Surfactant adsorption behavior detection system based on oblique incident light reflection difference technology

Abstract

The invention relates to the technical field of photoelectric detection, and provides a surfactant adsorption behavior detection system based on an oblique incident light reflection difference technology, which comprises a laser, a polarizer, a photoelastic modulator, a phase shifter, a first lens, a sample table, a second lens, an analyzer, a photoelectric detector, a first lock-in amplifier, a second lock-in amplifier and a computer, the laser emits probe light which is changed into p polarized light through the polarizer; the light is modulated into p polarized light and s polarized light by the photoelastic modulator; the p polarized light and the s polarized light are emitted alternately, and a phase shifter generates a fixed phase difference between the p polarized component and the s polarized component; the light is focused by the first lens and obliquely enters the surface of a sample on the sample table; the laser reflected from the surface of the sample passes through the second lens, then enters the polarization analyzer, is received by the photoelectric detector and is converted into an electric signal; and the fundamental frequency signal and the frequency multiplication signal are recorded by the computer. According to the method, the adsorption process, the adsorption state and other properties of the surfactant can be analyzed.

Description

Technical Field

[0001] The invention relates to the technical field of photoelectric detection, and in particular to a surfactant adsorption behavior detection system based on oblique incident light reflection difference technology. Background Art

[0002] The study of the interfacial adsorption behavior of surfactants has always been one of the important topics in the fields of physics, chemistry and engineering, and has an important impact on the application of surfactants in the fields of chemical engineering, biomedicine, materials science, etc. The interaction of interfacial molecules is a hot issue in many fields such as petroleum. Surfactants with amphiphilic structures can be adsorbed on the surface of liquids to reduce the surface tension of liquids. Due to this characteristic, surfactants are widely used in improving oil recovery in oil fields. The displacement efficiency of surfactants is an important indicator in the process of residual oil displacement. Factors such as surfactant type, molecular density, and cluster structure have a great influence on its performance. During the displacement process, surfactant molecules will undergo physical and chemical changes such as micelle dissociation, diffusion, adsorption, and desorption. Therefore, detecting the molecular behavior of surfactant molecules during dynamic adsorption helps to fundamentally understand the dynamic adsorption characteristics of surfactants in different time and space, thereby improving oil recovery, and will provide a reference for designing new surfactants and optimizing the application of surfactants in tertiary oil recovery.

[0003] From a microscopic perspective, the essence of surfactants in reducing interfacial tension is to change the density, cluster structure and distribution of molecules on the interface. Surfactant solutions can only significantly reduce interfacial tension when the concentration is lower than the critical micelle concentration (CMC). Within this concentration range, surfactant molecules are arranged on the interface in a single molecule state. It can be seen that the research object is the molecules arranged on the nanoscale interface or the nanoscale spherical micelles in the solution. This is a challenge to current research methods. For example, molecular simulation can simulate the adsorption process of molecules, but on the one hand, certain assumptions must be made about the experimental conditions; on the other hand, due to the limitation of computing power, a large number of interactions between molecules are difficult to calculate. For atomic force microscopy (AFM), it can detect the molecular arrangement, density and other parameters of the surface, but it is difficult to detect surfactant molecules between the oil and water interface. In addition, given the complexity of surfactant types and adsorption behaviors, various characterization techniques have their own advantages and disadvantages. When exploring the adsorption state at the interface during the surfactant adsorption process and the micelle morphology formed in the solution, more microscopic techniques need to be combined. Summary of the invention

[0004] The present invention mainly solves the technical problems existing in the current characterization technology of surfactant adsorption behavior, such as contact measurement, macroscopic detection, low precision, and inability to measure in real time. A surfactant adsorption behavior detection system based on oblique incident light reflection difference technology is proposed, which has the characteristics of microscopic real-time detection, low cost, high precision, and non-contact measurement, and can analyze the properties such as the surfactant adsorption process and adsorption state.

