Test Liquids Research Articles

New Radio-Frequency Liquid Permittivity Measurement System Using Filter-Based Microfluidic Sensor

A new radio-frequency (RF) liquid permittivity measurement system using a filter-based microfluidic sensor is proposed in this paper. Integrating the filter-based sensor with an RF source, a power divider, and a gain/phase detector can form a new permittivity measurement system without using a bulky and expensive vector network analyzer (VNA) to acquire measured data. Since two coupled resonators with a strong coupling synthesize the filter-based sensor, it can provide a stronger electric-field concentration in the sensing area and improve the sensor’s sensitivity. The 8-μL water-ethanol mixtures with ethanol volume fractions (EVF) ranging from 10% - 90% in 10% increments are used as the test liquids to evaluate the proposed sensor and system. Compared with the measured results using the commercial dielectric probe kit, the maximum errors of ε′ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and ε″ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> using the filter-based sensor with a VNA are -4.34% and 13.24%, respectively. At the same time, ε′ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and ε′ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> errors are 8.28% and 14%, respectively, using the proposed permittivity measurement system. Since the proposed permittivity measurement system can flexibly synthesize the sensing area size, control the electric-field intensity, and get rid of a VNA, it makes it easier to satisfy the requirements of various microfluidic sensing scenarios.

Quantitative stray-field T1 relaxometry with the matrix pencil method

The matrix pencil method (MPM) is tested as an approach to quantitatively process multiexponential low-field nuclear magnetic resonance T1 relaxometry data. The data is obtained by measuring T1 saturation recovery curves in the highly inhomogeneous magnetic field of a stray-field sensor. 0.9% brine solutions, doped with different concentrations of a Gd3+ containing contrast agent, serve as test liquids. Relaxation-times as a function of contrast-agent concentration along with the T1 relaxation curves for combinations of multiple different test liquids are measured, and the results from processing using MPM as well as inverse Laplace transformation as a benchmark are compared. The relaxation-time resolution limits of both procedures are probed by gradually reducing the difference between the relaxation-times of two liquids measured simultaneously. The sensitivity to quantify the relative contribution of each component to the magnetization build-up curve is explored by changing their volume ratio. Furthermore, the potential to resolve systems with more than two components is tested. For the systems under test, MPM shows superior performance in separating two or three relaxation components, respectively and effectively quantifying the time constants.

Hierarchically Structured Nanoparticle-Free Omniphobic Membrane for High-Performance Membrane Distillation.

The functional loss of membranes caused by pore wetting, mineral scaling, or structural instability is a critical challenge in membrane distillation (MD), which primarily hinders its practical applications. Herein, we propose a novel and facile strategy to fabricate omniphobic membranes with exceptionally robust MD performance. Specifically, a substrate with a hierarchical re-entrant architecture was constructed via spray-water-assisted non-solvent-induced phase separation (SWNIPS), followed by a direct fluorinated surface decoration via "thiol-ene" click chemistry. Deionized (DI) water contact angle measurements revealed an ultrahigh surface water contact angle (166.8 ± 1.8°) and an ultralow sliding angle (3.6 ± 1.1°) of the resultant membrane. Destructive abrasion cycle and ultrasonication tests confirmed its structural robustness. Moreover, the membrane possessed excellent wetting resistance, as evidenced by the prevention of membrane pore penetration by all low-surface-tension testing liquids, allowing stable long-term MD operation to treat brine wastewater with a surfactant content of 0.6 mM. In a desalination experiment using shale gas wastewater, the omniphobic membrane exhibited robust MD performance, achieving a high water recovery ratio of ∼60% without apparent changes in water flux and permeate conductivity over the entire membrane process. Overall, our study paves the way for a nanoparticle-free methodology for the scalable fabrication of high-performance MD membranes with surface omniphobicity and structural robustness in hypersaline wastewater treatment.

