Method for obtaining dynamic properties and ion structure of ionic liquid in situ by using graphene colloid probe technology

Abstract

The invention discloses a method for obtaining dynamic properties and an ion structure of ionic liquid in situ by using a graphene colloid probe technology. According to the method, a graphene colloid probe with high conductivity and mechanical stability is utilized, an atomic force microscope is combined, meanwhile, the ion migration capacity of the graphene colloid probe is tested through electrochemical impedance spectroscopy, and in cooperation with molecular dynamics simulation, space orientation changes of an interface cation side chain and an imidazole ring are quantitatively analyzed. The method has the advantages of high non-destructiveness, high spatial resolution, short response time and the like, and provides a novel test scheme and theoretical support for applications such as ionic liquid lubrication, electrochemical energy storage, sensor interfaces and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of ionic liquid interface characterization, and relates to a method for in-situ acquiring the kinetic properties and ionic structure of ionic liquids by utilizing graphene colloid probe technology. Background Art

[0002] Ionic liquids are widely used in cutting-edge technologies such as micro-nano lubrication, energy storage devices, electrocatalysis, and interface regulation due to their good thermal stability, wide electrochemical window, and excellent lubrication properties. Studies have shown that the near-interface structure of ionic liquids on solid surfaces significantly affects their kinetic behavior, such as ion diffusion rate, friction response, and electrical conductivity, which in turn affects their application performance in related devices. On two-dimensional materials, especially carbon-based surfaces such as graphene, ionic liquids often exhibit obvious structural reorganization behavior, and their ionic configuration can be controlled by electric fields, thereby triggering "switchable" responses of interfacial lubrication and electrochemical behaviors. Therefore, establishing a precise method to characterize the coupling relationship between the ionic structure and kinetic response of ILs on charged graphene interfaces is of great significance for the development of adjustable lubrication systems and high-performance energy storage devices.

[0003] Currently, although atomic force microscopy (AFM) has been used to detect the interface characterization of ionic liquids on solid surfaces, there are interface differences between traditional AFM probe materials and actual device materials (such as graphene), making it difficult to truly simulate the ionic liquid-device material interface under application conditions. In addition, existing testing methods are often unable to simultaneously obtain the kinetic properties and arrangement structure of ionic liquids, limiting the ability to systematically understand and control the interfacial behavior of ionic liquids. Therefore, there is an urgent need for a method that can truly simulate the graphene interface and can simultaneously obtain the ionic structure chromatography and ion dynamic migration behavior of ionic liquids in situ under an applied bias to meet the research needs of high-precision interface control and material design. Summary of the Invention

[0004] The present invention aims to provide a method for in situ characterization of the kinetic properties and ionic structure of ionic liquids using graphene colloidal probe technology. This method utilizes highly conductive and stable graphene colloidal probes, combined with atomic force microscopy (AFM) nanomechanical testing, electrochemical impedance spectroscopy (EIS) measurements, and molecular dynamics (MD) simulations, to achieve multidimensional, quantitative characterization of ionic liquid interfacial behavior under realistic graphene interface conditions.

[0005] The technical solutions for achieving the purpose of the present invention are as follows:

[0006] The method for in situ obtaining the kinetic properties and ionic structure of ionic liquids using graphene colloid probe technology comprises the following steps:

[0007] (1) coating the ionic liquid solution on the surface of the graphene substrate and vacuum drying to form an ionic liquid film;

[0008] (2) Graphene was coated on the surface of silica microspheres by chemical vapor deposition (CVD) to prepare a graphene colloidal probe, and then the graphene colloidal probe was fixed to the end of the AFM cantilever by adhesive;

[0009] (3) Grounding the graphene substrate, applying a bias voltage to the graphene colloid probe, and regulating the charge state of the graphene surface by changing the magnitude of the bias voltage;

[0010] (4) The conductivity change was obtained by measuring the interfacial ion migration impedance under different bias voltages through EIS; and the anion and cation orientation of the ionic liquid membrane structure was analyzed by combining the surface structure characterization of the ionic liquid and molecular dynamics simulation.

[0011] Furthermore, in step (1), the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), 1-octyl-3-methylimidazolium chloride ([OMIM][Cl]), 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([DMIM][TFSI]), 1-allyl-3-methylimidazolium chloride ([AMIM][Cl], 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM][BF4]) or 1-hexyl-2,3-dimethylimidazolium bromide ([HDMIM][Br]), preferably [BMIM][BF4].

[0012] Furthermore, in step (1), in the ionic liquid solution, the volume ratio of the ionic liquid to the solvent is 10 -7 :1~10 -2 :1, preferably 10 -3 :1, the solvent is ethanol, etc.

[0013] Furthermore, in step (1), the drop coating density of the ionic liquid solution is 0.5 to 5 μL / cm 2 , preferably 1 μL / cm 2 .

[0014] Furthermore, in step (1), the vacuum drying temperature is 35°C ± 5°C, and the drying time is 12 ± 4 hours.

