TAYLOR CONE ELECTROHYDRODYNAMICS. THE MINIMUM AND MAXIMUM FLOW RATES IN ELECTROSPRAYING

The surface charge at the liquid–gas interface in cone-jet electrospraying, almost relaxed from an electrochemical point of view, is driven by the radial electric field created to supply the current to the cone tip that the microjet withdraws. The electric stress applied on the liquid surface provokes a low or high Reynolds number motions in the electrified meniscus depending on a dimensionless parameter which relates the liquid viscosity and its electrical conductivity. The analysis of the surface motion is essential to quantify the surface current convected to the cone’s tip, which is shown to be negligible compared to the one driven by bulk conduction. In the case of high Reynolds number motions, we show mathematically, and also experimentally, the emergence of an interesting self-rotation phenomenon.In addition, an analysis of the equations governing the electrohydrodynamics of the charged liquid ligament issuing from the tip of an electrified meniscus in a steady cone-jet suggests the mechanisms which set the stability limits of this steady regime. It is shown that for low and moderate liquid polarities (less than 40 times the vacuum permittivity), the minimum liquid flow rate that can be electrosprayed in a steady cone-jet is reached when the surface tension stress at the cusp from which the jet issues, which provokes a resulting pressure gradient against the flow, overcomes the electrostatic “suction” effect. To show the role of the different forces involved, we have carried the calculation of the intervening ones in the momentum equation using the digitized shape of a cone-jet close to the minimum flow rate in the case of a permittivity 6.5 times larger than the vacuum one. For larger polarities, which impose large electrical conductivities as well, the role of viscous forces, polarization forces, and charge relaxation effects is discussed. In addition, we have carried out experimental measurements of the minimum flow rate using several different liquids. These results are discussed and compared with the experimental data from different authors, as well as with other previously given scaling laws and estimations of the minimum flow rate in cone-jet electrospraying.     

THE ELECTROHYDRODYNAMICS OF THE CHARGED LIQUID JET ISSUING FROM AN ELECTRIFIED TAYLOR CONE. UNIVERSAL SCALING LAWS

A hybrid experimental–numerical approach to study the dynamics of capillary electrified jets, which uses a quasi-one-dimensional model and the experimentally measured shape of an actual liquid thread (Gañán-Calvo (1997) J. Fluid Mech. 335, 165–188) has been employed in this work to analyze the electrohydrodynamics of the liquid micro-jets issuing from Taylor cones. Different liquids have been used in this study, with electrical permittivities from 6.5 to 38 times the vacuum permittivity, and electrical conductivities ranging from 8.5 to 4.5e-4 S m^-1. Up to 25 different jet shapes corresponding to steady and absolutely stable conditions have been digitized, and the corresponding surface charge distribution, normal external and internal electric fields at the surface, the axial electric field (the slender approach allows to consider the axial electric field constant in the transversal direction), the liquid velocity distribution, the electric current convected by the surface and the one driven through the bulk by Ohmic conduction at each axial point have been calculated. In particular, one of the liquid jets analyzed corresponded to the onset of stability of the steady cone-jet mode, where we supply just the (minimum) liquid flow rate that the electrostatic suction effect at the cone-jet neck is able to withdraw at the minimum needle–electrode potential difference for a given stable cone elongation. This has revealed a surprising result: even in this critical situation, the inner normal electric displacement is at most a mere 15% of the outer one, and this happens only at one point of the whole cone-jet, located close to the point at which the convected electric current equals the current driven by bulk conduction (i.e. a little downstream of the cone-jet neck), being the inner displacement at other points of the jet and the cone hundreds of times smaller than the outer displacement. As one increases the liquid flow rate, the ratio of the maximum inner displacement to the outer displacement becomes proportionally smaller. This result clarifies for the first time the controversy about charge relaxation phenomena in cone-jet electrosprays, since it can be used to show from a physicochemical argument that the charge layer at the whole cone-jet surface is almost relaxed even at the onset of stability, at least for liquid permittivities of the order of the ones used in this study. This result also guarantees a homogeneous bulk conductivity along the hole cone-jet. Secondly, and similarly interesting, the kinetic energy per unit volume acquired by the liquid in the jet results independent of the flow rate for a given liquid and a cone elongation, explained by the fact that the normal electric field (or surface charge distribution) which provokes the main acceleration force (the electrostatic suction effect, at the cone-jet neck and the beginning of the jet) results independent of the flow rate as well. A universal scaling of the electro-hydrodynamic variables, jet size and total emitted electric current is proposed, and the experimental results are collapsed into a universal collection of distributions of non-dimensional variables along the axis. The resulting droplet size, also measured in the same experiments, scales as the jet radius, and the droplet charge results proportional to its surface, a result shown by many investigators but never explained. Other previously used electrohydro-dynamic hypotheses and scaling laws are discussed under these new results.     