[0005] The present invention provides a surfactant adsorption behavior detection system based on oblique incident light reflection difference technology, comprising: a laser, a polarizer, a photoelastic modulator, a phase shifter, a first lens, a sample stage, a second lens, an analyzer, a photodetector, a first lock-in amplifier, a second lock-in amplifier and a computer;

[0006] The photoelectric detector is connected to the first lock-in amplifier and the second lock-in amplifier respectively; the first lock-in amplifier is connected to the first acquisition card signal, and the second lock-in amplifier is connected to the second acquisition card signal; the first acquisition card and the second acquisition card are connected to the computer signal;

[0007] The laser emits a detection light, which is converted into p-polarized light by a polarizer and modulated into p-polarized light and s-polarized light by a photoelastic modulator;

[0008] The p-polarized light and the s-polarized light are emitted alternately, and a fixed phase difference is generated between the p-polarized component and the s-polarized component by a phase shifter; and then the p-polarized light is focused by a first lens and incident obliquely onto the sample surface on the sample stage;

[0009] The laser reflected from the sample surface passes through the second lens and then enters the analyzer, where it is then received by the photodetector and converted into an electrical signal.

[0010] The first lock-in amplifier measures the baseband signal, the second lock-in amplifier measures the multiplied frequency signal, and the computer records the baseband signal and the multiplied frequency signal;

[0011] The computer performs surfactant adsorption behavior analysis based on the recorded fundamental frequency signal and frequency doubling signal.

[0012] Preferably, the laser is a He-Ne laser with a wavelength of 632.8 nm.

[0013] Preferably, the polarizer and analyzer are Glan Taylor prisms with an extinction ratio of 500:1.

[0014] Preferably, the phase shifter is a Pockel cell, a half-wave plate or a quarter-wave plate.

[0015] Preferably, the photodetector is a photodiode.

[0016] Preferably, the computer performs surfactant adsorption behavior analysis based on the recorded fundamental frequency signal and frequency doubling signal, including the following process:

[0017] Calculate the light intensity I received by the photodetector photodiode :

[0018] I photodiode =I dc +I(Ω)sinΩt+I(2Ω)cos2Ωt (1)

[0019] In the formula, I photodiode is the signal received by the photodetector; I dc is a DC signal; I(Ω) is a baseband signal; I(2Ω) is a frequency-multiplied signal; Ω is the modulation frequency, in Hz; t is the modulation time, in s;

[0020] The DC signal, baseband signal, and frequency-multiplied signal can be approximated as follows:

[0021] I dc ≈I 0 |r p 2 cos 2 α(2)

[0022] I(Ω)≈2I 0 |r p 2 cos 2 αIm{Δp-Δs}J 1 (A)(3)

[0023] I(2Ω)≈2I 0 |r p 2 cos 2 αRe{Δp-Δs}J 2 (A)(4)

[0024] In the formula, I 0 is the initial incident light intensity; α is the polarization angle, the unit is rad; J 1 (A) is the first-order Bessel function, J 2 (A) are the second-order Bessel functions, r p is the reflectivity of the sample to be tested to p-polarized light, r s is the reflectivity of the sample to be tested for s-polarized light; Δp-Δs is the reflection difference of oblique incident light, Im{Δp-Δs} is the imaginary part of the reflection difference of oblique incident light; Re{Δp-Δs} is the real part of the reflection difference of oblique incident light;

[0025] From formula (2), formula (3) and formula (4), it can be obtained that the imaginary part of the oblique incident light reflection difference Δp-Δs is:

[0026]

[0027] The real part of the reflection difference Δp-Δs of oblique incident light is:

[0028]

[0029] It can be seen from formula (5) and formula (6) that the imaginary signal of the reflection difference of the oblique incident light is proportional to the detected fundamental frequency signal. Similarly, the real signal of the reflection difference of the oblique incident light is proportional to the double frequency signal of the received light intensity.

[0030] From the Fresnel formula, we know that different objects have different reflectivity for p-polarized light and s-polarized light. When the surface properties change, the reflection difference Δp-Δs of the oblique incident light will also be different. Its definition is:

[0031]

[0032] In the formula, r p0 is the initial state reflectivity of p-polarized light, r s0 is the initial state reflectivity of s-polarized light, r p is the reflectivity of p-polarized light after the surface properties change, r s is the reflectivity of s-polarized light after the surface properties change;

[0033] The three-layer medium model of air-surfactant adsorption interface layer-water / oil is introduced to analyze the OIRD signal, and the air is determined as the upper layer of the medium model, the surfactant adsorption interface layer is the medium layer, and the water or crude oil is the base layer;

[0034] The reflection difference of oblique incident light in the dielectric layer Δp-Δs can be expressed as:

[0035]

[0036] Where λ is the wavelength of incident light, in nm; ε 0 is the relative dielectric constant of the air layer; ε d is the relative dielectric constant of the dielectric layer; ε s is the relative dielectric constant of the substrate layer; d is the thickness of the dielectric layer, nm; is the angle of incidence, in rad;

[0037] Therefore, after measuring the DC signal, baseband signal, and frequency-multiplied signal, the relative dielectric constant ε of the dielectric layer can be calculated according to formula (5), formula (6), and formula (8): d and thickness d; further, according to formula (8), the adsorption process and adsorption state of the surfactant can be analyzed.

