Method for evaluating variance stability and method for comparing variance stability

Abstract

This dispersion stability evaluation method is a method for evaluating a dispersion stability of a dispersoid dispersed in a dispersion medium. The dispersion stability evaluation method includes: a first step of holding a specimen containing the dispersion medium and the dispersoid on a reflective surface; and a second step of causing terahertz waves to be incident on the reflective surface from the side thereof opposite to the specimen, and detecting the terahertz waves reflected by the reflective surface. In the second step, a plurality of detection results corresponding respectively to a plurality of mutually separate time periods are acquired while a state in which the dispersoid can move toward the reflective surface is maintained.

Description

Technical Field

[0001] The present disclosure relates to a method for evaluating dispersion stability and a method for comparing dispersion stabilities.

Background Art

[0002] Conventionally, a method for evaluating the dispersion stability of a dispersed substance dispersed in a dispersion medium has been known (for example, see Patent Document 1). In such a method, among a sample containing a dispersion medium and a dispersed substance dispersed in the dispersion medium, the moving speed of the dispersed substance is grasped based on the change in the liquid surface position of the precipitation part generated by the precipitation of the dispersed substance, and the dispersion stability of the dispersed substance is evaluated based on the moving speed of the dispersed substance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method as described above, the liquid surface position of the precipitation part may be measured, for example, by visual inspection by an operator. However, in such a case, the variation in the measurement results regarding the liquid surface position of the precipitation part becomes large, and as a result, the accuracy of the dispersion stability evaluation may decrease.

[0005] As a method for improving the accuracy of the dispersion stability evaluation, a technique for specifying the liquid surface position of the precipitation part by the incidence of light has been known (for example, see Patent Document 2). In such a method, the liquid surface position of the precipitation part is specified by changing the light incidence position on the sample (scanning the light on the sample). However, when changing the light incidence position, a mechanism or the like for changing the light incidence position is required, and as a result, the entire apparatus may become complicated.

[0006] This disclosure aims to provide a dispersion stability evaluation method and a dispersion stability comparison method that can evaluate the dispersion stability of a dispersed substance with high accuracy using a simple configuration. [Means for solving the problem]

[0007] One aspect of the present disclosure is a method for evaluating the dispersion stability of a dispersed phase dispersed in a dispersion medium, comprising: a first step of holding a sample containing the dispersion medium and the dispersed phase on a reflective surface; and a second step of incidenting a terahertz wave onto the reflective surface from the opposite side of the sample and detecting the terahertz wave reflected by the reflective surface, wherein in the second step, while maintaining a state in which the dispersed phase can move toward the reflective surface, a plurality of detection results corresponding to a plurality of time intervals apart from each other are obtained.

[0008] In the second step of this dispersion stability evaluation method, multiple detection results corresponding to multiple time points at different distances from each other are obtained while maintaining a state in which the dispersed phase can move toward the reflective surface. This allows the movement speed of the dispersed phase toward the reflective surface to be determined based on the time-dependent change in frequency characteristics calculated using the detection results, thereby enabling the evaluation of the dispersion stability of the dispersed phase. Furthermore, in the second step, the above-mentioned detection results are obtained by the incidence and detection of terahertz waves. Therefore, the dispersion stability of the dispersed phase can be evaluated with higher accuracy compared to, for example, visual measurement. Also, in the second step, the dispersion stability of the dispersed phase is evaluated by incidenting terahertz waves toward the reflective surface from the opposite side of the sample and detecting the terahertz waves reflected by the reflective surface, as described above. This allows the dispersion stability of the dispersed phase to be evaluated with a simpler configuration compared to, for example, changing the incident position of light on the sample. Thus, according to this dispersion stability evaluation method, the dispersion stability of a dispersed phase can be evaluated with high accuracy using a simple configuration.

[0009] The above dispersion stability evaluation method may further include a third step of calculating multiple frequency characteristics corresponding to multiple time points based on each of multiple detection results, and a fourth step of determining the migration velocity of the dispersed mass toward the reflective surface based on the time-dependent changes in the multiple frequency characteristics. This makes it possible to evaluate the dispersion stability of the dispersed mass based on the migration velocity of the dispersed mass toward the reflective surface.

[0010] In the third step, the absorption spectrum of the sample for terahertz waves may be calculated as one of several frequency characteristics. This allows the dispersion stability of the dispersed phase to be evaluated using the absorption spectrum.

[0011] In the third step, the refractive index spectrum of the sample for terahertz waves may be calculated as one of several frequency characteristics. This allows the dispersion stability of the dispersed phase to be evaluated using the refractive index spectrum.

[0012] In the third step, the absorbance of the sample to terahertz waves may be calculated as one of several frequency characteristics. This allows the dispersion stability of the dispersed phase to be evaluated using absorbance. Furthermore, the configuration of the apparatus, such as the light source, can be simplified, allowing the dispersion stability of the dispersed phase to be evaluated with a simpler configuration.

[0013] In the fourth step, values ​​within the peak frequency range corresponding to the dispersed phase may be used as each of the multiple frequency characteristics. This allows for more accurate acquisition of information corresponding to the dispersed phase in the sample, and enables a more accurate evaluation of the dispersion stability of the dispersed phase.

[0014] In the fourth step, values ​​within a base frequency range different from the peak frequency range corresponding to the dispersed mass may be used for each of the multiple frequency characteristics. This makes it possible to evaluate the dispersion stability even for dispersed masses that do not have an absorption peak for terahertz waves incident on the reflective surface.

[0015] The above dispersion stability evaluation method further comprises a fifth step of stirring the sample while holding it on a reflective surface, and the strength of stirring may be adjusted in the fifth step. This allows the dispersed phase to be dispersed into the dispersion medium by increasing the stirring strength while the sample is held on the reflective surface, and the dispersed phase to be moved toward the reflective surface by decreasing the stirring strength. Therefore, it is easy to maintain a state in which the dispersed phase can move toward the reflective surface.

[0016] The dispersion medium may be a liquid, and the dispersed phase may be a solid. This allows for the evaluation of the dispersion stability of a solid dispersed in a liquid.

[0017] In the first step, the sample is held so that it faces the reflective surface from above in a vertical direction relative to the reflective surface, and in the second step, the dispersed phase may be maintained in a state where it can settle toward the reflective surface in the vertical direction. This makes it easy to move the dispersed phase toward the reflective surface when the specific gravity of the dispersed phase is greater than the specific gravity of the dispersion medium.

[0018] One aspect of the dispersion stability comparison method of this disclosure comprises the steps of performing the above-described dispersion stability evaluation method for each of a plurality of samples, and comparing the dispersion stability of each of the plurality of samples.

