A magnetic liquid and a preparation method thereof

Abstract

The present invention provides a magnetic liquid and a preparation method thereof, belonging to the technical field of magnetic materials. The magnetic liquid comprises nano-scale magnetic particles, a composite surfactant and a base carrier liquid; the composite surfactant is a combination of a long-chain fatty acid containing more than 20 carbon atoms and a medium-short-chain fatty acid containing less than 8 carbon atoms; and the base carrier liquid is a motor oil with a viscosity grade of LAN 32 or above. Through the interaction of the composite surfactant, the stability of the high-viscosity magnetic liquid can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials, and in particular relates to a magnetic liquid and a preparation method thereof. Background Art

[0002] Magnetic fluid is a new type of functional material that combines the fluidity of liquid with the response characteristics of solid magnetic materials to magnetic fields. It has a wide range of applications in the engineering field, among which rotary seals are one of the many applications of magnetic fluids. Compared with traditional seals, magnetic fluid rotary seals have the advantages of zero leakage, high reliability, low wear, and long life. Therefore, they play a very important and irreplaceable role in many fields.

[0003] Typically, a magnetic liquid is a colloidal liquid consisting of nanoscale magnetic particles highly dispersed in a base carrier liquid, wherein the surface of each nanoscale magnetic particle is coated with a surfactant to provide sufficient repulsive force to prevent the magnetic particles from agglomerating together under the action of gravity, inter-particle magnetic force or van der Waals force.

[0004] For example, patent application document CN104091678A discloses a method for preparing oleic acid-coated nano-Fe3O4 dispersed in a kerosene-based magnetic liquid. The magnetic liquid is prepared from three parts: nano-sized Fe3O4 as magnetic particles, oleic acid as a surfactant and kerosene as a base liquid; firstly, a chemical co-precipitation method is used to prepare a precipitate of bare Fe3O4 nanoparticles; then, oleic acid is added as a surfactant to coat the surface of the Fe3O4 nanoparticles; finally, the modified Fe3O4 magnetic nanoparticles are mixed with the kerosene-based liquid, heated and continuously stirred to finally form a uniform and stable kerosene-based Fe3O4 magnetic liquid.

[0005] For example, patent application document CN106847460A discloses a method for preparing a kerosene-based magnetic liquid, which uses a chemical precipitation method in an alkaline medium to prepare a precursor, and then uses a ferrous chloride solution with a temperature of 40-90°C and a concentration of 0.03-0.5 mol / L to prepare magnetic particles after washing and separation, and avoids the use of acid and alkali in the process of wrapping the magnetic particles with oleic acid. Finally, the oleic acid-wrapped magnetic particles are washed and separated with acetone or ethanol and then dispersed in a kerosene-based liquid to remove free oleic acid. Summary of the invention

[0006] The present invention is based on the inventor's discovery and understanding of the following facts and problems: From the above related technologies, when preparing low-viscosity magnetic liquids, a surfactant can basically provide the above functions, for example, oleic acid is usually selected as a surfactant. However, the inventor found that in the preparation process of high-viscosity magnetic liquids, the traditional preparation method using a surfactant will not provide sufficient repulsion to ensure the stability of the magnetic liquid.

[0007] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a magnetic liquid and a preparation method thereof.

[0008] The magnetic liquid of the embodiment of the present invention comprises nano-scale magnetic particles, a composite surfactant and a base carrier liquid; the composite surfactant is a combination of long-chain fatty acids containing more than 20 carbon atoms and medium-chain fatty acids containing less than 8 carbon atoms; the base carrier liquid is engine oil with a viscosity grade of LAN-32 or above.

[0009] The advantages and technical effects brought by the magnetic liquid of the embodiment of the present invention are as follows:

[0010] (1) The magnetic liquid of the embodiment of the present invention uses engine oil with a viscosity grade of LAN-32 or above as the base carrier liquid. Since the viscosity of the base carrier liquid is relatively high, the viscosity of the magnetic liquid of the embodiment of the present invention is also relatively high, and has the advantages of anti-scouring and high self-healing performance. Compared with low-viscosity magnetic liquids, it is more suitable for sealing liquid media and has the characteristics of quickly restoring a certain sealing ability after the seal is broken;