[0038] The surfactant adsorption behavior detection system based on oblique incident light reflection difference technology provided by the present invention has the following advantages compared with the prior art:

[0039] 1. Low cost: Compared with electron microscopes, CT and traditional optical technologies, the technology based on oblique incident light reflection difference (OIRD) requires fewer optical devices, has a simple optical path structure, occupies less space, is easy to install, move and maintain, and has lower operating and maintenance costs, which greatly reduces the cost of detecting surfactant adsorption behavior.

[0040] 2. Non-contact: OIRD detects sample surface information by detecting the difference in the relative changes in the reflectivity of the s- and p-polarized components of the probe light on the sample surface, thus achieving label-free and contactless detection of surfactants.

[0041] 3. Real-time dynamic microscopic detection: Adsorption behavior characterization methods represented by surface tension method can only detect changes in solution properties from a macroscopic perspective, but cannot analyze the state of molecular aggregation from a microscopic perspective. The method of the present invention can carry more microscopic information, detect the dynamic adsorption process of surfactants in real time, and reveal the adsorption behavior of interface molecules from a microscopic perspective.

[0042] 4. High sensitivity and high accuracy: OIRD technology introduces a device for background noise zeroing (phase shifter, polarization analyzer). Compared with traditional polarization modulation ellipsometers, OIRD technology has higher sensitivity. Under the condition of oblique laser incidence, the reflectivity of the material surface to s and p polarized light is different. When the incident angle is constant, the reflectivity is very sensitive to the dielectric constant or thickness change of the sample surface layer, and the changes in the composition, structure, density, etc. of the surface / interface will directly affect these two parameters. Therefore, OIRD technology, as an emerging optical technology, can realize high-precision real-time detection of interface information. It is a label-free, real-time, non-destructive optical detection method that can track the adsorption process of surfactants in real time and dynamically capture its behavior changes, providing accurate data for adsorption characteristics research. Based on the OIRD detection results, microscopic information such as the molecular adsorption state and micelle formation on the interface layer can be inferred, which has unique advantages in the study of the adsorption behavior of surfactant molecules. The detection accuracy of this technology in the direction perpendicular to the interface can reach the nanometer level, and the detection accuracy is extremely high, so it can be used to detect the adsorption behavior of surfactant molecules at the oil / gas interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the arrangement of a surfactant adsorption behavior detection system based on the oblique incident light reflection difference technology provided by the present invention;

[0044] Figure 2It is a schematic diagram of the detection process of the surfactant adsorption behavior detection system based on the oblique incident light reflection difference technology provided by the present invention;

[0045] Figure 3 It is a schematic diagram of the three-layer medium model of air-adsorption interface layer-water body / oil established by the present invention;

[0046] Figure 4 This is the OIRD test result diagram of the dynamic adsorption process of surfactant molecules;

[0047] Figure numerals: 1. laser; 2. polarizer; 3. photoelastic modulator; 4. phase shifter; 5. first lens; 6. sample stage; 7. second lens; 8. analyzer; 9. photodetector; 10. first phase-locked amplifier; 11. second phase-locked amplifier; 12. computer. DETAILED DESCRIPTION

[0048] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all the contents.

[0049] like Figure 1-2 As shown, the surfactant adsorption behavior detection system based on the oblique incident light reflection difference technology provided by an embodiment of the present invention includes: a laser 1, a polarizer 2, a photoelastic modulator 3, a phase shifter 4, a first lens 5, a sample stage 6, a second lens 7, an analyzer 8, a photodetector 9, a first phase-locked amplifier 10, a second phase-locked amplifier 11 and a computer 12.

[0050] The present invention is based on the oblique incident light reflection difference technology, utilizes the p and s polarization state modulation technology, and acquires the information of the target object by analyzing the optical signal, so the light source is required to have good linear polarization characteristics.

[0051] During the adsorption process of the sample (surfactant), the laser 1 emits a detection light. Specifically, this embodiment uses a laser with a wavelength of λ=632.8nm emitted by a helium-neon laser as the detection light; the detection light is converted into p-polarized light by the polarizer 2; and is modulated into p-polarized light and s-polarized light by the photoelastic modulator 3, with a modulation frequency of 50kHz.

