Block copolymer, and method for preparing graphene using same

Abstract

The present invention relates to a method for preparing graphene using a novel block copolymer. The present invention has features that, by using the block copolymer to mediate graphene that is hydrophobic and a solvent of a feed solution that is hydrophilic, the exfoliation efficiency of graphene as well as the dispersion stability thereof can be increased during high-pressure homogenization.

Claims

1. A method for preparing graphene, comprising the step of passing a feed solution including graphite through a high-pressure homogenizer including an inlet, an outlet, and a micro-channel that connects between the inlet and the outlet and has a diameter in a micrometer scale, wherein the feed solution includes a block copolymer comprising a repeating unit represented by the following Chemical Formula 1 and a repeating unit represented by the following Chemical Formula 2: ##STR00009## in Chemical Formula 1, X is a bond or oxygen, R.sub.1 and R.sub.2 are each independently hydrogen; C.sub.1-4 alkyl; carboxy group; or C.sub.6-20 aryl substituted with a carboxy group or a sulfonic acid group, provided that when X is a bond, R.sub.2 is not hydrogen and C.sub.1-4 alkyl, n is an integer of 1 to 10,000, and n′ is an integer of 0 to 2, ##STR00010## in Chemical Formula 2, R.sub.3 and R.sub.4 are each independently hydrogen; C.sub.6-20 aryl; —COO—(C.sub.6-20 aryl); or —COO—(C.sub.1-4 alkylene)-(C.sub.6-20 aryl), and m is an integer of 1 to 10,000.

2. The method for preparing graphene according to claim 1, wherein the block copolymer is represented by the following Chemical Formula 3: ##STR00011## in Chemical Formula 3, X is a bond or oxygen, R.sub.1 and R.sub.2 are each independently hydrogen; C.sub.1-4 alkyl; carboxy group; or C.sub.6-20 aryl substituted with a carboxy group or a sulfonic acid group, provided that when X is a bond, R.sub.2 is not hydrogen and C.sub.1-4 alkyl, R.sub.3 and R.sub.4 are each independently hydrogen; C.sub.6-20 aryl; —COO—(C.sub.6-20 aryl); or —COO—(C.sub.1-4 alkylene)-(C.sub.6-20 aryl), n is an integer of 1 to 10,000, and m is an integer of 1 to 10,000.

3. The method for preparing graphene according to claim 2, wherein X is a bond, R.sub.1 is hydrogen; or C.sub.1-4 alkyl, and R.sub.2 is a carboxy group; or C.sub.6-20 aryl substituted with a carboxyl group or a sulfonic acid group.

4. The method for preparing graphene according to claim 2, wherein X is oxygen and R.sub.1 and R.sub.2 are each independently hydrogen.

5. The method for preparing graphene according to claim 2, wherein R.sub.1 and R.sub.2 are each independently hydrogen; methyl; carboxy group; or phenyl substituted with a sulfonic acid group, and R.sub.3 and R.sub.4 are each independently hydrogen; phenyl; naphthyl; pyrene-2-ylmethoxycarbonyl; or 4-(pyrene-2-yl)butoxycarbonyl.

6. The method for preparing graphene according to claim 1, wherein the block copolymer is represented by the following chemical formula: ##STR00012##

7. The method for preparing graphene according to claim 1, wherein the ratio of n:m is 2-10:1.

8. The method for preparing graphene according to claim 1, wherein the block copolymer includes a repeating unit represented by the following Chemical Formula 4 and a repeating unit represented by the following Chemical Formula 5: ##STR00013## in Chemical Formula 4, X′ is C.sub.1-3 alkylene, and n is an integer of 1 to 10,000, ##STR00014## in Chemical Formula 5, R.sub.4 is C.sub.6-20 aryl, or —COO—(C.sub.1-4 alkylene)-(C.sub.6-20 aryl), and m is an integer of 1 to 10,000.

9. The method for preparing graphene according to claim 8, wherein X′ is ethylene (—CH.sub.2—CH.sub.2—).

10. The method for preparing graphene according to claim 8, wherein R.sub.4 is phenyl, naphthyl, or —COOCH.sub.2-(pyrenyl).

11. The method for preparing graphene according to claim 8, wherein the block copolymer is represented by the following Chemical Formula 6: ##STR00015## in Chemical Formula 6, R′ is C.sub.1-3 alkoxy, X′, R.sub.4, n and m are as defined in claim 8.

12. The method for preparing graphene according to claim 1, wherein the graphite in the feed solution is exfoliated while passing through the micro-channel under application of a shear force, thereby preparing the graphene.

