Method and device for simultaneous measurement of nanoparticle size, shape and distribution by dynamic light scattering

Abstract

The present application relates to a kind of dynamic light scattering nanoparticle particle size shape and distribution synchronous measurement method and device, using microlens array type polarization camera, simultaneously capture the dynamic light scattering image signal of 0°, 45°, 90° and 135° four polarization direction images of nanoparticle group in set scattering direction, utilize 0° polarization direction dynamic light scattering image to obtain the particle size and particle size distribution information of particle, utilize all four polarization direction dynamic light scattering image to obtain the particle shape and particle shape distribution information of particle, realize the synchronous measurement of particle size and particle shape and distribution.The concept of optical sphericity is proposed, which quantitatively describes the morphology characteristics of the measured nanoparticle group. It can be used to evaluate the degree of approximation of the nanoparticle to the standard spherical particle. The present application has fast measurement speed and simple operation. It can simultaneously obtain the particle size and particle shape and distribution information of the nanoparticle, and is applicable to the measurement of solid nanoparticles, nanobubbles and nanodroplets.

Description

Technical Field

[0001] This invention relates to an optical analysis technique, and more particularly to a method and apparatus for simultaneously measuring the particle size, shape, and distribution of dynamic light scattering nanoparticles. Background Technology

[0002] Traditional dynamic light scattering (DLS) techniques utilize laser irradiation of a nanoparticle system. A photomultiplier tube (PMT) receives the dynamically scattered light signals at one or more scattering angles, and a correlator is used to solve for the autocorrelation function of the scattered light signals, thereby obtaining the average particle size and particle size distribution of the nanoparticle system. Simultaneously, the depolarization effect of the scattering process causes a change in the polarization state of the laser light after passing through the particle system. The polarization information of the scattered light can be used to evaluate the particle morphology.

[0003] Current nanoparticle measurement techniques mostly utilize the principle of dynamic light scattering to determine nanoparticle size information. This typically involves using photomultiplier tubes to collect scattered light intensity signals, followed by time-domain autocorrelation calculations using digital correlators, resulting in relatively slow measurement speeds. Alternatively, prism or fiber optic beam splitting techniques are used to obtain light intensity signals of different polarization scattered components, and then autocorrelation of perpendicular and parallel polarization scattering is used to obtain the aspect ratio of rod-shaped particles, or particle shape classification is obtained using the polarization characteristic parameters of the scattered light. While published image-based dynamic light scattering techniques offer faster measurement speeds, they only provide particle size information and not particle morphology information. Summary of the Invention

[0004] To address the need for further advancements in nanoparticle measurement technology, a method and apparatus for simultaneous measurement of the size, shape, and distribution of dynamic light-scattering nanoparticles are proposed, meeting the requirements for rapid determination of nanoparticle size, morphology, and consistency.

[0005] The technical solution of this invention is as follows: a method for synchronously measuring the particle size, shape, and distribution of dynamic light scattering nanoparticles. This method employs a microlens array polarization camera to simultaneously capture dynamic light scattering image signals of a nanoparticle group at four polarization directions (0°, 45°, 90°, and 135°) along a set scattering direction. The particle size and distribution information are obtained using the dynamic light scattering image at 0° polarization direction, and the particle shape and distribution information are obtained using the dynamic light scattering images at all four polarization directions, thus achieving synchronous measurement of particle size, shape, and distribution.

[0006] Furthermore, the method for acquiring particle shape and distribution information involves: acquiring multiple consecutively captured polarized scattering images at 0°, 45°, 90°, and 135°; using the image grayscale values ​​to represent the various polarization components of the light intensity; obtaining the linear polarization degree (DoLP) of the scattered light using the following formula; defining optical sphericity as equal to the linear polarization degree (DoLP); and using optical sphericity to quantitatively describe the degree to which the particle group deviates from a spherical shape. One optical sphericity value is obtained from a single measurement, and multiple optical sphericity values ​​are obtained from multiple measurements, thus obtaining multiple particle shape measurement results. The particle shape distribution of the particle group can then be statistically analyzed.

