Graphene oxide having excellent solvent dispersibility and characteristics through selective oxidation of edge of graphene and control of oxidation degree, and inkjet printing ink and dispenser printing ink using same

Abstract

The present invention relates to a low-concentration and low-viscosity ink for inkjet printing and a high-concentration and high-viscosity ink for dispenser printing, which are manufactured by using edge-oxidized graphene which can be safely dispersed in a solvent without a dispersant. In addition, the present invention relates to preparing a graphene-PEDOT:PSS nanocomposite ink by simply mixing edge-oxidized graphene, which can be safely dispersed in a solvent without a dispersant, with a PEDOT:PSS solution, and a transparent film having excellent electrical conductivity, which is manufactured using same. A film, which can be naturally dried in the air after printing without a post-treatment process and has excellent electrical conductivity and transparency, can be manufactured.

Description

Graphene oxide with excellent solvent dispersibility and properties through edge-selective oxidation and oxidation degree control of graphene, and inkjet printing ink and dispenser printing ink using the same

[0001] The present invention relates to a low-concentration and low-viscosity ink for inkjet printing and a high-concentration and high-viscosity ink for dispenser printing manufactured using edge-oxidized graphene that can be safely dispersed in a solvent without a dispersant.

[0002] Graphene, a single layer of carbon atoms arranged in a hexagonal honeycomb lattice, has been the subject of intense research for over 20 years due to its remarkable properties and numerous potential applications. Despite promising academic research, industrial adoption of graphene has been slower than expected, primarily due to difficulties in mass-producing high-quality graphene and its poor processability for industrial applications. Advanced liquid-phase exfoliation methods, such as shear rotor exfoliation and microfluidization, have been developed to achieve scalable production of high-quality graphene. While these approaches have been shown to produce high-quality graphene at the laboratory scale, recent studies have shown that most commercial graphene flakes consist of graphite microplatelets with a wide dimensional variation. Obtaining highly concentrated, true graphene flakes (<10 flakes) is also challenging, necessitating continued efforts to achieve scalable, high-efficiency production of high-quality graphene flakes.

[0003] Another major challenge hindering the commercialization of graphene is its poor processability. Due to its hydrophobic nature, graphene is not dispersed in most solvents used in industrial applications. To address this, surfactants or polymers are added to disperse the graphene flakes, but these additives detrimentally affect the properties of graphene. Post-treatment processes, such as high-temperature or photonic annealing, have been employed to remove the additives, but complete removal is impossible even after post-treatment. These post-treatment processes add further complexity and cost to the manufacturing process, posing a significant obstacle to the commercialization of graphene. Another method to improve graphene processability is to synthesize graphite oxide under harsh acidic conditions and then exfoliate it into graphene oxide (GO) through ultrasonication. However, this process results in the loss of graphene's unique properties. While reduction of GO can partially restore graphene's properties by removing oxygen-containing functional groups, the structural properties are difficult to restore, resulting in reduced GO (rGO) that is inferior to pristine graphene. Additionally, effective reduction methods involve high-temperature annealing or the use of toxic chemicals such as hydrazine. The purification process for obtaining high-purity GO and rGO is also time-consuming and environmentally harmful.

[0004] Recently, a study demonstrated that ball milling graphite in the presence of dry ice can selectively functionalize the edges of graphite while minimizing damage to the basal plane. This novel approach demonstrated improved dispersibility in some solvents and the ability to impart diverse functional groups to the treated graphite for targeted applications. However, the properties of edge-selectively functionalized graphite / graphene were not comparable to those of pristine graphene flakes, likely due to their small, thick dimensions and the presence of defects and impurities generated during the ball milling process. Furthermore, the solvent that best dispersed carboxylated edge graphene was NMP (N-methyl-2-pyrrolidone), which proved unsuitable for general industrial use. In conclusion, no method has been available that achieves the production of graphene flakes rich in few-layer graphene, high dispersibility in a variety of solvents, and the versatility of pristine graphene.

[0005] Therefore, the present invention presents a simple and effective approach for producing few-layer concentrated graphene with excellent dispersibility in a variety of solvents while maintaining its unique properties. This is achieved by simply modifying the improved Hummer's method and applying it to graphene flakes rather than graphite. Optimizing the amount of oxidizer allows for tunable, selective edge oxidation of the graphene flakes, resulting in thinner flakes that are highly dispersible in a variety of solvents, while maintaining their original properties. This approach is also effective for powders thicker than 10 sheets, demonstrating universal applicability regardless of powder thickness. The excellent processability and properties of selective edge-oxidized graphene (SEO-graphene) are demonstrated by preparing a variety of processable SEO-graphene inks for inkjet printing, spin coating, dispenser printing, and nanocomposites. For inkjet printing, spin coating, and dispenser printing, the inks are formulated solely with solvent and SEO-graphene flakes, without any additives. In particular, we developed the first pure aqueous graphene ink for inkjet printing, enabling the application of highly concentrated pure graphene ink (105 mg / mL in EtOH / H2O) to dispenser printing without stabilizers. SEO-graphene and inks manufactured using it exhibited performance similar to or even superior to that of pure graphene, demonstrating that selective edge oxidation does not damage the unique properties of graphene. Furthermore, the absence of additives and the subsequent elimination of post-treatment offer significant advantages, enabling cost-effective and environmentally friendly processes. SEO-graphene flakes and inks with excellent processability and physical properties have the potential to significantly impact various related fields, including electronics, energy, biomedicine, and nanocomposites. Furthermore, compared to conventional GO and rGO, the production process for SEO-graphene is simpler and more environmentally friendly, contributing to the sustainable development of graphene-related technologies.

[0006] The present invention has been devised to solve the above problems, and an object of the present invention is to provide an ink composed only of a pure solvent and graphene particles without a dispersant.

[0007] In addition, it is an object of the present invention to provide a nanocomposite ink composed only of pure graphene particles and PEDOT:PSS without a dispersant.

[0008] In addition, it is an object of the present invention to provide an ink that can be naturally dried in the air after printing without a post-processing process.

[0009] In addition, it is an object of the present invention to provide a nanocomposite ink that can be naturally dried in the air after printing without a post-processing process.

[0010] In addition, it is an object of the present invention to provide not only low-concentration graphene ink but also high-concentration and high-viscosity water-phase graphene ink.