13. The method for preparing graphene according to claim 1, wherein the micro-channel has a diameter of 10 to 800 μm.

14. The method for preparing graphene according to claim 1, wherein the feed solution is introduced in the inlet of the high-pressure homogenizer under application of a pressure of 100 to 3,000 bar and passed through the micro-channel.

15. The method for preparing graphene according to claim 1, wherein a solvent of the feed solution is one or more selected from the group consisting of water, NMP (N-methyl-2-pyrrolidone), acetone, DMF (N,N-dimethylformamide), DMSO (dimethyl sulfoxide), CHP (cyclohexyl-pyrrolidinone), N12P (N-dodecyl-pyrrolidone), benzyl benzoate, N8P (N-octyl-pyrrolidone), DMEU (dimethyl-imidazolidinone), cyclohexanone, DMA (dimethylacetamide), NMF (N-methyl formamide), bromobenzene, chloroform, chlorobenzene, benzonitrile, quinoline, benzyl ether, ethanol, isopropyl alcohol, methanol, butanol, 2-ethoxyethanol, 2-butoxyethanol, 2-methoxypropanol, THF (tetrahydrofuran), ethylene glycol, pyridine, N-vinylpyrrolidone, methyl ethyl ketone (butanone), alpha-terpineol, formic acid, ethyl acetate and acrylonitrile.

16. The method for preparing graphene according to claim 1, wherein the step of passing the material recovered in the inlet through the micro-channel is additionally repeated once to 9 times.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows the results of .sup.1H-NMR (FIG. 1(a)) and GPO (FIG. 1(b)) analysis of PtBA-b-PS block copolymer prepared in Example 1 of the present invention.

(2) FIG. 2 shows the results of .sup.1H-NMR analysis of PAA-b-PS block copolymer before purification prepared in Example 1 of the present invention.

(3) FIG. 3 shows the results of .sup.1H-NMR analysis of PAA-b-PS block copolymer after purification prepared in Example 1 of the present invention.

(4) FIG. 4 shows SEM images of the dispersions of graphene prepared in Example 1 (FIGS. 4(a) and 4(b)) and Example 2 (FIGS. 4(c) and 4(d)) of the present invention.

(5) FIG. 5 shows a Raman spectrum of the dispersion of graphene prepared in Example 1 of the present invention.

(6) FIG. 6 shows the sedimentation velocity of the dispersion of graphene prepared in Example 1 of the present invention.

(7) FIG. 7 shows .sup.1H-NMR results (FIG. 7a) and FT-IR results (FIG. 7b) of PEO-CTA prepared in one embodiment of the present invention.

(8) FIG. 8 shows .sup.1H-NMR results (FIG. 8a) and GPO analysis results (FIG. 7b) of PEO-b-PS prepared in one embodiment of the present invention.

(9) FIG. 9 shows .sup.1H-NMR results of PEO-b-PVN prepared in one embodiment of the present invention.

(10) FIG. 10 shows SEM images of the dispersions of graphene prepared in Example 3 (FIGS. 10(a) and 10(b)) and Example 4 (FIGS. 10(c) and 10(d)).

(11) FIG. 11 shows SEM images of the dispersion of graphenes prepared in Example 3 (FIGS. 11(a) and 11(b)) and Example 4 (FIGS. 11(c) and 11(d)).

(12) FIG. 12 shows a TEM image of the dispersion of graphene prepared by using the block copolymer of the present invention as a dispersant.

(13) FIG. 13 shows Raman spectra of the dispersion of graphene prepared by using the block copolymer of the present invention as a dispersant.

(14) FIG. 14 shows the graphene particle size according to the number of high-pressure homogenization processes of the dispersion of graphene prepared by using the block copolymer of the present invention as a dispersant.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(15) Hereinafter, preferred embodiments are presented to aid in understanding of the invention. However, the following examples are provided only to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

(16) Step 1) Preparation of block copolymer

(17) 10 g of tert-butyl acrylate (tBA), 454 mg of CDB (cumyldithiobenzoate) and 27.3 mg of AIBN (azobisisobutyronitrile) were mixed to prepare a reaction solution, oxygen was removed by freeze and thaw, and then the reaction was carried out at 70° C. for 24 hours. The reaction solution was cooled and then put into an excess amount of water/ethanol (1:3) solution to obtain 9.0 g of a red polymer (PtBA) powder.

(18) 2.0 g of the polymer (PtBA) thus prepared, 4.0 g of styrene and 3.6 mg of AIBN were mixed to prepare a reaction solution, oxygen was removed, and the reaction was carried out at 85° C. for 48 hours. The reaction solution was cooled and then put into an excess amount of water/ethanol (1:3) solution to obtain 9.0 g of a red polymer powder. The reaction solution cooled and then put into an excess amount of water/ethanol (1:5) solution to obtain 3.0 g of red polymer (PtBA-b-PS) powder.