[0015] Furthermore, in step (2), the diameter of the silica microspheres is 5 to 15 μm, preferably 10 μm, and the number of graphene layers of the graphene colloid probe is multiple layers.

[0016] Furthermore, in step (3), the bias voltage is a positive bias voltage or a negative bias voltage, and the bias voltage range is -5V to +5V, -4V to +4V, -3V to +3V or -2V to +2V, preferably -2V to +2V.

[0017] Furthermore, in step (4), the ionic conductivity was measured by EIS, with the graphene substrate as the working electrode, applying an open circuit potential of -1V to +1V, a 10mV perturbation, and a frequency range of 0.01-10 6 Hz; analyzed by molecular dynamics simulation, calculated by MD simulation of cations [BMIM] + Normal angle of imidazole ring and the distribution probability of the butyl chain tilt angle (θ).

[0018] Furthermore, in step (4), a voltage was applied to the graphene substrate surface along the Z axis using a constant potential method. Three-dimensional periodic boundary conditions were applied in all directions in the simulation chamber, and a 5 nm vacuum gap was set on top of the ionic liquid to eliminate image effects in the Z axis. All equilibrium simulation systems used a Nose Hoover thermostat. The motion of atoms was described by the classical Newtonian equations and solved using the velocityVerlet algorithm. The particle-particle-mesh method was used to calculate long-range electrostatic interactions. All MD simulations were performed using a large-scale atomic / molecular massively parallel simulation software package.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) Sensitive and realistic interface simulation: Graphene colloidal probes are used to replace traditional silicon needles. Multilayer graphene is coated on SiO2 microspheres by CVD method, so that the AFM probe material matches the graphene substrate. This can simulate the actual interface of graphene devices with high fidelity, and achieve high consistency between test results and actual applications.

[0021] (2) In-situ multimodal synchronous measurement: The method of the present invention can simultaneously obtain the ionic structure chromatography information (force curve) and electrical conductivity (EIS) of ionic liquids under bias control, breaking through the "single indicator" testing limitation of traditional methods.

[0022] (3) Perfectly fit for the design of ionic liquid interface structure based on electrical regulation: by adjusting the graphene bias, the continuous regulation of the molecular structure of the ionic liquid interface can be achieved, providing an experimental basis for the construction of intelligent responsive lubrication systems and electrochemical surfaces.

[0023] (4) Strong versatility and easy promotion: The method of the present invention does not rely on specific ion types or material surfaces. It only requires the preparation of graphene-coated probes and bias loading, and can be applied to a variety of electroactive materials and interface lubrication systems, and has wide application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Nyquist and Bode plots of BB at -1, 0, and +1 volts when graphene is used as the electrode.

[0025] Figure 2 Under bias voltages of -2, -1, 0, +1, and +2 V, [BMIM] + Angular probability distribution of the cationic imidazole ring and long butyl chain on graphene. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0027] Example 1

[0028] (1) The ionic liquid [BMIM][BF4] was mixed at a volume ratio of 10 -3 : 1 was dissolved in ethanol to prepare [BMIM][BF4] ionic liquid solution.

[0029] (2) 1 μL of the prepared ionic liquid solution was dropped onto the surface of the graphene substrate with a surface area of ​​1 × 1 cm 2 The coated graphene substrate was then dried in a vacuum environment at 35°C for 12 hours until the solvent was completely evaporated to form a stable ionic liquid film.

[0030] (3) Silica microspheres with an average diameter of 10 μm were selected and multilayer graphene was grown on their surfaces using the CVD method, forming graphene microspheres with high conductivity and high rigidity. The graphene microspheres were bonded to the end of the AFM cantilever using an epoxy resin mixture (BDMA:DDSA:CY212 = 1:10:10). After curing for 24 hours, a "graphene colloidal probe" (GrP) was formed, which has good structural stability and electrical connectivity.

[0031] (4) The graphene substrate is grounded as a reference electrode, and bias voltages (±1 V, ±2 V) are applied to the graphene colloidal probe, with the potential controlled and stabilized by the power supply system. Because graphene has a high specific surface area and high current carrying capacity, applying voltage can induce high-density charges at the interface, significantly affecting the spatial orientation and stacking state of cations or anions in the ionic liquid.

[0032] (5) Under different bias voltages (-2V, -1V, 0V, +1V, +2V), an AC disturbance with an amplitude of 10mV is applied to the system, and the scanning frequency range is 10 5 Hz to 10 -2 Hz, the recorded Nyquist spectrum and Bode phase diagram are as follows Figure 1As shown. According to the equivalent circuit model, the impedance data was fitted to obtain the interface ion migration resistance (R ct ) and membrane capacitance (C dl ), and then calculate the change in conductivity. The results show that under positive bias conditions (+1 to +2V), the ion migration impedance is minimized and the interfacial conductivity is significantly improved, indicating that the negative ion enrichment interface and enhanced channel continuity are conducive to rapid ion transport. However, under 0V or negative bias, the interfacial conductivity decreases significantly due to the interference of the stacking of larger cation side chains.