[0011] In addition, it is an object of the present invention to provide a film having excellent electrical conductivity and transparency even without a post-processing process.

[0012] The technical problems to be solved by the invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0013]

[0014] (1) Method for manufacturing edge-oxidized graphene-based inkjet printing ink

[0015] A step for preparing a graphene oxide dispersion by dispersing edge-oxide graphene particles in distilled water;

[0016] Including an inkjet printing ink manufacturing step of centrifuging the edge oxide graphene dispersion dispersed in the distilled water and then taking the upper liquid;

[0017] The above edge oxide graphene is,

[0018] Graphene flake manufacturing step for manufacturing graphene flakes;

[0019] A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above;

[0020] A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated;

[0021] A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent;

[0022] An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes;

[0023] An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed in a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed;

[0024] A SEO-graphene flake precipitation step of centrifuging the above ultrasonically treated oxidized mixture to precipitate SEO-graphene flakes;

[0025] It is characterized by including an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them by ultrasonic treatment.

[0026]

[0027] (2) Method for manufacturing edge-oxidized graphene PEDOT:PSS nanocomposite ink

[0028] The method for manufacturing edge oxide graphene PEDOT:PSS nanocomposite ink according to the present invention is as follows:

[0029] A step for preparing a graphene oxide dispersion by dispersing edge-on graphene oxide particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA);

[0030] A step for manufacturing a nanocomposite ink, comprising: centrifuging the above-mentioned graphene oxide dispersion and then taking the supernatant;

[0031] The above edge oxide graphene is,

[0032] Graphene flake manufacturing step for manufacturing graphene flakes;

[0033] A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above;

[0034] A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated;

[0035] A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent;

[0036] An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes;

[0037] An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed in a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed;

[0038] A SEO-graphene flake precipitation step of centrifuging the above ultrasonically treated oxidized mixture to precipitate SEO-graphene flakes;

[0039] It is characterized by including an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them by ultrasonic treatment.

[0040]

[0041] (3) Edge-oxidized graphene-based inkjet printing ink

[0042] The edge oxide graphene-based inkjet printing ink according to the present invention is

[0043] Including an inkjet printing ink manufactured by dispersing the edge oxide graphene particles in distilled water,

[0044] The above edge oxide graphene is,

[0045] Graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0046]

[0047] (4) Edge-oxidized graphene PEDOT:PSS nanocomposite ink

[0048] The edge oxide graphene PEDOT:PSS nanocomposite ink according to the present invention,

[0049] A nanocomposite ink prepared by dispersing the edge-oxidized graphene particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA),

[0050] The above edge oxide graphene is,

[0051] Graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0052]

[0053] (5) Method for manufacturing edge-oxidized graphene-based dispenser printing ink

[0054] The method for manufacturing edge oxide graphene-based dispenser printing ink according to the present invention is as follows:

[0055] A step for preparing a graphene oxide dispersion by dispersing edge-oxide graphene particles in distilled water;

[0056] A step of producing an edge oxide graphene particle filter cake by vacuum filtering the edge oxide graphene dispersion dispersed in the distilled water using a polytetrafluoroethylene (Hydrophilic membrane, HP020047D) filter;

[0057] A step for manufacturing ink for dispenser printing, comprising: taking edge oxide graphene particles from the above-mentioned filter cake, immersing them in a mixture of distilled water and ethanol, and then mixing them;

[0058] The above edge oxide graphene is,

[0059] Graphene flake manufacturing step for manufacturing graphene flakes;

[0060] A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above;

[0061] A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated;

[0062] A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent;

[0063] An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes;

[0064] An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed in a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed;

[0065] SEO-graphene flake precipitation step of centrifuging the above ultrasonic treated oxidation mixture to precipitate SEO-graphene flakes;

[0066] It is characterized by including an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them by ultrasonic treatment.

[0067]

[0068] (6) Edge-oxidized graphene-based dispenser printing ink

[0069] The edge oxide graphene-based dispenser printing ink according to the present invention comprises:

[0070] Including an ink for dispenser printing manufactured by taking edge oxide graphene particles from a filter cake obtained by vacuum-filtering the edge oxide graphene dispersion dispersed in distilled water,

[0071] The above edge oxide graphene is,

[0072] Graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0073]

[0074] (7) Method for manufacturing transparent film using edge-oxidized graphene PEDOT:PSS nanocomposite

[0075] The method for manufacturing a transparent film using edge-oxidized graphene PEDOT:PSS nanocomposite according to the present invention is as follows:

[0076] A step for preparing a graphene oxide dispersion by dispersing edge-on graphene oxide particles in a PEDOT:PSS solution dispersed in IPA;

[0077] A nanocomposite manufacturing step of centrifuging the above graphene oxide dispersion and then taking the supernatant;

[0078] A ratio control step for controlling the ratio of PEDOT:PSS to graphene oxide particles (PEDOT:PSS / edge graphene oxide, w / w) in the above nanocomposite;

[0079] A glass substrate manufacturing step for converting hydrophilicity of a glass substrate to be used as a film substrate through UV treatment and ozone treatment;

[0080] A nanocomposite deposition step of spin-coating and depositing the nanocomposite with the above-described ratio on the hydrophilic-converted glass substrate;

[0081] A film manufacturing step of manufacturing a transparent film by drying a glass substrate on which the above nanocomposite is deposited at room temperature;

[0082] The above edge oxide graphene is,

[0083] Graphene flake manufacturing step for manufacturing graphene flakes;

[0084] A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above;

[0085] A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated;

[0086] A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent;

[0087] An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes;

[0088] An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed in a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed;

[0089] A SEO-graphene flake precipitation step of centrifuging the above ultrasonically treated oxidized mixture to precipitate SEO-graphene flakes;

[0090] It is characterized by including an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them by ultrasonic treatment.

[0091]

[0092] (8) Transparent film using edge-oxidized graphene PEDOT:PSS nanocomposite

[0093] A transparent film using edge oxide graphene PEDOT:PSS nanocomposite according to the present invention,

[0094] A nanocomposite prepared by dispersing the edge-oxidized graphene particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA); and

[0095] A transparent film deposited by spin-coating the above nanocomposite on a glass substrate; including,

[0096] The above edge oxide graphene is,

[0097] Graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0098]

[0099] By means of solving the above problem, the present invention can provide an ink composed only of a pure solvent and graphene particles without a dispersant.

