Method and device for measuring Zeta potential by cosine fitting technology

Abstract

The present invention relates to a method for measuring Zeta potential by cosine fitting technology, comprising the following steps: modulating reference light to generate a fixed frequency shift, applying an alternating square wave voltage to both ends of an electrophoresis electrode, causing the direction of the electric field between the two electrodes to change alternately, and causing charged particles in a dispersed system between the two electrodes to alternately perform uniform motion in a positive or negative direction, coherently superimposing scattered light of the particles with the modulated reference light, and converting the superimposed light beams into a series of electric signal strings after passing through a photoelectric detector, respectively calculating the average values ​​of autocorrelation functions under positive and negative electric fields, and then performing high-pass filtering and Hilbert transform processing, and finally performing cosine function fitting on the processed positive and negative autocorrelation function signals to obtain cosine angular frequency values ​​Ω" and Ω' of the positive and negative signals, and combining the two to calculate the movement speed of the particles, and finally obtaining the Zeta potential. The calculation method proposed by the present invention significantly improves the repeatability of Zeta potential testing, and its performance is significantly better than that of the existing measurement method.

Description

Technical Field

[0001] The invention relates to the field of Zeta potential measurement, and in particular to a method and a device for measuring Zeta potential by using a cosine fitting technique. Background Art

[0002] Zeta potential is an important indicator for characterizing the stability of a dispersed system. Electrophoretic light scattering (ELS) is an important Zeta potential test method and is widely used. The principle of electrophoretic light scattering is as follows: Figure 1 , the dispersed system is placed in a measuring cell 5, an upper electrode 7 and a lower electrode 11 are placed inside the cell, and the two electrodes are connected to the two output ends of the electrophoresis power supply 8, thereby generating a voltage difference, that is, an electric field exists between the two electrodes. The charged particles 10 in the dispersed system move under the action of the electric field, and the movement speed is proportional to the Zeta potential of the dispersed system. Now a beam of laser (illumination light) 9 is irradiated onto the particles 10, and the scattered light 13 generated by these particles will undergo a frequency shift, and the frequency shift amount is proportional to the movement speed of the particles, so as long as the frequency shift amount is measured, the Zeta potential can be calculated.

[0003] The basic idea of ​​measuring the frequency shift of scattered light is to introduce a frequency-shifted reference beam 2 (see Appendix Figure 1 ). The reference light and the illumination light 9 come from the same laser tube light source and pass through the optical modulator 3 to produce a modulated frequency shift. The scattered light 13 and the reference light 2 are coherently superimposed after passing through the beam combiner 14, and the superimposed light beam 15 is projected onto the photodetector 16 and converted into an electrical signal. By analyzing the electrical signal, the frequency shift of the scattered light can be obtained.

[0004] There are currently two methods for obtaining the frequency shift of scattered light: Fourier transform spectrum method (FFT) and phase analysis light scattering (PALS). The spectrum analysis method has a relatively low accuracy in measuring frequency shift due to the spectrum broadening caused by the random motion of particles. When the absolute value of the Zeta potential is small, or the effective electrophoretic electric field strength is low, or the electrophoretic electric field is applied for a very short time (for high conductivity samples), the test error of the Zeta potential will be large. Compared with the spectrum analysis method, the phase analysis method has effectively improved the measurement accuracy, but because the average value of the light scattering signal amplitude still has a large amplitude jitter within the limited measurement time, the measurement repeatability is still not ideal, and the repeatability deviation is approximately + / -10mV. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the deficiencies of the prior art and to provide a method and device for measuring Zeta potential by using a cosine fitting technique.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] Specifically, a method for measuring Zeta potential by cosine fitting technology is proposed, including the following:

[0008] Obtain an electrical signal string to be analyzed, wherein the electrical signal string is obtained in the following manner:

[0009] After the original reference light passes through the optical modulator, a fixed frequency shift Ω occurs; the electrophoresis voltage applied to the upper electrode and the lower electrode is a square wave with a fixed amplitude, that is, except for the moment when the direction of the electric field changes, the electric field strength between the upper and lower electrodes is constant. During this period, the charged particles move at a uniform speed between the upper and lower electrodes. The scattered light of the particles and the frequency-shifted modulated light are coherently superimposed after passing through the beam combiner. The intensity of the superimposed light beam is recorded as I(t). The superimposed light beam is irradiated onto the photodetector and becomes a randomly changing string of electrical signals. The string of signals obtained when the upper electrode is positive and the lower electrode is negative is defined as a positive signal, and vice versa as a negative signal; during the entire measurement process, the direction of the electric field alternates up and down for N cycles, and N strings of positive signals and N strings of negative signals are obtained;

