Method for measuring the elastic shear modulus of a viscoelastic liquid based on the particle tracking method

Abstract

The application discloses a method for measuring the elastic shear modulus of a viscoelastic liquid based on a particle tracking method. The method comprises the following steps: adding tracking particles into a viscoelastic solution to prepare a liquid film containing the viscoelastic solution with the tracking particles, dropping a surfactant droplet on the liquid film to generate a surface tension gradient on the surface of the liquid film, measuring the maximum displacement of the tracking particles when the viscoelastic liquid is in a shearing spreading motion, obtaining the strain size of the shearing motion of the viscoelastic liquid film, and obtaining the shearing stress size at the moment according to the motion displacement of the liquid film and the surface tension gradient, so as to establish a correlation model of the shearing stress and the shearing strain under the shearing action and calculate the elastic shear modulus of the viscoelastic liquid film. Compared with the existing rheometer technology for measuring the shearing modulus of an elastic liquid, the application provides a new method for measuring the elastic shear modulus of a viscoelastic liquid, and the required sample amount is greatly reduced, which is of great significance for measuring precious liquids.

Description

Technical Field

[0001] This invention belongs to the field of microfluidic liquids assisted by particle tracer experiments, and specifically relates to a method for measuring the elastic shear modulus of viscoelastic fluids. Background Technology

[0002] Unlike elastomers (such as rubber and metals) that can only store mechanical energy and viscous fluids (such as water and glycerol) that can only dissipate mechanical energy, viscoelastic liquids possess both the ability to store and dissipate mechanical energy. They are liquids that primarily store mechanical energy within a characteristic time τ and primarily dissipate it outside of that time, exhibiting both elastic deformation and viscous dissipation capabilities. Measuring the elastic shear modulus of viscoelastic liquids typically requires a high-precision rheometer, which is very expensive. Furthermore, the measurement involves heavy machinery such as rotor motors, and the required sample volume varies depending on the rotor used. For example, a conical rotor requires 1-2 ml of sample, while a cylindrical rotor requires 10-15 ml. For some precious liquids, each measurement requires expensive reagents, and repeated measurements consume large quantities of reagents, resulting in high costs. Summary of the Invention

[0003] To address the technical problems of high cost and large liquid consumption in the measurement of the elastic shear modulus of viscoelastic liquids, this invention provides a method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method, which can reduce the liquid volume consumed in a single measurement by more than 10 times.

[0004] The technical solution of the present invention is as follows:

[0005] A method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method includes the following steps:

[0006] Multiple tracer particles are added to the viscoelastic liquid sample to be tested, wherein the density difference between the tracer particles and the density of the viscoelastic liquid to be tested is less than or equal to 5%.

[0007] The surface tension S1 of a viscoelastic liquid containing tracer particles was measured.

[0008] The surface tension S2 of the surfactant was measured;

[0009] The viscoelastic liquid to be tested, to which tracer particles are added, is spread on a smooth surface to form a liquid film;

[0010] The surfactant is added dropwise to the surface of the liquid film, causing the liquid film and tracer particles to move under the action of the surface tension gradient;

[0011] Observe the movement of the liquid film and tracer particles, and obtain the distance x between the leading edge of the liquid film and the droplet position of the surfactant at the inflection point when the tracer particles retract, and the maximum displacement δr of the tracer particles at that moment.

[0012] The shear strain ε is calculated using the formula ε=δr / h0, and the shear stress σ is calculated using the formula σ=S / x; where h0 is the initial average thickness of the liquid film, S is the surface tension difference, and S=S1-S2;

[0013] The shear stress and shear strain data corresponding to multiple tracer particles are plotted in the XY coordinate system, and linear fitting is performed. The slope of the fitted line is the elastic shear modulus G.

[0014] Compared with the prior art, the beneficial effects of this invention are:

[0015] 1. This invention provides a novel method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method.

[0016] 2. Compared with existing methods for measuring elastic shear modulus using a rheometer, the present invention requires only 0.1ml-0.2ml of sample, which greatly reduces the required sample volume and is of great significance for the measurement of precious liquids.

[0017] 3. In the process of measuring the elastic shear modulus, the required measuring instruments are more readily available, and only a common surface tension measuring instrument is needed; the measurement method is also relatively simple and easy to implement. Attached Figure Description

[0018] Figure 1 This is a distribution diagram of tracer particles inside the liquid film in the shearing and spreading experiment of the method of the present invention. In the figure, a is the moving boundary of the liquid film and b is the filamentous structure.