ONE-DIMENSIONAL SIMULATION OF THE BREAKUP OF CAPILLARY JETS OF CONDUCTING LIQUIDS. APPLICATION TO E.H.D. SPRAYING

Nonlinear breakup of charged liquid jets is numerically analyzed in this work in the limit of a very small electrical Strouhal number T_e/T_b≪1 (i.e. negligible charge relaxation effects, applicable to highly conducting liquids), where T_e is the electric relaxation time of charges, and T_b is the breakup time in a Lagrangian framework following the liquid jet at its average axial velocity. The influence of the electrical Bond’s number and viscosity on (i) the capillary Rayleigh’s most probable breakup length, (ii) the breakup time, (iii) the volume of the satellite, and (iv) the charge of both main drop and satellite, are analyzed. The model is related to the microjet break-up phenomena in the electrospraying of liquids in steady cone-jet mode, and its range of applicability to those particular problems discussed. Previous experimental results [Mutoh et al., 1979, Convergence and disintegration of liquid jets induced by an electrostatic field. J. Appl. Phys. 50, 3174–3179; Clopeau and Prunet-Foch, 1989, Electrostatic spraying of liquids in cone-jet mode. J. Electrostatics 22, 135–159.] support our numerical finding that the influence of the electrical Bond’s number on Rayleigh’s length is small within the usual parametrical limits of stability of a steady Taylor cone-jet at atmospheric pressure.     

Millisecond mixing of liquids using a novel jet nozzle

A millisecond mixing process for liquids was implemented using a new mixer design, i.e., a jet nozzle connected with a trumpet-shaped module. The jet nozzle can facilitate two or three liquid channels, performing an initial impingement mixing of liquid sheets in the thickness at millimeters. Then, the joint liquids sheet out of the jet nozzle was stretched thinner and thinner on the expanded solid surface of the trumpet-shaped module, which significantly intensified the liquid mixing process. Accordingly, dual controls on the liquid mixing can be accomplished flexibly by optimizing the operating conditions and the module configuration. Experiments were carried out to investigate the influencing factors on the mixing performance, where the planar laser induced fluorescence (PLIF) technique was used to measure the mass transport of fluorescent dye between the liquids. The intensity of segregation (IOS) and 95% mixing time (τ₉₅) were employed to characterize the mixing performance. The results showed that the module with a greater curvature surface possessed a better mixing performance owing to the rapid reduction of the liquid sheet thickness, which strengthened the mixing process in the lateral direction along the flow development. The mixing behaviors are greatly influenced by the flow rate ratio between the liquids. An optimum mixing state could be achieved when Q_S1/Q_S2 is 1:1. An increase of Q_T under the same flow rate ratio does not affect the mixing pattern in space, but the corresponding τ₉₅ is almost linearly shortened. By splitting one liquid stream into two surrounding streams, the so called Sandwich operation brought further improved mixing performance compared with the two liquids mixing process. Using the novel jet nozzle design, millisecond(s) mixing of liquids can be easily achieved with flexible control.     

