Ionic Liquid Devices: Volume 29 (Smart Materials Series) - Hardcover

Hardcover

ISBN 10: 1788011813 ISBN 13: 9781788011815

Publisher: Royal Society of Chemistry, 2017

Synopsis

An overview of the innovative uses of ionic liquids from sensors and actuators to biomedical applications.

About this title

From the Back Cover

Ionic liquids are attractive because they offer versatility in the design of organic salts. As ion-rich media, ionic liquids can control the systems properties by tuning the size, charge, and shape of the composing ions. Whilst the focus has mainly been on the potential applications of ionic liquids as solvents, they also provide innovative opportunities for designing new systems and devices. Limitations from the high viscosity and expensive purification of the ionic liquids are also not a barrier for applications as devices.

Written by leading authors, Ionic Liquid Devices introduces the innovative applications of ionic liquids. Whilst the first chapters focus on their characterization, which can be difficult in some instances, the rest of the book demonstrates how ionic liquids can play substantial roles in quite different systems from sensors and actuators to biomedical applications.

The book provides a comprehensive resource aimed at researchers and students in materials science, polymer science, chemistry and physics interested in the materials and inspire the discovery of new applications of ionic liquids in smart devices.

Excerpt. © Reprinted by permission. All rights reserved.

Ionic Liquid Devices

By Ali Eftekhari

The Royal Society of Chemistry

Copyright © 2018 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78801-181-5

Contents

Chapter 1 Novel Analytical Techniques for Smart Ionic Liquid Materials Tetsuya Tsuda, Chih-Yao Chen and Charles L. Hussey, 1, 
Chapter 2 Electron Microscopy of Wet Materials Using Ionic Liquids C. Takahashi, 30, 
Chapter 3 Ionic Liquid-based Surfactants: A Step Forward Idaira Pacheco-Fernández, Providencia González-Hernández, Verónica Pino, Juan H. Ayala and Ana M. Afonso, 53, 
Chapter 4 Surfactant Fluorinated Ionic Liquids A. B. Pereiro, J. M. M. Araújo, J. M. S. S. Esperanca and L. P N. Rebelo, 79, 
Chapter 5 Ion Solvation and Transport in Ionic Liquids and Ionogels L. M. Varela, E. Lopez-Lago and O. Cabeza, 103, 
Chapter 6 Laser Deposition of Nano-ionic Liquids and Their Process Applications in a Vacuum Yuji Matsumoto and Shingo Maruyama, 136, 
Chapter 7 Smart Design of Sustainable and Efficient Ils Giuseppe Musumarra, Alessio Paternd and Salvatore Scire, 168, 
Chapter 8 Applications of Ionic Liquids in Organic Electronic Devices Satoru Ohisa and Junji Kido, 196, 
Chapter 9 Applications of Ionic Liquid Materials in Microfluidic Devices Tugce Akyazi, Janire Saez, Alexandru Tudor, Colm Delaney, Wayne Francis, Dermot Diamond, Lourdes Basabe-Desmonts, Larisa Florea and Fernando Benito-Lopez, 234, 
Chapter 10 Recognition-based Smart Ionic Liquids Yi-Pin Chang and Yen-Ho Chu, 272, 
Chapter 11 Ionic Liquid-based Physical Sensors Yi-Chung Tung, Hsiao-Mei Wu and Tse-AngLee, 296, 
Chapter 12 Aspects of Recent Advances in Smart Ionic Liquid Based Sensors B. Natesh Kumar, G. G. Redhi and C. Rajasekhar, 321, 
Chapter 13 Smart Ionic Liquids-based Gas Sensors Chuan Zhao, Richard Gondosiswanto and D. Brynn Hibbert, 337, 
Chapter 14 Design and New Energy Application of Ionic Liquids Shiro Seki, Shimpei Ono, Nobuyuki Serizawa, Yasuhiro Umebayashi, Seiji Tsuzuki, Kazuhide Ueno and Masayoshi Watanabe, 365, 
Chapter 15 Ionic Liquid Based Nanocarriers for Topical and Transdermal Drug Delivery M. Moniruzzaman, H. Mahmood and M. Goto, 390, 
Chapter 16 Bioactivity of Ionic Liquids Ricardo Ferraz, Catia Teixeira, Paula Gomes and Cristina Prudencio, 404, 
Chapter 17 Functional DNA in Ionic Liquids B. Olave and T Schäfer, 423, 
Subject Index, 445, 