[0011] (2) The composite surfactant is designed for magnetic liquids whose base carrier liquid is engine oil with a viscosity grade of LAN-32 or above. The number of long-chain fatty acids that can be adsorbed on the surface of nano-scale magnetic particles in the base carrier liquid is small, but each molecule thereof can provide a large repulsive force between two particles, and can provide partial repulsive force when the distance between the two particles is large; at the same time, although each molecule of medium- and short-chain fatty acids can provide a small repulsive force between two particles, they are easier to complete adsorption in the base carrier liquid, and thus can effectively increase the number of surfactants coated on the surface of nano-scale magnetic particles, thereby increasing the mutual repulsion between nano-scale magnetic particles; therefore, the magnetic liquid of the embodiment of the present invention selects the combination of long-chain fatty acids and medium- and short-chain fatty acids as composite surfactants, which can overcome the shortcomings of using only one surfactant and obtain a stable high-viscosity magnetic liquid;

[0012] (3) The long-chain fatty acid used in the magnetic liquid of the embodiment of the present invention is a long-chain fatty acid containing more than 20 carbon atoms. If it is a long-chain fatty acid with less than 20 carbon atoms, it will not play a corresponding role; similarly, the medium-chain fatty acid used in the magnetic liquid of the embodiment of the present invention is a medium-chain fatty acid containing less than 8 carbon atoms. If it is a medium-chain fatty acid with more than 8 carbon atoms, it will not play a corresponding role.

[0013] In some embodiments, the long-chain fatty acids are selected from at least one of arachidic acid, erucic acid, 22-tricosenoic acid, nervonic acid, lignin acid and octacosanoic acid; and / or, the medium- and short-chain fatty acids are selected from at least one of propionic acid, acrylic acid, butyric acid, butenoic acid, acrylic acid, valeric acid, pentenoic acid, hexanoic acid, heptanoic acid, heptenoic acid, octanoic acid and octenoic acid.

[0014] In some embodiments, in the complex surfactant, the mass ratio of the long-chain fatty acid to the short-chain fatty acid is 1:(0.8-1.4).

[0015] In some embodiments, based on the total mass of the magnetic liquid being 100%, the mass fraction of the nanoscale magnetic particles is 45-55%, the mass fraction of the complex surfactant is 15-25%, and the mass fraction of the base carrier liquid is 25-40%.

[0016] In some embodiments, the magnetic liquid is in the absence of a magnetic field, at a temperature of 25°C and a shear rate of 5 -1 The viscosity at s is 600-1000 mmPa·s; and / or, the temperature is 25°C, the shear rate is 5 -1 The viscosity at s is 1800-2500mmPa·s.

[0017] In some embodiments, the saturation magnetization of the magnetic liquid is greater than 600 Gauss.

[0018] In addition, an embodiment of the present invention further provides a method for preparing a magnetic liquid, which is characterized by comprising the following steps:

[0019] (1) preparing the nanoscale magnetic particles;

[0020] (2) The base carrier liquid and the composite surfactant are stirred and mixed to obtain a mixed liquid, and then the mixed liquid and the nano-scale magnetic particles are stirred and mixed in a water bath to obtain the magnetic liquid.

[0021] The advantages and technical effects brought by the preparation method of the embodiment of the present invention are:

[0022] The method for preparing the magnetic liquid in the embodiment of the present invention is relatively simple, and can well solve the problem of unstable preparation of high-viscosity magnetic liquid caused by insufficient repulsive force.

[0023] In some embodiments, in step (2), the mixture is incubated in a water bath at 80-90° C. for 1.5-3 h.

[0024] In some embodiments, in step (2), the base carrier liquid, the composite surfactant and the volatile organic solvent are stirred and mixed to obtain the mixed liquid.

[0025] In some embodiments, in step (2), the volatile organic solvent is selected from n-heptane and / or n-hexane; and / or, the volume ratio of the volatile organic solvent to the base carrier liquid is 1:(0.8-1.2). BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a test photograph of the pinning phenomenon of the LAN-46 engine oil-based magnetic fluid of Example 1;

[0027] Figure 2 is the magnetic viscosity curve of the LAN-46 engine oil-based magnetic fluid of Example 1;

[0028] Figure 3 is the magnetic viscosity curve of the LAN-68 engine oil-based magnetic fluid of Example 3;

[0029] Figure 4 This is a photo of the pinning phenomenon test of the LAN-46 engine oil-based product of Comparative Example 1;

[0030] Figure 5 This is a photo of the pinning phenomenon test of the LAN-68 engine oil-based product of Comparative Example 2;

[0031] Figure 6 is the magnetization curve of the LAN-46 engine oil-based magnetic liquid of Example 1;

[0032] Figure 7 This is the magnetization curve of the LAN-5 engine oil-based magnetic liquid of Comparative Example 4. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0034] An embodiment of the present invention provides a magnetic liquid, comprising nanoscale magnetic particles, a composite surfactant and a base carrier liquid; the composite surfactant is a combination of long-chain fatty acids containing more than 20 carbon atoms and medium- and short-chain fatty acids containing less than 8 carbon atoms; the base carrier liquid is engine oil with a viscosity grade of LAN-32 or above.