[0019] Figure 2 This is a plot of particle position distribution and velocity field after PTV identification;

[0020] Figure 3 It is an experimental data point and fitting curve of stress-strain inside the liquid film based on the movement of tracer particles. Detailed Implementation

[0021] The present invention will now be described in detail based on its principles.

[0022] This invention measures the elastic shear modulus of viscoelastic liquids using the particle tracer method, a widely used experimental method for characterizing solution flow across an entire plane of motion. By tracking the trajectory of each particle, the local motion of the liquid near a point can be described at a microscopic scale. Furthermore, by tracking the trajectories of a large number of particles to describe all the motion details across the entire plane, this method is efficient and provides a broader spatial description of liquid properties.

[0023] This invention uses a particle tracer method to obtain the displacement field of a liquid film shear spreading across the entire plane. By measuring the maximum displacement of the tracer particles from their initial rest state to just before retraction during the shear spreading motion of the viscoelastic liquid, the magnitude of the strain during the shear motion of the viscoelastic liquid film can be determined. Since the driving force for liquid film spreading is the surface tension gradient, the magnitude of which is determined by the position of the spreading leading edge, the corresponding shear stress can be obtained based on the position of the spreading leading edge. From this, the stress-strain relationship of the spreading process can be obtained, and thus the elastic shear modulus of the liquid film can be derived.

[0024] The method includes the following steps:

[0025] Multiple tracer particles are added to the viscoelastic liquid sample to be tested, and the density difference between the tracer particles and the density of the viscoelastic liquid to be tested is less than or equal to 5%.

[0026] The surface tension S1 of a viscoelastic liquid containing tracer particles was measured.

[0027] The surface tension S2 of the surfactant was measured;

[0028] The viscoelastic liquid to be tested, to which tracer particles are added, is spread on a smooth surface to form a liquid film;

[0029] The surfactant is added dropwise to the surface of the liquid film, causing the liquid film and tracer particles to move under the action of the surface tension gradient;

[0030] Observe the movement of the liquid film and tracer particles, and obtain the distance x between the leading edge of the liquid film and the droplet position of the surfactant at the inflection point when the tracer particles retract, and the maximum displacement δr of the tracer particles at that moment.

[0031] The shear strain ε is calculated using the formula ε=δr / h0, and the shear stress σ is calculated using the formula σ=S / x; where h0 is the initial average thickness of the liquid film, S is the surface tension difference, and S=S1-S2;

[0032] The shear stress and shear strain data corresponding to multiple tracer particles are plotted in the XY coordinate system, and linear fitting is performed. The slope of the fitted line is the elastic shear modulus G.

[0033] The applicable conditions for the measurement method of this invention are: the surface tension gradient formed by the surfactant droplets on the liquid surface is sufficiently large, and the liquid film formed by the viscoelastic liquid is able to cause the tracer particles inside to move and retract under the action of the surface tension gradient. In application, a suitable surfactant can be selected according to the properties of the viscoelastic liquid being measured.

[0034] In addition, the following points should be noted when selecting tracer particles in this invention:

[0035] First, the density of the tracer particles must be close to that of the viscoelastic liquid being measured, allowing them to remain suspended within the liquid without sinking during the liquid film spreading timescale. Generally, the density difference between the tracer particles and the liquid film density should be within 5%.

[0036] Second: The diameter of the particles is nearly an order of magnitude smaller than the thickness of the liquid film to be prepared. In this case, the relative motion between the particles and the liquid can be ignored, and the particles are considered to move entirely with the movement of the liquid.

[0037] When selecting the diameter of the tracer particles, the viscosity value η1 of the viscoelastic liquid and the viscosity value η2 of the surfactant droplet can be measured first. The thickness h0 of the liquid film can then be estimated based on h0(mm)≤(η1-η2)×3 / 400, where the units of the viscosity values ​​η1 of the viscoelastic liquid and η2 of the surfactant droplet are millipascals per second, the unit of 3 / 400 is meters per second, and the unit of the thickness range calculation result is mm.

[0038] Third: The concentration of tracer particles in the viscoelastic solution should ideally be within a suitable range. Too low a concentration will result in too few observable tracer particles in the field of view, making it impossible to obtain sufficient displacement data. Too high a concentration will cause the tracer particles to be too close together and aggregate rapidly, making them difficult to identify and affecting the accuracy of PTV identification. Optionally, the concentration of tracer particles in the viscoelastic solution should be around 1.6 × 10⁻⁶. 7 pcs / cm 2 Order of magnitude.

