KR102049575B1 - Method for preparation of graphene by using a polyethyleneoxide-based dispersion - Google Patents

Abstract

The present invention relates to a method for producing graphene using a polymer represented by Formula 1 below, using a polymer according to the present invention, exfoliation of graphene during high pressure homogenization through a solvent of a hydrophobic graphene and a hydrophilic feed solution It is characterized by high efficiency and high dispersion stability.
[Formula 1]

Wherein R, X and n are as defined in the specification.

Description

Graphene manufacturing method using a polyethylene oxide-based dispersant {Method for preparation of graphene by using a polyethyleneoxide-based dispersion}

The present invention relates to a method for producing graphene using a polyethylene oxide-based dispersant.

Graphene is a semimetallic material having a thickness corresponding to a carbon atom layer in an arrangement in which carbon atoms are connected in a hexagonal shape by sp2 bonds in two dimensions. Recently, as a result of evaluating the characteristics of the graphene sheet having a single layer of carbon atoms, it has been reported that the electron mobility may exhibit very good electrical conductivity of about 50,000 cm 2 / Vs or more.

In addition, graphene is characterized by structural, chemical stability and excellent thermal conductivity. In addition, it is easy to process one-dimensional or two-dimensional nanopattern consisting of only carbon, a relatively light element. Due to such electrical, structural, chemical and economic characteristics, it is expected that graphene may be substituted for silicon-based semiconductor technology and transparent electrodes in the future. In particular, it is expected that the graphene may be applied to flexible electronic devices with excellent mechanical properties.

Due to the many advantages and excellent properties of the graphene, various methods for mass production of graphene from carbon-based materials such as graphite have been proposed or studied. In particular, various studies have been made on how to easily produce graphene sheets or flakes having a thinner thickness and larger area so that excellent characteristics of graphene can be more dramatically expressed. Such conventional graphene manufacturing methods include the following.

First, a method of peeling a graphene sheet from graphite by a physical method such as using a tape is known. However, this method is unsuitable for mass production and the peel yield is also very low.

It is known to obtain graphene or an oxide thereof obtained by exfoliation by a chemical method such as oxidizing graphite or exfoliation from an intercalation compound in which an acid, a base, a metal, or the like is inserted between the carbon layers of the graphite.

However, in the former method, a plurality of defects may be generated on the final manufactured graphene in the process of oxidizing graphite to proceed with peeling and reducing the graphene oxide obtained therefrom to obtain graphene. This may adversely affect the properties of the final prepared graphene. In addition, the latter method may further require a process such as using and treating an intercalation compound, and thus, the overall process may be complicated, the yield may not be high enough, and the economic efficiency of the process may be reduced. Furthermore, it is not easy to obtain large area graphene sheets or flakes in this method.

Due to the problems of these methods, in recent years, a method of preparing graphene by peeling carbon layers included in graphite by a milling method using ultrasonic irradiation or a ball mill in the state of dispersing graphite or the like in liquid phase has been most applied. However, these methods also have problems such as difficulty in obtaining graphene having a sufficiently thin thickness and a large area, many defects on the graphene during peeling, or insufficient peeling yield.

For this reason, there is a continuing need for a manufacturing method that can easily produce graphene sheets or flakes having a thinner thickness and larger area with higher yields.

The present invention is to provide a method for producing graphene that can be produced with excellent efficiency by using a high pressure homogenization and polyethylene oxide-based dispersant.

In order to solve the above problems, the present invention is a high-pressure homogenizer comprising a feed solution containing graphite, the inlet, the outlet and the micro-channel having a diameter of the micrometer scale connecting between the inlet and the outlet Including the step of passing, The feed solution, provides a graphene manufacturing method comprising a polymer represented by the following formula (1):

[Formula 1]

Where

X is a bond, or C _{4 -100} aryl or heteroaryl,

R is hydrogen, C _{3 -100} alkyl, SH, OH, NH ₂ or CH ₂ NH _2,

n is an integer from 2 to 300.

