Method for changing lubricating property of lubricant by regulating and controlling size of ionic liquid

Abstract

The invention discloses a method for changing the lubricating property of a lubricant through the ion size, which comprises the following steps: dissolving an ionic liquid in a solvent, dispensing the solvent on a substrate, and carrying out vacuum drying to remove the solvent to obtain an ionic liquid membrane, the cation size in the ionic liquid is 0.75-2.90 nm, the anion size is 0.32-1.66 nm, and the difference between the cation size and the anion size is not more than 0.03. According to the invention, when ions are from 0.54 nm to 2.90 nm and under the load of 25.5 GPa, the friction coefficient is changed from 0.0019 to 0.0035, so that the lubricating property of the lubricant is changed.

Description

Technical Field

[0001] The present invention belongs to the field of nano-friction and relates to a method for changing the lubrication performance of a lubricant by regulating the size of an ionic liquid. Background Art

[0002] Ionic liquids refer to salts that are liquid at or near room temperature and are composed of organic cations and inorganic / organic anions. The equal number of cations and anions makes them electrically neutral as a whole, and they are also known as room temperature ionic liquids or low-temperature molten salts. Due to their unique physical and chemical properties, such as very low vapor pressure, non-flammability, excellent thermal stability, and high electrical conductivity, ionic liquids (ILs) have received extensive attention. Their melting points and viscosities, especially their thermal stability and chemical inertness, as well as the ability to quickly spread on the surface of various materials and form regular layered structures, show good potential as lubricants. The uniqueness of ionic liquids lies in that their compositions can be flexibly designed by adjusting the types of cations and anions to meet specific application requirements, providing a wider range of application scopes and performance options for ionic liquids.

[0003] With the rapid development of technology, the demand for lubricants and their performance requirements in modern mechanical equipment have increased. For example, mechanical instruments, electronics, automobiles, textiles, energy, aerospace vehicles, etc. all have relatively high demands for lubricants. The ionic liquid friction film is composed of oriented and densely packed molecules, and these molecules react by adsorbing on the friction surface, especially under boundary lubrication conditions. This tough friction layer mainly depends on the types of anions and cations in the ionic liquid, which helps to enhance the friction and anti-wear capabilities of the lubricant for sliding materials. Summary of the Invention

[0004] The object of the present invention is to provide a method for effectively regulating the lubrication performance of an ionic liquid by ionic size. The method uses ionic liquids with different ionic sizes to prepare an ionic liquid film with a certain thickness on the surface of a workpiece to simulate the longitudinal position of the ionic liquid on the solid surface. And measure its apparent thickness, friction coefficient, and hardness to verify the correlation between the ionic liquid size and nano-friction performance. It is beneficial to guide the regulation and design of the ionic liquid-solid lubrication interface and provide a basis for reducing friction and wear energy consumption.

[0005] The technical solution for achieving the object of the present invention is as follows:

[0006] In the first aspect, the present invention provides a method for changing the lubrication performance of a lubricant by ionic size, including the following steps:

[0007] Dissolve the ionic liquid in a solvent, then drop-coat it on a substrate, and obtain an ionic liquid film after vacuum drying to remove the solvent. The size of the cation in the ionic liquid is 0.75 - 2.90 nm, the size of the anion is 0.32 nm - 1.66 nm, and the size difference between the cation and the anion is not more than 0.03.

[0008] Furthermore, the solvent can be any one of acetonitrile, dimethylsulfoxamide, ethanol, and carbon tetrafluoride, and ethanol is preferred. Furthermore, the ionic liquid can be any one of dioctylmethylimidazolium sulfosuccinate ([N8,8,8,16][DOSS]), 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]), 1-butyl-3-methylimidazolium dicyanamide ([BMIIM][DCA]), 1-butyl-3-methylhexafluoroimidazolium phosphate ([BMIM][PF6]), etc. 1-butyl-3-methylimidazolium dicyanamide ([BMIIM][DCA]) is preferred.

