Optical measurement method and optical measurement device

Abstract

Provided are an optical measurement method and an optical measurement device for accurately measuring the particle diameter and the particle size distribution of particles contained in a particle-containing dispersion. This optical measurement method for a particle-containing dispersion comprises: an acquisition step for acquiring sequentially over time a plurality of particle images, which are captured by illuminating the dispersion with illumination light while varying the intensity thereof, for each intensity of the illumination light; a measurement step for measuring a moving average distance of the particles for each intensity of the illumination light from the plurality of images acquired sequentially over time for each intensity of the illumination light through the acquisition step; and a calculation step for calculating an apparent particle diameter of the particles for each intensity of the illumination light from the moving average distance of the particles obtained for each intensity of the illumination light through the measurement step, and determining a true particle diameter of the particles from the apparent particle diameter of the particles calculated for each intensity of the illumination light.

Description

Light measurement method and light measurement device

[0001] The present invention relates to an optical measurement method and an optical measurement device for a dispersion liquid containing particles.

[0002] In a wide range of fields, including industry, the environment, medicine, and academia, accurate size quantification of nanoparticles of approximately 1 to 100 nm in liquid is important and necessary. Representative techniques for quantifying nanoparticles include dynamic light scattering, low-coherence dynamic light scattering, particle tracking analyzers that measure particle displacement under a microscope, and multimodal light scattering measurement methods that combine Mie scattering angle profiles and dynamic light scattering information. These techniques are used to measure the diffusion coefficient of particles, which is then converted into particle size. More specific particle measurement methods are currently being proposed.

[0003] Patent Document 1 proposes a method for determining the particle diameter of a microparticle by calculating the distance traveled by the microparticle between images taken at different times from dark-field images (video) taken using a zonal optical system, and performing a calculation using the Einstein-Stokes equation (see equation (A) below) between the average travel distance and the diffusion time.

[0004]

[0005] Japanese Patent Application Laid-Open No. 2005-164560

[0006] Patent Document 1 describes the determination of particle size and particle size distribution using the Einstein-Stokes relationship between the average migration distance and diffusion time (see Equation (A)) as described above. However, Patent Document 1 does not take into account particle light absorption. When particles absorb light, their temperature may increase. Here, the Einstein-Stokes relationship includes a temperature term, and accurate particle size cannot be obtained when the temperature changes, such as when the particle temperature increases. For this reason, Patent Document 1 is unable to accurately determine the particle size and particle size distribution for black particles such as carbon black and particles that have the property of absorbing light, such as pigment particles. To avoid the influence of particle light absorption, it is possible to use a light source with a wavelength that is not absorbed by the particles, but in this case, preparing the light source is costly. Furthermore, since black particles and the like absorb light over a wide wavelength range, it is difficult to eliminate the influence of light absorption. As such, at present, it is not possible to deal with particles with various properties.

[0007] An object of the present invention is to provide an optical measurement method and an optical measurement device for accurately measuring the particle size and particle size distribution of particles contained in a dispersion liquid containing particles.

[0008] To achieve the above-mentioned object, invention [1] is an optical measurement method for a dispersion containing particles, comprising: an acquisition step of acquiring multiple images of particles successively over time for each intensity of incident light by irradiating the dispersion with incident light of varying intensities; a measurement step of measuring the average particle movement distance for each intensity of incident light from the multiple images successively acquired over time for each intensity of incident light obtained in the acquisition step; and a calculation step of calculating the apparent particle size for each intensity of incident light from the average particle movement distance for each intensity of incident light obtained in the measurement step, and determining the true particle size from the apparent particle size for each intensity of incident light. Note that in this invention, the true particle size refers to the particle size determined from the diffusion coefficient in a state unaffected by the temperature rise of the particles due to photothermal conversion. Furthermore, the apparent particle size refers to the particle size determined from the diffusion coefficient in a state affected by the temperature rise of the particles due to photothermal conversion.

[0009] Invention [2] is an optical measurement method for a dispersion liquid containing particles, the optical measurement method comprising: an acquisition step of acquiring, successively over time, a plurality of particle images for each intensity of incident light obtained by irradiating incident light at different intensities into the dispersion liquid; a measurement step of measuring an average moving distance of particles for each intensity of incident light from the plurality of images acquired successively over time for each intensity of incident light obtained in the acquisition step; and a calculation step of calculating an apparent particle size distribution for each intensity of incident light from the average moving distance of particles for each intensity of incident light obtained in the measurement step, and determining a true particle size distribution from the apparent particle size distribution for each intensity of incident light.

[0010] Invention [3] is an optical measurement method for a dispersion liquid containing particles, comprising: an acquisition step of acquiring, successively over time, a plurality of particle images for each intensity of incident light obtained by irradiating the dispersion liquid with incident light of varying intensities; a measurement step of measuring an average moving distance of the particles for each intensity of incident light from the plurality of images acquired successively over time for each intensity of incident light obtained in the acquisition step; and a calculation step of calculating a diffusion coefficient for each intensity of incident light from the average moving distance of the particles for each intensity of incident light obtained in the measurement step, determining a diffusion coefficient when the intensity of incident light is zero from the diffusion coefficients for each intensity of incident light, and determining a true particle size of the particles from the diffusion coefficient when the intensity of incident light is zero.

[0011] Invention [4] is the optical measurement method according to Invention [1] or [2], in which the calculation step determines the relationship between the apparent particle size of the particles and the intensity of the incident light, assuming that the dependency of the apparent particle size of the particles on the intensity of incident light is linear, thereby determining the true particle size of the particles. Invention [5] is the optical measurement method according to Invention [3], in which the calculation step determines the relationship between the diffusion coefficient of the particles and the intensity of the incident light, assuming that the dependency of the diffusion coefficient of the particles on the intensity of incident light is linear, thereby determining the diffusion coefficient at zero intensity of the incident light. Invention [6] is the optical measurement method according to Invention [2], in which the calculation step calculates a plurality of particle sizes of a certain proportion in the integral distribution of the apparent particle size distribution of the particles, and determines the relationship between the particle size of the certain proportion and the intensity of the incident light, assuming that the dependency of the particle sizes of the plurality of certain proportions on the intensity of incident light is linear, thereby determining the true particle size distribution. Invention [7] is the optical measurement method according to Invention [6], wherein the certain proportion is a proportion of 10% of all particles constituting the particle size distribution, a proportion of 50% of all particles constituting the particle size distribution, or a proportion of 90% of all particles constituting the particle size distribution. Invention [8] is the optical measurement method according to Invention [4], further comprising the steps of obtaining a second temperature after the temperature of particles at a first temperature has risen due to optical absorption of incident light, and determining the true particle size of the particles from the diffusion coefficient after the temperature has risen using an equation expressing the diffusion coefficient when the temperature has risen.

[0012] Invention [9] is an optical measurement device for a dispersion liquid containing particles, comprising: a light source that causes incident light to be incident on the dispersion liquid at varying intensities; an image acquisition unit that acquires a plurality of images of particles successively over time for each intensity of the incident light obtained by causing incident light to be incident on the dispersion liquid at varying intensities; a measurement unit that measures the average moving distance of the particles for each intensity of the incident light from the plurality of images acquired successively over time for each intensity of the incident light by the image acquisition unit; and a calculation unit that calculates the apparent particle size of the particles for each intensity of the incident light from the average moving distance of the particles for each intensity of the incident light obtained by the measurement unit, and determines the true particle size of the particles from the apparent particle size of the particles for each intensity of the incident light.

[0013] Invention

[10] is an optical measurement device for a dispersion liquid containing particles, the optical measurement device comprising: a light source that causes incident light to be incident on the dispersion liquid with its intensity changed; an image acquisition unit that acquires, successively over time, a plurality of images of particles obtained by causing incident light to be incident on the dispersion liquid with its intensity changed, for each intensity of the incident light; a measurement unit that measures an average moving distance of particles for each intensity of the incident light from the plurality of images acquired successively over time for each intensity of the incident light by the image acquisition unit; and a calculation unit that calculates an apparent particle size distribution for each intensity of the incident light from the average moving distance of particles for each intensity of the incident light obtained by the measurement unit, and determines a true particle size distribution from the apparent particle size distribution for each intensity of the incident light.

[0014] Invention

[11] is an optical measurement device for a dispersion liquid containing particles, the optical measurement device comprising: a light source that causes incident light to be incident on the dispersion liquid with varying intensities; an image acquisition unit that acquires a plurality of images of particles successively over time for each intensity of the incident light, obtained by causing incident light to be incident on the dispersion liquid with varying intensities; a measurement unit that measures an average moving distance of the particles for each intensity of the incident light from the plurality of images acquired successively over time for each intensity of the incident light by the image acquisition unit; and a calculation unit that calculates a diffusion coefficient for each intensity of the incident light from the average moving distance of the particles for each intensity of the incident light obtained by the measurement unit, determines a diffusion coefficient when the intensity of the incident light is zero from the diffusion coefficients for each intensity of the incident light, and determines a true particle size of the particles from the diffusion coefficient when the intensity of the incident light is zero.

