•An advanced Wilhelmy plate method is proposed for irregular shapes.•The sample perimeter of irregular shapes obtains from optical image processing.•Wetting force data measured by the force ...tensiometer is manipulated using the profile plot.
One of the most accurate methods for measuring the dynamic contact angle of liquids on solid surfaces is the Wilhelmy plate method. This method generally requires the use of rectangular samples having a constant perimeter in the liquid during advancing and receding cycles. A new formulation based on the Wilhelmy force balance equation to determine the contact angle for plate samples with irregular shapes has been developed. This method employs a profile plot obtained from an optical image to determine the perimeter (i.e. wetted length) of the sample as a function of the immersion depth. The raw force data measured by the force tensiometer is manipulated using the profile plot and the Wilhelmy equation to determine the wetting force and consequently advancing and the receding contact angle. This method is verified with both triangular and irregular PTFE samples in water, and measured contact angles are in good agreement with results from conventional regular shaped samples with a constant perimeter.
Food foams are thermodynamically unstable systems. Their stabilization remains a challenge in the industry. To understand the interactions between an electrostatic field (SEF) and food foam, a ...microscopic study was conducted. Using a specially designed tensiometer, a liquid droplet (water, WPI solution, chickpea liquor) was placed between two parallel electrodes and subjected to an SEF (0 to 800 kV/m). Images of the pendant droplet were recorded throughout the experiment. Based on Laplace's equation, the surface tension was calculated as function of the applied voltage.
The geometry of the droplet was deformed under SEF. The surface tension decreased proportionally to the rise of the voltage (γdistilled water=21.7.10−3 N/m at 800 kV/m).
The mechanism causing surface tension reduction was found to be the electric charge existing on the liquid surface. By reducing surface tension, drops are likely to break up more easily during expansion, which improves the organoleptic qualities of the foam.
•Tensiometer measures liquid droplets surface tension under electric field.•3 model solutions used: water, WPI solution, and chickpea aquafaba.•For protein solutions, significant reduction of surface tension was determined.
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Early characterization of new drug substances intended for oral application includes not only physicochemical properties and stability but also the ability of the substance to ...permeate through the intestinal mucosa. In this work, a rapid screening method, surface activity profiling (SAP), is proposed as an alternative to animal studies and screening in cell cultures. Measurements are made with a multichannel tensiometer and require only 50 µl of stock solution for the complete permeability analysis. Correlation of SAP results with human absorption was demonstrated for marketed drugs and with absorption in rats for development compounds of Boehringer Ingelheim. Cross-laboratory results for marketed drugs showed excellent agreement. For early stage investigations of lead compounds, where only small amounts of the compound are available, the SAP method appears to be an effective and fast tool to accurately predict fa, provided the compound is amphiphilic.
The benefits of closed-loop irrigation control have been demonstrated in grower trials which show the potential for improved crop yields and resource usage. Managing water use, by controlling ...irrigation in response to soil or substrate moisture changes, to meet crop water demands is a popular approach but requires substrate specific moisture sensor calibrations and knowledge of the moisture levels that result in water deficit or over-watering. The use of water tension sensors removes the need for substrate specific calibration and enables a more direct relationship with hydraulic conductivity. In this paper, we present a novel dielectric tensiometer that has been designed specifically for use in soil-free substrates such as coir, peat and Rockwool with a water tension measurement range of −0.7 kPa to −2.5 kPa. This new sensor design has also been integrated with a precision PID-based (drip) irrigation controller in a small-scale coir substrate strawberry growing trial: 32 strawberry plants in 4 coir growbags under a polytunnel. The data illustrates that excellent regulation of water tension in coir can be achieved which delivers robust and precise irrigation control - matching water delivery to the demands of the plants. During a 30-day growing period vapour pressure deficit (VPD) and daily water use data was collected and the irrigation controller set to maintain coir water tension at the following levels: −0.90 kPa, −0.95 kPa and −1 kPa for at least 7 consecutive days at each level. For each set-point the coir water tension was maintained by the irrigation controller to within ±0.05 kPa. Meanwhile the polytunnel VPD varied diurnally from 0 to a maximum of 5 kPa over the trial period. Furthermore, the combination of the dielectric tensiometer and the method of PID-based irrigation control resulted in a linear relationship between daily average VPD and daily water use over 10 days during the cropping period.
•A novel dielectric tensiometer sensor for use in high porosity soil-free substrates.•Sensor measurement range of −0.7 kPa to −2.5 kPa.•Sensor with precision PID irrigation controller achieves ±0.05 kPa control in coir.•Precise regulation of water tension achieved over a wide range of VPD.•Stable water status enables daily water use to be correlated with average daily VPD.
The purpose of this study was to quantitatively assess Achilles tendon mechanical behavior during gait in children with cerebral palsy (CP). We used a newly designed noninvasive sensor to measure ...Achilles tendon force in 11 children with CP (4F, 8–16 years old) and 15 typically developing children (controls) (9F, 8–17 years old) during overground walking. Mechanical work loop plots (force‐displacement plots) were generated by combining muscle‐tendon kinetics, kinematics, and EMG activity to evaluate the Achilles tendon work generated about the ankle. Work loop patterns in children with CP were substantially different than those seen in controls. Notably, children with CP showed significantly diminished work production at their preferred speed compared to controls at their preferred speed and slower speeds. Despite testing a heterogeneous population of children with CP, we observed a homogenous spring‐like muscle‐tendon behavior in these participants. This is in contrast with control participants who used their plantar flexors like a motor during gait. Statement of Clinical Significance: These data demonstrate the potential for using skin‐mounted sensors to objectively evaluate muscle contributions to work production in pathological gait.
