CN112595635A - Method and device for measuring three-dimensional distribution of particle sizes of nanoparticles in solution - Google Patents
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Abstract
The invention discloses a method for measuring three-dimensional distribution of nanometer particle size in a solution, which comprises the following steps: irradiating the nanoparticles by using laser beams, forming holographic interference fringes by interference of formed scattered light and reference light modulated by a light path, and recording the holographic interference fringes on a camera to obtain a nanoparticle digital hologram; performing three-dimensional reconstruction on the digital hologram to obtain a focused image of the nano-particles; and (4) according to the scattering signal in the focused image, and based on the dynamic light scattering principle and the correlation between the particle size of the nano particles and the diffusion coefficient, obtaining the particle size of the nano particles. The invention also discloses a device for measuring the three-dimensional distribution of the particle size of the nano particles in the solution, which comprises the following steps: the signal transmitting unit comprises a continuous laser and a light path adjusting section; a signal receiving unit including a camera recording holographic interference fringes; and the signal processing unit is connected behind the signal receiving unit and is used for processing the nanoparticle digital hologram. The method and the device realize the in-situ measurement of the instantaneous particle size distribution of the nanoparticles at the three-dimensional position in the sample cell.
Description
Technical Field
The invention relates to the field of nanoparticle size measurement, in particular to a method and a device for measuring three-dimensional distribution of nanoparticle sizes in a solution.
Background
Nanotechnology is a novel interdisciplinary technology based on various modern advanced scientific technologies, and has been successfully applied in the fields of medicine, pharmacy, environmental governance, biological detection, optics, national defense and the like. Nanomaterials produced by nanotechnology are of great interest to various disciplines. For example, carbon materials of nanometer size represented by graphene and carbon nanotubes can be successfully applied to capacitors, energy storage batteries, and the like; the composite nano material represented by the nano zero-valent iron has important advantages in the field of remediation of organic pollutants and heavy metals in soil and underground water due to the unique adsorbability and reducibility; the nano material in biomedicine can be well applied to the specific recognition and high-sensitivity detection of cancer cells; the mixing of the nano-particles and the rocket metal propellant can obviously improve the combustion characteristic and improve the combustion efficiency and speed.
The premise of the nanoparticles exerting the specific advantages is the controllable preparation of the nanoparticle material, the particle size of the material is a key factor determining the performance of the nanoparticle material, and the particle size measurement mode at present is mainly divided into an off-line method and an on-line method. The off-line method mainly comprises a screening method, a sedimentation method and a microscopy method, wherein a Scanning Electron Microscope (SEM) and a Transmission Electron Microscope (TEM) are commonly used characterization methods for nano particles, the resolution can reach 1nm or even smaller, the data is intuitive and easy to understand, but in-situ real-time measurement cannot be realized, the sampling amount is small, and the sample preparation process can seriously affect the result; the on-line method mainly comprises an electrical method, an acoustic method and an optical method, a laser particle size analyzer is the most extensive mode in optics, the laser particle size analyzer is used for measuring nano particles and mainly uses the principle of dynamic light scattering (photon correlation spectroscopy), the nano particles in liquid mainly take Brownian motion as the main part, and the migration rate of the nano particles dispersed in the liquid is measured to obtain corresponding particle size distribution. However, the sampling usually uses a photomultiplier tube, the measurement needs about 1.5min, the intensity of the brownian motion is related to factors such as temperature, particle size and liquid viscosity, the measurement time is long, a temperature control device is needed, the instrument structure is complex, the price is high, and the particle size distribution in the instantaneous three-dimensional space field cannot be obtained.
The on-line digital holographic technique is a real-time three-dimensional measurement technique, not only can realize the characteristics of full field, no calibration and no contact of an optical means, but also can simultaneously realize the measurement of the three-dimensional position of the particles by a single camera. Laser beams enter, beams passing through a particle field are scattered into object light, the unscattered light is reference light, the object light and the reference light are interfered to form a hologram (interference fringes) which is recorded by a CCD or CMOS camera, the obtained signal contains amplitude and phase information, compared with a traditional chemical silver salt dry plate, the digital signal transmission of the hologram can be realized, the depth of particles can be obtained through digital reconstruction, and the measurement of the particle size distribution condition of nanoparticles in a medium is realized. Compared with the traditional method of singly recording the dynamic light scattering signals of the whole field by using a CCD or a CMOS, the method can obtain the light scattering signals of all the cross sections of the whole field by shooting a picture by using a digital holography method, thereby greatly improving the accuracy and the efficiency of the measurement of the particle size of the nano particles.