The term 'graphite' used in the present invention is a material, also called graphite or quartz, which is a mineral belonging to a hexagonal system having a crystal structure such as crystal, and is black and has a metallic luster. Graphite has a plate-like structure, and one layer of graphite is called 'graphene' to be manufactured in the present invention, and thus graphite is a main raw material of graphene production.

In order to peel the graphene from the graphite, it is necessary to apply energy to overcome the π-π interaction between the stacked graphenes. In the present invention, a high pressure homogenization method is used as described below. The high pressure homogenization method is capable of applying a strong shear force to the graphite is excellent graphene peeling efficiency, but since the aggregation of the graphene to be produced is required to use a dispersant capable of dispersing the peeled graphene.

The dispersant serves to maintain their dispersed state through the solvent of the hydrophobic graphite or graphene hydrophilic feed solution, and is also called a surfactant or a peeling aid in other terms. In particular, the present invention is characterized in that the use of the polyethylene oxide-based dispersant represented by the formula (1) for the effective peeling of the graphene, there is a feature that the peeling efficiency is significantly higher than the conventional dispersant.

Hereinafter, the present invention will be described in detail.

Polyethylene oxide Dispersant (Formula 1)

The polyethylene oxide-based dispersant represented by the general formula (1) used in the present invention has a hydrophilic polyethylene oxide block and a hydrophobic substituent (R). Accordingly, the hydrophobic portion is bonded to the graphene, and the hydrophilic portion is bonded to the solvent and hydrogen bonds, thereby providing steric hindrance and thus suppressing the aggregation of the graphene. The exfoliated graphene can be stably dispersed.

In Formula 1, n denotes the number of repeating units of the polyethylene oxide block, and the larger the value thereof, the more the hydrophilic portion in the polymer may be provided and sufficient steric hindrance may be provided, thereby increasing dispersion stability of graphene. Preferably, said n is an integer of 20-300, More preferably, it is an integer of 20-100.

Also preferably X is a bond or any of the following structures:

,

,

,

,

,

,

,

,

,

,

,

,

,

And

In the above,

Each A is independently O, S, Se or NH,

n1 is an integer of 0 to 12,

v and w are each independently 0 or 1,

R ₁ is each independently hydrogen, C ₁ alkyl, _{-100, -100} C ₁ alkoxy, C _{2 -100} alkenyl, C _{2 -100} alkynyl, or C _{4 -100} aryl or heteroaryl.

Also preferably, X is a bond or a phenylene, R is a C ₅ to a _-20 alkyl, more preferably R is a C _{5 -20} linear alkyl. Most preferably, R is octadecyl or nonyl.

Representative examples of the polyethylene oxide-based dispersant represented by Formula 1 are as follows:

,

, And

.

The polymer represented by Chemical Formula 1 may be purchased commercially or used or synthesized as necessary, and will be described in more detail by the following examples.

Feed  solution

The term 'feed solution' used in the present invention refers to a solution containing the graphite and the polymer represented by the formula (1), and means a solution added to a high pressure homogenizer to be described later.

The concentration of graphite in the feed solution is preferably 0.5 to 5% by weight. If the concentration is less than 0.5% by weight is too low, the graphene peeling efficiency is lowered, if the concentration is higher than 5% by weight is too high may cause problems such as blocking the flow path of the high pressure homogenizer.

In addition, the polymer represented by Formula 1 in the feed solution is preferably used in 2 to 50% by weight, more preferably 4 to 40% by weight relative to the graphite parts. At less than 2% by weight, the concentration of the polymer is so low that graphene peeling efficiency and dispersion effect are lowered, and at above 50% by weight, the graphene peeling efficiency and dispersion effect is substantially no longer increased.

The solvent of the feed solution is water, N-Methyl-2-pyrrolidone (NMP), acetone, DMF (N, N-dimethylformamide), DMSO (dimethyl sulfoxide), CHP (Cyclohexyl-pyrrolidinone), N12P (N-dodecyl- pyrrolidone), benzyl benzoate, N-Octyl-pyrrolidone (N8P), dimethyl-imidazolidinone (DMEU), cyclohexanone, dimethylacetamide (DMA), N-Methyl Formamide (NMF), bromobenzene, chloroform, chlorobenzene, benzo Nitrile, quinoline, benzyl ether, ethanol, isopropyl alcohol, methanol, butanol, 2-ethoxy ethanol, 2-butoxy ethanol, 2-methoxy propanol, THF (tetrahydrofuran), ethylene glycol, pyridine, N-vinylpyrroli One or more selected from the group consisting of don, methyl ethyl ketone (butanone), alpha-terpinol, formic acid, ethyl acetate and acrylonitrile may be used, and water may be preferably used.

