WO2021235169A1

WO2021235169A1 - Number based particle diameter distribution measurement method and measurement system

Info

Publication number: WO2021235169A1
Application number: PCT/JP2021/016368
Authority: WO
Inventors: 晴久加藤
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2020-05-20
Filing date: 2021-04-22
Publication date: 2021-11-25

Abstract

Provided are a method capable of promptly and easily measuring a particle diameter distribution based on the number of particles having a distribution within a wide particle diameter range from a nanometer size to a micrometer size, and a measurement system. Provided are a measurement method comprising emitting a laser beam over microparticles undergoing Brownian motion in a dispersion medium, imaging bright spots due to scattered light at certain time intervals, and, from a movement trajectory of the bright spots in a thus obtained image, measuring the particle diameter and number of microparticles so as to measure a number based particle diameter distribution, and a measurement system therefor. Microparticles dispersed in a dispersion medium are provided with a flow field in the dispersion medium, arranged, and classified in the dispersion medium in accordance with the particle diameter, and a laser beam is emitted over the dispersion medium containing the classified microparticles to obtain an image. Prior to such imaging, the dispersion medium is divided so as to contain microparticles within a certain particle diameter range, and the number concentration is adjusted without changing the number of microparticles in each divided dispersion medium.

Description

Number-based particle size distribution measurement method and measurement system

The present invention relates to a number-based particle size distribution measurement method and measurement system for fine particles in a dispersion medium, and in particular, a number-based particle size distribution for particles having a wide particle size distribution from nanometer size to micrometer size. Regarding measuring methods and measuring systems.

In the method of measuring the particle size distribution using diffraction or scattering by laser light, it is common to measure the particle size distribution on a volume basis, but it is also required to convert this into a particle size distribution based on the number. For example, the particle size distribution is measured from the particle size and the number concentration by using a classification method such as the FFF (Field Flow Fractionation) method.

For example, in Non-Patent Document 1, after size classification by the FFF method, the particle size and the light scattering intensity concentration are calculated by an online multi-angle scattering measuring device, and the light scattering intensity concentration is converted into a number concentration according to the theory of Mie scattering. It discloses that the particle size distribution based on the number is calculated. In addition, as an offline method, after size classification by the FFF method, the particle size distribution and number concentration of each fraction are calculated by a scanning electron microscope, and the results are reconstructed to obtain a number-based particle size distribution. The method of measurement is also disclosed. Further, a method of measuring the particle size distribution based on the number of particles by evaluating all of them with a scanning electron microscope is also disclosed.

On the other hand, in Non-Patent Document 2, a Stop-flow mode particle tracking analysis (PTA) device is connected to the subsequent stage of the FFF method, and the particle size distribution and the number concentration are measured for each fraction. Discloses a method for obtaining a particle size distribution based on the number of particles by reconstructing. Further, Non-Patent Document 3 and Patent Document 1 disclose a number-based particle size measuring method by a flow field particle tracking (FPT) method.

International Publication No. 2016/159131 Pamphlet

As described above, by combining the flow field separation (FFF) method and other measurement methods, it is possible to evaluate the particle size distribution based on the number of particles. On the other hand, in the evaluation method that combines the FFF method with an online multi-angle scattering measuring device, the scattering theory of Rayleigh scattering or Mie scattering is applied if the refractive index of the particles is not known in the conversion from the measured light scattering intensity to the number concentration. It is not possible to calculate the particle size distribution based on the number.

On the other hand, in the method of counting with a scanning electron microscope or the method of combining the scanning electron microscope with the FFF method, the particle size distribution based on the number can be calculated even if the refractive index of the particles is unknown. However, since the particles are individually measured with a scanning electron microscope, rapid measurement is not possible. Further, by combining the FFF method with the FPT method, the particle size distribution based on the number can be calculated quickly and easily, but in the FPT method in which the particle size is measured from the scattered light intensity from the particles, the scattered light intensity is the particle size. On the other hand, it changes greatly non-linearly, and accurate measurement cannot be performed with particles having a wide particle size range distribution.

The present invention has been made in view of the above circumstances, and quickly and easily measures the particle size distribution based on the number of particles having a distribution in a wide particle size range from nanometer size to micrometer size. It seeks to provide possible methods and measurement systems.