[0019] According to this dispersion stability comparison method, as described above, the dispersion stability of multiple samples can be compared with high accuracy using a simple configuration. [Effects of the Invention]

[0020] This disclosure makes it possible to provide a dispersion stability evaluation method and a dispersion stability comparison method that can evaluate the dispersion stability of a dispersed substance with high accuracy using a simple configuration. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a diagram showing the configuration of a spectrometer according to an embodiment. [Figure 2]FIG. 2 is an exploded view of the peripheral structure of the arrangement shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the arrangement and the holder shown in FIG. 2. [Figure 4] FIG. 4 is a schematic diagram showing the stirring state of the sample accommodated in the accommodation space of the holder. [Figure 5] FIG. 5 is a diagram showing a plurality of frequency characteristics corresponding to each of a plurality of times. [Figure 6] FIG. 6 is a diagram showing the change over time of the frequency characteristics. [Figure 7] FIG. 7 is a diagram showing the change over time of the frequency characteristics of each of a plurality of samples. [Figure 8] FIG. 8 is a flowchart of the dispersion stability comparison method of the embodiment. [Figure 9] FIG. 9 is a diagram showing the frequency characteristics of each of the dispersion medium and the sample in the first stirring state. [Figure 10] FIG. 10 is a diagram showing a plurality of frequency characteristics corresponding to each of a plurality of times. <00001​​​​​​​​​​​​​​​​​​​​​​​​​Figure 19 shows the change over time in the relative values ​​of the frequency response. [Figure 20] Figure 20 shows the time-dependent changes in the relative frequency characteristics of multiple samples. [Figure 21] Figure 21 is a diagram showing the configuration of a modified spectrometer. [Figure 22] Figure 22 shows the method for determining the frequency when the spectrometer shown in Figure 21 is used. [Figure 23] Figure 23 shows the method for calculating the frequency response. [Figure 24] Figure 24 shows the change over time in the relative values ​​of the frequency response. [Figure 25] Figure 25 shows the change over time in the relative values ​​of the frequency response. [Modes for carrying out the invention]

[0022] Embodiments of this disclosure will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0023] [Spectroscopy equipment] As shown in Figure 1, the spectrometer 1 comprises an output unit 20, a placement unit 30, an adjustment unit 40, a reflection unit 50, a detection unit 60, and a processing unit 70. The spectrometer 1 is a device for performing attenuated total reflection spectroscopy (ATR) using terahertz waves.

[0024] The output unit 20 outputs terahertz waves T. Specifically, the output unit 20 includes a light source 21, a branching unit 22, a chopper 23, a plurality of mirrors M1 to M3, and a terahertz wave generating element 24. The light source 21 outputs light by pulse oscillation. The light source 21 outputs pulsed laser light, for example, with a pulse width of approximately femtoseconds. In other words, the light source 21 is a femtosecond pulsed laser light source.

[0025] The branching section 22 is, for example, a beam splitter. The branching section 22 splits the light output from the light source 21 into pump light P1 and probe light P2. The chopper 23 alternately passes and blocks the pump light P1 output from the branching section 22 at a constant period.

[0026] Each mirror M1 to M3 sequentially reflects the pump light P1 that has passed through the chopper 23. After the pump light P1 that has passed through the chopper 23 is sequentially reflected by each mirror M1 to M3, it is incident on the terahertz wave generating element 24. In the following, the optical system of the pump light P1 from the branching section 22 to the terahertz wave generating element 24 will be referred to as the "pump optical system".

[0027] The terahertz wave generating element 24 outputs a terahertz wave T when pump light P1 reflected by mirror M3 is incident on it. The terahertz wave generating element 24 includes, for example, a nonlinear optical crystal (e.g., ZnTe), a photoconductive antenna element (e.g., an optical switch using GaAs), a semiconductor (e.g., InAs), or a superconductor. When the terahertz wave generating element 24 includes a nonlinear optical crystal, the terahertz wave generating element 24 generates a terahertz wave T through a nonlinear optical phenomenon that occurs in conjunction with the incidence of pump light P1.

[0028] Terahertz waves T have properties intermediate between light waves and radio waves. Terahertz waves T are electromagnetic waves with frequencies corresponding to the intermediate region between light waves and radio waves. Terahertz waves T have frequencies of approximately 0.01 THz to 100 THz. Terahertz waves T are generated with a constant repetition period and have a pulse width of several picoseconds. In other words, the terahertz wave generating element 24 generates a pulse light train containing multiple terahertz waves T arranged at a predetermined time interval (pulse interval). In the following, the optical system for terahertz waves T from the terahertz wave generating element 24 to the detector 61 described later will be referred to as the "terahertz wave optical system".

[0029] The arrangement section 30 is, for example, a so-called aberration-free prism. The arrangement section 30 has an incident surface 30a, an exit surface 30b, a reflecting surface 30c, a first sub-reflecting surface 30d, and a second sub-reflecting surface 30e. The incident surface 30a and the exit surface 30b are parallel to each other. The reflecting surface 30c is perpendicular to the incident surface 30a and the exit surface 30b. In this embodiment, the reflecting surface 30c faces upward in the vertical direction. The sample S is placed on the reflecting surface 30c. The first sub-reflecting surface 30d and the second sub-reflecting surface 30e are surfaces on the arrangement section 30 opposite to the reflecting surface 30c, and form a recess. The surface formed by the first sub-reflecting surface 30d and the second sub-reflecting surface 30e is recessed toward the reflecting surface 30c.

[0030] The arrangement section 30 is transparent to the terahertz waves T output from the terahertz wave generating element 24. The refractive index of the arrangement section 30 is higher than that of the sample S. The material of the arrangement section 30 is, for example, silicon. The terahertz waves T incident on the incident surface 30a of the arrangement section 30 are sequentially reflected by the first sub-reflection surface 30d, the reflection surface 30c, and the second sub-reflection surface 30e, and then output to the outside from the output surface 30b. By detecting the attenuation reflectance of the evanescent waves that seep out when the terahertz waves T undergo total internal reflection at the reflection surface 30c, it is possible to obtain information in the terahertz wave band related to the sample S.

[0031] The adjustment unit 40 has multiple mirrors M4 to M8. The probe light P2 output from the branching unit 22 is sequentially reflected by each mirror M4 to M8, then reflected again by the reflection unit 50, and then incident on the detector 61. The reflection unit 50 is a mirror. Hereafter, the optical system of the probe light P2 from the branching unit 22 to the detector 61 will be referred to as the "probe optical system".

[0032] In the adjustment unit 40, the optical path length between mirror M4 and mirror M5, and the optical path length between mirror M6 and mirror M7 are adjusted by the movement of mirrors M5 and M6. This adjusts the optical path length of the probe optical system. The adjustment unit 40 adjusts the difference between "the optical path length obtained by adding the optical path length of the pump optical system from the branching unit 22 to the terahertz wave generating element 24 to the optical path length of the terahertz wave optical system from the terahertz wave generating element 24 to the detector 61" and "the optical path length of the probe optical system from the branching unit 22 to the detector 61".

[0033] The detection unit 60 detects the terahertz wave T output from the placement unit 30. Specifically, the detection unit 60 includes a detector 61, an I / V conversion amplifier 62, a lock-in amplifier 63, and an A / D converter 64. When the terahertz wave T output from the placement unit 30 and the probe light P2 reflected by the reflection unit 50 are incident on the detector 61, the detector 61 detects the correlation between the terahertz wave T and the probe light P2.

[0034] Specifically, the detector 61 includes a photoconductive antenna, etc. When probe light P2 is incident on the detector 61, photocarriers are generated in the detector 61. When a terahertz wave T is incident on the detector 61 where photocarriers have been generated, the photocarriers flow in response to the electric field of the terahertz wave T, and as a result, a current is output from the detector 61. The amount of current output from the detector 61 depends on the electric field strength of the terahertz wave T.

[0035] The current output from the detector 61 is input to the I / V conversion amplifier 62. The I / V conversion amplifier 62 converts the current output from the detector 61 into a voltage, amplifies the voltage, and outputs it to the lock-in amplifier 63. The lock-in amplifier 63 synchronously detects the electrical signal output from the I / V conversion amplifier 62 at the repetition frequency of the passage and blockage of the pump light P1 in the chopper 23. The A / D converter 64 converts the analog signal from the lock-in amplifier 63 into a digital signal. The signal output from the lock-in amplifier 63 has a value that depends on the electric field strength of the terahertz wave T. In this way, the detection unit 60 detects the correlation between the terahertz wave T and the probe light P2 and detects the electric field amplitude of the terahertz wave T.