[0100] In addition, the present invention can produce a nanocomposite ink composed only of pure graphene particles and PEDOT:PSS without a dispersant.

[0101] In addition, the present invention can provide ink that can be naturally dried in the air after printing without the existing post-processing process using high temperature and light.

[0102] In addition, the present invention can provide a nanocomposite ink that can be naturally dried in the air after printing without a post-processing process.

[0103] In addition, the present invention can provide not only low-concentration graphene ink but also high-concentration and high-viscosity water-based graphene ink.

[0104] In addition, the present invention can provide a film having excellent electrical conductivity and transparency even without a post-processing process.

[0105]

[0106] FIG. 1 is a schematic diagram for producing SEO-graphene having pure graphene properties and excellent dispersibility in various solvents according to one embodiment of the present invention.

[0107] FIG. 2 is a schematic diagram of a manufacturing process for SEO-graphene according to one embodiment of the present invention.

[0108] FIG. 3 shows the characteristics of pure graphene flakes produced by FLPE according to one embodiment of the present invention, including (a) a TEM image, (b) an FFT image, (c) an HRTEM image for calculating the number of layers, (d) a histogram for statistical analysis of the number of layers, (e) a Raman scattering, and (f) an XPS spectrum.

[0109] FIG. 4 shows the characteristic results of pure and SEO-graphene having different Ox / G ratios according to one embodiment of the present invention: (a) Raman spectra, (b) Id / IG as a function of FWHM(G), (c) XRD patterns, (d) XPS O / C ratios, (e) zeta potential values ​​(inset: zeta potential variation of 0.7-SEO-graphene as a function of pH), and (f) sheet resistance.

[0110] FIG. 5 shows XPS scan results of pure and SEO-graphene according to one embodiment of the present invention.

[0111] FIG. 6 is an XPS C1s deconvolution of graphene samples according to an embodiment of the present invention, namely (a) pure graphene, (b) 0.3-SEO-graphene, (c) 0.7-SEO-graphene, (d) 1.0-SEO-graphene, (e) 1.3-SEO-graphene, and (f) 1.7-SEO-graphene.

[0112] Figure 7 shows the dispersibility results of SEO-graphene in various solvents according to one embodiment of the present invention.

[0113] FIG. 8 is a photograph and respective SEM images of graphene filter cakes according to one embodiment of the present invention, including (a) pure graphene, (b) 0.3-SEO-graphene, (c) 0.7-SEO-graphene, (d) 1.0-SEO-graphene, (e) 1.3-SEO-graphene, and (f) 1.7-SEO-graphene.

[0114] FIG. 9 is a TEM image of a 0.7-SEG-graphene flake and (b) a corresponding selected area diffraction (SAM) image, (c) a HRTEM image of a 0.7-SEO-graphene flake and (d) a corresponding SAD image of the edge (blue rectangle) and the inner region (red rectangle) and (e) an EEL spectrum of the 0.7-SEO-graphene flake detecting the oxygen state of the entire flake surface, according to an embodiment of the present invention.

[0115] FIG. 10 is a HRTEM image of 0.3-SEO-c-graphene flakes with characteristics of c-graphene and SEO-c-graphene according to an embodiment of the present invention, including (a) sheet resistance values ​​according to Ox / G ratio, (b) Raman scattering, (c) XRD pattern, (d) Cls XPS spectrum of 0.3-SEO-c-graphene c-graphene sample, (e) TEM, and (f) FFT images of edge (blue square) and inner region (red square).

[0116] FIG. 11 is a TEM and HRTEM image of a commercial graphene flake according to an embodiment of the present invention.

[0117] FIG. 12 is a TEM and HRTEM image of a 0.3-SEO-c-graphene flake according to an embodiment of the present invention (yellow arrows indicate the width of the oxidation region along the edge).

[0118] FIG. 13 is a planar SEM image showing (a) c-graphene, (b) 0.3-SEO-c-graphene flake, (c) intermediate 0.3-SEO-c-graphene flake, and (d) a close-up view showing the enlarged interlayer spacing, according to one embodiment of the present invention.

[0119] FIG. 14 shows the results of dispersibility of SEO-graphene in various solvents using c-graphene (a) and SEO-c-graphene (b) according to one embodiment of the present invention.

[0120] FIG. 15 is an AFM image of (a) c-graphene according to one embodiment of the present invention, and shows the results showing the thickness according to distance in green (b), black (c), red (d), and blue (e) of the AFM image.

[0121] FIG. 16 is an AFM image of SEO-c-graphene according to one embodiment of the present invention, (a), and shows the results showing the thickness according to distance in green (b), black (c), red (d), and blue (e) of the AFM image.

[0122] FIG. 17 is an AFM image of SEO-c-graphene according to one embodiment of the present invention, (a), and shows the results showing the thickness according to distance in red (b) and blue (e) of the AFM image.

[0123] FIG. 18 shows the FWHM(G) according to the Raman scattering ID / IG of (a) Indian graphene, SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method according to a comparative experimental example of the present invention, (b) XRD of Indian graphene, SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method, (c) filter cake photograph and measured sheet resistance of SEO-c-graphene produced by the traditional Hummer method, (d) Raman scattering of Indian graphene, SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method, (e) Indian graphene and SEO-c-graphene synthesized by the improved Hummer method. Comparison of the sheet resistance values ​​of SEO-c-graphene (I-SEO) and SEO-c-graphene (H-SEO) produced by the traditional Hummer method.

[0124] FIG. 19 is a diagram showing (a) an aqueous edge-oxide graphene particle ink having a concentration of 1.0 g / L for inkjet printing, (b) an ink suitable for inkjet printing in which ink droplets ejected from an inkjet printing nozzle show a stable trajectory without additional droplet formation, (c) a graphene pattern printed on photographic paper, (d) sheet resistance of the pattern, and (e) a large-area inkjet printing pattern, according to one embodiment of the present invention.

[0125] FIG. 20 is a drawing showing a large-area graphene pattern printed through dispenser printing using (a) dispenser graphene ink composed only of edge-oxidized graphene particles, (b) a line-shaped pattern with a width of 578 μm printed on a PI substrate, and (c) a logo printed on a PET substrate, according to one embodiment of the present invention.

