A method for measuring the average sheet diameter of two-dimensional materials

Abstract

The present invention relates to a method for measuring the average lamella diameter of a two-dimensional material. The method comprises the following steps: uniformly mixing a two-dimensional material to be measured, an adhesive, and a solvent so that the two-dimensional material is dispersed in the solvent and the adhesive is dissolved in the solvent to obtain a two-dimensional material / adhesive mixed solution; filtering the two-dimensional material / adhesive mixed solution on a filter membrane to obtain a two-dimensional material / adhesive composite film having an area S and a thickness T; measuring the gas permeability P of the two-dimensional material / adhesive composite film; and calculating the average lamella diameter of the two-dimensional material to be measured based on the relationship between the average lamella radius R of the two-dimensional material to be measured and the gas permeability P: R=(ASx-PTSx) / PmB. The method of the present invention is simple and fast, and can quickly and directly obtain the average lamella diameter and average lamella radius of a large number of two-dimensional materials through gas permeability testing and calculation.

Description

Technical Field

[0001] The present invention relates to a method for measuring the average lamella diameter of dense two-dimensional materials, and in particular to a method for estimating the average lamella diameter of dense two-dimensional materials, belonging to the field of two-dimensional material size measurement. Background Art

[0002] Today, the application of two-dimensional materials in various fields is a very popular frontier research direction. Generally speaking, two-dimensional materials refer to materials in which electrons can move freely only on the nanoscale (1-100nm) in two dimensions, and have a special planar structure. For example, the well-known graphene (including graphene oxide, functionalized graphene, etc.), as well as boron nitride, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, MXene, etc. can all be used as two-dimensional materials. Due to the anisotropy of the electrical and mechanical properties of two-dimensional materials, conductive two-dimensional materials have very broad application prospects in flexible electronic materials (such as field-effect transistors, optoelectronic devices, thermoelectric devices, etc.); due to the anisotropy of their optical and thermal properties, they have great development potential in the fields of polarized optoelectronic devices, polarized thermoelectric devices, bionic devices, polarized light detection, etc.

[0003] The size of a two-dimensional material—its extent in the two-dimensional expansion direction—has a significant impact on its mechanical, electrical, optical, and thermal properties. It directly determines its performance as a raw material for industrial applications. Therefore, controlling the size (or average size) of two-dimensional materials is a crucial technology.

[0004] However, as a nanomaterial, the size consistency of two-dimensional materials cannot be guaranteed during the preparation process. It can only be guaranteed that the size of most materials is within a certain range. Therefore, a simple and fast testing method is needed to statistically average the size of the prepared two-dimensional materials. Currently, the size of two-dimensional materials is generally obtained through direct observation, such as:

[0005] (1) Optical microscope. The size distribution of two-dimensional materials can be directly observed using an optical microscope. However, due to the limited resolution of the microscope, it is difficult to observe two-dimensional materials at the micron level.

[0006] (2) Atomic force microscopy. By scanning the surface of a material using an atomic force microscope, the thickness and size distribution of the two-dimensional material can be characterized based on the surface undulations. However, due to the atomic-level precision of the atomic force microscope, the test range is small (usually within a few square microns), making it difficult to test large-scale two-dimensional materials.

[0007] (3) Electron microscopy (SEM, TEM, etc.). This technique directly observes the size distribution of two-dimensional materials within a certain range using an electron microscope. However, the observation position is generally limited to a small range and can be manually selected, which is subject to subjective factors.

[0008] The above methods can all obtain the size distribution data of two-dimensional materials. However, there are also the following problems:

[0009] (1) Only the material distributed on the surface can be observed, and the material inside cannot be observed. If the size of the internal material is different from that of the surface material, the measurement data will be inaccurate.

[0010] (2) The range is limited. Generally, only the size of two-dimensional materials within a small range can be observed. However, the size uniformity of a large number of nanomaterials is not necessarily perfect, and the material size at different locations may vary greatly. Therefore, the observed data within a small range may have a large error from the actual statistical average.

[0011] (3) After the test, a more complex statistical analysis is required, which requires measuring the size of a large number of single pieces of material, analyzing the size distribution of the material, and finally calculating the statistical average of the size. However, this statistical average is only the average value within the observation range, not for all materials.