[0009] Furthermore, the substrate can be made of mica, graphite, titanium material, or aluminum alloy, and graphite (HOPG) is preferred.

[0010] Furthermore, the volume ratio of the ionic liquid to the solvent is 10 -7 :1 - 10 -2 :1, and 10 -3 :1 is preferred.

[0011] Furthermore, dissolve the ionic liquid in a solvent, then drop-coat it on a substrate, and 2 - 6 μL, preferably 4 μL, is drop-coated per cm 2 of the substrate.

[0012] Furthermore, the vacuum drying temperature is 35 ± 5 °C, and the drying time is 12 ± 4 h.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. By precisely adjusting the composition, thickness, and surface properties of the ionic liquid film, the present invention can effectively reduce the friction coefficient to about 0.002.

[0015] 2. The Young's modulus of the ionic liquid film prepared by the present invention is as high as 150 GPa.

[0016] 3. The ionic liquid film of the present invention exhibits excellent tribological properties under different loads. This superior friction performance enables it to play a role in a wider range of applications. Especially under extreme working conditions such as high load and high-speed operation, it shows a longer service life and lower energy consumption. Description of the Drawings

[0017] Figure 1For Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 (surface topography diagrams of ionic liquid membranes under four systems). Figure 2 For Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, the friction force - load curve diagram (a) of the ionic liquid membrane and the bar charts of friction coefficient and Young's modulus (b). Detailed implementation manners

[0018] The present invention will be further described in detail below in conjunction with specific examples and drawings.

[0019] Example 1:

[0020] ① Use a microsyringe to take 10 -3 mL of ionic liquid 1 - butyl - 3 - methylimidazolium dicyanamide ([BMIIM][DCA]) and dissolve it in a glass bottle containing 1 mL of ethanol. Ultrasonic it evenly to obtain an ethanol solution of the ionic liquid.

[0021] ② Measure 4 μL of the above - mentioned ethanol solution of the ionic liquid and drop it onto the surface of a 1×1 cm 2 fresh mica surface, and then place it in a vacuum drying oven and treat it at 35 °C for 12 h to remove the ethanol on the mica surface, thus preparing an ionic liquid thin film with a certain thickness.

[0022] ③ Measure the friction force between the probe and the [BMIIM][DCA] ionic liquid membrane. The image is as shown in a of Figure 2 . Calculate the friction coefficient and Young's modulus according to the friction force. The results are as shown in b of Figure 2 . Its friction coefficient is close to 0.002, and the Young's modulus reaches 150 GPa, which reflects the good lubricity and hardness of the [BMIIM][DCA] ionic liquid membrane. The test process is as follows: Keep the probe in the state of scanning the sample. At the same time, change the feedback from Amplitude to TM Deflection mode, and change the scanning angle to 90°. Given a positive load (0 - 85 nN), make the probe friction on the surface, and measure the friction force between the probe and the ionic liquid membrane under different loads.

[0023] ④ Use AFM to measure the surface topography diagram of the [BMIIM][DCA] ionic liquid membrane after friction with the probe. The results are as shown in Figure 1As shown, at different voltages ((+2V, +1V, 0V, -1V, -2V)), the surface topography of the [BMIIM][DCA] ionic liquid membrane hardly changes after being rubbed by the probe, indicating that it does not undergo reorganization under voltage, is more stable, and can achieve ideal lubrication performance. The test process is as follows: After the friction is completed, keep the probe scanning the sample state, change the feedback from TM Deflection back to Amplitude mode, and change the scanning angle back to 0°, restore to the original tapping mode scanning state, and still scan in situ at the original 5μm×5μm position and range to obtain the voltage surface topography of the nano-trimmed ionic liquid membrane at different voltages (+2V, +1V, 0V, -1V, -2V).

