Measurement assembly and method for measuring interfacial tension

Abstract

To disclose a measurement assembly and method for measuring interfacial tension between two liquids.SOLUTION: A measurement assembly for measuring interfacial tension includes a container (10) having a chamber (11) containing a carrier liquid (31). A sample liquid (36) is supplied dropwise to the chamber (11) via a supply device (20). A magnetic field source (40) generates a non-uniform magnetic field with a vertical magnetic field gradient in the chamber (11). A measurement device (50) detects at least a part of a contour of a droplet (37) of the sample liquid (36) formed in the chamber (11) during operation of the measurement assembly.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application relates to a measurement assembly and method for measuring the interfacial tension between two liquids, and in particular to an optical tensiometer that optically detects the contour of a liquid drop. [Background technology]

[0002] Tensiometers for measuring surface or interfacial tension can be used to monitor industrial processes and determine the flow behavior of liquids. Knowledge of flow behavior can be incorporated into the design and development of products, technological processes, and industrial plants. Optical tensiometers for droplet contour analysis measure the shape of droplets and infer the surface or interfacial tension from the shape parameters.

[0003] In contact angle measurements, a drop of the liquid to be analyzed is placed on a solid surface, the contact angle between the drop and the solid surface is measured using optical methods, and the surface tension of the liquid to be analyzed is calculated from the contact angle using Young's equation.

[0004] The trapped bubble method involves generating gas bubbles in the liquid under analysis, which then attach to the surface of a solid immersed in the liquid. Again, the contact angle between the droplet and the solid surface is measured using optical methods, and the surface tension of the liquid under analysis is estimated from the contact angle using Young's equation.

[0005] In the pendant drop technique, the shape of a drop of the liquid being analyzed hanging from a capillary is optically detected. The Young-Laplace equation can be used to estimate the interfacial tension from the location of a characteristic point on the drop's surface and / or the drop's size at breakoff.

[0006] The static drop method involves placing a drop of the liquid to be analyzed on a semicircular solid base and detecting its shape. Surface tension is estimated using the Young-Laplace equation.

[0007] In the spinning drop method, a drop of sample liquid is added to a heavier phase in a horizontally mounted cylindrical cannula. Rotating the cannula about its longitudinal axis changes the droplet's profile. The interfacial tension between the sample liquid and the heavier phase can be estimated from the change in profile using the Vonnegut and Young-Laplace equations.

[0008] The effect of a uniform magnetic field on the shape of a droplet was investigated in the papers Sudo, S. Hashimoto, H., Ikeda, A: Measurements of the Surface Tension of a Magnetic Fluid and Interfacial Phenomena; JSME international journal (1989), Series II, Vol.1, pp.47-51, Flament C. et al.: Measurements of ferrofluid surface tension in confined geometry; Phys.Rev. E (1996), Vol.53, 4801, und Hayakawaab, M. et al.: Effect of moderate magnetic fields on the surface tension of aqueous liquids: a reliable assessment; RSC Adv., 2019, 9, 10030-100033. Summary of the Invention [Problem to be solved by the invention]

[0009] The present application aims to measure the interfacial tension between two liquids in a simple manner.

[0010] This object is achieved by a measurement assembly and a method according to the independent claims. Advantageous embodiments are derived from the dependent claims.