High pressure Homogenization

High pressure homogenization of the feed solution to peel off the graphene from the graphite in the feed solution.

The term 'high pressure homogenization' means applying a high pressure to a microchannel having a diameter of a micrometer scale and applying a strong shear force to a material passing therethrough. In general, high pressure homogenization is performed using a high pressure homogenizer comprising an inlet, an outlet, and a microchannel having a diameter of micrometer scale that connects between the inlet and the outlet.

As described above, since the solvent of the hydrophobic graphene and the hydrophilic feed solution is mediated by the polymer represented by Chemical Formula 1 in the feed solution, the graphene exfoliation effect by the high pressure homogenization is excellent, Dispersion stability is excellent.

It is preferable that the fine flow path has a diameter of 10 to 800 µm. In addition, the feed solution is preferably introduced into the inlet of the high pressure homogenizer under pressure application of 100 to 3000 bar to pass through the fine flow path.

In addition, the feed solution passed through the micro-path can be re-introduced into the inlet of the high pressure homogenizer, thereby further peeling off the graphene.

The re-insertion process may be performed by repeating 2 to 10 times. The re-insertion process may be performed by using the high pressure homogenizer used repeatedly, or by using a plurality of high pressure homogenizers. In addition, the re-insertion process may be performed separately for each process, or may be performed continuously.

On the other hand, it may further comprise the step of recovering and drying the graphene from the graphene dispersion recovered in the outlet. The recovery step may be carried out by centrifugation, reduced pressure filtration or pressure filtration. In addition, the drying step may be carried out by vacuum drying at a temperature of about 30 to 200 ℃.

The graphene prepared above may be redispersed in various solvents and used for various purposes. The application field of the graphene, conductive paste composition, conductive ink composition, heat dissipation substrate forming composition, electrically conductive composite, EMI shielding composite or battery can be used for the use of the existing graphene, such as a conductive material or slurry.

The present invention is characterized by using a polyethylene oxide-based dispersant, it is possible to increase the graphene peeling efficiency and dispersion stability during high pressure homogenization through the solvent of the hydrophobic graphene and hydrophilic feed solution.

Figure 1 shows an SEM image of graphene in the graphene dispersion prepared in one embodiment and comparative example of the present invention.
Figure 2 shows the absorbance of the graphene dispersion prepared in one embodiment and comparative example of the present invention.
Figure 3 shows the SEM image of the graphene in the graphene dispersion prepared in one embodiment of the present invention.
Figure 4 shows a TEM image of graphene in the graphene dispersion prepared in one embodiment of the present invention.
Figure 5 shows the graphene sedimentation rate of the graphene dispersion prepared in one embodiment of the present invention.
Figure 6 shows the Raman spectrum of the graphene in the graphene dispersion prepared in one embodiment of the present invention.
Figure 7 shows the particle size of the graphene in the graphene dispersion prepared in one embodiment of the present invention.

Hereinafter, preferred embodiments are presented to help understand the invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited thereto.

EXAMPLE  One

A dispersion solution was prepared by mixing 2.5 g of graphite (BNB90) and 1 g of a polymer of the following formula as a dispersant with 500 mL of water.

The feed solution was fed to the inlet of the high pressure homogenizer. The high pressure homogenizer has a structure including a microchannel having a diameter of a micrometer and connecting the inlet of the raw material, the outlet of the separation result, and the inlet and the outlet.

The feed solution was introduced while applying a high pressure of 1,600 bar through the inlet, so that a high shear force was applied while passing through a microchannel having a diameter of 75 μm. The feed solution recovered to the outlet was re-injected into the inlet of the high pressure homogenizer, and the high pressure homogenization process was repeated, and the graphene dispersion was prepared until the high pressure homogenization process was repeated 10 times in total.

