The Effect of AC Frequency on the Electrowetting Behavior of Ionic Liquids (original) (raw)
Related papers
Electrowetting of Ionic Liquids: Contact Angle Saturation and Irreversibility
Journal of Physical Chemistry C, 2009
In this work, electrowetting of several room temperature ionic liquids having in common the cation or the anion, [EMIM][EtSO 4 ], [EMPy][EtSO 4 ], [EMIM][NTf 2 ], [BMIM][BF 4 ], [BMIM][TFA], and [OMIM][BF 4 ], on poly(tetrafluoroethylene) (PTFE) was investigated. The typical behavior of aqueous salt solutions was found: symmetric parabolic curves of contact angle versus (positive and negative) applied voltage, at low voltages, and contact angle saturation after a threshold voltage. Furthermore, the contact angle did not recover its initial value when the voltage decreased, and this irreversibility was found even at low voltages. The dependence of the contact angle with the applied voltage is generally described by the Young-Lippmann equation before contact angle saturation. In contrast, the Langevin function as well as a modified form of the Young-Lippmann equation were found to fit the experimental electrowetting curves in the whole range of voltages. A correlation between the electrowetting behavior and the surface tension of the liquids was reported. Some physical effects that have been pointed out as possible causes for the contact angle saturation were investigated. The most plausible explanation for contact angle saturation in our systems seems to be the charge trapped across the solid/liquid interface.
Analytical Chemistry, 2008
Water or aqueous electrolytes are the dominant components in electrowetting on dielectric (EWOD)-based microfluidic devices. Low thermal stability, evaporation, and a propensity to facilitate corrosion of the metal parts of integrated circuits or electronics are drawbacks of aqueous solutions. The alternative use of ionic liquids (ILs) as electrowetting agents in EWOD-based applications or devices could overcome these limitations. Efficient EWOD devices could be developed using task-specific ILs. In this regard, a fundamental study on the electrowetting properties of ILs is essential. Therefore electrowetting properties of 19 different ionic liquids, including mono-, di-, and tricationic, plus mono-and dianionic ILs were examined. All tested ILs showed electrowetting of various magnitudes on an amorphous flouropolymer layer. The effects of IL structure, functionality, and charge density on the electrowetting properties were studied. The enhanced stability of ILs in electrowetting on dielectric at higher voltages was studied in comparison with water. Deviations from classical electrowetting theory were confirmed. The physical properties of ILs and their electrowetting properties were tabulated. These data can be used as references to engineer task-specific electrowetting agents (ILs) for future electrowetting-based applications. . Electrowetting curves of IL4 and water saturated IL4.
Electrical Double Layer in Mixtures of Room-Temperature Ionic Liquids
The Journal of Physical Chemistry C, 2009
The interfacial structure at the Hg electrode in mixtures of room-temperature ionic liquids (1-ethyl-3methylimidazolium tetrafluoroborate (EMIBF 4) and 1-octyl-3-methylimidazolium tetrafluoroborate (OMIBF 4)) has been studied for the first time by the measurement of surface tension and differential capacitance. Surface tension, charge density on the electrode surface, and capacitance decrease with increasing the addition of OMIBF 4 in EMIBF 4 , which has been found to be the consequence of the preferential adsorption of the octyl group on the Hg surface and increasing extent of heterogeneity of the mixtures. The continuous widening of the electrocapillary maxima (ECM) with increasing addition of OMIBF 4 in EMIBF 4 also supports the above reasoning. In accordance with the ECM, the potential corresponding to the minimum of the capacitance-potential curve is assigned as the potential of zero charge (PZC). The probable cause for the appearance of the PZC at the minimum of the capacitance-potential curve has been discussed.
On the interfacial behavior of ionic liquids: Surface tensions and contact angles
Journal of Colloid and Interface Science, 2009
In this work the liquid/vapour and the solid/liquid interfaces of a series of ionic liquids: 1-ethyl-3-methylpyridinium ethyl sulfate, [EMPy][EtSO 4 ], 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO 4 ], 1-ethanol-3-methylimidazolium tetrafluoroborate, [C 2 OHMIM][BF 4 ], 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF 4 ], and 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF 4 ], were investigated. The surface tension was measured in a wide temperature range, (298-453) K. The contact angles were determined on substrates of different polarities. Both on the polar (glass) and the non-polar substrates ((poly-(tetrafluoroethylene) and poly-(ethylene)), the liquids with maximum and minimum surface tensions lead, respectively, to the highest and the lowest contact angles. The dispersive, c d L , and non-dispersive, c nd L , components of the liquid surface tension, c L , were calculated from the contact angles on the non-polar substrates using the Fowkes approach. The polarity fraction, c nd L =c L , was compared with the polarity parameter, k, obtained from the fitting of the surface tension vs. temperature data to the Eötvös equation. Good agreement was found for the extreme cases: [OMIM][BF 4 ] exhibits the lowest polarity and [BMIM][BF 4 ], the highest. When compared with the polarity fractions of standard liquids considered as ''polar" liquids, the ionic liquids studied may be considered as moderately polar.
Journal of Molecular Liquids, 2017
A classical density functional theory has been used to study the structure and phase behavior of the electrical double layer of a dense ionic liquid. The model for IL consists of a trimer cation (with a charged head and two neutral segments) and a monomer anion. The effect of dispersion interactions on the density profile and differential capacitance curve has been investigated. Increasing the contribution of dispersion interactions leads to a camelshape differential capacitance curve. In the case of bell-shape curve, the maximum of the differential capacitance increases with decreasing the dispersion forces. These observations are related to the depletion or accumulation of ions near electrode with zero or low surface charge density.
