Surface active agent adsorption behavior detection system based on oblique incidence light reflection difference technology

Abstract

The application relates to the technical field of photoelectric detection, and provides a surfactant adsorption behavior detection system based on oblique incidence light reflection difference technology, which comprises a laser, a polarizer, a photoelastic modulator, a phase shifter, a first lens, a sample stage, a second lens, a detector, a photoelectric detector, a first lock-in amplifier, a second lock-in amplifier and a computer; the laser emits detection light; the detection light becomes p-polarized light through the polarizer; the p-polarized light and s-polarized light are modulated by the photoelastic modulator; the p-polarized light and s-polarized light are alternately emitted, and a fixed phase difference is generated between the p-polarized component and the s-polarized component by the phase shifter; the p-polarized light and s-polarized light are focused by the first lens and obliquely incident on the sample surface of the sample stage; the laser reflected from the sample surface is incident into the detector through the second lens, then is received by the photoelectric detector and is converted into an electric signal; and the fundamental frequency signal and the multiple frequency signal are recorded by the computer. The application can analyze the surfactant adsorption process and the adsorption state and other properties.

Description

Technical Field

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

[0002] The study of interfacial adsorption behavior of surfactants has always been a crucial topic in physics, chemistry, and engineering, significantly impacting their applications in chemical engineering, biomedicine, and materials science. Interfacial molecular interactions are a hot topic in many fields, including petroleum. Surfactants with amphiphilic structures can adsorb onto liquid surfaces, reducing surface tension. Due to this property, surfactants have wide applications in oilfield enhanced oil recovery. The displacement efficiency of surfactants is a key indicator in the displacement of residual oil. Factors such as surfactant type, molecular density, and cluster structure significantly influence its performance. During displacement, surfactant molecules undergo physical and chemical changes including micellar 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 times and spaces, thereby improving oil recovery and providing reference for designing novel surfactants and optimizing their application in tertiary oil recovery.

[0003] From a microscopic perspective, the essence of surfactants reducing interfacial tension lies in altering the density, cluster structure, and distribution of molecules at the interface. Surfactant solutions can only significantly reduce interfacial tension when their concentration is below the critical micelle concentration (CMC). Within this concentration range, surfactant molecules are arranged in a monomolecular state at the interface. It can be seen that the research object is molecules arranged at nanoscale interfaces or nanoscale spherical micelles in solution. This presents a challenge to current research methods. For example, molecular simulations can simulate molecular adsorption processes, but on the one hand, certain assumptions must be made about experimental conditions; on the other hand, due to limitations in computational power, the interactions between a large number of molecules are difficult to calculate. Atomic force microscopy (AFM) can detect the molecular arrangement, density, and other parameters on a surface, but it is difficult to detect surfactant molecules existing between the oil and water interfaces. Furthermore, given the complexity of surfactant types and adsorption behaviors, various characterization techniques have their own advantages and disadvantages. Investigating the adsorption state at the interface and the morphology of micelles formed in solution during surfactant adsorption requires the combination of more microscopic techniques. Summary of the Invention

[0004] This invention addresses the technical problems of current surfactant adsorption behavior characterization techniques, such as contact measurement, macroscopic detection, low accuracy, and inability to measure in real time. It proposes a surfactant adsorption behavior detection system based on oblique incident light reflection difference technology, which features real-time microscopic detection, low cost, high accuracy, and non-contact measurement, and can analyze the properties of surfactant adsorption process and adsorption state.

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

[0006] The photodetector is connected to a first lock-in amplifier and a second lock-in amplifier respectively; the first lock-in amplifier is connected to a first data acquisition card, and the second lock-in amplifier is connected to a second data acquisition card; the first data acquisition card and the second data acquisition card are connected to a computer.

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

[0008] The p-polarized light and 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; then they are focused by the first lens and obliquely incident on the sample surface on the sample stage.

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

[0010] The fundamental frequency signal is measured by the first lock-in amplifier, the harmonic signal is measured by the second lock-in amplifier, and the fundamental frequency signal and harmonic signal are recorded by the computer.

