JP7041968B2 - Surface tension measuring method and surface tension measuring device - Google Patents

Description

The present invention relates to a surface tension measuring method and a surface tension measuring device.

Surface tension, which is the interfacial tension between the liquid phase and the gas phase, is an important physical property of the liquid as well as the viscosity, fluidity, and wettability of the liquid. This measurement of surface tension is carried out in many research fields such as engineering, agriculture, pharmacy, or at production sites. Surface tension is defined as a Gibbs energy change when the surface area of a liquid surface is changed under constant temperature and pressure, or a Helmholtz energy change under constant temperature and constant volume. As a method for measuring surface tension, many measuring methods have been conventionally proposed. However, all of the conventional methods for measuring surface tension are insufficient in terms of reliability, and it cannot be said that a method for measuring surface tension has been established.

As a conventional surface tension measuring method, a suspension plate method (see, for example, Non-Patent Document 1) and an annular method (see, for example, Non-Patent Document 2) are known. The suspension plate method is a widely used surface tension measuring method. When a platinum plate is immersed in a liquid to be measured, the force exerted by the liquid in the direction of pulling the platinum plate is measured. It is a method of measuring the surface tension. Similar to the suspension plate method, the ring method measures the force acting on the ring by the liquid film formed between the ring and the liquid surface when the special ring is immersed in the liquid to be measured and separated from the liquid. By doing so, the surface tension of the liquid is measured. These surface tension measuring methods are standard methods for directly measuring the surface tension of the force acting on the platinum plate or ring mechanically using a torsion scale or a spring scale.

Further, as a surface tension measuring method, a suspension method is provided (see, for example, Non-Patent Document 3). This suspension method is a method of calculating the surface tension from the shape and volume of a droplet suspended from the tip of a capillary tube using a capillary tube. In recent years, a method for measuring the shape more accurately from the image measurement of a droplet has been reported, and it is also used in a commercially available device.

However, in the case of the suspension plate method and the ring ring method, it takes time to measure the dynamic surface tension of the liquid to be measured. Further, in the case of the suspension plate method and the ring ring method, if the platinum plate or ring is contaminated or is not wet with the liquid to be measured, the measurement error becomes large. Further, these surface tension measuring methods utilize the interaction between the platinum plate or ring and the liquid to be measured when the liquid level of the liquid to be measured is stretched in the direction of gravity. Therefore, gravity acting on each part of the liquid to be measured or the viscosity and viscoelasticity of the liquid are likely to cause a measurement error. In particular, when the liquid to be measured is a solution containing a solute such as a surfactant or a polymer, or a two-phase liquid in which a thin liquid film is formed near the liquid surface, such a measurement error is likely to occur. .. Furthermore, in a measuring device that employs the suspension plate method or the ring ring method, a platinum plate or ring of a certain size is required to improve the measurement accuracy, so it is difficult to reduce the size of the platinum plate or ring, and it is difficult to reduce the size of the platinum plate or ring. It is also difficult to reduce the amount of liquid to be measured. The ring method is a surface tension measuring method currently specified by industrial standards such as Japan, the United States, and Germany. The liquid formed between the ring and the liquid level with respect to the obtained measured value. Measurement is difficult because correction is required according to the shape of the film. Further, in the case of the suspension method, the degree of contamination at the tip of the thin tube to be used greatly affects the measurement accuracy.

Therefore, the maximum foam pressure method is provided as a surface tension measuring method for eliminating the disadvantages of the above-mentioned suspension plate method, ring ring method, and suspension method (see, for example, Non-Patent Document 4). In the maximum foam pressure method, air is supplied into the thin tube in a state where the tip of the cylindrical thin tube arranged in a vertical direction is immersed in the liquid to be measured. Then, using the Young-Laplace relational expression, the pressure of the air inside the thin tube when the air bubble generated at the tip of the thin tube separates from the tip of the thin tube and the pressure received by the air bubble generated at the tip of the thin tube from the liquid. The surface tension of the liquid is calculated from the pressure difference of. When the liquid to be measured contains a substance such as a surfactant that has a function of lowering the surface tension of the liquid, the surface tension of the liquid changes dynamically when the surfactant collects on the liquid surface. That is, the wettability of the liquid to be measured changes with time. The maximum foam pressure method is effective for measuring the surface tension of a liquid in which the surface tension changes dynamically.

However, in this maximum bubble pressure method, the Young-Laplace relational expression is used when the air bubbles generated at the tip of the thin tube are assumed to be hemispherical. However, the shape of the air bubbles generated at the tip of the thin tube immediately before leaving the tip of the thin tube is that the contact angle between the liquid to be measured and the inner wall of the thin tube is not 0 degrees, that is, it is not a strict hemisphere. There are many. In fact, when the surface tension of the liquid to be measured is high and the side wall of the thin tube has a certain thickness, the air bubbles generated at the tip of the thin tube often become nearly spherical. It has also been reported that when the inner diameter of the thin tube is increased, the shape of the air bubble generated at the tip of the thin tube becomes a spheroidal shape. Therefore, in this maximum method of pressure, the measured value of the surface tension measured for the standard liquid whose accurate surface tension is known in advance and the measured value of the surface tension of the liquid to be measured are compared with each other to measure the surface tension of the object to be measured. It is necessary to calculate the surface tension of the liquid. Therefore, it takes a certain amount of time to measure the surface tension. However, if the difference between the surface tension of the liquid to be measured and the surface tension of the standard liquid is large, the difference in the shape of the air bubbles generated at the tip of the thin tube becomes significant, and the accuracy of the calculated surface tension decreases. Resulting in. When measuring the dynamic surface tension of the liquid to be measured by the maximum foam pressure method, the measurement is performed while continuously supplying air into the capillary tube to repeatedly generate and disintegrate bubbles. At this time, the flow or vibration generated in the liquid to be measured may excessively promote the collapse of bubbles generated at the tip of the thin tube, which may cause an error in the calculated surface tension.

On the other hand, the wavelength of the surface tension wave (ripron) generated on the surface of the liquid is specified from the light scattered on the liquid surface of the liquid by irradiating the liquid to be measured with laser light, and the specified ripron wavelength. A surface tension measuring method for calculating the surface tension of the liquid based on the propagation velocity of the lipron calculated from the above has been proposed (see, for example, Non-Patent Document 5). Further, a surface tension measuring method for measuring the surface tension of a liquid to be measured from dynamic light scattering by a lipron in a minute region of the liquid surface of the liquid to be measured has also been proposed (see, for example, Non-Patent Document 6). Furthermore, the inner diameter of the thin tube is specified from the interference pattern generated when the laser beam is irradiated from the side of the thin tube whose tip is immersed in the liquid to be measured, and the height of the liquid to be measured that has penetrated into the thin tube is determined. A surface tension measuring method for measuring the surface tension of the liquid using the density of the liquid and the inner diameter of the thin tube has also been proposed (see, for example, Non-Patent Document 7). These surface tension measuring methods can shorten the time required for measuring the surface tension and can also measure the dynamic surface tension of the liquid to be measured.

In addition, the light beam is irradiated from vertically above the cell with the liquid to be measured confined in the cell, and the intensity of the reflected light or transmitted light is measured while changing the angle of incidence of the light beam on the cell. A surface tension measuring method for measuring the surface tension of a liquid to be measured has been proposed (see, for example, Patent Document 1).

L. Wilhelmy, Ann. Phys. Chem. Reiche 4, 29, 177 (1863). P. L. du Nouy, J. Gen. Physiol., 1, 521 (1919). J. M. Andreas, E. A. Hauser, and W. B. Tucker, J. Phys. Chem .., 42, 1001 (1938). M. Simon, Ann. Chim. Phys., 33, 5-41 (1851). S. Hard and R. D. Neuman, J. Colloid Interface Sci., 83, 3315 (1981). C. Pigot and A. Hibara, Anal. Chem., 84, 2557-2561 (2012). T. Munguio and C. A. Smith, J. Chem. Edu., 78, 343-344 (2001).

Special Table 2003-528258 Gazette

However, in order to improve the measurement accuracy of the surface tension in the surface tension measuring method described in Non-Patent Documents 5 and 6, it is necessary to detect the scattered light with high accuracy. Further, in order to improve the measurement accuracy of the surface tension in the surface tension measuring method described in Non-Patent Document 7, it is necessary to detect the interference pattern with high accuracy. Therefore, these surface tension measuring methods require a complicated and large-scale measuring system for detecting scattered light or interference patterns with high accuracy. Then, it takes time to adjust the measurement system and the like, and it may take a long time to measure the surface tension. Further, in the case of the surface tension measuring method described in Patent Document 1, it is necessary to measure the intensity of the reflected light or the transmitted light a plurality of times while changing the angle of incidence of the light beam on the cell. The time required to measure the tension becomes long. In addition, since a mechanism for changing the angle of incidence of the light beam on the cell is required, the measurement system becomes complicated accordingly.