[0126] FIG. 21 is a graph showing viscosity and viscoelastic properties of (a) and (b) dispenser-printed 0.3-SEO-graphene inks according to an embodiment of the present invention (inset: optical image of ink), and (c) an optical image of dispenser-printed 0.3-SEO-GMs patterns having widths of 120 μm and 1,200 μm (sheet resistance of 1,200 μm pattern: 250 Ω / sq).

[0127] FIG. 22 is an optical image of a PEDOT:PSS / 0.3-SEO-c-graphene nanocomposite ink having different weight ratios of PEDOT:PSS vs. 0.3-SEO-c-graphene according to an embodiment of the present invention, where the weight ratio (w / w) represents the weight of PEDOT:PSS relative to 0.3-SEO-c-graphene.

[0128] FIG. 23 is a UV-vis spectrum of a PEDOT:PSS / 0.3-SEO-c-graphene nanocomposite ink having different weight ratios of PEDOT:PSS vs. 0.3-SEO-c-graphene according to an embodiment of the present invention.

[0129] FIG. 24 shows the transmittance of PEDOT:PSS / 0.3-SEO-c-graphene nanocomposite films having different weight ratios of PEDOT:PSS vs. 0.3-SEO-c-graphene according to one embodiment of the present invention.

[0130] FIG. 25 is a comparative AFM image photograph according to one embodiment of the present invention, showing (A) a pure PEDOT:PSS film (white dot ovals indicate pore regions) and (B) a PEDOT:PSS / 0.3-SEO-c-graphene nanocomposite film (scale bar: 0.5 μm).

[0131] FIG. 26 is a graph comparing the transmittance and sheet resistance of a reported graphene-based transparent film and PEDOT:PSS / 0.3-SEO-c-graphene according to one embodiment of the present invention.

[0132] Figure 27 shows the Raman spectra of a pure PEDOT:PSS film and a PEDOT:PSS / 0.3-SEO-c-graphene nanocomposite film according to one embodiment of the present invention, wherein the nanocomposite film was prepared using PEDOT:PSS / 0.3-SEO-c-graphene ink (2.7 w / w).

[0133]

[0134] The terms used in this specification will be briefly explained, and the present invention will be described in detail.

[0135] The terms used in this invention have been selected from widely used, common terms, taking into account their functions. However, these terms may vary depending on the intentions of those skilled in the art, precedents, the emergence of new technologies, etc. Therefore, the terms used in this invention should be defined based on their meaning and the overall content of the invention, rather than simply their names.

[0136] When a part of a specification is said to include a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0137] Below, with reference to the attached drawings, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0138] Specific details, including the problems to be solved, means of solving them, and the effects of the invention, are included in the embodiments and drawings described below. The advantages and features of the present invention, and methods for achieving them, will become clearer with reference to the embodiments described below in detail, along with the accompanying drawings.

[0139]

[0140] Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

[0141]

[0142] (1) Method for manufacturing edge-oxidized graphene-based inkjet printing ink

[0143] As shown in FIGS. 1 and 2, the method for manufacturing edge-oxidized graphene-based inkjet printing ink of the present invention is specifically performed by the following steps.

[0144] First, step 1 (S100) is a step for preparing a graphene oxide dispersion. More specifically, step 1 (S100) involves washing the edge graphene oxide particles three times in distilled water using a centrifugal separation method and then redispersing them in distilled water.

[0145]

[0146] Here, it is preferable that the edge oxidation graphene is performed by steps 1-0 (S10) to 8-0 (S80) below.

[0147] First, Step 1-0 (S10) is the graphene flake manufacturing step. Step 1-0 (S10) is performed using the liquid phase exfoliation (FLPE) method to manufacture graphene flakes, and is specifically performed through the following steps.

[0148] Step 1-1 (S11) is a step for preparing a graphite dispersion. In Step 1-1 (S11), a graphite dispersion is prepared by dispersing graphite powder in deionized water containing sodium dodecyl sulfate (SDS). 1 part by weight of the graphite is dispersed in 15 to 25 parts by weight of the deionized water, and it is preferable that 0.075 to 0.080 parts by weight of the sodium dodecyl sulfate (SDS) is included in 100 parts by weight of the deionized water.

[0149] Step 1-2 (S12) is the graphite dispersion exfoliation step. Step 1-2 (S12) exfoliates the prepared graphite dispersion after ultrasonic treatment. The prepared graphite dispersion is ultrasonically treated for 3 to 7 minutes and transferred to a SUS tube reactor by a peristaltic pump. The FLPE process performs exfoliation by circulating the graphite dispersion under the influence of ultrasonic waves, and is performed at a temperature of 13 to 17°C using a chiller installed in the ultrasonic bath.

[0150] Step 1-3 (S13) is a graphene flake separation step. Step 1-3 (S13) manufactures graphene flakes by centrifuging the exfoliated graphite dispersion. Here, the centrifugation is performed at 450 to 550 rpm for 50 to 70 minutes to separate the graphene flakes from the unexfoliated graphite.

[0151]

[0152] Next, step 2-0 (S20) is a graphene flake precipitation step. The steps after step 2-0 (S20) are shown in Fig. 2. In step 2-0 (S20), the manufactured graphene flakes are precipitated by centrifugation.

[0153] Here, the centrifugation is performed at 9,800 to 12,000 rpm for 25 to 35 minutes to cause precipitation.

[0154]

[0155] Next, step 3-0 (S30) is a graphene flake redispersion step. In step 3-0 (S30), the precipitated graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated.

[0156] Here, the sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent is mixed in a ratio of 9:1.

[0157]

[0158] Next, step 4-0 (S40) is a graphene flake heating and stirring step. In step 4-0 (S40), graphene flakes redispersed in the solvent are heated and stirred.

[0159] Here, the graphene flakes redispersed in the solvent are heated and stirred at 45 to 55°C for 8 to 12 minutes.

[0160]

[0161] Next, step 5-0 (S50) is an oxidizing agent addition step. In step 5-0 (S50), an oxidizing mixture is prepared by adding an oxidizing agent to the heated and stirred graphene flakes.

[0162] Here, the oxidizing agent is preferably potassium permanganate (KMnO4), and potassium chlorate (KClO3) and potassium ferrate (K2FeO4) may be used as needed.

