Ultra-high concentration shear-thickening fluids and their preparation methods and applications

Abstract

This invention discloses an ultra-high concentration shear-thickening fluid and its preparation method and applications. The fluid is composed of nanoparticles and a solvent, with the volume fraction of the nanoparticles in the fluid being 0.63-0.65, and the solvent being a liquid polymer polyol. The nanoparticles are premixed and dispersed by strong shear until the "Tyndall effect" appears. Further uniform mixing is achieved using a high-power circulator, resulting in increased uniformity of the fluid. Finally, the fluid is dried until the total content of small-molecule alcohol impurities falls below 3.5 wt%. The shear-thickening fluid of this invention has a concentration of 0.63-0.65, which is greater than the thickening range of all conventional discontinuous shear-thickening fluids (the ratio of maximum to minimum concentration is up to 1000 times greater), and it exhibits superior impact energy absorption and significantly improved impact resistance in applied products.

Description

[Technical Field]

[0001] The present invention relates to ultra-high concentration shear thickening fluids and their preparation methods and applications, and belongs to the technical field of nanofluid materials. [Background technology]

[0002] Shear-thickening fluids are particle suspensions whose concentration changes with changes in external force. They are composed of nanoparticles and a solvent. When an external force is applied to the fluid, the particles aggregate to form particle clusters, and the viscosity of the fluid doubles as the particle clusters form. When the external force is removed, the particle clusters disperse, the particles return to a dispersed and suspended state, and the viscosity of the fluid decreases to an equilibrium state. This property allows the fluid to absorb impact, making it a potential application market in many fields, including knife-proofing, bulletproofing, and collision prevention.

[0003] The shock absorption capacity of a fluid increases dramatically with increasing nanoparticle volume fraction (Φ) in the fluid (i.e., concentration). The highest concentration reported in the literature is Φ = 0.62. The nanoparticle concentrations of other published shear-thickening fluids are generally concentrated between 0.46 and 0.62. To date, no ultra-high-concentration shear-thickening fluids with Φ ≥ 0.63 have been reported.

[0004] The difficulty in preparing ultra-high concentration shear-thickening fluids lies in the dispersion of agglomerated nanoparticles. Conventional preparation techniques mainly involve vortex vibration, low-speed ball milling, and ultrasonic dispersion. When preparing medium- to low-concentration fluids, these preparation techniques can effectively disperse agglomerated nanoparticles and provide the fluid with good shear-thickening properties. However, when the fluid concentration increases to 0.63 or higher, conventional techniques are unable to effectively disperse agglomerated particles, and the prepared fluid lacks discontinuous shear-thickening properties. Therefore, it is necessary to invent a preparation process that can effectively disperse agglomerated nanoparticles and prepare shear-thickening fluids with concentrations of 0.63 or higher. Summary of the Invention

[0005] The objective of the present invention is to overcome the shortcomings of the prior art by providing an ultra-high concentration shear thickening fluid capable of reaching a fluid concentration of 0.63-0.65, which has stable discontinuous shear thickening properties, and the thickening amplitude (the ratio of the maximum concentration to the minimum concentration) can exceed 1000 times.

[0006] Another object of the present invention is to provide a method for preparing the above ultra-thick shear-thickening fluid.

[0007] A third object of the present invention is to provide applications for the above-mentioned ultra-high concentration shear-thickening fluid.

[0008] The object of the present invention is achieved by the following technical means. The ultra-high concentration shear-thickening fluid composed of nanoparticles and a solvent is characterized in that the volume fraction of the nanoparticles in the fluid is 0.63 to 0.65, and the solvent is a liquid polymer polyol.

[0009] In the present invention, the nanoparticles have a particle size of 250 to 900 nm, are monodisperse, and are made of an inorganic compound such as silicon dioxide or calcium carbonate.

[0010] The method for preparing the above ultra-thick shear-thickening fluid is characterized by comprising the following steps: a. Premixing: Nanoparticles are slowly added to a solvent and stirred slowly until no clumps are visible to the naked eye, to obtain a premixed solution. b. Shear dispersion: The fine particles in the preliminary mixture are strongly sheared and dispersed to obtain a primary fluid until the "Tyndall effect" can be observed in the fluid under the irradiation of a laser pointer. c. Uniform mixing: A powerful circulator is used to mix the primary fluid more uniformly, resulting in a highly uniform fluid. d. Drying: The fluid is dried until the sum of the contents of water and small molecule alcohol impurities in the fluid is below 3.5 wt %, to obtain a discontinuous shear thickening fluid.