[0011] The computer analyzes the adsorption behavior of surfactants based on the recorded fundamental frequency signal and harmonic frequency 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 bubbler 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 harmonic frequency signal, including the following process:

[0017] The light intensity Iphotodiode received by the photodetector was calculated:

[0018]

[0019] In the formula, I photodiode The signal received by the photodetector; I dc It is a DC signal; I (Ω) represents the fundamental frequency signal; I (2Ω) represents the frequency harmonic signal; Ω represents the modulation frequency, measured in Hz. t The modulation time is measured in seconds (s).

[0020] DC signal, base frequency signal, and frequency multiplication signal can be respectively:

[0021]

[0022] In the formula, I 0 represents the initial incident light intensity; α This is the polarization angle, measured in rad. J 1( A ) is a first-order Bessel function ，J 2( A ) is a second-order Bessel function. for p Reflectivity of polarized light after changes in surface properties; The difference in reflection of oblique incident light This represents the imaginary part of the reflection difference of obliquely incident light; This represents the real part of the reflection difference of the obliquely incident light;

[0023] From formulas (2), (3), and (4), we can obtain the reflection difference of obliquely incident light. The imaginary part is:

[0024]

[0025] Poor reflection of obliquely incident light Δp - Δs The real part is:

[0026]

[0027] From formulas (5) and (6), it can be seen that the imaginary part of the oblique incident light reflection difference is proportional to the detected fundamental frequency signal. Similarly, the real part of the oblique incident light reflection difference is proportional to the harmonic signal of the received light intensity.

[0028] According to Fresnel's formula, different objects... p polarized light, s Different polarized light has different reflectivities; when surface properties change, the reflection difference of obliquely incident light increases. Δp - Δs It will also be different, and its definition is:

[0029]

[0030] In the formula, for p The initial reflectivity of polarized light. for s The initial reflectivity of polarized light. for s Reflectivity of polarized light after changes in surface properties;

[0031] A three-layer media model of air-surfactant adsorption interface layer-water / oil is introduced to analyze OIRD signals, and air is determined to be the upper layer of the media model, the surfactant adsorption interface layer is the media layer, and water or crude oil is the base layer.

[0032] The oblique incident light reflection difference Δp-Δs of the dielectric layer can be expressed as:

[0033]

[0034] In the formula, l The wavelength of the incident light is measured in nm. The relative permittivity of the air layer; The relative permittivity of the dielectric layer; The relative permittivity of the substrate layer; d The dielectric layer thickness is expressed in nm. The angle of incidence is expressed in rad.

[0035] Therefore, after measuring the DC signal, fundamental frequency signal, and harmonic frequency signal, the relative permittivity of the dielectric layer can be calculated according to formulas (5), (6), and (8). and thickness d Furthermore, the adsorption process and adsorption state of surfactants can be analyzed based on formula (8).

[0036] The present invention provides a surfactant adsorption behavior detection system based on oblique incidence light reflection difference technology, which has the following advantages compared with the prior art:

[0037] 1. Low cost: Compared with electron microscopy, CT and traditional optical technology, optical devices based on oblique incident light reflection difference (OIRD) technology require less, have a simple optical path structure, occupy less space, are easy to install, move and maintain, and have lower operating and maintenance costs, thus greatly reducing the detection cost of surfactant adsorption behavior.

[0038] 2. Non-contact: OIRD detects surface information of the sample by detecting the difference in the relative change of reflectivity of the sample surface to the s and p polarization components of the probe light, thus realizing label-free and non-contact detection of surfactants.

[0039] 3. Real-time dynamic microscopic detection: Adsorption behavior characterization methods, such as the surface tension method, can only detect changes in solution properties from a macroscopic perspective and cannot analyze the state of molecular aggregation from a microscopic perspective. The method of this invention, however, can carry more microscopic information, detecting the dynamic adsorption process of surfactants in real time and revealing the adsorption behavior of interfacial molecules from a microscopic perspective.