EXAMPLE  2

A graphene dispersion was prepared in the same manner as in Example 1, except that 1 g of the polymer of the following formula was used as a dispersant.

EXAMPLE  3

A graphene dispersion was prepared in the same manner as in Example 1, except that 1 g of the polymer of the following formula was used as a dispersant.

Comparative example  One

A dispersion solution was prepared by mixing 2.5 g of graphite (BNB90) and 1 g of the polymer used in Example 2 as a dispersant with 500 mL of water. The dispersion solution was placed in a beaker in an ice-bath and homogenized at 6,000 rpm for 1 hour with a high speed homogenizer (L5M high shear mixer) to prepare a graphene dispersion.

Comparative example  2

A dispersion solution was prepared by mixing 2.5 g of graphite (BNB90) and 1 g of the polymer used in Example 2 as a dispersant with 500 mL of water. The dispersion solution was placed in a beaker in an ice-bath, placed so that the probe of the Tip-sonicator (Ultrasonic processor UP400S) was locked, and sonicated twice for 30 minutes at 80% amplitude of sonication power of up to 400W , Graphene dispersion was prepared.

Comparative example  3

A graphene dispersion was prepared in the same manner as in Example 1, except that a polyurethane copolymer (BYK198, BYK) was used as the dispersant.

Experimental Example  1: according to the peeling method Graphene  Shape comparison

Graphene in the graphene dispersion of Example 2, Comparative Example 1 and Comparative Example 2 prepared using the same dispersant was observed by SEM image, the results are shown in FIG.

First, in the case of Example 2 of the present invention subjected to high pressure homogenization, the overall peeling efficiency was high, and when the dry sample was observed by dropping the peeling solution on the silicon wafer, the surface roughness was improved because relatively thin graphene was made. I could see a small one. If the thickness is thick, the graphene overlaps randomly, so the surface roughness is large, but in the case of thin graphene, the roughness is very small as if a sheet of paper adheres to the surface (Fig. 1 (a) and (b)).

On the other hand, in the case of Comparative Example 1 subjected to the high speed homogenization, the peeling was not effective and the part having a shape similar to graphite as a whole was observed and the thickness of the graphene was generally thick (FIGS. 1 (c) and 1 (d)).

In addition, in the case of Comparative Example 2 subjected to the ultrasonic treatment, vibration energy was transmitted only to the local region near the probe, so that the overall exfoliation efficiency was greatly decreased, except that the exfoliated graphene was relatively thin and small in size. 1 (e) and 1 (f)).

Experimental Example  2: according to the peeling method Graphene  Peeling Efficiency Comparison

In order to compare the graphene peeling efficiency of Example 2 and Comparative Example 2 prepared using the same dispersant, each graphene dispersion was centrifuged at 3,000 rpm for 10 minutes, and then 160 µl of the supernatant was taken to give 5 mL of water. Was mixed to prepare a sample. As a reference, the solution of 0.01 g of the dispersant used in 5 mL of water was measured as a reference, and the degree of light absorption of the sample was measured. The results are shown in FIG. 2.

As shown in FIG. 2, the absorbance measured at 480 nm was 0.30178 for the Example 2 sample and 0.17881 for the Comparative Example 2 sample. As absorbance is proportional to the concentration by Beer's Law, the concentration of thin and small graphene present in the supernatant after centrifugation at 3,000 rpm was confirmed to be greater in Example 2.

Experimental Example  3: In dispersant  According Graphene  Shape observation

Graphene in the graphene dispersion of Examples 1 to 3, each prepared using a different dispersant, was observed by SEM image, and the results are shown in FIG. 3. 3 (a) and 3 (b) show the SEM images of Example 1, FIGS. 3 (c) and (d) show Example 2, and FIGS. 3 (e) and 3 (f) show the Example 3. FIG. As shown in FIG. 3, in Examples 1 to 3, thin graphene was prepared, and the surface roughness was small because the amount of chunk was small and the graphene was made relatively thin.

