Density-viscosity Product Research Articles

Determination of the Physical Properties of Room Temperature Ionic Liquids Using a Love Wave Device

In this work, we have shown that a 100 MHz Love wave device can be used to determine whether room temperature ionic liquids (RTILs) are Newtonian fluids and have developed a technique that allows the determination of the density-viscosity product, ρη, of a Newtonian RTIL. In addition, a test for a Newtonian response was established by relating the phase change to insertion loss change. Five concentrations of a water-miscible RTIL and seven pure RTILs were measured. The changes in phase and insertion loss were found to vary linearly with the square root of the density-viscosity product for values up to (ρη)(1/2) ~ 10 kg m(-2) s(-1/2). The square root of the density-viscosity product was deduced from the changes in either phase or insertion loss using glycerol as a calibration liquid. In both cases, the deduced values of ρη agree well with those measured using viscosity and density meters. Miniaturization of the device, beyond that achievable with the lower-frequency quartz crystal microbalance approach, to measure smaller volumes is possible. The ability to fabricate Love wave and other surface acoustic wave sensors using planar metallization technologies gives potential for future integration into lab-on-a-chip analytical systems for characterizing ionic liquids.

Electrochemical deposition of silver from 1-ethyl-3-methylimidazolium trifluoromethanesulfonate

Silver was successfully electrodeposited from the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIm][TfO]) containing silver ions in various concentrations. The electrochemical windows of the electrolytes were determined by cyclic voltammetry. Moreover, the conductivity and the viscosity–density product were studied with electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance (EQCM). Potentiodynamic and potentiostatic depositions were performed at different temperatures. The morphology of the deposited Ag layers depends on temperature and concentration. Thus, by choosing the right experimental conditions one can optimize the properties of the deposited layers. The thus obtained layers can be used in different surface finishing processes, such as in decorative plating, catalysis or for electrical contacts.

Characterization of the behaviour of a quartz crystal resonator fully immersed in a Newtonian liquid by impedance analysis

The response in resonance frequency and dissipation of a quartz crystal resonator totally immersed in a liquid medium was theoretically and experimentally studied as a function of overtone number along a wide overtone range. In the experimental part it was observed that parasitic effects caused by finite crystal size and interference with inharmonic modes reduce the experimental valid overtone domain. In particular, it was shown that the fundamental mode significantly deviates from other harmonics trend. In the valid working domain, it was observed that the dissipation and resonance frequency follow a regular behaviour versus overtone number. A model that accounts for the interfacial factors through two parameters in addition to viscous damping was developed to reproduce the experimental behaviour observed as a function of overtone order. One parameter represents the thickness of a virtual viscoelastic layer deposited onto the crystal surface whereas another parameter takes into account the contribution of interfacial effects on the dissipation. The proposed model leads to an excellent agreement with experiments of both resonance frequency and bandwidth despite the presence of only one parameter in each expression. Moreover, carrying out comparison with various liquids having an electrical conductivity below 10 −6 S/m and covering a wide range of viscosity-density product shows that the parameter occurring in the expression of dissipation only depends on the quartz resonator characteristics whereas the other coefficient is linked to both quartz oscillator and liquid behaviours.

Miniature density–viscosity measurement cell utilizing electrodynamic-acoustic resonator sensors

Miniaturized physical sensors for precise density and viscosity measurement are required as supplement or replacement for complex and expensive laboratory instruments. Utilizing miniature mechanical resonators as transducers, one can greatly reduce the necessary liquid volume, measurement time, and complexity of the experimental setup. In this contribution, we describe the development of a miniature, modular measurement setup for a large viscosity range. We devised and fabricated an inexpensive flow-through cell using milling technology of multiple PCB layers and Parafilm or Teflon sealing for easy assembly and disassembly. The mechanical resonator is designed as a suspended plate using electrodynamic Lorentz force excitation and movement induction detection. Quality factor and frequency shift of the resonator are evaluated and related to the density–viscosity product of different test liquids at multiple resonant modes of vibration at low operating frequencies for different temperatures and over a wide range of different viscosities.

Small volume laboratory on a chip measurements incorporating the quartz crystal microbalance to measure the viscosity-density product of room temperature ionic liquids.

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of approximately 10 kg m(-2) s(-0.5). This method has reduced the sample size needed for characterization from 1.5 ml to only 30 mul and allows the measurement to be made in an enclosed system.