[0052] The p-polarized light and the s-polarized light are emitted alternately, and a fixed phase difference is generated between the p-polarized component and the s-polarized component by the phase shifter 4; then the light is focused by the first lens 5 and incident obliquely onto the sample surface on the sample stage 6, and the incident angle is equal to the Brewster angle. At this time, the reflectivity of the p-polarized light and the s-polarized light differs greatly.

[0053] The laser reflected from the sample surface passes through the second lens 7 and then enters the polarizer 8, and is then received by the photodetector 9 and converted into an electrical signal;

[0054] The first lock-in amplifier 10 measures the base frequency signal, the second lock-in amplifier 11 measures the double frequency signal, and the computer 12 records the base frequency signal and the double frequency signal of the sample adsorption process.

[0055] In the above scheme, the oblique incident light reflection difference method is based on the difference of the change amount of the p and s polarization components for detection, so the light source is required to have good linear polarization characteristics. Therefore, the present invention uses a linear polarization laser source with a continuous wavelength, and the laser 1 uses a He-Ne laser with a wavelength of 632.8nm. Generally, in order to make full use of the output energy of the laser, the resonant cavity of the laser 1 is rotated so that the polarization direction of the emitted linear polarized light is kept consistent with the transmission direction of the polarizer 2 as much as possible.

[0056] The function of the polarizer 2 is to ensure that the emitted light is linearly polarized and its polarization direction is in the same direction as the optical axis of the polarizer 2. By rotating the polarizer 2, the emitted linearly polarized light is incident in the p polarization direction, which refers to the direction parallel to the incident plane formed by the incident light and the interface normal. When the incident light passes through the polarizer orthogonal to the p polarization direction and extinction occurs or the light intensity is the weakest, it can be ensured that the laser 1 is incident with p polarized light. The polarizer 2 used is made of two calcite cuboids cut along the diagonal edges and adhered together with a certain thickness of air layer. Its working principle is that when a light beam containing both p and s polarization states is incident perpendicular to the surface, due to the difference in refractive index, the critical angles of the p and s polarization states are different when the light is totally reflected from the calcite to the air medium for the first time. The cutting angle is selected between the two critical angles, so that the light in one polarization direction deviates from the main light path in the form of total reflection, and the light in the other polarization direction is emitted in the main light path through transmission. The linearly polarized light is ensured to be incident in the p-polarization direction (the electric vector direction is parallel to the incident plane formed by the incident light and the interface normal) by rotating the transmission axis of the polarizer 2. In this embodiment, the polarizer 2 is a Glan Taylor prism with an extinction ratio of 500:1.

[0057] The photoelastic modulator 3 modulates the incident polarized light and is used to modulate and change the polarization state of the light beam at a fixed frequency. The photoelastic modulator 3 is composed of a photoelastic crystal, a controller and electrical components to achieve conversion modulation between p and s polarization states, and the modulation frequency is 50kHz. The working principle of the photoelastic modulator (PEM) 3 is like a "dynamic wave plate", which can produce a periodically changing refractive index difference between the fast axis and the slow axis, thereby controlling the periodic change of the polarization of the transmitted light beam. Specifically, when the linearly polarized light passes through the photoelastic crystal, it is incident at a 45° angle to its modulation axis. When the crystal is not affected by external force, the polarization state of the incident light will not change after passing through the crystal; when the crystal is stretched by external force, the propagation speed of the linear polarization component parallel to the crystal modulation axis will be slower than the propagation speed of the vertical component, that is, the parallel component "lags behind" the vertical component. When the crystal is squeezed by external force, the polarization component parallel to the modulation axis after the polarized light passes through the crystal will "advance". The photoelastic modulator 3 utilizes the phenomenon that an isotropic material will produce birefringence after being subjected to an external force field, that is, it utilizes the photoelastic effect. In its working state, the birefringence phenomenon can be "artificially" modulated by controlling the amplitude of vibration and driving the piezoelectric sensor. In this embodiment, the photoelastic modulator 3 uses PEM-100 produced by Hinds Instruments.