[0011] The following figures illustrate embodiments of the measurement assembly of the present invention or embodiments of the method of the present invention. The elements and structures shown in the figures are not necessarily drawn to scale relative to each other. Identical reference numerals indicate identical or corresponding elements and structures. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows a schematic diagram of a measurement assembly for measuring the interfacial tension between a carrier liquid and a sample liquid according to one embodiment. [Figure 2] FIG. 2 shows the profile of a droplet of sample liquid during a measurement of the measurement assembly shown in FIG. 1 when a measurement is made according to one embodiment. [Figure 3] FIG. 3 shows a perspective view of the container, feeding device, and magnetic field source of the measurement assembly shown in FIG. [Figure 4] FIG. 4 shows a perspective view of details of the measurement assembly shown in FIG. [Figure 5] FIG. 5 shows a schematic diagram of a measurement assembly for measuring interfacial tension, according to one embodiment, including a dosing pump for delivering sample liquid drop by drop and an optical device for measuring the shape of the droplets. [Figure 6] FIG. 6 shows a schematic perspective view of a measurement assembly for measuring interfacial tension using impedance / resistance measuring sensors / electrodes located on the walls of a cuvette having a rectangular base area in one embodiment. [Figure 7] FIG. 7 shows a schematic perspective view of a measurement assembly for measuring interfacial tension using impedance / resistance measuring sensors / electrodes located on the walls of a cuvette having a circular base area in one embodiment. [Figure 8A] FIG. 8A shows a schematic diagram of a carrier liquid-filled chamber of a measurement assembly during a step in a method for measuring interfacial tension, in one embodiment. [Figure 8B] FIG. 8B shows a schematic diagram of the carrier liquid-filled chamber of the measurement assembly at different stages of a method for measuring interfacial tension, in one embodiment. [Figure 8C] FIG. 8C shows a schematic diagram of the carrier liquid-filled chamber of the measurement assembly at different stages of a method for measuring interfacial tension, in one embodiment. [Figure 8D] FIG. 8D shows a schematic diagram of the carrier liquid-filled chamber of the measurement assembly at different stages of a method for measuring interfacial tension, in one embodiment. [Figure 9] FIG. 9 shows a schematic diagram of a process line with a measurement assembly placed in the bypass to measure interfacial tension in another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] In the following detailed description, reference is made to the accompanying drawings, which form a part of the description and which show, by way of illustration, specific embodiments that may be used to practice the present invention. Directional terms such as "up," "down," "front," "rear," "forward," and "rearward" are used with reference to the orientation of the figures being described. Because components of the embodiments may be oriented in multiple different orientations, these directional terms are for descriptive purposes only and should not be construed as limiting in any way. Other embodiments exist in addition to the illustrated embodiment. Structural or logical changes may be made to the embodiments shown in the figures and / or described in the following text without departing from the claimed subject matter. Unless explicitly or inherently indicated otherwise, features of the described embodiments may be combined with one another. Vertical axes and directions are parallel or approximately parallel to the direction of gravity.

[0014] One aspect of the present disclosure relates to a measurement assembly for measuring the interfacial tension of a sample liquid, the measurement assembly comprising a vessel having a chamber for containing a carrier liquid, a supply device, a magnetic field source, and a measurement device.

[0015] For example, the container is a cuvette having plane-parallel sides suitable for optical inspection of its contents. The material of at least two opposing sides is transparent in the wavelength range used for optical inspection. The transparent material is glass (e.g., fused silica) or transparent plastic. Except for the entrance opening, the cuvette may be closed and sealed, or open.

[0016] The supply device is designed to supply the sample liquid drop by drop into the chamber. For example, the supply device may comprise a cannula connectable to a dosing pump, the cannula having an outlet opening at its free end within the chamber. The supply device may have a guide for fixing the free end of the cannula in a working position within the chamber of the cuvette.

[0017] The magnetic field source is configured to generate a non-uniform magnetic field with a vertical magnetic field gradient within the chamber. The magnetic field source may be, for example, an electromagnet or a permanent magnet in a fixed relationship to the vessel. The magnetic field source may be permanently connected to the vessel in a forced-locking arrangement, or the vessel and magnetic field source may be temporarily connected to each other in a forced-locking arrangement.

[0018] If the density of the sample liquid ρ is less than the density of the carrier liquid ρ, the magnetic field source can be located above the chamber. If the density of the sample liquid ρ is greater than the density of the carrier liquid ρ, the magnetic field source can be located below the chamber.

[0019] The measurement device is designed to detect at least one section of the contour of a droplet of sample liquid formed in the chamber during operation of the measurement assembly. The droplet is at least approximately point-symmetric in a horizontal cross section. The contour is a parallel projection of the maximum vertical cross-sectional area of ​​the droplet onto a vertical plane. The measurement device can detect one or more sections of the droplet's contour, or the entire contour, in one plane or multiple non-parallel planes.

[0020] In operation of the measurement assembly, the container is filled with a paramagnetic carrier liquid. A dispensing device injects at least one drop of sample liquid into the carrier liquid. After several successive drops are injected, the injected drops solidify into a single drop.

[0021] The position of the droplet on a vertical axis parallel to the direction of gravity results from the equilibrium of gravity, buoyancy, and magnetic gradient forces.

[0022] In a non-uniform magnetic field, the droplet contour is noticeably deformed, and the droplet shape depends on the local magnetic field strength and the material properties of the carrier and sample liquids. In this process, the side of the droplet exposed to strong magnetic pressure becomes flatter than the side exposed to weaker magnetic pressure. Depending on the droplet's position relative to the magnetic field source, either the top or bottom side may be exposed to stronger magnetic pressure.