[0011] In the preparation method of the present invention, step c can be repeated with the dried fluid to mix it uniformly again, thereby increasing the uniformity of the entire fluid. When the fluid flows, it must be a uniform substance without partial stratification.

[0012] In the present invention, the high-intensity shear dispersing device used for shear dispersion is a ball mill, a bead mill or a three-roll mill.

[0013] In the present invention, the powerful circulator used for uniform mixing is a vortex mixer or a roller bottle device.

[0014] The application of the above ultra-high concentration shear thickening fluid can be used in composite cut-proof materials or collision prevention protectors.

[0015] Compared with the prior art, the present invention has the following advantages: The concentration of the shear thickening fluid of the present invention is 0.63 to 0.65, which is larger than the range of discontinuous shear thickening of all conventional fluids (the ratio of the maximum concentration to the minimum concentration exceeds 1000 times at most), and it has a higher effect of absorbing impact energy, resulting in a significant improvement in the impact resistance of applied products.

[0016] In the present invention, after premixing the nanoparticles, all aggregated nanoparticle microclusters are broken down by applying strong shear stress, the fluid is further homogenized by a homogenizing mixer, and finally, the mass fraction of water and small molecule alcohol impurities in the fluid is controlled by drying to improve the fluid's energy absorption effect. Although the preparation method is simple, the present invention can obtain a stable shear-thickening fluid with a fluid concentration of 0.63-0.65, and the higher the viscosity, the greater the fluid's energy absorption effect, ensuring a wider range of applications for shear-thickening fluids. [Brief explanation of the drawings]

[0017] [Figure 1]FIG. 1 is a graph showing the relationship between the viscosity of shear-thickening fluids of different concentrations obtained by dispersing silica spheres with a particle size of 520±49 nm in polyethylene glycol with a relative molecular mass of 200 in Example 1 and the change in viscosity with shear rate. [Figure 2A] FIG. 2A is a graph showing the relationship between the viscosity of the fluids prepared in Examples 2-1 and 2-2 and the change in shear rate, where the curve with hollow circles represents Fluid 2-1 and the curve with filled squares represents Fluid 2-2. [Figure 2B] FIG. 2B is a diagram showing the relationship between the viscosity of the fluids prepared in Examples 2-1 and 2-2 and the change in shear stress, in which the curve with hollow circles represents Fluid 2-1 and the curve with filled squares represents Fluid 2-2. [Figure 3] FIG. 3 is a log-log curve of the relationship of viscosity with shear stress for the fluid prepared in Example 4. [Figure 4] FIG. 4 is a graph showing the relationship between the viscosity of the fluid prepared in Example 5 and the shear rate. [Figure 5] FIG. 5 is a graph showing the relationship between the viscosity of the fluid prepared in Example 6 and the shear rate. [Figure 6] FIG. 6 is a graph showing the relationship between viscosity and shear rate for the fluid prepared in Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0018] The ultra-high concentration shear thickening fluid is composed of nanoparticles and a solvent, and the fluid concentration is 0.63-0.65. The preparation method of the fluid includes the following steps: a. Preparation of premix: Nanoparticles are slowly added to the solvent while stirring slowly to prevent the formation of macroscopic agglomerates to obtain a premix. b. Shear dispersion: The premixed liquid is treated with high shear dispersion to obtain a primary fluid, which should exhibit a good Tyndall effect under the irradiation of a laser pointer. c. Uniform mixing: A powerful circulator is used to mix the primary fluid more uniformly, resulting in a fluid that is highly uniform and does not separate into layers during flow. d. Drying: The fluid is dried until the sum of the contents of water and small molecule alcohol impurities in the fluid is below 2.5 wt %, to obtain a discontinuous shear thickening fluid. e. Use a powerful circulator to mix the dried fluid again for a certain period of time to ensure that the fluid has good uniformity.

[0019] The nanoparticles may be nanosilica spheres or nanocalcium carbonate granules, and the solvent may be a liquid polyol such as ethylene glycol, polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300, or polyethylene glycol 400. The nanoparticles have a particle size of 250-900 nm, are monodisperse, and the difference between the maximum and minimum particle sizes does not exceed 40%.