[0007] Formula for calculating the degree of linear polarization (DoLP) of scattered light: The Stokes vector describes the polarization state of light and contains four components, denoted by S0, S1, S2, and S3, as shown in the following expression:

[0008]

[0009] Where: I0, I 90 I 45 I 135 I R I L These represent the 0° polarization component, 90° polarization component, 45° polarization component, 135° polarization component, right-handed polarization component, and left-handed polarization component of the light intensity, respectively.

[0010] Furthermore, the method of obtaining particle size and particle size distribution information by using dynamic light scattering images with 0° polarization direction involves: acquiring multiple scattering images with 0° polarization direction taken continuously, calculating the cross-correlation between adjacent two images to obtain the average particle size measurement result of a particle group, and statistically analyzing the average particle size of multiple particle groups to obtain the particle size distribution of the particle group.

[0011] Furthermore, the specific calculation method for obtaining particle size and particle size distribution information using dynamic light scattering images with a 0° polarization direction is as follows:

[0012] The correlation function G(τ) of two consecutive nanoparticle scattering images with a 0° polarization direction is expressed by the following equation:

[0013]

[0014] In the formula: C m,n and B m,n Let C and B be the gray values ​​of the pixels in the m-th row and n-th column of two consecutive images; C and B are the average gray values ​​of all pixels in the two images, respectively; τ is the relaxation time. When calculating the correlation between two consecutive images, τ is the time interval between the two images, which is the reciprocal of the camera frame rate.

[0015] The attenuation rate Γ of the correlation function and the translational diffusion coefficient D of the particles Tsatisfy:

[0016] Γ=D T q 2 (3)

[0017] In the formula: q is the scattering vector, whose mode is a function of the laser wavelength λ and the scattering angle θ.

[0018]

[0019] In the formula: n is the refractive index of the dispersion medium;

[0020] The translational diffusion coefficient D of the particles can be calculated using equations (1)-(4). T Then, using the Stokes-Einstein relation, the particle size can be determined.

[0021]

[0022] In the formula: k B η is Boltzmann's constant, T is the absolute temperature, η is the viscosity coefficient of the dispersion medium, and x is the hydrodynamic diameter.

[0023] A dynamic light scattering nanoparticle size, shape, and distribution synchronous measurement device is disclosed. A laser beam emitted by a laser is irradiated onto nanoparticles in a sample cell through a polarizer. The scattered light signal in the 90° scattering direction is captured by a microlens array polarization camera. The microlens array polarization camera transmits the simultaneously captured scattering images in four polarization directions (0°, 45°, 90°, and 135°) to a computer for analysis and processing to obtain the particle size, shape, and distribution of the nanoparticle group.

[0024] Preferably, the frame rate of the microlens array polarization camera is set to 500-10000fps depending on the size of the measured particle. The pixels on the CMOS of the microlens array polarization camera are divided into 4 groups to receive polarization signals in four directions respectively.

[0025] Preferably, the polarizer is a linear polarizer, and the polarization angle is preferably 90°.

[0026] The beneficial effects of this invention are as follows: The method and apparatus for simultaneous measurement of particle size, shape, and distribution of nanoparticles using dynamic light scattering employ a microlens array polarization camera instead of a traditional photomultiplier tube, significantly improving the measurement speed; by using a microlens array polarization camera instead of a conventional industrial camera, it can not only achieve the measurement of nanoparticle size and distribution but also simultaneously achieve the measurement of nanoparticle shape and distribution; the invention proposes the concept of optical sphericity, which can be obtained through the described polarization dynamic light scattering method for quantitatively describing particle morphology. This invention offers fast measurement speed, simple operation, and the ability to simultaneously obtain information on the particle size, shape, and distribution of nanoparticles; it is applicable to the measurement of solid nanoparticles, nanobubbles, and nanodroplets. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the measuring device structure of the present invention;

[0028] Figure 2a The image shows the polarization scattering of rod-shaped particles obtained by the device of this invention.