Electrowetting of Room Temperature Ionic Liquids (RTILs) for Capillary Force Manipulation
Volume 12: Micro and Nano Systems, Parts A and B, 2009
The feasibility of using room temperature ionic liquids (RTILs) as the electrowetting liquid for capillary force microgrippers was studied. The non-volatility and thermal stability of ionic liquids make them suitable for droplet based microgripping application in high temperature and vacuum environments. Electrowetting on co-planar electrodes was utilized to dynamically change the contact angle of a 1-butyl-3methylimidazolium hexafluorophosphate (BmimPF 6 ) liquid bridge to control the capillary lifting forces. The lifting force generated by the liquid bridge was experimentally characterized. The maximum capillary force was 146µN. The dynamic response of the BmimPF 6 liquid bridge was also characterized.
Effect of Water on the Electrochemical Window and Potential Limits of Room-Temperature Ionic Liquids
The effect of water content on room-temperature ionic liquids (RTILs) was studied by Karl Fischer titration and cyclic voltammetry in the following ionic liquids: tris(P-hexyl)tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P14,6,6,6][NTf2], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [C4mpyrr][NTf2], 1-hexyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate [C6mim][FAP], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4mim][NTf2], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4dmim][NTf2], N-hexyltriethylammonium bis(trifluoromethylsolfonyl)imide [N6,2,2,2][NTf2], 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][NTf2], 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim][BF4], 1-hexyl-3-methylimidazolium iodide [C4mim][I], 1-butyl-3-methylimidazolium trifluoromethylsulfonate [C4mim][OTf], and 1-hexyl-3-methylimidazolium chloride [C6mim][Cl]. In addition, electrochemically relevant properties such as viscosity, conductivity, density, and melting point of RTILs are summarized from previous literature and are discussed. Karl Fisher titrations were carried out to determine the water content of RTILs for vacuum-dried, atmospheric, and wet samples. The anion in particular was found to affect the level of water uptake. The hydrophobicity of the anions adhered to the following trend: [FAP]− > [NTf2]− > [PF6]− > [BF4]− > halides. Cyclic voltammetry shows that an increase in water content significantly narrows the electrochemical window of each ionic liquid. The electrochemical window decreases in the following order: vacuum-dried > atmospheric > wet at 298 K > 318 K > 338 K. The anodic and cathodic potentials vs ferrocene internal reference are also listed under vacuum-dried and atmospheric conditions. The data obtained may aid the selection of a RTIL for use as a solvent in electrochemical applications. http://pubs.acs.org/doi/abs/10.1021/je800678e
Acs Applied Materials & Interfaces, 2009
Efficient and facile synthesis of novel linear tricationic room-temperature ionic liquids was performed, and their physiochemical properties were determined. Different physiochemical properties were observed according to the structural variations such as the cationic moiety and the counteranion of the ionic liquid. The electrowetting properties of these ionic liquids were also investigated, and linear tricationic ionic liquids were shown to be advantageous as effective electrowetting materials due to their high structural flexibility.
Dielectric Characteristics of Ionic Liquids and Usage in Advanced Energy Storage Cells
Progress and Developments in Ionic Liquids, 2017
Before the application of ionic liquids, it is important to know their fundamental physical and chemical properties. Practical experience has shown that it is important to look at these materials in the behaviour of the function frequency and temperature. To understand obtained information understanding the molecular-physic bases is needed. Research and application of ionic liquids have attracted an increasing attention in the areas of nuclear industry, oil and gas industry, petrochemical industry, chemical and electrochemical industry. The number of studies dealing with the question is proliferating which opens up new horizons in the field of chemical operations in microwave field with ionic liquids (organic chemical synthesis, catalytic operations, etc.). As a result of the relatively high destroying temperature of ionic liquids, a wider temperature range of operations can be done and it offers environmental friendly solution in the replacement of the toxic solvents with generally low evaporating temperatures. The area of application is becoming more widespread as electrolyte of novel battery cells. Being aware of the physical and chemical properties of ionic liquids is necessary in order to apply them. The main goal of this research was to test the dielectric properties, viscosity and temperature dependence of the electrical conductivity. Based on our results, we can claim that significant temperature dependence of the three properties can be shown in the case of ionic liquids. These findings are crucial for the usability of applications, planning and preparing of production and optimization processes. The significance and importance of these results become even more obvious if we consider the fact that these energy storage cells are exposed to large temperature differences. The present study discusses the
Phase Transitions and Electrochemical Properties of Ionic Liquids and Ionic Liquid—Solvent Mixtures
Molecules, 2021
Recent advances in studies of ionic liquids (IL) and ionic liquid–solvent mixtures are reviewed. Selected experimental, simulation, and theoretical results for electrochemical, thermodynamical, and structural properties of IL and IL-solvent mixtures are described. Special attention is paid to phenomena that are not predicted by the classical theories of the electrical double layer or disagree strongly with these theories. We focus on structural properties, especially on distribution of ions near electrodes, on electrical double layer capacitance, on effects of confinement, including decay length of a dissjoining pressure between confinig plates, and on demixing phase transition. In particular, effects of the demixing phase transition on electrochemical properties of ionic liquid–solvent mixtures for different degrees of confinement are presented.