Fabrication of a durable superhydrophobic surface with corrosion resistance on copper

In order to fabrication a durable superhydrophobic surface with corrosion resistance, we have constructed a copper oxide layer with a hierarchical structure in situ on the copper surface by using a chemical treatment. The corrosion resistance and superhydrophobic durability of the surface are enhanced due to the chemical stability of the oxide and the stability of the hierarchical structure. The surface morphology, composition and phase structure were characterized by SEM, EDS, XPS, FT-IR and XRD. The superhydrophobicity of the surface was investigated by wettability tests. The superhydrophobicity durability was investigated by acidic and alkaline solution contact angle test, water immersion test, and UV irradiation test. Electrochemical tests were conducted to examine the potentiodynamic polarization curves and electrochemical impedance spectra to investigate the corrosion resistance of the superhydrophobic specimen. The experimental results are as follows. The oxide formed by chemical treatment is CuO. In the oxide layer, the nano-needles are aggregated into bundles, and the bundles are intertwined with each other to form a stable pyramidal hierarchical structure. The superhydrophobic surface has a water contact angle of 160° and a sliding angle of less than 2°. The superhydrophobic surface is chemically stable. The contact angle is greater than 150 ° for both acidic and alkaline test liquids. The superhydrophobic surface retains its hydrophobicity for a long time when immersed in water. After 20 days of exposure to UV light, the surface remains superhydrophobic. The superhydrophobic specimen has a low corrosion rate and high impedance. The superhydrophobic surface is corrosion resistant and can provide corrosion protection to the substrate.

Symmetric expressions of surface tension components

ABSTRACT Surface tensions of solid materials have been studied over 200 years and widely used for industrial or engineering applications. The surface tensions and surface tension components can be calculated using measured contact angles, for example, by the model studied by Owens and Wendt. The model is often represented in an asymmetric linear form, called the Owens-Wendt-Rabel-Kaelble method, with the use of the linear least squares method. However, due to the practical preference not to use many types of test liquids, the existing statistical analysis is unsuitable, especially when the data measured are scattered. The present work proposes symmetric linear and circular expressions of the model of the two surface tension components. The symmetric linear expression can be used for obtaining the polar and dispersion components of surface tension of a solid; it enables appropriate choices for test liquids, physically meaningful screening of measured values, and clear validation of deduced surface tension components of solids. The symmetric circular expressions can be applied to deduce polar and dispersion components of liquids by using test solids. In conjunction with this, appropriate choices of test solids can be determined.

Study of surface phenomena in nickel-plated electrolytes using a K-100 tensiometer

Modern electroplating usually suggests using electrolytes with special additives in the form of surface-active substances (surfactants). This is especially important for nickel plating electrolytes because of pitting, porosity, and low adhesion strength often accompanying the deposition of coatings is those electrolytes. We present the results of studying surface phenomena in nickel plating electrolytes using a K-100 KRUSS processor tensiometer. The Wilhelmy plate method was used to determine the surface tension of the standard Watts electrolyte and nickel-plating electrolytes added with surfactants, i.e., brightening (saccharin) and anti-pitting (RADO-11) additives. Surface phenomena at the electrolyte-solid interface have been analyzed using the OWRK model. The free energy of the solid surface (steel sample) has been estimated using the contact angle of the sample in test liquids (distilled water, re-hexane). It is shown that the anti-pitting additive RADO-11 is more effective compared to saccharin in increasing the wettability of steel samples and the adhesion strength at the electrolyte-solid interface. The results obtained can be used for nickel plating of plastics and polymer composite materials.