Miniature flow-through resonator cell for density and viscosity sensing

Miniaturized physical sensors for precise density and viscosity analysis are required as supplement or replacement for complex and expensive laboratory instruments. Utilizing miniature mechanical resonators as transducers, one can greatly reduce the necessary liquid volume, measurement time, and complexity of the experimental setup. In this contribution, we describe the development of a miniature, modular measurement setup for a large viscosity range. We devised and fabricated an inexpensive flow-through cell using milling technology of multiple PCB layers and Parafilm sealing for easy assembly and disassembly. The mechanical resonator is designed as a suspended plate using Lorentz force excitation and movement induction detection. The Qfactor of the resonator is evaluated and related to the density-viscosity product of different test liquids at multiple resonant modes of vibration at low operating frequencies for over a wide range of different viscosities.

Characterization of viscoelastic properties of adsorbed biomolecules and biomolecular assemblies with high frequency micromachined quartz resonators

Micromachined quartz crystal resonator arrays operating in the 66–69 MHz fundamental mode range were tested for their ability to provide high sensitivity to mass loading and viscoelastic properties of biomolecules and biomolecular assemblies. Calibrations using viscous water–glycerol mixtures give the expected linear dependence on the square root of the density–viscosity product. Sequential adsorption of avidin layers interspersed with dithiobis(sulfosuccinimidylpropionate) (DTSSP) or biotynilated bovine albumin (BBA) cross-linker layers provided thick and planar viscoelastic layers for testing. The data reveal a high Q-factor sensitivity and the observed complex impedance changes could be accounted for using a layer dependent, variable viscosity model treated with continuum mechanics approach. The best interpretation of the frequency and Q-factor changes indicates that the layer material properties are most likely dominated by the frictional effects arising from the inter-linking molecules between the layers. These results show the ability of these high frequency micro resonators as an incisive tool for analyzing both static loading and dynamic viscoelastic properties of bimolecular adsorbates.

Density−Viscosity Product of Small-Volume Ionic Liquid Samples Using Quartz Crystal Impedance Analysis

Quartz crystal impedance analysis has been developed as a technique to assess whether room-temperature ionic liquids are Newtonian fluids and as a small-volume method for determining the values of their viscosity-density product, rho eta. Changes in the impedance spectrum of a 5-MHz fundamental frequency quartz crystal induced by a water-miscible room-temperature ionic liquid, 1-butyl-3-methylimiclazolium trifluoromethylsulfonate ([C4mim][OTf]), were measured. From coupled frequency shift and bandwidth changes as the concentration was varied from 0 to 100% ionic liquid, it was determined that this liquid provided a Newtonian response. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][NTf2], with concentration varied using methanol, was tested and also found to provide a Newtonian response. In both cases, the values of the square root of the viscosity-density product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods; the pure ionic liquids had the largest difference of approximately 10%. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained; these 12 all had a Newtonian response. The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of square root(rho eta) approximately 18 kg m(-2) s(-1/2), but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.

Real-Time Viscosity Measurement for Condition-Based Monitoring Using Solid-State Viscosity Sensor

For optimal condition-based monitoring the measurement of viscosity is essential. Consideration of the manufacturing sector renders laboratory approaches as unsuitable, due to the lag-time between sampling and results reporting. Therefore, the continuous measurement approach has been considered the most ideal, yielding instantaneous results reporting and quality control feedback. The historical design of viscometers has resulted in a complex, highly mechanical device associated with a high cost and selling price. Highly sensitive solid-state viscosity sensors in an online configuration will provide the benefits of fast results reporting, simple fluidics management, and advantageous cost/benefit relation. The sensor measures viscous damping of a surface shear wave on a quartz crystal to obtain the viscosity-density product of the sample. The sensor offers solid-state reliability, real-time response time, and is immune to flow conditions and vibration while designed for the challenging process control environments and for OEM applications.

Decoupling of the Liquid Response of a Superhydrophobic Quartz Crystal Microbalance

Recent reports using particle image velocimetry and cone-and-plate rheometers have suggested that a simple Newtonian liquid flowing across a superhydrophobic surface demonstrates a finite slip length. Slippage on a superhydrophobic surface indicates that the combination of topography and hydrophobicity may have consequences for the coupling at the solid--liquid interface observed using the high-frequency shear-mode oscillation of a quartz crystal microbalance (QCM). In this work, we report on the response of a 5 MHz QCM possessing a superhydrophobic surface to immersion in water--glycerol mixtures. QCM surfaces were prepared with a layer of SU-8 photoresist and lithographically patterned to produce square arrays of 5 mum diameter circular cross-section posts spaced 10 microm center-to-center and with heights of 5, 10, 15, and 18 microm. Non-patterned layers were also created for comparison, and both non-hydrophobized and chemically hydrophobized surfaces were investigated. Contact angle measurements confirmed that the hydrophobized post surfaces were superhydrophobic. QCM measurements in water before and after applying pressure to force a Cassie-Baxter (non-penetrating) to Wenzel (penetrating) conversion of state showed a larger frequency decrease and higher dissipation in the Wenzel state. QCM resonance spectra were fitted to a Butterworth-van Dyke model for the full range of water-glycerol mixtures from pure water to (nominally) pure glycerol, thus providing data on both energy storage and dissipation. The data obtained for the post surfaces show a variety of types of behavior, indicating the importance of the surface chemistry in determining the response of the quartz crystal resonance, particularly on topographically structured surfaces; data for hydrophobized post surfaces imply a decoupling of the surface oscillation from the mixtures. In the case of the 15 microm tall hydrophobized post surfaces, crystal resonance spectra become narrower as the viscosity-density product increases, which is contrary to the usual behavior. In the most extreme case of the 18 microm tall hydrophobized post surfaces, both the frequency decrease and bandwidth increase of the resonance spectra are significantly lower than that predicted by the Kanazawa and Gordon model, thus implying a decoupling of the oscillating surface from the liquid, which can be interpreted as interfacial slip.