[0023] The measurement device detects at least a portion of the contour and the position of the droplet relative to the magnetic field. The interfacial tension between the carrier liquid and the sample liquid can be inferred from the contour, the local magnetic field strength, and the material properties of the carrier liquid and the sample liquid.

[0024] The measurement assembly facilitates the measurement of interfacial tension. It detects the droplet contour when the droplet is completely surrounded by the carrier liquid and not directly adjacent to a third solid phase. The influence of such a third phase on the measurement result is eliminated. There is little or no measurement error due to temperature changes, vibrations, or air movement, which are common in other optical tensiometers.

[0025] According to one embodiment, the measurement assembly comprises an evaluation unit designed to determine significant parameters of the contour (contour parameters) from sections of the droplet contour detected by the measurement device.

[0026] Examples of such significant contour parameters include the maximum vertical extension of the droplet, the vertical distance between the geometric top and bottom of the droplet, the vertical extension along the vertical axis of symmetry of the droplet, the maximum horizontal diameter of the droplet, and the local curvature between the droplet and the surrounding liquid at a selected point (e.g., in the area of ​​the vertical axis of symmetry or in the plane of the maximum horizontal extension).

[0027] In one embodiment, the evaluation unit is designed to determine the interfacial tension between the droplet and the carrier liquid from significant parameters acting locally on the droplet and the magnetic field strength.

[0028] For example, the interfacial tension can be calculated from significant parameters using the Young-Laplace equation by considering the magnetic pressure acting in the perpendicular direction, the magnetic susceptibility of the carrier liquid, and the densities of the carrier and sample liquids.

[0029] In one embodiment, the outlet opening of a delivery device disposed within the chamber is blocked by an open capillary whose diameter is sufficiently narrow that the amount of sample liquid required to form small-volume droplets completely fills the length of the capillary.

[0030] In one embodiment, the measurement assembly comprises a dosing pump connected to the inlet opening of the delivery device, the dosing pump being designed to deliver the sample liquid drop by drop into the chamber of the container.

[0031] In one embodiment, the measurement device comprises a radiation source for electromagnetic waves and a radiation sensor for the electromagnetic waves emitted by the radiation source, the container being positioned in a beam path between the radiation source and the radiation sensor.

[0032] The radiation source emits measurement radiation. The radiation sensor detects a portion of the measurement radiation that passes through the container with spatial resolution. For example, the measurement radiation is broadband or narrowband radiation in the visible wavelength range, the infrared range, and / or the ultraviolet range. The radiation sensor includes a camera with a high-resolution image sensor, such as a far-field optical microscope. The image sensor can be designed to detect a portion of the profile relative to a horizontal plane from at least one side. In another example, the radiation source is an X-ray source and the radiation sensor is an X-ray image sensor.

[0033] In one embodiment, the measurement device includes a plurality of electrodes disposed on the container and an impedance measurement device designed to determine the electrical impedance between every two electrodes.

[0034] The electrodes may be attached to the interior surface of the chamber or embedded in the walls of the chamber. The electrodes may be arranged in two or more rows, with electrodes in the same row being positioned at the same height above the base area of ​​the chamber around the circumference of the chamber.

[0035] The impedance measuring device can transmit a periodic signal as an excitation signal to at least some of the electrodes and measure the complex impedance between two electrodes located at different points on the chamber wall. Alternatively or additionally, the impedance measuring device can include a resistance measuring device, which is designed to determine the electrical resistance between each two electrodes in each case.

[0036] For each electrode, one additional electrode, multiple additional electrodes, or all additional electrodes may be used to perform impedance and / or resistance measurements.

[0037] Due to the different electrical conductivities and dielectric properties of the carrier and sample liquids, the impedance between the electrodes varies as a function of the droplet shape and size, which are reflected in different characteristics of the established impedance or resistance.

[0038] The impedance or electrical resistance between each pair of electrodes provides information about the droplet contour. Based on tomographic reconstruction, the local curvatures of the upper and lower sides of the droplet can be determined, and the interfacial tension can be determined using the Young-Laplace equation.

[0039] In one embodiment, an apparatus for treating or using a process liquid includes a measurement assembly in which the process liquid is permanently supplied to the measurement assembly as a carrier liquid or is removed at predetermined time intervals or by user action, and a controllable process element of the apparatus is controllable as a function of the interfacial tension established by the measurement assembly.