[0035] The base carrier liquid used by the magnetic liquid of the embodiment of the present invention is a motor oil with a viscosity grade of LAN-32 or above, for example, LAN-32 motor oil, LAN-46 motor oil, LAN-68 motor oil, LAN-100 motor oil, LAN-150 motor oil, etc., all of which are LAN total loss system oils that meet the national standard GB 443-1989. Since the motor oils of the above viscosity grades have a high viscosity, the viscosity of the obtained magnetic liquid is also high. In order to develop a high-viscosity magnetic liquid, it is necessary to design a composite surfactant suitable for the high-viscosity magnetic liquid.

[0036] Among the composite surfactants, the number of long-chain fatty acids that can be adsorbed on the surface of nano-scale magnetic particles in the base carrier liquid is relatively small, but each molecule thereof can provide a relatively large repulsive force between the two particles, and can provide partial repulsive force when the distance between the two particles is relatively large; at the same time, although each molecule of medium- and short-chain fatty acids can provide a relatively small repulsive force between the two particles, it is easier to complete adsorption in the base carrier liquid, and thus can effectively increase the number of surfactants coated on the surface of the nano-scale magnetic particles, thereby increasing the mutual repulsion between the nano-scale magnetic particles, and the combination of the two ultimately makes the repulsion between the nano-scale magnetic particles sufficient to balance the attraction, thereby achieving a stable effect. If long-chain fatty acids or medium- and short-chain fatty acids are used alone, it will be difficult to provide sufficient mutual repulsion because the number of surfactants adsorbed on the nano-scale magnetic particles is relatively small or the chain length of the surfactant is relatively short, and the repulsive force between the two particles that each molecule can provide is relatively small, and thus the above-mentioned effect cannot be achieved.

[0037] Long-chain fatty acids containing more than 20 carbon atoms can be saturated fatty acids or unsaturated fatty acids as long as the main chain carbon number is more than 20, and can be at least one of arachidic acid, erucic acid, 22-tricosenoic acid, nervonic acid, lignin acid, and octacosanoic acid. Similarly, medium- and short-chain fatty acids containing less than 8 carbon atoms can be saturated fatty acids or unsaturated fatty acids as long as the main chain carbon number is less than 8, and can be at least one of propionic acid, acrylic acid, butyric acid, butenoic acid, acrylic acid, valeric acid, pentenoic acid, caproic acid, heptanoic acid, heptenoic acid, octanoic acid, and octenoic acid.

[0038] In some embodiments, in the composite surfactant, the mass ratio of the long-chain fatty acid to the short-chain fatty acid is 1:(0.8-1.4), such as 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, etc. When the ratio is too low or too high, it is not conducive to providing sufficient mutual repulsion to the nano-scale magnetic particles, thereby not being conducive to improving the stability of the magnetic liquid.

[0039] In some embodiments, based on the total mass of the magnetic liquid as 100%, the mass fraction of the nanoscale magnetic particles is 45-55%, such as 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, etc., the mass fraction of the composite surfactant is 15-25%, such as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc., and the mass fraction of the base carrier liquid is 25-40%, such as 25%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc. The mass fraction of each component within the above range is helpful to improve the saturation magnetization and stability of the magnetic liquid. When the mass fraction of nano-scale magnetic particles is too low, it is not conducive to improving the saturation magnetization of the magnetic liquid; when the mass fraction of nano-scale magnetic particles is too high, the mass fractions of the composite surfactant and the base carrier liquid are too low, which is not conducive to improving the stability of the magnetic liquid. When the mass fraction of the composite surfactant is too low, it is not conducive to improving the stability of the magnetic liquid; when the mass fraction of the composite surfactant is too high, the effect of improving the stability of the magnetic liquid is no longer significant.