[0015] Invention

[12] is the optical measurement device according to Invention [9] or

[10] , in which the calculation unit determines the relationship between the apparent particle size of the particle and the intensity of the incident light, assuming that the dependency of the apparent particle size of the particle on the intensity of the incident light is linear, to thereby determine the true particle size of the particle. Invention

[13] is the optical measurement device according to Invention

[11] , in which the calculation unit determines the relationship between the diffusion coefficient of the particle and the intensity of the incident light, assuming that the dependency of the diffusion coefficient of the particle on the intensity of the incident light is linear, to thereby determine the diffusion coefficient at zero intensity of the incident light. Invention

[14] is the optical measurement device according to Invention

[10] , in which the calculation unit calculates a plurality of particle sizes of a certain percentage in the integral distribution of the apparent particle size distribution of the particles, and determines the relationship between the particle size of the certain percentage and the intensity of the incident light, assuming that the dependency of the particle sizes of the plurality of certain percentages on the intensity of the incident light is linear, to thereby determine the true particle size distribution. Invention

[15] is the optical measurement device according to Invention

[14] , wherein the certain proportion is a proportion of 10% of all particles constituting the particle size distribution, a proportion of 50% of all particles constituting the particle size distribution, or a proportion of 90% of all particles constituting the particle size distribution. Invention

[16] is the optical measurement device according to Invention

[12] , wherein the calculation unit obtains a second temperature after the particles at the first temperature have risen in temperature due to light absorption of the incident light, and calculates the true particle size of the particles from the diffusion coefficient after the temperature rise using an equation representing the diffusion coefficient when the temperature rises.

[0016] Invention

[17] is the light measurement device according to any one of Inventions [9] to

[11] , wherein the light source emits incident light including a first laser beam having a wavelength in the optical absorption wavelength range of the particle and a second laser beam having a wavelength outside the optical absorption wavelength range of the particle, and the light source changes the intensity of the incident light by changing the intensity of the first laser beam. Invention

[18] is the light measurement device according to Invention

[17] , wherein a filter that attenuates light with a wavelength in the optical absorption wavelength range of the particle is provided between the dispersion liquid and the image acquisition unit. Invention

[19] is the light measurement device according to any one of Inventions [9] to

[18] , comprising a storage unit that stores the dispersion liquid, the storage unit comprising an optical element and a transparent substrate, the dispersion liquid being stored between the optical element and the transparent substrate, and the optical element being a trapezoidal prism, a semicylindrical prism, or a semicircular prism. Invention

[20] is an optical measurement device according to any one of Inventions [9] to

[18] , which has a storage unit with a flow path in which a dispersion liquid is stored, and a lens provided between the flow path and an image acquisition unit, in which the dispersion liquid is stored in the flow path, and incident light from a light source is incident on the dispersion liquid in the flow path.

[0017] According to the present invention, it is possible to provide an optical measurement method and an optical measurement device for accurately measuring the particle size and particle size distribution of particles contained in a dispersion liquid containing particles.

[0018] 1 is a graph showing the relationship between the diffusion coefficient of particles and the intensity of incident light. FIG. 2 is a graph showing the relationship between the reciprocal of the particle diameters of multiple types of particles and the intensity of incident light. FIG. 3 is a graph showing the relationship between the diffusion coefficient of particles and the intensity of incident light for each wavelength of incident light. FIG. 4 is a graph showing the relationship between the reciprocal of the particle diameter and the intensity of incident light. FIG. 5 is a schematic diagram showing a first example of an optical measurement device according to an embodiment of the present invention. FIG. 6 is a schematic diagram showing an example of a plurality of images acquired continuously in time. FIG. 7 is a schematic diagram showing an example of a particle movement trajectory. FIG. 8 is a graph showing the relationship between the reciprocal of the average particle diameter and the intensity of incident light. FIG. 9 is a graph showing the relationship between the reciprocal of the average particle diameter and the intensity of incident light. FIG. 10 is a graph showing the relationship between particle diameter and cumulative frequency. FIG. 11 is a graph showing the particle size distribution of particles. FIG. 12 is a schematic diagram showing a second example of an optical measurement device according to an embodiment of the present invention. FIG. 13 is a schematic diagram showing a third example of an optical measurement device according to an embodiment of the present invention.

[0019] The light measurement method and light measurement device of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. Note that the drawings described below are merely illustrative for explaining the present invention, and the present invention is not limited to the drawings shown below. Note that in the following, the "to" symbol indicating a numerical range includes the numerical values ​​written on both sides. For example, when ε is a numerical value ε α ~Number ε β That is, the range of ε is the number ε α and the number ε β The range includes ε α ≦ε≦ε β Unless otherwise specified, specific angles, perpendicularity, etc., include a generally accepted error range in the relevant technical field. Similarly, unless otherwise specified, temperatures also include a generally accepted error range in the relevant technical field.

[0020] (Measurement principle of optical measurement) First, the measurement principle of particle diameter will be described. A method is known in which the diffusion coefficient of a particle is measured and converted to a particle diameter from the diffusion coefficient. From the Stokes-Einstein formula shown in the following formula (1), the particle diameter d ０ In the following formula (1), k Ｂ is the Boltzmann constant, T ０ is the temperature of the solvent, η ０ is the viscosity of the solvent. The viscosity η of the solvent is calculated using the following formula (1): ０ is the same as the viscosity coefficient μ of the fluid in the above formula (A). Therefore, the diffusion coefficient of the particles can be expressed as the following formula (1) using the viscosity coefficient μ of the fluid. In the following formula (1), the absorption of light by the particles is not taken into consideration. Note that the solvent is the solvent in the dispersion liquid containing the particles. Here, particle absorption of light means that light incident on the particles is taken into the interior of the particles. When particles absorb light, the temperature of the particles may increase. Therefore, when particles have the property of absorbing light, the temperature of the particles may increase when they absorb light. Note that light absorption is used to mean the same as absorbing light as described above.

[0021]

[0022] Here, when considering the light absorption of particles, the relationship between the diffusion coefficient of particles and the intensity of incident light for particles with light-absorbing properties was investigated and found to be linear, as shown in Figure 1, for example, as indicated by line 10. That is, the dependence of the diffusion coefficient of the particles on the intensity of incident light is linear. In this case, the particle size obtained by extrapolating the diffusion coefficient of the above-mentioned line 10 to a value where the intensity of incident light is 0 (zero) is the true particle size independent of the intensity of incident light. By utilizing this linear dependence of the diffusion coefficient of the particles on the intensity of incident light, even for particles with light-absorbing properties, the true particle size independent of the intensity of incident light can be obtained. Therefore, even if the dispersion contains particles with various properties, such as light absorption, the particle size of the particles contained in the dispersion can be accurately measured. Note that the extrapolation method for extrapolating the intensity of incident light to 0 is not limited to linear. Even if the extrapolation is nonlinear, it is possible to perform extrapolation by fitting with an arbitrary function.

[0023] The relationship between the particle diffusion coefficient and the intensity of incident light also applies to particles other than those shown in FIG. 1 . While the diffusion coefficient was used in the above analysis example, even if the reciprocal of the particle diameter is used instead of the diffusion coefficient, the same relationship between the reciprocal of the particle diameter and the intensity of incident light applies. Specifically, for example, the relationship between the reciprocal of the particle diameter and the intensity of incident light applies, as shown by lines 13 and 14 in FIG. 2 . Note that while the vertical axis in FIG. 1 represents the diffusion coefficient, the vertical axis in FIG. 2 represents the reciprocal of the particle diameter. On the other hand, for particles with low light absorption, such as particles transparent to light of the wavelength of the incident light, the dependency on the intensity of incident light is extremely small, as shown by line 15 in FIG. 2 . Therefore, the difference between the particle diameter obtained by extrapolating the intensity of incident light to 0 (zero) and the particle diameter obtained when the intensity of incident light is greater than 0 (zero) is extremely small. Therefore, for particles with low light absorption, it is not necessary to obtain the particle diameter by extrapolating the intensity of incident light to 0 (zero).

[0024] Here, when the complex refractive index of the material that makes up a particle is expressed as N≡n+ik, the particle is said to be transparent when k=0. In other words, a transparent particle is a particle where k=0 in N≡n+ik. In the formula N≡n+ik that represents the complex refractive index, i represents an imaginary number. The real part n of the complex refractive index is called the refractive index. The imaginary part k of the complex refractive index is called the extinction coefficient, which represents absorption. Furthermore, although it depends on the intensity of the irradiated light, even if k=0 is not strictly true, particles can be treated as being almost transparent when k≒0.

[0025] Line 13 shows the results for a dispersion of a red pigment using PR254 (C.I. Pigment Red 254) as the red pigment. Line 14 shows the results for a dispersion of a red pigment using PR272 (C.I. Pigment Red 272) as the red pigment. Lines 13 and 14 are measured at a wavelength of 488 nm. Line 15 shows the results for a dispersion using polystyrene particles with a particle size of 100 nm. The polystyrene particles have low light absorption, and Nanobead NIST Traceable Particle Size Standard, 100 nm, was used. The solvent for the above dispersion is water. Line 15 is measured at a wavelength of 488 nm.

[0026] Even when measurements are taken on a dispersion containing the same particles with different wavelengths of incident light, the particle size can be obtained from the diffusion coefficient, which is the value extrapolated to an incident light intensity of 0 (zero), regardless of the wavelength of the incident light, as shown in Figure 3. Note that Figure 3 is a graph showing the relationship between the particle diffusion coefficient and the incident light intensity for each wavelength of incident light. In Figure 3, line 16 shows the results when the incident light wavelength is 488 nm. Line 17 shows the results when the incident light wavelength is 633 nm. The results are for a yellow pigment dispersion using the yellow pigment PY74 (C.I. Pigment Yellow 74) as the particles. The solvent for the above-mentioned yellow pigment dispersion is water.