Piezoelectric resonator and high-frequency admittance study of viscosity and density changes in a thin water layer adjacent to the electrode surface

Analysis of the admittance of quartz resonator in contact with water has shown that the viscosity–density product of water at a metallic electrode surface decreases during the positive potential scan. This decrease is more pronounced when the electrode surface is coated by a thin layer of polymer. Literature data provide evidence that the density of water in the first layer attached to the surface increases when the potential is shifted into the positive direction. It is concluded that during such potential scan the decrease of viscosity is larger than the increase of density.

Characteristics of the series resonant-frequency shift of a quartz crystal microbalance in electrolyte solutions

We report the novel characteristics of the series resonant-frequency shift, DeltaF, of a one-face sealed quartz crystal microbalance (QCM) in solutions of monovalent electrolytes and divalent electrolytes. In the present study, we used NaCl, KCl, LiCl, NaNO3 and CH3COONa as monovalent electrolytes, and MgCl2, CaCl2, MgSO4 and Na2SO4 as divalent electrolytes. These experiments reveal that, in all the solutions, the DeltaF values vary linearly with an increase in the square root of the density-viscosity product of the solutions, and the immersion angle dependence of DeltaF appears. Moreover, we have found that the intercept values of DeltaF are dependent only on the cation species, and that the slope values of DeltaF with the viscosity and density of the solutions are related only to the valence of ions. We also suggest that the DeltaF values are independent of anion species, conductivity and permittivity of the solutions.

Liquid density analysis of sucrose and alcoholic beverages using polyimide guided Love-mode acoustic wave sensors

A liquid density sensor using Love-mode acoustic waves has been developed which is suitable for use in the food and drinks industries. The sensor has an open flat surface allowing immersion into a sample and simple cleaning. A polyimide waveguide layer allows cheap and simple fabrication combined with a robust chemically resistant surface. The low shear modulus of polyimide allows thin guiding layers giving a high sensitivity. A dual structure with a smooth reference device exhibiting viscous coupling with the wave, and a patterned sense area to trap the liquid causing mass loading, allows discrimination of the liquid density from the square root of the density–viscosity product (ρη)0.5. Frequency shift and insertion loss change were proportional to (ρη)0.5 with a non-linear response due to the non-Newtonian nature of viscous liquids at high frequencies. Measurements were made with sucrose solutions up to 50% and different alcoholic drinks. A maximum sensitivity of 0.13 µg cm−3 Hz−1 was achieved, with a linear frequency response to density. This is the highest liquid density sensitivity obtained for acoustic mode sensors to the best of our knowledge.

The effect of SU-8 patterned surfaces on the response of the quartz crystal microbalance

In this work we present data showing the effect of patterning layers of SU-8 photoresist on a quartz crystal microbalance (QCM) and subsequent chemical treatment to increase their hydrophobicity. Patterns with 5 μm diameter pillars spaced every 10 μm have been fabricated with heights of 3, 5 and 10 μm in addition to equivalent thickness flat layers. Contact angle measurements have been made before and after the hydrophobic chemical treatment. The change in resonant frequency of the QCM has been investigated as the surfaces were submerged in solutions of water/PEG with changing viscosity–density product.

High sensitivity Love-mode liquid density sensors

An experimental study into Love-mode liquid sensors using polyimide for a waveguide layer has been carried out. Love devices were built on Y-ST quartz with 40 μm wavelength inter-digitated transducers operating up to 124.7 MHz, and polyimide layers between 0.65 and 1.5 μm thick. The optimum polyimide thickness was 0.85 μm exhibiting a minimum insertion loss of 16 dB. Surface corrugations from 2.5 μm wide and 0.5 μm deep were etched in the polyimide to discriminate the liquid density from the square root of the density–viscosity product. A maximum sensitivity of up to 0.36 μg cm −3 Hz −1 has been obtained, a higher value than found in most other studies.