[0040] In some embodiments, the magnetic liquid is in the absence of a magnetic field, at a temperature of 25°C and a shear rate of 5 -1 The viscosity at s is 600-1000 mmPa·s, such as 600 mmPa·s, 700 mmPa·s, 800 mmPa·s, 900 mmPa·s, 1000 mmPa·s, etc.; and / or, when the magnetic field reaches 0.3 T, the temperature is 25° C., the shear rate is 5 -1 The viscosity at 1000 mmPa·s is 1800-2500 mmPa·s, such as 1800 mmPa·s, 1900 mmPa·s, 2000 mmPa·s, 2100 mmPa·s, 2200 mmPa·s, 2300 mmPa·s, 2400 mmPa·s, 2500 mmPa·s, etc. Compared with low-viscosity magnetic liquids, the high-viscosity magnetic liquids mentioned above are not easily carried away by the leaked medium when the magnetic liquid seal fails, thereby providing self-healing properties of the magnetic liquid seal and having higher application value.

[0041] In some embodiments, the saturation magnetization of the magnetic liquid is 600 or more Gauss, such as 600 Gauss, 620 Gauss, 650 Gauss, 680 Gauss, 700 Gauss, 720 Gauss, 750 Gauss, 780 Gauss, 800 Gauss, etc. Because the magnetic liquid of the embodiment of the present invention solves the stability problem under high viscosity conditions, the content of nano-scale magnetic particles can be increased to enhance the saturation magnetization of the magnetic liquid. Under the same conditions, the higher the saturation magnetization of the magnetic liquid, the better the sealing ability of the magnetic liquid.

[0042] In the embodiments of the present invention, there is no particular limitation on the specific type of the nano-sized magnetic particles in the magnetic liquid, and they can be any nano-sized magnetic particles in the related art, as long as the magnetic liquid with qualified performance can be obtained. For example, the nano-sized magnetic particles can be metal oxides (Fe3O4), ferrites (CoFe2O4, (Mn-Zn)Fe3O4, etc.), metals (iron, cobalt, nickel and their alloys), and ferromagnetic iron nitride (Fe x N(2 < x < 8)), etc., at least one of them.

[0043] In addition, the embodiments of the present invention also provide a preparation method of a magnetic liquid, which is characterized by including the following steps:

[0044] (1) Prepare the nano-sized magnetic particles;

[0045] (2) Stir and mix the base carrier liquid and the composite surfactant to obtain a mixed liquid, and then stir and mix the mixed liquid and the nano-sized magnetic particles under the water bath condition to obtain the magnetic liquid.

[0046] The preparation method of the magnetic liquid in the embodiments of the present invention is relatively simple, and can well solve the preparation problem of the instability of the high-viscosity magnetic liquid caused by insufficient repulsive force.

[0047] There is no particular limitation on the preparation method of the nano-sized magnetic particles in step (1) in the preparation method of the embodiments of the present invention, as long as the target nano-sized magnetic particles can be obtained. The specific preparation method can refer to the preparation methods of various nano-sized magnetic particles in the related art, which will not be elaborated here.

[0048] In some embodiments, in step (2), under the condition of 80 - 90 °C, such as 80 °C, 82 °C, 84 °C, 86 °C, 88 °C, 90 °C, etc., carry out water bath for 1.5 - 3 h, such as 1.5 h, 2 h, 2.5 h, 3 h, etc. Under the above water bath conditions, it is helpful for the composite surfactant to uniformly coat the nano-sized magnetic particles, thereby helping to improve the stability of the high-viscosity magnetic liquid.

[0049] In some embodiments, in step (2), stir and mix the base carrier liquid, the composite surfactant and the volatile organic solvent to obtain the mixed liquid. Adding the volatile organic solvent is to provide a liquid medium when the composite surfactant coats the nano-sized magnetic particles, so that the composite surfactant is more likely to be adsorbed onto the nano-sized magnetic particles, improving the uniformity of the coating, and thus improving the stability of the high-viscosity magnetic liquid. It is required that the organic solvent is volatile, so that the organic solvent gradually volatilizes during the process of stirring and mixing the mixed liquid and the nano-sized magnetic particles under the water bath condition, without affecting the composition of the base carrier liquid of the magnetic liquid and the stability of the magnetic liquid.

[0050] The preparation method of the embodiment of the present invention has no particular limitation on the type of the volatile organic solvent, and it can be any volatile organic solvent in the related art, for example, it can be n-heptane and / or n-hexane.