[0058] The phase shifter 4 usually uses a wave plate (phase delay plate), which is made of a birefringent material. It can introduce a phase shift to the two mutually orthogonal polarization components passing through the wave plate, and realize the background zeroing of the oblique incident light reflection difference signal. The phase shifter 4 uses a Pockel cell, a half-wave plate or a quarter-wave plate; the Pockel cell utilizes the electro-optic effect to achieve the modulation of the phase difference of the p and s polarization components by changing the external bias voltage; the half-wave plate or the quarter-wave plate uses a crystal cut along the parallel optical axis direction. When the light beam is incident on the crystal, the o light and the e light will propagate in the crystal at different speeds. After exiting, a phase difference is generated between the o light and the e light:

[0059]

[0060] In the formula, λ 0 is the vacuum wavelength, and d is the crystal thickness. From the above formula, we can see that when the thickness d of the crystal is changed, that is, when the propagation distance of light in the crystal is changed, the phase difference of the two orthogonal components can be changed. Therefore, the optical axis of the half-wave plate or 1 / 4 wave plate is fixed, and the crystal thickness is changed by rotating the wave plate to adjust the phase difference between the p and s polarization components. Therefore, the phase difference can be continuously adjusted by using the wave plate.

[0061] The first lens 5 can focus the original incident light beam. The sample platform 6 is used to place the sample. The second lens 7 can better collect the signal light reflected by the sample point.

[0062] The polarizer 8 has a similar principle to the polarizer 2, and the polarizer 8 is used to implement the zeroing operation of the frequency-doubled signal. In this embodiment, the polarizer 8 uses a Glan-Taylor prism with an extinction ratio of 500:1.

[0063] The photodetector 9 is connected to the first lock-in amplifier 10 and the second lock-in amplifier 11 respectively; the first lock-in amplifier 10 is connected to the first acquisition card signal, and the second lock-in amplifier 11 is connected to the second acquisition card signal; the first acquisition card and the second acquisition card are connected to the computer 12 signal.

[0064] The photodetector 9 can be a photodiode as a detector element. The core part is a PN junction. In the working state, the two ends of the photodiode are connected to a reverse bias. When there is no light, the reverse dark current is very small and the influence on the signal can be ignored. When light irradiates the detector surface, the photon enters the PN junction and transfers energy to the bound electrons on the covalent bond, so that some electrons are excited to escape from the covalent bond state, thereby generating electron-hole pairs, which can move charges and are called photogenerated carriers. Under the action of reverse bias, they drift and move, making the reverse current (photocurrent) significantly larger. The reverse current is proportional to the light intensity. This characteristic is called "photoconductivity". If a load is connected to the external circuit, a voltage signal is obtained on the load, and this voltage signal also changes with the light intensity. In this embodiment, the photodetector 9 uses the DET-200-004 photodiode produced by Hinds Instruments.

[0065] The first phase-locked amplifier 10 and the second phase-locked amplifier 11 are used to detect weak signals, and use phase-sensitive detection technology to extract the amplitude and phase of the signal at the reference frequency. At the same time, they can suppress the noise on the non-reference frequency, and realize the function of frequency domain noise suppression. The first phase-locked amplifier 10 (i.e., phase detector) is used to amplify the electrical signal collected by the photodetector 9 and transmit it to the first acquisition card. The second phase-locked amplifier 11 (i.e., phase detector) is used to amplify the electrical signal collected by the photodetector 9 and transmit it to the second acquisition card. The phase-locked amplifier can suppress various non-reference carrier frequencies, thereby realizing signal amplification of a specific carrier frequency. After receiving the signal, the acquisition card converts it into a digital signal that can be collected by a computer.

[0066] The computer 12 is used to analyze and process the data of the sample adsorption process. The analysis process can be realized through the independently compiled LabView program. In addition to its intuitive image, the biggest advantage of LabView is its multi-threading and parallel processing features, and its advantages in program structure design that cannot be matched by statement programming languages.

[0067] The computer 12 performs surfactant adsorption behavior analysis based on the recorded fundamental frequency signal and frequency doubling signal of the sample adsorption process: the relative dielectric constant ε of the dielectric layer is calculated. d And thickness d, the properties such as the surfactant adsorption process and adsorption state are analyzed. The specific process is as follows:

[0068] Calculate the light intensity I received by the photodetector 9 photodiode :

[0069] I photodiode =I dc +I(Ω)sinΩt+I(2Ω)cos2Ωt (1)

[0070] In the formula, I photodiode is the signal received by the photodetector 9; dc is a DC signal; I(Ω) is a baseband signal; I(2Ω) is a double frequency signal; Ω is a modulation frequency in Hz; t is a modulation time in s.

