Titanium dioxide coated lanthanum-doped MOF nanoparticle electrorheological fluid and preparation method thereof
By preparing a core-shell structure of titanium dioxide-coated lanthanum-doped MOF nanoparticles, the problems of insufficient electric field response speed, dispersion stability and electrorheological efficiency of electrorheological fluid materials were solved, and the comprehensive performance of the material was improved, making it suitable for large-scale production.
Patent Information
- Application Number
- CN202511533964.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-25
- Publication Date
- 2026-01-23
AI Technical Summary
Existing electrorheological fluid materials have shortcomings in terms of electric field response speed, dispersion stability, and electrorheological efficiency, making it difficult to meet the requirements for rapid adjustment of mechanical transmission.
A two-step method was used to prepare lanthanum-doped MOF nanoparticles coated with titanium dioxide. Lanthanum-doped MOF nanoparticles were synthesized by solvothermal method and TiO2 shell was constructed by hydrolysis to form a core-shell composite material. The combination of the protection of the core-shell structure and the enhanced conductivity of ion doping improved the electric field response speed and dispersion stability of the material.
It significantly improves the material's mechanical strength, electric field response speed, and dispersion stability, and enhances electrorheological efficiency, making it suitable for large-scale applications.
Smart Images
Figure CN121379157A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to an electrorheological fluid material and a preparation method thereof, in particular to a titanium dioxide-coated lanthanum-doped MOF nanoparticle electrorheological fluid and a preparation method thereof. BACKGROUND
[0002] An electrorheological fluid (ERF) is a typical smart material, and the core electrorheological effect thereof provides a unique way of quickly and reversibly regulating the fluid mechanics performance through an electric field. The most core and most valuable characteristic of the ERF is the electrorheological effect: under the action of an applied electric field, the rheological properties (mainly apparent viscosity and shear stress) can change significantly, quickly and reversibly within milliseconds. When no electric field exists, the dispersed-phase particles are irregularly dispersed in the continuous-phase medium in disorder. When an electric field is applied, the dispersed-phase particles are polarized, strong electrostatic interactions (attractive forces) are generated between the particles, the particles are driven to align along the direction of the electric field and are aggregated into chains, and with the increase of the electric field strength, the attractive forces between the particles are continuously increased, and on the basis of the chain structure, a columnar structure is formed, and the flow performance similar to that of a solid appears. After the electric field is removed, the fluid can quickly return to the initial low-viscosity state. The unique controllable rheological properties make the ERF have great potential in application fields requiring active and rapid regulation of mechanical transmission or damping.
[0003] As a kind of crystalline coordination polymer, metal-organic frameworks (MOFs) have shown breakthrough potential in the electrorheological fluid system due to their highly ordered three-dimensional porous topological structure. The super-high specific surface area and adjustable pore size distribution provide an ideal carrier for interfacial polarization; the MOFs have good anti-settling ability and significantly enhance the electric field response strength. Metal-doped MOFs, by precisely regulating the dielectric response, space charge distribution and structural stability of the material, become a core technical path to improve the performance of the electrorheological fluid. Lanthanum doping improves the dielectric constant of the MOF framework, and the titanium dioxide-coated lanthanum-doped MOF nanoparticles (TiO2@La-MOF) exhibit unique potential in the field of electrorheological fluids due to their adjustable core-shell structure.
[0004] Purpose and content of the application
[0005] The purpose of the application is to provide a titanium dioxide-coated lanthanum-doped MOF nanoparticle electrorheological fluid, wherein the dispersed phase is titanium dioxide-coated lanthanum-doped MOF nanoparticles, and the continuous phase is dimethyl silicone oil.
[0006] The application also aims to provide a method for preparing the titanium dioxide coated lanthanum doped MOF composite material, which is prepared by a two-step method.
[0007] The application can be achieved by the following technical solutions.
[0008] The prepared electrorheological fluid has a dispersed phase of the titanium dioxide coated lanthanum doped MOF nanoparticles and a continuous phase of dimethyl silicone oil.
[0009] (1) 3.5 g of terephthalic acid and 0.7 g of cetyltrimethylammonium bromide are placed in a mixed liquid of 60 mL of N,N dimethylformamide (DMF) and 10 mL of methanol, stirred for 20 min, and then x mg of lanthanum nitrate hexahydrate (x is the amount of lanthanum doping) is added.