[0051] In some embodiments, the volume ratio of the volatile organic solvent to the base carrier liquid is 1:(0.8-1.2), such as 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc. When the ratio is too low, the encounter between the composite surfactant and the nanoscale magnetic particles will be reduced, thereby reducing the reaction rate; when the volume ratio is too high, less liquid medium is provided, which is not conducive to improving the uniformity of the coating.

[0052] In addition, the embodiments of the present invention also provide the use of the magnetic liquid of the embodiments of the present invention or the magnetic liquid obtained by the preparation method of the embodiments of the present invention in an optional sealing device.

[0053] Since the magnetic liquid of the embodiment of the present invention or the magnetic liquid obtained by the preparation method of the embodiment of the present invention has excellent stability, the stability of the sealing effect of the optional sealing device can be effectively improved.

[0054] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0055] Example 1

[0056] LAN-46 engine oil-based magnetic liquid, the preparation method comprises the following steps:

[0057] ① Weigh 32.5g of FeCl3 and 19.9g of FeCl2·4H2O, dissolve in 300mL of deionized water, and stir in a 45℃ water bath at a speed of 350r / min;

[0058] ② When the salt is completely dissolved to obtain a salt solution, pour 65mL of ammonia water into the salt solution by drainage with a glass rod. The speed of the stirrer is fixed at 350r / min, the water bath temperature is maintained at 45℃, and the reaction is carried out for 45min. At this time, the solution has completely turned black.

[0059] ③ The obtained solution is washed with ultrapure water for several times until the pH of the upper clear liquid is 7, and then the clear liquid is poured out to obtain 0.1 mol of nano-sized Fe3O4 magnetic particles;

[0060] ④ Take 20mL LAN-46 engine oil, 4g erucic acid, and 4mL octanoic acid, mix and stir thoroughly in a 45°C water bath to obtain a base carrier liquid mixed with a composite surfactant, then pour it into the nano-sized Fe3O4 magnetic particles prepared in the previous step in a 90°C water bath, maintain stirring at a speed of 350r / min for 2h, and finally obtain 45.5g LAN-46 engine oil-based magnetic liquid.

[0061] Taking the total mass of the LAN-46 engine oil-based magnetic liquid as 100%, the mass fraction of the nano-sized Fe3O4 magnetic particles is 50.8%, the mass fraction of the composite surfactant is 16.8%, and the mass fraction of the LAN-46 engine oil is 32.4%. In the composite surfactant, the mass ratio of erucic acid to n-octanoic acid is 1:0.9.

[0062] Example 2

[0063] The preparation method of the LAN-46 engine oil-based magnetic liquid of this embodiment is the same as that of Example 1, except that, in step ④, 20 mL of No. 46 engine oil, 4 g of erucic acid, 4 mL of n-octanoic acid, and 20 mL of n-hexane are mixed and stirred in a 45° C. water bath to obtain a base carrier liquid mixed with a composite surfactant, which is then poured into the nano-sized Fe3O4 magnetic particles obtained in the previous step in a 90° C. water bath, and stirred at a speed of 350 r / min for 2 hours to finally obtain 45.5 g of LAN-46 engine oil-based magnetic liquid.

[0064] Taking the total mass of the LAN-46 engine oil-based magnetic liquid as 100%, the mass fraction of the nano-sized Fe3O4 magnetic particles is 50.8%, the mass fraction of the composite surfactant is 16.8%, and the mass fraction of the LAN-46 engine oil is 32.4%. In the composite surfactant, the mass ratio of erucic acid to n-octanoic acid is 1:0.9.

[0065] Example 3

[0066] LAN-68 engine oil-based magnetic liquid, the preparation method comprises the following steps:

[0067] ① Weigh 32.5g of FeCl3 and 19.9g of FeCl2·4H2O, dissolve in 300mL of deionized water, place in a 45℃ water bath and stir at a stirrer speed of 350r / min;

[0068] ② When the salt solution is completely dissolved, pour 65mL of ammonia water into the salt solution by drainage with a glass rod. The speed of the stirrer is fixed at 350r / min, the water bath temperature is maintained at 45℃, and the reaction is carried out for 45min. At this time, the solution has completely turned black.