[0029] Figure 2b The image shows the polarization scattering of a spherical particle obtained by the device of this invention.

[0030] Figure 3 Normalized polarization scattered light intensity curves of nanoparticles with different morphologies are shown in the figure.

[0031] Figure 4 The results of measuring the optical sphericity of nanoparticles with different morphologies in this invention;

[0032] Figure 5a The results of electron microscopy measurements of T1 particles in industrial titanium dioxide;

[0033] Figure 5b The results of electron microscopy measurements of T5 particles in industrial titanium dioxide;

[0034] Figure 6a The particle size and distribution diagram of industrial titanium dioxide T1 particles are shown in the figure.

[0035] Figure 6b The optical sphericity and distribution of industrial titanium dioxide T1 particles were measured for this invention.

[0036] Figure 6c The particle size and distribution diagram of industrial titanium dioxide T5 particles are shown in the figure.

[0037] Figure 6d The optical sphericity and distribution of industrial titanium dioxide T5 particles are measured according to the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0039] like Figure 1 The schematic diagram of the measuring device of the present invention shows that a laser beam emitted by the laser 1 is irradiated into the nanoparticles in the sample cell 3 through the polarizer 2. The scattered light signal in the 90° scattering direction is captured by the polarization camera 4. The polarization camera 4 transmits the scattered images in four polarization directions of 0°, 45°, 90° and 135° to the computer 5 for analysis and processing.

[0040] The laser 1 is a semiconductor laser, which has stable power, good collimation and small size; the polarizer 2 is a linear polarizer, and the preferred polarization angle is 90°.

[0041] The sample cell 3 is a transparent sample cell, preferably made of optical quartz glass.

[0042] The polarization camera 4 is a microlens array polarization camera, capable of simultaneously capturing images in at least four polarization directions: 0°, 45°, 90°, and 135°. Depending on the size of the measured particle, the frame rate can be set to 500-10000 fps. The polarization camera equips each pixel with a microlens and a polarizer of a specific orientation in front of the CMOS sensor. Here, one polarization camera 4 simultaneously captures images in four polarization directions, and the pixels on the CMOS sensor are divided into four groups, each receiving polarization signals from one of the four directions.

[0043] Because nanoparticle samples undergo continuous random Brownian motion, their scattered light signal exhibits fluctuations over time under stable incident light illumination. The smaller the nanoparticle size, the faster the fluctuations; conversely, the larger the size, the slower the fluctuations. This method utilizes cross-correlation calculations on multiple 0° polarization direction scattering images to obtain the nanoparticle size and distribution. The principle is as follows: the fluctuation characteristics of the scattered light intensity from nanoparticles in the 0° polarization direction can be represented by the scattered light correlation function G(τ):

[0044] G(τ)=A(1+βexp(-2Γτ))-1 (1)

[0045] In the formula: A is the baseline of the autocorrelation curve, which is taken as 1 when the image signal-to-noise ratio is high; β is the instrument constant; Γ is the decay rate of the correlation function, which is related to the particle size; τ is the relaxation time. When calculating the correlation between two consecutive images, τ is the time interval between the two images, which is the reciprocal of the camera frame rate.

[0046] At this point, the correlation function G(τ) of two consecutive nanoparticle scattering images with a 0° polarization direction can also be expressed by the following formula:

[0047]

[0048] In the formula: C m,n and B m,n Let C and B be the gray values ​​of the pixels in the m-th row and n-th column of two consecutive images; C and B are the average gray values ​​of all pixels in the two images, respectively.

[0049] Attenuation rate Γ and particle translational diffusion coefficient D T satisfy:

[0050] Γ=D T q 2 (3)

[0051] In the formula: q is the scattering vector, whose mode is a function of the laser wavelength λ and the scattering angle θ.

[0052]

[0053] In the formula: n is the refractive index of the dispersion medium.

[0054] The translational diffusion coefficient D of the particles can be calculated using equations (1)-(4). T Then, the particle size can be obtained using the Stokes-Einstein relation.