[0071] The DC signal, baseband signal, and frequency-multiplied signal can be approximated as follows:

[0072] I dc ≈I 0 |r p | 2 cos 2 α (2)

[0073] I(Ω)≈2I 0 |r p | 2 cos 2 αIm{Δp-Δs}J 1 (A) (3)

[0074] I(2Ω)≈2I 0 |r p | 2 cos 2 αRe{Δp-Δs}J 2 (A) (4)

[0075] In the formula, I 0 is the initial incident light intensity; α is the polarization angle, the unit is rad; J 1 (A) is the first-order Bessel function, J 2 (A) are the second-order Bessel functions, r p is the reflectivity of the sample to be tested to p-polarized light, r sis the reflectivity of the sample to be tested to s-polarized light; Δp-Δs is the oblique incident light reflection difference (OIRD), that is, the difference in the change of p-polarized light and s-polarized light, Im{Δp-Δs} is the imaginary part of the oblique incident light reflection difference; Re{Δp-Δs} is the real part of the oblique incident light reflection difference, that is, the real part of the difference in the change of p-polarized light and s-polarized light.

[0076] From formula (2), formula (3) and formula (4), it can be obtained that the imaginary part of the oblique incident light reflection difference Δp-Δs is:

[0077]

[0078] The real part of the reflection difference Δp-Δs of oblique incident light is:

[0079]

[0080] It can be seen from formula (5) and formula (6) that the imaginary signal of the reflection difference of the oblique incident light is proportional to the detected fundamental frequency signal. Similarly, the real signal of the reflection difference of the oblique incident light is proportional to the double frequency signal of the received light intensity.

[0081] Therefore, by measuring the fundamental frequency signal or the harmonic frequency signal of the surfactant adsorption interface layer and calculating the light reflection difference signal of the dynamic adsorption process, the concentration of the surfactant and the information of the interaction between molecules can be studied.

[0082] From the Fresnel formula, we know that different objects have different reflectivity for p-polarized light and s-polarized light. When the surface properties change, the reflection difference Δp-Δs of the oblique incident light will also be different. Its definition is:

[0083]

[0084] In the formula, r p0 is the initial state reflectivity of p-polarized light, r s0 is the initial state reflectivity of s-polarized light, r p is the reflectivity of p-polarized light after the surface properties change, r s is the reflectivity of s-polarized light after the surface properties change.

[0085] In order to better analyze the interface properties from a microscopic perspective, a three-layer medium model of air-surfactant adsorption interface layer-water / oil is introduced to analyze the OIRD signal, such as Figure 3 As shown, according to the difference in the distribution of dielectric properties, air is determined as the upper layer of the medium model, the surfactant adsorption interface layer is the medium layer, and water or crude oil is the base layer.

[0086] The reflectance difference of oblique incident light Δp-Δs at the surfactant adsorption interface layer (medium layer) can be expressed as:

[0087]

[0088] Where λ is the wavelength of incident light, in nm; ε 0 is the relative dielectric constant of the air layer; ε d is the relative dielectric constant of the dielectric layer; ε s is the relative dielectric constant of the substrate layer; d is the thickness of the dielectric layer, nm; is the angle of incidence in rad.

[0089] Keep the environment and system stable, the incident light wavelength λ, the relative dielectric constant ε of the air layer 0 , relative dielectric constant of the substrate layer ε s , angle of incidence The relative dielectric constant ε of the dielectric layer is the only factor that affects the oblique incident light reflection difference signal. d and thickness d, the interaction between surfactant molecules causes the dielectric constant ε of the molecular layer d and its thickness d, so the obtained light reflection difference signal Δp-Δs is also different, and there is no need to mark the detected surfactant.

[0090] Therefore, after measuring the DC signal, baseband signal, and frequency-multiplied signal, the relative dielectric constant ε of the dielectric layer can be calculated according to formula (5), formula (6), and formula (8): d And thickness d. Furthermore, according to formula (8), the properties such as the surfactant adsorption process and adsorption state can be analyzed. From formula (8), it can be seen that when the incident angle is constant, the oblique incident light reflection difference signal (Δp-Δs) is related to the dielectric layer thickness d and the dielectric layer relative dielectric constant ε d Therefore, when the thickness of the dielectric layer is constant, the oblique incident light reflection difference signal is related to the surface dielectric constant of the sample (relative dielectric constant of the dielectric layer). The dissociation, diffusion, adsorption and other processes of surfactant molecules in the solution will cause changes in the relative dielectric constant of the dielectric layer, and the changes caused in different stages are different. Therefore, the adsorption process and adsorption state of the surfactant can be inverted based on the signal change curve collected by the system. Figure 4 As shown in Figure 1, in stage I, the surfactant solution is injected into the bottom of the container, the micelles dissociate and gradually transform into single surfactant molecules, and the OIRD imaginary signal increases with increasing concentration. In stage II, under the action of the concentration gradient, a large number of surfactant molecules diffuse from the bulk phase and gather in the near-interface layer, and the dielectric constant of the substrate layer ε s In the third stage, a large number of surfactant molecules are adsorbed to the surface (dielectric layer), which increases the dielectric constant ε of the dielectric layer. d , so the OIRD imaginary signal increases.