[0010] (2) 0.5 g of the La-MOF nanoparticles is placed in a beaker, 90 mL of DMF is poured into the beaker, stirred for 4 h, and then 1.25 mL of TBT is added.
[0011] (3) The sample is mixed with dimethyl silicone oil to prepare an electrorheological fluid with a solid particle to silicone oil weight ratio of 10 wt%.
[0012] Compared with the prior art, the application has the following significant technical advantages.
[0013] The present application adopts solvothermal method and hydrolysis method to prepare the required sample. The solvothermal method synthesizes lanthanum-doped MOF nanoparticles in a high-pressure reaction kettle under high temperature (usually 100-250 DEG C) and high pressure conditions by using organic solvent as the reaction medium. The crystal phase is precisely controlled by adjusting the temperature, pressure and time, the high crystallinity significantly improves the dielectric constant of the particles, and the electrorheological effect is enhanced. According to the scanning electron microscope, the lanthanum-doped MOF is a monodisperse nanosphere, which is beneficial to the rapid formation of chain structure under the electric field.
[0014] The hydrolysis method constructs a high-dielectric TiO2 shell layer on the surface of the MOF, reduces the leakage current of the particles, and realizes the "core-shell" synergistic enhancement effect. The hydrolysis method operates at normal temperature and pressure, avoids the destruction of the MOF structure caused by high temperature, and seamlessly connects with the MOF core prepared by the solvothermal method. The process is relatively simple, low in cost, easy to scale up, and especially suitable for preparing ER particles such as titanium dioxide which has specific requirements for crystal form. It has more advantages in large-scale applications of cost-sensitive and specific crystal form materials. BRIEF DESCRIPTION OF DRAWINGS
[0015] Figure 1 Scanning electron microscope picture of MLa-80 nanoparticles
[0016] Figure 2 Transmission electron microscope picture of MLa-80 nanoparticles
[0017] Figure 3 XRD diagram of MLa-60, MLa-80, TiO2@MLa-60, TiO2@MLa-80 and TiO2 nanoparticles
[0018] Figure 4 Shear strength-shear rate relationship diagram of MLa-80 nanoparticles
[0019] Figure 5 Scanning electron microscope picture of TiO2@MLa-80 nanoparticles
[0020] Figure 6 Transmission electron microscope picture of TiO2@MLa-80 nanoparticles
[0021] Figure 7 Shear strength-shear rate relationship diagram of TiO2@MLa-80 nanoparticles
[0022] Figure 8 Scanning electron microscope picture of TiO2@MLa-60 nanoparticles
[0023] Figure 9 Transmission electron microscope picture of TiO2@MLa-60 nanoparticles
[0024] Figure 10Relationship between shear strength and shear rate of TiO2@MLa-60 nanoparticles
[0025] Figure 11 Scanning electron microscope image of TiO2@MLa-70 nanoparticles
[0026] Figure 12 Relationship between shear strength and shear rate of TiO2@MLa-70 nanoparticles Detailed Implementation
[0027] Experimental Example 1 (Preparation of 80 mg Lanthanum-doped MOF Nanoparticles)
[0028] Take 3.5 g of terephthalic acid and 0.7 g of hexadecyltrimethylammonium bromide, and place them in a mixture of 60 mL of N,N-dimethylammonium bromide (DMF) and 10 mL of methanol. Stir for 20 min, then add 80 mg of lanthanum nitrate hexahydrate. Add 3.5 mL of acetic acid and 3 mL of tetrabutyl titanate (TBT) to the above mixture, and stir for another 30 min. Place in a reaction vessel and react at 150 °C for 24 h in a forced-air drying oven. Wash the resulting product twice each with methanol, DMF, and ethanol, and dry in a 75 °C oven for 24 h to obtain lanthanum-doped MOF (MLa-80).