Disclosure of Invention
The invention aims to provide a method and a device for measuring the three-dimensional distribution of the particle size of nanoparticles in a solution, which solve the problem that the three-dimensional distribution of the particle size of nanoparticles in the solution is difficult to measure in situ in real time at present.
The invention provides the following technical scheme:
a method of measuring the three-dimensional distribution of nanoparticle sizes in a solution, the method comprising the steps of:
(1) irradiating nanoparticles in a sample cell by using laser beams, interfering scattered light formed by the nanoparticles with reference light modulated by a light path to form holographic interference fringes, and recording the holographic interference fringes on a camera photosensitive chip at a time interval of delta tau and an angle theta to obtain a series of digital holograms of the nanoparticles which do Brownian motion in a measurement period;
(2) performing three-dimensional reconstruction on the nanoparticle digital hologram recorded in the step (1) to obtain a focused image of nanoparticles in a sample cell on any x-y section, wherein the x-y section is a section vertical to incident light;
(3) according to the scattering signal in the focused image in the step (2), based on the dynamic light scattering principle, according to the granularity D and the diffusion coefficient D of the nano-particlesTThe particle size d of the nanoparticles in the cross section is obtained.
In the step (1), Δ τ is adjusted according to the measured granularity range, the angle θ may be 10 °, and the angle θ may be adjusted according to the frame rate of the camera.
In the step (1), the brightness stripes of the nanoparticle digital hologram are as follows:
IH＝|O+R|2＝IO+IR+OR*+O*R
when the holographic image is reconstructed by using the same light beam as the original reference light, the holographic reconstructed image satisfies:
IH R＝|OO*|R+|RR*|R+|RR*|O+O*|RR*|
wherein O is the complex amplitude distribution of the scattered light; r is reference light; the first term and the second term are direct current phases; the third term forms a virtual phase; the fourth term forms a real image.
The method for three-dimensionally reconstructing the digital hologram of the nanoparticles in the step (2) to obtain the focused image of the nanoparticles in any x-y section in the sample cell comprises the following steps:
using convolution reconstruction method to carry out three-dimensional reconstruction and holographic reconstructionThird term | RR in the image*I O contains object-light information, and the complex amplitude distribution of the hologram reconstructed by using the rayleigh-solifife diffraction formula can be expressed as:
where (x, y) and (u, v) are the coordinates of the holographic plane and the reconstruction plane, respectively, zrFor the reconstruction distance, Γ represents the complex amplitude distribution of the reconstructed light field;
rewriting the above formula into a volume form:
wherein g (u, v, z)r) Comprises the following steps:
the numerical calculation is performed by performing fourier transform and inverse fourier transform twice on the above equation:
obtaining different reconstruction distances z of the hologramrA focused image of the x-y cross section of (a).
The method for obtaining the particle size d of the nanoparticles in the cross section in the step (3) comprises the following steps:
(3-1) deriving an autocorrelation function from the scatter signal of the focused image of the x-y section:
the correlation analysis coefficient G (τ) is:
G(τ)＝exp(-2Γτ)
wherein gamma is the attenuation line width, and tau is the attenuation time;
Γ satisfies the equation:
wherein D isTIs the particle diffusion coefficient; q is a scattering vector; theta is a scattering angle; λ is the wavelength of the light wave in vacuum; n is the refractive index of the dispersion medium;
(3-2) obtaining the relation between the particle size and the diffusion coefficient by using the Stokes-Einstein equation with the autocorrelation function as a base line:
coefficient of particle diffusion DT：
Wherein, KBIs the Boltzmann constant; t is the absolute temperature; η is the viscosity; d is the particle size of the nanoparticles to be detected;
(3-3) obtaining the particle size d of the nano particles according to the relation between the particle size and the diffusion coefficient:
finally, the particle size distribution of the nanoparticles on each section in the sample cell is obtained.