[0040] 4. High Sensitivity and High Accuracy: OIRD technology incorporates devices for zeroing background noise (phase shifter, polarization analyzer), offering higher sensitivity compared to traditional polarization-modulated ellipsometers. Under oblique laser incidence, the reflectivity of material surfaces differs for s- and p-polarized light. When the incident angle is constant, reflectivity is highly sensitive to changes in the dielectric constant or thickness of the sample surface layer, and variations in the composition, structure, and density of the surface / interface directly affect these parameters. Therefore, OIRD technology, as an emerging optical technique, enables high-precision real-time detection of interface information. It is a label-free, real-time, and non-destructive optical detection method capable of tracking the adsorption process of surfactants in real time and dynamically capturing their behavioral changes, providing accurate data for adsorption characteristic studies. Based on OIRD detection results, microscopic information such as the molecular adsorption state and micelle formation on the interface layer can be inferred, offering unique advantages in the study of surfactant molecule adsorption behavior. This technology achieves nanometer-level detection accuracy in the perpendicular interface direction, making it extremely precise and suitable for detecting surfactant molecule adsorption behavior at oil / gas interfaces. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the layout of the surfactant adsorption behavior detection system based on oblique incidence light reflection difference technology provided by the present invention;

[0042] Figure 2 This is a schematic diagram of the detection process of the surfactant adsorption behavior detection system based on oblique incidence light reflection difference technology provided by the present invention;

[0043] Figure 3 This is a schematic diagram of the three-layer medium model of air-adsorption interface layer-water / oil established in this invention;

[0044] Figure 4 This is a graph showing the OIRD detection results of the dynamic adsorption process of surfactant molecules;

[0045] Reference numerals in the attached figures: 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 lock-in amplifier; 11. Second lock-in amplifier; 12. Computer. Detailed Implementation

[0046] To make the technical problems solved by this invention, the technical solutions adopted, and the technical effects achieved clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings, not all of them.

[0047] like Figure 1-2 As shown, the surfactant adsorption behavior detection system based on oblique incident light reflection difference technology provided in this embodiment of the 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 lock-in amplifier 10, a second lock-in amplifier 11, and a computer 12.

[0048] This invention is based on oblique incidence light reflection difference technology and utilizes p and s polarization state modulation technology to obtain information about the target object by analyzing the light signal. Therefore, the light source needs to have good linear polarization characteristics.

[0049] During the adsorption process of the sample (surfactant), the laser 1 emits a probe light. Specifically, in this embodiment, a laser with a wavelength of λ=632.8nm emitted by a helium-neon laser is used as the probe light. The probe light is converted into p-polarized light by the polarizer 2. It is then modulated into p-polarized light and s-polarized light by the photoelastic modulator 3, with a modulation frequency of 50kHz.

[0050] The p-polarized light and 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. The light is then focused by the first lens 5 and obliquely incident on the sample surface on the sample stage 6 at an incident angle equal to Brewster's angle. At this time, the reflectivity of the p-polarized light and the s-polarized light are very different.

[0051] The laser reflected from the sample surface passes through the second lens 7 and enters the analyzer 8, where it is then received by the photodetector 9 and converted into an electrical signal.

[0052] The fundamental frequency signal is measured by the first lock-in amplifier 10, the harmonic frequency signal is measured by the second lock-in amplifier 11, and the fundamental frequency signal and harmonic frequency signal of the sample adsorption process are recorded by the computer 12.

[0053] In the above scheme, the oblique incidence light reflection difference method is based on the difference in the changes of p and s polarization components, thus requiring the light source to have good linear polarization characteristics. Therefore, this invention selects a linearly polarized laser source with a continuous wavelength, and the laser 1 is a He-Ne laser with a wavelength of 632.8 nm. Generally, in order to make full use of the laser's output energy, the resonant cavity of the laser 1 is rotated to make the polarization direction of the emitted linearly polarized light as consistent as possible with the transmission direction of the polarizer 2.

[0054] The function of polarizer 2 is to ensure that the emitted light is linearly polarized and that its polarization direction is in the same direction as the optical axis of polarizer 2. By rotating 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 exhibits extinction or the light intensity is at its weakest after passing through the polarizer orthogonal to the p-polarization direction, it can be ensured that laser 1 is incident with p-polarized light. The polarizer 2 used is made by adhering two calcite cuboids cut along their diagonal edges together with an air layer of a certain thickness. Its working principle is that when a beam containing both p and s polarization states is incident perpendicularly to the surface, the difference in refractive index causes the critical angles for the first total internal reflection of the p and s polarized light from the calcite to the air medium to be different. By selecting the cut angle between the two critical angles, the light of one polarization direction is deflected from the main optical path through total internal reflection, allowing the light of the other polarization direction to be transmitted and emitted into the main optical path. 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 normal to the interface of the incident light) 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.