[0010] Calculating the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal, including,

[0011] Calculate the autocorrelation function of each string of the signal to obtain N positive autocorrelation functions and N negative autocorrelation functions, calculate the average value of the N positive autocorrelation functions and the average value of the N negative autocorrelation functions, remove the low-frequency terms in the averaged positive correlation function and the negative correlation function respectively through digital high-pass filtering, and adjust the amplitudes of the cosine waveforms in the two filtered correlation functions to 1 respectively, and calculate through cosine function fitting to obtain the angular frequency of the positive signal as Ω" and the angular frequency of the negative signal as Ω';

[0012] The zeta potential ζ of the dispersed system is calculated based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal.

[0013] Further, specifically, based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal in the electrical signal string, the Zeta potential of the dispersed system is calculated, including:

[0014] The autocorrelation function of the superimposed light intensity is obtained through mathematical derivation.

[0015]

[0016] Where: τ is the autocorrelation delay time; I R is the intensity of the reference light; is the average intensity of scattered light; c is the instrument constant related only to scattered light; d is the instrument constant related to interference; q = k S -k I is the scattering vector, k S is the wave vector of scattered light, k I is the wave vector of the illumination light, and the modulus length of q is Where λ 0 is the wavelength of the incident light in vacuum, θ is the scattering angle, m is the refractive index of the dispersion medium; v is the speed of the particle in uniform linear motion, and the positive direction is defined as from bottom to top; Ω is the frequency shift of the reference light; β (1) (τ) is the autocorrelation function of the scattered light amplitude corresponding to the Brownian motion of the particle,

[0017] Since the first term of the autocorrelation function is a constant term, and the second term is a slow-changing term. In the actual measurement signal processing, both items can be removed by digital high-pass filtering, and the third item The amplitude varies with β (1) (τ) changes in the cosine oscillation function. In actual signal processing, its amplitude The algorithm is adjusted to 1, so the cosine function is obtained

[0018] cos[(Ω-qv)τ]

[0019] So for negative signals,

[0020] Ω'=Ω-qv e -qv c (2)

[0021] For the positive signal,

[0022] Ω”=Ω+qv e -qv c (3)

[0023] The directional motion velocity v of the particles consists of two parts. One is the electrophoretic migration of the particles under the action of the electric field, which is denoted as v. e The second is the particle movement caused by electroosmosis, thermal convection, sinking, etc., denoted as v c .

[0024] Further, specifically, based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal, the Zeta potential ζ of the dispersed system is calculated, including:

[0025] By rearranging equation (3) and equation (2), the electromigration (movement) velocity of the particles is:

[0026]

[0027] The electrophoretic mobility is:

[0028]

[0029] Where: E is the electric field strength, U is the potential difference between the upper and lower electrodes, i.e., the voltage, and d is the distance between the upper and lower electrodes;

[0030] The Zeta potential of the dispersed system is

[0031]

[0032] Where: ε is the dielectric constant, η is the medium viscosity, f(κa) is the Henry function, 1 / κ is the thickness of the double layer, i.e. the Debye length, and a is the radius of the particle.

[0033] Further, specifically, when zeta potential is measured in aqueous media and medium electrolyte concentration, the Smoluchowski approximation is used, and f(κa) is 1.5; for lower dielectric constant media in non-aqueous phases, the Hückel approximation is usually used, and f(κa) is 1.0.

[0034] The present invention also proposes a device for measuring Zeta potential by cosine fitting technology, comprising the following:

[0035] The reference light modulation module is used to make the original reference light produce a fixed frequency shift Ω, thereby converting it into a frequency-shifted reference light.