[0033] (6) Molecular dynamics simulation was used to model and analyze the interface arrangement behavior of the [BMIM][BF4] system under different bias environments. The results are as follows: Figure 2 As shown in the figure, the simulation data show that under no bias (0V), the cations and anions are staggered and have no obvious orientation. The orientation distribution of the butyl chain is a bimodal structure (about 50° and 115°), and the interface structure is relatively loose. Under positive bias (+2V), the anion [BF4] - It is enriched at the graphene interface, with cations gathering away from the interface, imidazole rings stacking parallel to the surface, and butyl chains showing a single-peak distribution vertically outward (centered at 115°), indicating that the structural order is significantly enhanced; under negative bias conditions, cations accumulate at the interface due to charge attraction, but their spatial structure is relatively loose, the butyl chain arrangement angle distribution is wider, and the overall arrangement is reduced.

[0034] In summary, the present invention proposes a method for in situ acquisition of the kinetic properties and ionic structure of ionic liquids using graphene colloid probe technology, which can achieve multi-parameter simultaneous characterization of the interfacial behavior of ionic liquids at the nanoscale. This method utilizes highly conductive and stable graphene colloid probes to evaluate the migration ability of ions through electrochemical impedance spectroscopy (EIS) technology, and then introduces molecular dynamics simulation to further quantitatively reveal the mechanism of spatial orientation change of cationic side chains and imidazole rings at the interface under voltage regulation. This method has significant advantages such as high resolution and reversible control means. It provides a theoretical basis and practical technical support for cutting-edge fields such as electronically controlled lubrication, electrochemical energy storage, and micro-nano interface regulation, and has broad application prospects and promotion value.

Claims

1. A method for in situ acquisition of kinetic properties and ionic structure of ionic liquids using graphene colloid probe technology, characterized in that: The following steps are involved: (1) Coating the ionic liquid solution on the surface of the graphene substrate and forming an ionic liquid film after vacuum drying; (2) Graphene was coated on the surface of silica microspheres by chemical vapor deposition to prepare a graphene colloidal probe, and then the graphene colloidal probe was fixed to the end of the AFM cantilever by adhesive; (3) Grounding the graphene substrate and applying a bias voltage to the graphene colloidal probe, and regulating the charge state of the graphene surface by changing the magnitude of the bias voltage; (4) EIS was used to measure the interface ion migration impedance under different bias voltages to obtain the change in conductivity; Combined with the surface structure characterization of ionic liquids and molecular dynamics simulation, the anion and cation orientation of the ionic liquid membrane structure are analyzed.

2. The method according to claim 1, wherein In step (1), the ionic liquid is [BMIM][BF4], [EMIM][OAc], [OMIM][Cl], [DMIM][TFSI], [AMIM][Cl], [BDMIM][BF4] or [HDMIM][Br].

3. The method according to claim 1, characterized in that In step (1), the volume ratio of ionic liquid to solvent in the ionic liquid solution is 10 -7 :1~10 -2 :1, the solvent is ethanol.

4. The method according to claim 1, wherein In step (1), the drop coating density of the ionic liquid solution is 0.5~5 μL / cm².

5. The method according to claim 1, wherein In step (1), the drop coating density of the ionic liquid solution is 1 μL / cm².

6. The method according to claim 1, characterized in that In step (1), the vacuum drying temperature is 35°C ± 5°C, and the drying time is 12 ± 4 hours.

7. The method according to claim 1, wherein In step (2), the diameter of the silica microspheres is 5 to 15 μm, preferably 10 μm, and the number of graphene layers of the graphene colloid probe is multilayer.

8. The method according to claim 1, characterized in that In step (3), the bias voltage is a positive bias voltage or a negative bias voltage, and the bias voltage range is -5V~+5V, -4V~+4V, -3V~+3V or -2V~+2V.

9. The method according to claim 1, wherein In step (4), the ionic conductivity was measured by EIS with the graphene substrate as the working electrode, an open circuit potential of -1 V to +1 V, a 10 mV perturbation, and a frequency range of 0.01-10 6 Hz; molecular dynamics simulation analysis, the distribution probability of the imidazole ring normal angle (φ) and the butyl chain tilt angle (θ) of the cation [BMIM]⁺ was calculated by MD simulation.

10. The method according to claim 1, wherein In step (4), a voltage is applied to the surface of the graphene substrate along the Z axis by a constant potential method, a three-dimensional periodic boundary condition is applied in all directions in the simulation box, and a vacuum gap of 5 nm is set on the top of the ionic liquid to eliminate the image effect in the Z axis direction; All equilibrium simulations were performed using a NoseHoover thermostat. Atomic motion was described by classical Newtonian equations, solved using the velocity Verlet algorithm. Long-range electrostatic interactions were calculated using a particle-particle-mesh approach. All MD simulations were performed using a large-scale atomic / molecular massively parallel simulation software package.

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