[0091] The adsorption behavior of surfactants is jointly determined by two forces, namely the mutual repulsion of the hydrophilic ends and the mutual attraction of the hydrophobic ends. The adsorption behavior of surfactants causes changes in the degree of aggregation on the interface, resulting in changes in the thickness and polarity of the interface layer, which in turn affects the change in the dielectric constant. The oblique incident light reflectance difference (OIRD) technology used in the present invention is a precision optical polarization measurement technology, which has opened up a new way for the detection of surfactant adsorption behavior with its non-contact, non-destructive, high-throughput and real-time monitoring capabilities. The OIRD technology uses the relative change difference in the reflectivity of p and s linear polarized light to evaluate the characteristics of the tested surface. It can sensitively capture small changes in surface properties, and then characterize the dynamic adsorption process of surfactants on the interface, and then explain the adsorption mechanism of surfactant molecules from a molecular level. As for the detection principle of OIRD technology, it measures the difference Δp-Δs between the reflectivity of p linear polarized light and s linear polarized light to obtain the imaginary signal Im{Δp-Δs} and the real signal Re{Δp-Δs}. The intensity of the detected difference signal Δp-Δs is determined by the dielectric constant and scale of the relevant surface. Therefore, the OIRD method can be used to achieve label-free detection of changes in liquid surface properties caused by the surfactant adsorption process. Specifically, according to the Fresnel formula, when the laser is irradiated at an oblique angle of incidence, there is a difference in the reflectivity of the tested surface to p-polarized light and s-polarized light. When the incident angle does not change, the relative change in reflectivity is mainly caused by the refractive index of the medium, and the change in the refractive index of the medium is related to the dielectric constant of the medium. Therefore, when the material composition, density and structure of the medium surface change, the dielectric constant of the surface will also change accordingly, thereby causing a change in reflectivity. At the same time, there is a difference in the reflectivity change of p-polarized light and s-polarized light. Therefore, by measuring the difference in the relative change of the reflectivity of p-polarized light and s-polarized light, relevant information about the tested surface can be obtained. The traditional surface tension method mainly shows the macroscopic properties of the solution. The relationship between the molecular diffusion rate and concentration is obtained through real-time monitoring of the dynamic surface tension, which reflects the adsorption behavior on the interface. The OIRD technology can infer microscopic information such as the molecular adsorption state and micelle formation on the interface layer based on the detection results. It has unique advantages in nano-level detection, analysis of molecular aggregation state and calculation of dielectric constant.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that modifying the technical solutions described in the aforementioned embodiments, or replacing some or all of the technical features therein by equivalents, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A surfactant adsorption behavior detection system based on oblique incident light reflection difference technology, characterized in that: include: A laser (1), a polarizer (2), a photoelastic modulator (3), a phase shifter (4), a first lens (5), a sample stage (6), a second lens (7), an analyzer (8), a photodetector (9), a first lock-in amplifier (10), a second lock-in amplifier (11), and a computer (12); The photoelectric detector (9) is connected to a first lock-in amplifier (10) and a second lock-in amplifier (11) respectively; the first lock-in amplifier (10) is connected to a first acquisition card signal, and the second lock-in amplifier (11) is connected to a second acquisition card signal; the first acquisition card and the second acquisition card are connected to a computer (12) signal; The laser (1) emits a detection light, which is converted into p-polarized light by a polarizer (2) and modulated into p-polarized light and s-polarized light by a photoelastic modulator (3); The p-polarized light and the s-polarized light are emitted alternately, and a fixed phase difference is generated between the p-polarized component and the s-polarized component by a phase shifter (4); the light is then focused by a first lens (5) and incident obliquely onto a sample surface on a sample stage (6); The laser light reflected from the sample surface passes through a second lens (7) and then enters a polarizer (8), and is then received by a photodetector (9) and converted into an electrical signal; The first lock-in amplifier (10) measures the baseband signal, the second lock-in amplifier (11) measures the multiplied frequency signal, and the computer (12) records the baseband signal and the multiplied frequency signal; The computer (12) performs surfactant adsorption behavior analysis based on the recorded fundamental frequency signal and frequency doubling signal.