The invention also provides a device for measuring the three-dimensional distribution of the particle size of the nano particles in the solution, which comprises a signal transmitting unit, a signal receiving unit and a signal processing unit;
the signal transmitting unit comprises a continuous laser and a light path adjusting section, wherein one part of laser beams generated by the continuous laser is converged and then irradiates the nanoparticles to form scattered light, the other part of the laser beams is used as reference light through the light path adjusting section, and the scattered light and the reference light are interfered to form holographic interference fringes;
the signal receiving unit comprises a camera, and records holographic interference fringes at a time interval of delta tau to obtain a series of digital holograms of nanoparticles which do Brownian motion in a measuring time interval;
the signal processing unit is connected to the signalAfter receiving the unit, the processing for the nanoparticle digital hologram: including removing background noise; carrying out three-dimensional reconstruction on the nanoparticle digital hologram to obtain a focusing image of the nanoparticle on any x-y section; according to a scattering signal given by a focusing image, based on a dynamic light scattering principle, according to the particle size D and the diffusion coefficient D of the nano particlesTThe particle size of the cross-section nanoparticles is obtained.
Preferably, the laser wavelength of the continuous laser is in a visible light band of 350nm-700nm, and the power is 1-500 mW. Wherein the continuous laser can adjust the laser wavelength and power according to the scattering characteristics of the nanoparticles.
Preferably, the laser beam generated by the continuous laser is divided into a first laser beam and a second laser beam by a first beam splitter, and the first laser beam is converged by a convex lens and irradiates nanoparticles to form scattered light; the second laser beam sequentially passes through a reflector, a spatial filter, a collimating lens and an attenuation sheet to form reference light; the scattered light and the reference light are adjusted to be on the same main optical axis by the second beam splitter.
The spatial filter consists of a microscope objective and a pinhole.
The first beam splitter divides the laser beam into two first laser beams and two second laser beams with the same energy. The reflector, the spatial filter, the collimating lens and the attenuation sheet form a light path adjusting section: the spatial filter consists of a microscope objective and a pinhole, and improves the beam quality of the laser refracted by the reflector; the collimating lens collimates the diffused light into parallel light beams, and then is connected with the attenuation sheet to attenuate laser energy, so that the situation that the reference light energy is too strong and cannot interfere with scattered light to form clear holographic interference fringes is avoided, and the situation that the laser energy is too strong to damage a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) camera photosensitive chip is avoided. And finally, the reference light subjected to light path adjustment and the measured scattered light are positioned on the same main optical axis by the second beam splitter.
Preferably, the camera is a CCD or CMOS high-speed camera, the sampling frequency is 20kHz-50kHz, and the exposure time is less than 500 ns. And the photosensitive chip of the CCD or CMOS high-speed camera is vertical to the propagation direction of scattered light.
The invention utilizes the digital holographic technology to carry out three-dimensional reconstruction on different reconstruction distances, and can obtain the scattering light intensity distribution of the nano particles of each section in a sample pool at a certain moment; the space light field is divided and intercepted by the holographic technology, and light field information at different positions in the space is restored by using a single image. The holographic stripes of the particles are recorded at the time interval of delta tau by using a high-speed camera, dynamic light scattering signals of all sections of the sample pool are inverted, and the particle size distribution of the nanoparticles at different spatial positions in the solution can be obtained because the light scattering signal pulsation is generated by the Brownian motion of the nanoparticles and the scattering pulsation frequency is related to the diffusion coefficient of the particles.
The method and the device for measuring the three-dimensional distribution of the particle size of the nano particles in the solution have the beneficial effect of realizing the in-situ measurement of the instantaneous particle size distribution of the nano particles at the three-dimensional position in the sample cell. Through digital holographic three-dimensional reconstruction and dynamic light scattering related algorithm processing, the measurement time can be shortened to microsecond level. The measurement method can extend the measurement precision of the holographic technology to the nanometer level, and compared with the traditional Photon Correlation Spectroscopy (PCS) nanoparticle particle size instrument based on the dynamic light scattering principle, the particle size measurement of the in-situ instantaneous specific three-dimensional position of the nanoparticles is realized in the measurement speed and dimension.