[0020] The present invention will be described in more detail below in conjunction with specific examples, and all percentages unless otherwise specified are percentages. Example 1:

[0021] material: Nanoparticles: nanosilica spheres with a diameter of 520±49 nm Solvent: Polyethylene glycol with a relative molecular mass of 200 Objective: Prepare shear-thickening fluids with fluid densities of 0.62, 0.63, and 0.64, hereafter referred to as Fluid 1-1, Fluid 1-2, and Fluid 1-3. The preparation method is as follows. a. Premixing: The silica spheres are divided into lots and slowly added to the polyethylene glycol, and at the same time, slowly stirred until the silica spheres added in each lot no longer form lumps visible to the naked eye, to obtain a premixed liquid. b) Shear dispersion: Disperse the mixture using a high-power planetary ball mill at a rotation speed of 800 RPM with a ball to premix ratio of 2:1 for 16-18 hours to obtain the primary fluid. c) Uniform mixing: By using a vortex mixer to uniformly mix the primary fluid for 48 hours or more, the phenomenon of "stratification splitting" caused by local viscosity variations when the fluid flows is prevented, and a fluid with excellent uniformity is obtained. d. Drying: Using a vacuum dryer, dry the fluid under conditions of a vacuum of -0.1 MPa and a temperature of 85°C until the total content of water and small molecular alcohol impurities in the fluid is below 2.5 wt%, to obtain a discontinuous shear thickening fluid. e. Re-mixing: Use the vortex mixer again to mix the dried fluid for 3 to 5 hours. This is sufficient to ensure uniformity of the fluid.

[0022] The relationship between shear rate and the fluid viscosity of the Φ=0.62 fluid (Fluid 1-1), Φ=0.63 fluid (Fluid 1-2), and Φ=0.64 fluid (Fluid 1-3) prepared in Example 1 was shown using a rheometer (MCR302, Anton Paar). A cone-and-plate test system with a 25 mm diameter and a 2° taper angle was used for the test. Prior to the test, a "pre-shear" treatment was performed: the stress was slowly increased from 0.3 Pa to 300 Pa over a 5-minute period, and then slowly decreased back to 0.3 Pa over the same period. This treatment removed any non-uniformity present during sample placement. To better capture the change in fluid viscosity under high shear stress, the rheometer's "control stress" mode was used to scan the shear stress range of 10-2 to 10-4 Pa. The results were plotted as "viscosity vs. shear rate," as shown in Figure 1.

[0023] At Φ = 0.62, the density of Fluid 1-1 reached the highest reported value. At a shear rate of approximately 12 s-1, the density of the fluid dramatically increased from 4 Pa.s to a maximum of 150 Pa.s, a 37.5-fold increase (150 / 4 = 37.5). At Φ = 0.63, the density of Fluid 1-2 increased even more significantly, from a minimum of 4 Pa.s to approximately 1000 Pa.s, a 250-fold increase. At Φ = 0.64, the density of Fluid 1-3 increased from a minimum of 8 Pa.s to 10,000 Pa.s, a 1250-fold increase. This suggests that the fluid density increases significantly with each 1% increase in volume fraction. This suggests that fluids with Φ ≥ 0.63 have a better impact energy absorption effect than all other fluids, resulting in a more significant improvement in the impact resistance of products. Example 2-1:

[0024] Based on the preparation method of Example 1, fluid 2-1 was prepared using silica spheres with a particle size of 520±49 nm and polyethylene glycol with a relative molecular mass of 200, and had a diameter of Φ≈0.63. Example 2-2:

[0025] Based on the preparation method of Example 1, step c was omitted, and fluid 2-2 with Φ≈0.63 was prepared using silica spheres with a particle size of 520±49 nm and polyethylene glycol with a relative molecular mass of 200.