[0055]

[0056] In the formula: k B η is Boltzmann constant, T is absolute temperature, η is viscosity coefficient of the dispersion medium, and x is hydrodynamic diameter.

[0057] By using multiple consecutive 0° polarization scattering images, the cross-correlation between adjacent images is calculated to obtain the average particle size of a single particle group. The particle size distribution of the particle group is obtained by statistically analyzing the average particle size of multiple particle groups.

[0058] Because light undergoes depolarization after being scattered by nanoparticles, its polarization state changes. Different morphologies of nanoparticles have varying effects on the polarization state of the scattered light. This method utilizes multiple polarization scattering images at 0°, 45°, 90°, and 135°. Grand total Light intensity Calculating optical sphericity enables a quantitative description of the morphology and morphology distribution of nanoparticles.

[0059] The Stokes vector can be used to describe the polarization state of light. It contains four components, denoted by S0, S1, S2, and S3, and is expressed as follows:

[0060]

[0061] Where: I0, I 90 I 45 I 135 I R I L These represent the 0° polarization component, 90° polarization component, 45° polarization component, 135° polarization component, right-handed polarization component, and left-handed polarization component of the light intensity, respectively.

[0062] The degree of linear polarization (DoLP) of the scattered light can be calculated using the following formula:

[0063] A single measurement using a polarization camera can simultaneously capture scattering images at four polarization directions: 0°, 45°, 90°, and 135°. The image grayscale values ​​represent the various polarization components I0, I... 90 I 45 I 135 The linear polarization degree DoLP of the scattered light can be obtained according to equations (6) and (7). The depolarization effect is weakest in spherical particles, and the polarization state of the scattered light is almost the same as that of the incident light, i.e., the linear polarization degree is 1. The greater the deviation of the particle from the spherical shape, the stronger the depolarization effect and the smaller the linear polarization degree. Therefore, the optical sphericity Ф = DoLP is defined to quantitatively describe the particle morphology. One measurement can obtain one optical sphericity value, and multiple measurements can obtain multiple optical sphericity values, i.e., the morphological distribution of the particle group can be obtained.

[0064] like Figure 2a , 2b The images shown are scattering images of standard polystyrene particles (spherical) and gold nanorod particles (rod-shaped) taken by a polarization camera in four polarization directions. Clearly, the scattering image characteristics differ between the two types of particles in different polarization directions, especially at 90° polarization, where the spherical particles show almost no signal while the rod-shaped particles still have a significant signal. Particle size can be obtained by performing spatial cross-correlation calculations using the scattering images at 0° polarization. By using multiple consecutive dynamic light scattering images at 0° polarization, the cross-correlation between adjacent images is calculated to obtain the particle group size measurement results. Statistical analysis of multiple particle group size measurements yields the particle size distribution. Optical sphericity can be calculated using the cumulative light intensity of the 0°, 45°, 90°, and 135° polarization images, quantitatively describing the degree to which the measured particle group deviates from a spherical shape. Multiple consecutive measurements using a polarization image sensor are used to obtain the cumulative light intensity of multiple sets of scattering images at 0°, 45°, 90°, and 135° polarization directions, thus obtaining multiple particle group shape measurement results. Statistical analysis of these results yields the particle group shape distribution.

[0065] like Figure 3The graphs shown depict the normalized polarization scattered light intensity curves of nanoparticles with different morphologies. Significant differences exist in the normalized scattered light intensity curves at 0°, 45°, 90°, and 135° polarization directions after 1000 measurements of five different nanoparticle morphologies (including spherical, octahedral, flat, rod-shaped, and linear). For spherical particles, the normalized light intensity at 0° polarization is close to 1, at 90° polarization is close to 0, and at 45° and 135° polarization directions, the normalized light intensity is equal, both at 0.5. For octahedral particles, the normalized light intensity at 0° polarization is slightly less than 1, at 90° polarization is slightly greater than 0, and at 45° and 135° polarization directions, the normalized light intensity is not equal, both deviating slightly from 0.5. For both flat and rod-shaped particles, the normalized light intensity in the 0° polarization direction is significantly less than 1, while the normalized light intensity in the 90° polarization direction is significantly greater than 0. The normalized light intensities in the 45° and 135° polarization directions are close to 0.5, with some fluctuations in the results across different measurement runs. For linear particles, the normalized light intensity in the 0° polarization direction is the lowest, while the normalized light intensity in the 90° polarization direction is the highest. The normalized light intensities in the 45° and 135° polarization directions show significant separation, both deviating from 0.5, and the results fluctuate dramatically across different measurement runs.