Drawings
FIG. 1 is a schematic diagram of holographic reconstruction of nanoparticle scattering signals;
FIG. 2 is a schematic structural diagram of a measuring apparatus for three-dimensional distribution of nanoparticles in a solution according to the present invention;
the device comprises a laser 1, a laser 2, a first beam splitter 3, a convex lens 4, a first reflector 5, a second reflector 6, a microscope objective 7, a pinhole 8, a collimating lens 9, an attenuation sheet 10, a second beam splitter 11, a sample cell 12 and a high-speed camera.
Detailed Description
The invention provides a method and a device for measuring the three-dimensional distribution of the particle size of nanoparticles in a solution, and the steps of the specific embodiment of the technology are given in detail by combining the accompanying drawings.
Example 1
As shown in fig. 1 and 2, the method for measuring the three-dimensional distribution of the particle size of the nanoparticles in the solution by using the device provided by the invention comprises the following steps:
step 1: turning on a laser 1, dividing a laser beam into two beams by a first beam splitter 2, and converging and irradiating the nanoparticles by a convex lens 3 to generate scattered light, as shown in a in fig. 1; the other beam of reference light is formed by a first reflective mirror 4 and a second reflective mirror 5 through a spatial filter consisting of a microscope objective 6 and a pinhole 7, and then through a collimating lens 8 and an attenuation sheet 9; the scattered light and the reference light are adjusted to be on the same axis by the second beam splitter 10 in front of the sample cell 11, and the scattered light generated by the nanoparticles is interfered with the reference parallel beam at an angle theta as object light to form hologram interference fringes, and the hologram interference fringes are recorded by the high-speed camera 12. Recorded by a CCD high-speed camera at a time interval delta tau with a camera sampling frequency of 20kHz, resulting in a hologram at each instant, as shown in b in figure 1.
Wherein: the laser 1 has a laser wavelength of 350nm-700nm in visible light band and a power of 1-500mW, and the laser wavelength and the power can be adjusted according to the scattering characteristics of the nanoparticles. The first beam splitter 2 splits the laser light into two beams, and the second beam splitter 10 adjusts the reference light to be on the same axis as the scattered light at the measured scattering angle. The convex lens 3 converges the laser, so that the situation that the scattered light generated by the nano particles cannot be measured due to too low laser energy is avoided. The spatial filter comprises a microscope objective 6 and a pinhole 7, the microscope objective has a magnification of 10 to 50, and the pinhole has an aperture of 5 to 10 μm. The spatial filter can filter out light of other spatial frequencies, and the quality of light beams is improved. The collimator lens 8 collimates the diffused light into a parallel light beam. The transmittance of the attenuation sheet 9 is selected to be 1% -35% to match the laser intensity, the exposure time of the high-speed camera and the visibility of the hologram. In the sample cell 11, nanoparticles of a known medium are contained. The high-speed camera 12 is a CCD or CMOS high-speed camera, the photosensitive chip is vertical to the propagation direction of the tested scattered light, the sampling frequency is 20kHz-50kHz, and the exposure time is less than 500 ns.
Step 2: the high-speed camera 12 transmits the hologram signal pattern to the signal processing unit for processing:
step 2-1: and removing background noise and a direct current phase.
Step 2-2: and (3) performing three-dimensional reconstruction on the nanoparticle digital hologram to obtain a focusing image of the nanoparticles on any x-y section, as shown by c in figure 1.
Particularly, a convolution reconstruction method is utilized to carry out three-dimensional reconstruction, and | RR in a holographic reconstruction image formula*I O contains object-light information, and the complex amplitude distribution of the hologram reconstructed by using the rayleigh-solifife diffraction formula can be expressed as:
where (x, y) and (u, v) are the coordinates of the holographic plane and the reconstruction plane, respectively, zrFor the reconstruction distance, Γ represents the complex amplitude distribution of the reconstructed light field;
rewriting the above formula into a volume form:
wherein g (u, v, z)r) Comprises the following steps:
the numerical calculation is performed by performing fourier transform and inverse fourier transform twice on the above equation:
obtaining different reconstruction distances z of the hologramrA focused image of the x-y cross section of (a).
Step 2-3: according to a scattering signal given by a focusing image, based on a dynamic light scattering principle, according to the particle size D and the diffusion coefficient D of the nano particlesTThe particle size of the cross-section nanoparticles is obtained.