[0163] It is preferable that the oxidizing agent is used in an amount of 0.3 to 1.7 parts by weight relative to 1 part by weight of the graphene flakes.

[0164] When the oxidizing mixture produced after adding the above oxidizing agent changes from green to black, the following steps are performed, characterized in that 50 to 70 minutes have passed since mixing the above oxidizing agent.

[0165]

[0166] Next, step 6-0 (S60) is a step of ultrasonic treatment of an oxidation mixture. In step 6-0 (S60), the oxidation mixture is mixed with a solvent of distilled water / ethanol (DI water / EtOH), hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed.

[0167] When the oxidation mixture changes from green to black in the above step 5-0 (S50), it is mixed with the distilled water / ethanol solvent. Here, the mixture of the distilled water / ethanol (DI water / EtOH) solvent is preferably 1:1.

[0168] Afterwards, the hydrogen peroxide (H2O2) is added and ultrasonic treatment is performed at 8 to 12°C for 18 to 22 minutes. Here, it is preferable to mix 0.03 parts by weight of the 30 (w / w)% hydrogen peroxide (H2O2) with respect to 1 part by weight of the distilled water / ethanol solvent mixture.

[0169]

[0170] Next, step 7-0 (S70) is a precipitation step of SEO-graphene flakes. In step 7-0 (S70), the sonicated oxidation mixture is centrifuged to precipitate SEO-graphene flakes.

[0171] Here, the sonicated oxidation mixture is centrifuged at 3 to 5 °C and 9,800 to 12,000 rpm to precipitate the SEO-graphene flakes.

[0172]

[0173] Next, step 8-0 (S80) is a step for purifying SEO-graphene flakes. In step 8-0 (S80), the precipitated SEO-graphene flakes are redispersed in a distilled water / ethanol (DI water / EtOH) solvent and then purified through ultrasonic treatment.

[0174] Here, it is preferable that the mixture of the distilled water / ethanol (DI water / EtOH) solvent be 1:1, and the mixture is sonicated for 15 to 25 minutes.

[0175] In addition, in the above step 8-0 (S80), purification of SEO-graphene flakes is repeatedly performed until the pH of the SEO-graphene flakes becomes 6, and it is preferable to repeat redispersion and ultrasonic treatment in the distilled water / ethanol (DI water / EtOH) solvent up to 4 times.

[0176]

[0177] Next, the second step (S200) is the inkjet printing ink manufacturing step. In the second step (S200), the edge oxide graphene dispersion dispersed in the distilled water manufactured in the first step (S100) is centrifuged and the supernatant is collected to manufacture inkjet printing ink.

[0178] In the second step (S200), centrifugation is performed at 900 to 1,100 rpm for 25 to 35 minutes.

[0179] Here, the concentration of the ink for inkjet printing is prepared at 1 g / L.

[0180] When the ink for the above inkjet printing was put into an inkjet cartridge (Dimatix DMC-11610 cartridge, 10 pL) and printed on photographic paper using a Dimatix printer (DMP-2831), the photographic paper was used in its purchased condition, and the printed pattern was dried in the air at room temperature for 12 hours.

[0181]

[0182] (2) Method for manufacturing edge-oxidized graphene PEDOT:PSS nanocomposite ink

[0183] Meanwhile, in the step of manufacturing the above graphene oxide dispersion (S100), a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA) may be used instead of distilled water.

[0184] That is, the method for manufacturing edge-oxidized graphene PEDOT:PSS nanocomposite ink according to the present invention can be specifically performed by the following steps.

[0185] The above-described method for producing edge-oxidized graphene PEDOT:PSS nanocomposite ink comprises: a step of producing an oxide graphene dispersion by dispersing edge-oxidized graphene particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA); a step of producing a nanocomposite ink by centrifuging the oxide graphene dispersion and then collecting a supernatant; wherein the edge-oxidized graphene comprises: a graphene flake producing step of producing graphene flakes; a graphene flake precipitation step of centrifuging and precipitating the produced graphene flakes; a graphene flake redispersion step of redispersing the precipitated graphene flakes in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treating them; a graphene flake heating and stirring step of heating and stirring the graphene flakes redispersed in the solvent; an oxidant adding step of adding an oxidant to the heated and stirred graphene flakes to produce an oxidized mixture; It is characterized by including an oxidation mixture sonication step of mixing the oxidation mixture in a distilled water / ethanol (DI water / EtOH) solvent, adding hydrogen peroxide (H2O2), and then sonicating the mixture; an SEO-graphene flake precipitation step of centrifuging the sonicated oxidation mixture to precipitate SEO-graphene flakes; and an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then sonicating them to purify them.

[0186]

[0187] (3) Edge-oxidized graphene-based inkjet printing ink

[0188] Below, an edge-oxidized graphene-based inkjet printing ink (hereinafter, “inkjet printing ink”) characterized by being manufactured by the edge-oxidized graphene-based inkjet printing ink manufacturing method described above will be described.

[0189] The above inkjet printing ink includes an inkjet printing ink manufactured by dispersing the edge-oxidized graphene particles in distilled water, wherein the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0190]

[0191] Here, the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0192] It is characterized in that the oxidizing agent is 0.3 to 1.7 parts by weight of the graphene flakes.

[0193] The zeta potential of the above graphene oxide is characterized by being -35 mV or less.

[0194] The above graphene oxide is characterized by increased solvent dispersibility in at least one of water, 2-ME (2-Methoxyethanol), NMP (1-Methyl-2-pyrrolidinone), H2O / EtOH solvent, and IPA (Isopropyl alcohol).

[0195] When the oxidizing agent is 0.3 and 0.7 parts by weight relative to 1 part by weight of the graphene flake, the sheet resistance of the graphene oxide is characterized by being 14 Ω / sq.

[0196] The above-mentioned graphene oxide is characterized by an average thickness of 1.5 nm or less (excluding 0 nm).

[0197] The above graphene flakes are characterized by being composed of 81 to 90% carbon and 10 to 19% oxygen.

[0198] When the oxidizing agent is 0.3 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, the XRD peak of the (002) basal plane diffraction of the graphene oxide appears at 2θ = 26.10º to 26.40º, and when the oxidizing agent is 1.0 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, a new XRD peak of the graphene oxide is formed at 13.80º to 12.15º.

[0199] The above edge oxide graphene is characterized by an average thickness of 1.5 nm or less (excluding 0 nm).