The present invention has been made in view of the above reasons, and an object of the present invention is to provide a surface tension measuring method and a surface tension measuring device capable of measuring the surface tension of a liquid easily and with high accuracy in a short time.

In order to achieve the above object, the surface tension measuring method according to the present invention is:
The other end of the thin tube is immersed in the liquid to be measured stored in the liquid storage cell whose bottom wall transmits light in a preset wavelength band at least at one end of the cylindrical thin tube in the tubular axis direction. A meniscus generation step of forming a meniscus at the interface between the gas in the thin tube and the liquid at the tip of the thin tube by supplying a gas from the tube.
When a laser beam is incident from the other end of the thin tube in the tubular axis direction toward the one end, the light transmitted from the other end of the thin tube through the lens arranged vertically below the meniscus and the liquid storage cell. A distance calculation step for calculating an optical first distance between the lens and the tip of the thin tube, and an optical second distance between the focal position of the lens and the lens.
A radius of curvature calculation step for calculating the radius of curvature of the meniscus based on the first distance and the second distance,
A surface tension calculation step of calculating the surface tension of the liquid from the pressure applied from the gas supplied into the capillary tube in the meniscus, the pressure applied from the liquid in the meniscus, and the radius of curvature of the meniscus is included. ..

The surface tension measuring device according to the present invention from another viewpoint is
A liquid storage cell that stores the liquid to be measured and at least the bottom wall transmits light in a preset wavelength band.
A thin tube that is cylindrical and has one end in the axial direction immersed in the liquid.
A first aperture arranged vertically above the thin tube and provided with a first pinhole having a diameter smaller than the inner diameter of the thin tube.
A gas supply unit that supplies gas from the other end of the thin tube in the tubular axis direction,
A lens placed vertically below the tip of the thin tube,
When a laser beam is incident from the other end of the thin tube in the tubular axial direction toward the one end in a state where a meniscus is generated at the interface between the gas in the thin tube and the liquid at the tip of the thin tube, the thin tube is formed. For light transmitted through the first pinhole, the meniscus, and the lens from the other end of the lens, the first optical distance between the lens and the tip of the thin tube, and the focal point of the light emitted from the lens. A distance calculation unit that calculates the optical second distance between the position and the lens, and
It includes a surface tension calculation unit that calculates the surface tension of the liquid from the pressure applied from the gas supplied into the thin tube in the meniscus, the pressure applied from the liquid in the meniscus, and the radius of curvature of the meniscus. ..

According to the present invention, in the meniscus generation step, meniscus is generated at the tip of the thin tube immersed in the liquid to be measured stored in the liquid storage cell, and in the distance calculation step, from the other end of the thin tube in the tubular axis direction. The first distance and the second distance are measured for the light transmitted through the meniscus and the lens when the light is incident. Then, in the step of calculating the radius of curvature, the radius of curvature of the meniscus is calculated based on the first distance and the second distance, and in the step of calculating the surface tension, the surface tension of the liquid is calculated using the radius of curvature of the meniscus. As described above, using a simple configuration including a liquid storage cell, a thin tube, and a lens, the surface tension of the liquid to be measured can be calculated simply by measuring the first distance and the second distance, which is convenient. Moreover, the surface tension of the liquid can be measured in a short time. In addition, since the radius of curvature of the meniscus generated at the tip of the thin tube is directly calculated optically and the surface tension of the liquid is calculated using the calculated radius of curvature of the meniscus, there is an advantage that the measurement accuracy is higher than that of the maximum foam pressure method. be.

It is a block diagram of the surface tension measuring apparatus which concerns on embodiment of this invention. It is a block diagram of the surface tension measuring unit which concerns on embodiment. It is a block diagram of the processing part which concerns on embodiment. It is a figure which shows the state of the refraction of light in a meniscus generated at the tip of the thin tube which concerns on embodiment. It is a flowchart which shows an example of the flow of the surface tension measurement processing executed by the processing unit which concerns on embodiment. It is a figure which shows the relationship between the pressure difference between the pressure of the air in a thin tube and the pressure applied from the liquid to be measured about pure water, the radius of curvature of a meniscus, and the surface tension calculated from this radius of curvature. It is a photograph of the air bubble generated at the tip of the thin tube when the pressure of the air in the thin tube is around 280 Pa (when the radius of curvature of the meniscus M is the minimum). Air bubbles generated at the tip of the thin tube when the pressure of the air in the thin tube is near 318 Pa (when the pressure of the air in the thin tube 13 is near the pressure (maximum bubble pressure) at which the air bubbles separate from the tip of the thin tube 13). It is a photograph of. It is a figure which shows the correlation between the surface tension measured by using the surface tension measuring apparatus which concerns on this Embodiment, and the literature value of a surface tension. It is a figure which shows the correlation between the surface tension measured by using the surface tension measuring apparatus which concerns on this Embodiment, and the literature value of a surface tension. It is a block diagram of the surface tension measuring unit which concerns on the modification. It is a block diagram of the surface tension measuring unit which concerns on the modification. It is a figure which shows the relationship between the dispersion and the surface tension which concerns on a modification. It is a figure which shows the relationship between the radius of curvature of the meniscus which concerns on a modification, and the pressure difference. It is a schematic diagram for demonstrating the surface tension measuring method which concerns on a modification. It is a figure which shows the relationship between the pressure difference of the pressure applied to the meniscus which concerns on a modification, and the volume of the region inside the meniscus. It is a figure which shows the relationship between the Gibbs energy of the meniscus and the surface area of the meniscus which concerns on a modification.

Hereinafter, the surface tension measuring device according to the embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the surface tension measuring device according to the present embodiment includes a surface tension measuring unit 10, a laser light source 41, an analog-to-digital conversion unit (hereinafter referred to as “ADC”) 32, and a processing unit. 51 and. Further, the surface tension measuring device has an aperture 42 provided with a pinhole 42a for adjusting the beam diameter of the laser light emitted from the laser light source 41, and a surface tension measuring unit for the laser light emitted from the laser light source 41. The mirrors 61 and 62 for guiding to 10 are provided. The laser beam emitted from the laser light source 41 travels along the optical axis J1. The laser light source 41 is, for example, a semiconductor laser or a He-Ne laser.

The surface tension measuring unit 10 includes an optical cell 11, a thin tube 13, a liquid storage cell 14, an air supply unit 81 which is a gas supply unit, a lens 15, a lens holder 71, a lens drive unit 72, and a first. It includes an aperture 21 which is an aperture, an aperture 22 which is a second aperture, a mirror 63, and an optical detector 31. The laser beam emitted from the laser light source 41, reflected by the mirrors 61 and 62, and introduced into the surface tension measuring unit 10 passes through the aperture 21 and is incident on the thin tube 13 arranged in the optical cell 11. The air supply unit 81 pressurizes the inside of the optical cell 11 and the thin tube 13 by supplying air to the optical cell 11 via the supply tube 82.

The lens holder 71 holds the lens 15. The lens driving unit 72 moves the lens 15 from a preset origin position along the optical axis J1 (see arrow AR1). Specifically, the lens driving unit 72 drives the lens holder 71 in the direction along the optical axis J1 according to the control information input from the processing unit 51. The lens driving unit 72 has, for example, a mechanism for driving a micrometer with a motor, and can finely move the position of the lens 15 in the optical axis J1 direction. Further, the lens driving unit 72 generates lens position information indicating a position relative to the origin position Pos 10 of the lens 15 and transmits it to the processing unit 51. The lens driving unit 72 generates lens position information from, for example, the rotation speed and rotation direction of the micrometer from the state where the lens 15 is at the origin position Pos 10. The lens driving unit 72 may be configured to include, for example, a rack gear fixed to the lens holder 71 along the optical axis J1 and a pinion gear that meshes with the rack gear and is rotated by a motor. In this case, the lens driving unit 72 may generate lens position information by detecting, for example, the displacement of the rack gear from the state where the lens 15 is at the origin position Pos 10.

As shown in FIG. 2, the optical cell 11 has a cylindrical main body portion 111, a translucent window portion 114, and a lid body 112 attached above the main body portion 111. The main body portion 111 has a cylindrical main portion 1111 and a cylindrical small diameter portion 1112 having a diameter smaller than that of the main portion 1111. The main portion 1111 is provided with an air introduction port 113 for introducing air (see arrow A) into the main portion 1111. As shown in FIG. 1, the air introduction port 113 is connected to the air supply unit 81 through the supply pipe 82. The lid 112 has a bottomed cylindrical shape, and the bottom wall is provided with an opening 112a for introducing the laser beam LA1 into the main body 111. The window portion 114 is formed of, for example, transparent glass or resin, and is interposed between the upper portion of the main portion 1111 and the bottom wall of the lid 112. An O-ring 115 is interposed between the peripheral portion of the window portion 114 and the bottom wall of the lid 112.