[0012] Therefore, based on existing methods, it is basically impossible to quickly and directly obtain the statistical average values of the sizes of a large number of two-dimensional materials. Summary of the Invention

[0013] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for quickly measuring the average sheet diameter of a two-dimensional material.

[0014] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0015] A method for measuring the average sheet diameter of a two-dimensional material comprises the following steps:

[0016] S1. Evenly mixing the two-dimensional material to be measured, the binder, and the solvent, so that the two-dimensional material is dispersed in the solvent and the binder is dissolved in the solvent, to obtain a two-dimensional material / binder mixed solution;

[0017] Wherein, under the same thickness condition, the gas permeability of the two-dimensional material to be measured is less than the gas permeability of the adhesive;

[0018] S2. Filtering the two-dimensional material / adhesive mixed solution on a filter membrane and drying it to obtain a two-dimensional material / adhesive composite film with an area of S and a thickness of T;

[0019] Wherein, the pore size of the filter membrane is smaller than the size of the two-dimensional material;

[0020] S3, measuring the gas permeability P of the two-dimensional material / adhesive composite film;

[0021] S4. According to the relationship between the average sheet radius R of the two-dimensional material to be measured and the gas permeability P: Calculate and obtain the average sheet diameter (i.e., 2R) of the two-dimensional material to be measured;

[0022] Where m is the mass of the two-dimensional material in the two-dimensional material / adhesive composite film, x is the theoretical surface density of the two-dimensional material, and A and B are constants.

[0023] Optionally, the constant A is determined by one of the following methods: preferably, the constant A is determined by method 2, which can be used as a reliable method for determining the constant A;

[0024] Method 1: Prepare a pure adhesive film and measure the gas permeability P0 and thickness T0 of the adhesive film. The constant A =

[0025] P0×T0;

[0026] Method 2: (1) Set the average sheet diameter to 2R Y The same two-dimensional material, binder and solvent are uniformly mixed, so that the two-dimensional material is dispersed in the solvent and the binder is dissolved in the solvent, thereby obtaining a two-dimensional material / binder mixed solution;

[0027] (2) Filtering the two-dimensional material / adhesive mixed solution on a filter membrane (preferably, the filtering method is suction filtration) to obtain an area of S Y , thickness is T Y Two-dimensional material / adhesive composite film'; preferably, T Y 0.8-1.2 times of T;

[0028] (3) Measuring the gas permeability P of the two-dimensional material / adhesive composite film Y ;

[0029] (4) According to the relationship Calculate the constant A;

[0030] Among them, m Y is the mass of the 2D material in the 2D material / adhesive composite film, x Y The average sheet diameter is 2R Y The theoretical areal density of the two-dimensional material. Optionally, the constant B=0.85.

[0031] During filtration, the two-dimensional material to be tested in the two-dimensional material / binder mixed solution tends to be distributed flatly, and the material layers are bonded by the binder to form a "brick wall structure". The schematic diagram of the "brick wall structure" is shown in the figure. Figure 1In the present invention, the adhesive not only plays a bonding role, helping to form a composite film with a more stable structure to facilitate gas permeability testing, but also can impart a more appropriate gas permeability to the composite film, helping to obtain more accurate gas permeability measurement results, thereby improving the accuracy of the final results.

[0032] Furthermore, in S1, the mass ratio of the two-dimensional material to be measured to the adhesive is 1:0.2-10.

[0033] Furthermore, the two-dimensional material includes one or more of graphene, graphene oxide, boron nitride, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, and MXene.

[0034] Furthermore, the adhesive includes one or more of starch, dextrin, polyethyleneimine, polyvinyl alcohol, carboxymethyl cellulose, resin, and rubber; and the solvent is water or an organic solvent.

[0035] Furthermore, in S1, the two-dimensional material to be measured is uniformly dispersed in a solvent in a monolayer state. Optionally, conventional stirring and ultrasonic vibration are used to uniformly and stably disperse the two-dimensional material in the solvent in a monolayer state.