The method specifically comprises the following steps:
(2-3-1) deriving a self-correlation function from the scatter signal of the focused image of the x-y section:
the correlation analysis coefficient G (τ) is:
G(τ)＝exp(-2Γτ)
wherein gamma is the attenuation line width, and tau is the attenuation time;
Γ satisfies the equation:
wherein D isTIs the particle diffusion coefficient; q is a scattering vector; theta is a scattering angle; λ is the wavelength of the light wave in vacuum; n is the refractive index of the dispersion medium;
(2-3-2) obtaining the relation between the particle size and the diffusion coefficient by using the Stokes-Einstein equation with the autocorrelation function as a base line:
coefficient of particle diffusion DT：
Wherein, KBIs the Boltzmann constant; t is the absolute temperature; η is the viscosity; d is the particle size of the nanoparticles to be detected;
(2-3-3) obtaining the particle size d of the nano particles according to the relation between the particle size and the diffusion coefficient:
finally, the particle size distribution of the nanoparticles on each section in the sample cell is obtained.
The above is a detailed description of the present invention with reference to the implementation case, but the implementation of the present invention is not limited to the implementation case, for example, the scattering angle measured in step 1 is 10 °, and the recorded scattering angle θ can be adjusted with the change of the sampling frequency of the high-speed CCD or CMOS camera, but at the same time, the angle of the reflector is adjusted to ensure that the object light and the reference light are on the same axis. The holographic three-dimensional reconstruction algorithm in the step 2 is not limited to the convolution reconstruction method, and any other changes, substitutions, combination simplifications and the like which are made under the guiding idea of the patent core of the invention are included in the protection scope of the patent of the invention.
Claims (10)
1. A method for measuring the three-dimensional distribution of the particle size of nanoparticles in a solution, comprising the steps of:
(1) irradiating nanoparticles in a sample cell by using laser beams, interfering scattered light formed by the nanoparticles with reference light modulated by a light path to form holographic interference fringes, and recording the holographic interference fringes on a camera photosensitive chip at a time interval of delta tau and an angle theta to obtain a series of digital holograms of the nanoparticles which do Brownian motion in a measurement period;
(2) performing three-dimensional reconstruction on the nanoparticle digital hologram recorded in the step (1) to obtain a focused image of nanoparticles in a sample cell on any x-y section, wherein the x-y section is a section vertical to incident light;
(3) according to the scattering signal in the focused image in the step (2), based on the dynamic light scattering principle, according to the granularity D and the diffusion coefficient D of the nano-particlesTThe particle size d of the nanoparticles in the cross section is obtained.
2. The method for measuring the three-dimensional distribution of the particle sizes of the nanoparticles in the solution according to claim 1, wherein in the step (1), the brightness stripes of the digital hologram of the nanoparticles are:
IH＝|O+R|2＝IO+IR+OR*+O*R
when the holographic image is reconstructed by using the same light beam as the original reference light, the holographic reconstructed image satisfies:
IH R＝|OO*|R+|RR*|R+|RR*|O+O*|RR*|
wherein O is the complex amplitude distribution of the scattered light; r is reference light; the first term and the second term are direct current phases; the third term forms a virtual phase; the fourth term forms a real image.
3. The method for measuring the three-dimensional distribution of the particle sizes of the nanoparticles in the solution as claimed in claim 2, wherein the step (2) of three-dimensionally reconstructing the digital hologram of the nanoparticles to obtain the focused image of the nanoparticles in the sample cell at any x-y section comprises the following steps:
performing three-dimensional reconstruction by using convolution reconstruction method, and holographically reconstructing a third term | RR in an image*I O contains object-light information, and the complex amplitude distribution of the hologram reconstructed by using the rayleigh-solifife diffraction formula can be expressed as:
where (x, y) and (u, v) are the coordinates of the holographic plane and the reconstruction plane, respectively, zrFor the reconstruction distance, Γ represents the complex amplitude distribution of the reconstructed light field;
rewriting the above formula into a volume form:
wherein g (u, v, z)r) Comprises the following steps:
the numerical calculation is performed by performing fourier transform and inverse fourier transform twice on the above equation:
obtaining different reconstruction distances z of the hologramrA focused image of the x-y cross section of (a).
