A rheological test method for concentrated suspension stress breakdown
By decomposing the stress of concentrated suspensions through shear reversal and stop experiments using a rheometer, the problem of the inexplicable stress contribution of concentrated suspensions within large-amplitude oscillation periods was solved, enabling the optimization of concentrated suspension formulations and improving their processing performance.
Patent Information
- Application Number
- CN202310790074.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-30
- Publication Date
- 2026-02-06
- Estimated Expiration
- 2043-06-30
AI Technical Summary
Existing technologies cannot explain the relative contribution of stress generated by the microscopic processes in concentrated suspensions during large-amplitude oscillation periods, which leads to the difficulty in processing concentrated suspensions and the difficulty in adjusting the formulation.
Pre-shearing was used to eliminate the shear history of the sample preparation process. Shear reversal and shear stop experiments were conducted using the arbitrary wave mode of the rheometer. The total stress was decomposed into hydrodynamic force, Brownian force and contact force. The relative contribution of each stress was obtained by extrapolation and fitting.
Accurately obtaining the relative contribution and variation relationship of each component stress in the large amplitude oscillation range can guide the design of concentrated suspension formulations and improve their processing performance.
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Figure CN116754434B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a rheological test method for stress decomposition of concentrated suspensions, in particular, to a rheological test method for stress decomposition of non-colloidal hard sphere particle concentrated suspensions. BACKGROUND
[0002] Non-colloidal concentrated suspensions have been applied in many fields, including food production, construction industry and solid propellants. The particle size of such systems is between 100 nm and 500 μm, and the volume fraction is greater than 0.3, which usually exhibits shear thickening rheological behavior. At present, the rheological test method for concentrated suspensions mainly focuses on steady-state rheological properties, which adjusts the formulation of the suspension by testing the macroscopic viscosity characteristics of the suspension, however, such macroscopic test method is difficult to guide the adjustment direction of the formulation. Large amplitude oscillatory shear (LAOS) rheological test is an effective method to characterize the nonlinear rheological response of materials under the processing flow field, for example, Chinese patent CN110186810A discloses a stress large amplitude oscillatory shear loading asphalt nonlinear rheological property test method. Under a fixed frequency, when the applied amplitude (strain or stress) increases from small to large, the response of the material may exhibit a transition from linear to nonlinear, which helps to comprehensively evaluate the processing performance of the material. Concentrated suspensions will exhibit obvious shear thickening behavior during large amplitude oscillatory shear, which greatly increases the processing difficulty of concentrated suspensions. At present, it is generally believed that the existence and growth of contact force between suspended particles is the main reason for the shear thickening of concentrated suspensions during processing. Therefore, quantitative analysis of the response of contact force and other partial stress contributing to total stress of concentrated suspensions under large amplitude shear flow field is of great significance for guiding the formulation design of concentrated suspensions and optimizing the processing performance of concentrated suspensions.
[0003] At present, the stress composition in most concentrated suspensions is based on the assumption of rheological model, under the applied shear flow field, the total stress mainly includes hydrodynamic force (σH), contact force of particles (σC) and Brownian force (σB), which has the following relationship:
[0004] σT=σC+σB+σH
[0005] Among them, the hydrodynamic force is generated by the viscous damping of the solvent, which is proportional to the applied strain rate. When the applied strain is large enough, the particles will be closely packed along the shear direction, thereby generating contact stress (derived from the normal force and friction force between particles). The Brownian force comes from the thermal disturbance of the particles and the anisotropy of their distribution.
[0006] However, based on the rheological model, it is usually impossible to explain the relative contribution of the stress generated by various microscopic processes that determine the rheological properties of the system during or within the large amplitude oscillation cycle. SUMMARY
[0007] The present application aims to overcome the defects of the prior art and provide a rheological test method for stress decomposition of concentrated suspensions, which analyzes the size and change of fluid dynamics force, Brownian force and contact force that contribute to the total stress in a large-amplitude oscillatory shear cycle or between different cycles, which is of great significance for understanding the stress response of concentrated suspensions under large-amplitude shear flow field and guiding the formulation design of concentrated suspensions.
[0008] The purpose of the present application can be achieved by the following technical scheme: a rheological test method for stress decomposition of concentrated suspensions, first, pre-shear is used to eliminate the shear history generated in the sample preparation process; then, shear reversal experiment is carried out by using the arbitrary wave mode of the rheometer to determine the relationship between the stress before and after reversal and the contact force and Brownian force; then, shear stop experiment is carried out, the size of Brownian force is obtained by extrapolation, and the relative contribution of each stress is obtained in combination with the shear reversal experiment.