[0066] like Figure 4 The results of measuring the optical sphericity of nanoparticles with different morphologies are shown. The average optical sphericity Φ of five different morphologies (including spherical, octahedral, flat, rod-shaped, and linear) after 1000 measurements show a trend consistent with the theoretical Wadell sphericity ψ, proving that optical sphericity can accurately describe the degree to which particles deviate from a spherical shape. Wadell sphericity is defined as: the surface area of ​​a sphere with the same volume as the object / the actual surface area of ​​the object. It is a three-dimensional morphology expression. In practical applications, Wadell sphericity is difficult or even impossible to measure because the actual surface area of ​​the object cannot be measured. Here, we define optical sphericity Φ based on the principle of optical sphericity measurement. It provides three-dimensional morphological information of particles and has a specific numerical value, allowing for a quantitative description of particles. Φ = 1 represents a sphere, and the smaller Φ is than 1, the greater the degree to which the particle deviates from a sphere. Optical sphericity Ф is numerically equal to the linear polarization degree DoLP, and can be calculated by the cumulative light intensity of scattered images from four polarization directions (0°, 45°, 90°, and 135°) recorded in a single measurement by a microlens array polarization image sensor, thus obtaining the particle shape measurement result of a single particle group. Experimental tests demonstrate that the variation law of optical sphericity values ​​for particles of different shapes is consistent with Wadell sphericity, indicating that the relationship between the degree of particle deviation from a sphere described by optical sphericity is reliable. Optical sphericity is therefore more operable and practical.

[0067] like Figure 5a , 5bAs shown, electron micrographs of two different industrial titanium dioxide particles, T1 and T5, indicate that T1 particles are smaller in size and have relatively smoother edges, with better spherical shape; while T5 particles are larger in size and have relatively sharper edges, with poorer spherical shape.

[0068] like Figures 6a-6d As shown, the dynamic light scattering measurement results of polarization images of two different industrial titanium dioxide particles, T1 and T5, indicate that T1 particles have an average particle size of 255 nm and a distribution width standard deviation of 22, indicating a narrower particle size distribution. T5 particles have an average particle size of 392 nm and a distribution width standard deviation of 43, indicating a wider particle size distribution. The average optical sphericity of T1 particles is 0.9578 nm, with a distribution width standard deviation of 0.0019, indicating a narrower morphological distribution. The average optical sphericity of T5 particles is 0.7958 nm, with a distribution width standard deviation of 0.0164, indicating a wider morphological distribution. Based on the particle size and shape results, T5 particles are larger, deviate more from spherical shapes, and exhibit poorer particle uniformity.

[0069] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for simultaneous measurement of particle size, shape, and distribution of dynamic light scattering nanoparticles, characterized in that, A microlens array polarization camera is used to simultaneously capture dynamic light scattering image signals of nanoparticle groups in four polarization directions: 0°, 45°, 90°, and 135°. The particle size and particle size distribution information are obtained using the dynamic light scattering image in the 0° polarization direction, and the particle shape and particle shape distribution information are obtained using the dynamic light scattering images in all four polarization directions, thus achieving synchronous measurement of particle size, particle shape, and distribution. The method for obtaining particle shape and particle shape distribution information involves acquiring multiple consecutively captured polarization scattering images at 0°, 45°, 90°, and 135°. The grayscale values ​​of the images represent the various polarization components of the light intensity. The linear polarization degree of the scattered light is then obtained using the following formula. DoLP Optical sphericity is defined as equal to the degree of linear polarization. DoLP Optical sphericity is used to quantitatively describe the degree to which a particle group deviates from a spherical shape. A single measurement yields one optical sphericity value, and multiple measurements yield multiple optical sphericity values, thus obtaining multiple particle group shape measurement results. Statistical analysis can then be used to obtain the particle shape distribution of the particle group. Linear polarization degree of scattered light DoLP Calculation formula: (7), The Stokes vector describes the polarization state of light and contains four components, each represented by a different symbol. S 0、 S 1. S 2 and S 3 represents the following expression: (6) In the formula: I 0、 I 90 , I 45 , I 135 , I R , I L These represent the 0° polarization component, 90° polarization component, 45° polarization component, 135° polarization component, right-handed polarization component, and left-handed polarization component of the light intensity, respectively.