[0200] The above graphene flakes are characterized by being composed of 81 to 90% carbon and 10 to 19% oxygen.

[0201] The above edge oxide graphene is characterized by an absorption wavelength of 265 to 270 nm in the UV-Vis spectrum.

[0202] The pattern printed with the inkjet printing ink manufactured above is characterized by having a surface resistance of 1.5 kΩ / sq or less.

[0203] Since the above edge-oxidized graphene particles are well dispersed in water without a dispersant, a pure aqueous SEO-graphene dispersion of the inkjet printing ink can be prepared.

[0204] As shown in Fig. 19(a), an aqueous edge-oxidized graphene particle ink with a concentration of 1.0 g / L was prepared for inkjet printing. The UV-Vis spectrum shows that the edge-oxidized graphene particles have an absorption wavelength of 269 nm, which is lower than the absorption wavelength of typical graphene oxide of 235 nm, indicating that the edge-oxidized graphene is partially oxidized.

[0205] In addition, as shown in Fig. 19(b), the ink droplets ejected from the inkjet printing nozzle showed a stable trajectory without forming additional droplets, demonstrating that the ink is suitable for inkjet printing. As shown in Fig. 19(c), a square graphene pattern measuring 3 mm in width and 1 mm in height was produced on photographic paper through 50 printing processes using the manufactured inkjet printing ink.

[0206] The printed pattern was then dried in air at room temperature for 12 hours without any post-processing. The sheet resistance of the pattern was measured to be 1.46 kΩ. As shown in Fig. 19(d), the sheet resistance value is superior to that of previously reported r-GO patterns for inkjet printing, and is also superior to inkjet-printed graphene patterns that require a post-processing process.

[0207] As shown in Fig. 19(e), the invention demonstrates the feasibility of large-area inkjet printing patterns using the ink. Previous studies have required post-processing steps, such as thermal or photothermal heating, chemical or plasma reduction, to remove additives from inkjet-printed graphene and its derivatives. However, the present invention is the first to apply a pure aqueous graphene dispersion to inkjet printing, demonstrating its potential for environmentally friendly and highly efficient printing of graphene patterns in related fields.

[0208] It is expected that electrical conductivity can be further improved by optimizing printing parameters and substrate.

[0209]

[0210] (4) Edge-oxidized graphene PEDOT:PSS nanocomposite ink

[0211] Meanwhile, the present invention provides an edge-oxidized graphene PEDOT:PSS nanocomposite ink characterized by being manufactured by a method for manufacturing edge-oxidized graphene PEDOT:PSS nanocomposite ink.

[0212] The edge-oxidized graphene PEDOT:PSS nanocomposite ink includes a nanocomposite ink prepared by dispersing edge-oxidized graphene particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA), wherein the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and edges are selectively oxidized.

[0213]

[0214] (5) Method for manufacturing edge-oxidized graphene-based dispenser printing ink

[0215] In addition, it is preferable that the edge oxide graphene-based dispenser printing ink manufacturing method of the present invention is manufactured by additionally performing the following steps in the edge oxide graphene-based inkjet printing ink manufacturing method described above.

[0216] After performing the first step (S100) of the above edge oxidation graphene-based inkjet printing ink manufacturing method, the third step (S300) to the fourth step (S400) below are performed.

[0217] First, the third step (S300) is a step for producing an edge-oxidized graphene particle filter cake. In the third step (S300), the edge-oxidized graphene dispersion dispersed in the distilled water is vacuum filtered using a polytetrafluoroethylene (Hydrophilic membrane, HP020047D) filter.

[0218] Here, it is preferable that the polytetrafluoroethylene (Hydrophilic membrane, HP020047D) filter is 0.45 ㎛.

[0219]

[0220] Next, the fourth step (S400) is a step for manufacturing ink for dispenser printing. In the fourth step (S400), edge oxide graphene particles are taken from the generated filter cake, placed in a mixture of distilled water and ethanol, and then mixed.

[0221] Here, 0.2 to 0.25 g of edge oxide graphene particles are taken from the filter cake produced above, placed in 2 ml of a mixture of distilled water and ethanol (1:1), and then mixed to produce a high-concentration and high-viscosity ink for dispenser printing.

[0222] In addition, the ink for the dispenser print manufactured above is filled into a syringe, printed on a PET substrate, and then dried in the air at room temperature for 12 hours.

[0223] Additionally, it is desirable to perform UV / ozone treatment to make the PET substrate hydrophilic before printing.

[0224]

[0225] (6) Edge-oxidized graphene-based dispenser printing ink

[0226] Below, we will describe an edge-oxidized graphene-based dispenser printing ink (hereinafter, “dispenser printing ink”) characterized by being manufactured by the edge-oxidized graphene-based dispenser printing ink manufacturing method described above.

[0227] The above dispenser printing ink comprises an ink for dispenser printing manufactured by taking edge-oxidized graphene particles from a filter cake obtained by vacuum-filtering the edge-oxidized graphene dispersion dispersed in distilled water, wherein the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0228]

[0229] Here, the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0230] It is characterized in that the oxidizing agent is 0.3 to 1.7 parts by weight of the graphene flakes.

[0231] The zeta potential of the above graphene oxide is characterized by being -35 mV or less.

[0232] The above edge oxide graphene is characterized by increased solvent dispersibility in at least one of water, 2-ME (2-Methoxyethanol), NMP (1-Methyl-2-pyrrolidinone), H2O / EtOH solvent, and IPA (Isopropyl alcohol).

[0233] When the oxidizing agent is 0.3 and 0.7 parts by weight relative to 1 part by weight of the graphene flake, the edge oxidized graphene is characterized in that the sheet resistance is 14 Ω / sq.

[0234] The above edge oxide graphene is characterized by an average thickness of 1.5 nm or less (excluding 0 nm).

[0235] The above graphene flakes are characterized by being composed of 81 to 90% carbon and 10 to 19% oxygen.

[0236] When the oxidizing agent is 0.3 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, the XRD peak of the (002) basal plane diffraction of the edge-oxidized graphene appears at 2θ = 26.10º to 26.40º, and when the oxidizing agent is 1.0 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, a new XRD peak of the edge-oxidized graphene is formed at 13.80º to 12.15º.