The particle size distribution measuring method according to the present invention irradiates fine particles that move brown in a dispersion medium with laser light, and images bright spots due to scattered light at predetermined time intervals. It is a method of measuring the particle size and the number of fine particles and measuring the particle size distribution based on the number of fine particles by forming a flow field in the dispersion medium for the fine particles diffusing in the dispersion medium. A classification step of arranging particles in the dispersion medium according to the particle size and classifying the particles, and an imaging step of irradiating the dispersion medium containing the classified fine particles with the laser beam to obtain the image are included. Prior to the imaging step, the dispersion medium is divided so as to include the fine particles in a predetermined particle size range, and the number concentration is adjusted without changing the number of the fine particles in each of the divided dispersion media. It is characterized by including an adjustment step to be performed.

Further, in the particle size distribution measurement system according to the present invention, the moving locus of the bright spot of the image obtained by irradiating the fine particles that move brown in the dispersion medium with laser light and imaging the bright spot by the scattered light at predetermined time intervals. It is a system that measures the particle size and the number of the fine particles and measures the particle size distribution based on the number of the fine particles, and forms a flow field in the dispersion medium for the fine particles diffusing in the dispersion medium. The classification device in which the fine particles are arranged in the dispersion medium according to the particle size and classified, and the dispersion medium containing the classified fine particles are guided from the classification device to a cell and irradiated with the laser beam. The dispersion medium is divided between the classification device and the cell so as to include the fine particles in a predetermined particle size range, including an image pickup device for obtaining an image, and in each of the divided dispersion media. It is characterized by including a concentration adjusting device for adjusting the number concentration without changing the number of the fine particles.

According to such a feature, an image can be obtained under conditions suitable for each of the divided dispersion media in the imaging with the imaging device, and the number of particles having a distribution in a wide particle size range from nanometer size to micrometer size. The particle size distribution based on the standard can be measured quickly and easily.

In the above-described invention, the density adjusting device and the adjusting step performed here adjust the particle size range so that bright spots due to scattered light can be obtained for the fine particles imaged in the imaging step. It may be a feature. According to such a feature, it is not necessary to expand or switch the dynamic range of the image pickup apparatus in response to the scattered light intensity which is non-linear with respect to the particle size, and the measurement can be performed quickly and easily.

In the above-mentioned invention, the number concentration may be adjusted by adding or separating the dispersion medium in each of the divided dispersion media. According to such a feature, the number concentration can be adjusted by a simple method, and the rapid measurement of the particle size distribution on the basis of the number can be simplified.

In the above-described invention, the flow field is obtained by adding a flow in a liquid feeding direction along the flow path and a flow in a direction substantially perpendicular to the flow field, and the fine particles are arranged so as to intersect the liquid feeding direction. May be a feature. Alternatively, in the above-described invention, the flow field is obtained by applying a centrifugal force in a liquid feeding direction along a flow path and a direction substantially perpendicular to the flow field so as to intersect the fine particles in the liquid feeding direction. It may be characterized by arranging them. According to such a feature, the classification by the particle size in the classification device and the classification step performed here can be easily performed.

It is a block diagram which shows an example of the apparatus composition used for the measuring method of the particle size distribution of this invention. It is explanatory drawing about the principle of flow FFF. It is explanatory drawing about the principle of centrifugal FFF.

One embodiment of the present invention will be described with reference to FIGS. 1 to 3.

As shown in FIG. 1, the particle size distribution measurement system used in the particle size distribution evaluation method includes a classification device 1, a connection unit 2, and a flow field particle tracking (FPT:) by a flow field separation method (FFF: Field Flow Fractionation). It is equipped with a measuring device 3 and an arithmetic processing device 4 by the Flow particle Tracking method.

The classification device 1 includes an eluent introduction unit 11 for introducing a dispersion medium, and a sample introduction unit 12 for injecting a dispersion liquid in which fine particles that move in Brownian motion in the dispersion medium are dispersed in the dispersion medium into a flow path continuing from the eluent introduction unit. And an FFF device 13 for classifying fine particles according to particle size. As the FFF device 13, a flow FFF device 14 (see FIG. 2) or a centrifugal FFF device 15 (see FIG. 3) can be preferably used.

As shown in FIG. 2, the flow FFF device 14 has a liquid feeding direction along a flow path from the inflow port 16 to the outflow port 18, and is provided with a microfiltration membrane 19 provided on one side wall of the flow path. As a result, the flow 50 in the direction substantially perpendicular to the liquid feeding direction by the dispersion medium 17 can be formed as a crossing force field. Due to the flow 50 orthogonal to the liquid feeding direction, the fine particles 51 once collected at one place on the surface of the microfiltration membrane 19 diffuse from the microfiltration membrane 19 toward the center of the flow path to the particle diameter. It is classified according to the difference in diffusion rate based on it. Specifically, the particles are arranged in a direction intersecting the liquid feeding direction so that the particle size becomes smaller as the particle size approaches the center of the flow path. Further, in the laminar flow along the liquid feeding direction, since there is a velocity gradient that increases from the outer periphery of the flow path toward the center, the particles are classified by proceeding in the flow path in order from the fine particles 51 having a small particle size near the center of the flow path. The fractionation of the fine particles 51 is facilitated.