[0040] The process liquid may be the liquid being processed or may be an auxiliary liquid that contributes to the process but is not consumed. The measurement assembly allows for continuous monitoring of processes that act on or depend on the interfacial tension of the carrier liquid during operation.

[0041] Another aspect of the present disclosure relates to a measurement assembly for measuring the interfacial tension of a sample liquid in an operating state. Such a measurement assembly includes a paramagnetic carrier liquid in a chamber of a container, a droplet of sample liquid in the carrier liquid, a magnetic field source, and a measurement device. The magnetic field source is designed to generate a non-uniform magnetic field with a vertical magnetic field gradient in the chamber. The sample liquid is less paramagnetic than the carrier liquid. The sample liquid and the carrier liquid are immiscible. The measurement device is designed to detect at least a portion of the droplet's contour.

[0042] According to one embodiment, the sample liquid comprises a diamagnetic liquid or consists entirely of a diamagnetic liquid except for impurities.

[0043] According to one embodiment, the carrier liquid is an aqueous solution and the sample liquid is a hydrophobic liquid, or the sample liquid is an aqueous solution and the carrier liquid is a hydrophobic liquid, and the carrier liquid and the sample liquid may have different densities.

[0044] According to one embodiment, the carrier liquid is an aqueous solution containing a rare earth salt or salts of rare earths, the anion portion of the dissolved salts including, for example, chloride, nitrate, sulfate, hydrogen sulfate, phosphate, hydrogen phosphate, dihydrogen phosphate, carbonate, and / or bicarbonate ions.

[0045] The cation portion of the dissolved salt can include, for example, dysprosium(III), holmium(III), erbium(III), and / or gadolinium(III) ions. The carrier liquid can be or include, for example, a dysprosium(III) chloride solution (DyCl).

[0046] The sample liquid is, for example, a diamagnetic oil such as paraffin or naphthene. The sample liquid can be selected from the group of organic solutions such as carbon tetrachloride, chlorobenzene, cyclohexane, heptane, hexane, pentane, toluene, triethylamine, etc.

[0047] According to another example, the carrier liquid is a superparamagnetic liquid, for example a ferrofluid, and the sample liquid is a liquid elemental metal, for example mercury, or a liquid metal alloy, for example galinstan.

[0048] Another aspect of the present disclosure relates to a method for determining interfacial tension, the method comprising generating a magnetic field within a chamber of a container having a vertical magnetic field gradient, generating a droplet of a sample liquid within the chamber filled with a carrier liquid, the sample liquid being less paramagnetic than the carrier liquid, the sample liquid and the carrier liquid being immiscible and having different densities, and detecting a significant parameter of the droplet profile, where the sample liquid may be diamagnetic.

[0049] According to one embodiment, the method further comprises determining the interfacial tension from significant parameters acting locally on the droplet and the magnetic field strength.

[0050] According to one embodiment, the droplets are formed by first ejecting a small amount of sample liquid into a chamber to form a precursory nucleus droplet, then ejecting further sample liquid into the chamber to cause it to merge with the precursory nucleus droplet, and ejecting sample liquid into the chamber until the outline of the droplet generated from the precursory nucleus droplet reaches a size that meets a predetermined standard.

[0051] The predetermined criterion may be the maximum difference in height of the flat sides of the droplet over a predetermined minimum horizontal plane, such that if the sides of the droplet are sufficiently flat, significant parameters of the droplet profile can be determined with high accuracy.

[0052] FIG. 1 shows a measurement assembly having a cuvette 15 as a container 10 with a chamber 11 for receiving a carrier liquid 31. The cuvette 15 has a rectangular base plate and two pairs of plane-parallel sides made of transparent plastic. The transparent plastic may be polyimide, polytetrafluoroethylene (PTFE), or polymethyl methacrylate (acrylic glass). The horizontal cross-sectional area of ​​the chamber 11 is, for example, 0.5 cm. 2 2 cm from 2 Within the range of approximately 1 cm 2 The height of the chamber 11 perpendicular to the base plate is at least 0.5 cm to 5 cm, for example, about 1 cm.