[0036] The electrical signal string acquisition module is used to acquire the electrical signal string to be analyzed, wherein the electrical signal string is acquired in the following manner:

[0037] Through the action of the reference light modulation module, the original reference light undergoes a fixed frequency shift Ω after passing through the light modulator, and the electrophoresis voltage applied to the upper electrode and the lower electrode is a square wave with a fixed amplitude, that is, except for the moment when the direction of the electric field is changed, the electric field strength between the upper and lower electrodes is constant. During this period, the charged particles move at a uniform speed between the upper and lower electrodes, and the scattered light of the particles and the frequency-shifted modulated light undergo coherent superposition after passing through the beam combiner. The superimposed light beam is irradiated onto the photodetector and becomes a randomly changing string of electrical signals. A string of signals obtained when the upper electrode is positive and the lower electrode is negative is defined as a positive signal, and vice versa, it is defined as a negative signal. During the entire measurement process, the direction of the electric field alternates up and down for N cycles, and N strings of positive signals and N strings of negative signals are obtained;

[0038] The cosine waveform angular frequency fitting module is used to calculate the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal, including:

[0039] Calculate the autocorrelation function of each string of the signal to obtain N positive autocorrelation functions and N negative autocorrelation functions, calculate the average value of the N positive autocorrelation functions and the average value of the N negative autocorrelation functions, remove the low-frequency terms in the averaged positive correlation function and the negative correlation function respectively through digital high-pass filtering, and adjust the amplitudes of the cosine waveforms in the two filtered correlation functions to 1 respectively, and calculate through cosine function fitting to obtain the angular frequency of the positive signal as Ω" and the angular frequency of the negative signal as Ω';

[0040] The Zeta potential calculation module calculates the Zeta potential ζ of the dispersed system based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal.

[0041] Further, specifically,

[0042] The fixed frequency shift of the original reference light is achieved by projecting the original reference light onto a reflector, and the uniform motion of the reflector causes a frequency shift of the reflected light;

[0043] The reflector is driven by a piezoelectric ceramic. At the moment when the electrophoretic electric field is first applied or the direction of the electrophoretic electric field changes, the piezoelectric driving power supply starts to pressurize the ceramic from 0, and the voltage increases linearly with time, so that the reflector moves at a uniform speed. At the moment when the direction of the electrophoretic voltage changes again, the ceramic driving voltage reaches the maximum, then immediately drops to 0, and pressurizes again from 0, and this cycle is repeated continuously for a total of 2N times;

[0044] During a period of time when the electrophoresis voltage remains constant and the reflector moves at a constant speed, the signal output by the photodetector is a series of signals.

[0045] The synchronous control module is used to realize the synchronous control of electrophoresis voltage, ceramic driving voltage and photoelectric signal sampling.

[0046] The present invention also proposes a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for measuring Zeta potential by cosine fitting technology as described in any one of the above items are implemented.

[0047] The beneficial effects of the present invention are:

[0048] The present invention modulates the original reference light to produce a fixed frequency shift, and applies an alternating square wave voltage at both ends of the electrophoresis electrode, so that the particles in the dispersed system to be tested alternately move at a uniform speed in a positive or negative direction (related to the charged polarity) under the action of the positive and negative electric fields, and the scattered light of the particles is coherently superimposed with the modulated reference light. The superimposed light beam is converted into a series of electrical signal strings after passing through a photoelectric detector, and the autocorrelation function of each string of signals is calculated, and then the autocorrelation function under the positive electric field and the autocorrelation function under the negative electric field are averaged respectively, and then the averaged positive and negative autocorrelation functions are high-pass filtered and Hilbert transformed, and finally the processed positive and negative autocorrelation function signals are fitted and calculated using a cosine function, respectively, to obtain the cosine angular frequency values ​​of the positive and negative signals, and the movement speed of the charged particles is calculated from the difference between the two, and finally the value of the Zeta potential is obtained. The technical method proposed by the present invention significantly improves the repeatability of the Zeta potential test, and the performance is significantly better than the existing measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0050] Figure 1 FIG. 1 is a schematic diagram of the structure of the entire measuring device used in the method for measuring Zeta potential by cosine fitting technology of the present invention;

[0051] Figure 2 It is a schematic diagram of a device (optical modulator) that uses piezoelectric ceramics to drive a reflector to move so as to cause a frequency shift of a reference light in one embodiment of a method for measuring Zeta potential by a cosine fitting technique of the present invention;

[0052] Figure 3 It is a schematic diagram of synchronous control of modulation signal, electrophoresis signal and data acquisition in one embodiment of the method for measuring Zeta potential by cosine fitting technology of the present invention;

[0053] Figure 4 Shown are positive (upper) and negative (lower) autocorrelation cosine waveforms actually measured and obtained in one embodiment of the method for measuring Zeta potential by cosine fitting technology of the present invention;

[0054] Figure 5 FIG. 1 is a schematic structural diagram of the entire measuring device of another embodiment of the method for measuring Zeta potential by using the cosine fitting technique of the present invention. DETAILED DESCRIPTION

[0055] The following will be combined with the embodiments and drawings to clearly and completely describe the concept, specific structure and technical effects of the present invention, so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other without conflict. The same reference numerals used throughout the drawings indicate the same or similar parts.