As shown in FIG. 3, the centrifugal FFF device 15 has a liquid feeding direction along a flow path from the inlet 16 to the outlet 18, and the flow path is substantially perpendicular to the liquid feeding direction by the dispersion medium 17. Centrifugal force 52 is applied as a crossing force field. For example, although not shown, such a centrifugal force 52 can be applied by using a flow path having a curvature that curves the liquid feeding direction. Due to this centrifugal force 52, the fine particles 51 once collected at one place on the surface of the outer peripheral wall 19'diffuse from the outer peripheral wall 19' toward the center of the flow path, and the diffusion velocity and mass based on the particle diameter. It is classified according to the difference. Specifically, the particles are arranged in a direction intersecting the liquid feeding direction so that the particle size becomes smaller as the particle size approaches the center of the flow path. Further, in the laminar flow along the liquid feeding direction, since there is a velocity gradient that increases from the outer periphery of the flow path toward the center, the particles are classified by proceeding in the flow path in order from the fine particles 51 having a small particle size near the center of the flow path. The fractionation of the fine particles 51 is facilitated.

That is, the classification device 1 is a mechanism capable of classifying fine particles having a wide range of particle sizes by the particle size and guiding them to the connection portion 2 by the flow field separation method. As the flow field separation method, a method such as heat, magnetic field, electric field, etc. that gives other energy as a crossing force field can be appropriately selected according to the fine particles.

The connecting portion 2 is a mechanism that divides the dispersion medium into a plurality of particles so as to contain fine particles classified so as to contain fine particles in a predetermined particle size range, and guides each of them to the measuring device 3 in the subsequent stage. For example, the dispersion can be divided as described above by partitioning the time and amount until the dispersion liquid is derived from the classification device 1 at a predetermined value. Further, it is a concentration adjusting device that controls the amount of the dispersion medium for each of the divided dispersion liquids without changing the number of fine particles and leads to the measuring device 3 described later. Thereby, the number concentration of the fine particles 51 can be adjusted so that the measurement by the measuring device 3 can be easily performed. Here, in the flow field particle tracking method in the subsequent stage, the fine particles 51 are tracked as bright spots on the image, so that the bright spots are sufficiently separated from each other so that the individual bright spots can be accurately discriminated by image analysis. To reduce the number concentration. Further, the number density may be increased so that the density of bright spots on the image is not sparse and the time efficiency of measurement is not reduced. Therefore, the dispersion is diluted or concentrated so that the number concentration of the fine particles 51 is within a desired range.

As the connecting portion 2, for example, in the FFF device 13, the dispersion medium 17 on the side opposite to the collected side of the fine particles 51 (on the tip side in the diffusion direction) is removed to increase the number concentration of the fine particles 51. A split that leads to the measuring device 3 in the subsequent stage, or a syringe pump or a diaphragm pump that dilutes the dispersion liquid by adding a dispersion medium 17 to reduce the concentration of the number of fine particles 51 can be used. The configuration of the connecting portion 2 can be appropriately selected according to the characteristics of the dispersion liquid consisting of the fine particles 51 to be classified and the dispersion medium 17 as a fluid. The divided dispersion may be guided to different flow paths. In this case, each of the divided dispersion liquids may be provided with an optical cell of the measuring device 3 described later for each flow path.

It is preferable to divide the group of the classified fine particles 51 so that the range of the particle size is suppressed within about 2 to 3 times as the difference in particle size. As a result, in the measuring device 3 described later, when measuring the particle size by the flow field particle tracking method, conditions suitable for the range of the particle size of the fine particles 51 contained in each of the divided dispersions can be set, and the particles can be set. Makes it easy to measure the diameter.