[0026] Using the test method of Example 1, the viscosity of Fluid 2-1 and Fluid 2-2 was measured and analyzed to determine their relationship with shear rate and shear stress, resulting in the characteristic rheological characteristics shown in Figures 2A and 2B. As shown by the hollow circle curve in Figure 2A, Fluid 2-1 prepared by the present invention begins to thicken at a shear rate of 15 s-1, and its viscosity then increases linearly. The shear rate is limited to around 15 s-1, with a concentration increase of approximately 500 times. In Figure 2B, the viscosity of Fluid 2-1 increases linearly with increasing shear stress, and the slope of the viscosity increase in the viscosity vs. shear stress curve is approximately 1, which is a typical discontinuous shear thickening characteristic. Fluid 2-2, prepared at the same concentration but omitting step c (filled square curves in Figures 2A and 2B), exhibits only a 10-fold increase in concentration, with a slope of less than 1 in Figure 2B, and does not exhibit discontinuous shear thickening. Example 3:

[0027] Based on the preparation method of Example 1, step b was omitted, and fluid 3-1 with Φ≈0.63 was prepared using silica spheres with a particle size of 400±34 nm and polyethylene glycol with a relative molecular mass of 200.

[0028] Upon standing for 24 hours, the silica spheres in Fluid 3-1 precipitated and separated out, so the fluid was unable to reach a steady state where the rheological properties could be measured. Example 4:

[0029] Using silica spheres with a particle size of 350±62 nm and polyethylene glycol with a relative molecular mass of 200 as raw materials, and based on the preparation method of Example 1 and controlling the parameters of step d, Fluid 4-1, Fluid 4-2, Fluid 4-3, Fluid 4-4, Fluid 4-5, Fluid 4-6, Fluid 4-7, Fluid 4-8, Fluid 4-9, Fluid 4-10, Fluid 4-11, Fluid 4-12, Fluid 4-13, Fluid 4-14, Fluid 4-15, Fluid 4-16, Fluid 4-17, Fluid 4-18, Fluid 4-19, Fluid 4-20, Fluid 4-21, Fluid 4-22, Fluid 4-23, Fluid 4-24, Fluid 4-35, Fluid 4-36, Fluid 4-37, Fluid 4-18, Fluid 4-29, Fluid 4-21, Fluid 4-22, Fluid 4-34, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-39, Fluid 4-19, Fluid 4-21, Fluid 4-22, Fluid 4-34, Fluid 4-39 ...19, Fluid

[0030] When the shear stress of an external impact on a shear-thickening fluid exceeds a critical value, the nanoparticles in the fluid instantly aggregate to form particle clusters, absorbing or dissipating the impact energy. The greater the shear stress, the more particle clusters formed in the fluid, the greater the energy absorption effect, and the greater the viscosity of the fluid. Numerous theoretical models have shown that, under ideal circumstances, viscosity follows an exponential relationship with changes in shear stress. In a log-log diagram of viscosity versus shear stress, the increase in viscosity with changes in shear stress is linear, and the closer the slope is to 1, the more discontinuous shear-thickening the fluid is, and the more efficiently the fluid per unit volume can absorb energy.

[0031] For fluids 4-1, 4-2, and 4-3 in Example 4 shown in Figure 3, when the mass fraction of impurities such as water and small-molecule alcohols in the fluid is between 1.5 and 2.5 wt%, the slope of the viscosity increase is very close to 1, indicating that the fluid has discontinuous shear thickening properties and that the fluid per unit volume has a high energy absorption effect. When the impurity mass fraction reaches 4 wt%, the viscosity increase with shear stress becomes small, indicating that the fluid has already lost its discontinuous shear thickening properties and that the fluid per unit volume has only very weak energy absorption properties. As the impurity mass fraction continues to increase, the fluid completely loses its energy absorption properties. In other words, the total mass of impurities such as water and small-molecule alcohols in the fluid plays a crucial role in determining whether the fluid has discontinuous shear thickening properties and whether the fluid per unit volume can effectively absorb energy.

[0032] Furthermore, because the polarity of water and small molecular alcohols is greater than that of polymer polyols, once the content of water and small molecular alcohols exceeds the critical value of 4 wt%, the stability of the nanosilica spheres in the polymer polyol is destroyed, causing the silica spheres to precipitate and separate out, resulting in the loss of the discontinuous shear thickening properties of the fluid. Example 5:

[0033] A small amount of purchased silicon dioxide nanoparticles was taken, dispersed in deionized water by vibration, and analyzed by DLS (Dynamic Light Scattering) using a nanoparticle analyzer (model number Malvern ZetaSizer Nano-S). The particle size of the silicon dioxide particles was found to be 273 nm, with a 10% particle size difference. The particle size measured through electron microscopy was 268 ± 22 nm, which closely matches the DLS measurement results. This confirms that the particle size of the silicon dioxide is 273 nm, with a 10% particle size difference.