(19) In order to hydrolyze the tert-butyl acrylate block, 2.0 g of the prepared red polymer (PtBA-b-PS) was dissolved in 2.0 g of methylene chloride and then 10 equivalents of TFA (trifluoroacetic acid) per tBA monomer was added dropwise under reflux, and the mixture was reacted for 48 hours. After the reaction, the reaction solution was precipitated in excess hexane to recover a polymer. The recovered polymer was purified by Soxhlet with cyclohexane, and finally 0.8 g of a polymer (PAA-b-PS, FAA:PS (weight ratio)=2:1, molecular weight: 4.4 K) was produced.

(20) Step 2) Preparation of graphene

(21) 2.5 g of graphite and 1 g of the block copolymer prepared in Example 1 or the block copolymer prepared in Example 2 were mixed with 500 mL of water to prepare a dispersion solution. The feed solution was fed in the inlet of the high-pressure homogenizer. The high-pressure homogenizer has a structure including an inlet of the raw material, an outlet of the exfoliated product, and a micro-channel that connects between the inlet and the outlet and has a diameter in a micrometer scale.

(22) The feed solution was introduced in the inlet while applying high-pressure of 1,600 bar, and a high shear force was applied while passing through a micro-channel having a diameter of 75 μm. The feed solution recovered from the inlet was reintroduced into the inlet of the high-pressure homogenizer and the high-pressure homogenization process was repeated. The repetition was made until the number of the high-pressure homogenization processes became 10 times in total, to prepare a dispersion of graphene.

Example 2

(23) A polymer (PAA-b-PS, PAA:PS (weight ratio)=4:1) was prepared in the same manner as in Example 1, except that 4.0 g of PtBA and 4.0 g of styrene were used. A dispersion of graphene was prepared by using the above polymer.

Experimental Example 1

(24) The PtBA-b-PS and PAA-b-PS prepared in Example 1 were subjected to .sup.1H-NMR and GPC analysis, respectively, and the results were shown in FIGS. 1 to 3.

(25) FIG. 1 shows the results of .sup.1H-NMR and GPC analysis of PtBA-b-PS prepared in Example 1 above. As shown in FIG. 1 (a), the peak at 1.38 ppm is due to the butyl group of PtBA, and the peaks at 6.60 ppm and 7.05 ppm were due to the phenyl group of PS. It was confirmed through the ratio of these peaks that the ratio (n:m) of the number (n) of repeating units of PtBA to the number (m) of repeating units of PS was about 2.8:1. Further, as shown in FIG. 1(b), it was confirmed that a block copolymer having a narrow molecular weight distribution was synthesized.

(26) Further. FIG. 2 shows the results of .sup.1H-NMR analysis of PAA-b-PS prepared in Example 1 before being purified by Soxhlet with cyclohexane, and FIG. 3 shows the results of .sup.1H-NMR analysis of PAA-b-PS prepared in Example 1 after being purified by Soxhlet with cyclohexane.

(27) As shown in FIG. 2, peaks at 6.60 ppm and 7.05 ppm due to the phenyl group of PS were maintained, while peaks at 1.38 ppm due to the butyl group of PtBA disappeared. Consequently, it was confirmed that PtBA was selectively converted to FAA. Further, as shown in FIG. 3, it was confirmed that peaks at 6.60 and 7.10 ppm due to the phenyl group of PS were reduced by purification, and consequently the polymer other than PAA-b-PS was removed. In addition, it was confirmed through the ratio of the peaks in FIG. 3 that the ratio (n:m) of the number (n) of repeating units of PAA and the number (m) of repeating units of PS was about 2.8:1 similarly to PtBA-b-PS.

Experimental Example 2

(28) The dispersions of graphene prepared in Examples 1 and 2 were observed with an SEM image, and the results were shown in FIG. 4.

(29) As shown in FIG. 4, it was confirmed that graphene flakes were well exfoliated and the surface roughness was smooth.

Experimental Example 3

(30) The dispersion of graphene prepared using the block copolymer of Example 1 was coated thinly on a Si/SiO.sub.2 wafer and Raman spectra were measured. The results were shown in FIG. 5.

(31) As shown in FIG. 5, the I.sub.D/I.sub.G value was 0.104, which was almost equal to the I.sub.D/I.sub.G value (0.107) of the graphite before high-pressure homogenization, and thus it was confirmed that there were less graphene defects.

