른 이온성 액체에 대한 충전 거동을 고찰하였다. 이온성 액체 액적의 충전 현상은 이전 수용 액적의 충전 현상과 유사한 특징을 나타내었으며 기본적으로 완전 도체 이론으로 설명이 가능하였다. 하지만 이온 종류에 따른 상세 거동은 다소의 변화가 관찰되었다. 본 연구의 결과는 청정 용매 및 촉매로 각광 받고 있는 이온성 액체의 전기화학적 특성을 이해하고 분석하는데 유용하게 활용될 수 있을 것으로 기대된다. Ionic liquid (IL) is a salt presents in a liquid form at room temperature. Recently, it attracts huge attention due to its possibilities as a clean solvent, electrolyte, and catalyst. In the present work, the charging behavior of six different ILs were investigated using droplet contact charging phenomenon in a dielectric medium. Basically, the charging of an IL droplet can be explained by a perfect conductor theory. However, there were several different features depending on the species of ions of ILs, which requires rigorous molecular level modeling of charge transport through electrochemical reaction of IL. We hope the present results contribute to build up fundamental understanding of electrochemical charge transport of IL.