[0055] The photoelastic modulator 3 modulates incident polarized light to modulate and change the polarization state of the beam at a fixed frequency. The photoelastic modulator 3 consists of a photoelastic crystal, a controller, and electrical components, achieving modulation between p and s polarization states at a modulation frequency of 50 kHz. The working principle of the photoelastic modulator (PEM) 3 is like a "dynamic waveplate," which can generate a periodically changing refractive index difference between the fast and slow axes, thereby controlling the periodic change of the polarization of the transmitted beam. Specifically, when linearly polarized light passes through the photoelastic crystal at a 45° angle to its modulation axis, the polarization state of the incident light remains unchanged when the crystal is not subjected to external force. When the crystal is stretched, the propagation speed of the linearly polarized component parallel to the crystal's modulation axis will be slower than that of the perpendicular component, i.e., the parallel component "lags" behind the perpendicular component. When the crystal is compressed, the polarized component parallel to the modulation axis will "lead" after the polarized light passes through the crystal. The photoelastic modulator 3 utilizes the phenomenon that isotropic materials will produce birefringence when subjected to an external force field, which is the photoelastic effect. In its operating state, the birefringence phenomenon can be "artificially" modulated by controlling the amplitude of vibration and driving it with a piezoelectric sensor. In this embodiment, the photoelastic modulator 3 uses a PEM-100 manufactured by Hinds Instruments.

[0056] The phase shifter 4 typically uses a waveplate (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 waveplate, achieving background zeroing of the oblique incident light reflection difference signal. The phase shifter 4 employs a Paulck cell, a half-wave plate, or a quarter-wave plate; the Paulck cell utilizes the electro-optic effect, modulating the phase difference between the p and s polarization components by changing the applied bias voltage; the half-wave plate or quarter-wave plate uses a crystal cut along the parallel optical axis. When the beam is incident perpendicularly on the crystal, the o-ray and e-ray will propagate at different speeds within the crystal, resulting in a phase difference between the o-ray and e-ray after exiting.

[0057]

[0058] In the formula, Vacuum wavelength, Let be the crystal thickness. From the above formula, it can be seen that when the crystal thickness is changed... When the propagation distance of light in a crystal is changed, the phase difference between the two orthogonal components can be altered. Therefore, by fixing the optical axis of a half-wave plate or a quarter-wave plate and rotating the wave plate to change the crystal thickness, the phase difference between the p and s polarization components can be adjusted. Thus, a wave plate can be used to achieve continuously adjustable phase difference.

[0059] The first lens 5 can focus the original incident beam. The sample platform 6 is used to place the sample. The second lens 7 can better collect the signal light reflected after passing through the sample point.

[0060] The analyzer 8 operates on a similar principle to the polarizer 2, and is used to perform zeroing operations on the harmonic signal. In this embodiment, the analyzer 8 employs a Glan Taylor prism with an extinction ratio of 500:1.

[0061] 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, and the second lock-in amplifier 11 is connected to the second acquisition card; the first acquisition card and the second acquisition card are connected to the computer 12.

[0062] The photodetector 9, as a detector element, can be a photodiode. Its core component is a PN junction. In operation, the photodiode is reverse-biased. When there is no light, the reverse dark current is very small and its impact on the signal is negligible. When light shines on the detector surface, photons enter the PN junction and transfer energy to bound electrons in covalent bonds. This causes some electrons to escape from the covalent bond state, generating electron-hole pairs, which can move charge and are called photogenerated carriers. Under the action of the reverse bias, they generate a photocurrent. These carriers drift under the reverse voltage, causing the reverse current (photocurrent) to increase significantly. The reverse current is directly proportional to the light intensity; this characteristic is called "photoconductivity." If a load is connected to the external circuit, a voltage signal is obtained across the load, and this voltage signal also changes with the light intensity. In this embodiment, the photodetector 9 uses a DET-200-004 photodiode manufactured by Hinds Instruments.