Experimental Example 4

(32) The sedimentation velocity of the dispersion of graphene prepared using the block copolymer of Example 1 was measured as described below. For comparison, a dispersion of graphene was prepared in the same manner as in Example 1, except that SDBS was used instead of the block copolymer in Step 2, and the sedimentation velocity was measured as described below.

(33) Specifically, 1 mL of each dispersion of graphene was put into the cell, and the particles were sedimented artificially by applying a centrifugal force. The sedimentation velocity of the particles was varied according to the dispersion state, and the dispersion stability was compared relatively within the same conditions by measuring the sedimentation velocity of the particles within a certain interval, and the results were shown in FIG. 6.

(34) As shown in FIG. 6, the sedimentation velocity of the dispersion of graphene prepared using the block copolymer of Example 1 was about 15% slower than that of the dispersion of graphene prepared using SDBS, which means that the dispersion stability was excellent.

Example 3: Preparation of PEO-b-PS Block Copolymer

(35) Step 1) Preparation of PEO-CTA

(36) 5.4 g of polyethylene oxide (PEO) having a molecular weight of 5,000 g/mol (n˜113), one end of which was substituted with methoxy, 0.60 g of 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid, and 26 mg of DMAP were put into DCM to prepare a mixed solution. Argon gas was injected therein to remove oxygen, to which 330 mg of DCC was added and the reaction was carried out at 40° C. for 24 hours. The reaction solution was cooled and then put into an excess amount of ether to obtain 5.2 g of red PEO macrochain transfer agent powder, which was named ‘PEO-CTA’.

(37) The .sup.1H-NMR and FT-IR results of the PEO-CTA thus prepared were shown in FIG. 7. As shown in FIG. 7 (a), peaks at 3.65 ppm due to the ethylene group of PEO and peaks at 7.57 and 7.40 ppm due to the phenyl group of CTA were observed simultaneously. From the FT-IR results of FIG. 7(b), the peak of ester appearing at 1735 cm.sup.−1 after substitution was confirmed, whereby CTA was well bonded to the end of PEO.

(38) Step 2) Preparation of PEO-b-PS Block Copolymer

(39) 0.5 g of PEO macrochain transfer agent prepared in the step 1, 2 g of styrene and 1.6 mg of AIBN (azobisisobutyronitrile) were mixed to prepare a reaction solution. After removing oxygen, the reaction was carried out at 85° C. for 72 hours. The reaction solution was cooled and then was put into an excess amount of hexane to finally obtain 0.9 g of a polymer (PEO:PS (weight ratio)=1:1.4, number average molecular weight: 12 k, n˜113, m˜72), which was named ‘PEO-b-PS’.

(40) The results of .sup.1H-NMR and GPC analysis of PEO-b-PS thus prepared were shown in FIG. 8. As shown in FIG. 8(a), peaks at 3.65 ppm were due to the ethylene groups of PEO, peaks at 6.60 ppm and 7.05 ppm were due to the phenyl group of PS. It was confirmed through the ratio of these peaks that the ratio (n:m) of the number (n) of repeating units of PEO and the number (m) of repeating units of PS was about 1.6:1. Further, as shown in FIG. 8(b), it was confirmed that a block copolymer having a narrow molecular weight distribution was synthesized.

Example 4: Preparation of PEO-b-PVN Block Copolymer

(41) 0.8 g of the PEO-CTA prepared in Step 1 of Example 3, 1.6 g of 2-vinylnaphthalene and 2.1 mg of AIBN were mixed to prepare a reaction solution. After removing oxygen, the reaction was carried out at 85° C. for 72 hours. The reaction solution was cooled and then put into an excess amount of hexane to obtain 1.0 g of PEO-PVN polymer (PEO:PVN (weight ratio)=1:0.6, number average molecular weight: 8.1 k, n˜113, m˜20).

(42) The PEO-b-PVN thus prepared was analyzed by .sup.1H-NMR, and the results were shown in FIG. 9. As shown in FIG. 9, the peaks at 3.65 ppm were due to the ethylene groups of PEO, and the peaks at 6.30-8.00 ppm were due to the naphthalene groups of PVN. It was confirmed through the ratio of these peaks that the ratio (n:m) of the number (n) repeating units of PEO and the number (m) of repeating units of PVN was about 5.7:1.

Experimental Example 5: Preparation of Dispersion of Graphene

(43) 2.5 g of graphite (BNB90) and 1 g of the block copolymer (PEO-b-PS) prepared in Example 3 were mixed with 500 ml of water to prepare a feed solution (concentration of graphite: 5 mg/mL, concentration of the block copolymer: 2 mg/mL).