The thin tube 13 has a long cylindrical shape, and is arranged in a state where the lower end, which is one end in the tubular axial direction, is immersed in the liquid S. Then, the laser beam LA1 is incident from the upper end, which is the other end in the tubular axis direction of the thin tube 13. The thin tube 13 is fixed to the small diameter portion 1112 via an O-ring 116 interposed between the thin tube 13 and the inner wall of the small diameter portion 1112. The capillary tube 13 is made of, for example, glass, metal or resin. At the lower end of the thin tube 13, meniscus M is generated at the interface between the air and the liquid S in the thin tube 13.

The aperture 21 is arranged vertically above the thin tube 13. The aperture 21 is provided with a pinhole 21a, which is a first pinhole. The pinhole 21a has a circular shape in a plan view, and its diameter is smaller than the inner diameter of the thin tube 13.

The liquid storage cell 14 stores the liquid S to be measured. The liquid storage cell 14 is formed of transparent glass or resin in a bottomed tubular shape, and the entire peripheral wall thereof transmits light in the wavelength band of visible light. The entire peripheral wall of the liquid storage cell 14 does not have to be transparent, and at least the bottom wall may be one that allows the laser beam LA1 to pass through. For example, when the wavelength band of the laser beam LA1 is set to a wavelength band of 640 nm to 790 nm, the bottom wall transmits light in a wavelength band longer than this wavelength band, but for light in a wavelength band shorter than 640 nm. It may have a low transmittance. Further, the liquid storage cell 14 may be provided with, for example, a temperature controller (not shown) that keeps the temperature of the liquid S constant.

The air supply unit 81 supplies air from the upper end of the thin tube 13 into the thin tube 13 by supplying air into the optical cell 11. The air supply unit 81 airs into the optical cell 11 and the thin tube 13 until the pressure of the air in the optical cell 11 and the thin tube 13 reaches the pressure indicated by the pressure information based on the pressure information included in the control information received from the processing unit 51. Supply. The air supply unit 81 includes, for example, a manometer for measuring the pressure of air in the optical cell 11 and the thin tube 13. Then, the air supply unit 81 adjusts the amount of air supplied into the optical cell 11 and the thin tube 13 so that the pressure value indicated by the manometer becomes equal to the pressure value indicated by the pressure information. The air supply unit 81 may be configured to supply air to the optical cell 11 and the thin tube 13 by, for example, a syringe pump. Further, the air supply unit 81 may be configured to measure the pressure of the air in the optical cell 11 by a pressure sensor instead of the manometer.

The lens 15 is, for example, a convex lens, and is arranged vertically below the tip of the thin tube 13, that is, the lower end of the thin tube 13.

The photodetector 31 is, for example, a Si photodiode, a Ge photodiode, or a photomultiplier tube, and detects the laser beam LA3 transmitted through the lens 15. The photodetector 31 outputs an analog signal corresponding to the intensity of the received light to the ADC 32. The aperture 22 is arranged on the optical axis J1 of the light transmitted through the lens 15 and incident on the photodetector 31, and is provided with a pinhole 22a which is a second pinhole. The laser beam LA3 that has passed through the pinhole 22a of the aperture 22 is incident on the light receiving portion of the photodetector 31.

Returning to FIG. 1, the ADC 32 converts the analog signal input from the photodetector 31 into a digital signal and outputs it to the processing unit 51.

The processing unit 51 is, for example, a personal computer, and transmits control information to the lens driving unit 72 and the air supply unit 81. Further, the processing unit 51 calculates the surface tension of the liquid to be measured based on the digital signal input from the ADC 32 and the lens position information input from the lens driving unit 72. As shown in FIG. 3, for example, the processing unit 51 includes a CPU (Central Processing Unit) 511, a main storage unit 512, an auxiliary storage unit 513, an input unit 514, a display unit 515, and a communication interface (hereinafter, "I / F"). 516, ADCI / F517, and a bus 518 connecting each part are provided. The main storage unit 512 is composed of a volatile memory such as a RAM (Random Access Memory). This memory is used as a work area of the CPU 511. The auxiliary storage unit 513 has a non-volatile memory such as a magnetic disk or a semiconductor memory. The auxiliary storage unit 513 stores a program executed by the CPU 511, various parameters, and the like. The input unit 514 is, for example, a keyboard. The display unit 515 is, for example, a liquid crystal display. The communication I / F 516 is connected to the air supply unit 81 and the lens drive unit 72. The ADCI / F517 is connected to the ADC 32.

The auxiliary storage unit 513 has an initial parameter DB 5131 that stores initial parameters required for surface tension measurement. The initial parameter DB 5131 stores information indicating each of the distances h, L10, and L20 shown in FIG. Here, h is the distance from the liquid level of the liquid S to be measured to the lower end of the thin tube 13. L10 is the optical distance from the lower end of the thin tube 13 to the origin position Pos10 of the lens 15, and L20 is the optical distance from the origin position Pos10 of the lens 15 to the aperture 22. Here, the origin position Pos 10 is defined as the intersection of the flat surface of the lens 15 on the thin tube 13 side and the optical axis J1 in the state where the lens 15 is at the origin position. Further, the initial parameter DB 5131 stores information indicating the focal length of the lens 15. Further, the initial parameter DB 5131 includes information indicating the refractive index of the liquid S to be measured, information indicating the refractive index and thickness of the peripheral wall of the liquid storage cell 14, and information indicating the density of the liquid S to be measured. , Information indicating gravity acceleration and information are stored. These information are stored in the initial parameter DB 5131 when the user inputs a numerical value via the input unit 514.

The CPU 511 reads the program stored in the auxiliary storage unit 513 into the main storage unit 512 and executes it, so that the pressurization control unit 5111, the drive control unit 5112, the strength position acquisition unit 5113, the distance calculation unit 5114, and the surface tension calculation unit are executed. Functions as 5115. The pressurization control unit 5111 transmits control information including pressure information indicating the pressure of the air in the optical cell 11 to the air supply unit 81. Then, the pressurization control unit 5111 notifies the surface tension calculation unit 5115 of the pressure information included in the transmitted control information.

The drive control unit 5112 transmits control information including information indicating the movement direction and the movement distance when the lens 15 is moved along the optical axis J1 to the lens drive unit 72. Further, when the drive control unit 5112 starts the operation of sweeping the lens 15 along the optical axis J1, the drive control unit 5112 transmits control information including the sweep start position to the lens drive unit 72.

The intensity position acquisition unit 5113 acquires the intensity of the light transmitted through the lens 15 and the pinhole 22a and detected by the photodetector 31 and the position of the lens 15 relative to the origin position Pos10. The intensity position acquisition unit 5113 acquires the intensity of the laser light received by the photodetector 31 from the ADC 32 via the ADCI / F517, and drives the lens position information indicating the relative position of the lens 15 with respect to the origin position Pos10. Obtained from unit 72.

The distance calculation unit 5114 calculates the first distance L1 and the second distance L2 shown in FIG. 2 for the laser beams LA1, LA2, and LA3 light transmitted through the pinhole 21a, the meniscus M, and the lens 15 from the upper end of the thin tube 13. .. The first distance L1 is the optical distance between the lens 15 and the lower end of the thin tube 13, and the second distance L2 is the optical distance between the focal position of the laser beam LA2 transmitted through the lens 15 and the lens 15. Distance. The distance calculation unit 5114 calculates the first distance L1 and the second distance L2 from the relative positions of the lens 15 with respect to the origin position Pos 10 when the intensity of the light acquired by the intensity position acquisition unit 5113 is maximized. Here, the distance calculation unit 5114 refers to the information indicating the distances h, L10, and L20 stored in the initial parameter DB 5131. Further, the distance calculation unit 5114 notifies the surface tension calculation unit 5115 of the calculated information indicating the first distance L1 and the second distance L2.

The surface tension calculation unit 5115 calculates the surface tension of the liquid S from the pressure applied from the air supplied into the thin tube 13 in the meniscus M, the pressure applied from the liquid S in the meniscus M, and the radius of curvature of the meniscus M. The surface tension calculation unit 5115 uses the Young-Laplace relational expression described later to calculate the surface tension of the liquid S to be measured from the first distance L1, the second distance L2, and the distance h calculated by the distance calculation unit 5114. Is calculated.