[0039] Specifically, when this invention is used to measure a Boger viscoelastic solution composed of polyethylene oxide (PEO) and polyethylene oxide (PEG), the tracer particles can be polystyrene particles, or other materials such as metal microspheres or plexiglass microspheres. The plane used to spread the Boger viscoelastic solution must be sufficiently smooth, with pits smaller than 1 micrometer to avoid the surface irregularities affecting the spreading of the liquid film. This plane must also be hydrophilic to avoid shrinkage and deformation of the viscoelastic liquid film due to the hydrophobic properties of the material surface; optionally, this plane can be a glass plane. The surfactant must be a nonionic surfactant to avoid the interaction between the anions or cations in the surfactant and the dissolved polymers in the viscoelastic liquid film, thus altering the elastic properties of the liquid film. The surfactant needs to be above 10 times the critical micelle concentration (CMC) to ensure its surface tension remains stable at its plateau value. Optionally, the surfactant is an aqueous solution of Triton X-100. The concentration of the Triton X-100 aqueous solution is 40 cmc.

[0040] The following is in conjunction with the appendix Figure 1 Appendix Figure 2 and attached Figure 3 The present invention will be described in detail using a Boger viscoelastic solution composed of polyethylene oxide (PEO) and polyethylene oxide (PEG) as an example.

[0041] The following method is a laboratory method and therefore includes the step of preparing a viscoelastic Boger solution. When the method of the present invention is applied to the actual measurement of viscoelastic liquids, it directly starts from step 2 of the following method.

[0042] Step 1: Prepare a viscoelastic Boger solution with constant viscosity.

[0043] 2g of 5M Da polyethylene oxide (PEO) powder was mixed with 250ml of deionized water and stirred at 100 rpm for 72 hours using a magnetic stirrer until the flocculent matter in the solution was completely dissolved, thus preparing 250ml of 8g / L aqueous solution of 5M Da PEO polymer. Separately, 4g of 8k Da polyethylene oxide (PEG) powder was dissolved in 6g of deionized water and stirred until dissolved, thus preparing 10g of 40wt% 8k Da PEG polymer aqueous solution.

[0044] Take 5g of a 40wt% aqueous solution of PEG with a molecular weight of 8kDa, add 5.7784g of deionized water, and then add 1.1976g of an 8g / L aqueous solution of PEO with a molecular weight of 5MDa. Shake and mix thoroughly. This yields a Boger viscoelastic solution with constant viscosity, containing 16.7wt% PEG (8kDa) and 0.08wt% PEO (5MDa).

[0045] By proportionally increasing or decreasing the mass fraction of PEO and PEG powders in this formulation, Boger viscoelastic solutions with constant viscosity and varying degrees of viscosity and elasticity can be obtained. The mass fractions of the two viscoelastic solutions described in this invention are as follows:

[0046] Boger 1 solution: 33.4 wt% PEG (8 kDa), 0.16 wt% PEO (5 MDa);

[0047] Boger2 solution: 16.7 wt% PEG (8 kDa), 0.08 wt% PEO (5 MDa).

[0048] Step 2: Treat the glass surface and prepare a viscoelastic liquid film containing tracer particles.

[0049] Take 0.16 ml of the prepared viscoelastic solution into a test tube. Use a pipette to aspirate 0.002 ml of tracer particles (polystyrene microspheres) with a diameter of 10 μm into the test tube, and stir until fully mixed with the viscoelastic solution. Separately, wash a 3 cm square glass with alcohol, rinse with deionized water, dry, and then treat it in a Harrick Plasma PDC-32G-2 plasma analyzer for 35 seconds. After removing the glass, quickly drop 0.16 ml of the viscoelastic solution containing the tracer particles onto the glass surface, then remove 0.1 ml, leaving 0.06 ml of liquid on the glass surface.

[0050] Step 3: Shear and spread the liquid film, and record the displacement of the tracer particles.

[0051] The initial position of the tracer particles was observed using a microscope with 4x magnification, and video recording was started. A drop of 3 μL of 40 cmc Triton X-100 aqueous solution (1 cmc corresponds to 0.01229 wt% Triton X-100 solution) was dropped into the upper left corner of the liquid film, and the movement of the liquid film and the tracer particles during the spreading process was recorded using a high-speed camera connected to the microscope.