[0036] Optionally, a dispersant is added to the two-dimensional material / binder mixed solution of S1 to better disperse the two-dimensional material in the solvent.

[0037] Furthermore, in S2, the two-dimensional material / adhesive mixed solution is filtered on a filter membrane to obtain a two-dimensional material / adhesive composite membrane with an area of S and a thickness of T.

[0038] Preferably, S2 and step (2) are filtered on a filter membrane with the same area and pore size. More preferably, the parameters such as filtration power and filtration time in the filtration process of S2 and step (2) are the same.

[0039] Furthermore, in S2, the mixture is dried at 35-45°C for 0.5-1.5 hours; furthermore, the mixture is dried at 38-43°C for 0.8-1.2 hours.

[0040] Furthermore, in S3, the gas permeability is measured by a pressure difference method or an isobaric method. Preferably, the gas used in the measurement is a neutral gas without special chemical properties, such as nitrogen, argon, etc.

[0041] Furthermore, the filter membrane is a water-based filter membrane or an organic filter membrane; preferably, the water-washable filter membrane is a cellulose acetate filter membrane, and the organic filter membrane is a polytetrafluoroethylene filter membrane.

[0042] The average sheet diameter of the two-dimensional material to be measured is related to the gas barrier performance (gas permeability) of the two-dimensional material / adhesive composite film. The larger the average sheet diameter, the stronger the gas barrier performance. This is because gas molecules find it difficult to penetrate dense two-dimensional materials (such as the absolute barrier effect of graphene on gas molecules). During the permeation process, they will bypass the dense two-dimensional material and tend to migrate only in the middle of the adhesive with higher gas permeability. Therefore, the larger the average sheet diameter of the two-dimensional material, the longer the distance that gas molecules need to bypass to penetrate the composite film (such as Figure 3 The specific relationship and calculation process between the average sheet diameter of the two-dimensional material and the gas permeability are as follows:

[0043] (1) The two-dimensional material / adhesive composite film prepared by the above method is arranged in a stacked manner due to the flexibility of the two-dimensional material. Assuming that each layer is covered with two-dimensional material, the mass is m (mg) and the theoretical surface density is x (mg m -2 ) of a two-dimensional material with an area of S(m 2 ) In the two-dimensional material / adhesive composite film, a total of n layers of two-dimensional material are covered. Among them:

[0044]

[0045] (2) Since gas molecules cannot penetrate dense two-dimensional materials or tend to migrate only in the middle of the adhesive with higher gas permeability, their migration process can only be realized in the adhesive, such as Figure 3 、 Figure 4 As shown. The gas diffusion coefficient and gas solubility coefficient in the adhesive are only related to the composition and structure of the adhesive itself, and do not change with the change of the average sheet diameter of the two-dimensional material. Therefore, the total average migration path length L of gas molecules in the two-dimensional material / adhesive composite film is z It directly determines the gas permeability P of the composite film, and the two are inversely proportional, namely:

[0046] or

[0047] Where A is a constant.

[0048] (3) The shape of the two-dimensional material is not fixed. In this paper, the two-dimensional material is approximated as a circular model (radius R) (this is also the most commonly used model when characterizing the size parameters of two-dimensional materials). According to the geometric relationship, the total average migration path length L of the gas molecules in the composite film is z It can be calculated by the following formula:

[0049] L z =n×L d +T

[0050] Where T is the thickness of the 2D material / adhesive composite film, L d is the average migration path length of gas molecules in the monolayer, which is related to the radius of the two-dimensional material:

[0051] L d =B×R

[0052] B is a constant. According to the geometric relationship and the principle of free diffusion, it can be deduced that B is approximately 0.85.

[0053] Therefore, the relationship between the gas permeability (P) of the 2D material / adhesive composite film and the radius R of the 2D material is:

[0054]

[0055]

[0056] Among them, S, m, P, and T can all be measured by conventional means. The theoretical surface density x of the two-dimensional material can be easily calculated based on the two-dimensional material model, and B is a constant.