Next, the surface tension measuring method adopted in the surface tension measuring device according to the present embodiment will be described. In the surface tension measuring method according to the present embodiment, first, air is supplied from the upper end of the thin tube 13 in a state where the lower end of the thin tube 13 is immersed in the liquid S to be measured stored in the liquid storage cell 14. As a result, a meniscus M is generated at the interface between the air and the liquid S in the thin tube 13 at the tip of the thin tube 13 (meniscus generation step). The meniscus M functions as a concave lens with respect to the laser beam LA1 propagating in the thin tube 13. That is, as shown in FIG. 4, the laser beam LA1 propagating in the thin tube 13 propagates in the liquid S to be measured after being refracted by the meniscus M.

Next, the first distance L1 and the second distance L2 are calculated for the laser beams LA1, LA2, and LA3 that pass through the meniscus M and the lens 15 from the upper end of the thin tube 13 (distance calculation step). Here, the first distance L1 and the second distance L2 are between the lower end of the thin tube 13 and the lens 15 in a state where the focal position of the laser beam LA3 transmitted through the lens 15 substantially coincides with the pinhole 22a of the aperture 22. Corresponds to the distance between the lens 15 and the aperture 22.

ここで、ｆ１はメニスカスＭの焦点距離、ｆ２はレンズ１５の焦点距離を示す。第１距離Ｌ１［ｈｏ］は、第１距離Ｌ１について、被測定対象の液体Ｓの屈折率と、液体貯留セル１４の周壁の屈折率および厚さと、に基づいて補正した光学的距離を示す。Subsequently, the radius of curvature of the meniscus M is calculated based on the first distance L1 and the second distance L2 (curvature radius calculation step). Here, first, the focal length f1 of the meniscus M shown in FIG. 4 is calculated based on the calculated first distance L1 and second distance L2 and the focal length of the lens 15 using the following equation (1). do.

Here, f1 indicates the focal length of the meniscus M, and f2 indicates the focal length of the lens 15. The first distance L1 [ho] indicates an optical distance corrected for the first distance L1 based on the refractive index of the liquid S to be measured and the refractive index and thickness of the peripheral wall of the liquid storage cell 14.

ここで、ＲはメニスカスＭの曲率半径を示し、ｎは被測定対象の液体Ｓの屈折率を示す。Next, the radius of curvature of the meniscus M is calculated from the focal length f1 of the meniscus M using the following equation (2).

Here, R indicates the radius of curvature of the meniscus M, and n indicates the refractive index of the liquid S to be measured.

ここで、γは被測定対象の液体Ｓの表面張力を示し、ＰはメニスカスＭにおける細管１３内の空気から加わる圧力を示す。また、ＰｓはメニスカスＭにおける液体Ｓから加わる圧力を示す。更に、ρは被測定対象の液体Ｓの密度を示し、ｇは重力加速度を示し、ｈは、図２に示す被測定対象の液体Ｓの液面から細管１３の下端までの距離を示す。After that, the surface tension of the liquid S is calculated from the pressure applied from the air supplied into the thin tube 13 in the meniscus M, the pressure applied from the liquid S in the meniscus M, and the radius of curvature R of the meniscus M (surface tension calculation step). ). Specifically, the surface tension of the liquid S is calculated using the Young-Laplace equation represented by the following equation (3).

Here, γ indicates the surface tension of the liquid S to be measured, and P indicates the pressure applied from the air in the capillary tube 13 in the meniscus M. Further, Ps indicates the pressure applied from the liquid S in the meniscus M. Further, ρ indicates the density of the liquid S to be measured, g indicates the gravitational acceleration, and h indicates the distance from the liquid surface of the liquid S to be measured to the lower end of the capillary tube 13 shown in FIG.

As described above, in the surface tension measuring method according to the present embodiment, the liquid S is obtained by optically calculating the radius of curvature R of the meniscus M generated at the interface between the air and the liquid S in the thin tube 13 at the lower end of the thin tube 13. Calculate the surface tension of.

By the way, the inner diameter of the thin tube 13 is determined based on the refraction angle of the laser beam LA1 in the meniscus M. As the inner diameter of the thin tube 13 becomes larger, the radius of curvature R of the meniscus M becomes larger and the refraction angle of the laser beam LA1 becomes smaller. Then, the distance difference between the second distance L2 between the focal length of the lens 15 of the optical system composed of the meniscus M and the lens 15 and the lens 15 and the focal length of the lens 15 becomes small. When this distance difference becomes equal to or less than the resolution of the moving distance in the direction along the optical axis J1 of the lens 15, the accuracy of the first distance L1 and the second distance L2 deteriorates. Therefore, the refraction angle of the laser beam LA1 in the meniscus M needs to be set so that the distance difference is at least larger than the resolution of the moving distance of the lens 15. Therefore, the inner diameter of the thin tube 13 is set to a size that causes the meniscus M in which the refraction angle of the incident laser beam LA1 is such that the distance difference is at least larger than the resolution of the moving distance of the lens 15.

Further, the meniscus M often has a radius of curvature different from the radius of curvature in the vicinity of the tubular axis of the thin tube 13 due to the influence of the interaction between the inner wall of the thin tube 13 and the liquid S in the vicinity of the inner wall of the thin tube 13. On the other hand, in the surface tension measuring device according to the present embodiment, as described above, the diameter of the pinhole 21a of the aperture 21 is smaller than the inner diameter 2r of the thin tube 13. The beam diameter D of the laser beam LA1 propagating in the thin tube 13 is smaller than the inner diameter 2r of the thin tube 13. That is, the first distance L1 and the second distance L1 and the second with respect to the laser beam LA3 transmitted through the lens 15 and the projection region in a circular shape in a plan view having a diameter smaller than the inner diameter of the thin tube 13 centered on the tubular axis of the thin tube 13 in the meniscus M. Calculate the distance L2. This makes it possible to eliminate the influence of the interaction between the inner wall of the thin tube 13 and the liquid S on the radius of curvature of the meniscus M. Therefore, the surface tension of the liquid S can be calculated with high accuracy.

Next, the surface tension measuring process executed by the surface tension measuring device according to the present embodiment will be described with reference to FIG. In this surface tension measurement process, after the user operates the input unit 514 to start an application for executing the surface tension measurement process, the input unit 514 performs an operation for starting the execution of the surface tension measurement process. It will be started with that as an opportunity. Further, at the start of execution of this surface tension measurement process, the pressurization control unit 5111 of the processing unit 51 transmits control information to the air supply unit 81 in advance, and the air supply unit 81 sends air into the optical cell 11 and the thin tube 13. It is assumed that the pressure of the air in the thin tube 13 is adjusted to a preset pressure by supplying the air.

The surface tension measuring device first sweeps the relative position of the lens 15 along the optical axis J1 to specify the position of the lens 15 that maximizes the intensity of the laser beam LA2 detected by the photodetector 31. do. For this purpose, the surface tension measuring device first moves the lens 15 to a preset sweep start position (step S101). Specifically, the drive control unit 5112 of the processing unit 51 transmits control information including information indicating the sweep start position of the lens 15 to the lens drive unit 72. Then, the lens driving unit 72 moves the lens 15 to the sweep start position based on the received control information.

Next, the surface tension measuring device acquires the intensity of the laser beam LA3 detected by the photodetector 31 (step S102). Specifically, the intensity position acquisition unit 5113 of the processing unit 51 acquires intensity information indicating the intensity of the laser beam LA3 from the photodetector 31 via the ADC 32. Further, the strength position acquisition unit 5113 stores the acquired strength information in the main storage unit 512.

Subsequently, the surface tension measuring device acquires lens position information indicating the relative position of the lens 15 from the lens driving unit 72 (step S103). Specifically, the intensity position acquisition unit 5113 of the processing unit 51 acquires lens position information from the lens drive unit 72. Further, the intensity position acquisition unit 5113 stores the acquired lens position information in the main storage unit 512 in association with the intensity information.

After that, the surface tension measuring device determines whether or not the position of the lens 15 is a preset sweep end position (step S104). When the surface tension measuring device determines that the position of the lens 15 is not the sweep end position (step S104: No), the surface tension measuring device moves the lens 15 toward the sweep end position by a preset distance (step S105). Specifically, the drive control unit 5112 of the processing unit 51 transmits control information including information indicating a preset movement direction and movement distance of the lens 15 to the lens drive unit 72. Then, the lens driving unit 72 moves the lens 15 toward the sweep end position by a preset distance based on the received control information. Next, the surface tension measuring device executes the process of step S102 again.