[0027] The above description is an example of an analysis of a particle dispersion system with a low concentration, for example, 0.1 to 0.001% by volume. While the diffusion coefficient was used in the above analysis example, the reciprocal of the particle diameter can be used instead of the diffusion coefficient, as shown in FIG. 2. By extrapolating the reciprocal of the particle diameter to a value where the intensity of incident light is 0 (zero), the true particle diameter can be determined, independent of the intensity of incident light. While the above description is focused on low concentrations, even in the case of a particle dispersion system with a high concentration, for example, 1 to 20% by volume, the true particle diameter can be determined, independent of the intensity of incident light, by extrapolating the intensity of incident light to a value where the intensity of incident light is 0 (zero), as in the case of the low concentrations described above. For example, as shown in FIG. 4, there is a linear relationship between the reciprocal of the particle diameter and the intensity of incident light. The particle diffusion coefficient and the intensity of incident light are represented by the straight line 18 shown in FIG. 4. Although the vertical axis in FIG. 4 is the reciprocal of the particle diameter, as described above, there is also a linear relationship between the diffusion coefficient and the intensity of incident light even when the vertical axis is the diffusion coefficient.

[0028] Next, we will explain the case where a particle absorbs light and the temperature rises. When light absorption causes a local temperature rise near the particle and the system reaches equilibrium, the diffusion coefficient D' is expressed by the following formula (2). T' in the following formula (2) is the temperature of the solvent after light absorption, and η' in the following formula (2) is the viscosity of the solvent at temperature T'. In this case, it is assumed that the temperature rise is localized only near the particle, and the temperature cannot be detected by the thermometer attached to the device. In this case, the thermometer attached to the device measures temperature T ０ If the particle size measured using dynamic light scattering (DLS) is the apparent particle size d', the relationship between the particle size d' and the above-mentioned diffusion coefficient D' is expressed by the following formula (3). The following formula (4) can be obtained from formulas (2) and (3).

[0029]

[0030]

[0031]

[0032] Here, if the temperature rise in the vicinity of the particle due to light absorption is ΔT, the temperature rise is expressed by the following formula (5): T′=T ０+ΔT (5) If the following equation (6) is established between the intensity I of the incident light and the temperature rise ΔT of the particle due to light absorption, then substituting equations (4) and (5) into equation (3) yields the following equation (7): ΔT=α·I (6)

[0033]

[0034] The relationship between the viscosity of a solvent and the temperature of the solvent is expressed by the Andrade equation as follows: In the equation (8), B is a proportionality constant, E is flow activation energy, and R is a gas constant.

[0035]

[0036] Here, the following formula (9) is defined for 1 / η'. Then, when the following formula (9) is expanded by Taylor with respect to temperature, the following formula (10) is obtained. Then, when the following formula (9) is substituted into formula (6), the following formula (11) is obtained.

[0037]

[0038]

[0039]

[0040] Here, in equation (11), ΔT<T ０ In this case, the reciprocal of the particle size is linear with respect to the intensity I of the incident light. In this case, the following equation (12) is obtained. In the following equation (12), if only the linear terms are considered, the following equation is obtained, which further becomes the following equation (13).

[0041]

[0042]

[0043]

[0044] The term proportional to the intensity I of the incident light in equation (11) is defined as β, and β is defined as in equation (14) below. In this case, 1 / d' can be expressed by equation (15) below. Using equation (15) below, d ０ When solving for, the following equation (16) is obtained.

[0045]

[0046]

[0047] Furthermore, multiplying equation (15) by kBT / (3πη) gives the following equation (15-1). In equation (15-1), D' and D ０ is the diffusion coefficient. D' = D ０ +βD ０ ・I (15-1)

[0048] d ０ = (1 + β) I d' (16) From equation (15-1), the slope of the line 10 showing the intensity dependency of the incident light shown in FIG. 1 is βD ０ and the intercept of the line 10 is the diffusion coefficient D ０ From this, it can be seen that the slope of βD ０ and the intercept, i.e., the diffusion coefficient D ０ The above-mentioned β can be obtained from the equation (15-1) using the incident light intensity I and the diffusion coefficient D' at the incident light intensity I. ０ can be obtained, and the particle size d ０ The above-mentioned β is an index value representing the temperature dependency of particle diameter. The particle diameter d' when the intensity of incident light is I can also be obtained from equation (3) using the diffusion coefficient D'. When the vertical axis of the above-mentioned FIG. 1 is the reciprocal of the particle diameter, for example, in FIG. 2, from equation (15), the slope of the line 10 showing the dependency on the intensity of incident light is β / d ０ and the intercept of the line 10 is the particle size d ０ From this, it can be seen that the slope β / d ０ and the intercept, i.e., the particle size d ０ The particle diameter d' at the intensity I of the incident light can be calculated from the equation (15). ０ The above-mentioned β is an index value representing the temperature dependence of particle diameter. The particle diameter d' when the intensity of incident light is I can also be obtained from equation (3) using the diffusion coefficient D'.

[0049] Furthermore, from equation (13) and FIG. 1, the particle diameter d' and particle diameter d ０is known, the constant E / R related to the viscosity of the solvent and the temperature T ０ Since is known, the temperature rise ΔT at each intensity of incident light can be obtained. This allows the proportional coefficient α of the incident light intensity I and the temperature rise ΔT in equation (6) to be determined, and the true temperature during measurement T' = T ０ In this case, by measuring the particle size at an arbitrary incident light intensity, the particle size d ０ It is assumed that the temperature dependence of the viscosity of the solvent is known. From the above, it is possible to measure the particle size of particles contained in a dispersion with high accuracy even if the dispersion contains particles with various properties, such as light absorption.

[0050] (First Example of Optical Measurement Device) Next, an optical measurement device used in the optical measurement method will be described. FIG. 5 is a schematic diagram showing a first example of an optical measurement device according to an embodiment of the present invention. The optical measurement device 20 shown in FIG. 5 causes incident light Li to be incident on a dispersion liquid Lq containing particles with varying intensities, and acquires images of multiple particles successively over time for each intensity of the incident light Li to determine the true particle diameters of the particles. The optical measurement device 20 includes a light source 22, a storage unit 23, an objective lens 26, an imaging lens 28, an image acquisition unit 30, and a processing unit 32. Furthermore, the optical measurement device 20 includes a display unit 40 and an input unit 42.

[0051] The display unit 40 displays, for example, particle images, particle movement trajectories, and the apparent particle size, true particle size, apparent particle size distribution, and true particle size distribution of the particles obtained by the processing unit 32, and various known displays are used. The input unit 42 is an input device for inputting various pieces of information to the processing unit 32 in response to instructions from an operator. The input unit 42 is, for example, a mouse and a keyboard. The display unit 40 and the input unit 42 may be directly connected to the processing unit 32 or may be provided in a remote location away from the processing unit 32.

[0052] The storage section 23 stores a particle-containing dispersion liquid Lq and functions as a sample cell for the dispersion liquid Lq. The storage section 23 includes, for example, a transparent substrate 24 and an optical element 25. The dispersion liquid Lq is stored between the optical element 25 and the transparent substrate 24. The transparent substrate 24 is, for example, a transparent flat plate made of optical glass or optical plastic. The transparent substrate 24 also transmits scattered light Ls and the like generated by incident light Li incident on the dispersion liquid Lq. The scattered light Ls is emitted from the rear surface 24b of the transparent substrate 24. Here, unless otherwise specified, "transparent" means that the light transmittance is 40% or more, preferably 80% or more, and more preferably 90% or more, for the wavelength used. There are no particular limitations on the wavelength and wavelength range used, but a wavelength of 200 to 2500 nm, which is in the range from ultraviolet light to near-infrared light that can propagate through air, is desirable. The light transmittance is measured using "Plastics - Determination of total light transmittance and total light reflectance" as defined in JIS (Japanese Industrial Standards) K 7375:2008.

[0053] The optical element 25 is, for example, a trapezoidal prism 25a. The trapezoidal prism 25a has a configuration in which a bottom base 25b is wider than an top base. The bottom base 25b of the trapezoidal prism 25a is disposed in contact with the surface 24a of the transparent substrate 24. The dispersion liquid Lq provided on the surface 24a of the transparent substrate 24 is covered by the trapezoidal prism 25a. The storage unit 23 may be configured to include, for example, a temperature adjustment unit such as a Peltier element for adjusting the temperature of the dispersion liquid Lq.

[0054] The light source 22 is disposed at a position where incident light Li enters the dispersion liquid Lq on the transparent substrate 24. The light source 22 emits light, causing the incident light Li to enter the dispersion liquid Lq at a predetermined angle θ. An objective lens 26 is disposed facing the back surface 24b of the transparent substrate 24. An imaging lens 28 is disposed with its optical axis C aligned with that of the objective lens 26. The optical axis C is perpendicular to the surface 24a of the transparent substrate 24. Therefore, the incident light Li does not directly enter the objective lens 26. Note that the arrangement of the objective lens 26 and the imaging lens 28 is not particularly limited to arranging the optical axis C perpendicular to the surface 24a of the transparent substrate 24. The image acquisition unit 30 includes an image sensor 31. The processing unit 32 includes a measurement unit 34 and a calculation unit 36. The processing unit 32 includes a memory (not shown) for storing various information, such as image data output to the measurement unit 34 and data on the shape of the particle size distribution.