[0056] Reference Figure 1 , Embodiment 1, the present invention proposes a method for measuring Zeta potential by cosine fitting technology, comprising the following:

[0057] Obtain an electrical signal string to be analyzed, wherein the electrical signal string is obtained in the following manner:

[0058] After the original reference light passes through the optical modulator, a fixed frequency shift Ω occurs; the electrophoresis voltage applied to the upper electrode and the lower electrode is a square wave with a fixed amplitude (i.e., the voltage difference between the electrodes), that is, except for the moment when the direction of the electric field changes, the electric field strength between the upper and lower electrodes is constant. During this period, the charged particles move at a uniform speed between the upper and lower electrodes. The scattered light of the particles and the frequency-shifted modulated light are coherently superimposed after passing through the beam combiner. The superimposed light beam is irradiated onto the photodetector and becomes a randomly changing string of electrical signals. The string of signals obtained when the upper electrode is positive and the lower electrode is negative is defined as a positive signal, and vice versa as a negative signal. During the entire measurement process, the direction of the electric field alternates up and down for N cycles, and N strings of positive signals and N strings of negative signals are obtained.

[0059] Calculating the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal, including,

[0060] Calculate the autocorrelation function of each string of the signal to obtain N positive autocorrelation functions and N negative autocorrelation functions, calculate the average value of the N positive autocorrelation functions and the average value of the N negative autocorrelation functions, remove the low-frequency terms in the averaged positive correlation function and the negative correlation function respectively through digital high-pass filtering, and adjust the amplitudes of the cosine waveforms in the two filtered correlation functions to 1 respectively, and calculate through cosine function fitting to obtain the angular frequency of the positive signal as Ω" and the angular frequency of the negative signal as Ω';

[0061] The zeta potential ζ of the dispersed system is calculated based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal.

[0062] In this embodiment 1, the relevant structure of the entire measuring device used is as follows: Figure 1 As shown, its main components are introduced as follows:

[0063] 1——Data analysis device, which processes and analyzes the electrical signals detected by the photodetector, and finally calculates the value of the Zeta potential and outputs a test report. The device can be composed of a data acquisition card, a pulse counter, a correlator, a DSP, a computer and other components.

[0064] 2——Frequency-shifted reference light, that is, the laser beam obtained by modulating the original reference light split from the laser. Its frequency has changed relative to the frequency of the original laser beam, which is called frequency shift. It is used to interfere with scattered light.

[0065] 3——Optical modulator, a device used to modulate the reference light, which can be an acousto-optic modulator, an electro-optic modulator, a magneto-optic modulator, a piezoelectric ceramic-driven movable mirror, a current coil-driven movable mirror, various types of optical fiber modulators and other modulation devices, used to change the frequency of the reference light.

[0066] 4——The original reference light, that is, a beam of laser light emitted from a laser (which can be a semiconductor laser, He-Ne laser, solid-state frequency-doubled laser, etc.) and split by a beam splitter, will be used as a reference light to interfere with the scattered light after modulation.

[0067] 5——Measuring pool, a container for holding the sample to be tested, which can be a cuvette or other transparent container, and its making material can be glass, plastic, etc.

[0068] 6——Synchronous control module, used to control the synchronous conversion of the modulation signal of the optical modulator and the electrophoresis voltage.

[0069] 7 - Upper electrode, one of the electrodes inserted in the measuring cell, Figure 1 It is located above the measuring cell and is used in conjunction with the lower electrode.

[0070] 8——Electrophoresis power supply, providing the electrophoresis voltage required for the upper and lower electrodes.

[0071] 9——Illumination light, that is, a beam of laser emitted from a laser (which can be a semiconductor laser, He-Ne laser, solid-state frequency-doubled laser, etc.) and obtained after being split by a beam splitter, is used to irradiate the sample to be tested.

[0072] 10 – Charged particles, which are particles in the dispersed system to be measured.

[0073] 11——Lower electrode, one of the electrodes inserted into the solution in the measuring cell, used in conjunction with the upper electrode.