[0057] The above formula gives the relationship between the gas permeability (P) of the complete composite film and the radius R of the two-dimensional material. That is, by testing the gas permeability (P) of the composite film, the statistical average value of the size (radius R) of the two-dimensional material in the composite film can be obtained, and then the statistical average value of the average sheet diameter of the two-dimensional material can be obtained.

[0058] Precise L d The relationship with R and the derivation process of constant B are as follows:

[0059] like Figure 5 As shown, a two-dimensional material modeled as a circle. Let the radius of the two-dimensional material be R. During free permeation, gas molecules pass through and around the two-dimensional material (the permeation direction is the thickness of the two-dimensional material). Based on the definitions of free permeation and free diffusion, as well as the self-assembly and random distribution of two-dimensional materials, the initial contact point of gas molecules with the two-dimensional material has no macroscopic preference; that is, the probability of initial contact being at any point on the two-dimensional material is equal.

[0060] Then, the probability that the distance r between the initial contact position and the center O is:

[0061]

[0062] A gas molecule starts from the ring (for example, point C on the ring) and diffuses freely around the two-dimensional material. During the diffusion process, the probability of diffusion from point C in any direction is equal. Therefore, the probability of diffusion in a direction with an angle θ with the line connecting the center of the circle is:

[0063]

[0064] Diffusion at an angle θ, the distance L to the edge of the two-dimensional material, is the migration path length required to bypass the two-dimensional material and achieve penetration. According to the geometric relationship, L is a function of θ, that is, L(θ):

[0065]

[0066] After considering the normalized probability function, the average migration path length L required for gas molecules to bypass the two-dimensional material is d (The exact average migration path of gas molecules in a monolayer) is:

[0067]

[0068] It can be seen that the average migration path length L of a single layer d It is integral with the radius R. Calculate and get the result: L jd ≈0.85R. That is, constant B can be approximately taken as 0.85. When method 2 is used to determine constant A, the specific value of constant B does not affect the measurement result of the average lamella diameter.

[0069] The method of the present invention is simple and fast, and can quickly and directly obtain the average sheet diameter and average sheet radius of a large number of two-dimensional materials through gas permeability testing and calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the cross-sectional structure of a two-dimensional material / adhesive composite film of the present invention.

[0071] Figure 2 This is an SEM image of the cross section of a graphene oxide / PEI composite membrane.

[0072] Figure 3 Schematic diagram showing how the migration path length of gas molecules in large-scale two-dimensional material / adhesive composite films is affected by the size of the two-dimensional material.

[0073] Figure 4 Schematic diagram showing how the migration path length of gas molecules in small-sized two-dimensional material / adhesive composite films is affected by the size of the two-dimensional material.

[0074] Figure 5 This is a simplified diagram of the free penetration process of gas molecules. DETAILED DESCRIPTION

[0075] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0076] Example 1

[0077] In this embodiment, the method for measuring the average sheet diameter of graphene oxide is as follows:

[0078] (1) First, determine the constant A: Prepare graphene oxide G0 of known size (<3 layers, average sheet diameter of 2 μm, maximum diameter range of 0.5-3 μm, oxygen content of 31 wt%). The theoretical surface density of pure graphene is x0 = 0.77 mg m -2 , then the theoretical surface density of graphene oxide G0 is 1.12 mg m -2 . Weigh 100 mg of G0 and 100 mg of polyethyleneimine (PEI) and dissolve them in water. First, take 10w ultrasonic treatment for 10 minutes to convert graphene oxide G0 into a single layer. Then, use conventional ultrasonic dispersion and stirring at 60°C until a stable G0 / PEI dispersed aqueous solution is formed. Filter the G0 / PEI aqueous solution by suction filtration and deposit G0 / PEI on a cellulose acetate filter membrane (0.2μm pore size, 0.01m 2 Area), a G0 / PEI composite film was obtained. After being kept at 40°C for 1 hour, the film was dried. The thickness T0 of the G0 / PEI composite film was measured by SEM test to be 6.0 μm. The nitrogen permeability P at room temperature was measured by differential pressure gas permeation test. Y 4.1cm 3 m -2 day -1 atm -1 , according to the formula:

[0079]

[0080] The constant A is 3.1×10 4 μm cm 3 m -2 day -1 atm -1 .