ELECTROSPRAYS AND LIQUID-METAL ION SOURCES—SOME THEORETICAL SIMILARITIES AND DIFFERENCES

Electrosprays and the liquid–metal ion source (LMIS) have a clear similarity, in that both are electrohydrodynamically (EHD) driven devices operating in the cone-jet mode. There are also clear differences, not least the difference in the desired emission product. This paper begins by reviewing some of the main facts about liquid–metal ion sources. These include the nature of the emission mechanism, the size of the field at the end of the liquid emitter, the size of the end of the emitter, the fact that the emitter has an electrically well-defined surface, the absence of any significant voltage drop along the emitter, the existence of a high space charge above the end of the emitter, and the important role of the space charge in controlling the emission current, and the length of the liquid emitter cusp. Detailed discussion of LMIS behaviour may be found in Forbes (1997) Vacuum 48, 85.On the EHD side we may note the following about the LMIS: the existence of onset phenomena is well explained by Taylor’s arguments about the total “Maxwell” force on the emitter; the basic cone-jet shape is explained partially by Taylor’s arguments, partially by other EHD effects; the LMIS appears to be a device driven by negative pressure at its apex, with the formation of the liquid cusp being the electrical equivalent of a vena contracta.Our best understanding of LMIS behaviour is that the liquid–metal ion emitters operate mainly in an approximately steady-state-flow mode, but go unstable and emit microdroplets and/or nanodroplets between periods of approximately steady-state flow. Some possible reasons for the stability of the liquid–metal ion source, at least over short periods of time, will be put forward.Obviously, an important difference between a LMIS and an EHD sprayer is the difference in electrical conductivity. This appears to mean that for a LMIS there is no significant voltage drop along the liquid jet, but that for an EHD sprayer the voltage drop may be significant. Numerical arguments will be presented to suggest that, because of this difference in the voltage drop, the driving force for a LMIS is the Maxwell stress on the jet apex, but that for an EHD sprayer the driving force is the tangential electrical force on the quasi-cylindrical sides of the liquid jet.Another important difference appears to be in the size of the apex of the liquid cusp and the resultant difference in the size of the electric field there. It is the high field at the apex of the LMIS there that allows ion emission to be a significant method of removing material. It is an important question to decide why such small apex sizes and high fields cannot be achieved with EHD sprayers.A curious difference between the theories of the LMIS and the EHD sprayer is the difference in importance given to the parameter “flow rate”: this is an important parameter for the sprayer, but does not normally appear in standard LMIS theory. However, discussions of the LMIS make use of the concepts of a “viscous-drag-free source” (for which the cone base pressure is zero), and “viscous-drag-limited” sources (for which the cone base pressure is non-zero).Liquid–metal ion source operation has been modelled, both analytically and numerically. Progress in modelling the steady-state-flow mode has been substantial and successful. Attempts to model time-dependent EHD behaviour have run into fundamental computational difficulties.     

Flow visualization of the liquid emptying process in scaled-up gravure grooves and cells

The liquid-emptying process in scaled-up gravure grooves and cells is studied using flow visualization in order to better understand gravure coating and printing processes. Water and two different glycerin/water mixtures serve as the test liquids, and the emptying process is initiated by moving over the groove or cell a rotating roller or a glass top with a curved surface. For the scaled-up groove, a region of recirculating flow is observed to attach to the moving glass top. When the glass top is used to drive flow in the scaled-up cell, an air bubble may appear inside the cell when the gap between the bottom of the curved surface and the top of the cell is zero. When this gap is positive, a liquid bridge is formed, dragged across the cell, and then broken, leaving some liquid inside the cell. The amount of liquid remaining in the cell, V_r, is measured for different liquids, surface speeds, and gap distances for both the glass top and the rotating roller. The effect of using a soft elastomeric covering on the glass top and roller is also explored. For each liquid, V_r increases as the speed of the glass top or roller increases. The data are correlated by multiplying V_r by a liquid-dependent shift factor, which leads to a power-law relationship between the shifted V_r and the capillary number. These experimental observations and measurements can be used to benchmark theoretical calculations, which can then be applied to design gravure grooves and cells that empty in a controlled way.     