[0036] In the adjustment unit 40, the optical path length between mirrors M4 and M5, and between mirrors M6 and M7 are adjusted, thereby adjusting the optical path length of the probe optical system. This adjusts the timing difference between the terahertz wave T and the probe light P2 input to the detector 61. As described above, generally, the pulse width of the terahertz wave T is on the order of picoseconds, while the pulse width of the probe light P2 is on the order of femtoseconds. In other words, the pulse width of the probe light P2 is several orders of magnitude narrower than that of the terahertz wave T. As a result, the timing of the incidence of the probe light P2 to the detector 61 is swept by the adjustment unit 40, and the time waveform of the electric field amplitude of the terahertz wave T (hereinafter referred to as the "electric field waveform") is obtained. Hereafter, acquiring the electric field waveform by this method will simply be referred to as "acquiring the electric field waveform".

[0037] When the incidence timing of the probe light P2 is swept once, an electric field waveform of one terahertz wave T corresponding to a predetermined time is obtained. In this embodiment, the incidence timing of the probe light P2 to the detector 61 is swept multiple times by the adjustment unit 40. As a result, multiple electric field waveforms are obtained. In other words, the detection unit 60 acquires data that includes multiple electric field waveforms (detection results) corresponding to multiple time points that are far apart from each other.

[0038] The processing unit 70 acquires information about the sample S based on multiple electric field waveforms acquired by the detection unit 60. Specifically, the processing unit 70 calculates the frequency characteristics corresponding to each electric field waveform based on the signal output from the A / D converter 64. Frequency characteristics refer to optical characteristics with respect to frequency. Optical characteristics include light absorption, light reflectivity, or light transmittance. A frequency characteristic is, for example, an absorption spectrum. The processing unit 70 acquires information about the sample S based on each frequency characteristic. As a result, the spectrometer 1 measures the change in the sample S over time. The processing unit 70 is composed of a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc.

[0039] [Surrounding structure of the installation area] As shown in Figure 2, the spectrometer 1 further includes a stirring section 10 as a peripheral structure to the arrangement section 30. The stirring section 10 includes a substrate 11, a pair of supports 14, a holder 15, a sealing member 16, a mounting section 17, and a stirrer 18. The substrate 11 holds the arrangement section 30. The reflective surface 30c of the arrangement section 30 (see Figure 1) intersects in the Z-axis direction (vertical direction). The reflective surface 30c protrudes from the surface 11a of the substrate 11. The incident surface 30a of the arrangement section 30 (see Figure 1) intersects in the X-axis direction. The incidence of terahertz waves T on the incident surface 30a of the arrangement section and the emission of terahertz waves T from the emission surface 30b are possible on the back surface 11b side of the substrate 11.

[0040] Each support 14 is fixed to the surface 11a of the substrate 11. The pair of support 14s are positioned on both sides of the placement section 30 in the Y-axis direction. Each support 14 has a rectangular parallelepiped shape, for example, with the X-axis direction as its length. A hole 14b is formed on the mounting surface 14a of each support 14 that is opposite to the substrate 11.

[0041] The holder 15 is, for example, a container with a rectangular parallelepiped shape. The holder 15 includes a containment space 15c (see Figure 3) for containing the sample S. The holder 15 is positioned on the reflective surface 30c of the arrangement section 30 between the pair of support members 14. The sealing member 16 is positioned between the holder 15 and the reflective surface 30c.

[0042] The mounting portion 17 includes a plate body 171, a cylindrical body 172, and a pair of fixing members 173. The plate body 171 is, for example, a rectangular plate with the Y-axis direction as the length direction and the Z-axis direction as the thickness direction. The width of the plate body 171 in the X-axis direction is approximately the same as the width of the support 14 in the X-axis direction, and the width of the plate body 171 in the Y-axis direction is approximately the same as the distance between the respective end faces of the pair of support 14 in the Y-axis direction (end faces opposite to the arrangement portion 30 in the Y-axis direction).

[0043] The cylindrical body 172 penetrates the plate body 171. The cylindrical body 172 is, for example, rectangular in shape. The cylindrical body 172 extends along the Z-axis direction. The width of the cylindrical body 172 in the Y-axis direction is less than the distance between the pair of supports 14 in the Y-axis direction. The cylindrical body 172 is fixed to the plate body 171.

[0044] The retainer 15 is housed in the internal space of the cylindrical body 172. The width of the internal space of the cylindrical body 172 in the X-axis direction is slightly greater than the width of the retainer 15 in the X-axis direction. The width of the internal space of the cylindrical body 172 in the Y-axis direction is slightly greater than the width of the retainer 15 in the Y-axis direction. The retainer 15 can be inserted into the internal space of the cylindrical body 172 in the Z-axis direction.

[0045] A pair of fixing members 173 are provided on both sides of the cylindrical body 172 in the Y-axis direction. Each fixing member 173 penetrates the plate body 171. The plate body 171 is placed on the mounting surface 14a of each support 14 with the holder 15 inserted into the internal space of the cylindrical body 172. Each fixing member 173 is fixed to the hole 14b of each support 14. In this way, the holder 15 is attached to the placement section 30.

[0046] The agitator 18 includes a shaft 181, a propeller 182, a drive unit 183, and an adjustment member 184. The shaft 181 extends along the Z-axis direction. The propeller 182 is fixed to one end of the shaft 181. The propeller 182 is located within the housing space 15c of the holder 15 (see Figure 3). The drive unit 183 is provided at the other end of the shaft 181.

[0047] The drive unit 183 has a motor for rotating the shaft 181. The adjustment member 184 is located on the outside of the drive unit 183. The adjustment member 184 is a knob for controlling the motor's rotation speed. The operator can control the motor's rotation speed by rotating the adjustment member 184.

[0048] As shown in Figure 3, the holder 15 is positioned above the placement section 30 in the Z-axis direction. The holder 15 includes main surfaces 15a and 15b facing opposite directions in the Z-axis direction. Main surface 15a faces the reflective surface 30c of the placement section 30 in the Z-axis direction. Main surface 15a is in contact with the reflective surface 30c. The holder 15 includes a housing space 15c. The housing space 15c includes a first cylindrical portion 15g, a second cylindrical portion 15e, and a tapered portion 15d. The first cylindrical portion 15g opens to the main surface 15b. The second cylindrical portion 15e opens to the main surface 15a. Each of the first cylindrical portion 15g and the second cylindrical portion 15e is, for example, cylindrical. The width of the second cylindrical portion 15e is smaller than the width of the first cylindrical portion 15g.

[0049] The tapered portion 15d is located between the first cylindrical portion 15g and the second cylindrical portion 15e. The tapered portion 15d is connected to the end of the first cylindrical portion 15g on the side of the second cylindrical portion 15e, and to the end of the second cylindrical portion 15e on the side of the first cylindrical portion 15g. The tapered portion 15d has a frustoconical shape that narrows from the first cylindrical portion 15g towards the second cylindrical portion 15e.

[0050] The retainer 15 includes a recess 15f formed in the main surface 15a. The sealing member 16 is positioned in the recess 15f. The sealing member 16 includes a through hole. The width of the through hole in the sealing member 16 is approximately the same as the width of the second cylindrical portion 15e. The sealing member 16 seals the gap between the retainer 15 and the positioning portion 30.

[0051] The sample S is housed in the containment space 15c. The sample S is held by the holder 15 so as to face the reflective surface 30c from above in the Z-axis direction. The sample S is in contact with the reflective surface 30c. The terahertz wave T is reflected at the portion of the reflective surface 30c that is in contact with the sample S. The detection results obtained by detecting the terahertz wave T reflected by the reflective surface 30c are results for the sample S at a position close to the reflective surface 30c.