[0052] For experimental observation of tracer particles, please refer to the appendix. Figure 1It can clearly identify the position of each tracer particle and can capture the position of the moving boundary (a) and the filamentous stripes (b) formed on the liquid film during the movement. Preliminary analysis shows that the tracer particles inside the filamentous stripes will retract after moving a certain distance, while the tracer particles outside the filamentous stripes will always move forward with the liquid film and gradually stop without retracting.

[0053] See attached document Figure 2 Using the PTV particle tracer method, each tracer particle was analyzed to track its velocity and position, revealing the microscopic flow field of the liquid within the plane. The velocity at each point in the plane is represented by the size and color of the arrow. The tracer particles move as the liquid film spreads. Specifically, the tracer particles within the corresponding filamentary structure in the experiment gradually slow down and retract, reflecting the elastic properties of the liquid film when it begins to spread instantaneously under the influence of the surface tension gradient.

[0054] Analyzing the motion of the liquid film and tracer particles: Under the influence of the surface tension gradient, the liquid film begins to move, driving the tracer particles inside forward. The tracer particles within the filamentary striations of the liquid film move from a stationary state to their maximum displacement, while the surface tension gradient gradually decreases with the movement of the liquid film. When the surface tension gradient is just insufficient to maintain the elastic shear deformation of the liquid film, the tracer particles stop moving forward; at this point, the solution reaches its maximum shear deformation. At the next moment, the tracer particles will begin to retract, indicating that the gradually decreasing surface tension gradient on the liquid surface will be insufficient to maintain the elastic shear deformation of the liquid film. Using the surface tension gradient at the point where the tracer particles just begin to retract and the displacement of the tracer particles, the corresponding elastic shear stress and elastic shear strain can be obtained.

[0055] Because the viscoelastic liquid film of a polymer possesses both viscous and elastic properties, the ordinary viscous property is manifested in the fluidity of the liquid, and the tracer particles flow with the liquid; the special elastic property is manifested in the recoverable elastic deformation of the liquid, and the movement of the tracer particles reciprocates with the recovery of the liquid's elastic deformation. Therefore, the liquid and tracer particles inside the retracted filamentary structure exhibit the elastic properties of the liquid film at this time, hence the reference to the appendix. Figure 1 We selected tracer particles with retraction characteristics within the filamentous structure of the liquid film for analysis and calculated the elastic shear modulus at each tracer particle.

[0056] The next step will be to use these retracted tracer particles to calculate the elastic modulus.

[0057] Step 4: Measurement and statistics of shear strain and shear stress.

[0058] Surfactant solutions can stably maintain a certain surface tension value within a concentration range of 1 cmc to 40 cmc, meaning that diluting the droplet up to 40 times does not change its surface tension, thus satisfying the requirement for stable droplet surface tension in experiments. Furthermore, the surface tension of viscoelastic liquids is close to that of water; the preparation of the liquid film does not affect its surface tension, and its surface tension remains stable during the experiment. Therefore, the surface tension difference between the droplet and the liquid film remains constant during the experiment. The surface tensions of the droplet and the liquid film can be measured using a Dataphysics OCA20 surface tension meter. Before the experiment, the surface tensions of the viscoelastic solution containing tracer particles and the surfactant droplet are measured to obtain their surface tension difference. A surface tension gradient exists at the liquid-air interface formed by the droplet and the liquid film; this gradient is the ratio of the surface tension difference between the droplet and the liquid film to the distance the liquid film has traveled, and its magnitude varies with the distance the liquid film has traveled.

[0059] After a surfactant droplet is added, the liquid film begins to move. The leading edge of the liquid film moves to a specific position at a specific moment. Let the distance between the leading edge of the moving liquid film and the position where the surfactant droplet lands be *x*. Within this distance *x*, a surface tension difference *S* is formed on the surface of the liquid film; therefore, the surface tension gradient is *S / x*. Under the influence of this surface tension gradient, the liquid film undergoes shearing motion and deformation; therefore, the shear stress *o* inside the liquid film is *O* = *S / x*. The distance *x* gradually increases with the movement of the liquid; therefore, when the surface tension value is constant, the surface tension gradient *σ* gradually decreases with the movement of the liquid.