[0074] 12——Scattering angle, the angle between the scattered light hitting the beam combiner and the direction of the illumination light.

[0075] 13——Scattered light. When the illumination light hits the charged particles in the sample, light scattering occurs. The light scattered at this time is called scattered light.

[0076] 14——Beam combiner, used to combine the scattered light and the reference light in space and propagation direction, so that the two beams of light are combined into one beam of light, at which time the scattered light and the reference light interfere with each other.

[0077] 15--Superimposed beam: The beam formed by the scattered light and the reference light after passing through the beam combiner.

[0078] 16——Photodetector, used to convert the received optical signal into an electrical signal for subsequent signal processing, which can be a photomultiplier tube, avalanche tube, high-speed photodiode, etc.

[0079] The main process of the device in the present method is as follows: the laser beam emitted from the laser (not shown in the figure) is split to obtain reference light and illumination light. The reference light undergoes frequency shift after modulation, which is called frequency-shifted reference light. The scattered light generated by the frequency-shifted reference light and illumination light irradiating the moving particles interferes with each other. The optical signal is converted into an electrical signal by a photodetector, and the cosine frequency value can be accurately obtained by digital processing and fitting calculation using cosine fitting technology, thereby obtaining the moving speed of the charged particles and finally calculating the value of the Zeta potential.

[0080] Specifically, in one embodiment, a movable reflector driven by piezoelectric ceramics (see attached Figure 2 ) as an example to illustrate the test working process of the system. The optical modulator consists of a piezoelectric ceramic body 3-6, electrodes 3-1 and 3-5 at both ends of the ceramic body, a reflector 3-4 and a piezoelectric driving power supply 3-2. The reflector is pasted on one end of the ceramic and can move back and forth following the expansion and contraction of the ceramic. The amount of expansion of the ceramic is proportional to the voltage applied to it, so the displacement of the reflector can be controlled by changing the voltage applied to the piezoelectric ceramic. If the voltage changes linearly with time, the reflector on the piezoelectric ceramic will move at a uniform speed, and the frequency of the reflected light 2 will change, becoming a frequency-shifted reference light. Figure 2 As shown in Figure 2, when the reflector is moved from left to right at a speed of v, if the incident angle of the reference light is α and the wavelength of the light is λ o , then the frequency shift of the reflected light is

[0081]

[0082] Among them, 3-1 is the piezoelectric ceramic negative electrode; 3-2 is the piezoelectric driving power supply; 3-3 is the light incident angle; 3-4 is the reflector; 3-5 is the piezoelectric ceramic positive electrode; 3-6 is the ceramic body;

[0083] The driving voltage applied to the piezoelectric ceramic is Figure 3The sawtooth wave (the "modulation voltage" in the figure) is shown. Under the action of this voltage, the reflector first moves from left to right at a constant speed, and after reaching a certain displacement, it instantly returns to the origin, and then moves from left to right at a constant speed, and so on. The electrophoresis voltage applied between the two electrophoresis electrodes is a square wave that continuously switches direction. The synchronization relationship between the electrophoresis voltage, the piezoelectric ceramic voltage, and the signal sampling is shown in Figure 3 As shown. In one alternating cycle of the electrophoresis voltage, the reflector moves back and forth twice and collects two strings of signals. The signal obtained when the electrophoresis voltage is positive (positive on the electrode and negative on the bottom) is called a "positive signal", and vice versa, it is called a "negative signal". Assuming that a total of N electric field alternating cycles are measured, the computing device 1 obtains N strings of positive signals and N strings of negative signals.

[0084] After the data is processed by the data analysis device 1, the processing process is as follows:

[0085] Step 1, calculating the autocorrelation function of each string of forward signals to obtain N forward autocorrelation functions;

[0086] Step 2, calculating the average value of N forward autocorrelation functions to obtain an averaged correlation function;

[0087] Step 3, remove the low-frequency terms in the averaged correlation function through digital high-pass filtering;

[0088] Step 4: adjust the amplitude of the cosine signal to 1 through Hilbert transform or other algorithms with similar functions;

[0089] Step 5: Use the cosine function to fit the angular frequency Ω" of the forward signal;

[0090] Step 6: Calculate the angular frequency Ω' of the negative signal by following steps 1) to 5);

[0091] Step 7: Calculate the Zeta potential ζ of the dispersed system according to formulas (4) and (5).