[0053] The supply device 20, equipped with a tubular cavity 25 (cannula), is inserted into the cuvette 15. The supply device 20 has an inlet opening accessible from the outside of the chamber 11, a connection part 26 suitable for connection to a flexible tube or a dosing pump, and an upward-facing outlet opening 27 inside the chamber 11. The outlet opening 27 is closed with a capillary 29. The cannula 25 extends continuously from the inlet opening to the outlet opening 27, maintaining the same diameter all the way. The supply device 20 is made, for example, from a 3D-printed plastic part that fits under positive pressure into the lower part of the chamber 11.

[0054] The magnetic field source 40 of the measurement assembly consists of a ring magnet with a central opening. The ring magnet is, for example, a grade N45 neodymium magnet. The ring magnet seals the top of the chamber 11 or is placed on the lid of the cuvette 15. The longitudinal axis of the ring magnet and the longitudinal axis of the capillary 29 are coaxial and collinear. The ring magnet generates a non-uniform magnetic field with a vertical field gradient within the chamber 11.

[0055] At least a portion of chamber 11 above the exit opening of capillary 29 is filled with a carrier liquid 31. Carrier liquid 31 includes a paramagnetic phase having magnetic susceptibility χ and density ρf. The paramagnetic phase may, for example, include or consist of a paramagnetic salt in aqueous solution, multiple paramagnetic salts in aqueous solution, an ionic liquid, an organic solvent, and / or a silicone-based oil.

[0056] Sample liquid 36 is supplied dropwise into chamber 11 via supply device 20. Sample liquid 36 and carrier liquid 31 are immiscible with each other. As sample liquid 36 exits capillary 29, it forms one or more droplets, which detach from capillary 29 and oscillate along the vertical axis until, after a certain time, they reach a position above capillary 29 and away from capillary 29 and magnetic field source 40. During this process, the droplets coalesce into a single droplet 37. The shape of droplet 37 at its final position depends on the magnetic susceptibility χ and density ρf of the carrier liquid, the density ρo of the sample liquid, the magnetic field density at the lower and upper edges of droplet 37, and the interfacial tension between carrier liquid 31 and sample liquid 36.

[0057] The measuring device 50 has a configuration in which a radiation source 51 is arranged on a first side of the cuvette 15 and a radiation sensor 52 is arranged on the opposite side of the cuvette 15 from the radiation source 51. Image Sensor The radiation sensor 52 is, for example, an image sensor.

[0058] The evaluation unit 70 is connected to the measurement device 50 by data communication technology and receives image data describing the contour of the droplet 37 from the measurement device 50. The evaluation unit 70 determines significant parameters of the contour from the received image data (e.g., the local curvature κ of the geometric top edge of the droplet 37). Top and the local curvature κ of the geometric bottom edge of the droplet 37 Bot The geometric top is determined by the highest point on the surface of the drop, and the geometric bottom is determined by the lowest point on the surface of the drop relative to the Earth's surface.

[0059] The significant parameters are the difference in magnetic susceptibility between the sample liquid and the carrier liquid, χ, the density of the carrier liquid, ρf, the density of the sample liquid, ρ0, and the magnetic flux density, B, at the top and bottom ends of the droplet 37. Top and B Bot , and the local curvature κ at the geometric upper and lower edges of the droplet 37 Top and κ Bot Based on this, the evaluation unit 70 calculates the interfacial tension σ between the sample liquid 36 and the carrier liquid 31 according to, for example, Equation #1.

[0060] TIFF2025163670000002.tif10167

[0061] where μ is the vacuum magnetic permeability, g is the free-fall acceleration, h is the vertical distance between the top and bottom of the droplet 37 or the vertical distance between the geometric top and bottom of the droplet 37, and c is the molar concentration of the paramagnetic salt dissolved in the carrier liquid. For example, in a dysprosium(III) chloride solution (DyCl3) in water, c represents the concentration of dysprosium(III) ions in water.

[0062] 2 shows an image of a droplet 37 of process liquid 36 measured by radiation sensor 52 (configured as an image sensor). Droplet 37 is suspended in carrier liquid 31 at a distance z0 from the lower end of magnetic field source 40. Droplet 37 is generated from a number of smaller precursor droplets 32 which sequentially detach from capillary 29 and solidify to form droplet 37.

[0063] In the illustrated case, the upper side of droplet 37 is subjected to a stronger magnetic pressure and is relatively strongly flattened, while the lower side of droplet 37 is subjected to a weaker magnetic pressure and the local curvature of droplet 37 is only slightly reduced.

