Pendant capsule elastometry Hegemann, Jonas; Knoche, Sebastian; Egger, Simon ...
Journal of colloid and interface science,
03/2018, Letnik:
513
Journal Article
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We provide a C/C++ software for the shape analysis of deflated elastic capsules in a pendant capsule geometry, which is based on an elastic description of the capsule material as a ...quasi two-dimensional elastic membrane using shell theory. Pendant capsule elastometry provides a new in situ and non-contact method for interfacial rheology of elastic capsules that goes beyond determination of the Gibbs- or dilational modulus from area-dependent measurements of the surface tension using pendant drop tensiometry, which can only give a rough estimate of the elastic capsule properties as they are based on a purely liquid interface model. Given an elastic model of the capsule membrane, pendant capsule elastometry determines optimal elastic moduli by fitting numerically generated axisymmetric shapes optimally to an experimental image. For each digitized image of a deflated capsule elastic moduli can be determined, if another image of its undeformed reference shape is provided. Within this paper, we focus on nonlinear Hookean elasticity because of its low computational cost and its wide applicability, but also discuss and implement alternative constitutive laws. For Hookean elasticity, Young’s surface modulus (or, alternatively, area compression modulus) and Poisson’s ratio are determined; for Mooney-Rivlin elasticity, the Rivlin modulus and a dimensionless shape parameter are determined; for neo-Hookean elasticity, only the Rivlin modulus is determined, using a fixed dimensionless shape parameter. Comparing results for different models we find that nonlinear Hookean elasticity is adequate for most capsules. If series of images are available, these moduli can be evaluated as a function of the capsule volume to analyze hysteresis or aging effects depending on the deformation history or to detect viscoelastic effects for different volume change rates. An additional wrinkling wavelength measurement allows the user to determine the bending modulus, from which the layer thickness can be derived. We verify the method by analyzing several materials, compare the results to available rheological measurements, and review several applications. We make the software available under the GPL license at github.com/jhegemann/opencapsule.
The soil water retention curve is very critical in the assessment of unsaturated soil behavior. In the past, with the help of the axis translation technique, the pressure plate method was usually ...used to measure the soil water retention curve. However, this test was very time-consuming and required using specimens with the same loading history which was difficult to achieve. In this study, a simple device is proposed to measure the water retention curve of poorly graded sand with silt through a discrete evaporation test in which the soil suction and water content are measured using a high-capacity tensiometer and a digital balance, respectively. Measurement of representative soil suction was achieved through sealing the specimen to allow the water redistribution in the soil after a certain time of free evaporation. Results from this evaporation test indicate that the time required for the soil water retention curve can be significantly reduced from weeks to 1-2 days when compared with the conventional pressure plate method.
•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.
Water retention and shrinkage curves are two important characteristics of unsaturated soils. Conventionally, two curves are separately measured using multiple carefully prepared “identical” soil ...specimens. However, it is difficult or impossible to fabricate soil specimens with exactly identical stress history. The measurement of two curves was very time-consuming (each up to several weeks). Recently, a new method has been proposed to simultaneously measure two curves through shrinkage tests. The soil suction, water content, and volume during testing are monitored during testing for the construction of the water retention and shrinkage curves. Preliminary shrinkage test results prove that the new method is efficient in the measurement of two curves. In this study, a series of shrinkage tests on two types of soils were performed to evaluate this new method using a new device in which the soil suction, water content, and volume are, respectively, measured using a high-capacity tensiometer, digital balance, and a non-contact photogrammetric method. Test results indicate that the new method significantly reduces the time required for the measurement of two curves from weeks to 1 day. The new method allows simultaneous determination of the two curves using one single soil specimen, which also eliminates the influence of different stress histories on the test results. The axial strain distribution during drying can also be identified based on the reconstructed three-dimensional model of the soil, which is beneficial for examining the soil deformation non-uniformity and stress history. Finally, some discussions on the measurement of two curves using the new method are presented.
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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.
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