Investigation of alternating-flow mixing in microchannels

A number of different approaches to mixing liquids in microscale systems can be found in the literature. In the case of miscible liquids it is desirable to produce mixtures with residual non-uniformity in composition that is below some specified level. Yet very little quantitative information is available concerning the conditions required to produce a given level of mixture uniformity. A theoretical approach to this problem is described. Computational fluid dynamics and simple scaling are used to develop a quantitative understanding of the alternating flow method of mixing using pressure driven flow. In this approach, external flow control is used to produce alternating injection into a single microchannel of two or more solutions to be mixed. The resulting streamwise slugs of solution then mix by the stretching of the slugs into thin striations resulting from shear strain. The most challenging condition for mixing is where the Reynolds number is approaching zero and inertia effects are negligible, a common situation in microchannel flows, particularly where relatively high-viscosity liquids, for example ionic liquids, are involved. The scaling theory demonstrates that an initial time period of rapid mixing of fluid outside the core of the flow, scaling as Pe^-2/3, is followed by a far slower process of mixing in the core region, scaling as Pe^-1/2. An approximate correlation for the deviation from the perfectly mixed state as a function of time is found. This correlation applies over the range of Peclet number, slug length and solution mixture ratio that are of interest. The mixture uniformity produced is shown to be limited by the initial uniformity of each solution over the channel section resulting from the injection process.     

COSMO-RS modeling on the extraction of stimulant drugs from urine sample by the double actions of supercritical carbon dioxide and ionic liquid

This work presents the first research linking chemical engineering and sport science as far as we know. The COSMO-RS (conductor-like screening model for real solvents) model was used to make a priori prediction for the extraction of stimulants from aqueous solution by the double action of supercritical carbon dioxide (SC CO₂) and ionic liquid. It was found that the suitable ionic liquids should have small molecular volume, unbranched group and no sterical shielding effect around anion charge center, and thus [C₂MIM]⁺[OAc]^- is the best among all the ionic liquids investigated. The calculated results from the COSMO-RS model were qualitatively consistent with those from experiments. On this basis, partition coefficients of amphetamine (C9N) and nikethamide (C10N) between aqueous phase and supercritical fluid (or MTBE) phase at different temperatures were calculated. It was shown that the separation efficiency of supercritical extraction with ionic liquid is generally higher than that of traditional liquid-liquid extraction. The modeling present can also be extended to the separation of trace amount of organic substances from aqueous solutions for other purposes.     