[0052] Sample S contains a dispersion medium Sa and a dispersed phase Sb. The dispersion medium Sa is a liquid. In this embodiment, the dispersion medium Sa is, for example, water. The dispersion medium Sa is mixed with, for example, a dispersant. In this embodiment, the dispersant is, for example, a surfactant. The dispersed phase Sb is a suspended substance that is poorly soluble in the dispersion medium Sa. The dispersed phase Sb is a solid. The dispersed phase Sb is, for example, a powder. The specific gravity of the dispersed phase Sb is greater than the specific gravity of the dispersion medium Sa.

[0053] As shown in Figure 4(a), when the rotation speed of the propeller 182 becomes relatively high, the agitation strength of the sample S becomes relatively high (hereinafter referred to as the "first agitation state"), and the dispersed phase Sb is dispersed in the dispersion medium Sa. In the first agitation state, a state in which the dispersed phase Sb is relatively uniformly dispersed in the dispersion medium Sa (hereinafter referred to as the "dispersed state") is maintained. In the dispersed state, the amount of dispersed phase Sb contained in the sample S at positions close to the reflective surface 30c (in this embodiment, the second cylindrical portion 15e and the tapered portion 15d) becomes relatively small, so a detection result close to that of the dispersion medium Sa can be obtained.

[0054] As shown in Figure 4(b), when the rotation speed of the propeller 182 becomes relatively small, and the agitation strength of the sample S becomes less than that of the first agitation state (hereinafter referred to as the "second agitation state"), the dispersed phase Sb becomes able to move toward the reflective surface 30c. The dispersed phase Sb settles toward the reflective surface 30c in the Z-axis direction. The dispersed phase Sb accumulates on the reflective surface 30c. In the second agitation state, the state in which the dispersed phase Sb moves toward the reflective surface 30c (hereinafter referred to as the "movement state") is maintained. In this embodiment, the second agitation state is the state in which the rotation of the propeller 182 has stopped. In this embodiment, the movement state is maintained by stopping the rotation of the propeller 182. In the movement state, the amount of dispersed phase Sb contained in the sample S at a position close to the reflective surface 30c increases over time, so a detection result close to that of the dispersed phase Sb can be obtained.

[0055] Figure 5 shows the frequency characteristics of sample S when transitioning from the first stirring state to the second stirring state. Each frequency characteristic L1, L2, and L3 shown in Figure 5 is calculated based on detection results detected at multiple time points separated from each other. In Figure 5, the vertical axis represents optical characteristics and the horizontal axis represents frequency. In this embodiment, the optical characteristic is the absorption coefficient. That is, the frequency characteristics L1, L2, and L3 are absorption spectra. Frequency characteristic L1 corresponds to the first stirring state. Frequency characteristics L2 and L3 correspond to the second stirring state.

[0056] As shown in Figure 5, the frequency response L1 increases smoothly with increasing frequency. In other words, the frequency response L1 does not contain a peak in the peak frequency range F. This is because, in the first stirring state, the sample S is in a dispersed state (see, for example, Figure 4(a)), and therefore detection results close to those of the dispersion medium Sa are obtained. The peak frequency range F corresponds to the dispersed phase Sb and is the frequency band corresponding to the intrinsic peak originating from the dispersed phase Sb. The frequency response L2 contains peak P2 in the peak frequency range F, and the frequency response L3 contains peak P3 in the peak frequency range F. This is because, in the second stirring state, the sample S is in a moving state (see, for example, Figure 4(b)), and therefore detection results close to those of the dispersed phase Sb are obtained. The magnitude of peak P3 is larger than the magnitude of peak P2. This is because, in the second stirring state, the sample S is in a moving state, and therefore the amount of dispersed phase Sb contained in the sample S at a position close to the reflective surface 30c increases over time.

[0057] A "peak" in a frequency response refers to the portion of the frequency response where the rate of change of the optical characteristics changes in accordance with the change in frequency. For example, if the horizontal axis is frequency and the vertical axis is optical characteristics, and a point representing the optical characteristics corresponding to a predetermined frequency between one frequency and another frequency is located on one or the other side of the baseline connecting a point representing one optical characteristic corresponding to one frequency and another point representing another optical characteristic corresponding to another frequency, then the portion of the frequency response between one frequency and another frequency is the peak. The baseline may be a straight line or a curve. As another example, if the horizontal axis is frequency and the vertical axis is optical characteristics, and there is a portion of the frequency response where the rate of change of the optical characteristics changes from a positive number to a negative number or from a negative number to a positive number in accordance with the change in frequency, then that portion is the peak of the frequency response.

[0058] "Peak magnitude" refers to the degree to which a peak is far from the baseline. When a peak is far from the baseline, the peak magnitude is large. When a peak is far from the baseline, the peak magnitude is small. When the maximum distance between the peak and the baseline is large, the peak magnitude is large. When the maximum distance between the peak and the baseline is small, the peak magnitude is small. Note that the frequencies corresponding to the maximum distances may be the same or different. When the area between the peak and the baseline is large, the peak magnitude is large. When the area between the peak and the baseline is small, the peak magnitude is small.

[0059] Figure 6 shows the change in peak magnitude over time. In Figure 6, the vertical axis represents the second derivative of the frequency characteristic in the peak frequency range F (hereinafter simply referred to as "second derivative in the peak frequency range F"), and the horizontal axis represents time. In Figure 6, an increase in the second derivative in the peak frequency range F means a decrease in peak magnitude, and a decrease in the second derivative in the peak frequency range F means an increase in peak magnitude. As shown in Figure 6, during the period after the transition time T0 from the first stirring state to the second stirring state (hereinafter referred to as "transition time") (second stirring state), the second derivative in the peak frequency range F gradually decreases over time. In other words, during the period after the transition time T0, the peak magnitude gradually increases over time. This is because, during the period after the transition time T0, the sample S is in a moving state, and therefore the amount of dispersed phase Sb contained in the sample S near the reflective surface 30c increases over time. During the period after the transition time T0, the second derivative in the peak frequency range F gradually decreases over time and then maintains a constant value. In other words, during the period after transition time T0, the peak magnitude gradually increases over time and then remains constant. This is because a predetermined amount of dispersed phase Sb is deposited near the reflective surface 30c, resulting in the amount of dispersed phase Sb contained in the sample S near the reflective surface 30c no longer changing over time.

[0060] Based on the period from the transition time T0 to the time (hereinafter referred to as "settling time") T at which the peak magnitude begins to maintain a constant value, the migration speed of the dispersed particle Sb can be determined, and the dispersion stability of the dispersed particle Sb can be evaluated. The longer the period from the transition time T0 to the settlement time T, the smaller the migration speed of the dispersed particle Sb. The smaller the migration speed of the dispersed particle Sb, the better the dispersion stability of the dispersed particle Sb. In other words, the smaller the migration speed of the dispersed particle Sb, the more stable the dispersion state of the dispersed particle Sb in the dispersion medium Sa.

[0061] Figure 7 shows the time-dependent changes in the magnitude of the peaks for each of the multiple samples S1, S2, and S3. Similar to Figure 6, the vertical axis of Figure 7 represents the second derivative in the peak frequency range F, and the horizontal axis represents time. As shown in Figure 7, the period from the transition time T0 to the deposition time T1 of sample S1 is longer than the period from the transition time T0 to the deposition time T2 of sample S2, and the period from the transition time T0 to the deposition time T2 is longer than the period from the transition time T0 to the deposition time T3 of sample S3. In other words, the migration velocity of the dispersed phase Sb in sample S1 is smaller than the migration velocity of the dispersed phase Sb in sample S2, and the migration velocity of the dispersed phase Sb in sample S2 is smaller than the migration velocity of the dispersed phase Sb in sample S3. Based on the results shown in Figure 7, the dispersion stability of the dispersed phase Sb in each sample S1, S2, and S3 can be compared by comparing the migration velocities of the dispersed phase Sb in each sample S1, S2, and S3. Specifically, since the migration speed of the dispersed phase Sb in sample S1 is lower than that of the dispersed phase Sb in sample S2, the dispersion stability of the dispersed phase Sb in sample S1 is better than that of the dispersed phase Sb in sample S2. Similarly, since the migration speed of the dispersed phase Sb in sample S2 is lower than that of the dispersed phase Sb in sample S3, the dispersion stability of the dispersed phase Sb in sample S2 is better than that of the dispersed phase Sb in sample S3.