CHAPTER 1

Novel Analytical Techniques for Smart Ionic Liquid Materials

TETSUYA TSUDA, CHIH-YAO CHEN AND CHARLES L. HUSSEY

Introduction

As described elsewhere, an ionic liquid (IL), which is sometimes called a room-temperature ionic liquid (RTIL), a room-temperature molten salt (RTMS), or an ambient-temperature molten salt (ATMS), has many unique properties. But, the most important point is that one IL combines nearly all of these features. For this reason, many scientists and engineers are keeping an eye on ILs as liquid materials and functional reaction media for supporting the development of future technologies, e.g., electrolytes for next generation secondary batteries and PEM fuel cells, functional solvents for organic synthesis and nanoparticle preparation, extraction solvents for rare metal ions and CO2, and lubricants for precision instruments. Some scientists have attempted to establish novel analytical techniques that combine ILs with analysis equipment operating under vacuum conditions, e.g., scanning electron microscopes (SEM), transmission electron microscopes (TEM), energy dispersive X-ray analysis (EDX), electron diffraction (ED), and X-ray photoemission spectroscopy (XPS). The negligible vapor pressure and antistatic properties of ILs enables analytical techniques that were previously considered to be impossible. Now these techniques have become widely recognized and accepted as powerful tools to reveal various chemical reaction processes in IL and ionic conformation change at the interface between IL and other phases. In this chapter, we divide these cutting-edge techniques into roughly three categories, SEM, TEM, and XPS, as described below.

1.2 SEM Observations with ILs

SEM is firmly established as a powerful tool for obtaining a three-dimensional surface image of specimens, and it is suitable for observing relatively large objects on a micrometer scale. The entire microscope has to be held at high vacuum for several reasons: First, gas in the gun assembly would interfere with electron emission and degrade the electron source. Second, electron beams will be scattered by any gas in the chamber, degrading column performance. Finally, the ionization of gas could cause electrical discharge and destroy the detector. These conditions imply that specimens must be vacuum tolerant, so they are traditionally dry solids. Wet specimens are typically frozen or desiccated before observation. This means that it is not easy for us to directly observe variations in the sample during dynamic experiments. For non-conductive/insulating specimens, creating a thin conductive coating (tens of nanometres) of a metal or carbon, although not mandatory, can prevent charging and improve the secondary electron signal. The most common vacuum coating methods are sputtering and thermal evaporation.

The extremely low vapor pressure (and thermal stability) of ILs match up well to the requirements of electron microscopy. The introduction of ILs into SEM chambers was first suggested in 2006 by Kuwabata et al. (Figure 1.1). It has been reported that Ils act as electrically conductive materials with high fluidity and can be directly observed by SEM without the accumulation of electron charges. Since this milestone work, many publications have followed. It is important to note that other solvents that possess negligible volatility such as silicone oil are also compatible with the vacuum conditions. However, the images for samples coated with these oils are distorted and fluctuate greatly owing to the build-up of charge on the sample. The distinct behavior observed for ILs could be attributed to their ability to solvate electrons and allow them to move in the liquid. It has been reported that even if the accelerating voltage is reduced to 1 kV, clear images are obtained for ILs, suggesting that such low energies are sufficient for injecting electrons into ILs. This unique property of ILs is useful as an alternative way to afford electrical conductivity to non-conductive materials. Over the past decade, the application of ILs for SEM observation can be divided into the following two categories: (i) as pre-treatment reagents to make the sample vacuum tolerant and electrically conductive and (ii) as media for (electro)chemical reactions proceeding under vacuum conditions.

1.2.1 ILs as Pre-treatment Reagents

Specimen preparation is decisive with any microscopic technique, the basic concern being that the specimen prepared is truly representative of the sample of interest. Although the preparation of SEM specimens is easy in comparison to TEM because there is no strict requirement to make the specimen exceedingly thin, it could still be challenging for specific samples. For instance, most biological specimens are made up largely of water and non-dense tissue materials. Thus, the sample must first be chemically fixed with aldehyde, dehydrated through an acetone or alcohol series, and then dried at the critical point (in order to mitigate specimen deformation due to tension during drying). Finally it must be coated with a conductive film prior to SEM observation. This conventional protocol is laborious and time-consuming, not to mention that it introduces unwanted artifacts and/or contaminants throughout the whole course of sample preparation that are mistakenly identified as features of the specimen. Although environmental SEM (ESEM) used under relaxed vacuum conditions can examine wet or hydrated samples, the images are of limited resolution.