4. The method for measuring the three-dimensional distribution of the particle sizes of the nanoparticles in the solution according to claim 3, wherein the method for determining the particle size d of the nanoparticles in the cross section in the step (3) comprises:
(3-1) deriving an autocorrelation function from the scatter signal of the focused image of the x-y section:
the correlation analysis coefficient G (τ) is:
G(τ)＝exp(-2Γτ)
wherein gamma is the attenuation line width, and tau is the attenuation time;
Γ satisfies the equation:
Γ＝DTq2、
wherein D isTIs the particle diffusion coefficient; q is a scattering vector; theta is a scattering angle; λ is the wavelength of the light wave in vacuum; n is the refractive index of the dispersion medium;
(3-2) obtaining the relation between the particle size and the diffusion coefficient by using the Stokes-Einstein equation with the autocorrelation function as a base line:
coefficient of particle diffusion DT：
Wherein, KBIs the Boltzmann constant; t is the absolute temperature; η is the viscosity; d is the particle size of the nanoparticles to be detected;
(3-3) obtaining the particle size d of the nano particles according to the relation between the particle size and the diffusion coefficient:
finally, the particle size distribution of the nanoparticles on each section in the sample cell is obtained.
5. The device for measuring the three-dimensional distribution of the particle sizes of the nano particles in the solution is characterized by comprising a signal transmitting unit, a signal receiving unit and a signal processing unit;
the signal transmitting unit comprises a continuous laser and a light path adjusting section, wherein one part of laser beams generated by the continuous laser is converged and then irradiates the nanoparticles to form scattered light, the other part of the laser beams is used as reference light through the light path adjusting section, and the scattered light and the reference light are interfered to form holographic interference fringes;
the signal receiving unit comprises a camera, and records holographic interference fringes at a time interval of delta tau to obtain a series of digital holograms of nanoparticles which do Brownian motion in a measuring time interval;
the signal processing unit is connected behind the signal receiving unit and used for processing the nanoparticle digital hologram: including removing background noise; carrying out three-dimensional reconstruction on the nanoparticle digital hologram to obtain a focusing image of the nanoparticle on any x-y section; according to a scattering signal given by a focusing image, based on a dynamic light scattering principle, according to the particle size D and the diffusion coefficient D of the nano particlesTThe particle size of the cross-section nanoparticles is obtained.
6. The apparatus as claimed in claim 5, wherein the continuous laser has a laser wavelength in the visible light range of 350nm-700nm and a power of 1-500 mW.
7. The apparatus for measuring the three-dimensional distribution of the particle sizes of the nanoparticles in the solution according to claim 5, wherein the laser beam generated by the continuous laser is divided into a first laser beam and a second laser beam by a first beam splitter, and the first laser beam is converged by a convex lens and then irradiates the nanoparticles to form scattered light; the second laser beam sequentially passes through a reflector, a spatial filter, a collimating lens and an attenuation sheet to form reference light; the scattered light and the reference light are adjusted to be on the same main optical axis by the second beam splitter.
8. The apparatus for measuring the three-dimensional distribution of the particle sizes of nanoparticles in a solution according to claim 7, wherein the spatial filter is composed of a microscope objective and a pinhole.
9. The apparatus of claim 5, wherein the camera is a CCD or CMOS high speed camera, the sampling frequency is 20kHz-50kHz, and the exposure time is less than 500 ns.
10. The apparatus of claim 9, wherein the photosensitive chip of the CCD or CMOS high-speed camera is perpendicular to the propagation direction of the scattered light.
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| CN114166699A (en) * | 2021-11-12 | 2022-03-11 | 清华大学深圳国际研究生院 | Optical measurement device and method for volume of suspended particles |
| CN117420099A (en) * | 2023-09-04 | 2024-01-19 | 北京大学长三角光电科学研究院 | Method and device for detecting heterogeneous solution based on optical diffraction chromatography |
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| CN114166699A (en) * | 2021-11-12 | 2022-03-11 | 清华大学深圳国际研究生院 | Optical measurement device and method for volume of suspended particles |
| CN117420099A (en) * | 2023-09-04 | 2024-01-19 | 北京大学长三角光电科学研究院 | Method and device for detecting heterogeneous solution based on optical diffraction chromatography |
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