[0055] As described above, the light source 22 has a function of changing the intensity of the incident light Li and making it incident on the dispersion liquid Lq on the transparent substrate 24. The light source 22 can change the intensity of the incident light Li. Furthermore, the light source 22 is, for example, a laser that emits laser light containing light with a wavelength in the light absorption wavelength range of the particles contained in the dispersion liquid Lq. The light source 22 can also be, for example, a xenon light source or a superluminescence diode (SLD).

[0056] The objective lens 26 collects scattered light Ls generated by incident light Li incident on the dispersion liquid Lq. Of the scattered light Ls generated by the incident light Li, the scattered light Ls that has passed through the objective lens 26 is incident on the imaging lens 28. The imaging lens 28 forms an image of the scattered light Ls that has passed through the objective lens 26 on the light receiving surface 31 a of the image sensor 31.

[0057] The image sensor 31 has a light-receiving surface 31a that receives light imaged by the imaging lens 28. The scattered light Ls imaged by the imaging lens 28 is image light of the particles to be measured. The image sensor 31 captures an image of the particles, for example, by converting the light received by the light-receiving surface 31a into an electrical signal through photoelectric conversion. More specifically, the image sensor 31 captures an image of the particles by allowing scattered light containing the image of the particles to be measured to be incident on the light-receiving surface 31a, and then photoelectrically converting the scattered light to capture an image of the particles. In this manner, the image sensor 31 acquires particle image data, and an image of the particles is obtained. The particle image data is output from the image sensor 31 to the measurement unit 34 of the processing unit 32, and the processing unit 32 performs various processes on the particle image data. The processing unit 32 can temporarily store the particle image data in the memory (not shown) to perform various processes.

[0058] Since a plurality of particle image data are acquired successively in time, for example, a video is acquired at a preset frame rate in the image sensor 31, and time-series particle image data can be acquired from the acquired video data. The frame rate is not particularly limited, but is preferably 0.1 to 1000 fps (frames per second) from the viewpoint of accuracy of particle movement trajectories.

[0059] As long as it is possible to acquire multiple particle image data consecutively over time as described above, the image sensor 31 is not particularly limited, and may be, for example, a conventionally known photoelectric conversion element. More specifically, the image sensor 31 may be a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0060] In the light measurement device 20, incident light Li is incident from the inclined surface 25c of the trapezoidal prism 25a, and the incident light Li is incident on the dispersion liquid Lq at a preset angle θ, causing the incident light Li to be absorbed by the particles in the dispersion liquid Lq. At this time, scattered light Ls is generated that is scattered at an angle different from the incident light Li, and the scattered light Ls is collected by the objective lens 26 and imaged by the imaging lens 28 on the image sensor 31. As a result, the image sensor 31 obtains dark-field image data of the particles as image data of the particles. A plurality of image data of the particles is acquired continuously over time.

[0061] In the light measurement device 20, as described above, the optical axis C is perpendicular to the surface 24a of the transparent substrate 24, and the incident light Li is obliquely incident at an angle θ to the surface 24a of the transparent substrate 24. As a result, the incident light Li does not directly enter the objective lens 26. Therefore, when scattered light Ls is not generated, the incident light Li does not directly enter the objective lens 26, resulting in a dark image. On the other hand, when scattered light Ls is generated, an image based on the scattered light Ls, i.e., an image of the particle, is obtained. In the light measurement device 20, the optical element 25 is not limited to the trapezoidal prism 25a; instead, a semicylindrical prism or a semicircular prism can be used. Furthermore, although the light measurement device 20 is configured to include the trapezoidal prism 25a as the optical element 25, a configuration without an optical element 25 such as the trapezoidal prism 25a is also possible.

[0062] Here, Fig. 6 is a schematic diagram showing an example of a plurality of images acquired successively in time. Fig. 7 is a schematic diagram showing an example of a particle movement trajectory. The first image 44a and the second image 44b shown in Fig. 6 are successive images acquired using incident light Li of a specific intensity. The first image 44a and the second image 44b are examples of dark-field images. The first image 44a is taken at time t １ and the second image 44b is an image at time t ２In each of the first image 44a and the second image 44b, for the purpose of explanation, three particles, a first particle 45a, a second particle 45b, and a third particle 45c, are shown. From the multiple images acquired successively in time for each intensity of the incident light Li obtained by the image acquisition unit 30, the measurement unit 34 measures the average moving distance of all particles included in the images, i.e., all measured particles, for each intensity of the incident light Li.

[0063] For example, the center of gravity is determined as the position of each of the first particle 45a, the second particle 45b, and the third particle 45c shown in FIG. 6 . The center of gravity can be determined by known image analysis. For example, the contours of the first particle 45a, the second particle 45b, and the third particle 45c are extracted from the first image 44a and the second image 44b, respectively. Next, the position of the geometric center of the area surrounded by the contours of the first particle 45a, the second particle 45b, and the third particle 45c is determined. The position of the geometric center is the center of gravity. From the positions of the first particle 45a, the second particle 45b, and the third particle 45c in the first image 44a and the second image 44b, the movement trajectories (not shown) of the first particle 45a, the second particle 45b, and the third particle 45c are calculated. The movement trajectories of the particles can be determined by known image analysis. For example, the difference or sum between the first image 44a and the second image 44b is calculated to determine the nearest particle position, and the movement direction and movement amount of each particle are identified from the positions of the first particle 45a, the second particle 45b, and the third particle 45c in the first image 44a and the positions of the first particle 45a, the second particle 45b, and the third particle 45c in the second image 44b, to calculate the displacement vector of each particle and calculate the movement trajectory of each particle.The movement amount of the particle per unit shooting time interval is calculated from the movement trajectory of the particle between the first image 44a and the second image 44b arranged in time series.The unit shooting time interval is, for example, time t １ and time t ２ The unit shooting time interval corresponds to Δt in formula (A). Furthermore, if the first image 44a and the second image 44b are images that constitute a moving image, the frame rate of the moving image corresponds to Δt in formula (A).

[0064] The amount of movement of a particle per unit imaging time interval is the particle movement distance. The particle movement distance 46b shown in FIG. 7 corresponds to the displacement vector. A movement trajectory is obtained using multiple temporally consecutive images, for example, a movement trajectory 46a as shown in image 46 in FIG. 7 for the first particle 45a. The movement of a particle between images is represented by a displacement vector. Here, the average movement distance of a particle due to Brownian motion is defined as Sp, as shown in the following formula. The average movement distance of a particle corresponding to the above-mentioned displacement vector is calculated to obtain the average movement distance Sp of a particle due to Brownian motion. The measurement unit 34 measures the average movement distance of a particle for each intensity of the incident light Li using multiple images acquired temporally consecutively for each intensity of the incident light Li by the image acquisition unit 30. Then, the average movement distance Sp of a particle due to Brownian motion is obtained for each intensity of the incident light Li.

[0065]

[0066] The calculation unit 36 ​​calculates the apparent particle size of the particles for each intensity of the incident light Li from the average particle movement distance for each intensity of the incident light Li obtained by the measurement unit 34. The true particle size of the particles is determined from the apparent particle size for each intensity of the incident light Li. Specifically, using the average particle movement distance Sp due to Brownian motion for each intensity of the incident light Li, the apparent particle size of all measured particles for each intensity of the incident light Li is calculated from the above-mentioned formula (A). It is also possible to calculate the average apparent particle size for each intensity of the incident light Li from the apparent particle sizes of all measured particles.

[0067] The calculation unit 36 ​​determines the true particle size of the particles by determining the relationship between the apparent particle size of the particles and the intensity of the incident light, assuming that the apparent particle size of the particles is linearly dependent on the intensity of the incident light. For example, as shown in FIG. 8, the apparent average particle size is plotted with the vertical axis representing the reciprocal of the average particle size and the horizontal axis representing the intensity of the incident light. In this case, it is assumed that the apparent average particle size is linearly dependent on the intensity of the incident light. Therefore, an approximate straight line 50 is obtained for the value of the apparent average particle size. On the approximate straight line 50, the point P at which the intensity of the incident light is extrapolated to 0 (zero) is １The average particle size at the intercept of the approximation line 50 is the true average particle size that is independent of the intensity of incident light. In other words, the average particle size at the intercept of the approximation line 50 is the true average particle size that is independent of the intensity of incident light. In this way, the true particle size that is independent of the intensity of incident light is obtained. Therefore, even if the dispersion contains particles with various properties, such as the property of absorbing light, the particle size of the particles contained in the dispersion can be measured with high accuracy.

[0068] The average particle size of the entire system of the particle-containing dispersion liquid Lq is the average particle size of the particles in the system of the particle-containing dispersion liquid Lq. For the average particle size of the entire observed particles, the relational expression of the apparent particle size d' that depends on the intensity I of the incident light is 1 / d' = 1 / d ０ + βI / d ０ By calculating this relational expression, the average particle diameter d of the system when the intensity of the incident light is zero can be calculated. ０ is calculated by extrapolation. Note that β is defined by the formula (14). d' of the apparent particle size distribution ρ(d') composed of apparent particle sizes is calculated by d ０ By converting it into ０ ) can be obtained.