EXPERIMENTAL STUDY OF THE JET BREAK UP FOR EHDA OF LIQUIDS IN THE CONE-JET MODE

The scaling laws developed by Fernández de la Mora (1994, J. Fluid Mech. 260, 155–184) and by Gañán-Calvo (1994, J. Aerosol Sci. 25S, S309–S310) have been verified since then through various experiments. Chen and Pui (1997, Aerosol Sci. Technol. 27, 367–380) investigated the dependence of the current and droplet diameter with the permittivity of the liquid. Hartman et al. (1997) developed a physical model to describe the spraying of liquids in the cone-jet mode. These two approaches compare remarkably concerning the current produced by the cones. Nonetheless some differences have appeared concerning the jet break up. Namely, the scaling of the jet diameter with the flow rate and the conductivity is different in both approaches.Thus, we present here an original experimental study to investigate these differences. It was conducted using a High-Speed Spray Imaging System (HSSIS) purchased from Oxford Laser. This system consists of a digital camera (KODAK) connected to a computer which is equipped with a frame grabber. A long-distance microscopic lens is fixed to a camera. The illumination of the subject is done by an infrared laser. A control box synchronizes the camera and the laser. Pictures can be made with an illumination time down to 0.5 ms and the separation between two following pictures can be down to 15 ms. The optical system allows us to see objects down to a few micrometers but only objects bigger than 10 mm can be accurately measured. The experiments were done using five different liquids namely, ethanol, butanol, isobutanol, 2-butanone and ethylene glycol. For each liquid the conductivity and the flow rate were varied. For each situation photos were taken to determine the jet size, the break up of the jet, the droplet size and the droplet velocity. Moreover, for every situation the spray current was measured.Our results show that the jet diameter for the different liquids studied exhibits a dependence on the flow rate at a power ∼0.6. This indicates firstly, that the model developed by Hartman is correct in its calculation of the jet diameter and secondly, that the break up of the jet cannot be assimilated to the one of an unchanged jet. Nevertheless our results must be put in perspective with the fact that the jet diameter is measured at a fixed distance from the cone, while the jet length varies with the flow rate. Further, our study brought some other interesting results.First, concerning the jet break-up mechanism. It is a known fact that within the range where IμQ^1/2 the jet can break up due to varicose or kink instabilities. The results showed that for a given liquid the break up was going from varicose to kink with the flow rate going up. Second, they also showed that the number of satellites produced between two main droplets increases with the flow rate.Moreover, we have tried to define, as a function of liquid properties, a limit which separates the two types of jet break up mechanism (varicose or kink). This is of primary importance because it is known that the size distribution of the main droplets is much narrower when the jet breaks up due to varicose instability.     

Numerical characterisation of folding flow microchannel mixers

Micromixers have been considered in numerous recent studies with the aim of mixing different liquid streams for the common circumstance of non-inertial flow, i.e., in the Stokes flow regime. Under such conditions, the diffusion of momentum is dominant but the diffusion of species remains weak because the Schmidt number of liquids is large. Most mixers that have potential for application in the Stokes regime make use of a folding flow pattern that approximates the baker's transformation. In the work presented here, the general scaling of mixers of this type is developed from the exact equation for species transport and computations are made for a specimen mixer geometry to test the effectiveness of the resulting scaling. The scaling relation developed is found to give an excellent representation of the actual mixing characteristics of the specimen mixer over the entire range of Péclet number of practical interest. Finite volume computations are employed to solve the governing equations up to around Pe=10³. At higher Péclet numbers, where finite volume numerical solution becomes inaccurate with affordable mesh sizes, the species equation is solved using a Monte Carlo method instead. Finally, the scaling relation is used to develop the design relations needed to determine the number of mixing elements, the pressure drop incurred and the Péclet number of operation to achieve a given mixture uniformity within a specified mixing time.     

Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites

Complex permittivity and related AC conductivity measurements in the frequency range between 10⁻⁴ and 10⁷ Hz are presented for composites of polycarbonate (PC) filled with different amounts of multiwalled carbon nanotubes (MWNT) varying in the range between 0.5 and 5 wt%. The composites were obtained by diluting a PC based masterbatch containing 15 wt% MWNT by melt mixing using a Micro Compounder. From DC conductivity measurements it was found that for samples processed at a mixing screw speed of 150 rpm for 5 min, the percolation occurs at a threshold concentration (p_c) between 1.0 and 1.5 wt% MWNT. For concentrations of MWNT near the percolation threshold, the processing conditions (screw speed and mixing time) were varied. The differences in the dispersion of the MWNT in the PC matrix could be detected in the complex permittivity and AC conductivity spectra, and have been explained by changes in p_c. The AC conductivity and permittivity spectra are discussed in terms of charge carrier diffusion on percolation clusters and resistor-capacitor composites.     