[0024] Comparative Example 1:

[0025] ① Use a microinjector to take 10 -3 mL of the ionic liquid trioctylhexadecylammonium succinate ([N 8,8,8,16 [DOSS]) and dissolve it in a glass bottle containing 1 mL of ethanol, and ultrasonically mix it evenly to obtain a solution of the ionic liquid in ethanol.

[0026] ② Measure 4 μL of the above solution and drop it onto the surface of a 1×1 cm 2 fresh mica (obtain a fresh surface by tearing off the mica surface layer with double-sided tape), and then place it in a vacuum drying oven and treat it at 35°C for 12 h to remove the ethanol on the mica surface to prepare an ionic liquid thin film with a certain thickness. The test process is the same as that in Example 1.

[0027] ③ Measure the frictional force between the probe and the [N 8,8,8,16 [DOSS] ionic liquid membrane. The image is as shown in Figure 2 a. Calculate the friction coefficient and Young's modulus according to the frictional force. The results are as shown in Figure 2 b. Its friction coefficient is close to 0.0035, and the Young's modulus reaches 150 GPa, indicating its poor lubricity and relatively soft properties, and it is prone to change under load. The test process is the same as that in Example 1.

[0028] ④ Use AFM to measure the surface topography of the [N 8,8,8,16 [DOSS] ionic liquid membrane after friction with the probe. The results are as shown in Figure 1 As shown, the surface topography of Comparative Example 1 changes greatly after being rubbed by the probe, indicating that it undergoes reorganization under voltage, is unstable, and has poor lubrication performance.

[0029] Comparative Example 2:

[0030] ① Use a microinjector to take 1 mL of 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]) and dissolve it in a glass bottle containing 1 mL of ethanol, and ultrasonically mix it evenly to obtain 10-3 A solution of ionic liquid / ethanol of mL.

[0031] ② Measure 4 μL of the above solution and drop it onto the surface of 1×1 cm 2 fresh mica), then place it in a vacuum drying oven and treat it at 35 °C for 12 h to remove the ethanol on the mica surface, obtaining an ionic liquid film with a certain thickness.

[0032] ③ Measure the friction force between the probe and the [OMIM][PF6] ionic liquid film. The image is as shown in Figure 2 a in, calculate the friction coefficient and Young's modulus according to the friction force, and the results are as shown in Figure 2 b in. Its friction coefficient is slightly larger than 0.002, and the elastic modulus is close to 50 GPa, indicating its poor lubricity and relatively soft property (harder than Comparative Example 1 and softer than Comparative Example 3).

[0033] ④ Use AFM to measure the surface topography map of the [OMIM][PF6] ionic liquid film after friction with the probe. The results are as shown in Figure 1 shown. The surface topography map of Comparative Example 2 hardly changes after being rubbed by the probe, indicating that it does not undergo reorganization at different voltages, is relatively stable, and its lubrication performance is medium (better than Comparative Example 1).

[0034] Comparative Example 3:

[0035] ① Use a microinjector to take 1 mL of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and dissolve it in a glass bottle containing 1 mL of ethanol, and ultrasonically mix it evenly to obtain 10 -3 mL of ionic liquid / ethanol solution.

[0036] ② Measure 4 μL of the above solution and drop it onto the surface of 1×1 cm 2 fresh mica surface, then place it in a vacuum drying oven and treat it at 35 °C for 12 h to remove the ethanol on the mica surface, obtaining an ionic liquid film with a certain thickness.

[0037] ③ Measure the friction force between the probe and the [BMIM][PF6] ionic liquid film. The image is as shown in Figure 2 a in, calculate the friction coefficient and Young's modulus according to the friction force, and the results are as shown in Figure 2 b in. Its friction coefficient is slightly lower than 0.002, and the elastic modulus is close to 60 GPa, indicating its moderate lubricity and moderate hardness (harder than Comparative Example 2 and softer than Example 1).

