Standard number: GB∕T 38431-2019
Standard name: Static multiple light scattering method for evaluating the stability of particle dispersion system
English name: Particulate-Dispersion stability analysis--Static multiple light scattering
Standard format: PDF
Release time: 2019-12-31
Implementation time: 2020-03-01
Standard size: 4.18M
Standard introduction: 1 Scope
This standard specifies the method for evaluating the stability of dispersion system using the principle of static multiple light scattering, including principles and methods, measurement system verification and calibration, measurement and test reports.
This standard is applicable to dispersion systems with particle size of 50mm~1mm and volume fraction of 0.01%~60%. Dispersion systems of other concentrations can be implemented as a reference.
2 Terms and definitions
The following terms and definitions apply to this document
Disperse system
A mixed system formed by dispersing one or more particulate substances into a fluid substance. The former substance is called the dispersed phase and the latter substance is called the continuous phase or dispersion medium
Dispersion stability
The change of the dispersion state of particles in the dispersion system over time
Static multiple light scattering
The phenomenon that light is scattered multiple times by the dispersed particles when it is injected into a sample containing the dispersion system.
The particles in the sample can be solid particles, droplets, bubbles and other substances
Photon mean free path
The average distance between two adjacent scattered particles
This standard specifies the method for evaluating the stability of a dispersion system using the principle of static multiple light scattering, including the principle and method, measurement system, measurement system verification and calibration, and measurement and test report. This standard is applicable to dispersed systems with particle sizes of 50 nm~1 mm and volume fractions of 0.01%~60%. Dispersed systems of other concentrations can be implemented for reference.

ICS19.120
National Standard of the People's Republic of China
GB/T38431—2019
Evaluation of the stability of dispersed systems
Static multiple light scattering
ParticulateDispersion stability analysis-Static multiple light scatteringPublished on 2019-12-31
State Administration for Market Regulation
National Administration of Standardization
Implementation on 2020-03-01
GB/T38431—2019
Terms and Definitions
Symbols and Abbreviations
3.1 Symbols
Abbreviations
Principles and Methods
Measurement System
Measurement System Verification and Calibration||t t||Installation requirements
Sample loading
Data processing
8Test report
Appendix A (informative)
Appendix B (informative)
Appendix C (informative)
References
Multiple light scattering (MLS) theory and measurement principleInstability treatment example
Dispersion system stability test report
This standard was drafted in accordance with the rules given in GB/T1.1-2009. GB/T38431—2019
This standard was proposed and managed by the National Technical Committee for Particle Characterization and Sorting and Screen Standardization (SAC/TC168). The drafting units of this standard are: China Institute of Metrology, Beijing Powder Technology Association, Shenzhen Defang Nanotechnology Co., Ltd., Peking University Pioneer Technology Industry Co., Ltd., Beijing Physical and Chemical Analysis and Testing Center, Institute of Process Engineering, Chinese Academy of Sciences, China Machinery Productivity Promotion Center, South China Normal University Tianxue, Zhuhai Zhenli Optical Instrument Co., Ltd., Beijing Coast Hongmeng Standard Material Technology Co., Ltd., Zhejiang Doppler Environmental Protection Technology Co., Ltd., China University of Metrology, Hangzhou Wahaha Group Co., Ltd., Shanghai Chuangyuan Cosmetics Co., Ltd., Zhejiang Xin'an Chemical Group Co., Ltd., Beijing Langdisen Technology Co., Ltd., National Center for Nanoscience and Technology, Changsha Leyuan Chemical Technology Co., Ltd. The main drafters of this standard are: Zhang Wenge, He Wei, Shang Weili, Zhou Henghui, Gao Yuan, Li Zhaojun, Zhou Lan, Wang Yuanhang, Zhou Suhong, Yu Fang, Han Peng, Zhang Fugen, Li Li, Zou Zongyong, Yu Mingzhou, Jiang Xiaorui, Gao Jie, Zhu Xiaoyang, Liu Junjie, Han Dun, Peng Li, Wu Weidu, Qian Zhigang, Zeng Sili, Huang Kaibing, and Wu Fenxia.