[0069] ③ The obtained solution is washed with ultrapure water for several times until the pH of the upper clear liquid is 7, and then the clear liquid is poured out to obtain 0.1 mol of nano-sized Fe3O4 magnetic particles;

[0070] ④ Take 20mL LAN-68 engine oil, 4g erucic acid, and 5mL octanoic acid, mix and stir thoroughly in a 45°C water bath to obtain a base carrier liquid mixed with a composite surfactant (i.e., a mixed liquid), and then pour it into the nano-sized Fe3O4 magnetic particles prepared in the previous step in a 90°C water bath, maintain stirring at a speed of 350r / min for 2h, and finally obtain 46.2g LAN-68 engine oil-based magnetic liquid.

[0071] Taking the total mass of the LAN-68 engine oil-based magnetic liquid as 100%, the mass fraction of the nano-sized Fe3O4 magnetic particles is 50.1%, the mass fraction of the composite surfactant is 18.5%, and the mass fraction of the LAN-68 engine oil is 31.4%; in the composite surfactant, the mass ratio of erucic acid to n-octanoic acid is 1:1.1.

[0072] Example 4

[0073] The preparation method of the LAN-68 engine oil-based magnetic liquid of this embodiment is the same as that of Example 1, except that, in step ④, 20 mL of LAN-68 engine oil, 4 g of erucic acid, 5 mL of n-octanoic acid, and 20 mL of n-hexane are mixed and stirred in a 45° C. water bath to obtain a base carrier liquid mixed with a composite surfactant, which is then poured into the nano-sized Fe3O4 magnetic particles obtained in the previous step in a 90° C. water bath, and stirred at a speed of 350 r / min for 2 hours to finally obtain 46.2 g of LAN-68 engine oil-based magnetic liquid.

[0074] Taking the total mass of the LAN-68 engine oil-based magnetic liquid as 100%, the mass fraction of the nano-sized Fe3O4 magnetic particles is 50.1%, the mass fraction of the composite surfactant is 18.5%, and the mass fraction of the No. 68 engine oil is 31.4%; in the composite surfactant, the mass ratio of erucic acid to n-octanoic acid is 1:1.1.

[0075] Comparative Example 1

[0076] The preparation method of this comparative example is the same as that of Example 1, except that octanoic acid is omitted in step ④, and the mass of erucic acid is 7.644 g; agglomeration of the nano-scale magnetic particles occurs, which is manifested as the nano-scale magnetic particles and the base carrier liquid being separated and unable to be evenly dispersed therein, and the final LAN-46 engine oil-based product obtained is a separated liquid.

[0077] Comparative Example 2

[0078] The preparation method of this comparative example is the same as that of Example 1, except that erucic acid is omitted in step ④, and the mass of n-octanoic acid is 7.644 g; the LAN-68 engine oil-based product finally obtained is a stratified liquid.

[0079] Comparative Example 3

[0080] The preparation method of this comparative example is the same as that of Example 1, except that oleic acid is used instead of erucic acid in step ④, and the obtained LAN-46 engine oil-based product is a stratified liquid.

[0081] Comparative Example 4

[0082] The preparation method of LAN-5 engine oil-based magnetic liquid is the same as that of Example 1, except that, in step ④, 20 mL of LAN-5 engine oil and 7 mL of oleic acid are mixed and stirred in a 45°C water bath to obtain a base carrier liquid mixed with a surfactant, which is then poured into the nano-sized Fe3O4 magnetic particles obtained in the previous step in a 90°C water bath, and stirred at a speed of 350 r / min for 2 hours to finally obtain 42.4 g of LAN-5 engine oil-based magnetic liquid.

[0083] Taking the total mass of the LAN-5 engine oil-based magnetic liquid as 100%, the mass fraction of the nano-sized Fe3O4 magnetic particles is 54.6%, the mass fraction of the surfactant is 14.7%, and the mass fraction of the LAN-5 engine oil is 30.8%.

[0084] Performance Test:

[0085] (1) Pin phenomenon test

[0086] Magnetic liquid is magnetic under the action of a magnetic field. Referring to the textbook (Li Decai. Magical Magnetic Liquid [M]. Beijing: Science Press, 2016.), a small magnet is moved closer to the bottom of the beaker to observe the reaction of the liquid. As the small magnet moves closer, "thorns" appear on the surface of the magnetic liquid, and as the magnet moves, the "thorns" in the magnetic liquid also move. As the distance of the magnet changes, the size and shape of the "thorns" will also change. This phenomenon is called the pin phenomenon of magnetic liquid. By testing whether the magnetic liquid of each embodiment and the product of the comparative example have the pin phenomenon, it can be determined whether it is a magnetic liquid.