[0038] ④ Use AFM to measure the surface topography map of the [BMIM][PF6] ionic liquid film after friction with the probe. The results are as shown in Figure 1As shown, the surface topography of Comparative Example 3 hardly changes after probe friction, indicating that it does not undergo reorganization at different voltages, is relatively stable, and has medium lubricating performance (superior to Comparative Example 2 and inferior to Example 1).

[0039] The names and structural formulas of the ionic liquids of Example 1 and Comparative Examples 1-3 are as follows.

[0040]

[0041] In the ionic liquid membranes of the embodiments of the present invention under a lower load (such as 50 N), the frictional forces on the ND and BP ionic liquid membranes are about 0.25 nN, while the frictional force on the BD ionic liquid membrane is about 0.20 nN, a reduction of about 20% ( Figure 2 in a)). And from the fitted curves, it can be obtained that the friction coefficient of BD is about 0.0019, lower than 0.0036 of ND, 0.0020 of BP, and 0.0021 of OP. Compared with the tetrazole-based ionic liquid membranes (0.1 - 0.9) in the literature (JIXIA Q, JIAHUAM, ZIJING B, et al. Tribological Behaviors of TetrazoleBased Protic Ionic Liquids as Additives in Water[J]. 2025), it is also nearly two orders of magnitude lower, which means that BD has better performance under higher loads.

[0042] The Young's modulus of the ionic liquid membranes prepared in the present invention is as high as 150 GPa, significantly higher than that of the control group ND (about 20 GPa), OP (about 30 GPa), and BP (about 50 GPa) ionic liquid membranes ( Figure 2 in b)). It has excellent mechanical properties and wear resistance and can withstand higher loads and more severe working environments. The ionic liquid lubricant shows high stability during use, especially under high-temperature (>150 °C) and low-temperature (< -50 °C) conditions. Compared with traditional lubricants, the friction coefficient of the ionic liquid lubricating film can still be maintained below 0.06 under high-temperature environments, while the friction coefficient of traditional lubricants will increase significantly at high temperatures, even reaching above 0.12. And after 500 hours of long-term use of the ionic liquid membrane, the change in the friction coefficient is less than 5%, far superior to traditional lubricants (REEVES C J, KASARAK, MENEZES P L JJ O C P. Tribological performance of environmental friendly ionic liquids for high-temperature applications[J]. 2021, 279:123666).

Claims

1. A method for changing the lubricating properties of a lubricant by ion size, characterized in that: The following steps are involved: The ionic liquid is dissolved in a solvent, then drop-coated on a substrate, and vacuum dried to remove the solvent to obtain an ionic liquid membrane. The cation size in the ionic liquid is 0.75-2.90 nm, the anion size is 0.32 nm-1.66 nm, and the size difference between the cation and anion is no more than 0.

03.

2. The method according to claim 1, characterized in that The solvent is any one of acetonitrile, dimethylsulfamide, ethanol and carbon tetrafluoride, preferably ethanol.

3. The method according to claim 1, characterized in that The ionic liquid is any one of dioctylmethylimidazolium sulfosuccinate ([N8,8,8,16][DOSS]), 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]), 1-butyl-3-methylimidazolium dicyanamide ([BMIIM][DCA]), and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), preferably 1-butyl-3-methylimidazolium dicyanamide ([BMIIM][DCA]).

4. The method according to claim 1, characterized in that The substrate is made of mica, graphite, titanium or aluminum alloy, preferably graphite.

5. The method according to claim 1, characterized in that The volume ratio of ionic liquid to solvent is 10 -7 :1~10 -2 :1, preferably 10 -3 :

1.

6. The method according to claim 1, characterized in that The ionic liquid is dissolved in a solvent and then drop-coated on the substrate. 2 2 to 6 μL, preferably 4 μL, is drop-coated on the substrate.

7. The method according to claim 1, characterized in that The vacuum drying temperature is 35±5℃ and the drying time is 12±4h.

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