[0063] The first lock-in amplifier 10 and the second lock-in amplifier 11 are used to detect weak signals. Phase-sensitive detection technology is used to extract the amplitude and phase of the signal at the reference frequency, while simultaneously suppressing noise at non-reference frequencies, achieving frequency domain noise suppression. The first lock-in amplifier 10 (i.e., the phase detector) amplifies the electrical signal collected by the photodetector 9 and transmits it to the first acquisition card. The second lock-in amplifier 11 (i.e., the phase detector) amplifies the electrical signal collected by the photodetector 9 and transmits it to the second acquisition card. The lock-in amplifiers can suppress various non-reference carrier frequencies, thereby achieving signal amplification for specific carrier frequencies. After receiving the signal, the acquisition card converts it into a digital signal that can be acquired by a computer.

[0064] The computer 12 is used to analyze and process the data of the sample adsorption process. The analysis process can be implemented through a self-developed LabVIEW program. LabVIEW's biggest advantages, besides being visually intuitive, are its multi-threaded and parallel processing capabilities, and its program structure design has advantages that statement-based programming languages ​​cannot match.

[0065] The computer 12 analyzes the surfactant adsorption behavior based on the recorded fundamental and harmonic signals of the sample adsorption process, and calculates the relative permittivity of the dielectric layer. and thickness d The adsorption process and adsorption state of surfactants were analyzed. The specific process is as follows:

[0066] The intensity of light received by photodetector 9 was calculated. I photodiode :

[0067]

[0068] In the formula, I photodiode The signal received by photodetector 9; I dc It is a DC signal; I (Ω) represents the fundamental frequency signal; I (2Ω) represents the frequency harmonic signal; Ω represents the modulation frequency, measured in Hz. t The modulation time is measured in seconds (s).

[0069] DC signals, fundamental frequency signals, and harmonic signals can be approximated as follows:

[0070]

[0071] In the formula, I 0 represents the initial incident light intensity; α This is the polarization angle, measured in rad. J 1( A ) is a first-order Bessel function ，J 2( A ) is a second-order Bessel function. for p Reflectivity of polarized light after changes in surface properties; Δp - Δs This refers to the oblique incident light reflection difference (OIRD), i.e. p polarized light, s The difference in polarization of light I am { Δp - Δs} represents the imaginary part of the reflection difference of obliquely incident light; Re { Δp - Δs} represents the real part of the reflection difference of obliquely incident light, i.e. p polarized light, s The real part of the difference in the amount of polarization change of light.

[0072] From formulas (2), (3), and (4), we can obtain the reflection difference of obliquely incident light. Δp - Δs The imaginary part is:

[0073]

[0074] Poor reflection of obliquely incident light Δp - Δs The real part is:

[0075]

[0076] As can be seen from formulas (5) and (6), the imaginary part of the oblique incident light reflection difference is proportional to the detected fundamental frequency signal. Similarly, the real part of the oblique incident light reflection difference is proportional to the harmonic signal of the received light intensity.

[0077] Therefore, by measuring the fundamental or harmonic 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 on the interaction between molecules can be studied.

[0078] According to Fresnel's formula, different objects... p polarized light, s Different polarized light has different reflectivities; when surface properties change, the reflection difference of obliquely incident light increases. Δp - Δs It will also be different, and its definition is:

[0079]

[0080] In the formula, for p The initial reflectivity of polarized light. for s The initial reflectivity of polarized light. for s The reflectivity of polarized light after changes in surface properties.

[0081] To better analyze interfacial properties from a microscopic perspective, a three-layer media model of air-surfactant adsorption interface layer-water / oil is introduced to analyze OIRD signals, such as... Figure 3 As shown, based on the differences in dielectric property distribution, air is determined as the upper layer of the dielectric model, the surfactant adsorption interface layer is the dielectric layer, and water or crude oil is the base layer.