GB/T38431—2019
A dispersion system is a mixed system formed by dispersing one or more substances into another substance, including liquid-liquid dispersion emulsions, solid-liquid dispersion suspensions, and gas-liquid dispersion foams. Dispersion systems have unique physical and chemical properties and are widely used in almost all industrial fields such as petroleum, chemical industry, food, pharmaceuticals, ceramics, coatings, pigments, batteries, vaccines, etc. Dispersion systems are thermodynamically unstable systems. After the particles (liquid particles, solid particles or bubbles) as the dispersed phase are dispersed into the continuous phase, there will be weak physical interactions or strong charge attraction between the particles and the continuous phase, or between the particles, thus forming flocculation or aggregation: Due to the different specific gravities of different substances in the dispersion system, under the influence of gravity, particles will precipitate or float after being placed for a long time. These unstable phenomena will have a significant impact on the final quality of the product and affect the storage time of the product. Therefore, it is very important to quickly determine the long-term stability of the dispersion system in the shortest time under actual storage conditions. Static multiple light scattering (SMLS) technology can qualitatively and quantitatively analyze the instability phenomena of dispersed systems, such as floating, sedimentation, flocculation, aggregation, etc., without diluting the sample. Detecting the initial changes of these instability phenomena is very important for shortening the time gate of stability testing, predicting the shelf life of products, and inferring the instability mechanism of the system. This technology can achieve direct measurement under the actual storage conditions of the sample.
1 Scope
Evaluation of stability of particle dispersion system
Static multiple light scattering method
GB/T38431—2019
This standard specifies the method for evaluating the stability of dispersed systems using the principle of static multiple light scattering, including principles and methods, measurement systems, measurement system verification and calibration, and measurement and test reports. This standard applies to dispersed systems with particle sizes of 50nm1mm and volume fractions of 0.01%~60%: other concentrations of dispersed systems can be implemented as a reference.
Terms and definitions
The following terms and definitions apply to this document. 2.1
dispersesystem
Disperse system
A mixed system formed by dispersing one or more particulate substances into a fluid substance. The former substance is called dispersed phase, and the latter substance is called continuous phase or dispersion medium. 2.2
Dispersion system stability
dispersion stability
The change of the dispersion state of particles in the dispersion system over time 2.3
fstaticmultiplelight scattering
The phenomenon that light is irradiated into a sample containing a dispersion system and the dispersed particles are scattered multiple times. Note: The particles in the sample can be solid particles, liquid droplets, bubbles and other substances. 2.4
Photon mean free path
photonmeanfreepath
The average distance between two particles where two adjacent scatterings occur 2.5
Photon transmission mean free path
photon propagation mean freepath The mean free path in anisotropic media. 2.6
Instability index
unstabilityindex
Measurement of the stability of a dispersed system
Note: The most stable system is when the change intensity is 0, and the larger the change value, the more unstable it is. 3
Symbols and abbreviations
3.1 Symbols
The following symbols apply to this document.
d: particle diameter
GB/T38431—2019
g: asymmetry factor
Ius: instability index
l: photon mean free path
1: photon transmission mean free path
nt:Refractive index of continuous phase
n: Refractive index of particles
Q: Scattering efficiency
T. : Incident light intensity
: Particle volume ratio
Abbreviations
The following abbreviations apply to this document.