[0060] Because the elastic properties differ between different local areas within the liquid film, the retraction time of different tracer particles within the liquid film varies. Due to the shearing action of the solution, the maximum displacement of a tracer particle before retraction is measured and denoted as δ. r The initial thickness of the liquid film can be obtained by dividing the volume V of the liquid film on the glass slide by the surface area S of the glass slide. The movement and retraction of the tracer particles are manifestations of the elastic properties of the liquid, and this maximum displacement δ r This represents the elastic displacement of the liquid film at the location of the tracer particle under shear stress. From this, the elastic shear strain of the liquid film at the location of the tracer particle can be obtained. At this point, the corresponding shear stress in the liquid is the elastic stress that causes this shear deformation, which is the surface tension gradient S / x at this time. m , where x m This is the distance x between the leading edge of the liquid film and the position where the surfactant droplets fall, at the moment when the tracer particle just begins to stop retracting. From this, the shear stress and corresponding shear strain of the liquid film at the tracer particle during shear deformation are obtained.

[0061] Record the movement distance δ of all retracted tracer particles inside the liquid filamentary structure. rThe elastic shear strain of the liquid film at each tracer particle can be obtained. And record the distance x from the leading edge of the liquid film to the droplet's landing position at the exact moment when the tracer particle just begins to not retract. m The corresponding surface tension gradient S / x m During the shear spreading of this viscoelastic Boger liquid film, stress-strain data sets (stress σ = S / x) were obtained at the location of each tracer particle within the filamentary structure. m The strain ε = δr / h0). Since only retracted tracer particles can reflect the elastic properties of the liquid film, this invention uses retracted tracer particles for statistical analysis and calculation. Furthermore, the elastic shear stress of the liquid when the tracer particles are just not retracted is σ = S / x. m This corresponds precisely to the elastic shear deformation ε=δr / h0 calculated from the displacement of the tracer particle at this time. The ratio of stress to strain is the elastic shear modulus. Therefore, the data for fitting the shear modulus in this invention is the data of the tracer particle at the moment when it does not retract.

[0062] Step 5, Calculation of elastic modulus.

[0063] Plot the shear stress and shear strain data corresponding to all the retracted tracer particles in the stress-strain coordinate plane, as shown in the appendix. Figure 3 The dotted data set represents the shear stress-shear strain data obtained from the Boger2 polymer solution during tracer particle retraction following steps 2 and 3; the star-shaped data set represents the shear stress-shear strain data obtained from the Boger1 polymer solution during tracer particle retraction following steps 2 and 3; the horizontal axis represents shear strain. The vertical axis represents shear stress. The initial average thickness of the liquid film can be obtained by dividing the volume of the liquid forming the film by the area of ​​the glass; and η1 is the viscosity value of the viscoelastic liquid, and η2 is the viscosity value of the surfactant droplet; the units of η1 and η2 are millipascals per second, and the unit of 3 / 400 is meters per second (Pa·s); from the stress-strain relationship of the elastic body σ = G ε The ratio of stress to strain is the shear modulus G.

[0064] Figure 3 The table shows stress-strain data sets for two different viscoelastic solutions. Linear fitting was performed on each set of data, with the fitting equation set as y = Gx. The slope of the fitted line is the elastic shear modulus G. The elastic shear modulus of Boger 1 solution is 1.23 Pa, and that of Boger 2 solution is 0.45 Pa. The local shear modulus at each tracer particle is shown in Table 1 below. This is the final result of the method of this invention for measuring the elastic shear modulus of the liquid film.

[0065] Table 1: Shear stress-shear strain data sets for Boger 1 and Boger 2 solutions and the corresponding shear modulus for each data set:

[0066]

[0067] verify:

[0068] To verify the rationality of this invention, the viscosity values ​​of Boger1 and Boger2 solutions were measured using an Anton-Paar MCR 301 rheometer. The test procedure and method are as follows:

[0069] Measurements were performed using a CP50-1 cone-plate rotor. Two milliliters of the test solution were pipetted and placed in the center of the rheometer's measurement platform. The rheometer rotor position was set, and the cone-plate rotor was lowered to a measurement position close to the liquid surface. A plastic scraper was used to remove excess liquid located outside the rotor, ensuring the solution was completely beneath it. The rheometer's measurement speed range was set to 1-10000 s. -1 Begin measurement. Record the shear rate. The viscosity result η and the first normal stress difference N1 are given. The two elastic shear moduli G of the viscoelastic solution are then calculated. N and G η The elastic shear modulus G of a polymer solution is itself a range, with its value falling between two values.

[0070] According to Formula 1: The relaxation time τ can be obtained. N Where N1 is the first normal stress difference of the solution, N is the number of polymers per unit volume of polymer solution, and k is determined by the concentration of the polymer solution to be tested. B is the Boltzmann constant, with a value of 1.38 × 10⁻⁶. -23 J / K, T is absolute temperature, which is 273+ degrees Celsius. The first normal stress difference N1 measured by the rheometer and the corresponding shear rate at the time of measurement. The relaxation time τ can be obtained. N That is, the shear modulus value G corresponding to the first normal stress difference measured by the rheometer is obtained. N =η / τ N .