On the other hand, it is assumed that the surface tension measuring device determines that the position of the lens 15 is the preset sweep end position (step S104: Yes). In this case, the surface tension measuring device specifies the lens position where the intensity of the laser beam LA3 detected by the photodetector 31 is maximized (step S106). Specifically, the distance calculation unit 5114 of the processing unit 51 refers to the intensity information and the lens position information stored in the main storage unit 512 to specify the lens position information corresponding to the intensity information indicating the maximum intensity.

Subsequently, the surface tension measuring device calculates the distances L1 and L2 when the lens 15 is at the specified lens position (step S107). Specifically, the distance calculation unit 5114 of the processing unit 51 calculates the first distance L1 and the second distance L2 from the specified lens position and the distance L10 and the distance L20 stored in the initial parameter DB 5131.

After that, the surface tension measuring device receives the calculated first distance L1 and second distance L2, the pressure applied from the air in the thin tube 13 in the meniscus M, the pressure applied from the liquid S in the meniscus M, and the surface tension of the liquid S. Is calculated (step S108).

Next, the result of measuring the surface tension using the surface tension measuring device according to the present embodiment will be described. First, the measurement result when the liquid S to be measured is pure water at 20 ° C. will be described. Here, as the thin tube 13, a glass thin tube having an inner diameter (2r) of 0.92 mm was used, and the distance (h) of the liquid S stored in the liquid storage cell 14 at the tip of the thin tube 13 from the liquid surface was set to 5 mm. .. As the laser light source 41, a semiconductor laser having an oscillation wavelength of 650 nm and a beam diameter of 0.9 mm was adopted. A Si photodiode is used for the photodetector 31. As the aperture 21, a pinhole 21a having a diameter of 0.8 mm was adopted. As a result, the scattered light contained in the laser light LA1 can be removed, and the beam diameter D of the laser light LA1 can be narrowed down to about 0.8 mm. Then, the surface tension calculated from the radius of curvature of the meniscus M generated at the tip of the thin tube 13 when the pressure of the air in the thin tube 13 is changed, the pressure of the air in the thin tube 13, and the radius of curvature of the meniscus M. The relationship between and is shown in FIG. 6A. In FIG. 6A, the vertical axis on the left side shows the radius of curvature of the meniscus M, and the vertical axis on the right side shows the surface tension. The horizontal axis indicates the pressure difference between the pressure P of the air in the thin tube 13 and the pressure Ps that the air bubbles generated at the tip of the thin tube 13 receive from the liquid S (hereinafter, simply referred to as “pressure difference”). Further, FIG. 6B shows a photograph of the tip of the thin tube 13 when the radius of curvature of the meniscus M is the minimum. Further, FIG. 6C shows a photograph of the tip of the thin tube 13 when the pressure of the air in the thin tube 13 is near the pressure (maximum bubble pressure) at which air bubbles separate from the tip of the thin tube 13.

From the results shown in FIG. 6A, the minimum value of the radius of curvature of the meniscus M is about ½ of the inner diameter of the thin tube 13. From this, it was found that the radius of curvature of the meniscus M can be measured by using an optical measuring method. Further, in the pressure difference (about 312 Pa) when the radius of curvature of the meniscus M is about ½ of the inner diameter of the thin tube 13, the radius of curvature R of the meniscus M generated at the tip of the thin tube 13 becomes the minimum. However, when the pressure difference is made larger than about 312 Pa, the radius of curvature of the meniscus M gradually increases. Further, as shown in FIG. 6C, when the pressure difference is in the vicinity of about 318 Pa, that is, the pressure of the air in the thin tube 13 is in the vicinity of the maximum foam pressure, the shape of the meniscus M is not hemispherical, and the inner wall of the thin tube 13 and the liquid S. The contact angle between and (see θ1 in FIG. 4) is larger than 0 degrees. When the shape of the meniscus M is hemispherical, the contact angle is 0 degrees. As a result of FIG. 6A, the shape of the meniscus M becomes hemispherical as the pressure difference approaches 312 Pa, and the shape of the meniscus M becomes substantially hemispherical when the pressure difference approaches 312 Pa. It is considered that when the pressure difference becomes larger than 312 Pa, the shape of the substantially hemispherical meniscus M collapses. For this reason, in the surface tension measuring method that approximates the shape of the meniscus M to a hemispherical shape when the pressure of the air in the thin tube 13 is the maximum foam pressure, as in the above-mentioned maximum foam pressure method, there is an error in the measured value of the surface tension. Is expected to increase.

The reliable literature value of the surface tension of pure water at 20 ° C. is 72.75 mN / m. On the other hand, as a result of measurement using the surface tension measuring device according to the present embodiment, as shown in FIG. 6A, when the pressure difference is 280 Pa to 312 Pa, the error of the calculated surface tension with respect to the document value is 1. It is suppressed to about%. Further, when the pressure P of the air in the thin tube 13 is relatively low and the radius of curvature of the meniscus M is larger than 1/2 of the inner diameter of the thin tube 13, the measured value of the surface tension is substantially constant at around 72.5 mN / m. be. This is because the inner diameter of the thin tube 13 is 0.92 mm and the beam diameter of the laser beam LA1 is as small as about 0.8 mm, so that the interaction between the inner wall of the thin tube 13 and the liquid S to be measured is extremely small. It is considered that it is small and the influence of this interaction on the measured value of the surface tension is extremely small. That is, since the radius of curvature of the portion of the meniscus M that is deformed by the pressure of the air in the thin tube 13 can be selectively calculated, the condition to which the Young-Laplace equation can be applied can be reproduced well. It is considered that the measurement accuracy of the surface tension is improved.

On the other hand, when the pressure P of the air in the thin tube 13 is increased and the pressure difference (P—Ps) becomes the maximum pressure difference (near 318 Pa) at which the meniscus M is relatively stably formed, the surface tension becomes high. The measured value was about 75 mN / m, and the error from the literature value was about 3 to 4%. It is considered that this is because the radius of curvature of the meniscus M becomes small, the approximation of the meniscus M as a thin lens cannot be established, and the spherical aberration of the meniscus M is affected. In order to reduce the influence of the spherical aberration of the meniscus M, it is preferable to reduce the ratio of the beam diameter of the laser beam LA1 to the inner diameter of the thin tube 13. Based on the above, in the surface tension measuring device according to the present embodiment, the ratio of the beam diameter of the laser beam LA1 to the inner diameter of the thin tube 13 is made as small as possible, and the pressure difference (PPs) is made as small as possible to make the curvature of the meniscus M as small as possible. It is preferable to make the radius as large as possible.

Next, the measurement result when the liquid S to be measured is a liquid of a type other than pure water will be described. Table 1 shows the names of a plurality of types of liquids S to be measured, the refractive index and density used to calculate the surface tension, the pressure difference, the radius of curvature, and the calculated surface tension. In Table 1, the refractive index and the density show the measured values. However, the literature values are used for carbon disulfide. Further, the temperature around the liquid storage cell 14 was adjusted to 20 ° C.

As shown in Table 1, when the liquid S to be measured is toluene whose surface tension is relatively smaller than that of pure water, the surface tension is calculated to be 28.5 mN / m, and the document value of the surface tension is 28.52 mN. It almost matched with / m. The contact angle between the inner wall of the thin tube 13 and the liquid S was larger than 0 degrees, and a non-hemispherical meniscus M was observed.

Further, as shown in Table 1, when the liquid S to be measured is an aqueous solution of sodium dodecyl sulfate (hereinafter referred to as “SDS”), the surface tension is calculated to be 47.8 mN / m, and the surface tension document The error with respect to the value of 48.2 mN / m was within 1%. The molar concentration of SDS in the SDS aqueous solution was 5 × 10 ^-3 M. The literature values are values obtained by the ring method. This SDS aqueous solution is an anionic surfactant whose surface tension is between the surface tension of pure water and the surface tension of toluene. This SDS aqueous solution has a small surface tension, and air bubbles generated at the tip of the thin tube 13 are easily separated from the tip of the thin tube 13. In fact, the contact angle between the inner wall of the capillary tube 13 and the liquid S was larger than 0 degrees, and a non-hemispherical meniscus M was observed. Therefore, in the case of the maximum foam pressure foam that approximates that the meniscus M is hemispherical, the error of the calculated surface tension becomes large. On the other hand, in the surface tension measuring device according to the present embodiment, the surface tension can be calculated even if the meniscus M is not hemispherical, so that the surface tension can be calculated with high accuracy as described above. can.

Further, as shown in Table 1, even when the liquid S to be measured is benzene, hexadecane, hexane, or toluene, which are organic solvents other than toluene, the error in the calculated surface tension with respect to the literature value is within 1%. rice field. As described above, according to the surface tension measuring device according to the present embodiment, the surface tension is relatively small, the contact angle between the inner wall of the thin tube 13 and the liquid S is larger than 0 degrees, and the non-hemispherical meniscus M is formed. It was found that even the generated liquid S can measure the surface tension with high accuracy.