[0069] The calculation unit 36 ​​can also calculate multiple particle sizes of a certain percentage in the integral distribution of the apparent particle size distribution of particles using the particle size distribution composed of apparent particle sizes, and determine the relationship between the particle size of the certain percentage and the intensity of incident light by assuming that the dependence of the particle sizes of the certain percentage on the intensity of incident light is linear, thereby obtaining the true particle size distribution. Like the true particle size, the true particle size distribution is a particle size distribution in a state that is not affected by the temperature rise of particles due to photothermal conversion. The true particle size distribution does not depend on the intensity of incident light. The certain percentage refers to the percentage of 10% of all particles constituting the particle size distribution, the percentage of 50% of all particles constituting the particle size distribution, or the percentage of 90% of all particles constituting the particle size distribution. The percentage of 10% of all particles constituting the particle size distribution is referred to as D10. The percentage of 50% of all particles constituting the particle size distribution is referred to as D50. The percentage of 90% of all particles constituting the particle size distribution is referred to as D90. The particle sizes of a certain proportion in the integral distribution are, for example, the particle sizes at D10, D50, and D90 described above. The particle size distribution is composed of the particle sizes of all particles measured, and all particles constituting the particle size distribution are all particles measured as described above.

[0070] Specifically, as shown in Figure 9, the vertical axis is the reciprocal of the average particle size, and the horizontal axis is the intensity of incident light, and the apparent particle size for each intensity of incident light at D10, D50, and D90 is plotted. In this case, it is assumed that the apparent particle size is linearly dependent on the intensity of incident light. Therefore, an approximate straight line 52 is obtained for the apparent particle size value at D10. An approximate straight line 54 is obtained for the apparent particle size value at D50. An approximate straight line 56 is obtained for the apparent particle size value at D90. On the approximate straight line 52, a point P where the intensity of incident light is extrapolated to 0 (zero) is obtained. １０ The particle diameter at point P on the approximation line 54 is the true particle diameter of D10 that does not depend on the intensity of the incident light. ５０The particle diameter at D50 is the true particle diameter at D50, which does not depend on the intensity of incident light. On the approximation line 56, the point P ９０ The particle size at point P shown in FIG. 9 is the true particle size at D90, which does not depend on the intensity of incident light. In this way, the true particle size at D10, D50, and D90 described above, which does not depend on the intensity of incident light, is obtained. １０ , point P ５０ , point P ９０ are 1 / particle size D10 R , 1 / particle size D50 R , 1 / particle size D90 R is the value.

[0071] Furthermore, the calculation unit 36 ​​uses the above-described true particle diameters D10, D50, and D90 to convert them into an accurate particle size distribution corresponding to the shape of the particle size distribution, such as a Gaussian distribution or a Poisson distribution. This allows for a true particle size distribution that is independent of the intensity of incident light. More specifically, a Gaussian distribution or a Poisson distribution is selected as the shape of the particle size distribution. The above-described true particle diameter values ​​D10, D50, and D90 are input to the selected Gaussian distribution or Poisson distribution. The selected Gaussian distribution or Poisson distribution is fitted to the above-described true particle diameter values ​​D10, D50, and D90. This allows for a particle size distribution based on the above-described true particle diameter values ​​D10, D50, and D90. Note that particle size distribution shapes such as a Gaussian distribution and a Poisson distribution are stored, for example, as a library in a memory (not shown) of the processing unit 32, and are called from the library in the memory when calculating the particle size distribution.

[0072] In addition to the above-mentioned method, the particle size distribution can be calculated using the following method. First, the dependency of the incident light intensity, such as D10 shown in FIG. 9, is calculated for D10, D20, ..., D90. From the obtained dependency of D10, D20, ..., D90 on the incident light intensity, the true particle size D10 for each D10, D20, ..., D90 is calculated. R , D20 R , ..., D90 R Calculate the true particle size D10 R , D20 R , ..., D90R is calculated by extrapolating the incident light intensity to 0 (zero) as described above (point P １０ , point P ５０ , point P ９０ (See reference). The true particle size D10 R , D20 R , ..., D90 R By plotting the values ​​of D20 on a scatter diagram, for example, an integral distribution 57 shown in FIG. R and true particle size D10 R The cumulative frequency difference is the true particle size D20 R and true particle size D10 R The true particle size D30 is calculated as Y15 (see formula (17) below). R and true particle size D20 R Y25 is calculated in the same manner as Y15. R and true particle size D30 R Y35 is calculated for Y15 in the same manner as for Y15. After that, the same process as for Y15 is repeated to obtain the true particle diameter D90 R and true particle size D80 R Furthermore, the particle diameter X15 (see formula (18) below) is calculated by the following formula (19) R and D10 R The average value of particle size X25 is D30 R and D20 R Average value of particle size X85 to D90 R and D80 R The particle sizes X15 to X85 are calculated (see formula (18) below). Finally, by plotting (X15, Y15), (X25, Y25), ..., (X85, Y85) on a scatter diagram, for example, a particle size distribution 58 shown in FIG. 11 can be obtained.

[0073]

[0074]

[0075] Furthermore, the calculation unit 36 ​​can obtain a second temperature after the temperature of a particle at a first temperature rises due to light absorption of the incident light, and can use an equation representing the diffusion coefficient when a temperature rise occurs to calculate the true particle size of the particle from the diffusion coefficient after the temperature rise. Here, the first temperature is the temperature before the temperature rise due to light absorption. For example, if the particles are dispersed in a dispersion liquid Lq, it is the temperature of the dispersion liquid Lq before light absorption. Specifically, for the second temperature after the temperature rise due to light absorption of the incident light, first, the apparent particle size d' obtained at a certain intensity of the incident light and the true particle size d obtained by extrapolating the intensity of the incident light to 0 (zero) are calculated. ０ Using the above equation, ΔT is calculated from the experimental results using equation (13). As a result, the second temperature T' is obtained by T + ΔT. That is, the particle diameter d' and particle diameter d at an arbitrary incident light intensity I are ０ is known, the constant E / R related to the viscosity of the solvent and the temperature T ０ Since is known, the temperature rise ΔT at each intensity of incident light can be obtained. This allows us to calculate the proportionality coefficient α between the intensity I of incident light and the temperature rise ΔT in equation (6), and the true temperature during measurement T' = T ０ +ΔT is obtained. Temperature T ０ is the first temperature, and temperature T' is the second temperature. The equation that represents the diffusion coefficient when a temperature rise occurs is equation (2). In this case, the true particle size of the particle can be obtained from the diffusion coefficient after the temperature rise.

[0076] Since the calculation unit 36 ​​determines the true particle diameters of all the measured particles, it is possible to obtain the particle size distribution of the particles. The calculation unit 36 ​​calculates d for the obtained particle size distribution A(d) in the same manner as in equation (16). ０ = (1 + β) I d, the intensity of the incident light is expressed as d ０ = (1 + β) I d where I is the particle size distribution A(d) obtained. ０ ) is corrected to obtain the particle size distribution A(d ０ ) is obtained.

[0077] The calculation unit 36 ​​can also obtain the second temperature after the particles at the first temperature have risen in temperature due to light absorption of the incident light, and calculate the particle size distribution of the particles. In this case, the particle size distribution is obtained as described above. At this time, when calculating the particle size from the diffusion coefficient D, the temperature T' is used as shown in equation (2), i.e., the second temperature, and the viscosity η' of the solvent at temperature T'. This allows the particle size distribution A(d ０ ) is obtained.

[0078] The processing unit 32 determines the particle size distribution of particles as described above by executing a program (computer software) stored in a ROM (Read Only Memory) or the like in the processing unit 32. The processing unit 32 may be configured by a computer in which each part functions by executing the program as described above, or may be a dedicated device in which each part is configured by a dedicated circuit, or may be configured by a server to be executed on the cloud.

[0079] In the light measurement device 20, the storage unit 23 is not limited to a configuration using a transparent substrate 24 and a trapezoidal prism 25a. The storage unit 23 may also be configured to include a flow path (not shown) in which the dispersion liquid Lq is stored. In this case, a lens such as an objective lens 26 is provided between the flow path and the image acquisition unit 30, the dispersion liquid Lq is stored in the flow path, and incident light Li from the light source 22 is incident on the dispersion liquid Lq in the flow path. Scattered light generated by the incidence of the incident light Li is collected by the lens such as the objective lens 26, and an image of the particles is acquired by the image sensor 31 of the image acquisition unit 30. The flow path is transparent and transmits scattered light Ls and the like generated by the incident light Li incident on the dispersion liquid Lq. Furthermore, for example, the flow path is made of optical glass or optical plastic, and has a width of approximately several μm to several mm and a thickness of approximately several μm to several hundred μm.

[0080] (Second Example of Optical Measurement Device) The optical measurement device 20 is not limited to the configuration shown in Fig. 5, and may be an optical measurement device 20a shown in Fig. 12. Fig. 12 is a schematic diagram showing a second example of an optical measurement device according to an embodiment of the present invention. In Fig. 12, the same components as those in the optical measurement device 20 shown in Fig. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. The optical measurement device 20a shown in Fig. 12 has the same configuration as the optical measurement device 20 shown in Fig. 5, except that the configuration of the light source 22 is different from that of the optical measurement device 20.