[0009] The method specifically comprises the following steps:
[0010] S1, the concentrated suspension is placed on the parallel plate clamp of the rheometer, and pre-shear experiment is carried out under the set mode to eliminate the shear history generated in the sample preparation process and create the same initial condition;
[0011] S2, shear reversal experiment is carried out by selecting the arbitrary wave mode of the rheometer: for oscillatory shear with strain amplitude γ0 and angular frequency ω, before the reversal time, the shear strain changes with time as γ=γ0sin(ωt); at the reversal time t rev , the instantaneous strain and strain rate are γ0sin(ωt rev ) and γ0ωcos(ωt rev ) respectively, and the corresponding shear stress is σ T ; after the reversal time, the strain becomes γ=γ0sin(ωt rev )-γ0ωcos(ωt rev )(t-t rev ), and the shear stress at the reversal time becomes σ rev , the stress difference before and after the reversal is determined from the shear reversal experiment: σ T -σ rev =σ C +2σ B , wherein σ C and σ B represent the contact force and Brownian force respectively;
[0012] S3, shear stop experiment is carried out by selecting the arbitrary wave mode of the rheometer: at the stop time, the instantaneous strain and strain rate are γ0sin(ωt ces ) and γ0ωcos(ωtces ), the corresponding shear stress is σ T ; the Brownian force is obtained by exponential fitting the stress curve after inversion and extrapolation to t=0;
[0013] S4, by selecting different time points in the first and fourth quadrants of the Lissajous curve, the shear reversal time point in step S2 and the shear stop time point in step S3 are changed, steps S1 to S3 are repeated, the fluid dynamics force, the Brownian force and the contact force corresponding to each time are obtained;
[0014] S5, by changing the strain amplitude γ0 and the angular frequency ω in steps S2 and S3, steps S1 to S4 are repeated, and the contribution of each stress at different times on the Lissajous curve under different amplitudes and angular frequencies is obtained.
[0015] Further, the dense suspension is a particle suspension system composed of spherical and / or irregular particles with a particle size of 100 nm to 500 μm and a volume fraction of ≥0.3 and a viscous matrix.
[0016] Further, the particles in the dense suspension are one or more of aluminum powder, sodium sulfate, silicon dioxide, aluminum oxide, etc.
[0017] Further, the specific method of step S1 pre-shearing is to first perform an oscillation time scan under a large strain amplitude of 0.1<γ0<5 and a fixed frequency of 0.1-5 Hz, and the time range is 60-3600 s, and then stand for 60-300 s.
[0018] Further, two cycles of oscillatory shear are performed before the shear reversal experiment in step S2 to ensure that the sample reaches a stable state.
[0019] Further, two cycles of oscillatory shear are performed before the shear stop in step S3 to ensure that the sample reaches a stable state.
[0020] The application also provides an application of the rheological test method for stress decomposition of a dense suspension,
[0021] The method is used to compare the responses of different formulations of the dense suspension to the partial stress, the effects of different components and contents on the partial stress can be understood, which helps to guide the formulation design of the dense suspension, and further improves the processing performance of the dense suspension.
[0022] Compared with the prior art, the application has the following beneficial effects:
[0023] The rheological test method for stress decomposition of a concentrated suspension of the present application can decompose stress at any point on the entire Lissajous curve through shear reversal and shear stop test, so as to accurately obtain the relative contribution and change relationship of each partial stress in the large-amplitude oscillation interval. Through comparison of the results of suspensions with different formulations, the relative contribution of stress generated by various microscopic processes of the system rheology can be clearly determined, thereby guiding and optimizing the formulation design of the concentrated suspension, and facilitating to obtain a formulation with better processing performance. BRIEF DESCRIPTION OF DRAWINGS
[0024] Figure 1 The shear strain and strain rate change curves with time in the shear reversal experiment of Example 1 of the present application;
[0025] Figure 2 The stress before and after shear reversal and the stress-strain curve after shear reversal in the shear reversal experiment of Example 1 of the present application;
[0026] Figure 3 The shear strain and strain rate change curves with time in the shear stop experiment of Example 1 of the present application;
[0027] Figure 4 The stress change relationship with time and the determination method of Brownian force after shear stop in the shear stop experiment of Example 1 of the present application;
[0028] Figure 5 The hydrodynamic force, Brownian force and contact force obtained by stress decomposition at different points on the Lissajous curve determined by the method of the present application in Example 1 of the present application.