ILs offer a simple yet efficient approach to address these issues. Tsuda and co-workers have showed that dropping a predetermined amount of diluted ILs onto such samples allows clear visualization of the specimen close to its native state (Figure 1.2). Thus, in this case, ILs fulfil the important tasks of forming a conductive layer on the biological specimen and, at the same time, preserving its structure. For some types of samples with hard outer layers (e.g., exoskeletons or cell walls) that negate the need for fixation, the pre-treatment process can be completed within a couple of minutes. An additional benefit of using ILs as pre-treatment agents over common protocols is the fact that ILs keep the specimens wet and they minimize drying induced or vacuum-related artifacts. This is especially advantageous for biological specimen that are sensitive to environmental conditions, e.g., red blood cells and drug or vaccine carriers. Hyono et al. have reported that red blood cells treated by ILs maintain their size and shape well even under high vacuum conditions, whereas those pre-treated by conventional procedures show shrinkage and deformation. In addition, IL pretreatment has recently proven to be a safe alternative to the characterization of infectious pathogens by avoiding the risk of generating aerosols during the sputter coating process.

Notably, the selection and optimized usage of IL (concentration, amount, processing period and temperature, etc.) differ for each type of sample. Generally, hydrophilic ILs of moderate viscosity are found to be more suitable for pre-treating biological specimens than the hydrophobic ILs. This is why 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) and 1-ethyl-3-methylimidazolium acetate ([C2mim][CH3CO2]) are widely adopted. In addition, choline- and lactate-based ILs usually show a favorable biocompatibility. Image contrast and resolution are found to be enhanced by the combination of IL pre-treatment and Pt-blue staining, or with osmium tetroxide-coated coverslips. Thus far, IL pre-treatment methods have proven to work with several kinds of insulating materials (rock, ceramic, mineral, etc.), and are not limited to biological specimens.

1.2.2 ILs as Reaction Media and Electrolytes for Microscale Reactions

Dynamic processes associated with liquids, such as flow, diffusion, self-assembly, crystallization, and material synthesis, play crucial roles over a wide range of scientific and technological applications. However, their direct visualization by electron microscopy has been challenging due to the evaporation of the liquids. Again, ILs provide the platform to extend this knowledge. In this respect, Kashin et al monitored acid-catalyzed biomass conversion reactions by SEM and investigated how self-organized structures of binary IL/water and IL/alcohol systems influence the conversion efficiency and selectivity. Likewise, Kim et al. investigated the Brownian motion of nanomaterials dispersed within an IL thin film, and Horigome et al. reported the swelling of microgels in ILs via SEM.

It is well known that ILs can be utilized as an advantageous electrolyte for a broad set of electrochemical reactions. This has inspired researchers to extract detailed and time-resolved information in realistic environments (in situ or operando). As an early demonstration of in situ SEM, Arimoto and co-workers studied Ag electrodeposition from ILs and revealed the growth of granular and dendritic forms of the deposits. Being aware of the high potential of various families of ILs in energy-related applications, this same group recently focused on the anodic electrode reaction in lithium-ion batteries (LIBs). Silicon is one of the most promising active anode materials for any future LIBs as it offers pre-eminent theoretical capacity, nearly an order of magnitude beyond that of conventional graphite. However, the dramatic volume change (~300%) experienced by Si alloys/dealloys with lithium can induce severe pulverization and subsequent loss of electrical connectivity. Nanostructuring of Si to facilitate strain relaxation is generally regarded as an effective strategy. This is attested via in situ SEM techniques coupled with specially designed cells (Figure 1.3). The fracture resistance and volume variation characteristics of Si show strong size and shape dependencies (Figure 1.4). Among the samples studied, the thin flake form of Si outperforms microparticles and nanoparticles (not shown here) in terms of reversibility and retention of capacity. Serious damage of the Si thin flake is not recognized during the charge-discharge process. In addition, the feasibility of using backscattered electrons (BSEs) has also been examined to track the elemental distributions during operation. Similar SEM results have been obtained by other groups. Chen et al. found that SnO2 particles with dimensions greater than a few hundred nanometers behave differently from their smaller counterparts (below 100 nm). During lithiation, the larger SnO2 underwent irreversible volume changes together with the growth of cracks and extrusions, while no cracks were observed for the smaller particles. The formation of the extrusion, albeit the mechanism remains unclear, suggests that the lithiation is inhomogeneous within the larger SnO2 particles. For these experiments optimizing the beam energy and using appropriate probe currents, sometimes unavoidably accompanied by sacrifices in resolution and contrast, are prerequisite. Moreover, the amount and wetting condition of IL electrolytes on the working electrode largely affect the electrode performance and image quality. Abundant electrolyte enables the electrode to function well. However, it may disturb observations of electrode reactions because the electron beam cannot penetrate the thick IL. Maintaining a thin and sufficient IL electrolyte during reactions is of significance. As a rule of thumb, the penetration depth of the primary electron beam into ILs is estimated to be at least 1 µm.