[0062] [Dispersion stability comparison method] Next, the method for comparing dispersion stability will be explained. First, a sample S is prepared as shown in Figure 8 (step S1). In step S1, the sample S is held on the reflective surface 30c of the placement section 30. In step S1, the sample S is held so that it faces the reflective surface 30c from above in the Z-axis direction. Specifically, first, the holder 15 is attached to the placement section 30 by the mounting section 17. Subsequently, the stirrer 18 is positioned so that the propeller 182 is located in the housing space 15c of the holder 15.

[0063] Next, with the sample S not contained in the containment space 15c, a terahertz wave T is incident on the incident surface 30a to obtain a reference electric field waveform. Next, the dispersion medium Sa, which has been mixed with the dispersant, is introduced into the containment space 15c. Next, the dispersion medium Sa is stirred by rotating the propeller 182. The rotation speed of the propeller 182 is, for example, about 1600 rpm. Next, while maintaining the rotation of the propeller 182, the dispersed phase Sb is introduced into the containment space 15c. This disperses the dispersed phase Sb in the dispersion medium Sa. Step S1 corresponds to the first step.

[0064] Next, the sample S is held on the reflective surface 30c and stirred (step S2). Specifically, in step S2, the rotation speed of the propeller 182 is maintained to bring the sample S into a first stirring state. Step S2 is part of the fifth step. Next, a terahertz wave T is incident on the reflective surface 30c from the opposite side of the sample S, and the terahertz wave T reflected by the reflective surface 30c is detected (step S3). In step S3, the output unit 20 incidents a terahertz wave T on the incident surface 30a of the placement unit 30, and the detection unit 60 detects the correlation between the terahertz wave T emitted from the output surface 30b of the placement unit 30 and the probe light P2 reflected by the reflection unit 50. This allows the electric field waveform of the terahertz wave T to be obtained. In step S3, the terahertz wave T is continuously incident on the reflective surface 30c, and the terahertz wave T reflected by the reflective surface 30c is continuously detected. This allows for the acquisition of multiple electric field waveforms corresponding to multiple time points that are separated from each other. Specifically, in step S3, the adjustment unit 40 sweeps the incidence timing of the probe light P2 to the detector 61 multiple times to acquire multiple electric field waveforms. In step S3, the incidence position of the terahertz wave T on the incidence surface 30a is maintained. In other words, in step S3, the incidence position of the terahertz wave T on the sample S is not changed. Step S3 corresponds to the second step.

[0065] Next, the stirring strength is adjusted (step S4). In step S4, the stirring state of the sample S is transitioned from the first stirring state to the second stirring state. The stirring strength in the second stirring state is less than the stirring strength in the first stirring state. In step S4, the rotation speed of the propeller 182 is reduced. In step S4 of this embodiment, the rotation of the propeller 182 is stopped. In step S4, the dispersed phase Sb is maintained in a state where it can move toward the reflective surface 30c. In step S4, the dispersed phase Sb is maintained in a state where it can settle toward the reflective surface 30c in the Z-axis direction. Step S4 is part of the fifth step.

[0066] In step S3, terahertz waves T are incident on and detected while the dispersed phase Sb is kept in a state where it can move toward the reflective surface 30c. In this embodiment, step S3 is performed continuously during the respective execution periods of steps S1, S2, and S4. That is, multiple detection results corresponding to multiple time periods are obtained during each of the execution periods of steps S1, S2, and S4. In step S3, multiple detection results for the first stirring state and multiple detection results for the second stirring state are obtained.

[0067] Next, based on each of the multiple detection results obtained in step S3, multiple frequency characteristics corresponding to each of the multiple time points are calculated (obtained) (step S5). In this embodiment, in step S5, the absorption spectrum of the sample S to terahertz waves T is calculated as each of the multiple frequency characteristics. As shown in Figure 9, the frequency characteristics of the sample S in the first stirring state are in close agreement with the frequency characteristics of the dispersion medium Sa in the first stirring state. This is because, in the first stirring state, the sample S is in a dispersed state, so detection results close to those of the dispersion medium Sa are obtained. Figure 10 is a diagram showing the multiple frequency characteristics obtained in step S5. As shown in Figure 10, the multiple frequency characteristics change over time. Also, in the peak frequency range F, peaks in the frequency characteristics appear as time progresses.

[0068] Figure 11 shows the second derivative of the frequency characteristics shown in Figure 10. As shown in Figure 11, the second derivative in the peak frequency range F changes over time. In the base frequency range B, the absolute value of the second derivative of each frequency characteristic is less than or equal to a predetermined value. In this embodiment, the absolute value of the second derivative in the base frequency range B is approximately zero. In the base frequency range B, each frequency characteristic does not contain a peak (see Figure 10). The base frequency range B is the frequency band corresponding to the baseline of the frequency characteristics. The base frequency range B is a different region from the peak frequency range F. Note that periodic oscillations (ripples different from the peaks originating from the dispersed mass Sb) may appear in the analysis results due to data discontinuities that occur during analysis (e.g., Fourier transform), so the absolute value of the second derivative in the base frequency range B may be greater than zero. Step S5 corresponds to the third step.

[0069] Next, the migration velocity of the dispersed particle Sb toward the reflective surface 30c is determined based on the time-dependent changes in multiple frequency characteristics (step S6). In step S6, values ​​within the peak frequency range F are used as each of the multiple frequency characteristics. In step S6, the magnitude of the peak of the frequency characteristic is used as each of the multiple frequency characteristics. In step S6 of this embodiment, the second derivative in the peak frequency range F is used as the magnitude of the peak. Figure 12 shows the time-dependent change of the second derivative in the peak frequency range F. As shown in Figure 12, after transition time T0, the second derivative in the peak frequency range F gradually decreases over time.

[0070] Figure 13 shows a graph with the vertical axis representing the relative value of the second derivative in the peak frequency range F (hereinafter referred to as "peak relative value") and the horizontal axis representing time. The peak relative value is calculated by dividing the absolute value of the second derivative in the peak frequency range F by the maximum value among the absolute values ​​of multiple second derivatives in the peak frequency range F. The maximum value of the peak relative value is 1. As shown in Figure 13, the peak relative value gradually increases over time during the period after the transition time T0. The peak relative value maintains a constant value after reaching the reference value C. In other words, the time at which the peak relative value reaches the reference value C is the deposition time T. In this embodiment, the reference value C is, for example, 0.8. In step S6, the period from the transition time T0 to the deposition time T is determined as the migration velocity of the dispersed phase Sb. Step S6 corresponds to the fourth step. Each of the above steps corresponds to a dispersion stability evaluation method for evaluating the dispersion stability of the dispersed phase Sb dispersed in the dispersion medium Sa.

[0071] In this embodiment, steps S1 to S6 are performed for each of the multiple samples S. Subsequently, the dispersion stability of each of the multiple samples S is compared (step S7). Figure 14 shows the change over time of the relative peak values ​​of the multiple samples S, samples S10, S20, S30, and S40. The dispersion medium Sa of samples S10, S20, S30, and S40 is water, and the dispersed phase Sb of samples S10, S20, S30, and S40 is theophylline monohydrate. The particle size of the dispersed phase Sb is, for example, 63 μm or less. The dispersant of sample S10 is hydroxypropyl methylcellulose, the dispersant of sample S20 is hydroxypropyl cellulose, and the dispersant of sample S30 is poloxamer. The concentrations of the dispersants in samples S10, S20, and S30 are the same. Sample S40 does not contain a dispersant.