The measuring device 3 is a device that measures the particle size of each particle of the fine particles 51 by the flow field particle tracking method and counts the number of the particles. Specifically, the measuring device 3 includes an image pickup device 31 capable of capturing the scattered light from the fine particles 51 and recording a bright spot corresponding to a single particle as an image, and fine particles classified and having their number densities adjusted. It includes a transparent optical cell 32 through which a dispersion medium 17 including 51 is circulated, and a laser light source 33 for irradiating a laser beam toward the fine particles 51 in the optical cell 32. The image pickup device 31 captures an image in which pixels corresponding to elements of an image pickup device (CCD: Charge Coupled Device, CMOS image sensor, etc.) having a predetermined resolution are arranged in two dimensions via an optical system such as a lens, and uses the image data as image data. Output. The image pickup apparatus 31 executes shooting at a predetermined exposure time and a predetermined time interval Δt to continuously generate a plurality of images. The exposure time is shorter than the time interval Δt. For example, when the frame rate is 30 fps, the time interval Δt is about 33 ms, and the exposure time is 30 ms. The exposure time may be controlled by controlling the shutter speed or by illuminating the laser light source 33 in a pulsed manner. Further, the measuring device 3 adjusts the imaging conditions according to each of the divided dispersion liquids.

The arithmetic processing unit 4 has a built-in computer that executes a predetermined program, executes predetermined data processing according to the program, and operates as various processing units. Here, the arithmetic processing device 4 reconstructs the data analyzed by the image analysis unit 41, the particle size / number concentration analysis unit 43, and the particle size / number concentration analysis unit 43 to calculate the particle size distribution. It operates as a unit 44 and a control unit 45. Further, the arithmetic processing unit 4 includes a non-volatile storage device (flash memory, hard disk drive, etc.) as the storage unit 42.

The image analysis unit 41 controls the image pickup device 31, causes the image pickup device 31 to perform imaging in a predetermined range of the optical cell 32, and acquires image data of a plurality of images continuously generated by the image pickup device 31. The image analysis unit 41 may appropriately change the exposure time and detection sensitivity of each captured image in the image pickup device 31 according to the particle size of the fine particles 51 classified in the classification device 1. For example, the particle size of the fine particles derived from the FFF device 13 may be theoretically calculated or actually measured by a simple monitor to set the optimum imaging conditions. Further, it is possible to give a feedback signal for adjusting the range of the particle size of the fine particles 51 to be classified in the connection unit 2 so that the counting omission of the fine particles 51 does not occur from the bright spot in the image analysis unit 41. preferable.

The image analysis unit 41 identifies the movement locus of the bright spot on the image based on the acquired image data by the flow field separation method, and obtains the displacement of the fine particles 51 corresponding to the bright spot. Then, kB is the Boltzmann constant, T is the absolute temperature, η is the viscosity coefficient of the dispersion medium, d is the particle diameter, and the squared average value of the displacement of the fine particles 51 is proportional to kBT / 3πηd, so that the particle diameter is calculated. .. Further, the image analysis unit 41 counts the number of bright spots that have passed through the predetermined region together with the calculation of the particle size to obtain the number of fine particles 51. As described above, in the flow field separation method, the number of bright spots is counted while tracking the bright spots corresponding to the individual fine particles 51, so that the number can be counted regardless of the material forming the fine particles 51.

The image analysis unit 41 uses a known method (method disclosed in Patent Document 1, fluid simulation, etc.) to determine the flow velocity distribution of the dispersion medium 17 in the image pickup region in the optical cell 32 corresponding to the angle of view of the image pickup device 31. It is preferable to specify in advance, correct the displacement of the fine particles 51 based on the flow velocity distribution of the dispersion medium 17, and specify the average square displacement ΔMS of the fine particles 51 based on the corrected displacement. That is, by correcting the displacement of the fine particles 51 based on the flow velocity distribution, the displacement of the fine particles 51 due to the Brownian motion is obtained after excluding the influence of the flow field of the dispersion medium 17. The flow velocity distribution may be assumed to be constant (that is, the size and orientation are constant) within the imaging region.

Further, the image analysis unit 41 counts the number of fine particles 51 passing through a predetermined region in the optical cell.

By accumulating the particle size and the number of the above-mentioned fine particles, it is possible to calculate the particle size distribution based on the number in the dispersion liquid in which the fine particles 51 injected as a sample are dispersed in the sample introduction unit 12.

As described above, according to this embodiment, the particle size distribution based on the number of particles can be calculated. In particular, by classifying by the flow field separation method, the range of the intensity of scattered light from fine particles can be narrowed in the particle size measurement by the flow field particle tracking method, and the particle size to be easily classified. It is possible to count the number of each.

Further, since the classification device 1 and the measuring device 3 are connected via the connecting portion 2, it is possible to guide the dispersion liquid having a number concentration suitable for measurement to the measuring device 3, and each of the classified and fractionated dispersion liquids. You can measure the particle size and the number concentration online. Therefore, the particle size distribution based on the number can be measured quickly.