[0071] According to formula two: η=η s +Nk B T τ The relaxation time τ can be obtained. η , where η s Let N be the viscosity of the solvent in the polymer solution to be tested, N be the number of polymers per unit volume of the polymer solution, and k be the concentration of the polymer solution to be tested. Bis the Boltzmann constant, with a value of 1.38 × 10⁻⁶. -23 J / K, T is absolute temperature, which is 273+ degrees Celsius. Viscosity η is measured by a rheometer, and the viscosity η of the solvent is measured separately. s The relaxation time τ can be obtained. η This yields the shear modulus G corresponding to the viscosity value measured by the rheometer. η =η / τ η .

[0072] The table below shows the two shear moduli G of Boger 1 and Boger 2 solutions, respectively, measured by a rheometer. N Value and G η The value of the shear modulus of a viscoelastic solution is in the range of G. N <G<G η The shear modulus ranges of the two solutions measured by the rheometer were Boger 1: 0.61 < G < 1.42 and Boger 2: 0.28 < G < 0.89, respectively.

[0073]

[0074] Results analysis:

[0075] Comparing the range of elastic shear modulus G obtained by the rheometer with the elastic modulus at each particle position obtained by the particle tracing method of the present invention in the table, the ranges of elastic shear modulus obtained by the two methods are close, which shows the rationality of the present invention in solving the elastic shear modulus.

[0076] The above embodiment uses a specific viscoelastic solution to perform PTV particle tracer-assisted elastic modulus measurement. Its purpose is to help understand the essence of the invention. However, the scope of protection of this invention is not limited to this specific example. All equivalent substitutions based on this embodiment are protected by this invention patent.

[0077] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. A method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method, characterized in that: Includes the following steps: Multiple tracer particles are added to the viscoelastic liquid sample to be tested, wherein the density difference between the tracer particles and the density of the viscoelastic liquid to be tested is less than or equal to 5%. The surface tension S1 of a viscoelastic liquid containing tracer particles was measured. The surface tension S2 of the surfactant was measured; The viscoelastic liquid to be tested, to which tracer particles are added, is spread on a smooth surface to form a liquid film; The surfactant is dropped onto the surface of the liquid film, and the liquid film and tracer particles move under the action of the surface tension gradient. Observe the movement of the liquid film and tracer particles, and obtain the distance x between the leading edge of the liquid film and the droplet position of the surfactant at the inflection point when the tracer particles retract, as well as the maximum displacement δ of the tracer particles at that moment. r ; According to the formula ε=δ r The shear strain ε is calculated from h0, and the shear stress σ is calculated using the formula σ=S / x; where h0 is the initial average thickness of the liquid film, S is the surface tension difference, and S=S1-S2; The shear stress and shear strain data corresponding to multiple tracer particles are plotted in the XY coordinate system and linearly fitted. The slope of the fitted line is the elastic shear modulus G. The concentration of the tracer particles needs to be 1.6 × 10⁻⁶. 7 pcs / cm 2 Order of magnitude; The concentration of the surfactant is greater than 10 times the critical micelle concentration.

2. The method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method according to claim 1, characterized in that: The viscoelastic liquid to be tested is a Boger viscoelastic solution comprising polyethylene oxide (PEO) and polyethylene oxide (PEG).

3. The method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method according to claim 2, characterized in that: The tracer particles are polystyrene microspheres.

4. The method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method according to claim 3, characterized in that: The ratio of the diameter of the tracer particle to the thickness of the liquid film is less than 1 / 7.

5. The method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method according to claim 1, characterized in that: The pits on the smooth surface are less than 1 micrometer.

6. The method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method according to claim 5, characterized in that: The smooth surface is a glass surface, which has undergone cleaning, drying, and plasma treatment.

7. The method for measuring the elastic shear modulus of a viscoelastic liquid based on particle tracer method according to any one of claims 1 to 6, characterized in that: The surfactant is a nonionic surfactant.

8. The method for measuring the elastic shear modulus of viscoelastic liquids based on particle tracer method according to claim 7, characterized in that: The surfactant is an aqueous solution of Triton X-100.

9. The method for measuring the elastic shear modulus of a viscoelastic liquid based on particle tracer method according to claim 8, characterized in that: The concentration of Triton X-100 aqueous solution is 40 cmc.

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