[0081] The light source 22 emits a first laser beam L having a wavelength in the light absorption wavelength range of the particles of the dispersion liquid Lq. １ and a second laser beam L having a wavelength outside the light absorption wavelength range of the particles of the dispersion liquid Lq. ２ The light source 22 emits a first laser beam L having a wavelength in the light absorption wavelength range of the particle. １ and a second laser beam L having a wavelength outside the light absorption wavelength range of the particle. ２ The light measurement device 20a emits incident light Li including the incident light and the incident light Li. The light measurement device 20a is provided with, for example, a cubic beam splitter 62. The beam splitter 62 has a transmission-reflection surface 62a that combines the incident light into two beams. The transmission-reflection surface 62a is a diagonal surface of the beam splitter 62, and is an inclined surface inclined at an angle of 45°.

[0082] The first laser 60 and the second laser 61 emit a first laser beam L １ and the second laser light L ２ The first laser beam L is arranged so as to be incident on a predetermined position on the transmission / reflection surface 62a of the beam splitter 62. １ and the second laser light L ２ The incident light Li is obtained by combining the first laser beam L and the second laser beam L. The incident light Li is incident on the dispersion liquid Lq by adjusting the direction of the transmission-reflection surface 62a. ２ The first laser light L has a wavelength outside the light absorption wavelength range of the particle, and is therefore mainly used to obtain scattered light from the particle and to acquire an image of the particle. １The light source 22 emits the first laser beam L １ That is, by changing the intensity of the light emitted by the first laser 60, the intensity of the incident light Li is changed.

[0083] As described above, the first laser beam L １ and the second laser light L ２ By using the second laser light L, the incident light Li is incident on the inclined surface 25c of the trapezoidal prism 25a, and the incident light Li is incident on the dispersion liquid Lq at a preset angle θ, so that the particles absorb the incident light Li. ２ This generates scattered light Ls scattered at an angle different from that of the incident light Li, and the scattered light Ls is collected by the objective lens 26 and imaged by the imaging lens 28 on the image sensor 31. As a result, the image sensor 31 obtains dark-field image data of the particles as image data of the particles. A plurality of particle image data is acquired successively in time. The plurality of particle image data acquired successively in time is output to the measurement unit 34. The particle image data output to the measurement unit 34 is dark-field image data.

[0084] In the optical measurement device 20a, as described above, the optical axis C is also perpendicular to the surface 24a of the transparent substrate 24, and the incident light Li is obliquely incident at an angle θ to the surface 24a of the transparent substrate 24. Therefore, the incident light Li does not directly enter the objective lens 26. Therefore, when scattered light Ls is not generated, the incident light Li does not directly enter the objective lens 26, and a dark image is obtained. On the other hand, when scattered light Ls is generated, an image based on the scattered light Ls, i.e., an image of the particles, is obtained. Furthermore, in the optical measurement device 20a, the first laser light L having a wavelength in the light absorption wavelength range of the particles in the dispersion liquid Lq is incident on the first laser light L. １ and a second laser beam L having a wavelength outside the light absorption wavelength range of the particles of the dispersion liquid Lq. ２ Therefore, the first laser beam L emitted by the first laser 60 is １By changing the wavelength of the light, it is possible to determine the true particle size and true particle size distribution for multiple types of particles with different light absorption wavelength ranges. The light absorption wavelength range of a particle can be identified by measuring its absorption spectrum using a spectrophotometer.

[0085] In addition, the light measurement device 20a preferably has a filter 63 between the dispersion liquid Lq and the image acquisition unit 30 that attenuates light of wavelengths in the optical absorption wavelength range of the particles. More specifically, it is preferable to place the filter 63 between the objective lens 26 and the imaging lens 28. By providing the filter 63, it is possible to prevent light carrying an image of the particles that is incident on the image sensor 31 of the image acquisition unit 30 from including light of wavelengths in the optical absorption wavelength range of the particles. As a result, in the image of the particles, the first laser light L of a wavelength in the optical absorption wavelength range of the particles is prevented from being included. １ The filter 63 is not particularly limited as long as it can attenuate light of wavelengths in the light absorption wavelength range of the particles. For example, a filter that absorbs light in the light absorption wavelength range of the particles or a bandpass filter that blocks light in the light absorption wavelength range of the particles can be used as the filter 63.

[0086] (Third Example of Optical Measurement Device) FIG. 13 is a schematic diagram showing a second example of an optical measurement device according to an embodiment of the present invention. In FIG. 13, components identical to those in the optical measurement device 20 shown in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted. The optical measurement device 20b shown in FIG. 13 has the same configuration as the optical measurement device 20 shown in FIG. 5, except that it uses dark-field illumination and has a cover plate 68 instead of the optical element 25. The light source 22 of the optical measurement device 20b, like the optical measurement device 20, can change the intensity of the incident light Li and emits laser light containing light with a wavelength in the optical absorption wavelength range of the particle. The cover plate 68 is transparent to the incident light Li and is made of, for example, optical glass or optical plastic.

[0087] In the light measurement device 20b, a reflecting member 64 is provided on the surface 24a of the transparent substrate 24. The reflecting member 64 has a cylindrical shape on the surface 24a side of the transparent substrate 24, with a truncated cone connected to the cylinder. The reflecting member 64 has a bent portion 64b that is bent toward the surface 24a of the transparent substrate 24, and the inner surface 64a of the reflecting member 64 is a reflective surface. The reflecting member 64 also has an opening 64c facing the surface 24a. A ring-shaped mask 65 is provided in the opening 64c, and the opening 64c is blocked by the ring-shaped mask 65. The ring-shaped slit 65a is provided in the ring-shaped mask 65. The ring-shaped slit 65a is provided at a position facing the opening 64c. A reflecting portion 66 having a curved surface 66a that is convex relative to the surface 24a of the transparent substrate 24 is provided within the reflecting member 64, between the slit 65a of the ring-shaped mask 65 and the dispersion liquid Lq on the surface 24a of the transparent substrate 24.

[0088] Light emitted from the light source 22 passes through the slit 65a of the annular mask 65 and is formed into a circular light beam. The circular light beam is reflected by the curved surface 66a of the reflecting portion 66 toward the inner surface 64a of the bent portion 64b of the reflecting member 64. The light beam is further reflected by the inner surface 64a of the bent portion 64b of the reflecting member 64 and enters the dispersion liquid Lq as incident light Li at a predetermined angle θ with respect to the surface 24a of the transparent substrate 24. As a result, scattered light Ls is generated in the dispersion liquid Lq, scattered at an angle different from that of the incident light Li. The scattered light Ls is collected by the objective lens 26 and imaged by the imaging lens 28 on the image sensor 31. As a result, the image sensor 31 obtains dark-field image data of the particles as particle image data. A plurality of particle image data is acquired continuously over time. The plurality of particle image data acquired continuously over time is output to the measurement unit 34. The particle image data output to the measurement unit 34 is dark-field image data.

[0089] In the light measurement device 20b, as described above, the optical axis C is perpendicular to the surface 24a of the transparent substrate 24, and the incident light Li is obliquely incident at an angle θ to the surface 24a of the transparent substrate 24. Therefore, the incident light Li does not directly enter the objective lens 26. Therefore, when no scattered light occurs, the incident light Li does not directly enter the objective lens 26, and a dark image is obtained. On the other hand, when scattered light occurs, an image based on the scattered light, i.e., an image of the particles, is obtained. Therefore, a clear image of the particles can be obtained even if the particle size is small.

[0090] (First Example of Optical Measurement Method) Optical measurement is performed based on the measurement principle described above. For example, the optical measurement device 20 shown in FIG. 5 described above is used for the optical measurement. Note that the optical measurement device 20a shown in FIG. 12 and the optical measurement device 20b shown in FIG. 13 described above can obtain particle size, diffusion coefficient, and particle size distribution in the same manner as the optical measurement device 20 shown in FIG. 5 described above, except that the method of acquiring particle images is different. The first example of the optical measurement method is an optical measurement method for a dispersion liquid containing particles. In the first example of the optical measurement method, first, incident light Li is irradiated into the dispersion liquid Lq with varying intensities, and multiple particle images are acquired consecutively in time for each intensity of the incident light (acquisition step).

[0091] In the acquisition process, the particle-containing dispersion liquid Lq is measured using a laser, for example, emitting light with a wavelength in the particle light absorption wavelength range, as the light source 22 shown in FIG. 5 . Light is emitted from the light source 22, and incident light Li is incident on the dispersion liquid Lq at a preset angle θ, for example, via the inclined surface 25c of the trapezoidal prism 25a, causing the particles in the dispersion liquid Lq to absorb the incident light Li. At this time, scattered light Ls is generated, which is scattered at an angle different from that of the incident light Li. The scattered light Ls, which is the incident light Li scattered by the particles, is collected by the objective lens 26, incident on the imaging lens 28, and formed on the image sensor 31. As a result, the image sensor 31 obtains dark-field image data of the particles as particle image data. For example, particle images are acquired as a video at a preset frame rate, thereby acquiring multiple particle image data consecutively in time. In this case, for example, the first image 44a and the second image 44b shown in FIG. 6 are acquired. In the acquisition step, a plurality of pieces of image data of the above-mentioned particles are acquired successively in time for each intensity of incident light.