[0064] The right side of Figure 2 shows the parameters that can be used to calculate the interfacial tension σ obtained from the image on the left side of the figure, e.g., the local curvature κ at the top and bottom edges of the droplet 37. Top and κ Bot When the magnetic field generated by the magnetic field source 40 is known, the magnetic flux density B at the top and bottom of the droplet 37 is Top and B Bot can be calculated from the distances from the top and bottom ends of the droplet 37 to the bottom end of the magnetic field generating source 40.

[0065] FIG. 3 shows the coaxial arrangement of the longitudinal axis of the capillary 29 and the longitudinal axis 49 of the ring magnet 45 .

[0066] FIG. 4 shows typical dimensions for the outer diameter of ring magnet 45, the diameter of the opening of ring magnet 45, and the distance between the opening of capillary 29 and the bottom end of ring magnet 45, as well as a typical hydrodynamic length of droplet 37.

[0067] 5, a dosing pump 60 is connected to the supply device connection 26 via a hose line 65. A cuvette 15 is arranged in the beam path between a radiation source 51 and a radiation sensor 52. A droplet 37 is reproduced on the radiation-sensitive sensor surface of the radiation sensor 52.

[0068] 6 and 7 each show a measurement device 50 having multiple electrodes 55 arranged on the vessel 10. An excitation signal can be output or a measurement signal can be received via the electrodes 55. An impedance measurement device 56 receives the measurement signal from the electrodes 55 (a pair of electrodes) and measures the electrical impedance between two electrodes 55 arranged at different positions on the wall surface of the chamber.

[0069] The electrodes 55 are attached to the inner surface of the chamber 11 or embedded in the wall of the chamber 11. The electrodes 55 are arranged in at least two rows, and the electrodes 55 arranged in the same row are arranged at the same height above the base area of ​​the chamber 11 and along the periphery of the chamber 11.

[0070] The base area of ​​the chamber 11 shown in Figure 6 is rectangular, and the base area of ​​the chamber 11 shown in Figure 7 is circular.

[0071] In impedance measurements, the impedance measuring device 56 outputs a periodic excitation signal to at least one pair of electrodes and measures the complex impedance between the pair of electrodes. Alternatively, the impedance measuring device can measure the electrical resistance between the pair of electrodes.

[0072] Impedance and / or resistance measurements can be made for each electrode 55 using one additional electrode 55, multiple additional electrodes 55, or all additional electrodes 55. The impedance or electrical resistance between each pair of electrodes provides information about the contours of the droplet 37.

[0073] 8A to 8D show a procedure for measuring the interfacial tension between the carrier liquid 31 and the sample liquid based on a schematic longitudinal cross-sectional view of the cuvette 15. FIG.

[0074] Figure 8A shows a cuvette 15 filled with carrier liquid 31. Figure 8B schematically illustrates activation of a magnetic field source 40 that generates a magnetic field with a vertical field gradient within the cuvette 15. In Figure 8C, sample liquid 36 is injected into the cuvette 15 through a cannula 25 that is plugged with a capillary 29. The sample liquid 36 forms a droplet 37. Figure 8D shows the flattened droplet 37 positioned with its top side facing toward the magnetic field source 40.

[0075] 9 shows an apparatus for the treatment or use of a process liquid 81. A line 82 supplies the process liquid 81 to a controllable process device 80. Via a bypass 83, a portion of the process liquid 81 can be permanently drained as needed or at regular intervals and supplied as carrier liquid 31 to the cuvette 15 of the measurement assembly described above. After the interfacial tension has been measured, the carrier liquid can be drained from the cuvette 15 and resupplied, for example, to the line 82.

[0076] The evaluation unit 70 communicates the established interfacial tension to a controllable process device 80. The process device 80 is configured to control a process that is dependent on the interfacial tension of the carrier liquid and adjust process parameters to the most recently set interfacial tension to at least partially compensate for variations in the interfacial tension, or to terminate the process if the interfacial tension falls below or exceeds a predetermined value.

[0077] For example, if line 82 transports a Dy(III) solution and process equipment 80 extracts dysprosium therefrom, interfacial tension measurements using a standardized oil of known density and magnetic susceptibility will provide information about how far the extraction process has already progressed.

[0078] Alternatively, the phase to be examined (e.g., oil) can be introduced via inlet 29 into chamber 15 filled with a standardized carrier liquid of known density and known magnetic susceptibility. The established interfacial tension provides information about the current composition of the oil phase in the reactor. In rare earth extraction / separation processes, the interfacial tension can be used to estimate the content of rare earths in the oil phase.