[0072] As shown in Figure 14, the period from the transition time T0 to the deposition time T10 of sample S10 is longer than the period from the transition time T0 to the deposition time T20 of sample S20, the period from the transition time T0 to the deposition time T20 is longer than the period from the transition time T0 to the deposition time T30 of sample S30, and the period from the transition time T0 to the deposition time T30 is longer than the period from the transition time T0 to the deposition time T40 of sample S40. In other words, the migration velocity of the dispersed phase Sb in sample S10 is smaller than the migration velocity of the dispersed phase Sb in sample S20, the migration velocity of the dispersed phase Sb in sample S20 is smaller than the migration velocity of the dispersed phase Sb in sample S30, and the migration velocity of the dispersed phase Sb in sample S30 is smaller than the migration velocity of the dispersed phase Sb in sample S40.

[0073] Based on the results shown in Figure 14, the dispersion stability of the dispersed phase Sb in sample S10 is superior to that of the dispersed phase Sb in sample S20, the dispersion stability of the dispersed phase Sb in sample S20 is superior to that of the dispersed phase Sb in sample S30, and the dispersion stability of the dispersed phase Sb in sample S30 is superior to that of the dispersed phase Sb in sample S40. In other words, in terms of dispersant function, hydroxypropyl methylcellulose is superior to hydroxypropyl cellulose, hydroxypropyl cellulose is superior to poloxamer, and poloxamer is superior to water (without a dispersant).

[0074] Figure 15 shows the time course of the relative peak values ​​of samples S50, S60, and S70, which are multiple samples S. The dispersion medium Sa of samples S50, S60, and S70 is water, and the dispersed phase Sb of samples S50, S60, and S70 is nifedipine. The dispersant of sample S50 is hydroxypropyl methylcellulose, the dispersant of sample S60 is hydroxypropyl cellulose, and the dispersant of sample S70 is poloxamer.

[0075] As shown in Figure 15, the period from the transition time T0 to the deposition time T50 of sample S50 is longer than the period from the transition time T0 to the deposition time T60 of sample S60, and the period from the transition time T0 to the deposition time T60 is longer than the period from the transition time T0 to the deposition time T70 of sample S70. In other words, the migration velocity of the dispersed phase Sb in sample S50 is smaller than the migration velocity of the dispersed phase Sb in sample S60, and the migration velocity of the dispersed phase Sb in sample S60 is smaller than the migration velocity of the dispersed phase Sb in sample S70.

[0076] Based on the results shown in Figure 15, the dispersion stability of the dispersed phase Sb in sample S50 is superior to that of the dispersed phase Sb in sample S60, and the dispersion stability of the dispersed phase Sb in sample S60 is superior to that of the dispersed phase Sb in sample S70. In other words, even when the dispersed phase Sb is nifedipine, hydroxypropyl methylcellulose is superior to hydroxypropyl cellulose as a dispersant, and hydroxypropyl cellulose is superior to poloxamer. Each of the above steps corresponds to a dispersion stability comparison method for comparing the dispersion stability of multiple samples S.

[0077] As explained above, in step S3 (second step), while maintaining a state in which the dispersed particle Sb can move toward the reflective surface 30c, multiple detection results corresponding to multiple time points at different distances from each other are obtained. This makes it possible to determine the movement speed of the dispersed particle Sb toward the reflective surface 30c based on the time-dependent change in the frequency characteristics calculated using the detection results, and to evaluate the dispersion stability of the dispersed particle Sb. Moreover, in step S3, the above-mentioned detection results are obtained by the incidence and detection of terahertz waves T. Therefore, the dispersion stability of the dispersed particle Sb can be evaluated with higher accuracy compared to, for example, visual measurement. Furthermore, in step S3, the dispersion stability of the dispersed particle Sb is evaluated as described above by incidenting terahertz waves T onto the reflective surface 30c from the opposite side of the sample S and detecting the terahertz waves T reflected by the reflective surface 30c. In other words, in step S3, the incidence position of the terahertz waves T on the sample S is maintained. This allows for the evaluation of the dispersion stability of the dispersed phase Sb with a simpler configuration compared to, for example, changing the incident position of light on the sample (swiping light across the sample) (see, for example, Patent Document 2). Therefore, this dispersion stability evaluation method allows for highly accurate evaluation of the dispersion stability of the dispersed phase Sb with a simple configuration.

[0078] For example, when light is incident on a container containing a sample and the ratio of transmitted light intensity to scattered light intensity is measured (see, for example, Patent Document 2), the accuracy of the measurement results may decrease due to contamination of the container or air bubbles in the sample. In step S3 of the dispersion stability evaluation method of this disclosure, since terahertz waves T are incident on the arrangement section 30, the decrease in measurement results due to contamination of the holder 15 or air bubbles in the sample S is suppressed.

[0079] Furthermore, when changing the incident position of light on a sample (see, for example, Patent Document 2), it may be necessary to ensure a wide sweep range of light. Specifically, for example, if the sizes of the dispersed phases are different, the liquid level positions of the precipitated portions may also differ. If the size of the dispersed phases in one sample differs from the size of the dispersed phases in another sample, the liquid level positions of the precipitated portions in one sample may differ from those in the other samples. In such cases, in order to accurately determine the liquid level positions of the precipitated portions of multiple samples, it is necessary to widen the sweep range of light. In step S3 of the dispersion stability evaluation method of this disclosure, since the incident position of the terahertz wave T on the sample S is maintained, the dispersion stability of dispersed phases of different sizes can be easily evaluated.

[0080] The dispersion stability evaluation method comprises step S5 (third step) of calculating multiple frequency characteristics corresponding to multiple time points based on each of multiple detection results, and step S6 (fourth step) of determining the migration velocity of the dispersed particle Sb toward the reflective surface 30c based on the time-dependent changes in the multiple frequency characteristics. This makes it possible to evaluate the dispersion stability of the dispersed particle Sb based on the migration velocity of the dispersed particle Sb toward the reflective surface 30c. Specifically, compared to, for example, visually determining the time-dependent changes in frequency characteristics (see, for example, Patent Document 2), by quantifying the period from the transition time T0 to the deposition time T, the migration velocity of the dispersed particle Sb can be quantitatively determined, and the dispersion stability of the dispersed particle Sb can be quantitatively evaluated.

[0081] In step S5, the absorption spectrum of sample S for terahertz waves T is calculated as one of several frequency characteristics. This allows the dispersion stability of the dispersed particle Sb to be evaluated using the absorption spectrum.

[0082] In step S6, values ​​within the peak frequency range F corresponding to the dispersed phase Sb are used for each of the multiple frequency characteristics. This allows for more accurate and direct acquisition of information corresponding to the dispersed phase Sb in the sample S, and enables a more accurate evaluation of the dispersion stability of the dispersed phase Sb. Changes in the frequency characteristics over time may be due to, for example, the dissolution of the dispersed phase Sb into the dispersion medium Sa. In such cases, if values ​​within the base frequency range B are used, it may become difficult to determine whether the change in the frequency characteristics over time is due to the movement of the dispersed phase Sb to the reflective surface 30c or to the dissolution of the dispersed phase Sb into the dispersion medium Sa. When values ​​within the peak frequency range F corresponding to the dispersed phase Sb are used, it is possible to determine that the change in the frequency characteristics over time is due to the movement of the dispersed phase Sb, and the dispersion stability of the dispersed phase Sb can be evaluated more accurately. Furthermore, when values ​​within the peak frequency range F corresponding to the dispersed phase Sb are used, even if the absorption coefficient of the dispersed phase Sb and the absorption coefficient of the dispersion medium Sa are approximately the same, the dispersion stability of the dispersed phase Sb can be evaluated based on the change in peak magnitude. Furthermore, if a value within the peak frequency range F corresponding to the dispersed particle Sb is used, the crystalline state of the dispersed particle Sb can be determined.