[0034] Using the preparation method of Example 1, the nano-silicon dioxide particles were dispersed in polyethylene glycol with a relative molecular mass of 100 to obtain a shear-thickening fluid with a volume fraction of 0.65. The rheological properties of the fluid were measured using a rheometer (Anton Paar MCR302) in Control Stress mode, ranging from 10-2 to 10-3. The results are shown in Figure 4. The curve of viscosity versus shear rate shows a sudden increase in viscosity at a shear rate of approximately 1 s-1, characteristic of discontinuous shear thickening. After the viscosity of the fluid rises to 2000 Pa.s, it stabilizes and remains at around 3000 Pa.s as the shear rate increases. This does not mean that the viscosity of the fluid has reached its limit; rather, the viscosity is too high, resulting in excessive thickening and slippage with the cone-and-plate test system, making it impossible to measure the maximum viscosity of the fluid using the rheometer. Example 6:

[0035] Based on the method of Example 5, it was determined that the particle size of the purchased nano silicon dioxide was 556 nm, with a particle size difference of about 8%.

[0036] According to the method of Example 1, the nano silicon dioxide particles were dispersed in polyethylene glycol with a relative molecular mass of 200 to obtain a shear-thickening fluid with a particle volume fraction of 0.632. The rheological properties of the fluid were tested according to the method of Example 5 and are shown in Figure 5. From Figure 5, it can be seen that the fluid has discontinuous shear-thickening characteristics. Example 7:

[0037] Based on the method of Example 5, it was measured and confirmed that the particle size of the purchased calcium carbonate granules was 853 nm, with a particle size difference of approximately 25%.

[0038] According to the method of Example 1, the calcium carbonate granules were dispersed in polyethylene glycol with a relative molecular mass of 200 to obtain a shear-thickening fluid with a volume fraction of 0.63. According to the method of Example 5, the rheological properties of the fluid were tested and are shown in Figure 6. From Figure 6, it can be seen that the fluid has the characteristics of discontinuous shear-thickening.

Claims

1. An ultra-high concentration shear thickening fluid composed of nanoparticles and a solvent, characterized in that the volume fraction of the nanoparticles in the fluid is 0.63 to 0.65, and the solvent is a liquid polymer polyol.

2. The ultra-high concentration shear thickening fluid according to claim 1, wherein the nanoparticles have a particle size of 250 to 900 nm and are monodisperse in particle size.

3. 2. The ultra-concentrated shear thickening fluid of claim 1, wherein the inorganic compound selected as the nanoparticles is silicon dioxide or calcium carbonate.

4. 2. The method for preparing an ultra-concentrated shear-thickening fluid according to claim 1, a. Premixing: slowly adding nanoparticles to a solvent and slowly stirring until no visible lumps remain to obtain a premix; b. Shear dispersion: strongly shearing and dispersing the particles in the premix to form a primary fluid in which the "Tyndall effect" is visible to the naked eye under the illumination of a laser pointer; c) Uniform mixing: using a powerful circulator to further uniformly mix the primary fluid to obtain a highly uniform fluid; d. drying: drying the fluid until the sum of the content of water and small molecule alcohol impurities in the fluid is below 3.5 wt % to obtain a discontinuous shear thickening fluid; Method for preparing ultra-thick shear-thickening fluids.

5. The method for preparing an ultra-high concentration shear-thickening fluid according to claim 4, characterized in that step c can be repeated with the dried fluid to mix it uniformly again, thereby improving the uniformity of the entire fluid.

6. 5. The method for preparing an ultra-concentrated shear-thickening fluid according to claim 4, wherein the high shear device in step b is a ball mill, a bead mill or a three-roll mill.

7. 5. The method for preparing ultra-concentrated shear-thickening fluid according to claim 4, characterized in that the high-intensity circulator is a vortex mixer or a roller bottle device.

8. 10. An application of the ultra-high concentration shear thickening fluid of claim 1.

9. The application of the ultra-high concentration shear thickening fluid according to claim 8, characterized in that it is applied to composite anti-cutting materials or anti-collision protectors.

Images