[0087] (2) Viscosity test

[0088] An Anton Paar MCR-302 rheometer was used to test the viscosity of the magnetic liquid of each embodiment and the product of the comparative example. A certain amount of magnetic liquid / product was injected into the gap between the rotor and the stator of the rheometer, and the part that might overflow was wiped off. At the same time, a magnetic conductive cover was placed above the rotor to generate a uniform magnetic field in the vertical direction in the magnetic liquid / product area. Then the rheometer was started, and the shear motion inside the magnetic liquid / product was formed by the relative motion of the rotor and the stator surface. The upper computer software was used to record the change in viscosity of the magnetic liquid / product with the shear rate and the magnetic field.

[0089] (3) Saturation magnetization test

[0090] Performance test result analysis: The magnetization performance of the magnetic liquids in each embodiment and the products in the comparative example was tested using the EZ8 vibrating sample magnetometer produced by Microsense. This is an instrument that uses the principle of electromagnetic induction to measure magnetic properties, with high precision and sensitivity. During the measurement process, the sample is fixed at one end of the vibrating rod and placed in the middle of the detection coil. The vibrating rod will be subjected to micro-vibration of a certain frequency and amplitude. The system will measure the induced voltage caused by the vibration of the sample, and then finally calculate the magnetization performance of the sample through signal conversion processing.

[0091] Test result analysis:

[0092] (1) Analysis of pin phenomenon test results

[0093] like Figure 1 As shown, the magnetic liquid of Example 1 has a pinning phenomenon, indicating that the magnetic liquid prepared in Example 1 is a magnetic liquid. Similarly, the magnetic liquids of Examples 2-4 also have a pinning phenomenon (not shown in the figure), indicating that the magnetic liquids prepared in Examples 2-4 are also magnetic liquids.

[0094] In contrast, if Figure 4-5 As shown, the stratified liquid of Comparative Example 1-2 does not have the pinning phenomenon, indicating that the stratified liquid of Comparative Example 1-2 is not a magnetic liquid. The reason is that, due to the single surfactant used in Comparative Example 1-2, the nano-sized Fe3O4 magnetic particles are not dispersed into the base carrier liquid to form a stable colloidal solution. Therefore, when an external magnetic field is applied, the nano-sized Fe3O4 magnetic particles will agglomerate and will not "prick".

[0095] Similarly, the stratified liquid of Comparative Example 3 did not show the pinning phenomenon (not shown in the figure), indicating that the stratified liquid of Comparative Example 3 is not a magnetic liquid. The reason is that the composite surfactant used in Comparative Example 3 is a combination of oleic acid (C18) and n-octanoic acid. Oleic acid does not belong to the long-chain fatty acids above C20, and the repulsive force provided is insufficient, resulting in the aggregation of nano-scale magnetic particles, which is manifested as the nano-scale magnetic particles being separated from the base carrier liquid and unable to be evenly dispersed therein.

[0096] (2) Analysis of viscosity test results

[0097] like Figure 2 and Figure 3 As shown, the magnetic viscosity curves of the magnetic liquids of Examples 1 and 3 show that the viscosity of the magnetic liquid changes with the shear rate and the magnetic field in the following manner: at the same shear rate, the viscosity of the magnetic liquid increases with the increase of the magnetic field strength; at the same magnetic field strength, the viscosity of the magnetic liquid decreases with the increase of the shear rate. The above rules can explain that the magnetic liquids prepared in Examples 1 and 3 are shear-thinning magnetic liquids that can respond to the magnetic field. Similarly, the magnetic viscosity curves of the magnetic liquids of Examples 2 and 4 (not shown in the figure) also show the above rules, indicating that the magnetic liquids prepared in Examples 2 and 4 are shear-thinning magnetic liquids that can respond to the magnetic field.

[0098] In contrast, the layered liquid of Comparative Example 1-2 is not a magnetic liquid and has no magnetic viscosity curve.

[0099] In addition, the viscosity test results of the magnetic liquids of Examples 1-4 also show:

[0100] The No. 46 engine oil-based magnetic liquid of Example 1 is heated to 25°C and sheared at a rate of 5 -1 The viscosity is 645 mmPa·s at 0.5 T, and can reach 2079 mmPa·s when the magnetic field reaches 0.3 T.