Claims

1. 1. A measurement assembly for measuring the interfacial tension of a sample liquid, comprising: a container (10) having a chamber (11) containing a carrier liquid (31); a supply device (20) designed to supply a sample liquid (36) into said chamber (11); a magnetic field source (40) designed to generate a non-uniform magnetic field with a vertical magnetic field gradient within the chamber (11); A measurement assembly comprising a measurement device (50) designed to detect at least a portion of the contour of a droplet (37) of sample liquid formed in said chamber (11) during operation of said measurement assembly.

2. 10. The measurement assembly according to any one of the preceding claims, further comprising an evaluation unit (70) designed to measure significant parameters of the contour from the portion of the contour of the droplet (37) detected by the measurement device (50).

3. The measurement assembly according to the preceding claim, wherein the evaluation unit (70) is configured to measure the interfacial tension between the carrier liquid (31) and the sample liquid (36) from the significant parameter and the magnetic field strength acting locally on the droplet (37).

4. 10. A measuring assembly according to the preceding claim, wherein the outlet opening of the supply device (20) arranged in the chamber (11) is closed by a capillary (29).

5. 10. A measurement assembly according to any one of the preceding claims, comprising a dosing pump (60) connected to an inlet opening of the supply device and designed to dispense a sample liquid (36) into the chamber (11) in a dropwise manner.

6. 10. The measurement assembly of claim 9, wherein the measurement device (50) comprises a radiation source (51) and a radiation sensor (52), and the container (10) is arranged in a beam path between the radiation source (51) and the radiation sensor (52).

7. 10. The measurement assembly of claim 1, wherein the measurement device (50) comprises a plurality of electrodes (55) arranged on the container (10) and an impedance measurement device (56), the impedance measurement device (56) being configured to measure the electrical impedance between every two of the electrodes (55).

8. 1. An apparatus for treating a process liquid, comprising: A measurement assembly according to any one of the preceding claims, wherein the process liquid (81) acting as the carrier liquid (31) is supplied to and discharged from the measurement assembly by user operation or at predefined time intervals; and a controllable process device (80) for treating or using said process liquid (81), said process device (80) being controllable as a function of the interfacial tension established by the measurement assembly.

9. 1. A measurement assembly for measuring interfacial tension, comprising: a paramagnetic carrier liquid (31) in a chamber (11) of a container (10); a magnetic field source (40) designed to generate a non-uniform magnetic field with a vertical magnetic field gradient within the chamber (11); a droplet (37) of a sample liquid (36) in the carrier liquid (31), the sample liquid (36) being less paramagnetic than the carrier liquid (31), the sample liquid (36) and the carrier liquid (31) being immiscible and having different densities; A measuring device (50) designed to detect at least a portion of the contour of the droplet (37).

10. 10. The measurement assembly of claim 9, wherein the sample liquid (36) comprises a diamagnetic liquid.

11. 11. A measurement assembly according to claim 9, wherein the carrier liquid (31) is an aqueous solution and the sample liquid (36) is a hydrophobic liquid, or the sample liquid (36) is an aqueous solution and the carrier liquid (31) is a hydrophobic liquid.

12. 12. A measuring assembly according to any one of claims 9 to 11, characterized in that the carrier liquid (31) comprises an aqueous solution containing a salt of a rare earth element.

13. generating a magnetic field having a vertical magnetic field gradient within a chamber of the vessel; generating droplets (37) of a sample liquid (36) in a chamber filled with a carrier liquid (31), the sample liquid (36) being less paramagnetic than the carrier liquid (31), the sample liquid (36) and the carrier liquid (31) being immiscible and having different densities; detecting significant parameters of the droplet (37) profile.

14. 14. The method of claim 13, further comprising determining the interfacial tension from significant parameters acting locally on the droplet (37) and from the magnetic field strength.

15. The method according to claim 13 or 14, characterized in that the droplets (37) are formed by first ejecting a small amount of sample liquid into a chamber to form a precursor nucleus droplet (32) having an initial volume, further ejecting sample liquid into the chamber to cause it to merge with the precursor nucleus droplet (32), and ejecting sample liquid into the chamber until the outline of the droplet (37) generated from the precursor nucleus droplet (32) reaches a size that satisfies a predetermined standard.

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