BSI: Backscattered intensity MLS: Multiple light scattering SMLS: Static multiple light scattering TI: Transmitted intensity 4 Principle and method
Static multiple light scattering technology can detect the stability of dispersed systems, including the change in particle size and the migration (sedimentation/floating) speed of particles in the dispersed system. This technology is applicable to dispersed systems such as solid-liquid dispersion, liquid-liquid dispersion and gas-liquid dispersion. Appendix A provides some theoretical background on the use of multiple light scattering (MLS) to evaluate the stability of dispersed systems. In the definition of static multiple light scattering, the incident light is scattered multiple times after entering the sample. The intensity of the final emitted light depends on the wavelength of the incident light, the particle concentration, the particle size, the refractive index of the continuous and dispersed phases, and the absorption coefficient. In the multiple light scattering theory, the photon mean free path 1 is used as a length parameter to describe the scattering and transmission of light, as shown in formula (1): 2d
Where:
photon mean free path, in micrometers (um); d
particle diameter, in micrometers (μm); particle volume ratio:
scattering efficiency.
The scattering process is anisotropic and is usually described by the photon transmission mean free path 1. Its relationship with the photon mean free path 1 is shown in formula (2):
Where:
photon transmission mean free path, in micrometers (μm); photon mean free path, in micrometers (um); an asymmetry factor.
Q. , g can be obtained from the Mie light scattering theory, which is related to the size and refractive index of the particles. According to the Lambert-Beer law formula, the functional relationship between the transmitted light intensity (TI) and the photon mean free path 1 is shown in formula (3): TI-Tae--
GB/T38431—2019
Through experimental verification, the backscattering intensity (BSI) is inversely proportional to the photon transmission mean free path (I) 1/2, and the functional relationship is shown in formula (4): BSIoc
· (4)
The measurement system can directly measure the transmitted light intensity (TI) and the backscattering intensity (BSI) values. According to the relationship between the two and 1, 1, when the refractive index n of the particle, the refractive index n of the continuous phase, and the volume fraction of the particle or the average particle size of the particle are known, the average particle size or particle concentration of the particle can be calculated
The schematic diagram of the common static multiple light scattering (SMLS) measurement system is shown in Figure 1, which consists of a light source and two detectors (photodiodes, etc.). The backscattered light and transmitted light intensity can be measured simultaneously. The principle of light source selection is to minimize the absorption of particles and to maximize the penetration of light into the sample: for example, near-infrared light. The sample needs to be placed in a sealed sample cell to avoid the influence of sample evaporation or changes in environmental humidity. During the measurement, the light source must be stable and calibrated in real time, and the sample temperature change should be controlled within ±0.5°C.
Backscattered light
Transmitted light
Figure 1 Schematic diagram of static multiple light scattering (SMLS) with both backscattered light and transmitted light detectors The core component of the device is a detection probe consisting of a light source, backscattered light and transmitted light detectors. The detection probe is fixed on a plate that can move up and down and can move along the height direction of the sample cell. The detection probe is spaced a certain distance apart to collect data on backscattered light and transmitted light; the intensity of the light is determined by the concentration and particle size of the particles in the dispersed system. The difference in light intensity at different positions characterizes the difference in particle dispersion in the dispersed system: specify the number of times the measuring probe is moved, repeat the measurement, obtain the data of light intensity at different times and positions, and calculate the instability index Ius according to formula (5) or formula (6) to evaluate the stability of the sample. See Appendix B for examples of instability processing.
When TI>0.2%：
TI(h)-TI(h）
When TI≤0.2%：
Wherein：
TIrt(h)
BSIref(h)
BSI(h)
|BSIu(h)-BSI(h)|
The intensity of the transmitted light received by the detector at the reference time and the height of the sample h: The intensity of the transmitted light received by the detector at the end of the test and the height of the sample h: The overall height of the sample;
The intensity of the backscattered light received by the detector at the reference time and the height of the sample h; The intensity of the backscattered light received by the detector at the end of the test and the height of the sample h. ·(5)
.(6)
Note: The intensity of the light detected by the device needs to be calibrated. Use a non-absorbing, only reflective reference material (such as polytetrafluoroethylene) to calibrate the backscattered light intensity. Use a pure, particle-free, transparent reference material (such as silicone oil) to calibrate the transmitted light. Figure 2 is a schematic diagram of the multiple light scattering measurement system. 3
GB/T38431—2019
Description:
1 Sample:
2——Light source;wwW.bzxz.Net
3——Backscattered light detector;
4—Transmitted light detector;
5—Signal processing and computing system;
6—Display.