Further, as shown in Table 1, when the liquid S to be measured was glycerin, ethanol, acetone, or acetonitrile, the error in the calculated surface tension with respect to the literature value of the surface tension was about 2%. It is considered that this is because these liquids have high hygroscopicity and the surface is contaminated by water vapor in the atmosphere. Contamination of the surface of the liquid to be measured greatly affects the measured value of surface tension. With respect to the surface tension measuring device according to the present embodiment, if measures are taken to prevent the surface of the liquid S to be measured from being contaminated by water vapor, the accuracy of the calculated surface tension can be improved.

Further, as shown in Table 1, when the liquid S to be measured was diethyl ether or isopentane, the calculated surface tension was higher than the literature value of 17.06 mN / m. Here, the literature value is a value measured by the ring method. Liquids with a high boiling point and high vapor pressure, such as diethyl ether, have a refractive index gradient at the gas-liquid interface and can mislead optical measurements. However, the steam density has only an effect of increasing the fourth decimal place of the refractive index. It is considered that this is because the temperature of the surface of the liquid S became 20 ° C. or lower due to the evaporation of a part of diethyl ether. Therefore, in the surface tension measuring apparatus according to the present embodiment, if the temperature of the liquid to be measured is kept constant, the accuracy of the calculated value of the surface tension can be improved. Further, as shown in Table 1, when the liquid S to be measured was isopentane (2-methylbutane), the calculated surface tension was slightly higher than the literature value of 15.00 mN / m. Further, as shown in Table 1, when the liquid S to be measured was tetramethylsilane, the calculated surface tension was 14.0 ± 0.5 mN / m.

Further, as shown in Table 1, when the liquid S to be measured was carbon tetrachloride, the calculated surface tension had an error of about 2.5% with respect to the literature value of 26.92 mN / m. Further, even when the liquid S to be measured was chloroform, the calculated surface tension had an error of about 2.5% with respect to the literature value of 27.16 mN / m. However, as shown in Table 1, when the liquid S to be measured was tetradecafluorohexane (perfluorohexane), the calculated surface tension was substantially the same as the literature value of 11.91 mN / m. In denser solvents such as carbon tetrachloride (density 1.5940 g / cm ³ ), chloroform (density 1.4891 g / cm ³ ), tetradecafluorohexane (density 1.6690 g / cm ³ ), around the meniscus M. Distortion due to the gravity of the part causes an error. It is considered that the variation in the error for these liquids may be due to the fact that the value of the literature value includes the error due to the deformation of the liquid in the direction of gravity in the annular method. In tetradecafluorohexane (perfluorohexane), which is a liquid with a low refractive index, the meniscus becomes large due to its small surface tension, and since the refractive index is low, spherical aberration is unlikely to occur and accurate measurements are performed. it is conceivable that.

Since the surface tension measuring device according to the present embodiment calculates the surface tension based on the radius of curvature of the meniscus M obtained by optical measurement, it is affected by the refractive index of the liquid S to be measured. Therefore, the higher the refractive index of the liquid, the shorter the focal length of the meniscus M, so that spherical aberration in the meniscus M is likely to occur. Therefore, the focus formed on the pinhole 22a of the aperture 22 by the lens 15 is blurred. As shown in Table 1, when the liquid S to be measured was carbon disulfide having a low boiling point and a high refractive index, the calculated surface tension was higher than the literature value of 32.25 mN / m. It is considered that this is due to the influence of spherical aberration due to having a high refractive index and the influence of a decrease in the surface temperature of the liquid S due to evaporation due to its low boiling point. Therefore, in the present invention, if the influence of the refractive index is corrected, it is possible to measure the surface tension with higher accuracy.

The correlation between the calculated surface tension value and the literature value for each liquid shown in Table 1 is shown in FIGS. 7 and 8. As shown in FIGS. 7 and 8, the calculated values of the surface tension obtained by the surface tension measuring apparatus according to the present embodiment are the literature values for both the liquid having a relatively low surface tension and the liquid having a relatively high surface tension. It can be seen that there is little error with.

When the liquid S to be measured was liquid nitrogen, the calculated surface tension had an error of about 10% with respect to the literature value of 11.0 mN / m. It is considered that this is because the error is large due to the change in the inner diameter of the thin tube 13 due to the contraction of the thin tube due to the low temperature and the vibration of the liquid S due to the boiling of the liquid S.

As described above, according to the surface tension measuring method according to the present embodiment, a meniscus is generated at the tip M of the thin tube 13 immersed in the liquid to be measured stored in the liquid storage cell 14, and the thin tube 13 is formed. The first distance L1 and the second distance L2 are measured for the light transmitted through the meniscus M and the lens 15 when the light is incident from the upper end of the above. Then, the radius of curvature R of the meniscus M is calculated based on the first distance L1 and the second distance L2, and the surface tension of the liquid S is calculated using the radius of curvature R of the meniscus M. In this way, using a simple configuration including the liquid storage cell 14, the thin tube 13, and the lens 15, the surface tension of the liquid S to be measured is calculated only by measuring the first distance L1 and the second distance L2. Therefore, the surface tension of the liquid S can be measured easily and in a short time. Further, since the radius of curvature R of the meniscus M generated at the tip of the thin tube 13 is directly calculated optically and the surface tension of the liquid S is calculated using the calculated radius of curvature R of the meniscus M, the shape of the meniscus M is hemispherical. It also has the advantage of higher measurement accuracy than the maximum bubble pressure method approximated by.

Further, the inner diameter of the thin tube 13 according to the present embodiment is determined based on the refraction angle of the laser beam LA1 in the meniscus M. As a result, the accuracy of the radius of curvature R of the meniscus M is improved, so that the accuracy of the surface tension calculated from the radius of curvature R is also improved.

Further, since the surface tension measuring device according to the present embodiment uses a laser beam having high directivity, the first distance L1 calculated from the focal position of the optical system composed of the meniscus M and the lens 15 is the first. The accuracy of 2 distance L2 is improved. Therefore, since the accuracy of the radius of curvature R of the meniscus M is improved, the accuracy of the surface tension calculated from the radius of curvature R is also improved.

Further, the distance calculation unit 5114 according to the present embodiment moves the lens 15 from the position relative to the origin position Pos 10 of the lens 15 when the intensity of the light acquired by the intensity position acquisition unit 5113 becomes maximum. , The first distance L1 and the second distance L2 are calculated. As a result, the position of the thin tube 13 and the position of the photodetector 31 can be fixed. Therefore, for example, the aperture 22 and the photodetector 31 are moved along the optical axis J1 in order to detect the focal position of the lens 15. The surface tension measuring unit 10 can be miniaturized as compared with the configuration.

(Modification example)
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. For example, as shown in FIG. 9, the configuration includes a photodetector unit 2030 having a photodetector 31 and an aperture 22, and a photodetector unit drive unit (not shown) that drives the photodetector unit 2030. May be good. In FIG. 9, the same reference numerals as those in FIG. 2 are attached to the same configurations as those in the embodiment. The photodetection unit drive unit moves the photodetection unit 2030 from a preset origin position along the optical axis J1 (see arrow AR201). Further, the liquid storage cell 2014 may have a lens portion 2015 provided on the bottom wall. In FIG. 9, L201 is the distance from the tip of the thin tube 13 to the lens portion 2015, and L202 is the distance from the lens portion 2015 to the aperture 22 of the photodetection unit 2030. Further, L210 is a distance from the lens unit 2015 to the origin position of the photodetection unit 2030.

In this case, the intensity position acquisition unit 5113 of the processing unit 51 transmits the intensity of the light transmitted through the lens unit 2015 and the pinhole 22a and detected by the photodetector 31, and the position relative to the origin position Pos 20 of the photodetector unit 2030. And get. Here, the origin position Pos 20 is defined as the position of the pinhole 22a when the photodetection unit 2030 is in the origin position. Further, the distance calculation unit 5114 of the processing unit 51 has a first distance L201 and a first distance from a position relative to the origin position Pos 20 of the light detection unit 2030 when the intensity of the light acquired by the intensity position acquisition unit 5113 is maximized. Calculate the two-distance L202.

According to this configuration, since the first distance L201 is invariant, the process of calculating the surface tension is simplified.