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The architecture of complex-shaped fibres affects the motion of the contact line and the evolution of its associated menisci when a fibre is immersed into a liquid. Understanding and ...predicting the motion of the contact line is critical in the design of complex-shaped fibres for many engineering applications as well as for surface science. While wetting on classic circular cylinders has been well studied, singularities during the wetting process of complex-shaped fibres are not yet well understood.
The dynamic wetting behaviour of axisymmetric sinus-shaped fibres immersed vertically in a liquid volume was investigated. Fibres were 3D-printed down to micrometre dimensions, and the Wilhelmy method was used in parallel with meniscus shape analysis. Moreover, a quasi-static theoretical model predicting the contact line movement and free energy of the system evolution on these fibres is also proposed.
The observation of liquid advancing and receding fronts highlighted a stick-slip motion of the meniscus depending on both the fibre surface curvature and its intrinsic wettability. The model predicts that the behaviour of the seemingly pinned and then jumping contact line, with associated changes in apparent contact angles, can be explained by the interplay between a constant local contact angle and the movement of the bulk liquid, leading to the storage of energy which is suddenly released when the contact line passes a given point of fibre curvature. Besides, acceleration/deceleration events that take place before and after the jumps are experimentally observed in good agreement with the model.
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A new technique of utilizing the dynamic surface tension (ST) data for solubility determination was proposed, tested, and verified in this study. Dibutyl phthalate was chosen as the ...surface-active component and its solutions were prepared with 0, 1, and 5wt.% aqueous methanol (MeOH) solutions. The solutions for ST measurement were prepared by stirring the aqueous DBP mixtures in a heated water bath (45°C) for an extended duration of time. The data revealed that an increase in DBP concentration corresponded to a more rapid relaxation of dynamic ST and reached a lower equilibrium ST; similar to that observed amongst typical micelle forming surfactants (at C<cmc). Unlike surfactants, an increase in concentration beyond a certain value corresponded to near-identical relaxations of dynamic ST and the same equilibrium ST. For typical surfactants, although the equilibrium ST remained constant when concentration was increased at C>cmc, the dynamic ST relaxations became increasingly rapid. These inconsistencies in dynamic ST behavior pointed towards the absence of micelle formation amongst the DBP molecules. Based on the dynamic ST data, the solubility of DBP in water, 1wt.%, and 5wt.% MeOH(aq) were found to be ∼6.1, ∼4.4, and ∼4.7 (10−8mol/cm3), respectively.
Amphiphilic fluorocarbon substances are a trending topic of research due to their wide range of applications accompanied by an alarming environmental and health impact. In order to predict their fate ...in the environment, use them more economically, develop new water treatment methods, etc., a better understanding of their physicochemical behavior is required. Their hydrophobicity in water/oil systems is particularly sensitive to one key thermodynamic parameter: the free energy of transfer of a perfluoromethylene group from oil to water. However, for the –CF2– moiety, the transfer energy values reported in the literature vary by more than ±25%. Due to the exponential relationship between this energy and the adsorption constants or the partition coefficients, such an uncertainty can lead to orders of magnitude error in the predicted distribution of fluorinated species. We address this problem by presenting an experimental determination of the hydrophobic effect of a –CF2– moiety with a greater certainty than currently available. The transfer energy is determined by measuring the interfacial tension of water|hexane for aqueous solutions of short-chained fluorotelomer alcohols. The obtained results for the free energy of transfer of a –CF2– moiety from oil to water are 1.68±0.02×RT0, 1.75±0.02×RT0, and 1.88±0.02×RT0 at 288.15 K, 293.15 K, and 303.15 K, respectively.
•Tensiometer reading errors propagate to soil hydraulic parameters.•Digital tensiometer overestimates soil matric potential.•Larger errors in K(θ) are obtained by Bourdon gauge and digital ...tensiometer.•Alternative tensiometers cause errors in the estimation of van Genuchten equation parameters.
The tensiometer represents an excellent instrument for measuring in situ soil water status. However, measuring soil matric potential requires a tensiometer reading system sensitive enough to accurately record the matric potential. Hence, an instantaneous profile-type experiment was conducted in the field, to measure the soil matric potentials within a moisture range from saturation to field capacity. After that, matric potential, soil moisture, total potential gradient, flow density and hydraulic conductivity were calculated and van Genuchten equation parameters were estimated through inverse modeling. This study aimed to test the Bourdon pressure gauge and digital tensiometer compared with the mercury manometer to measure the soil matric potential and to examine the differences related to the estimations of soil water content and to the associated variables. In addition, the study also aimed to evaluate soil hydraulic parameters by inverse modeling, based on the matric potentials from each reading system. Bourdon pressure gauge replaces the Hg manometer in the measurement of soil water matric potential within the moisture range from saturation to field capacity; The use of digital tensiometer and Bourdon pressure gauge reduced hydraulic conductivity by four and three times and flow density by approximately three and two times, respectively, at 6 kPa tension and, therefore, are not recommended for the estimation of these hydraulic parameters; Regardless of reading system used in the tensiometer, inverse modeling estimates well van Genuchten equation parameters and, consequently, soil water matric potential.
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