2. The method for simultaneous measurement of particle size, shape, and distribution of dynamic light scattering nanoparticles according to claim 1, characterized in that, The method of obtaining particle size and particle size distribution information by using dynamic light scattering images with 0° polarization direction involves acquiring multiple scattering images with 0° polarization direction in succession, calculating the cross-correlation between adjacent two images to obtain the average particle size measurement result of a particle group, and statistically analyzing the average particle size of multiple particle groups to obtain the particle size distribution of the particle group.

3. The method for simultaneous measurement of particle size, shape, and distribution of dynamic light scattering nanoparticles according to claim 1 or 2, characterized in that, The specific calculation method for obtaining particle size and particle size distribution information using dynamic light scattering images with 0° polarization direction is as follows: The fluctuation characteristics of the intensity of scattered light from nanoparticles in the 0° polarization direction are analyzed using the correlation function of the scattered light. G ( τ To represent: (1) In the formula: A This is the baseline of the autocorrelation curve, set to 1 when the image signal-to-noise ratio is high; β This is the instrument constant; Γ The decay rate of the correlation function is related to the particle size; τ The relaxation time is used when calculating the correlation between two consecutive images. τ The time interval between two images is the reciprocal of the camera frame rate. Correlation function of two consecutive nanoparticle scattering images with 0° polarization direction G ( τ It can be expressed by the following formula: (2) In the formula: C m,n and B m,n For two consecutive images C and B In the m row and number n The grayscale value of the column pixels; and These are the average gray levels of all pixels in the two images, respectively. Decay rate of correlation function Γ Translational diffusion coefficient of particles D T satisfy: (3) In the formula: q It is the scattering vector, and its mode length is the laser wavelength. λ and scattering angle θ Functions: (4) In the formula: n It is the refractive index of the dispersion medium; The translational diffusion coefficient of the particles can be calculated using equations (1)-(4). D T Then, using the Stokes-Einstein relation, the particle size can be determined. (5) In the formula: k B Boltzmann's constant, T Absolute temperature η The viscosity coefficient of the dispersion medium. x The diameter is the hydrodynamic diameter.

4. A device for synchronously measuring the particle size, shape, and distribution of dynamic light scattering nanoparticles, characterized in that, A laser beam emitted by a laser is irradiated onto nanoparticles in a sample cell through a polarizer. The scattered light signal in the 90° scattering direction is captured by a microlens array polarization camera. The microlens array polarization camera transmits the simultaneously captured scattering images in four polarization directions (0°, 45°, 90°, and 135°) to a computer for analysis and processing. Using the particle shape and distribution information acquisition method in the dynamic light scattering nanoparticle size, shape, and distribution synchronous measurement method described in claim 1, the particle size, shape, and distribution of the nanoparticle group are obtained.

5. The device for synchronous measurement of dynamic light scattering nanoparticle size, shape, and distribution according to claim 4, characterized in that, The microlens array polarization camera has a frame rate set to 500-10000fps depending on the size of the particles being measured. The pixels on the CMOS of the microlens array polarization camera are divided into 4 groups to receive polarization signals in four directions.

6. The device for synchronous measurement of dynamic light scattering nanoparticle size, shape, and distribution according to claim 4 or 5, characterized in that, The polarizer used is a linear polarizer.

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