In addition, the graphene in the graphene dispersion of Example 1 and Example 3 was observed in a TEM image, the results are shown in FIG. 4 (a) and (b) show the TEM image of Example 1, and FIGS. 4 (c) and (d) show the third embodiment. As shown in FIG. 4, as in FIG. 3, all thin graphenes were prepared, and the amount of chunk was small and the surface roughness was small.

Experimental Example  4: In dispersant  According Graphene  Dispersion Stability Comparison

The dispersion stability of the graphene dispersions of Examples 1 to 3 prepared using different dispersants was compared, and the dispersion stability of the graphene dispersions of Comparative Example 3 was also compared for comparison. Specifically, 4 mL of the graphene dispersions of Examples 1 to 3 and Comparative Example 3 were placed in a transparent cell (thickness 2 mm, width 8 mm), followed by sedimentation of the graphene particles at 1,500 rpm. The rate of change of the point where the transmittance is 30% was measured relatively, and the results are shown in FIG. 5.

As shown in FIG. 5, in Examples 1 to 3 according to the present invention, the settling rate was relatively low compared to Comparative Example 3, and thus, it was confirmed that graphene dispersion stability was high.

In addition, in the dispersant used in Examples 1 and 2, there is a difference in the number of repeating units of polyethylene oxide, and the settling rate of Example 1, which has a larger number of repeating units, was smaller, and this resulted in more hydrophilic part and thus more solvent and This is due to the higher affinity of.

In addition, when comparing Example 2 and Example 3, the sedimentation rate of Example 3 having a phenyl group in addition to the alkyl group was smaller, which was more strongly bonded to the graphene surface by the phenyl group and thus more affinity with graphene. It is due to the elevation.

Experimental Example  5: Raman Spectrum Analysis

The graphene dispersion prepared in Example 1 was analyzed by Raman spectrum, and the results are shown in FIG. 6.

The ratio of I _D / I _G according to the Raman spectrum is a result of measuring the disordered carbon, which means a sp3 / sp2 carbon ratio. Therefore, the larger the I _D / I _G value, the higher the degree of change of sp2 carbon of pure graphene into sp3 carbon, which means that the inherent characteristics of pure graphene are weakened.

Graphite oxide prepared by Hummer's manufacturing method known in the art has many defects such that the I _D / I _G ratio of the Raman spectrum is close to about 1.0, but the I _D of the graphene dispersion prepared in Example 1 as shown in FIG. The value of / I _G was 0.176, which was larger than that of pure graphite (BNB90), but it was confirmed that the defects were remarkably small.

Experimental Example  6: Graphene  Particle size analysis

Prepared in the same manner as in Example 1, except that the fine channel diameter of the high pressure homogenizer was used to prepare a graphene dispersion using a diameter of 100 ㎛, the graphene particle size (lateral size) analysis according to the number of high pressure homogenization treatment It was.

In addition, in the manufacturing process of Example 2, the graphene particle size (lateral size) was analyzed according to the number of high pressure homogenization treatment, the results are shown in Figure 7 and Table 1 below.

Dispersant Microchannel diameter High Pressure Homogenization Recovery Average graphene particle size Fig. 7 (a) Dispersant of Example 1 100 μm 1 time 19.3038 ± 16.7418 μm Figure 7 (b) Dispersant of Example 1 100 μm 5th 4.7751 ± 2.7204 μm Figure 7 (c) Dispersant of Example 1 100 μm 10th 2.0779 ± 0.4225 μm Fig. 7 (d) Dispersant of Example 2 75 μm 1 time 22.7238 ± 20.8852㎛ Figure 7 (e) Dispersant of Example 2 75 μm 5 times 5.7977 ± 5.0818 μm Fig. 7 (f) Dispersant of Example 2 75 μm 10th 2.5031 ± 0.4695 μm

As shown in FIG. 7 and Table 1, although the dispersant used in Example 1 had a fine flow path diameter of 100 μm, the graphene particle size was larger than that of the graphene prepared using the dispersant used in Example 2. It could be confirmed that it is smaller, which is due to the greater number of polyethylene oxide repeat units of the dispersant used in Example 1 to fully effect the steric hindrance that prevents binding to adjacent graphene.