[0029] Figure 6 The hydrodynamic force, Brownian force and contact force obtained by stress decomposition at different points on the Lissajous curve determined by the method of the present application in Comparative Example 1 of the present application. DETAILED DESCRIPTION
[0030] The present application will be described in detail below in combination with the drawings and specific examples.
[0031] The rheological test method for rheological properties of a concentrated suspension of the present application, the specific steps are:
[0032] S1, place the concentrated suspension on the parallel plate clamp of the rheometer, and perform a pre-shear experiment in the set mode to eliminate the shear history generated during sample loading and sample preparation, and create the same initial conditions.
[0033] S2, select the arbitrary wave mode of the rheometer to perform the shear reversal experiment, as follows: for the oscillatory shear with strain amplitude γ0and angular frequency ω, the shear strain changes with time as γ = γ0sin(ωt) before the reversal. To ensure that the sample reaches a steady state, two periods of oscillatory shear are performed before the shear reversal experiment. At the reversal time t rev , the instantaneous strain and strain rate are γ0sin(ωt rev ) and γ0ωcos(ωt rev ), respectively, and the corresponding shear stress is σ T . After the reversal, the strain becomes γ = γ0sin(ωt rev )- γ0ωcos(ωt rev )(t-t rev ), and σ C decreases rapidly to 0 as the particles separate from each other in the suspension, σ H is the same in magnitude but opposite in direction, and σ B remains the same in magnitude and direction. Therefore, the stress after the reversal (σ rev ) is σ rev = σ H - σ B . Further, the shear reversal experiment can determine the stress difference before and after the reversal as σ T - σ rev = σ C + 2σ B .
[0034] S3, select the arbitrary wave mode of the rheometer to perform the shear stop experiment, as follows: before the shear stop, two periods of oscillatory shear are performed to ensure that the sample reaches a steady state. At the stop time, the strain rate decreases rapidly to 0. σ H is a function of the rate and also decreases rapidly to 0; σ C and σ B produce an elastic component that remains unchanged after the shear stop, but σ C decays too rapidly to be measured; due to the asymmetry of the particle distribution, σ B decays on a longer time scale, which can be obtained by extrapolating the stress change curve after the reversal to t = 0.
[0035] S4, by selecting different time points in the first and fourth quadrants of the Lissajous curve, the shear reversal time point in step two and the shear stop time point in step S3 are changed, steps S1 to S3 are repeated, and the fluid dynamics force, the Brownian force and the contact force at different times are obtained.
[0036] S5, repeat steps S1 to S4 by changing the strain amplitude γ0 and the angular frequency ω in steps S2, S3 to obtain the contribution of each stress at different time on the Lissajous curve at different amplitudes and angular frequencies.
[0037] Embodiment 1
[0038] A method for testing the rheological properties of a spherical aluminum powder particle suspension, comprising the following steps:
[0039] S1, place the spherical aluminum powder particle suspension with a solid content of 44.10 vol% in the parallel plate rheometer fixture, and perform a pre-shearing experiment in the set mode. Specifically, under the conditions of a strain amplitude of 100% and a frequency of 1 Hz, perform a time scan for 120 s, and then stand for 120 s.
[0040] S2, select the arbitrary wave mode of the rheometer to perform a shear reversal experiment. Specifically, for an oscillatory shear with a strain amplitude of γ0 and an angular frequency of ω, the shear strain changes with time as γ = γ0sin(ωt) before shear reversal. At the same time, in order to ensure that the sample reaches a steady state, two periods of oscillatory shear are performed before shear reversal. At the reversal time t rev , the instantaneous strain and strain rate are γ0sin(ωt rev ) and γ0ωcos(ωt rev ), respectively, and the corresponding shear stress is σ T . After reversal, the strain changes with time as γ = γ0sin(ωt rev )-γ0ωcos(ωt rev )(t-t rev ), and the shear stress is σ rev . The stress difference before and after shear reversal can be determined from the shear reversal experiment as follows: σ T -σ rev =σ C +2σ B .