[0092] Next, the average particle movement distance is measured for each intensity of incident light from multiple images acquired consecutively over time for each intensity of incident light obtained in the acquisition step (measurement step). In the measurement step, for example, the center of gravity positions are determined as the positions of the first particle 45a, the second particle 45b, and the third particle 45c in the first image 44a and the second image 44b shown in FIG. 6 . The center of gravity positions are determined by determining the geometric center positions of the areas surrounded by the outlines of the extracted particles in the first image 44a and the second image 44b, as described above. Next, movement trajectories (not shown) are calculated for the first particle 45a, the second particle 45b, and the third particle 45c, respectively, from the positions of the first particle 45a, the second particle 45b, and the third particle 45c in the first image 44a and the second image 44b. From the particle movement trajectories, the amount of movement of the particle per unit imaging time interval, i.e., the movement distance of the particle, is determined. The movement amounts of all the measured particles are calculated, and the above-mentioned average movement distance Sp is calculated for all the measured particles.

[0093] Next, the apparent particle size of each particle is calculated for each intensity of incident light from the average moving distance of each particle for each intensity of incident light obtained in the measurement step, and the true particle size of each particle is calculated from the apparent particle size for each intensity of incident light (calculation step). In the calculation step, the apparent particle size of all particles measured for each intensity of incident light Li is calculated from the above formula (A) using the above average moving distance Sp for each intensity of incident light Li of each particle. Next, assuming that the apparent particle size of each particle depends linearly on the intensity of incident light, the relationship between the apparent particle size of each particle and the intensity of incident light is calculated to determine the true particle size of the particle. In this regard, the relational expression for the apparent particle size d' dependent on the intensity I of incident light as described above is 1 / d' = 1 / d ０ + βI / d ０ By calculating this relational expression, the average particle diameter d of the system when the intensity of the incident light is zero can be calculated. ０ is calculated by extrapolation. Note that β is defined by equation (14). For example, as shown in FIG. 8, an approximate straight line 50 is obtained, which represents the relationship between the apparent average particle size and the intensity of incident light. The particle size when the intensity of incident light is zero on the approximate straight line 50 is calculated as the true particle size that is not affected by the temperature rise of the particles due to photothermal conversion. In this way, the true particle size of the particles can be calculated even for particles that have the property of absorbing light. Note that in the calculation step, the true particle size is calculated for all measured particles, and therefore the true particle size distribution can also be obtained from the calculated true particle sizes of all particles.

[0094] Furthermore, even if the particle absorbs light and the temperature rises, the true particle size can be determined as follows. In this case, a second temperature is obtained after the particle at the first temperature has risen in temperature due to the absorption of incident light. Next, the true particle size of the particle is determined from the diffusion coefficient after the temperature rise using the formula that represents the diffusion coefficient when the temperature rises. The first temperature is as described above. For the second temperature after the temperature rise due to the absorption of incident light, first, the apparent particle size d' obtained at a certain intensity of incident light and the true particle size d obtained by extrapolating the intensity of incident light to 0 (zero) are used. ０Using the above, ΔT is calculated from the experimental results using equation (13). As a result, the second temperature T' is obtained as T + ΔT. If the second temperature T' can be obtained, the diffusion coefficient after the temperature rise, i.e., the diffusion coefficient at the second temperature, is calculated using equation (2) which represents the diffusion coefficient when the temperature rise occurs. The true particle size d ０ where D' is the diffusion coefficient after the temperature rise, which in this case is the diffusion coefficient at the second temperature. As described above, T' is the temperature after the temperature rise, which in this case is the second temperature. η' is the viscosity of the solvent at temperature T', which in this case is the viscosity at the second temperature.

[0095] In the acquisition step, the above-mentioned particle image data is acquired multiple times consecutively for each incident light intensity, and the true particle size of the particle is determined in the next step, the calculation step. However, the calculation step may be performed after the above-mentioned particle image data is acquired multiple times consecutively for all incident light intensities to be measured in the acquisition step, i.e., after all particle image data is acquired for all incident light intensities to be measured. Furthermore, in the acquisition step, the calculation step may be performed continuously in time after the above-mentioned particle image data is acquired multiple times consecutively for each incident light intensity to be measured.

[0096] (Second Example of Optical Measurement Method) While the determination of true particle size has been described above, it is also possible to determine the true particle size distribution of particles. The second example of the optical measurement method is a method of determining the true particle size distribution of particles. The method of determining the true particle size distribution of the second example of the optical measurement method differs from the method of determining the true particle size of the first example of the optical measurement method described above in that the acquisition step and the measurement step are the same step, and the calculation step is a step of determining the true particle size distribution. Therefore, the calculation step of determining the true particle size distribution will be described below.

[0097] In the second example of the light measurement method, the calculation step for determining the true particle size distribution is a step of calculating an apparent particle size distribution for each intensity of incident light from the average moving distance of particles for each intensity of incident light obtained in the measurement step, and determining the true particle size distribution from the apparent particle size distribution for each intensity of incident light. In the calculation step, the apparent particle size of all measured particles is calculated for each intensity of incident light Li from the above-mentioned formula (A) using the average moving distance Sp for each intensity of incident light Li of each particle as described above. As a result, the apparent particle size for each intensity of incident light Li is obtained for all measured particles. From this, the apparent particle size distribution for each intensity of incident light Li is obtained for all measured particles. As described above, assuming that the apparent particle size of a particle depends linearly on the intensity of incident light, the relationship between the apparent particle size of a particle and the intensity of incident light is determined. The true particle size of all measured particles is calculated using the relationship between the apparent particle size of a particle and the intensity of incident light. The true particle size distribution is obtained from the calculated true particle sizes of all particles.

[0098] Furthermore, in the particle size distribution, even if the particles absorb light and the temperature rises as described above, the true particle size can be determined as described above. Therefore, the true particle size distribution can be obtained by using the true particle size of the particles determined from the diffusion coefficient after the temperature rises.

[0099] Alternatively, the calculation step may involve calculating multiple particle sizes at a certain percentage in the integral distribution of the apparent particle size distribution of the particles, assuming that the dependency of the particle sizes at the certain percentages on the intensity of incident light is linear, and determining the relationship between the particle sizes at the certain percentages and the intensity of incident light to obtain a true particle size distribution. The certain percentage is as described above. In this case, it is assumed that the dependency of the apparent particle sizes at D10, D50, and D90 for each intensity of incident light is linear, as described above. As shown in FIG. 9 , the relationship between the apparent particle sizes at D10, D50, and D90 for each intensity of incident light and the intensity of incident light is obtained, and the true particle sizes at D10, D50, and D90 when the intensity of incident light is zero are obtained. As described above, the true particle sizes at D10, D50, and D90 are converted into accurate particle size distributions according to the shape of the particle size distribution, such as a Gaussian distribution or a Poisson distribution. This allows obtaining a true particle size distribution that is independent of the intensity of incident light.

[0100] (Third Example of Optical Measurement Method) The third example of the optical measurement method is a method for determining the true particle size of particles. Compared to the method for determining the true particle size of the first example of the optical measurement method described above, the method for determining the true particle size of the third example of the optical measurement method has the same acquisition step and measurement step as the method for determining the true particle size, but a different calculation step for determining the true particle size. Therefore, the calculation step for determining the true particle size will be described. In the third example of the optical measurement method, the calculation step is a step of calculating a diffusion coefficient for each intensity of incident light from the average moving distance of the particle for each intensity of incident light obtained in the measurement step, determining a diffusion coefficient when the intensity of incident light is zero from the diffusion coefficients for each intensity of incident light, and determining the true particle size of the particle from the diffusion coefficient when the intensity of incident light is zero.

[0101] Here, the following formula (19) is obtained from the above formula (A) and formula (1), and the diffusion coefficient D is expressed by the following formula (20) from this formula (19). In addition, the following formula (20) also shows formula (1) related to the diffusion coefficient D. From the following formula (20), the particle size d ０ The following equation (21) is obtained for D ０ is the diffusion coefficient when the intensity of the incident light is zero, that is, the true diffusion coefficient. ０ From the true particle size d ０ can be obtained. From this, by determining the average particle movement distance Sp, the diffusion coefficient D can be calculated for each intensity of incident light. As with the apparent particle size, the diffusion coefficient is also assumed to have a linear dependency on the intensity of incident light as shown in Figures 1 and 3. This makes it possible to obtain the diffusion coefficient when the intensity of incident light is zero. Diffusion coefficient D when the intensity of incident light is zero ０ Using the formula (21), the true particle size d ０ This allows the true particle size of the measured particles in the dispersion Lq to be calculated. The true particle size distribution can be obtained from the calculated true particle sizes of all particles.

[0102]

[0103]

[0104]

[0105] In the above explanation, the acquisition of particle images from scattered light has been described, but the present invention is not limited to this. For example, if the particles have luminescent properties, the particles emit fluorescence due to incident light. The particle images are acquired from this fluorescence. Even in the case of fluorescence, the method for determining the particle positions from the particle images and the method for calculating the true particle diameter and true particle size distribution are the same as the method for determining the particle positions in the particle images acquired from scattered light described above and the method for calculating the true particle diameter and true particle size distribution in the particle images. Therefore, detailed explanations thereof will be omitted.

[0106] The present invention is basically configured as described above. Although the light measurement method and light measurement device of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements and modifications may be made without departing from the spirit and scope of the present invention.