[0081] (2) Measuring the size of the two-dimensional material to be tested: Prepare graphene oxide G1 of unknown size (oxygen content is 31 wt%). The theoretical surface density of pure graphene is 0.77 mg m -2 , then the theoretical surface density of the graphene oxide G1 is x1 = 1.12 mg m -2. Weigh 100 mg of G1 and 100 mg of polyethyleneimine (PEI) and dissolve them in water. First, take 10w ultrasonic treatment for 10 minutes to convert the graphene oxide G1 into a single layer. Then, use conventional ultrasonic dispersion and stirring at 60°C until a stable G1 / PEI dispersion aqueous solution is formed. Filter the G1 / PEI aqueous solution by the same filtration method as step (1), and deposit G1 / PEI on a cellulose acetate filter membrane (0.2μm pore size, 0.01m 2 The G1 / PEI composite film was obtained by maintaining it at 40°C for 1 hour to dry the film. The thickness T1 of the G1 / PEI composite film was measured by SEM to be 6.3 μm. The nitrogen permeability at room temperature was measured by differential pressure gas permeation test to be 4.3 cm 3 m -2 day -1 atm -1 , according to the formula:

[0082]

[0083] The average lamella radius R1 of the unknown-sized graphene oxide G1 was 0.95 μm, and the average lamella diameter was 1.90 μm. According to prior art, using a SEM to observe samples and calculate the average maximum diameter (i.e., observing the maximum diameter of a two-dimensional material within a certain range using a scanning electron microscope, recording the distribution of the maximum diameters, and calculating the statistical average of the sizes) yielded a value of 2.0 μm. By comparison, the average lamella diameter of the graphene oxide G1 measured in this example is very close to the corresponding value measured in prior art.

[0084] Example 2

[0085] In this embodiment, the method for measuring the average sheet diameter of graphene oxide is as follows:

[0086] (1) First, determine the constant A: Prepare graphene oxide G0 of known size (<3 layers, average sheet diameter of 2 μm, maximum diameter range of 0.5-3 μm, oxygen content of 31 wt%). The theoretical surface density of pure graphene is x0 = 0.77 mg m -2 , then the theoretical surface density of graphene oxide G0 is 1.12 mg m -2 . Weigh 100 mg of G0 and 100 mg of polyethyleneimine (PEI) and dissolve them in water. First, take 10w ultrasonic treatment for 10 minutes to convert graphene oxide G0 into a single layer. Then, use conventional ultrasonic dispersion and stirring at 60°C until a stable G0 / PEI dispersed aqueous solution is formed. Filter the G0 / PEI aqueous solution by suction filtration and deposit G0 / PEI on a cellulose acetate filter membrane (0.2μm pore size, 0.01m2 The G0 / PEI composite film was obtained by keeping it at 40℃ for 1 hour to dry the film. The thickness T0 of the G0 / PEI composite film was measured by SEM to be 6.0μm. The nitrogen permeability P of the composite film at room temperature was measured by differential pressure gas permeation test. Y 4.1cm 3 m -2 day -1 atm -1 , according to the formula:

[0087]

[0088] The constant A is 3.1×10 4 μm cm 3 m -2 day -1 atm -1 .

[0089] (2) Measuring the size of the two-dimensional material to be tested: Prepare graphene oxide G2 of unknown size with an oxygen content of 35 wt%. The theoretical surface density of pure graphene is 0.77 mg m -2 , then the theoretical surface density of the graphene oxide G2 is x2 = 1.18 mg m -2 . Weigh 100 mg of G2 and 100 mg of polyethyleneimine (PEI) and dissolve them in water. First, take 10w ultrasonic treatment for 10 minutes to convert the graphene oxide G2 into a single layer. Then, use conventional ultrasonic dispersion and stirring at 60°C until a stable G2 / PEI dispersed aqueous solution is formed. Filter the G2 / PEI aqueous solution by the same filtration method as step (1), and deposit G2 / PEI on a cellulose acetate filter membrane (0.2μm pore size, 0.01m 2 The G2 / PEI composite film was obtained by maintaining it at 40°C for 1 hour to dry the film. The thickness T2 of the G2 / PEI composite film was measured by SEM to be 5.8 μm. The nitrogen permeability at room temperature was measured by differential pressure gas permeation test to be 0.9 cm 3 m -2 day -1 atm -1 , according to the formula:

[0090]

[0091] The average sheet radius R2 of the graphene oxide G1 of unknown size is 4.78 μm, and the average sheet diameter is 9.56 μm. According to the prior art, the sample is observed using SEM and the average maximum diameter is calculated, and the test value is 10.3 μm.