[0041] S3, select the arbitrary wave mode of the rheometer to perform a shear stop experiment. Specifically, first perform two periods of oscillatory shear to ensure that the sample reaches a steady state, and the shear strain changes with time as γ = γ0sin(ωt). At the stop time, the instantaneous strain and strain rate are γ0sin(ωt ces ) and γ0ωcos(ωt ces ), respectively, and the corresponding shear stress is σ T . It should be noted that the time corresponding to the stop time in step two and the reversal time in step two should be the same. After the shear stop time, the strain rate becomes 0 and does not change with time, and the shear strain is fixed at γ0sin(ωt cesAfter shearing stops, the stress decay over time can be observed. However, due to instrument inertia, data within 40 ms after shearing stops are excluded. By fitting the stress change over time with a single exponential function and extrapolating it to t=0, the corresponding stress is the Brownian stress. By combining the shear reversal experiment and the shearing stop experiment in step two, the relative contributions of hydrodynamic force, Brownian force, and contact force at a certain moment can be calculated.
[0042] S4. By selecting the time points in the first and fourth quadrants of the Lissajous curve to change the shear reversal time point in step two and the shear stop time point in step three, repeat steps one to three to decompose the total stress and obtain the corresponding hydrodynamic force, Brownian force and contact force at each moment.
[0043] S5. By changing the strain amplitude γ0 and angular frequency ω in steps two and three, repeat steps one to four to obtain the contribution of each stress on the Lissajous curve under different amplitudes and angular frequencies.
[0044] like Figure 1 The figure shows the curves of shear strain and strain rate versus time in the shear reversal experiment in Example 1. As can be seen from the figure, at the reversal moment, the shear rate is equal in magnitude but opposite in sign to that before the reversal. At this time, the shear strain changes linearly with time.
[0045] like Figure 2 The figure shows the stress before and after shear reversal in the shear reversal experiment in Example 1, as well as the stress-strain curves after reversal. It can be seen from the figure that the stress after shear reversal is less than the stress before reversal. This is because after reversal, the particles separate from each other, causing the contact force to disappear. At this time, only the contribution of the hydrodynamic force remains.
[0046] like Figure 3 The figure shows the curves of shear strain and strain rate versus time in the shear stop experiment in Example 1. It can be seen from the figure that at the shear stop time, the shear rate becomes 0 and the shear strain remains unchanged.
[0047] like Figure 4 The figure shows the stress-time relationship after shearing stops in Example 1 and the method for determining the Brownian force. It can be seen from the figure that the stress decreases exponentially with time after shearing stops. By extrapolating the curve to the reversal time, the contribution of the Brownian force can be determined.
[0048] like Figure 5The figure shows the hydrodynamic forces, Brownian forces, and contact forces obtained from stress decomposition at different points on the Lissajous curve determined by the method described in this invention in Example 1. It can be seen from the figure that the total stress-strain curves obtained from shear reversal and shear cessation experiments coincide with the Lissajous curves obtained from LAOS testing, proving the accuracy of the method described in this invention. However, LAOS testing can only obtain the total stress variation curve. Compared with LAOS testing, the method described in this invention can accurately obtain the relative contribution and variation relationship of each component stress in the large amplitude oscillation range, thus understanding the changes in microstructure.
[0049] Table 1 shows the selected time points and their corresponding mechanical data in the embodiments.
[0050]
[0051]
[0052] As can be seen from Table 1 above, shear reversal and shear stop tests can be performed at any moment during large-amplitude oscillating shear, and the relative contributions of each component stress can be obtained.
[0053] Comparative Example 1
[0054] A rheological test method for contact force of irregular sodium sulfate particle suspension, except that the particles are irregularly shaped sodium sulfate particles, the other components and contents and preparation methods are the same as in Example 1.
[0055] like Figure 6 The figure shows the hydrodynamic forces, Brownian forces, and contact forces of the irregular sodium sulfate particle suspension determined by the method described in this invention in Comparative Example 1. It can be seen from the figure that the contact forces between irregularly shaped sodium sulfate particles are stronger than those between spherical aluminum powder particles, which is related to the greater friction between the irregular particles; the hydrodynamic forces are similar to those of spherical aluminum powder particles. Therefore, by improving the shape regularity of the particles, the contact forces of the particles in the concentrated suspension can be reduced, thereby reducing the shear thickening degree of the concentrated suspension in a large-amplitude shear flow field and improving the processing performance of the concentrated suspension.
[0056] The rheological testing method of stress decomposition of concentrated suspensions helps to analyze the contribution of stress corresponding to different components and contents in the formulation, which helps to guide the formulation design of concentrated suspensions and thus improve the processing performance of concentrated suspensions.