[0029] The scanning electron microscope image of the sample is as follows: Figure 1 As shown, MLa-80 is a nearly disc-shaped, solid, regularly shaped nanoparticle with a smooth exterior and no obvious agglomeration. Figure 2 Transmission electron microscopy reveals that MLa-80 consists of solid nanoparticles of similar size, exhibiting a tendency to be distributed in a chain-like pattern. Figure 3 With the XRD pattern of MLa-80, we can see that typical diffraction peaks of titanium-based MOFs are observed near 6.9°, 9.8°, 11.88°, 15.2°, 15.6° and 16.82°. This proves that titanium-based MOFs were successfully synthesized, and lanthanum doping did not change the crystal structure. The dopant ions may be located in the framework nodes or channels without significantly disrupting the long-range order. Figure 4 The shear stress curve of MLa-80 was obtained by mixing 0.15 g of dispersed phase MLa-80 with 1.5 mL of dimethyl silicone oil and applying a voltage of 0-3 kV / mm in an electrorheological tester. The curves show that the shear stress curves under an electric field strength of 1.5-3 kV / mm are basically overlapping, indicating that the shear stress of the MLa-80-based electrorheological fluid under high voltage does not increase with the increase of electric field strength, and does not show a good electrorheological effect.
[0030] Experimental Example 2 (Preparation of Titanium Dioxide Coated MLa-80 Nanoparticles)
[0031] Take 0.5 g of MLa-80 nanoparticles into a beaker, pour 90 mL of DMF, stir on the stirring table for 4 h, then add 1.25 mL of TBT. Prepare another beaker, add 1 mL of deionized water and 50 mL of DMF, continue to stir for a few minutes, then add to the previous beaker. Continue to stir for 8 h. The obtained sample is washed with ethanol three times, dried in a 75 ℃ oven for 24 h, and TiO2 coated MLa-80 (TiO2@MLa-80) nanoparticles are obtained.
[0032] The scanning electron microscope of the sample is shown in Figure 5 TiO2@MLa-80 is accumulated by multiple round cake-shaped particles, with obvious rough coating around the round cake, and the particle size is close to 800 nanometers; Figure 6 For transmission electron microscopy, it can be seen that there is no obvious hole, and the outer surface is rugged, indicating that TiO2 is coated on the periphery of MLa-80. Figure 3 The XRD pattern of TiO2@MLa-80 nanoparticles, the diffraction peak position of the coated sample changes little, and the diffraction peak of the titanium-based MOF is still visible, indicating that the crystal framework main structure of the MOF is not damaged during the coating process, and the intensity of the diffraction peak after coating is obviously decreased relative to the uncoated one, which may be that the TiO2 coating layer covers the MOF surface, which absorbs or scatters X-rays, weakening the signal of the internal MOF. Figure 7 The shear stress curve of TiO2@MLa-80 nanoparticles, the figure clearly shows that under the application of different intensity electric field (0.0 - 3.0 kV / mm), the rheological behavior of the material changes significantly. When the electric field is zero (0.0 kV / mm), the shear stress slowly rises with the increase of shear rate, showing a behavior similar to Newtonian fluid or weak non-Newtonian fluid (relatively constant or slightly changed viscosity), when the electric field intensity is 3.0 kV / mm, the shear rate is 0.1 s -1 The yield stress value is 482 Pa. After applying an electric field, all the curves move up as a whole, indicating that the shear stress increases significantly at the same shear rate. This is a direct manifestation of the electro-rheological effect: the electric field induces particle polarization and forms chain or columnar structure, enhancing the ability of the fluid to resist flow.
[0033] Experimental Example Three (Preparation of TiO2 Coated MLa-60 Nanoparticles)
[0034] Take 0.5 g MLa-60 nanoparticles in a beaker, pour into 90 mL DMF, after stirring on the stirring table for 4 h, add 1.25 mL TBT. Another beaker is prepared, add 1 mL deionized water and 50 mL DMF, continue to stir for a few minutes, then add to the former beaker. Continue to stir for 8 h. The obtained sample is washed with ethanol three times, dried in a 75 ℃ oven for 24 h, to obtain titanium dioxide coated MLa-60 (TiO2@MLa-60) nanoparticles.