Вільна конвекція — дослідження регулярного теплового режиму в різних шарах по висоті рідини

The rate of cooling (heating) of experimental liquids is investigated separately for five thermocouples located at different heights of the experimental probe. Research is carried out on an experimental stand in the system "environment I — body II", where "environment I" is water, and "body II" is the investigated liquid medium in a thin metal cylindrical shell under conditions of free convection. The rate of cooling (heating) is studied for test liquids: water, sunflower oil, distilled glycerin. The analysis of cooling (heating) processes during free convection of non-stationary heat exchange is carried out. This paper presents research carried out on an experimental stand, which consists of an external metal vessel, containing the environment with a temperature of t1, an internal cylindrical metal vessel containing an experimental liquid medium with a temperature of t2. Accordingly, probes with five thermocouples are placed in hot and cold liquids to take temperature values at a fixed time Non-stationary heat conduction processes occur during heating or cooling of bodies, substances, gaseous media and are accompanied by a change in enthalpy. Non-stationary and stationary processes of body heating due to the internal heat source, the electric heater, are considered in laboratory practice to determine the thermophysical properties of materials, bodies of substances and where cooling occurs due to the surrounding air. The analysis of the excess temperature, carried out separately for each thermocouple, placed along the height of the cylindrical volume, shows that the linearity of the dependence Ln ϑ = f(τ) is preserved, while the influence of free convection on the value of m is manifested. The value of m depends on the height of the liquid layer in which the temperature is measured.

Influence of surface properties of resins used as binders for coatings on the theoretical and experimental adhesion of bacteria

Resin materials are commonly used as binders for coatings that are susceptible to contamination by biofilms that form on any coated surfaces in buildings. In this study, the surface properties of resins (epoxy, acrylic and nitrocellulose) that could influence the theoretical and experimental adhesion of bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) were investigated. Surface roughness was measured by atomic force microscopy (AFM), surface wettability was evaluated using water contact angle measurements, and surface free energy was determined using the contact angle measurements of test liquids with different polarities. Bacterial adhesion was studied theoretically by surface thermodynamics and experimentally by optical microscopy technique. According to the total free energy (ΔGTot) of interactions, regardless of bacterial strain, nitrocellulose was found to be thermodynamically the most favorable for bacterial adhesion (ΔGTot more negative), followed by acrylic and then epoxy, and the theoretical adhesion trend was influenced by acid-base interactions. Compared to the minor difference in surface roughness between the different types of resins, the hydrophobicity and acid-base component of the resins were found to be the key factors influencing bacterial adhesion to resin surfaces. A good relationship was found between the thermodynamic approach and the adhesion experiments (the theoretical and experimental adhesion trend was similar). It was concluded that the thermodynamic approach could be effective in interpreting the initial adhesion behaviors between bacteria and resin surfaces. These results provide insights and tool to optimize the selection of appropriate resin materials as binders for coatings to reduce the risk of biofilm contamination on the coated surfaces in buildings.

Micro/nanofluidic transport by special fibers deposited by electrohydrodynamic direct-writing

Recently micro/nanofluidic transportation is important in many natural and engineering processes, such as water collection, fluid patterning and microfluidic chip. But the natural microstructures for fluid transportation are usually difficult to manufacture and adjust. Here we find that some fibers (the diameters < 10 μm) deposited by electrohydrodynamic direct-writing(EDW) can be directly used for micro/nanofluidic transportation due to the geometries of fibers. The liquid paraffin (its minimum width < 100 nm) can transport along the circular fiber because of the wedge microcavities formed by circular fiber and substrate. Ultrafast directional water transport (about 22 mm/s) has been achieved by oblique elliptic fiber array which has been placed at a distance of 300 μm above the substrate. Moreover, we found that the contact angles of the test liquids on the substrates and on the fiber materials also play a crucial role in this structure. So electrowetting has been used to change the contact angles of water on the substrate to fast switch (response time < 0.4 s) direction of water transport. We think electrohydrodynamic direct-writing the fibers with various geometries opens up new low-cost, high efficiency, fast and accurate pathways to realize fabric-based wearable microfluidic device.