5 Measurement system
2 Schematic diagram of the measurement system for multiple light scattering
The measurement system consists of the following parts:
a) Light source;
b) Columnar colorless transparent glass sample pool;
Optical detector;
d) Signal processing system;
Temperature control device.
Verification and calibration of measurement system
Warning: Radiation from monochromatic light can cause permanent eye damage. Do not look directly at the monochromatic light beam or its reflected beam. When the monochromatic light beam is on, do not use highly reflective surfaces. Be sure to comply with local safety regulations for the use of monochromatic light6.1
Installation requirements
The measurement system should be placed in a clean environment with an ambient temperature of 15℃ to 45℃ and a relative humidity of less than or equal to 75%. The workbench where the instrument is placed should be stable, avoid direct sunlight, and avoid large electronic noise and mechanical vibration. When using organic liquids (e.g. as refractive index matching liquids and/or as suspension media), health and safety requirements should be considered and good ventilation facilities should be provided. Other installation requirements should follow the manufacturer's specifications6.2
Use standard materials or standard samples with similar optical and physical properties and known particle size to calibrate the instrument measurement stability.
GB/T38431—2019
It is recommended to calibrate at least once a year. The calibration method should comply with the equipment manufacturer's instructions, relevant regulations or standards. 7 Measurement
7.1 Preheating
Turn on the power for preheating. The preheating time shall not be less than 30 minutes to stabilize the monochromatic light intensity of the instrument7.2 Sample loading
The sample to be measured should be measured in a uniform state. If there is precipitation or floating during measurement, the sample should be shaken first. If the solvent of the sample is an organic solvent or a volatile liquid medium, it should be kept sealed. Simply put the sample into the sample cell. The following points should be noted when adding samples:
a) When adding samples to the sample cell, avoid sticking to the wall. b) Avoid bubbles when adding samples.
Ensure that the sample has a good half-moon surface after adding the sample, and there is no contamination around the bottle wall d) For samples with high viscosity, use a wide sample cell. The sample volume depends on the size of the sample cell. Sampling with a large sample cell is more representative and can obtain better repeatability measurement results. 7.3 Test
7.3.1 Add the sample to the sample cell. See 7.2 for sample loading. Add the evenly dispersed sample to the sample cell and seal it. The outer wall of the sample cell should be clean.
7.3.2 Start measuring after preheating for 30 minutes. The temperature change during the measurement should be controlled within ±0.5℃. 7.3.3 Place the sample cell with the sample added into the measurement system and start measuring after keeping the temperature constant for 5 minutes. 7.3.4 Capture the signal of the sample's transmitted light and backscattered light intensity at the specified time, record and save. When the sample temperature is significantly different from the measurement temperature, the sample needs to be adjusted to the experimental temperature in advance before being placed in the sample pool for measurement. If the temperature change increases and causes the liquid level to shift, re-measurement is required.
7.3.5 The measurement time can be set according to the stability of the sample. The light intensity change value must exceed 1%, and at least 3 data points must be taken.
7.4 Data Processing
Static multiple light scattering technology can be applied to measure the average equivalent diameter and concentration of particles in a dispersed system. Through signal processing, we can obtain:
a) Curves of backscattered light intensity BSI and transmitted light intensity TI changing with time; b) Curves of average particle diameter changing with time; c) Curves of concentration changing with time at a certain position of the sample d) Curves of particle migration speed changing with time; Curves of layer thickness changing with time; e)
f) Instability index Is calculated according to formula (5) or formula (6) When calculating the average particle size of particles in the sample. It is necessary to provide the refractive index of particles in the dispersed system and the refractive index of the continuous phase: It is necessary to use other methods to measure or obtain information from the sample preparer Volume concentration of particles in the dispersed phase Test report
The test report should include but not be limited to the following: GB/T38431—2019
Sample information:
Sample name and number.