[0035] The scanning electron microscope of the sample is shown in Figure 8 TiO2@MLa-60 is also accumulated by multiple round cake-shaped particles, and there is an obvious rough coating layer around the round cake; Figure 9 For transmission electron microscopy, it can be seen that there is no obvious hole, and the outer surface is rugged, indicating that titanium dioxide is also coated on the periphery of MLa-60. The scanning electron microscope and transmission electron microscope of TiO2@MLa-60 nanoparticles show little difference from TiO2@MLa-80. Figure 10 The shear stress curve of TiO2@MLa-60 nanoparticles, after applying an electric field, all curves in the low shear rate region (about 1-10 s -1 -1 between) show a relatively flat platform, and the shear stress value corresponding to this platform is the dynamic yield stress of the fluid. In the medium-high shear rate region (0.1-1 s -1 -1 between) after the yield stress platform region, all the curves show that the shear stress increases with the increase of shear rate, but the slope gradually slows down. When the electric field strength is 3.0 kV / mm and the shear rate is 0.1 s -1 -1, the yield stress value is weaker than that of MLa-80 coated sample, mainly due to the lower lanthanum doping amount, resulting in insufficient strength of the polarization structure formed.
[0036] Experimental Example Four (Preparation of Titanium Dioxide Coated MLa-70 Nanoparticles)
[0037] Take 0.5 g MLa-70 nanoparticles in a beaker, pour into 90 mL DMF, after stirring on the stirring table for 4 h, add 1.25 mL TBT. Another beaker is prepared, add 1 mL deionized water and 50 mL DMF, continue to stir for a few minutes, then add to the former beaker. Continue to stir for 8 h. The obtained sample is washed with ethanol three times, dried in a 75 ℃ oven for 24 h, to obtain titanium dioxide coated MLa-70 (TiO2@MLa-70) nanoparticles.
[0038] The scanning electron microscope of the sample is shown in Figure 11As shown, TiO2@MLa-70 is also composed of multiple round cake-like particles accumulated together, with an obvious coarse coating layer around the cake, indicating that titanium dioxide is also coated on the periphery of MLa-70. The morphology shown by scanning electron microscopy is not much different from that of TiO2@MLa-80. Figure 12 The shear stress curve of TiO2@MLa-70 nanoparticles, at zero electric field, the fluid still shows near Newtonian or weak shear thinning characteristics, but the zero field viscosity is significantly higher than that of the 60 mg sample (higher shear stress at the same shear rate). It indicates that the increase of lanthanum content improves the intrinsic interaction between particles or the volume fraction of the dispersed phase. The yield stress and the overall stress level increase more significantly with the increase of electric field.
Claims
1. A titanium dioxide-coated lanthanum-doped MOF nanoparticle electrorheological fluid, characterized in that, The dispersed phase of the material is TiO2@La-MOF nanoparticles with a rough surface and a spherical structure with a coating layer, and the continuous phase is dimethyl silicone oil; the material is prepared by a two-step method, which includes synthesizing La-MOF nanoparticles by a modified solvothermal method and synthesizing TiO2@La-MOF composite materials by a controlled hydrolysis method; The TiO2@La-MOF composite material has a rough surface and a spherical structure with a coating layer, is anisotropic, and has the characteristics of core-shell structure protection, ion doping conductivity enhancement, and nanoparticle rapid response.
2. The titania-coated lanthanum-doped MOF nanoparticle electrorheological fluid of claim 1, wherein The preparation process includes the following steps: (1) 3.5 g of terephthalic acid and 0.7 g of cetyltrimethylammonium bromide are placed in a mixed liquid of 60 mL of N,N-dimethylformamide (DMF) and 10 mL of methanol; after stirring on a stirring table for 20 min, 80 mg of lanthanum nitrate hexahydrate is added, followed by the addition of 3.5 mL of acetic acid and 3 mL of titanium tetrabutoxide (TBT), and stirring for another 30 min; the stirred solvent is transferred to an autoclave, heated at 150 ℃ for 24 h; the suspension in the reaction kettle is centrifuged once, and then washed with DMF, methanol, and ethanol for two times, respectively, and dried in a 75 ℃ oven for 24 h to obtain La-MOF nanoparticle solid powder; (2) 0.5 g of La-MOF nanoparticles are placed in a beaker, 90 mL of DMF is poured into the beaker, stirred for 4 h, and then 1.25 mL of TBT is added; 1 mL of deionized water and 50 mL of DMF are taken, stirred for a few minutes, and then added to the previous beaker, and stirred for another 8-12 h; the above suspension is centrifuged, washed with ethanol for three times, and dried in a 75 ℃ oven for 24 h to obtain TiO2@La-MOF nanoparticle solid powder; (3) the dried sample is mixed with dimethyl silicone oil at a solid particle to silicone oil weight ratio of 10 wt% to prepare an electrorheological fluid.