[0101] The 46# engine oil-based magnetic liquid of Example 2 is heated to 25°C and sheared at 5°C without magnetic field. -1 The viscosity is 645 mmPa·s at 0.5 T, and can reach 2079 mmPa·s when the magnetic field reaches 0.3 T.

[0102] The 68# engine oil-based magnetic liquid of Example 3 is heated to 25°C and sheared at 5°C without magnetic field. -1 The viscosity is 986 mmPa·s at 0.5 T, and can reach 2260 mmPa·s when the magnetic field reaches 0.3 T.

[0103] The 68# engine oil-based magnetic liquid of Example 4 was heated to 25°C and sheared at 5°C without magnetic field.-1 The viscosity is 986 mmPa·s at 0.5 T, and can reach 2260 mmPa·s when the magnetic field reaches 0.3 T.

[0104] It can be seen that the composite surfactants of Examples 1-4 are suitable for preparing high-viscosity magnetic liquids.

[0105] (3) Analysis of saturation magnetization test results

[0106] like Figure 6 As shown in FIG. 1 , the saturation magnetization intensity of the magnetic liquid of Example 1 is 737.43 Gauss; in contrast, Figure 7 As shown, the saturation magnetization of the magnetic liquid of Comparative Example 4 is 522.88 Gauss. It can be seen that the saturation magnetization of the high-viscosity magnetic liquid containing a composite surfactant in Example 1 is increased by 41.03% compared with the conventional low-viscosity magnetic liquid containing oleic acid.

[0107] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0108] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A magnetic liquid, characterized in that: It comprises nano-scale magnetic particles, a composite surfactant and a base carrier liquid; the composite surfactant is a combination of a long-chain fatty acid containing more than 20 carbon atoms and a medium-short-chain fatty acid containing less than 8 carbon atoms; and the base carrier liquid is a motor oil with a viscosity grade of LAN-32 or above.

2. The magnetic liquid according to claim 1, characterized in that: The long-chain fatty acids are selected from at least one of arachidic acid, erucic acid, 22-tricosenoic acid, nervonic acid, lignin acid and octacosanoic acid; and / or, the medium- and short-chain fatty acids are selected from at least one of propionic acid, acrylic acid, butyric acid, butenoic acid, acrylic acid, valeric acid, pentenoic acid, hexanoic acid, heptanoic acid, heptenoic acid, octanoic acid and octenoic acid.

3. The magnetic liquid according to claim 1, characterized in that: In the composite surfactant, the mass ratio of the long-chain fatty acid to the medium- and short-chain fatty acid is 1:(0.8-1.4).

4. The magnetic liquid according to claim 1, characterized in that Taking the total mass of the magnetic liquid as 100%, the mass fraction of the nano-scale magnetic particles is 45-55%, the mass fraction of the composite surfactant is 15-25%, and the mass fraction of the base carrier liquid is 25-40%.

5. The magnetic liquid according to any one of claims 1 to 4, characterized in that: The magnetic liquid is in the absence of a magnetic field, at a temperature of 25°C and a shear rate of 5 -1 The viscosity at s is 600-1000 mmPa·s; and / or, the temperature is 25°C, the shear rate is 5 -1 The viscosity at s is 1800-2500mmPa·s.

6. The magnetic liquid according to any one of claims 1 to 4, characterized in that: The saturation magnetization intensity of the magnetic liquid is greater than 600 Gauss.

7. The method for preparing a magnetic liquid according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) preparing the nanoscale magnetic particles; (2) The base carrier liquid and the composite surfactant are stirred and mixed to obtain a mixed liquid, and then the mixed liquid and the nano-scale magnetic particles are stirred and mixed in a water bath to obtain the magnetic liquid.

8. The method for preparing a magnetic liquid according to claim 7, characterized in that: In step (2), the mixture is incubated in a water bath at 80-90° C. for 1.5-3 h.

9. The method for preparing a magnetic liquid according to claim 7, characterized in that: In step (2), the base carrier liquid, the composite surfactant and the volatile organic solvent are stirred and mixed to obtain the mixed liquid.

10. The method for preparing a magnetic liquid according to claim 9, characterized in that: In step (2), the volatile organic solvent is selected from n-heptane and / or n-hexane, and the volume ratio of the volatile organic solvent to the base carrier liquid is 1:(0.8-1.2).

Images