In the embodiment, the air supply unit 81 measures the surface tension of the liquid S to be measured while supplying air into the thin tube 13 so that the pressure of the air in the thin tube 13 becomes constant. An example was explained. However, the present invention is not limited to this, and for example, the gas supply unit may supply air into the thin tube 13 so that the pressure of the air in the thin tube 13 fluctuates periodically. In this case, the intensity position acquisition unit 5113 acquires the intensity of the component whose intensity fluctuates at the same frequency as the fluctuation frequency of the air pressure in the thin tube 13 contained in the light detected by the photodetector 31. do it.

According to this configuration, it is possible to measure the dynamic surface tension of the liquid S to be measured.

In the surface tension measuring device according to the embodiment, for example, as shown in FIG. 10, an aperture 3023 which is a third aperture provided with a pin hole 3023a which is a third pin hole is arranged vertically below the liquid storage cell 14. It may be a configured configuration.

According to this configuration, of the laser light LA2 transmitted through the meniscus M, the laser light transmitted through the vicinity of the inner wall of the thin tube 13 is blocked from being incident on the lens 15. As a result, it is possible to eliminate the influence on the shape of the meniscus M due to the interaction between the inner wall of the thin tube 13 and the liquid S to be measured, so that the accuracy of the calculated value of the surface tension of the liquid S is improved.

In the surface tension measuring method according to the embodiment, the curvature of the meniscus M obtained when the pressure difference between the pressure applied from the air supplied into the thin tube 13 in the meniscus M and the pressure applied from the liquid S in the meniscus M is changed. Surface tension may be calculated based on the radius. In this modification, when the pressure of the air supplied from the upper end of the thin tube 13 is changed to a plurality of types, the radius of curvature of the meniscus M, the pressure applied from the air supplied into the thin tube 13 in the meniscus, and the meniscus M are used. The pressure difference from the pressure applied from the liquid S is calculated. Then, based on the fact that the radius of curvature shown by the Young-Laplace equation in the above equation (3) and the above-mentioned pressure difference are in an inverse proportional relationship, the calculated radius of curvature of the meniscus M and the calculated pressure difference are obtained. Is the least squared fitting using the inverse proportional equation.

ここで、ｎは、データの数を示し、ｉは各データに付与されたインデックス番号を示し、Ｒ［ｉ］はインデックス番号「ｉ」のデータに対応するメニスカスＭの曲率半径を示す。また、Ｐ［ｉ］はインデックス番号「ｉ」のデータに対応するメニスカスＭにおける細管１３内に供給された空気から加わる圧力を示し、Ｐｓ［ｉ］はインデックス番号「ｉ」のデータに対応するメニスカスＭにおける液体Ｓから加わる圧力を示す。σ^２は、分散を示す。Specifically, a function represented by the relational expression of the following equation (4) is generated from the calculated data of the plurality of radii of curvature and the data of the above-mentioned pressure difference corresponding to them.

Here, n indicates the number of data, i indicates the index number assigned to each data, and R [i] indicates the radius of curvature of the meniscus M corresponding to the data of the index number “i”. Further, P [i] indicates the pressure applied from the air supplied into the thin tube 13 in the meniscus M corresponding to the data of the index number “i”, and Ps [i] indicates the pressure applied from the air corresponding to the data of the index number “i”. The pressure applied from the liquid S in M is shown. σ ² indicates the variance.

When the sample is water and the beam diameter of the laser beam LA1 used is 0.7 mm, the function represented by the equation (4) is represented by a curve as shown in FIG. Then, as shown in FIG. 11, the value of γ when the dispersion σ ² takes the minimum value (72.55 mN / m in the case of FIG. 11) is the value of the surface tension obtained.

FIG. 12 shows an example of the result of performing least squares fitting on the measurement data obtained when water is used as a sample. In FIG. 12, the circles indicate the relationship between the radius of curvature of the meniscus M and the standardized pressure difference, and the squares indicate the radius of curvature of a set of meniscus M corresponding to each circle and the standardized pressure. The value of the surface tension calculated using the difference is shown. Curves S21 and S22 show curves obtained by performing least squares fitting on the radius of curvature of the four sets of meniscus M and the pressure difference standardized by the preset pressure values.

The measurement results obtained by the surface tension measuring method according to this modification are shown in Table 2 below. Table 2 shows the names of a plurality of types of liquids S to be measured, the refractive index and density used for calculating the surface tension, and the calculated surface tension. In Table 2, the refractive index and the density show the measured values. However, the literature values are used for carbon disulfide. Further, the temperature around the liquid storage cell 14 was adjusted to 20 ° C. Table 1 also shows the data of the radius of curvature of the five different meniscus M and the pressure difference between the pressure applied from the air supplied into the thin tube 13 in the corresponding meniscus and the pressure applied from the liquid S in the meniscus M. The data and the results when using are shown. The error in the least squares fitting was ± 0.02 mN / m.

As shown in Table 2, the error between the calculated surface tension and its literature value could be kept within 1%. It is considered that this error is caused by an error in the temperature of the sample, the purity of the sample, and the like. If a lens drive unit 72 having a position accuracy on the order of millimeters is used and a pinhole 22a having a small aperture diameter is used and a pinhole 22a having a small aperture diameter is used, an error of 0.01 mN / m to 1 μN is used. It is considered that it can be reduced to about / m.

Further, in the surface tension measuring method according to the embodiment, it is calculated from the radius of curvature of the meniscus M, the volume of the meniscus M, the pressure applied from the air supplied into the thin tube 13 in the meniscus M, and the pressure applied from the liquid S in the meniscus M. The surface tension may be calculated from the surface area of the meniscus M to be formed and the Gibbs energy. In this case, first, the surface area of the meniscus M and the volume of the region inside the meniscus M are calculated from the radius of curvature of the meniscus M. Next, the Gibbs energy is calculated from the volume of the meniscus M and the pressure difference between the pressure applied from the air supplied into the thin tube 13 in the meniscus M and the pressure applied from the liquid S in the meniscus M. Then, the surface tension is calculated by performing linear least squares fitting on the surface area of the meniscus M and the Gibbs energy of the meniscus M.

ここで、ｉは各データに付与されたインデックス番号を示し、Ｒ［ｉ］はインデックス番号「ｉ」のデータに対応するメニスカスＭの曲率半径を示す。また、ｒは細管１３の内径を示し、Ｚｃ［ｉ］はインデックス番号「ｉ」のデータに対応するメニスカスＭの細管１３の下端からの突出量を示す。Ａ［ｉ］は、インデックス番号「ｉ」のデータに対応するメニスカスＭの表面積を示し、Ｖ［ｉ］は、インデックス番号「ｉ」のデータに対応するメニスカスＭの内側の領域の体積を示す。In this modification, as shown in FIG. 13, it is assumed that the meniscus M corresponds to a part of the virtual spherical surface SH. Here, it is assumed that the meniscus M corresponds to a part of the virtual spherical surface SH even if the sample has elasticity such as gel and can be plastically deformed. Then, when the pressure of the air supplied from the upper end of the thin tube 13 is changed into a plurality of types, the radius of curvature of the meniscus M, the pressure applied from the air supplied into the thin tube 13 in the meniscus, and the liquid S in the meniscus M are used. Calculate the pressure difference from the applied pressure. Then, using the following equations (5) to (7), the amount of protrusion of the meniscus M from the lower end of the thin tube 13, the surface area of the meniscus M, and the volume of the region inside the meniscus M are calculated from the calculated radius of curvature.

Here, i indicates an index number assigned to each data, and R [i] indicates the radius of curvature of the meniscus M corresponding to the data of the index number “i”. Further, r indicates the inner diameter of the thin tube 13, and Zc [i] indicates the amount of protrusion of the meniscus M corresponding to the data of the index number “i” from the lower end of the thin tube 13. A [i] indicates the surface area of the meniscus M corresponding to the data of the index number “i”, and V [i] indicates the volume of the inner region of the meniscus M corresponding to the data of the index number “i”.

The volume of the region inside the meniscus M calculated in this way and the pressure difference between the pressure applied from the air supplied into the capillary tube 13 in the meniscus and the pressure applied from the liquid S in the meniscus M are, for example, FIG. 14A. Shows the relationship as shown in. In FIG. 14A, the pressure difference is a pressure difference standardized by a preset pressure value. Then, the Gibbs energy of the meniscus M is obtained by integrating the pressure difference between the pressure applied from the air supplied into the thin tube 13 in the meniscus M and the pressure applied from the liquid S in the meniscus M with respect to the volume of the region inside the meniscus M. Is calculated.

ここで、γは試料の表面張力を示し、ＧはメニスカスＭのギブズエネルギーを示し、ＡはメニスカスＭの表面積を示す。Here, the relational expression shown in the following equation (8) is established between the surface tension of the sample, the Gibbs energy of the meniscus M, and the surface area of the meniscus M. That is, the surface tension of the sample corresponds to a value obtained by partially differentiating the Gibbs energy of the meniscus M with respect to the surface area of the meniscus M.