Swelling Behavior and Flow Rates of a Novel Hydrophilic Gasket Used in Composite Geomembrane Vertical Cutoff Walls and Infrastructures Exposed to Contaminated Groundwater

The swelling capacity of novel hydrophilic gaskets used in geomembrane cutoff walls and infrastructures is critical for decreasing the flow rates of contaminated groundwater. This study investigated the swelling behavior, relaxation characteristics, flow rates, and micro-morphology of a hydrophilic gasket with different testing liquids. The radial swelling tests were performed using a device modified from single-lever consolidation instrument. A flow rates model apparatus was manufactured and employed to measure the flow rates of the poor-sealing hydrophilic gasket. According to the test results, the swelling ratio of the hydrophilic gaskets soaked in the DIW were the highest, followed by the NaCl solution, the MSW landfill leachate, and the CaCl2 solution. Relaxation phenomena appeared in all the specimens regardless of the testing liquids. The flow rates of the specimens penetrated with DIW, NaCl, and CaCl2 decreased to a stable state, and then increased extremely slowly to stable values. Moreover, self-healing of the hydrophilic gasket was observed. The micro-morphology indicated that sodium polyacrylate (PAAS) with insufficient expansion could separate from the matrix under high multivalent ionic strength or loading pressure conditions. Therefore, it is critical to develop the modified hydrophilic gasket with resistance to contaminated groundwater for a better barrier performance for use in contaminated sites and infrastructures.

High-Sensitivity Slot-Loaded Microstrip Patch Antenna for Sensing Microliter-Volume Liquid Chemicals with High Relative Permittivity and High Loss Tangent.

This paper proposes a microwave sensor based on a high-sensitivity slot-loaded rectangular microstrip patch antenna (MPA) for measuring microliter-volume liquid chemicals with high relative permittivity and high loss tangent. A rectangular single-ring complementary split ring resonator (SR-CSRR) slot with a bottom-edge center split (BCS) was inserted along the upper radiating edge of the patch to enhance the relative permittivity sensitivity of the MPA. The first resonant frequency of the proposed SR-CSRR-BCS slot-loaded MPA showed the highest sensitivity compared to the resonant frequencies of the MPAs with other commonly used slots for varying the relative permittivity of the planar substrate type material under test from 1 to 10 when placed above the patch. After designing the scaled SR-CSRR-BCS slot-loaded MPA with the unloaded first resonant frequency at 2.5 GHz, a hollow acrylic cylindrical liquid container with an inner volume of approximately 18.6 μL was placed at the top-edge center of the SR-CSRR-BCS slot to achieve maximum sensitivity. A quarter-wavelength transformer was applied between the patch and the feed line of the MPA to improve the impedance mismatch that occurs when liquid chemicals with a high loss tangent are placed in the container. Water, methanol, and ethanol were carefully selected for test liquids to cover a broad range of relative permittivity and high loss tangents. The proposed SR-CSRR-BCS slot-loaded MPA was designed and fabricated on a 0.76 mm-thick RF-35 substrate, and a reference RS-loaded MPA was designed and fabricated for comparison. The shift in the first resonant frequency of the input reflection coefficient characteristic was used for the sensitivity comparison, and the container was filled with 15 μL of the liquids at 25 °C. The measured sensitivity (%) of the proposed SR-CSRR-BCS slot-loaded MPA for water was 0.45%, which was higher than other antenna-based microwave sensors in the literature.

Accuracy and precision of resonant piezoelectric MEMS viscosity sensors in highly viscous bituminous materials

This paper reports on the dynamic viscosity analysis of bituminous materials with piezoelectric MEMS plate-type resonators. To enable measurements even under such strong damping conditions in this high viscous environment, the 10th order roof-tile shaped vibrational mode is exploited. For actuation and sensing, a piezoelectric aluminium nitride (AlN) thin film is used in combination with a tailored electrode design. The resonator is calibrated by measuring its conductance frequency spectrum when immersed in six high viscosity (range: 150–45.000 mPa s) test liquids at temperatures from 30 °C to 100 °C. The determination of dynamic viscosity values of bituminous materials is done using the calibration function from the linear relationship between the quality factor Q and the inverse square root of the density-viscosity product ρμ−1/2 of the test liquids. Next, Q is mapped to ρμ−1/2 for bituminous materials measured at operating temperatures from 70 °C to 150 °C. Within the measurement accuracy a very good agreement of dynamic viscosity values determined by both the MEMS resonator and a rotational viscometer is demonstrated up to a maximum dynamic viscosity of about 60.000 mPa·s. Despite this limitation these results show the outstanding potential of piezoelectric MEMS sensors for the monitoring of even super high-viscous liquid properties.