With the aim to enhance the mechanical stability of Si, Xia et al. prepared Cu–Si core-shells by lithography-based methods. In situ SEM observations in an IL electrolyte disclosed that the sample can accommodate ~250% volumetric expansion without detectable crack formation, highlighting the importance of both rational material design and precise characterization. Likewise, the in situ SEM method can be applied to active cathode materials. Miller et al. studied the microstructural evolution of a single Li(Ni0.8.Co0.15.Al0.05)O2 particle during charge/discharge by using a focused ion beam SEM (FIB-SEM). The cross section of the sample exhibits progressive intergranular separation caused by the anisotropic changes in lattice parameters associated with the lithiation/delithiation process. These results suggest that the physical separation and isolation of grains may contribute to performance degradation of practical LIBs. Another example of new insight that in situ observations can provide is electrolyte penetration behavior, which undoubtedly influences the utilization and performance efficiency of the electrode. This information is hardly achievable by other methods.

Most previous studies about SEM observations of LIB components examined the tested electrode materials by post-mortem methods. Hence, extreme care must be taken to avoid contamination, deformation and air/ moisture exposure of the specimens during the cell disassembly, electrode washing, and drying. Meanwhile, the physical and chemical states of electrodes during reaction are continuously renewed (non-equilibrium states). In situ studies are therefore preferred to deepen the understanding of time- and potential-resolved changes. Indeed, Bridel and co-workers have pointed out that the electrode morphology evolves in a very different manner from that expected based on ex situ analysis. On the other hand, caution has to be exercised in interpreting the in situ results. As electrochemical cells are multifaceted systems in which critical components are relevantly influenced, researchers should be aware of the extent to which the cell setup for in situ experiments relates to practical applications.

1.3 TEM Observations with ILs

TEM is a distinguished characterization tool that can provide morphological, structural, and compositional information at nanoscale or even atomic resolution. Besides the EDX that is commonly used for elemental analysis, many other analytical methods have been employed in conjunction with TEM, including electron diffraction that allows nanocrystal structure determinations, electron energy loss spectroscopy (EELS) that probes electronic excited states of materials, and Lorentz imaging that identifies micro-magnetic structures. As a result, TEM has become the technique for addressing great challenges in materials science. Despite its versatility, TEM generally requires sophisticated skills for sample preparation. Because the sample has to be stable in vacuum and sufficiently thin (usually less than 100 nm) for electron beam penetration to form an image of reasonable resolution, preparing such specimens with minimal artifacts is a big challenge. This is even truer for liquid samples. Cryo-TEM is one of the approaches used to clear this hurdle, but additional freezing devices and temperature-sensitive preparation processes are required. Moreover, the images obtained at such extreme temperatures may not reflect the native state at room temperature.

With the recent advances in instrumentation, two approaches have been developed to circumvent the difficulties associated with viewing liquids by TEM. The first is to entrap a liquid film between two electron transparent membranes (e.g., silicon nitride or graphene) that can withstand the pressure difference between a liquid stage and the high vacuum in the chamber. The "closed" liquid cell makes imaging liquids by TEM a routine task and has attracted tremendous interest in diverse fields. Exciting progress has been made over the past few years, much of which is reviewed in ref. 46 and 47. The second approach is to use the "open" cell configuration, which utilizes ILs without the hermetic component. As already stated, ILs themselves can be directly imaged by SEM; they can also be viewed by TEM as long as their thicknesses are carefully managed. Another occasion is when the object of interest lies in a solid material around the ILs. For example, consider the case of an electrochemical reaction. In this example there is no requirement for the thickness and amount of the ILs that need to be present. The advantages of using the open cell over the closed cell are manifold: (i) sample preparation is simple; (ii) higher resolution is achievable due to the absence of a membrane; (iii) imaging can performed in a standard TEM; and (iv) the field of view is much larger. Below we discuss IL-based TEM observations and related experiments.

(Continues...)

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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2017
• Language: English
• ISBN 10: 1788011813
• ISBN 13: 9781788011815
• Binding: Hardcover
• Number of pages: 474
• Editor: Ali Eftekhari