[0107] 10, 13, 14, 15, 16, 17, 18 Straight line 20, 20a, 20b Light measurement device 22 Light source 23 Storage section 24 Transparent substrate 24a Front surface 24b Back surface 25 Optical element 25a Trapezoidal prism 25b Lower base 25c Slope 26 Objective lens 28 Imaging lens 30 Image acquisition section 31 Image sensor 31a Light receiving surface 32 Processing section 34 Measurement section 36 Calculation section 40 Display section 42 Input section 44a First image 44b Second image 45a First particle 45b Second particle 45c Third particle 46 Image 46a Movement trajectory 46b Movement distance 50, 52, 54, 56 Approximate straight line 57 Integral distribution 58 Particle size distribution 60 First laser 61 Second laser 62 Beam splitter 62a Transmissive / reflective surface 63 Filter 64 Reflective member 64a Inner surface 64b Bending portion 64c Opening 65 Annular mask 65a Slit 66 Reflective portion 66a Curved surface 68 Cover plate C Optical axis L １ First laser light L ２Second laser light Li Incident light Lq Dispersion liquid Ls Scattered light θ Angle

Claims

1. An optical measurement method for a dispersion liquid containing particles, comprising: an acquisition step of acquiring multiple images of the particles successively over time for each intensity of incident light obtained by irradiating incident light of varying intensities into the dispersion liquid; a measurement step of measuring an average moving distance of the particles for each intensity of incident light from the multiple images acquired successively over time for each intensity of incident light obtained by the acquisition step; and a calculation step of calculating an apparent particle size of the particles for each intensity of incident light from the average moving distance of the particles for each intensity of incident light obtained by the measurement step, and determining a true particle size of the particles from the apparent particle size of the particles for each intensity of incident light.

2. An optical measurement method for a dispersion liquid containing particles, comprising: an acquisition step of acquiring multiple images of the particles successively in time for each intensity of incident light obtained by irradiating incident light with varying intensities into the dispersion liquid; a measurement step of measuring an average moving distance of the particles for each intensity of incident light from the multiple images acquired successively in time for each intensity of incident light obtained by the acquisition step; and a calculation step of calculating an apparent particle size distribution for each intensity of incident light from the average moving distance of the particles for each intensity of incident light obtained by the measurement step, and determining a true particle size distribution from the apparent particle size distribution for each intensity of incident light.

3. An optical measurement method for a dispersion liquid containing particles, comprising: an acquisition step of acquiring multiple images of the particles successively over time for each intensity of the incident light obtained by irradiating the dispersion liquid with incident light of various intensities; a measurement step of measuring an average moving distance of the particles for each intensity of the incident light from the multiple images acquired successively over time for each intensity of the incident light obtained by the acquisition step; and a calculation step of calculating a diffusion coefficient for each intensity of the incident light from the average moving distance of the particles for each intensity of the incident light obtained by the measurement step, determining a diffusion coefficient when the intensity of the incident light is zero from the diffusion coefficient for each intensity of the incident light, and determining a true particle size of the particles from the diffusion coefficient when the intensity of the incident light is zero.

4. The optical measurement method according to claim 1 or 2, wherein the calculation step determines the true particle size of the particle by determining the relationship between the apparent particle size of the particle and the intensity of the incident light, assuming that the apparent particle size of the particle has a linear dependency on the intensity of the incident light.

5. The optical measurement method of claim 3, wherein the calculation step determines the relationship between the diffusion coefficient of the particle and the intensity of the incident light, assuming that the dependence of the diffusion coefficient of the particle on the intensity of the incident light is linear, and determines the diffusion coefficient when the intensity of the incident light is zero.

6. The optical measurement method according to claim 2, wherein the calculation step calculates a plurality of particle sizes of a certain percentage in an integral distribution of the apparent particle size distribution of the particles, and determines a relationship between the particle sizes of the certain percentage and the intensity of the incident light, assuming that the dependence of the particle sizes of the plurality of particle sizes of the certain percentage is linear, thereby determining a true particle size distribution.

7. The optical measurement method of claim 6, wherein the certain proportion is a proportion that represents 10% of all particles that make up the particle size distribution, a proportion that represents 50% of all particles that make up the particle size distribution, or a proportion that represents 90% of all particles that make up the particle size distribution.

8. The optical measurement method according to claim 4, further comprising the steps of: obtaining a second temperature after the particle at the first temperature has risen in temperature due to optical absorption of the incident light; and determining the true particle size of the particle from the diffusion coefficient after the temperature has risen, using an equation expressing the diffusion coefficient when the temperature has risen.

9. An optical measurement device for a dispersion liquid containing particles, comprising: a light source that causes incident light with changed intensity to be incident on the dispersion liquid; an image acquisition unit that acquires multiple images of the particles successively over time for each intensity of the incident light obtained by causing the incident light with changed intensity to be incident on the dispersion liquid; a measurement unit that measures an average moving distance of the particles for each intensity of the incident light from the multiple images acquired successively over time for each intensity of the incident light obtained by the image acquisition unit; and a calculation unit that calculates an apparent particle size of the particles for each intensity of the incident light from the average moving distance of the particles for each intensity of the incident light obtained by the measurement unit, and determines a true particle size of the particles from the apparent particle size of the particles for each intensity of the incident light.

10. An optical measurement device for a dispersion liquid containing particles, comprising: a light source that causes incident light with changed intensity to be incident on the dispersion liquid; an image acquisition unit that acquires multiple images of the particles successively over time for each intensity of the incident light obtained by causing the incident light with changed intensity to be incident on the dispersion liquid; a measurement unit that measures an average moving distance of the particles for each intensity of the incident light from the multiple images acquired successively over time for each intensity of the incident light obtained by the image acquisition unit; and a calculation unit that calculates an apparent particle size distribution for each intensity of the incident light from the average moving distance of the particles for each intensity of the incident light obtained by the measurement unit, and determines a true particle size distribution from the apparent particle size distribution for each intensity of the incident light.

11. An optical measurement device for a dispersion liquid containing particles, comprising: a light source that causes incident light with changed intensity to be incident on the dispersion liquid; an image acquisition unit that acquires multiple images of the particles successively over time for each intensity of the incident light obtained by causing the incident light to be incident on the dispersion liquid with changed intensity; a measurement unit that measures an average moving distance of the particles for each intensity of the incident light from the multiple images acquired successively over time for each intensity of the incident light obtained by the image acquisition unit; and a calculation unit that calculates a diffusion coefficient for each intensity of the incident light from the average moving distance of the particles for each intensity of the incident light obtained by the measurement unit, determines a diffusion coefficient when the intensity of the incident light is zero from the diffusion coefficient for each intensity of the incident light, and determines a true particle size of the particles from the diffusion coefficient when the intensity of the incident light is zero.

12. An optical measurement device as described in claim 9 or 10, wherein the calculation unit determines the true particle size of the particle by determining the relationship between the apparent particle size of the particle and the intensity of the incident light, assuming that the apparent particle size of the particle has a linear dependence on the intensity of the incident light.

13. The optical measurement device of claim 11, wherein the calculation unit determines the relationship between the diffusion coefficient of the particle and the intensity of the incident light, assuming that the dependence of the diffusion coefficient of the particle on the intensity of the incident light is linear, and determines the diffusion coefficient when the intensity of the incident light is zero.

14. The optical measurement device of claim 10, wherein the calculation unit calculates a plurality of particle sizes of a certain percentage in an integral distribution of the apparent particle size distribution of the particles, and determines a relationship between the particle sizes of the certain percentage and the intensity of the incident light, assuming that the dependence of the particle sizes of the plurality of particle sizes of the certain percentage is linear, thereby determining a true particle size distribution.

15. The optical measurement device of claim 14, wherein the certain percentage is a percentage that is 10% of all particles that make up the particle size distribution, a percentage that is 50% of all particles that make up the particle size distribution, or a percentage that is 90% of all particles that make up the particle size distribution.

16. The optical measurement device of claim 12, wherein the calculation unit obtains a second temperature after the particle at a first temperature has risen in temperature due to optical absorption of the incident light, and determines the true particle size of the particle from the diffusion coefficient after the temperature has risen using an equation expressing the diffusion coefficient when the temperature has risen.

17. An optical measurement device described in any one of claims 9 to 11, wherein the light source emits the incident light including a first laser light having a wavelength in the optical absorption wavelength range of the particle and a second laser light having a wavelength outside the optical absorption wavelength range of the particle, and the light source changes the intensity of the incident light by changing the intensity of the first laser light.

18. The light measurement device according to claim 17, further comprising a filter between the dispersion liquid and the image acquisition section, for attenuating light having a wavelength in the light absorption wavelength range of the particles.

19. An optical measurement device as described in any one of claims 9 to 11, comprising a storage section for storing the dispersion liquid, the storage section having an optical element and a transparent substrate, the dispersion liquid being stored between the optical element and the transparent substrate, and the optical element being a trapezoidal prism, a semicylindrical prism or a semicircular prism.

20. An optical measurement device as described in any one of claims 9 to 11, comprising: a storage section having a flow path in which the dispersion liquid is stored; and a lens provided between the flow path and the image acquisition section, wherein the dispersion liquid is stored in the flow path, and the incident light from the light source is incident on the dispersion liquid in the flow path.