A semi-empirical power-law model for the dip-coating of a substrate into a particle-containing,non-Newtonian,complex fluid system

The apparent viscosity of a particle suspension of ZrSi₂ particles, polyhydromethylsiloxane (PHMS) preceramic polymer and n-Octane solvent, used to process polymer-derived ceramic composite coatings, is shown by viscometric experiments to be shear-thinning. The suspension is dip-coated onto substrates and the measured entrained coating thickness, h_0, is observed to be a power-law function of U, the substrate extraction speed, as h₀ = 0.5051U^0.5. The experimentally observed semi-empirical model is directly compared to the results of a variety of theoretically derived Landau-Levich scaling laws and other models that have similar liquids and that include other effects. None of these cases predicts the scaling observed in these experiments. A correction factor is introduced to quantify the difference between the semi-empirical model with existing theoretical models. Possible explanations for the observed scaling behavior are presented.     

Volumetric properties of ionic liquids from cubic equation of state: Application to pure and mixture

In this work, we developed a cubic equation of state (CEOS) for modeling the volumetric properties of various ionic liquids (ILs). Two temperature-dependent parameters presented in the CEOS, have been determined from two sets of corresponding states correlations which are based on the critical point data or the surface tension of ILs. The predicted densities of pure ILs were compared with the experimental data over a broad pressure range from 1 to 100 MPa. The total average absolute deviations (AADs) of the calculated densities of 948 data points from the experimental data are 1.82% using the critical property and 0.96% using the surface tension and liquid density as scaling parameters. Furthermore, the proposed CEOS was successfully extended to mixtures including IL + IL and IL + solvent systems. 1282 literature data points for mixtures were taken to check the reliability of the mixture version of the proposed CEOS. The AAD of the calculated densities of the mixtures using the surface tension and liquid density as scaling parameter is 0.37%. Furthermore, the excess molar volumes (V^E) of the studied binary mixtures have been successfully computed by the use of the proposed CEOS.     

Performance and pressure drop of CO2 absorption into task-specific and halide-free ionic liquids in a microchannel

The gas–liquid two-phase flow pattern, absorption rate and pressure drop of CO₂ absorbed into the aqueous solution of the task-specific ionic liquids (1-aminopropyl-3-methylimidazole tetrafluoroborate [Apmim][BF₄] and 1-hydroxyethyl-3-methylimidazole tetrafluoroborate [OHemim][BF₄]) and halide-free ionic liquid 1-butyl-3-methylimidazolium methylsulfate [Bmim][CH₃SO₄] were investigated in a microreactor. The absorption mechanism of the three ionic liquids was analyzed employing the ¹³C NMR spectroscopy. The [Apmim][BF₄] was found to have the best ability of CO₂ capture compared with the other two ionic liquids, as chemical absorption occurred between [Apmim][BF₄] and CO₂, while only physical absorption took place between [OHemim][BF₄]/[Bmim][CH₃SO₄] and CO₂. The sequence of CO₂ absorption rate in three ionic liquids aqueous solutions is: [Apmim][BF₄] > [Bmim][CH₃SO₄] > [OHemim][BF₄]. Furthermore, the effects of gas–liquid flow rate and ionic liquids concentration on CO₂ absorption rate and pressure drop were studied, the pressure drop models based on various flow patterns were proposed.     

AN EXPERIMENTAL PHASE DOPPLER ANEMOMETER STUDY OF ELECTROHYDRODYNAMIC ATOMIZATION

In this work, measurements of the size of the primary droplets generated by electrospraying 10 different liquids with different densities and surface tensions (measured by a tensiometer, Lauda LD1), viscosities, electrical conductivities (WTW LF530) and permittivities (capacitance bridge, Philips) were carried out. To measure the size of the droplets, a Phase Doppler Anemometer (Dantec/INVENT) was used. Gañán-Calvo et al. (1997) obtained on the basis of a theoretical model the so-called scaling laws, which permit the prediction of the spray current and droplet size. The empirical constants in these formulas were obtained from the experimental measurements. Two different behaviors were found, depending on the dimensionless parameter δ_μδ^1/3=(ε²₀γ²/κ²μ³Q)^1/3. From our measurements, an intermediate regime with a much smaller slope is also found. This might also be due to the small flow rate, as the measurements which lie early below Gañán-Calvo’s fitting curve all satisfy the relation (Q/(ε_r−1)^1/2Q₀)^1/3<3.     