(44) The feed solution was fed to the inlet of the high-pressure homogenizer. The high-pressure homogenizer has a structure including an inlet of the raw material, an outlet of the exfoliated product, and a micro-channel that connects between the inlet and the outlet and has a diameter in a micrometer scale. The feed solution was introduced in the inlet while applying a high pressure of 1,600 bar, and a high shear force was applied while passing through a micro-channel having a diameter of 75 μm. A part of the feed solution recovered in the inlet was taken as a sample, and the remainder was reintroduced into the inlet of the high-pressure homogenizer and the high-pressure homogenization process was repeated. The repetition was made until the number of high-pressure homogenization processes became 10 times in total, to prepare a dispersion of graphene.

Experimental Example 6: Preparation of Dispersion of Graphene

(45) The feed solution (concentration of graphite: 5 mg/mL, concentration of the block copolymer: 2 mg/mL) was prepared in the same manner as in Experimental Example 5, except that 1 g of the block copolymer prepared in Example 4 was used instead of the block copolymer prepared in Example 3, thereby obtaining a dispersion of graphene.

Experimental Example 7: Preparation of Dispersion of Graphene

(46) A dispersion of graphene was prepared in the same manner as in Experimental Example 5 except that 500 mL of NMP was used instead of 500 mL of water during preparation of a feed solution.

Experimental Example 8: Preparation of Dispersion of Graphene

(47) A dispersion of graphene was prepared in the same manner as in Experimental Example 6 except that 500 mL of NMP was used instead of 500 mL of water during preparation of a feed solution.

Experimental Example 9: Analysis of Graphene

(48) 1) Observation of graphene shape according to dispersant

(49) The dispersion of graphene prepared in Experimental Examples 5 to 8 was dropped on a silicon wafer and dried. The resulting sample was observed with an SEM image, and the results were shown in FIG. 10 and FIG. 11. FIGS. 10(a) and (b) show SEM images of the dispersion of graphene of Experimental Example 5, FIGS. 10(c) and (d) show those of Experimental Example 6, FIGS. 11(a) and (b) show those of Experimental Example 7, and FIGS. 11(c) and (d) show those of Experimental Example 8.

(50) As shown in FIGS. 10 and 11, it was confirmed that the surface roughness was low because graphene having a relatively small thickness was formed. If the thickness was thick, the graphenes overlapped at random. Therefore, in case where the surface roughness was large but the thickness was thin, the roughness was very small as if one sheet of paper adhered to the surface.

(51) In addition, the graphene in the dispersion of graphene prepared in Experimental Example 5 was observed with a TEM image, and the result was shown in FIG. 12. As shown in FIG. 12, it was confirmed that a thin graphene was produced similarly to FIGS. 10 and 11.

(52) 2) Raman Spectrum Analysis

(53) The dispersion of graphene prepared in Experimental Example 5 was analyzed by Raman spectroscopy, and the results were shown in FIG. 13.

(54) The ratio of I.sub.D/I.sub.G by Raman spectrum is the result of measurement of the disordered carbon, which means sp3/sp2 carbon ratio. Therefore, the larger the I.sub.D/I.sub.G value, the higher the degree that sp2 carbon of pure graphene changed to sp3 carbon. This means that the characteristic inherent to pure graphene was deteriorated.

(55) In the oxidized graphite produced by the conventionally known Hummers process, the ratio of I.sub.D/I.sub.G by Raman spectrum was closer to about 1.0 and thus many defects occurred. As shown in FIG. 12, however, it was confirmed that the I.sub.D/I.sub.G value of the dispersion of graphene produced in Experiment Example 5 was 0.108, which was almost similar to the value of pure graphite (BNB 90), and the occurrence of defects was remarkably low.

(56) 3) Analysis of Graphene Particle Size

(57) The graphene particle size (lateral size) was analyzed according to the number of times of high-pressure homogenization processes of the dispersion of graphene prepared in Experimental Example 5. The results were shown in FIG. 14 and Table 1 below.

(58) TABLE-US-00001 TABLE 1 Number of high-pressure Distribution homogenization Average graphene base processes particle size FIG. 14(a) Area 1 times 12.88 ± 8.52 μm  FIG. 14(b) Area 5 times 5.27 ± 0.88 μm FIG. 14(c) Area 10 times 3.61 ± 0.49 μm FIG. 14(d) Volume 1 times 19.91 ± 17.48 μm FIG. 14(e) Volume 5 times 5.56 ± 4.46 μm FIG. 14(f) Volume 10 times 3.68 ± 0.49 μm

(59) As shown in FIG. 14 and Table 1, it was confirmed that as the number of high-pressure homogenization processes was increased, the size of graphene became smaller and the deviation became smaller, and thus uniform graphene was produced.