Probing the vapor-liquid phase behaviors of near-critical and supercritical fluids using a shear mode piezoelectric sensor.

With the rapidly expanding industrial and research applications of near-critical and supercritical technology there is a pressing need for a simple and inexpensive sensor that may be used to determine the phase coexistence regions of fluid mixtures and to establish whether a fluid system is below, at, or above, a critical point. Mechanically vibrating AT-cut quartz plates may be used to determine the product of the fluid density and viscosity of a fluid in which it is immersed, through measurement of the impedance minimum of the electrical equivalent circuit or of the corresponding frequency. The density-viscosity product changes abruptly between fluid phases and rapidly along the isotherm corresponding to the critical temperature, enabling such a plate to act as a sensor of these fluid features. We consider the limitations and linearity of such a sensor and its behavior when a liquid-gas meniscus crosses its surface. We demonstrate for the first time the effective use of an AT-cut quartz sensor in mapping the phase behavior of fluids, using measurements made on carbon dioxide and ethane for calibration and then investigating an ethane-carbon dioxide mixture. The advantages of this experimental approach are that (i) piezoelectric sensors are available for operation up to 1,000 degrees C and at extremely high pressures and (ii) the measurement of the density-viscosity product of supercritical fluids is inherently simpler than traditional techniques for determining phase behavior.

Network analysis based interface electronics for quartz crystal microbalance

The application of resonant sensors such as quartz crystal microbalance (QCM) resonators requires interface electronics to measure parameters that characterize sufficiently the resonant behavior of the sensor due to effects under investigation. Common oscillators as sensor electronics have two major disadvantages. Since they measure the resonant frequency shift as the only parameter their employment is restricted to mass sensing of thin and rigid films in terms of QCM. Because of spurious phase shifts the measured resonant frequency may be erratic. In order to characterize the sensor itself or a material on the sensor surface more parameters such as damping are to be measured. Therefore, a sensor electronics was developed that precisely acquires the impedance spectrum of the resonant sensor in a small frequency range which reflects properties like thickness of a sensor coating, its density, and shear moduli or the density-viscosity product when measuring in liquids. Originally developed as a sensor interface electronics this novel device can help researchers to investigate any effects or material parameters affecting the impedance spectrum of the sensor. In this article the measurement concept of the network analysis based device will be explained followed by details of realization on single printed cardboard. Measurement errors are estimated by simulation and by a comparison of measurement results from a commercially available network analyzer as a reference. Examples of laboratory and industrial applications will be given.

Measuring Newtonian viscosity from the phase of reflected ultrasonic shear wave

In this paper, an acoustic shear impedance model is employed to obtain a relation between the viscosity of a Newtonian fluid and phase characteristics of ultrasonic shear wave reflection from a solid–fluid interface. The phase and magnitude of the reflection coefficient can be decoupled in this model. The decoupling allows an independent relation between the acoustic shear impedance (viscosity–density product) and phase of the reflection coefficient. The model was experimentally verified for different fluid–solid combinations. Comparison of the results with the commonly used absolute reflection coefficient method demonstrates that phase measurement provides improved measurements.

Viscosity sensor utilizing a piezoelectric thickness shear sandwich resonator

This paper describes a novel quartz crystal sensor for measurement of the density-viscosity product of Newtonian liquids. The sensor element consists of two piano-convex AT-cut quartz crystals vibrating in a thickness-shear mode with the liquid sample in between. This special set-up allows suppression of disturbing resonances in the liquid layer. Such resonances are generated in the common single-plate arrangements due to compressional waves caused by spurious out-of-plane displacements of the shear vibrating finite plate. The primary measurands of the sensor are the fundamental resonance frequency and the associated resonance Q-value, which are influenced by the viscously entrained liquid contacting the quartz surface. The sensor allows the measurement of samples with viscosities from almost zero (air!) up to 200 cP with a sample volume of 130 microl.

Prediction ability of a lumped-element equivalent-circuit model for thickness-shear mode resonators in liquids

The viscosity-density prediction ability of a lumped-element equivalent-circuit model for a thickness-shear mode resonator operating in Newtonian liquids is examined. The model is a Butterworth-Van Dyke equivalent-circuit modification that describes the near-resonance electrical characteristics of a liquid-loaded resonator. By comparing the relative significance of different load contributions, a simplified liquid-phase lumped-element model is introduced. This model is calibrated with an admittance measurement on a resonator in contact with water. With the calibrated model, the liquid viscosity-density product is predicted from measurements made in aqueous glycerol solutions. These predictions are found to be accurate compared to the literature values. In addition, the predicted value for the average surface roughness of the resonator is consistent with the presented SEM micrographs.