Novel Microwave Frequency-Locked-Loop-Based Sensor for Complex Permittivity Measurement of Liquid Solutions

In this article, a new microwave frequency-locked-loop (FLL)-based sensor is proposed for complex permittivity measurement of liquid solutions. An interdigitated electrode split-ring resonator (IDESRR) is embedded in the FLL and used as a sensing device to distribute electric field in the near-field region and sense the permittivities of the liquid solutions with different concentrations. When the test liquid is placed on the IDESRR, a deviation will be introduced to the resonance frequency based on the perturbation theory. This frequency deviation accompanies a corresponding phase shift in the FLL operating frequency. The phase-shifted signal then leads the FLL to output a frequency-modulated (FM) signal, whose frequency deviation depends on the concentration level of the test liquid. The quadrature frequency discriminator is used to demodulate this FM signal and transfer it into dc voltages, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{I}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{Q}$ </tex-math></inline-formula> . Reference liquids with known permittivities are used to calibrate the proposed sensor and relate the measured voltages to the dielectric constant and loss tangent. In this article, the water–ethanol mixtures and water–glucose solutions are used as the test liquids to evaluate the measurement performance of the proposed FLL-based permittivity sensor. The measured results obtained using the proposed sensor agree very well with those obtained using the commercial dielectric probe. Moreover, since the proposed permittivity sensor has the benefits of a simple system architecture, high sensitivity, and not requiring a vector network analyzer (VNA), it has great potential to be developed as a new type of biomedical sample sensor.

Environment-dependent fluctuations of potentiometric pH dynamics in geomagnetic field

ABSTRACT This work explores fluctuations of potentiometric pH dynamics in environments with different configurations of geomagnetic fields. High-resolution pH measurements of test liquids are conducted in electromagnetically shielded and thermally stabilized conditions. External measurement environment in two laboratories is modulated by non-conducting/non-magnetic objects of organic and inorganic origins. Totally, 88 experiments in three groups have been conducted during 4 months. The affected pH dynamics at the level of 10−2-10−5 pH is detected in 93.5%, 82.2% and 74.4% depending on dielectric permittivity of environmental objects. Reaction of potentiometric system has a typical delay of 30–180 minutes. Experiments in both laboratories demonstrated 19% difference of reproducibility rate caused by different background fluctuations. To explain the obtained results, the paper discusses the effects of the Earth’s electric and magnetic fields in the form of magnetospheric Poynting vectors or spin-spin forces in geomagnetic field, which affects the productivity of ionic and free-radical reactions. Since the pH level of aqueous solutions controls various biochemical reactions, this mechanism can explain several biological effects with non-contact signal transmission observed in environmental biology and electromagnetic biophysics.

Revisiting the Surface Energy Parameters of Standard Test Liquids with a Corrected Contact Angle Method over Rough Surfaces.