That is, even for fine particles having a wide particle size range from nanometer size to micrometer size, for example, about 10 nm to 3 μm, the particle size distribution based on the number can be measured quickly and easily.

In addition, by considering the volume in the optical cell 32, the number concentration of the fine particles 51 in a plurality of outflow time ranges is calculated, and by reconstructing these, the number reference in the dispersion liquid of the injected fine particles can be obtained. The particle size distribution can be calculated.

Although typical examples of the present invention have been described above, the present invention is not necessarily limited to these, and those skilled in the art will not deviate from the gist of the present invention or the scope of the attached claims. , Various alternative and modified examples will be found.

1 Classification device 2 Connection part 3 Measuring device 4 Arithmetic processing device 12 Sample introduction unit 13 FFF device 14 Flow FFF device 15 Centrifugal FFF device 16 Inflow port 17 Dispersion medium 18 Outlet 18
19 Microfiltration membrane 31 Imaging device 32 Optical cell 33 Laser light source 41 Image analysis unit 42 Storage unit 43 Particle size / number concentration analysis unit 44 Particle size distribution analysis unit 45 Control unit 51 Fine particles

Claims

The particle size and number of the fine particles are measured from the movement locus of the bright spots in the image obtained by irradiating the fine particles that move in Brownian motion in the dispersion medium with laser light and imaging the bright spots due to the scattered light at predetermined time intervals. It is a method of measuring the particle size distribution based on the number of particles.
A classification step of forming a flow field in the dispersion medium for the fine particles diffusing in the dispersion medium and arranging the fine particles in the dispersion medium according to the particle size to classify them.
It comprises an imaging step of irradiating the dispersion medium containing the classified fine particles with the laser beam to obtain the image.
Prior to the imaging step, the dispersion medium is divided so as to contain the fine particles in a predetermined particle size range, and the number concentration is adjusted without changing the number of the fine particles in each of the divided dispersion media. A particle size distribution measuring method comprising an adjustment step for adjustment.
The particle size distribution measuring method according to claim 1, wherein the adjustment step adjusts the particle size range so that a bright spot due to scattered light can be obtained for the fine particles imaged in the image pickup step. ..
The particle size distribution measuring method according to claim 1, wherein the number concentration is adjusted by adding or separating the dispersion medium in each of the divided dispersion media.
The flow field is obtained by adding a flow in a liquid feeding direction along a flow path and a flow in a direction substantially orthogonal to the flow, and is characterized in that the fine particles are arranged so as to intersect the liquid feeding direction. Item 1. The particle size distribution measuring method according to Item 1.
The flow field is obtained by applying a centrifugal force in a liquid feeding direction along a flow path and a direction substantially perpendicular to the flow direction, and is characterized in that the fine particles are arranged so as to intersect the liquid feeding direction. The particle size distribution measuring method according to claim 1.
The particle size and number of the fine particles are measured from the movement locus of the bright spots in the image obtained by irradiating the fine particles that move in Brownian motion in the dispersion medium with laser light and imaging the bright spots due to the scattered light at predetermined time intervals. It is a system that measures the particle size distribution based on the number of particles.
A classifying device that forms a flow field in the dispersion medium for the fine particles diffusing in the dispersion medium and arranges the fine particles in the dispersion medium according to the particle size to classify them.
A device including an image pickup device that guides the dispersion medium containing the classified fine particles from the classifier to a cell and irradiates the cell with the laser beam to obtain the image.
The dispersion medium is divided between the classifier and the cell so as to contain the fine particles in a predetermined particle size range, and the number of the fine particles in each of the divided dispersion media is not changed. A particle size distribution measuring system characterized by including a concentration adjusting device for adjusting the number concentration.
The particle size distribution measurement according to claim 6, wherein the density adjusting device adjusts the particle size range so that a bright spot due to scattered light can be obtained for the fine particles imaged by the image pickup device. system.
The particle size distribution measuring system according to claim 6, wherein in the concentration adjusting device, the number concentration is adjusted by adding or separating the dispersion medium in each of the divided dispersion media.
In the classification device, the flow field is obtained by adding a flow in a liquid feeding direction along the flow path and a flow in a direction substantially perpendicular to the flow field, and the fine particles are arranged so as to intersect the liquid feeding direction. 6. The particle size distribution measuring system according to claim 6.
In the classification device, the flow field is obtained by applying a centrifugal force in a liquid feeding direction along a flow path and a direction substantially perpendicular to the flow field, and the fine particles are arranged so as to intersect the liquid feeding direction. The particle size distribution measuring system according to claim 6, wherein the particle size distribution is measured.