[0083] The dispersion stability evaluation method includes step S2 (fifth step), in which the sample S is held on the reflective surface 30c and stirred, and step S4 (fifth step) adjusts the stirring strength. As a result, while the sample S is held on the reflective surface 30c, increasing the stirring strength allows the dispersed phase Sb to be dispersed into the dispersion medium Sa, and decreasing the stirring strength allows the dispersed phase Sb to move toward the reflective surface 30c. Therefore, it is easy to maintain a state in which the dispersed phase Sb can move toward the reflective surface 30c.

[0084] The dispersion medium Sa is a liquid, and the dispersed phase Sb is a solid. This allows us to evaluate the dispersion stability of a solid dispersed in a liquid.

[0085] In step S1 (first step), the sample S is held so that it faces the reflective surface 30c from above in the Z-axis direction (vertical direction) relative to the reflective surface 30c, and in step S3, the dispersed phase Sb is maintained in a state where it can settle toward the reflective surface 30c in the vertical direction. This makes it easier to move the dispersed phase Sb toward the reflective surface 30c when the specific gravity of the dispersed phase Sb is greater than the specific gravity of the dispersion medium Sa.

[0086] According to the dispersion stability comparison method described above, as mentioned above, the dispersion stability of multiple samples S can be compared with high accuracy using a simple configuration.

[0087] [Differentiation] In this embodiment, an example is shown in which values ​​within the peak frequency range F are used as each of the multiple frequency characteristics in step S6. However, in step S6, values ​​within the base frequency range B may also be used as each of the multiple frequency characteristics. Figure 16 shows the relative values ​​of the frequency characteristics in the base frequency range B (hereinafter referred to as "base relative values") on the vertical axis and time on the horizontal axis. The base relative values ​​are calculated by normalizing the frequency characteristics in the base frequency range B. Specifically, the base relative values ​​are calculated such that the maximum value among the absolute values ​​of the multiple frequency characteristics in the base frequency range B is 1 and the minimum value is zero. As shown in Figure 16, during the period after the transition time T0, the base relative values ​​gradually decrease over time. The base relative values ​​maintain a constant value after reaching the reference value C. That is, the time it takes for the base relative values ​​to reach the reference value C is the accumulation time T. The reference value C is, for example, 0.2. Thus, even when values ​​within the base frequency range B are used as each of the multiple frequency characteristics, the period from the transition time T0 to the deposition time T can be understood as the migration velocity of the dispersed particle Sb, just as when values ​​within the peak frequency range F are used. In such cases, the dispersion stability of the dispersed particle Sb, which does not have an absorption peak for the terahertz wave T incident on the reflective surface 30c, can also be evaluated.

[0088] Figure 17 shows the time-dependent changes in the base relative values ​​of multiple samples S10, S20, S30, and S40. As shown in Figure 17, the period from transition time T0 to deposition time T11 for sample S10 is longer than the period from transition time T0 to deposition time T21 for sample S20, the period from transition time T0 to deposition time T21 is longer than the period from transition time T0 to deposition time T31 for sample S30, and the period from transition time T0 to deposition time T31 is longer than the period from transition time T0 to deposition time T41 for sample S40. Thus, even when values ​​within the base frequency range B are used for each of the multiple frequency characteristics, the dispersion stability of samples S10, S20, S30, and S40 can be compared in the same way as when values ​​within the peak frequency range F are used.

[0089] In this embodiment, an example was shown in which the absorption spectrum of sample S for terahertz waves T is calculated as each of the multiple frequency characteristics in step S5. However, in step S5, the refractive index spectrum of sample S for terahertz waves T may also be calculated as each of the multiple frequency characteristics. Figure 18 shows the refractive index spectrum as each of the multiple frequency characteristics obtained in step S5. As shown in Figure 18, the multiple frequency characteristics change over time. Also, in the base frequency range B, no peak in the frequency characteristics appears even as time passes.

[0090] Figure 19 shows the time-dependent change in the relative value of the frequency response (base relative value) in the base frequency range B. In Figure 19, the vertical axis represents the relative value of the refractive index spectrum in the base frequency range B, and the horizontal axis represents time. As shown in Figure 19, in the period after the transition time T0, the base relative value gradually decreases over time. The base relative value maintains a constant value after reaching the reference value C. In other words, the time at which the base relative value reaches the reference value C is the deposition time T. Thus, even when refractive index spectra are used as each of the multiple frequency response characteristics, the period from the transition time T0 to the deposition time T can be understood as the migration velocity of the dispersed phase Sb, similar to when absorption spectra are used. When refractive index spectra are used, the variability of measurement results can be reduced, and dispersion stability can be evaluated with higher accuracy.

[0091] Figure 20 shows the time-dependent changes in the base relative values ​​of multiple samples S10, S20, S30, and S40. As shown in Figure 20, the period from transition time T0 to deposition time T12 for sample S10 is longer than the period from transition time T0 to deposition time T22 for sample S20, the period from transition time T0 to deposition time T22 is longer than the period from transition time T0 to deposition time T32 for sample S30, and the period from transition time T0 to deposition time T32 is longer than the period from transition time T0 to deposition time T42 for sample S40. Thus, even when refractive index spectra are used as each of the multiple frequency characteristics, the dispersion stability of samples S10, S20, S30, and S40 can be compared in the same way as when absorption spectra are used.

[0092] In this embodiment, an example is shown in which the absorption spectrum of the sample S to terahertz waves T is calculated as each of the multiple frequency characteristics in step S5. However, in step S5, the absorbance of the sample S to terahertz waves T may also be calculated as each of the multiple frequency characteristics. In this case, the spectrometer 1A shown in Figure 21 is used. As shown in Figure 21, the spectrometer 1A differs from the spectrometer 1 mainly in that it has an output unit 20A instead of an output unit 20, and a detection unit 60A instead of a detection unit 60. The spectrometer 1A does not have an adjustment unit 40 and a reflection unit 50. The spectrometer 1A comprises an output unit 20A, a chopper 26, a placement unit 30, a detection unit 60A, and a processing unit 70.

[0093] The output unit 20A has multiple light sources 25. Each light source 25 outputs a terahertz wave T having a single wavelength. Each light source 25 outputs a terahertz wave T having a different frequency from each other. The light sources 25 are, for example, backward wave tubes or quantum cascade lasers. The chopper 26 alternately passes and blocks the terahertz wave T output from the light sources 25 at a constant period. The terahertz wave T output from the output unit 20A is incident on the incident surface 30a of the arrangement unit 30, reflected sequentially by the first sub-reflection surface 30d, the reflection surface 30c, and the second sub-reflection surface 30e, and then output to the outside from the exit surface 30b and incident on the detection unit 60A.

[0094] The detection unit 60A detects the terahertz wave T output from the arrangement unit 30. Specifically, the detection unit 60A includes a detector 65, a lock-in amplifier 63, and an A / D converter 64. The detector 65 is, for example, a Gohray cell, a bolometer, a Schottky barrier diode, or a resonant tunneling diode. The electrical signal output from the detector 65 is input to the lock-in amplifier 63. The lock-in amplifier 63 synchronously detects the electrical signal output from the detector 65 at the repetition frequency of the terahertz wave T's passage and cutoff in the chopper 23. The A / D converter 64 converts the analog signal from the lock-in amplifier 63 into a digital signal. The processing unit 70 calculates the frequency characteristics based on the signal output from the A / D converter 64. Note that the spectrometer 1A does not necessarily have to include a chopper 26 and a lock-in amplifier 63.