Interfacial free energy is a quantitative basis for explaining and predicting interfacial behavior that is ubiquitous in nature. The contact angle (CA) method can determine the surface free energy (γ) as well as Lifshitz-van der Waals (γLW) and Lewis acid/base (γ+/γ-) components of a solid material from its CAs with a set of known test liquids according to the extended Young-Dupré equation. However, the reliability of the "known" parameters of the test liquids is questioned due to the long-neglected surface roughness effect during calibration of the liquids. This study proposed a simple and practicable two-step approach to correct the energy parameters of several test liquids by incorporating Wenzel's surface roughness relationship into CA measurement. Step 1: water and two apolar liquids (diiodomethane and α-bromonaphthalene) were used as benchmarks to calibrate the surface roughness and energy parameters of two reference solids [apolar poly(tetrafluoroethylene) and monopolar poly(methyl methacrylate)], and step 2: the reference solids were used to calibrate any other test liquids by solving the energy parameters from their CAs in the extended Young-Dupré-Wenzel model. Monte Carlo simulation was used to evaluate error transmission and robustness of the model solutions. The obtained energy parameters (γLW/γ+/γ-) of four test liquids (dimethyl sulfoxide, formamide, ethylene glycol, and glycerol) are 28.01/13.68/4.67, 34.95/3.53/37.62, 26.26/7.51/15.74, and 32.99/9.24/26.02 mJ/m2, respectively, and different from the literature values. The liquids were applied to characterize an example solid surface with true γLW/γ+/γ- values of 28.00/1.00/8.00 mJ/m2 and a roughness index (r) of 1.60. Without correction of the liquid parameters, the calculated surface energy, hydration energy, and hydrophobic attraction energy of the solid sample can deviate by 50, 13, and 27%, respectively. This proves the necessity of correcting parameters of the test liquids before they can be used in CA and interfacial energy studies in the presence of surface roughness.

Possibility to Alter Dynamics of Luminescence from Surface of Polymer Membrane with Ultrasonic Waves.

The temporal dynamics of luminescence from the surface of Nafion polymer membranes have been studied. In fact, the polymer membrane was soaked in liquids with different contents of deuterium. The test liquids were ordinary (natural) water (deuterium content equal to 157 ppm) and deuterium-depleted water (deuterium content is equal to 3 ppm). Simultaneously with the excitation of luminescence, the Nafion plate was irradiated with ultrasonic pulses, having a duration of 1 μs. The ultrasonic waves were generated with different repetition rates and amplitudes, and irradiated the surface of Nafion in the geometry of grazing or normal incidence. Luminescence regimes were studied when the membrane was irradiated with one ultrasonic wave (one piezoelectric transducer) or two counter-propagating waves (two piezoelectric transducers). It turned out that ultrasonic waves, which fall normal to the membrane interface, do not affect the dynamics of luminescence. At the same time, in the case of ultrasonic irradiation in the grazing incidence geometry, sharp jumps in the luminescence intensity occur, and the behavior of these jumps substantially depends on the mode of irradiation: one or two piezoelectric transducers. This allows for control of the dynamics of luminescence from the polymer surface. In accordance with this model, the possibility of altering the luminescence dynamics is due to the effect of unwinding the polymer fibers from the surface toward the liquid bulk upon soaking. It is important that such unwinding does not occur in deuterium-depleted water, which was confirmed in a direct experiment with dynamic light scattering from polydisperse aqueous suspensions of Nafion nanometer-sized particles; these suspensions were prepared in ordinary water and deuterium-depleted water. Thus, ultrasonic irradiation affects the dynamics of luminescence only when Nafion is swollen in ordinary water; in the case of deuterium-depleted water this effect is missed.

Measuring liquid penetration in thin, porous sheets with ultrasound and drop absorption – scope and limitations

Measuring liquid absorption in thin, porous substrates is challenging, yet it is crucial for process performance and product properties in contexts like printing, textiles, or membranes. Drop absorption (DA) measurements and ultrasonic liquid penetration (ULP) measurements did not correlate in earlier work. This work explains the reasons for the poor agreement between the two methods and provides insight on the applicability and limitations of both. Two sets of systematically designed paper substrates and test liquids covering a wide range of penetration speeds were tested. DA and ULP correlated for most penetration speeds. DA results were more reliable in the low-absorbing region, while ULP measurements are especially suited to capture high absorption rates and detect smaller deviations in liquid penetration, which makes it well suited for industrial process control. Trustworthiness of the results has been found to be related to the contact angle of the liquid/substrate pair.