Test information:
Name and model of the equipment used in the measurement system; the standard based on which the test is conducted;
Test temperature;
Test location;
Test date;
Test personnel.
Test results:
The sample height curve corresponding to the TI or BSI light intensity change value, the superposition of the light intensity curves at different times; the instability index Ius.
Note: Appendix C gives an example of a typical test report. 6
A.1 Measurement principle
Appendix A
(Informative Appendix)
Multiple light scattering (MLS) theory and measurement principle GB/T38431—2019
When a monochromatic light source is used to illuminate the sample, the particles in the sample scatter the light entering the sample. When the light is scattered multiple times with multiple particles in the sample during transmission, it is called multiple light scattering. When the particle concentration of the sample is low, part of the incident light will pass through the sample pool to form transmitted light (T); when the particle concentration is high, part of the incident light will be scattered by the particles and form backscattered light (BS), as shown in Figure A.1a). A scattered light spot can be observed on the surface of the sample pool, as shown in Figure A.1b). Light Lake
Backscattered Light (BS)
OCUCEN
Transmitted Light (T)
Figure A.1 Schematic Diagram of Backscattered Light Spot
Since the light intensity of the scattered light spot is related to the particle concentration and particle size in the sample, the instability information of the dispersed system can be obtained by analyzing the scattered light intensity at the overall height of the sample at different times, such as particle size change, precipitation and floating. Physical Model of Backscattering Theory
When light passes through a highly concentrated opaque sample, a backscattered light spot will be observed on the sample pool due to the backscattering of light. This backscattered light spot consists of two parts, as shown in Figure A.2. GB/T38431—2019
Long-path light
Short-path photons
Figure A.2 Backscattering physical model diagram
The bright part in the middle of the spot represents the scattered light moving over a short distance: that is, the light has been scattered less times with the particles in the medium before it is emitted from the medium.
The dark part outside the spot: represents the scattered light moving over a long distance: that is, the light has been scattered many times with the particles in the medium before it is emitted from the medium.
In the theory of diffuse wave spectroscopy, l is defined as the mean free path of photon transmission, and its size represents the degree of correlation between the transmission direction of light changed by multiple scattering in the sample and the initial incident direction. In this regard, the radius of the backscattered spot is about 4 times the value of 1. According to formula (A.1), the backscattered light intensity BSI can be measured to obtain 1: BSIo
..A.1)
From Mie theory, we know that the mean free path of photon transmission 1 is inversely proportional to the volume fraction Φ of the particles, and proportional to the particle size d. Therefore, the backscattered light intensity measured by the instrument is determined by the particle size and volume fraction of the system, as shown in formula (A,2): 1*(dp)=
Wherein, g and Q are the parameters given by Mie scattering [2]A.3 Physical model of transmitted light theory
3g（1-g）Q
......A.2)
The mean free path of photons represents the average distance of light transmission between two consecutive scatterings when multiple scattering occurs during the transmission process. The stronger the transmitted light passing through the measuring cell, the higher the value of the photon mean free path. In Figure A.3, the light intensity gradually weakens as the light beam passes through the sample cell. Figure A.3 Physical model of transmitted light theory2)
The photon mean free path represents the average distance that light travels between two consecutive scatterings when multiple scattering occurs during the transmission process. The stronger the transmitted light passing through the measuring cell, the higher the photon mean free path value. In Figure A.3, the light intensity gradually weakens as the light beam passes through the sample cell. Figure A.3 Physical model diagram of transmitted light theory2)
The photon mean free path represents the average distance that light travels between two consecutive scatterings when multiple scattering occurs during the transmission process. The stronger the transmitted light passing through the measuring cell, the higher the photon mean free path value. In Figure A.3, the light intensity gradually weakens as the light beam passes through the sample cell. Figure A.3 Physical model diagram of transmitted light theory
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