[0092] Comparative Example 1

[0093] Example 1 was repeated, except that no binder was added.

[0094] The results showed that no stable composite membrane could be formed after filtration, and during the permeability test, a pressure difference of 1 atmosphere would destroy the composite membrane.

[0095] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art shall fall within the scope defined by the claims attached to this application.

Claims

1. A method for measuring the average sheet diameter of a two-dimensional material, characterized in that: The steps include: S1. Evenly mixing the two-dimensional material to be measured, the binder, and the solvent, so that the two-dimensional material is dispersed in the solvent and the binder is dissolved in the solvent, to obtain a two-dimensional material / binder mixed solution; Wherein, under the same thickness condition, the gas permeability of the two-dimensional material to be measured is less than the gas permeability of the adhesive; S2, filtering the two-dimensional material / adhesive mixed solution on a filter membrane and drying it to obtain an area of S , thickness is T Two-dimensional material / adhesive composite film; Wherein, the pore size of the filter membrane is smaller than the size of the two-dimensional material; S3. Measuring the gas permeability of the two-dimensional material / adhesive composite film P ; S4, according to the average sheet radius of the two-dimensional material to be measured R Gas permeability P The relationship between: Calculating and obtaining the average sheet diameter of the two-dimensional material to be measured; in, m is the mass of the 2D material in the 2D material / adhesive composite film, x is the theoretical surface density of the two-dimensional material, A 、 B are all constants; Determine the constant by one of the following methods: A : Method 1: Prepare a pure adhesive film and measure the gas permeability P0 and thickness T0 of the adhesive film. The constant A =P0×T0; Method 2: (1) Set the average sheet diameter to 2 R Y The same two-dimensional material, binder and solvent are uniformly mixed, so that the two-dimensional material is dispersed in the solvent and the binder is dissolved in the solvent, thereby obtaining a two-dimensional material / binder mixed solution; (2) Filter the two-dimensional material / adhesive mixed solution on a filter membrane to obtain an area of S Y , thickness is T Y Two-dimensional material / adhesive composite film; (3) Measuring the gas permeability of the two-dimensional material / adhesive composite film P Y ; (4) According to the relationship , calculate the constant A ; in, m Y is the mass of the 2D material in the 2D material / adhesive composite film, x Y The average sheet diameter is 2 R Y The theoretical surface density of two-dimensional materials; Constant B=0.

85.

2. The method according to claim 1, characterized in that In S1, the mass ratio of the two-dimensional material to be measured and the adhesive is 1:0.2-10.

3. The method according to claim 1, characterized in that The two-dimensional material includes one or more of graphene, graphene oxide, boron nitride, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, and MXene.

4. The method according to claim 1, wherein The adhesive comprises one or more of starch, dextrin, polyethyleneimine, polyvinyl alcohol, carboxymethyl cellulose, resin, and rubber; and the solvent is water or an organic solvent.

5. The method according to claim 1, wherein In S1, the two-dimensional material to be measured is uniformly dispersed in a solvent in a monolayer state.

6. The method according to claim 1, characterized in that In S2, the two-dimensional material / adhesive mixed solution is filtered on a filter membrane to obtain a two-dimensional material / adhesive composite membrane with an area of S and a thickness of T.

7. The method according to claim 1, characterized in that In S3, the gas permeability is measured by a pressure difference method or an equal pressure method.

8. The method according to claim 1, characterized in that The filter membrane is a water-based filter membrane or an organic filter membrane.

9. The method according to claim 8, characterized in that The aqueous filter membrane is a cellulose acetate filter membrane, and the organic filter membrane is a polytetrafluoroethylene filter membrane.

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