[0092] As a preferred embodiment of the present invention, specifically, the zeta potential is calculated based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal in the electrical signal string, including:

[0093] Calculate the particle electrophoresis velocity v e ,

[0094]

[0095] Calculate the electric mobility μ e :

[0096]

[0097] Among them, U is the potential difference between the two ends of the electrode (i.e., the amplitude of the electrophoresis voltage square wave), and d is the distance between the two electrodes.

[0098] Calculate the Zeta potential ζ of a dispersed system:

[0099]

[0100] Among them, ε is the dielectric constant, η is the medium viscosity, f(κa) is the Henry function, 1 / κ is the thickness of the double layer, i.e. the Debye length, and a is the radius of the particle.

[0101] As a preferred embodiment of the present invention, specifically, when the zeta potential is measured in an aqueous medium and a medium electrolyte concentration, the Smoluchowski approximation is used, and f(κa) is 1.5; for small particles in a non-aqueous phase with a lower dielectric constant medium, the Hückel approximation is usually used, and f(κa) is 1.0. In this preferred embodiment, two commonly used f(κa) function values ​​are given, and there may be other values ​​in other cases, depending on the specific situation.

[0102] As a preferred embodiment of the present invention, specifically, the amplitude of the cosine signal in the averaged correlation function is adjusted to 1 through Hilbert transform. Preferably, the Hilbert transform algorithm can be well suitable for the related operation of adjusting the amplitude of the cosine signal in the averaged correlation function to 1 in this solution, and of course other related algorithms that can achieve the same purpose are also possible.

[0103] As a preferred embodiment of the present invention, specifically, the least square method, gradient descent algorithm, Chahine iterative algorithm or any one of the Levenberg-Marquardt algorithms are used to perform cosine function fitting with the goal of minimizing the fitting residual, and find the corresponding cosine function angular frequency. Preferably, the cosine function fitting can be performed by the above-mentioned related algorithms, and of course other cosine function fitting algorithms applicable to the present method are also possible.

[0104] After the above steps of experiment, the data show that the autocorrelation cosine waveform measured by the device is very stable (such as Figure 4 As shown in the figure, the cosine fitting technique can be used to calculate the accurate angular frequency of the cosine function, and then calculate the frequency shift value of the particles under the action of the electric field, so as to achieve accurate measurement of the sample's Zeta potential. Cosine fitting technology is a new measurement technology that significantly improves the repeatability of Zeta potential testing. The repeatability deviation can reach + / -2mV, which is significantly better than Fourier transform spectrum method and phase analysis light scattering method.

[0105] Embodiment 2, the present invention also proposes a device for measuring Zeta potential by cosine fitting technology, see attached Figure 5 . Including the following:

[0106] The illumination light 9 is incident on the measuring cell from right to left at a certain angle and passes through the center of the measuring cell 5. The reference light 2 is incident on the measuring cell 5 from right to left from another inclined direction and also passes through the center of the measuring cell. The trajectories of the reference light and the illumination light in the measuring cell are symmetrical to each other, and the angle 12 is θ. The scattered light 13 of the particle is received by the detector 16. At this time, the scattering generated by the illumination light and the reference light are superimposed on each other to produce interference. The cosine variation characteristics of the superimposed beam are similar to the Figure 1 The acquisition and processing of the electric signal string, the fitting method of the cosine function angular frequency, etc. are the same as those in Example 1, with the slight difference being the particle electrophoresis velocity calculation formula, which is changed from formula (4) to

[0107]

[0108] Embodiment 3, the present invention also proposes a device for measuring Zeta potential by cosine fitting technology, comprising the following:

[0109] The reference light modulation module is used to make the reference light generate a fixed frequency shift Ω, thereby converting it into a frequency-shifted reference light.

[0110] The electrical signal string acquisition module is used to acquire the electrical signal string to be analyzed, wherein the electrical signal string is acquired in the following manner:

[0111] The reference light modulation module is used to make the reference light undergo a fixed frequency shift Ω; the electrophoresis voltage applied to the upper electrode and the lower electrode is a square wave with a constant amplitude, that is, except for the moment when the direction of the electric field is changed, the electric field strength between the upper and lower electrodes is constant. During this period, the charged particles move at a uniform speed between the upper and lower electrodes, and the scattered light of the particles and the frequency-shift modulated light are coherently superimposed after passing through the beam combiner. The intensity of the superimposed light beam is recorded as I(t). The superimposed light beam is irradiated onto the photodetector and becomes a randomly changing string of electrical signals. A string of signals obtained when the upper electrode is positive and the lower electrode is negative is defined as a positive signal, and vice versa, it is defined as a negative signal. During the entire measurement process, the direction of the electric field alternates up and down for N cycles, and N strings of positive signals and N strings of negative signals are obtained;