[0095] In the dispersion stability comparison method using spectrometer 1A, a single-wavelength terahertz wave T is incident on the sample S. The frequency of the terahertz wave T is determined as follows. Figure 22 shows the second derivative of the absorption spectrum of the dispersed particle Sb. First, as shown in Figure 22, the frequencies f1 and f2 that define the range of the peaks in the absorption spectrum of the dispersed particle Sb are determined, and the frequency fp corresponding to the maximum absolute value of the peak between frequencies f1 and f2 is determined. Subsequently, as shown in Figure 23, the terahertz wave T with frequency fp, the terahertz wave T with frequency f1, and the terahertz wave T with frequency f2 are incident on the sample S.

[0096] Next, Ap, A1, and A2 are calculated as frequency characteristics when the frequencies are fp, f1, and f2. Ap, A1, and A2 are absorbances. Then, Am is calculated based on Am = (A2-A1) × (fp-f1) / (f2-f1) + A1. Next, the difference between Ap and Am is calculated as the peak magnitude. By performing such measurements at each of several time points, the change in peak magnitude over time is determined. Figure 24 shows the change in the relative value of the peak magnitude (peak relative value) shown in Figure 23 over time. The peak relative value is calculated such that the maximum value is 1 and the minimum value is zero among the multiple frequency characteristics. As shown in Figure 24, in the period after the transition time T0, the peak relative value gradually increases over time. The peak relative value maintains a constant value after reaching the reference value C. That is, the time at which the peak relative value reaches the reference value C is the deposition time T. The reference value C is, for example, 0.8. Thus, even when absorbance is used as one of the multiple frequency characteristics, the period from the transition time T0 to the deposition time T can be determined as the migration velocity of the dispersed phase Sb, similar to the case where an absorption spectrum is used.

[0097] Even when using spectrometer 1A, in step S6, values ​​within the base frequency range may be used as each of the multiple frequency characteristics. Figure 25 shows the relative absorbance in the base frequency range (base relative value) on the vertical axis and time on the horizontal axis. As shown in Figure 25, during the period after transition time T0, the base relative value gradually decreases over time. The base relative value maintains a constant value after reaching the reference value C. That is, the time at which the base relative value reaches the reference value C is the deposition time T. The reference value C is, for example, 0.2. In this way, even when absorbance in the base frequency range is used as each of the multiple frequency characteristics, the period from transition time T0 to deposition time T can be understood as the migration velocity of the dispersed phase Sb. In such cases, the dispersion stability of the dispersed phase Sb can be evaluated using absorbance. Furthermore, the configuration of the light source and other components of the apparatus can be simplified, and the dispersion stability of the dispersed phase Sb can be evaluated with a simpler configuration. In addition, data analysis can be facilitated.

[0098] In this embodiment, step S4 shows an example where the rotation of the propeller 182 is stopped, but in step S4, the rotation speed of the propeller 182 may be reduced. In step S4, it is sufficient that the dispersed phase Sb remains in a state where it can move toward the reflective surface 30c. In this embodiment, step S2 shows an example where the sample S is stirred by the rotation of the propeller 182, but the manner of stirring the sample S is not limited. In step S2, for example, the container containing the sample S may be vibrated and then placed on the reflective surface 30c of the placement section 30. In this case, the spectrometer 1 does not need to have a stirrer 18.

[0099] In the embodiment, an example was shown in which step S3 is performed during the respective execution periods of steps S1, S2, and S4. However, step S3 only needs to be performed during the execution period of step S4. In other words, the incidence and detection of terahertz waves T only needs to be performed when the sample S is in motion.

[0100] In the embodiment, an example was shown where the dispersed phase Sb is a solid, but the dispersed phase Sb may be a liquid that is incompatible with the dispersion medium Sa. The dispersed phase Sb may be, for example, an oil. In the embodiment, an example was shown where the specific gravity of the dispersed phase Sb is greater than the specific gravity of the dispersion medium Sa, but the specific gravity of the dispersed phase Sb may be less than the specific gravity of the dispersion medium Sa. In this case, in step S3, the detection result may be obtained while maintaining a state in which the dispersed phase Sb floats in the Z-axis direction (vertical method). Furthermore, the reflective surface 30c of the placement section 30 is oriented downward in the Z-axis direction, and the sample S is held by the holder 15 so as to face the reflective surface 30c from below in the Z-axis direction relative to the reflective surface 30c.

[0101] The temperature of sample S may be adjusted at least during the execution period of step S3. By keeping the temperature of sample S constant, it is possible to measure the change in the frequency characteristics of sample S over time under predetermined temperature conditions. Therefore, it becomes possible to obtain information about sample S with good reproducibility.

[0102] An optical interference method may be used as the optical system for the detection units 60 and 60A. In this case, the absorption spectrum of the terahertz wave T can be directly obtained without acquiring the electric field waveform of the terahertz wave T by the detection units 60 and 60A. [Explanation of symbols]

[0103] 30c…Reflective surface, B…Base frequency range, F…Peak frequency range, S…Sample, Sa…Dispersion medium, Sb…Dispersed mass, T…Terahertz wave.

Claims

1. A method for evaluating the dispersion stability of a dispersed phase dispersed in a dispersion medium, A first step of holding a sample containing the dispersion medium and the dispersed phase on a reflective surface, A second step involves irradiating the reflective surface with terahertz waves from the opposite side of the sample and detecting the terahertz waves reflected by the reflective surface. The fifth step involves stirring the sample while holding it on the reflective surface, In the second step, while maintaining the dispersed phase in a state where it can move toward the reflective surface, multiple detection results corresponding to multiple time points separated from each other are acquired. The fifth step involves adjusting the strength of stirring, and is a method for evaluating dispersion stability.

2. A third step of calculating multiple frequency characteristics corresponding to each of the multiple time periods based on each of the multiple detection results, The dispersion stability evaluation method according to claim 1, further comprising a fourth step of determining the migration speed of the dispersed phase toward the reflecting surface based on the temporal changes of the plurality of frequency characteristics.

3. The dispersion stability evaluation method according to claim 2, wherein the third step involves calculating the absorption spectrum of the sample with respect to terahertz waves as each of the plurality of frequency characteristics.

4. The dispersion stability evaluation method according to claim 2, wherein the third step involves calculating the refractive index spectrum of the sample with respect to the terahertz wave as each of the plurality of frequency characteristics.

5. The dispersion stability evaluation method according to claim 2, wherein the third step involves calculating the absorbance of the sample with respect to the terahertz wave as each of the plurality of frequency characteristics.

6. The dispersion stability evaluation method according to any one of claims 2 to 5, wherein in the fourth step, a value within the peak frequency range corresponding to the dispersion mass is used as each of the plurality of frequency characteristics.

7. The dispersion stability evaluation method according to any one of claims 2 to 5, wherein in the fourth step, a value within a base frequency range different from the peak frequency range corresponding to the dispersion mass is used as each of the plurality of frequency characteristics.

8. The dispersion medium is a liquid, The dispersion stability evaluation method according to any one of claims 1 to 7, wherein the dispersed phase is a solid.

9. In the first step, the sample is held so that it faces the reflective surface from above in a vertical direction relative to the reflective surface. The dispersion stability evaluation method according to any one of claims 1 to 8, wherein in the second step, the dispersed phase is maintained in a state in which it can settle toward the reflective surface in the vertical direction.

10. A step of performing the dispersion stability evaluation method described in any one of claims 1 to 9 for each of the multiple samples, A method for comparing dispersion stability, comprising the step of comparing the dispersion stability of each of the aforementioned multiple samples.

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