[0237] The pattern printed with the above-mentioned manufactured dispenser printing ink is characterized by having a surface resistance of 250 Ω / sq or less.

[0238]

[0239] The above dispenser printing ink requires a high-viscosity graphene ink with a very high graphene content to continuously apply the filament ink to the substrate. Stable dispersion of graphene particles is crucial for stable filament ink formation and accurate printing pattern generation on the substrate, and thus a dispersant is typically used to ensure stable dispersion. As shown in Fig. 20(a), similar to the inkjet printing ink, a dispenser graphene ink was developed (ink concentration: 105 g / L) consisting solely of an ethanol / water solvent (5:5) and high-concentration edge-oxidized graphene particles.

[0240] The above dispenser printing ink exhibits shear thinning characteristics, where viscosity decreases with increasing shear rate, and the storage modulus (G′) is greater than the loss modulus (G′′) across the entire angular frequency range. This trend indicates that the ink is initially immobile, exhibits fluidity at high shear, and exhibits solidity after being deposited on the substrate, demonstrating that the ink exhibits rheological properties suitable for dispenser printing.

[0241] In Fig. 20(b), a line-shaped pattern with a width of 578 ㎛ was printed on the PI substrate, and its sheet resistance was measured to be 5 kΩ.

[0242] Similar to the inkjet printing ink pattern described above, the dispenser printing ink pattern was also dried at room temperature in air for 12 hours without post-processing. As shown in Fig. 20(c), a logo was printed on a PET substrate, confirming the ability to print large-area graphene patterns via dispenser printing.

[0243]

[0244] (7) Method for manufacturing transparent film using edge-oxidized graphene PEDOT:PSS nanocomposite

[0245] The method for manufacturing a transparent film using the edge-oxidized graphene PEDOT:PSS nanocomposite of the present invention is preferably manufactured by additionally performing the following steps in the method for manufacturing edge-oxidized graphene PEDOT:PSS nanocomposite ink described above.

[0246] After performing the step of preparing the oxide graphene dispersion or the step of preparing the nanocomposite ink of the above edge oxide graphene PEDOT:PSS nanocomposite ink preparation method,

[0247] The method may include a ratio adjustment step for adjusting the ratio of PEDOT:PSS to graphene oxide particles (PEDOT:PSS / edge graphene oxide, w / w) in the above nanocomposite; a glass substrate manufacturing step for converting hydrophilicity of a glass substrate to be used as a film substrate through UV treatment and ozone treatment; a nanocomposite deposition step for spin-coating and depositing the nanocomposite with the adjusted ratio on the glass substrate converted to hydrophilicity; and a film manufacturing step for drying the glass substrate on which the nanocomposite is deposited at room temperature to produce a transparent film.

[0248]

[0249] First, the ratio adjustment step adjusts the ratio of PEDOT:PSS to the graphene oxide particles in the nanocomposite (PEDOT:PSS / edge graphene oxide, w / w). Here, the ratio of PEDOT:PSS to the graphene oxide particles in the nanocomposite (PEDOT:PSS / edge graphene oxide, w / w) is characterized in that it is 0.1 to 2.7.

[0250]

[0251] Next, the glass substrate manufacturing step converts the glass substrate to be used as a film substrate into hydrophilic through UV treatment and ozone treatment.

[0252]

[0253] Next, the nanocomposite deposition step deposits the nanocomposite with the adjusted ratio by spin coating it on the hydrophilic-converted glass substrate.

[0254] More specifically, 0.1 ml of the nanocomposite is cast on the hydrophilically converted glass substrate, and then spin-coated at 1,800 to 2,200 rpm for 0.8 to 1.2 minutes, and the spin-coating is repeated as many times as desired. More preferably, spin-coating is performed by depositing at 2,000 rpm for 1 minute and repeating up to 50 times.

[0255]

[0256] Next, the film manufacturing step manufactures a transparent film by drying the glass substrate on which the nanocomposite is deposited at room temperature.

[0257]

[0258] (8) Transparent film using edge-oxidized graphene PEDOT:PSS nanocomposite

[0259] Below, a transparent film (hereinafter, “transparent film”) using edge-oxidized graphene PEDOT:PSS nanocomposite, characterized by being manufactured by a method for manufacturing a transparent film using the edge-oxidized graphene PEDOT:PSS nanocomposite described above, is described.

[0260] The above transparent film includes a nanocomposite manufactured by dispersing the edge-oxidized graphene particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA), and a transparent film deposited by spin-coating the nanocomposite on a glass substrate, wherein the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0261] Here, the edge-oxidized graphene is characterized in that graphene flakes are oxidized using an oxidizing agent, and the edges are selectively oxidized.

[0262] It is characterized in that the oxidizing agent is 0.3 to 1.7 parts by weight of the graphene flakes.

[0263] The zeta potential of the above graphene oxide is characterized by being -35 mV or less.

[0264] The above edge oxide graphene is characterized by increased solvent dispersibility in at least one of water, 2-ME (2-Methoxyethanol), NMP (1-Methyl-2-pyrrolidinone), H2O / EtOH solvent, and IPA (Isopropyl alcohol).

[0265] When the oxidizing agent is 0.3 and 0.7 parts by weight relative to 1 part by weight of the graphene flake, the edge oxidized graphene is characterized in that the sheet resistance is 14 Ω / sq.

[0266] The above edge oxide graphene is characterized by an average thickness of 1.5 nm or less (excluding 0 nm).

[0267] The above graphene flakes are characterized by being composed of 81 to 90% carbon and 10 to 19% oxygen.

[0268] When the oxidizing agent is 0.3 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, the XRD peak of the (002) basal plane diffraction of the edge-oxidized graphene appears at 2θ = 26.10º to 26.40º, and when the oxidizing agent is 1.0 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, a new XRD peak of the edge-oxidized graphene is formed at 13.80º to 12.15º.

[0269] The transparent film using the above nanocomposite is characterized by an optical transparency of 80% or more at a wavelength of 550 nm.

[0270] The transparent film using the above nanocomposite is characterized by having a surface resistance of 3.4 Ω / sq or less.

[0271]

[0272]

[0273] Hereinafter, the characteristics of the inkjet printing ink, dispenser printing ink, nanocomposite ink, and transparent film manufactured by the present invention will be specifically described.