[0112] The cosine waveform angular frequency fitting module is used to calculate the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal, including:

[0113] Calculate the autocorrelation function of each string of the signal to obtain N positive autocorrelation functions and N negative autocorrelation functions, calculate the average value of the N positive autocorrelation functions and the average value of the N negative autocorrelation functions, remove the low-frequency terms in the averaged positive correlation function and the negative correlation function respectively through digital high-pass filtering, and adjust the amplitudes of the cosine waveforms in the two filtered correlation functions to 1 respectively, and calculate through cosine function fitting to obtain the angular frequency of the positive signal as Ω" and the angular frequency of the negative signal as Ω';

[0114] The Zeta potential calculation module is used to calculate the Zeta potential ζ of the dispersed system based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal.

[0115] In this embodiment 2, a device corresponding to the method process in the present invention is proposed. When applied, as long as the relevant functional modules in this embodiment 2 are integrated into the data analysis device 1, the corresponding operation can be completed to complete the calculation of the Zeta potential of the dispersed system.

[0116] The present invention also proposes a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for measuring Zeta potential by cosine fitting technology as described in any one of the above items are implemented.

[0117] The modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution in this embodiment.

[0118] In addition, each functional module in each embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of software functional modules.

[0119] If the integrated module is implemented in the form of a software function module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0120] Although the description of the present invention has been quite detailed and specifically describes several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, but should be regarded as providing a broad possible interpretation of these claims in view of the prior art by reference to the appended claims, thereby effectively covering the intended scope of the present invention. In addition, the above description of the present invention is based on the embodiments foreseeable by the inventor, and its purpose is to provide a useful description, and those non-substantial changes to the present invention that have not yet been foreseen may still represent equivalent changes to the present invention.

[0121] The above is only a preferred embodiment of the present invention. The present invention is not limited to the above implementation. As long as the technical effect of the present invention is achieved by the same means, it should belong to the protection scope of the present invention. Within the protection scope of the present invention, its technical scheme and / or implementation method can have various modifications and changes.

Claims

1. A method for measuring Zeta potential by cosine fitting technique, characterized in that: Includes the following: Obtain an electrical signal string to be analyzed, wherein the electrical signal string is obtained in the following manner: After the original reference light passes through the optical modulator, a fixed frequency shift Ω occurs. The electrophoretic voltage applied to the upper electrode and the lower electrode is a square wave with a constant amplitude, that is, except for the moment when the direction of the electric field changes, the electric field strength between the upper and lower electrodes is constant. During this period, the charged particles move at a uniform speed between the upper and lower electrodes. The scattered light of the particles and the frequency-shifted modulated light are coherently superimposed after passing through the beam combiner. The superimposed light beam is irradiated onto the photodetector and becomes a randomly changing string of electrical signals. The string of signals obtained when the upper electrode is positive and the lower electrode is negative is defined as a positive signal, and vice versa as a negative signal. During the entire measurement process, the direction of the electric field alternates up and down for N cycles, and N strings of positive signals and N strings of negative signals are obtained. Calculating the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal includes, Calculate the autocorrelation function of each string of the signal to obtain N positive autocorrelation functions and N negative autocorrelation functions, calculate the average value of the N positive autocorrelation functions and the average value of the N negative autocorrelation functions, remove the low-frequency terms in the averaged positive correlation function and the negative correlation function respectively through digital high-pass filtering, and adjust the amplitudes of the cosine waveforms in the two filtered correlation functions to 1 respectively, and calculate through cosine function fitting to obtain the angular frequency of the positive signal as Ω" and the angular frequency of the negative signal as Ω'; The zeta potential ζ of the dispersed system is calculated based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal.

2. The method for measuring Zeta potential by cosine fitting technology according to claim 1, characterized in that: Specifically, based on the angular frequency Ω″ of the positive signal and the angular frequency Ω′ of the negative signal in the electrical signal, the Zeta potential of the dispersed system is calculated, including: Calculate the particle electromigration velocity v e , Where λ0 is the laser wavelength in vacuum, θ is the light scattering angle, and m is the refractive index of the dispersion medium. Calculate the electrophoretic mobility μ e : Where E is the electric field strength, U is the potential difference between the upper and lower electrodes, i.e., the voltage, and d is the distance between the upper and lower electrodes; Calculate the Zeta potential ζ of the dispersed system, Among them, ε is the dielectric constant of the dispersion medium, η is the medium viscosity, f(κa) is the Henry function, 1 / κ is the thickness of the double layer, i.e., the Debye length, and a is the radius of the particle.