Environmental Stress Cracking of High-Density Polyethylene Applying Linear Elastic Fracture Mechanics.

The crack propagation rate of environmental stress cracking was studied on high-density polyethylene compact tension specimens under static loading. Selected environmental liquids are distilled water, 2 wt% aqueous Arkopal N100 solution, and two model liquid mixtures, one based on solvents and one on detergents, representing stress cracking test liquids for commercial crop protection products. The different surface tensions and solubilities, which affect the energetic facilitation of void nucleation and craze development, are studied. Crack growth in surface-active media is strongly accelerated as the solvents induce plasticization, followed by strong blunting significantly retarding both crack initiation and crack propagation. The crack propagation rate for static load as a function of the stress intensity factor within all environments is found to follow the Paris–Erdogan law. Scanning electron micrographs of the fracture surface highlight more pronounced structures with both extensive degrees of plasticization and reduced crack propagation rate, addressing the distinct creep behavior of fibrils. Additionally, the limitations of linear elastic fracture mechanisms for visco-elastic polymers exposed to environmental liquids are discussed.

Controlling unequal surface energy results caused by test liquids: the case of UV/O3 Treated PET

Ultraviolet/ozone (UV/O3) treatment has been reported to be an effective method to modify properties such as wettability, adhesion or adsorption of plastic surfaces. The change in the surface is measured by contact angle analysis, which employs liquids and their surface tensions (ST) to estimate the surface energy (SE). We found two different practices in the scientific community: (1) the majority of researchers adopted the ST value of liquids from the literature, while (2) other researchers conducted real-time measurements in the lab under ambient conditions prior to SE estimation. To the best of our knowledge, there is no study that compares the difference between the two practices. One study was found to show different SE methods generating unequal SE values for the same substrate. However, there was no definitive conclusion backed by general thermodynamics rules. In this study, we presented (1) a statistical significance test that showed the literature and experimental ST values are significantly different, and studied (2) the effect of different liquid pairs on the SE estimation for UV/O3 treated poly(ethylene terephthalate) (PET) substrate. Modification techniques such as atmospheric pressure plasma or chemical modification were studied previously to examine PET’s wettability and the SE. The UV/O3 treatment was studied to improve adhesion and to modify its chemical properties for adsorption. In contrast, we studied (3) the effect of UV/O3 on wettability at different timeframes and addressed (4) how to control unequal SE based on a method that was refined on a rigorous thermodynamic three-phase system. It must be noted that this method can be generalized to other types of solid surfaces to estimate thermodynamically self-consistent SE values. This work also provides (5) a web-based calculator that complements computational findings available to the readership in the data availability section.

Piezoelectric-AlN resonators at two-dimensional flexural modes for the density and viscosity decoupled determination of liquids

A micromachined resonator immersed in liquid provides valuable resonance parameters for determining the fluidic parameters. However, the liquid operating environment poses a challenge to maintaining a fine sensing performance, particularly through electrical characterization. This paper presents a piezoelectric micromachined cantilever with a stepped shape for liquid monitoring purposes. Multiple modes of the proposed cantilever are available with full electrical characterization for realizing self-actuated and self-sensing capabilities. The focus is on higher flexural resonances, which nonconventionally feature two-dimensional vibration modes. Modal analyses are conducted for the developed cantilever under flexural vibrations at different orders. Modeling explains not only the basic length-dominant mode but also higher modes that simultaneously depend on the length and width of the cantilever. This study determines that the analytical predictions for resonant frequency in liquid media exhibit good agreement with the experimental results. Furthermore, the experiments on cantilever resonators are performed in various test liquids, demonstrating that higher-order flexural modes allow for the decoupled measurements of density and viscosity. The measurement differences achieve 0.39% in density and 3.50% in viscosity, and the frequency instability is below 0.05‰. On the basis of these results, design guidelines for piezoelectric higher-mode resonators are proposed for liquid sensing.