[0082] The difference in oblique incident light reflection Δp-Δs at the surfactant adsorption interface layer (medium layer) can be expressed as:

[0083]

[0084] In the formula, l The wavelength of the incident light is measured in nm. The relative permittivity of the air layer; The relative permittivity of the dielectric layer; The relative permittivity of the substrate layer; d The dielectric layer thickness is expressed in nm. f The angle of incidence is expressed in rad.

[0085] To maintain environmental and system stability, the incident light wavelength l Relative permittivity of air layer Relative permittivity of the substrate layer Angle of incidence f With all constants remaining constant, the only factor affecting the difference signal of obliquely incident light reflection is the relative permittivity of the dielectric layer. and thickness d The interaction between surfactant molecules causes the dielectric constant of this molecular layer. and its thickness d The change in the light reflectance signal Δp - Δs will result in a different signal, and no labeling of the surfactant being detected is required.

[0086] Therefore, after measuring the DC signal, fundamental frequency signal, and harmonic frequency signal, the relative permittivity of the dielectric layer can be calculated according to formulas (5), (6), and (8). and thickness d Furthermore, based on formula (8), the properties such as the adsorption process and adsorption state of the surfactant can be analyzed. From formula (8), it can be seen that when the incident angle is constant, the reflection difference signal (Δp-Δs) of oblique incident light is related to the thickness d of the dielectric layer and the relative permittivity of the dielectric layer. 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, and adsorption processes of surfactant molecules in solution will cause changes in the relative dielectric constant of the dielectric layer, and the changes differ at different stages. Therefore, the adsorption process and adsorption state of the surfactant can be inferred from the signal change curves collected by the system. Figure 4As shown, in stage I, the surfactant solution is injected into the bottom of the container, causing micelles to dissociate and gradually transform into individual surfactant molecules. The imaginary part of the OIRD signal increases with increasing concentration. In stage II, under the influence of the concentration gradient, a large number of surfactant molecules diffuse from the bulk phase and aggregate to the near-interface layer, increasing the dielectric constant of the substrate layer. As the dielectric constant increases, the imaginary part of the OIRD signal decreases. In stage III, a large number of surfactant molecules adsorb onto the surface (dielectric layer), increasing the dielectric constant of the dielectric layer. Therefore, the imaginary part of the OIRD signal increases.