Studies on scaling of membranes in desalination by direct contact membrane distillation: CaCO3 and mixed CaCO3/CaSO4 systems

Scaling of membranes by CaCO₃ and CaSO₄-CaCO₃ is of considerable concern in membrane desalination processes. It is particularly relevant for porous crossflow hollow fiber-based membrane distillation (MD) processes which can achieve high water recovery and can encounter heavy precipitation of scaling salts. Therefore an analysis of the scaling potential for CaCO₃ and mixed CaSO₄-CaCO₃ systems is presented first in terms of the saturation index profiles throughout the crossflow hollow fiber membrane module as a function of the location in the module for feed solutions resulting from high water recovery. Scaling experiments during DCMD with tap water, CaCO₃ and mixed CaSO₄/CaCO₃ were conducted over a wide range of values of saturation index (SI) (10<SI_calcite<64, 1.1<SI_Gypsum<1.5) using porous fluorosilicone coated crossflow hollow fiber membrane desalination modules. The effects of flow rates, flow patterns (cross vs. parallel flow) and the nature of the membrane surface on possible scaling scenarios were further investigated for the scaling salt CaSO₄. Experimental results at high saturation indices show that even when the precipitation rate was fast in the CaCO₃ system at elevated temperatures or high concentrations, no significant loss in water vapor permeation was observed suggesting no effect of scaling on membrane flux. However, for a few of the mixed CaSO₄-CaCO₃ systems, the water vapor flux dropped somewhat. Possible explanations have been provided and a method to solve this problem has been illustrated. Fast feed flow rate resulted in a shortened induction period. Crossflow flow pattern and the nature of the hydrophobic porous coating on the membrane surface were proven to be helpful in developing the resistance to scaling. Results of modeling show that concentration polarization effects are far more important than temperature polarization effects.     

Effect of oxygenation time on signal of a sensor based on ionic liquids

The paper presents an oxygen sensor based on ionic liquids and solid electrodes. The following ionic liquids have been employed: [BMIM][BF₄], [HMIM][Cl], [BMIM][N(CN₂)]. Minimum time of the sensor exposure to analyte, after which the signal (current intensity) was stable, has been evaluated. An impact of volumetric flow rate of analyte on the sensor exposure time and signal has been determined. A product of permeability coefficient and solubility of oxygen in ionic liquids has been estimated. A mechanism of oxygen reduction on a surface of the solid electrodes, in the ionic liquid environment has been presented. Overall cathodic coefficients of transition for the sensors with particular ionic liquids have been determined as a function of potential scan rate.     

Functional mesoporous poly(ionic liquid)-based copolymer monoliths: From synthesis to catalysis and microporous carbon production

Ionic liquid-functionalized mesoporous polymeric networks with specific surface area up to 935 m²/g have been successfully synthesized one pot by solvothermal copolymerization of divinylbenzene and monomeric ionic liquids. The as-obtained polymers exhibit a monolithic structure featuring large pore volumes, an abundant mesoporosity and an adjustable content of ionic liquids. The effect of the reaction conditions on the pore structure has been studied in detail. These poly(ionic liquid)-based porous networks (PILPNs) have then been employed as precursors in two distinct applications, namely organocatalysis and production of microporous carbon monoliths. Selected organocatalyzed reactions, including carbonatation of propylene oxide by cycloaddition with carbon dioxide, benzoin condensation, and cyanosilylation of benzaldehyde have been readily triggered by PILPNs acting as crosslinked polymer-supported (pre)catalysts. The two latter reactions required the prior deprotonation of the imidazolium salt units with a strong base to successfully generate polymer-supported N-heterocyclic carbenes, referred to as poly(NHC)s. Facile recycling and reuse of polymer-supported (pre)catalysts was achieved by simple filtration owing to the heterogeneous reaction conditions. Furthermore, PILPNs could be easily converted into microporous carbon monoliths via CO₂ activation.