3. The method for measuring Zeta potential by cosine fitting technology according to claim 2, characterized in that: Specifically, when zeta potential is measured in aqueous media and medium electrolyte concentrations, the Smoluchowski approximation is used, and f(κa) is 1.5; for small particles in non-aqueous phases with lower dielectric constant media, the Hückel approximation is usually used, and f(κa) is 1.

0.

4. The method for measuring Zeta potential by cosine fitting technology according to claim 1, characterized in that: Specifically, the amplitude of the cosine signal in the averaged forward and reverse autocorrelation functions is adjusted to 1 through Hilbert transform.

5. The method for measuring Zeta potential by cosine fitting technology according to claim 1, characterized in that: Specifically, any one of the least squares method, gradient descent algorithm, Chahine iterative algorithm or Levenberg-Marquardt algorithm is used to perform cosine function fitting with the goal of minimizing the fitting residual, and the angular frequencies of the cosine functions in the positive signal and the negative signal are respectively found.

6. A device for measuring zeta potential by cosine fitting technique, characterized in that: Includes the following: The reference light modulation module is used to make the original reference light produce a fixed frequency shift Ω, thus becoming a frequency-shifted reference light; The electrical signal string acquisition module is used to acquire the electrical signal string to be analyzed, wherein the electrical signal string is acquired in the following manner: Through the reference light modulation module, the original reference light undergoes a fixed frequency shift Ω after passing through the light modulator, and the electrophoresis voltage applied to the upper electrode and the lower electrode is a square wave with a constant amplitude, that is, except for the moment when the direction of the electric field is changed, the electric field strength between the upper and lower electrodes is constant. During this period, the charged particles move at a uniform speed between the upper and lower electrodes, and the scattered light of the particles and the frequency-shifted modulated light undergo coherent superposition after passing through the beam combiner. The superimposed light beam is irradiated onto the photodetector and becomes a randomly changing string of electrical signals. A string of signals obtained when the upper electrode is positive and the lower electrode is negative is defined as a positive signal, and vice versa, a negative signal. During the entire measurement process, the direction of the electric field alternates up and down for N cycles, and N strings of positive signals and N strings of negative signals are obtained. The cosine waveform angular frequency fitting module is used to calculate the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal, including: Calculate the autocorrelation function of each string of the signal to obtain N positive autocorrelation functions and N negative autocorrelation functions, calculate the average value of the N positive autocorrelation functions and the average value of the N negative autocorrelation functions, remove the low-frequency terms in the averaged positive correlation function and the negative correlation function respectively through digital high-pass filtering, and adjust the amplitudes of the cosine waveforms in the two filtered correlation functions to 1 respectively, and calculate through cosine function fitting to obtain the angular frequency of the positive signal as Ω" and the angular frequency of the negative signal as Ω'; The Zeta potential calculation module is used to calculate the Zeta potential ζ of the dispersed system based on the angular frequency Ω" of the positive signal and the angular frequency Ω' of the negative signal.

7. The device for measuring Zeta potential by cosine fitting technology according to claim 6, characterized in that: Specifically, The fixed frequency shift of the original reference light is achieved by projecting the original reference light onto a reflector, and the uniform motion of the reflector causes a frequency shift of the reflected light; The reflector is driven by a piezoelectric ceramic. At the moment when the electrophoretic electric field is first applied or the direction of the electrophoretic electric field changes, the piezoelectric driving power supply starts to pressurize the ceramic from 0, and the voltage increases linearly with time, so that the reflector moves at a uniform speed. At the moment when the direction of the electrophoretic voltage changes again, the ceramic driving voltage reaches the maximum, then immediately drops to 0, and pressurizes again from 0, and this cycle is repeated continuously for a total of 2N times; In any period of time when the electrophoresis voltage keeps increasing and the reflector moves at a uniform speed, the signal output by the photodetector is a series of signals. The synchronous control module is used to realize the synchronous control of electrophoresis voltage, ceramic driving voltage and photoelectric signal sampling.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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