Here, γ indicates the surface tension of the sample, G indicates the Gibbs energy of the meniscus M, and A indicates the surface area of the meniscus M.

The Gibbs energy of the meniscus M and the surface area of the meniscus M show a linear correlation as shown in FIG. 14B, for example. Therefore, in this modification, the surface tension of the sample is calculated from the slope of a straight line obtained by performing linear minimum square fitting on the data of the Gibbs energy of Meniscus M and the data of the surface area as shown in FIG. 14B, for example. ..

According to these surface tension measuring methods, the surface tension of the sample is calculated using the data under the pressure conditions applied to the multiple types of meniscus M, so that the surface tension when the surface tension of the sample is measured under a plurality of types of conditions is calculated. The average value of can be calculated. Further, according to these surface tension measuring methods, the measurement error can be increased to about ± 0.02 mN / m in consideration of the error in the position of the lens 15 or the error in the pressure applied to the meniscus M.

In the embodiment, for example, the liquid S to be measured may be one in which a thin film of another type of liquid is formed on one type of liquid. In this case, the interliquid tensions of the two types of liquids can be calculated.

In the embodiment, the surface tension of the liquid S to be measured is calculated in a state where the pressure of the air in the capillary tube 13 is relatively low, and then the surface tension of the liquid S is calculated a plurality of times while gradually increasing the pressure of the air in the capillary tube 13. Measure the tension. Then, a measured value having less pressure dependence of the air in the capillary tube 13 may be selected from the plurality of measured values of the surface tension obtained by the measurement, and the average value thereof may be adopted as the measured value of the surface tension.

In the embodiment, an example of supplying air from the air supply unit 81 into the thin tube 13 will be described, but the gas supplied into the thin tube 13 is not limited to air, and other gas such as an inert gas is used. It may be a type of gas, and a gas having little or no influence on the liquid S to be measured is preferable.

Although the embodiments and modifications of the present invention (including those described in the description; the same shall apply hereinafter) have been described above, the present invention is not limited thereto. The present invention includes a combination of embodiments and modifications as appropriate, and modifications thereof as appropriate.

This application is based on Japanese Patent Application No. 2017-106612 filed on May 30, 2017. The specification, claims and drawings of Japanese Patent Application No. 2017-106612 are incorporated herein by reference.

The present invention is a method for measuring surface tension with a simple structure, which enables highly accurate measurement because it is a surface tension measurement for a deformed portion due to air pressure, which is close to the definition of surface tension for a deformed portion in a substantially horizontal direction due to air pressure. And equipment can be provided.

10: Surface tension measuring unit, 11: Optical cell, 13: Thin tube, 14,2014: Liquid storage cell, 15: Lens, 21,22,42,3023: Aperture, 21a, 22a, 42a, 3023a: Pinhole, 31 : Optical detector, 32: ADC, 41: Laser light source, 51: Processing unit, 61, 62, 63: Mirror, 71: Lens holder, 72: Lens drive unit, 81: Air supply unit, 82: Supply pipe, 111 : Main body, 112: Lid, 112a: Opening, 113: Air inlet, 114: Window, 115, 116: O-ring, 511: CPU, 512: Main storage, 513: Auxiliary storage, 514: Input unit, 515: Display unit, 516: Communication I / F, 517: ADCI / F, 518: Bus, 1111: Main unit, 1112: Small diameter unit, 2015: Lens unit, 2030: Optical detection unit, 5111: Pressurization Control unit, 5112: Drive control unit, 5113: Strength position acquisition unit, 5114: Distance calculation unit, 5115: Surface tension calculation unit, 5131: Initial parameter DB, A: Air, f1: Focal length, J1: Optical axis, L1 , L201: 1st distance, L2, L202: 2nd distance, LA1, LA2, LA3: laser light, M: meniscus, R: radius of curvature, S: liquid

Claims (9)

The other end of the thin tube is immersed in the liquid to be measured stored in the liquid storage cell whose bottom wall transmits light in a preset wavelength band at least at one end of the cylindrical thin tube in the tubular axis direction. A meniscus generation step of forming a meniscus at the interface between the gas in the thin tube and the liquid at the tip of the thin tube by supplying a gas from the tube.
When a laser beam is incident from the other end of the thin tube in the tubular axis direction toward the one end, the light transmitted from the other end of the thin tube through the lens arranged vertically below the meniscus and the liquid storage cell. A distance calculation step for calculating an optical first distance between the lens and the tip of the thin tube, and an optical second distance between the focal position of the lens and the lens.
A radius of curvature calculation step for calculating the radius of curvature of the meniscus based on the first distance and the second distance,
A surface tension calculation step of calculating the surface tension of the liquid from the pressure applied from the gas supplied into the capillary tube in the meniscus, the pressure applied from the liquid in the meniscus, and the radius of curvature of the meniscus is included. ,
Surface tension measurement method. In the distance calculation step, light transmitted through a projection region having a circular shape in a plan view having a diameter smaller than the inner diameter of the thin tube centered on the tubular axis of the thin tube in the meniscus and a lens arranged vertically below the liquid storage cell. To measure the first distance and the second distance.
The surface tension measuring method according to claim 1. The inner diameter of the capillary is determined based on the refraction angle of the light in the meniscus.
The surface tension measuring method according to claim 1 or 2. Based on the radius of curvature of the meniscus obtained when the pressure difference between the pressure applied from the air supplied into the capillary tube of the meniscus and the pressure applied from the liquid in the meniscus is changed in the surface tension calculation step. , Calculate surface tension,
The surface tension measuring method according to any one of claims 1 to 3 . A liquid storage cell that stores the liquid to be measured and at least the bottom wall transmits light in a preset wavelength band.
A thin tube that is cylindrical and has one end in the axial direction immersed in the liquid.
A first aperture arranged vertically above the thin tube and provided with a first pinhole having a diameter smaller than the inner diameter of the thin tube.
A gas supply unit that supplies gas from the other end of the thin tube in the tubular axis direction,
A lens placed vertically below the tip of the thin tube,
When a laser beam is incident from the other end of the thin tube in the tubular axial direction toward the one end in a state where a meniscus is generated at the interface between the gas in the thin tube and the liquid at the tip of the thin tube, the thin tube is formed. For light transmitted through the first pinhole, the meniscus, and the lens from the other end of the lens, the first optical distance between the lens and the tip of the thin tube, and the focal point of the light emitted from the lens. A distance calculation unit that calculates the optical second distance between the position and the lens, and
It includes a surface tension calculation unit that calculates the surface tension of the liquid from the pressure applied from the gas supplied into the thin tube in the meniscus, the pressure applied from the liquid in the meniscus, and the radius of curvature of the meniscus. ,
Surface tension measuring device. A photodetector that detects the light transmitted through the lens, and
A second aperture that is arranged on the optical axis of the light that passes through the lens and is incident on the photodetector and is provided with a second pinhole.
A lens drive unit that moves the lens from a preset origin position along the optical axis.
Further provided with an intensity position acquisition unit that acquires the intensity of light transmitted through the lens and the second pinhole and detected by the photodetector and the position of the lens relative to the origin position.
The distance calculation unit calculates the first distance and the second distance from the relative position of the lens with respect to the origin position when the intensity of the light acquired by the intensity position acquisition unit is maximized.
The surface tension measuring device according to claim 5 . It has a photodetector that detects the light emitted from the lens, and a second aperture that is arranged on the optical axis of the light that passes through the lens and is incident on the photodetector and is provided with a second pinhole. Light detection unit and
A photodetector unit drive unit that moves the photodetector unit from a preset origin position along the optical axis.
When the light detection unit drive unit moves the light detection unit from the origin position by a preset distance along the optical axis, it passes through the lens and the second pinhole and is transmitted by the photodetector. Further equipped with an intensity position acquisition unit that acquires the intensity of the detected light,
The lens is a lens portion provided on the bottom wall of the liquid storage cell.
The distance calculation unit calculates the first distance and the second distance from the relative positions of the light detection unit with respect to the origin position when the intensity of the light acquired by the intensity position acquisition unit is maximized. ,
The surface tension measuring device according to claim 5 . The gas supply unit periodically fluctuates the pressure of the gas in the capillary tube.
The intensity position acquisition unit acquires the intensity of a component contained in the light detected by the photodetector whose intensity fluctuates at the same frequency as the fluctuation frequency of the pressure of the gas in the capillary tube.
The surface tension measuring device according to claim 6 or 7 . Further comprising a third aperture disposed between the liquid reservoir and the lens and provided with a third pinhole.
The surface tension measuring device according to any one of claims 5 to 8 .

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