2. The surfactant adsorption behavior detection system based on oblique incident light reflection difference technology according to claim 1 is characterized in that: The laser (1) adopts a He-Ne laser with a wavelength of 632.8 nm.

3. The surfactant adsorption behavior detection system based on oblique incident light reflection difference technology according to claim 1 is characterized in that: The polarizer (2) and the analyzer (8) are Glan Taylor prisms with an extinction ratio of 500:

1.

4. The surfactant adsorption behavior detection system based on oblique incident light reflection difference technology according to claim 1 is characterized in that: The phase shifter (4) adopts a Pockel cell, a half-wave plate or a quarter-wave plate.

5. The surfactant adsorption behavior detection system based on oblique incident light reflection difference technology according to claim 1 is characterized in that: The photodetector (9) is a photodiode.

6. The surfactant adsorption behavior detection system based on oblique incident light reflection difference technology according to claim 1 is characterized in that: The computer (12) performs surfactant adsorption behavior analysis based on the recorded fundamental frequency signal and the double frequency signal. The process includes: The light intensity I received by the photoelectric detector (9) is calculated as photodiode : I photodiode =I dc +I(Ω)sinΩt+I(2Ω)cos2Ωt (1) In the formula, I photodiode is the signal received by the photoelectric detector (9); dc is a DC signal; I(Ω) is a baseband signal; I(2Ω) is a double frequency signal; Ω is a modulation frequency in Hz; t is a modulation time in s; The DC signal, baseband signal, and frequency-multiplied signal can be approximated as follows: I dc ≈I0|r p 2 cos 2 a(2) I(Ω)≈2I0|r p 2 cos 2 αIm{Δp-Δs}J1(A)(3) I(2Ω)≈2I0|r p 2 cos 2 αRe{Δp-Δs}J2(A)(4) Where I0 is the initial incident light intensity; α is the polarization angle, in rad; J1(A) is the first-order Bessel function, J2(A) is the second-order Bessel function, and r p is the reflectivity of the sample to be tested to p-polarized light, r s is the reflectivity of the sample to be tested for s-polarized light; Δp-Δs is the reflection difference of oblique incident light, Im{Δp-Δs} is the imaginary part of the reflection difference of oblique incident light; Re{Δp-Δs} is the real part of the reflection difference of oblique incident light; From formula (2), formula (3) and formula (4), it can be obtained that the imaginary part of the oblique incident light reflection difference Δp-Δs is: The real part of the reflection difference Δp-Δs of oblique incident light is: It can be seen from formula (5) and formula (6) that the imaginary signal of the reflection difference of the oblique incident light is proportional to the detected fundamental frequency signal. Similarly, the real signal of the reflection difference of the oblique incident light is proportional to the double frequency signal of the received light intensity. From the Fresnel formula, we know that different objects have different reflectivity for p-polarized light and s-polarized light. When the surface properties change, the reflection difference Δp-Δs of the oblique incident light will also be different. Its definition is: In the formula, r p0 is the initial state reflectivity of p-polarized light, r s0 is the initial state reflectivity of s-polarized light, r p is the reflectivity of p-polarized light after the surface properties change, r s is the reflectivity of s-polarized light after the surface properties change; The three-layer medium model of air-surfactant adsorption interface layer-water / oil is introduced to analyze the OIRD signal, and the air is determined as the upper layer of the medium model, the surfactant adsorption interface layer is the medium layer, and the water or crude oil is the base layer; The reflection difference of oblique incident light in the dielectric layer Δp-Δs can be expressed as: Where λ is the wavelength of the incident light, in nm; ε0 is the relative dielectric constant of the air layer; ε d is the relative dielectric constant of the dielectric layer; ε s is the relative dielectric constant of the substrate layer; d is the thickness of the dielectric layer, nm; is the angle of incidence, in rad; Therefore, after measuring the DC signal, baseband signal, and frequency-multiplied signal, the relative dielectric constant ε of the dielectric layer can be calculated according to formula (5), formula (6), and formula (8): d and thickness d; further, according to formula (8), the adsorption process and adsorption state of the surfactant can be analyzed.

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