Experimental Example  7: Graphene Sheet resistance  Measure

After diluting the graphene dispersion prepared in Example 1 to a graphene concentration of 0.2 mg / mL, 31.5 mL of the diluent was vacuum filtered through an AAO membrane (200 nm pore, 4.5 cm in diameter) and dried at 55 ° C. for 2 days. I was. Sheet resistance of the AAO membrane was measured with 4-point-probe. All 10 measurements were taken to calculate the average value.

In addition, it was prepared in the same manner as in Example 1 for preparing a graphene dispersion using PVP58K as a dispersant, and then measured the sheet resistance by the same method as above, the results are shown in Table 2 below.

Example 1 PVP58K Rs (Ω / □) 15.612 34.557 Deviation 0.16263 2.30517

As shown in Table 2, the sheet resistance value of Example 1 according to the present invention was significantly lower than when PVP58K was used as a dispersant. The sheet resistance value is affected by the sheet size of exfoliated graphene. When PVP58K is used, the PSA value (area) is 1.6171 μm, which is smaller than that of Example 1 (2.0779 μm), and the sheet size is smaller. If it is small, the contact point may increase, resulting in an increase in sheet resistance. Therefore, when the graphite is peeled off using the dispersant according to the present invention, an improvement in sheet resistance may be obtained.

Claims (14)

Passing the feed solution comprising graphite through an inlet, an outlet, and a high pressure homogenizer comprising a microchannel having a diameter of micrometer scale and connecting between the inlet and outlet,
The feed solution, a graphene manufacturing method comprising a polymer represented by the following formula (1):
[Formula 1]

Where
X is a bond or phenylene,
R is C _5-20 alkyl,
n is an integer from 2 to 300.
delete delete The method of claim 1,
R is C _5-20 straight chain alkyl,
Manufacturing method.
The method of claim 4, wherein
R is octadecyl, or nonyl,
Manufacturing method.
The method of claim 1,
n is an integer of 20 to 100,
Manufacturing method.
The method of claim 1,
The polymer represented by Formula 1 is

,

, And

Characterized in that any one of,
Manufacturing method.
The method of claim 1,
The content of the polymer in the feed solution is characterized in that 2 to 50% by weight relative to the graphite parts,
Manufacturing method.
The method of claim 1,
The concentration of graphite in the feed solution is characterized in that 0.5 to 5% by weight,
Manufacturing method.
The method of claim 1,
Graphite in the feed solution is peeled while passing through the micro-channel under the application of shear force, characterized in that the graphene is produced,
Manufacturing method.
The method of claim 1,
The fine flow path is characterized in that having a diameter of 10 to 800 ㎛,
Manufacturing method.
The method of claim 1,
The feed solution is introduced into the inlet of the high pressure homogenizer under pressure application of 100 to 3000 bar, characterized in that it passes through the fine flow path,
Manufacturing method.
The method of claim 1,
The solvent of the feed solution is water, N-Methyl-2-pyrrolidone (NMP), acetone, DMF (N, N-dimethylformamide), DMSO (dimethyl sulfoxide), CHP (Cyclohexyl-pyrrolidinone), N12P (N-dodecyl-pyrrolidone) ), Benzyl benzoate, N-Octyl-pyrrolidone (N8P), dimethyl-imidazolidinone (DMEU), cyclohexanone, dimethylacetamide (DMA), N-Methyl Formamide (NMF), bromobenzene, chloroform, chlorobenzene, benzonitrile , Quinoline, benzyl ether, ethanol, isopropyl alcohol, methanol, butanol, 2-ethoxy ethanol, 2-butoxy ethanol, 2-methoxy propanol, THF (tetrahydrofuran), ethylene glycol, pyridine, N-vinylpyrrolidone , Methyl ethyl ketone (butanone), alpha-terpinol, formic acid, ethyl acetate, and at least one member selected from the group consisting of acrylonitrile,
Manufacturing method.
The method of claim 1,
Characterized in that the step of passing through the high pressure homogenizer with the recovered matter recovered in the outlet portion is repeated one to nine times further,
Manufacturing method.

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