[0057] The above examples are merely reference embodiments of the present invention. The scope defined by the claims of the present invention is not limited to the specific implementation details described above. It should be understood that any modifications, concentration changes, similar component substitutions, and modifications made by those skilled in the art to the present invention in accordance with the design principles of the present invention should be within the protection scope of the present invention.
Claims
1. A method of rheological testing of concentrated suspension stress breakdown, characterized by, Firstly, pre-shearing is used to eliminate the shear history generated in the sample preparation process; then, the shear reversal experiment is carried out by using the arbitrary wave mode of the rheometer to determine the relationship between the stress and the contact force and the Brownian force before and after the reversal; Then, the shear stop experiment is carried out, the size of the Brownian force is obtained by extrapolation, and the relative contribution of each stress is obtained in combination with the shear reversal experiment; The method specifically comprises the following steps: S1, the concentrated suspension is placed on the parallel plate clamp of the rheometer, and a pre-shearing experiment is carried out under a set mode to eliminate the shear history generated in the sample preparation process, and to create the same initial condition; S2. Select an arbitrary wave mode of the rheometer to conduct a shear reversal experiment: for strain amplitude of Gamma 0 angular frequency is Omega The oscillating shear, before the reversal moment, the waveform of shear strain changing with time is as follows: Gamma = gamma 0 Sin (omega t) At the reversal moment t rev Instantaneous strain and strain rate are respectively Gamma 0 Sin (omega t rev ) and Gamma 0 Omega cos (omega t rev ) The corresponding shear stress is Sigma T After the reversal time, the strain becomes γ= Gamma 0 Sin (omega t rev ) - gamma 0 Omega cos (omega t rev )(t - t rev ) The shear stress at the moment of reversal becomes Sigma rev The stress difference before and after the reversal was determined from the shear reversal experiment as follows: Sigma T -Sigma rev = sigma C + 2 sigma B ,in Sigma C and Gamma B These represent contact force and Brownian force, respectively. S3, arbitrary wave mode of rheometer was selected to perform shear stop experiment: at the stop moment, the instantaneous strain and strain rate were Sin (omega t 0 Gamma ces ) and Omega cos (omega t 0 Sigma ces ) corresponding shear stress was S4, by selecting different time points in the first and fourth quadrants of the Lissajous curve, the shear reversal time point in step S2 and the shear stop time point in step S3 are changed, steps S1 to S3 are repeated, and the fluid dynamics force, the Brownian force and the contact force corresponding to each time are obtained. T ; Brownian force was obtained by exponential fitting of the stress curve after inversion with time and extrapolation to t=0; The concentrated suspension is a particle suspension system composed of spherical and / or irregular particles with a particle size of 100 nm to 500 µm and a volume fraction of ≥ 0.3 and a viscous matrix. S5, repeat steps S1-S4 with different strain amplitudes The particles in the concentrated suspension are one or more of aluminum powder, sodium sulfate, silicon dioxide and aluminum oxide. 0 and angular frequencies The specific way of pre-shearing in step S1 is to first perform an oscillation time scan under a large strain amplitude of 0.1< gamma 0< 5 and a fixed frequency of 0.1-5 Hz, and the time range is 60-3600 s, and then stand for 60-300 s. , repeat steps S1-S4 with different strain amplitudes and angular frequencies to obtain the contribution of each stress at different times on the Lissajous curve.
2. A method of rheological testing of stress decomposition of concentrated suspensions according to claim 1, characterized in that, Two cycles of oscillatory shear are performed before the shear reversal experiment in step S2 to ensure that the sample reaches a stable state.
3. A method of rheological testing of stress decomposition of concentrated suspensions according to claim 2, characterized in that, Two cycles of oscillatory shear are performed before the shear stop in step S3 to ensure that the sample reaches a stable state.
4. A method of rheological testing of stress decomposition of concentrated suspensions according to claim 1, characterized in that, The method is used to compare the response of the stress of the concentrated suspension of different formulations, the influence of different components and contents on the stress can be understood, which helps to guide the formulation design of the concentrated suspension, and further improves the processing performance of the concentrated suspension.
5. A method of rheological testing of stress decomposition of concentrated suspensions according to claim 1, characterized in that, 6. A method of rheological testing of concentrated suspensions according to claim 1, characterized in that, 7. Use of a rheological test method for stress decomposition of concentrated suspensions according to any one of claims 1 to 6, characterized in that
Citation Information
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