[0087] The adsorption behavior of surfactants is determined by two forces: 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 at the interface, leading to alterations in the interfacial layer thickness and polarity, which in turn affect the dielectric constant. This invention utilizes oblique incident light reflectance difference (OIRD) technology, a precision optical polarization measurement technique. Its non-contact, non-destructive, high-throughput, and real-time monitoring capabilities open up new avenues for detecting surfactant adsorption behavior. OIRD technology assesses the characteristics of the tested surface by measuring the relative changes in reflectance of p- and s-polarized light. It can sensitively capture minute changes in surface properties, thus characterizing the dynamic adsorption process of surfactants at the interface and explaining the adsorption mechanism of surfactant molecules at the molecular level. In terms of the detection principle of OIRD technology, it obtains the imaginary part signal Im{Δp-Δs} and the real part signal Re{Δp-Δs} by measuring the difference Δp-Δs between the reflectance coefficients of p- and s-polarized light. 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 surfactant adsorption. Specifically, according to Fresnel's equations, when a laser is irradiated at an oblique angle, the reflectivity of the tested surface for p-polarized and s-polarized light differs. When the incident angle remains constant, the relative change in reflectivity is mainly due to the refractive index of the medium, which is related to the dielectric constant. Therefore, when the composition, density, and structure of the medium surface change, the dielectric constant of the surface will also change accordingly, leading to a change in reflectivity. Simultaneously, the reflectivity changes of p-polarized and s-polarized light differ. Therefore, by measuring the difference in the relative changes in reflectivity of p-polarized and s-polarized light, relevant information about the tested surface can be obtained. Traditional surface tension methods mainly represent the macroscopic properties of solutions, deriving the relationship between molecular diffusion rate and concentration through real-time monitoring of dynamic surface tension, thus reflecting adsorption behavior at the interface. OIRD technology can infer microscopic information such as the adsorption state of molecules and micelle formation on the interface layer based on the detection results. It has unique advantages in nanoscale detection, analysis of molecular aggregation state and calculation of dielectric constant.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some or all of the technical features, do 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 incidence light reflection difference technology, characterized in that, include: Laser (1), polarizer (2), photoelastic modulator (3), phase shifter (4), first lens (5), sample stage (6), second lens (7), analyzer (8), photodetector (9), first lock-in amplifier (10), second lock-in amplifier (11) and computer (12). The laser (1) is a He-Ne laser with a wavelength of 632.8 nm; the polarizer (2) and analyzer (8) are GranTaylor prisms with an extinction ratio of 500:1; the phase shifter (4) is a Pocker cell, a half-wave plate or a quarter-wave plate; the photodetector (9) is a photodiode. 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, and the second lock-in amplifier (11) is connected to the second acquisition card; the first acquisition card and the second acquisition card are connected to the computer (12). The laser (1) emits a probe light, which is converted into p-polarized light by a polarizer (2); and then modulated into p-polarized light and s-polarized light by a photoelastic modulator (3). The p-polarized light and 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 they are focused by the first lens (5) and obliquely incident on the sample surface on the sample stage (6); The laser reflected from the sample surface passes through the second lens (7) and enters the analyzer (8), where it is then received by the photodetector (9) and converted into an electrical signal. The fundamental frequency signal is measured by the first lock-in amplifier (10), the harmonic frequency signal is measured by the second lock-in amplifier (11), and the fundamental frequency signal and harmonic frequency signal are recorded by the computer (12). The computer (12) performs surfactant adsorption behavior analysis based on the recorded fundamental frequency signal and harmonic frequency signal, including the following process: The light intensity received by the photodetector (9) was calculated. I photodiode : ； In the formula, I photodiode The signal received by the photodetector (9); I dc It is a DC signal; I (Ω) represents the fundamental frequency signal; I (2Ω) represents the frequency harmonic signal; Ω represents the modulation frequency, measured in Hz. t The modulation time is measured in seconds (s). DC signal, base frequency signal, and frequency multiplication signal can be respectively: ； ； ； In the formula, I 0 represents the initial incident light intensity; α This is the polarization angle, measured in rad. J 1( A ) is a first-order Bessel function ，J 2( A ) is a second-order Bessel function. for p Reflectivity of polarized light after changes in surface properties; Δp - Δs The difference in reflection of oblique incident light Im { Δp - Δs } represents the imaginary part of the reflection difference of obliquely incident light; Re { Δp - Δs } represents the real part of the reflection difference of obliquely incident light; From formulas (2), (3), and (4), we can obtain the reflection difference of obliquely incident light. Δp - Δs The imaginary part is: ； Poor reflection of obliquely incident light Δp - Δs The real part is: ； From formulas (5) and (6), it can be seen that the imaginary part of the oblique incident light reflection difference is proportional to the detected fundamental frequency signal. Similarly, the real part of the oblique incident light reflection difference is proportional to the harmonic signal of the received light intensity. According to Fresnel's formula, different objects... p polarized light, s Different polarized light has different reflectivities; when surface properties change, the reflection difference of obliquely incident light increases. Δp - Δs It will also be different, and its definition is: ； In the formula, for p The initial reflectivity of polarized light. for s The initial reflectivity of polarized light. for s Reflectivity of polarized light after changes in surface properties; A three-layer media model of air-surfactant adsorption interface layer-water / oil is introduced to analyze OIRD signals, and air is determined to be the upper layer of the media model, the surfactant adsorption interface layer is the media layer, and water or crude oil is the base layer. The oblique incident light reflection difference Δp-Δs of the dielectric layer can be expressed as: ； In the formula, λ The wavelength of the incident light is measured in nm. The relative permittivity of the air layer; The relative permittivity of the dielectric layer; The relative permittivity of the substrate layer; The dielectric layer thickness is expressed in nm. The angle of incidence is expressed in rad. Therefore, after measuring the DC signal, fundamental frequency signal, and harmonic frequency signal, the relative permittivity of the dielectric layer can be calculated according to formulas (5), (6), and (8). and thickness d Furthermore, the adsorption process and adsorption state of surfactants can be analyzed based on formula (8).

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