[0274]

[0275] First, the process for producing high-quality, few-layer concentrated graphene flakes with high dispersibility in various solvents is illustrated in Figure 1. Two key factors that must be carefully controlled to produce graphene satisfying the aforementioned characteristics are selective edge oxidation of pure graphene flakes and fine-tuning the degree of edge oxidation. These requirements can be readily met by adjusting the ratio of oxidant to graphene (Ox / G ratio) to find the optimal Ox / G ratio for the desired SEO-graphene synthesis.

[0276]

[0277] To produce SEO-graphene with superior properties and high dispersibility, high-quality pure graphene must be prepared. In this invention, we utilized the fluid liquid phase exfoliation (FLPE) process to produce graphene flakes with several advantages over conventional ultrasonic LPE, including improved scalability and productivity. Figure 3 shows the characteristic results of graphene flakes produced using FLPE. The lateral size of the graphene flakes produced using FLPE is 1.5 ㎛. The high crystallinity of the flakes is confirmed by the bright spots in the FFT image. Raman scattering showed low D-band intensity and high G-band intensity, indicating the high structural quality of the flakes. The number of layers in the graphene flakes was determined by analyzing the edges of the graphene flakes using TEM. Statistical analysis of the number of layers in the graphene flakes showed that the FLPE process produced low-layer graphene flakes with an average layer number of 5 to 6. XPS analysis revealed that the graphene flakes were composed of 89.4% carbon and 10.6% oxygen. Overall, the results suggest that the graphene flakes produced by FLPE are clean with high chemical and structural integrity.

[0278]

[0279] Pure graphene flakes are converted to SEO-graphene through an oxidation reaction. The oxidation reaction used is based on Hummer's improved method. In our experiments, pure graphene flakes were oxidized using a significantly smaller amount of oxidant compared to Hummer's improved method. The ratio of oxidant to graphene (Ox / G ratio) was as high as 1.7, which is approximately one-sixth of the amount of oxidant used in conventional GO production methods. Because the entire surface of graphite, including the basal plane, must be oxidized to increase the interlayer spacing, conventional methods typically require a significant amount of oxidant to produce GO. In contrast, SEO-graphene requires a much smaller amount of oxidant to selectively oxidize the edges of the graphene flakes to the desired degree of oxidation, as the thin graphene flakes are the target of oxidation. After synthesis, thorough washing is essential to purify SEO-graphene. This involves washing the SEO-graphene repeatedly with a mixture of H2O and EtOH under sonication until a pH of 6 is reached. Compared to Hummer's improved method for producing GO, which requires cumbersome purification processes involving multiple washes and filtrations with HCl and various solvents, this washing process is relatively simple and environmentally friendly. The simplified purification process for SEO-graphene will facilitate the scalable production of SEO-graphene for industrial applications.

[0280]

[0281]

[0282] Hereinafter, the present invention will be described in more detail through comparative examples and experimental examples manufactured using conventional methods. The objectives, features, and advantages of the present invention will be readily understood through the following examples. The present invention is not limited to the examples described herein and may be embodied in other forms. The examples introduced herein are provided to ensure that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Therefore, the present invention should not be limited by the following examples.

[0283]

[0284] The materials used in the examples are as follows.

[0285] Graphite flakes (< 20 μm, synthetic), sodium dodecyl sulfate (SDS, 98.0%), potassium permanganate (KMnO4, 99.0%), and 2-methoxyethanol (2ME ≥99.3%) were purchased from SiC-graphene-Aldrich, respectively. Sulfuric acid (95.0%), phosphoric acid (85.0%), hydrogen peroxide (34.5%), N-dimethylformamide (DMF 99.0%), and 1-methyl-2-pyrrolidone (nmP 99.5%) were purchased from Samchun Chemical Co., Ltd. Ethyl alcohol (95.0%), 2-propanol (IPA, 99.5%), and methanol (99.5%) were purchased from Damul Chemical. Acetonitrile (ACN ≥99.9%) was purchased from JT Baker.

[0286]

[0287] Example 1: Synthesis of graphene using FLPE

[0288] Previous studies have reported the use of liquid-phase exfoliation (FLPE) to produce graphene flakes. The FLPE system consisted of an ultrasonic bath (JAC Ultrasonics KODO 3010, 40 kHz), a stainless steel tube reactor, polytetrafluoroethylene (PTFE) tubing (Materflex 96410-16), and a peristaltic pump (Masterflex, No. 7523-47). To prepare a graphite dispersion, 5 g of graphite powder was dispersed in 100 mL of deionized water containing 77 mg of sodium dodecyl sulfate (SDS). The dispersion was then sonicated for 5 min and transferred to the stainless steel tube reactor via a peristaltic pump. The FLPE process was initiated by circulating the dispersion under the influence of ultrasound, and the exfoliation temperature was maintained at approximately 15°C using a chiller installed in the ultrasonic bath. The dispersion produced after exfoliation was discharged from the reactor and centrifuged (LABOGENE 416) at 500 rpm for 1 hour to separate the graphene dispersion from the unexfoliated graphite.

[0289]

[0290] Example 2: Synthesis of SEO-graphene using graphene flakes synthesized with FLPE

[0291] The process for preparing SEO-graphene is illustrated in Figure 2. First, graphene flakes synthesized using the FLPE synthesized in Example 1 were centrifuged at 10 k rpm for 30 min to precipitate. The precipitated graphene flakes were redispersed in a mixture of H2SO4 / H3PO4 (18 mL / 2 mL) at a 9:1 ratio and then sonicated for 5 min. The mixture was heated to 50 °C and stirred for 10 min, after which the desired amount of KMnO4 was added to the mixture. The ratio of oxidant to graphene was adjusted to 0.3, 0.7, 1.0, 1.3, and 1.7. When the mixture turned from green to black (typically 1 h after adding KMnO4), it was poured into a mixture of distilled water / EtOH (50 mL:50 mL) solvent. Then, 30% H2O2 (3 mL) was added and sonicated at 10 °C for 20 min. The mixture was centrifuged at 4 °C and 10 K rpm for 30 min to precipitate SEO-graphene flakes. To purify the SEO-graphene flakes, the SEO-graphene precipitate was redispersed in a solvent mixture of DI water / EtOH (1:1) and sonicated for 20 min. This purification process was repeated up to four times through redispersion and centrifugation cycles until the pH of the SEO-graphene dispersion reached approximately 6. The mass ratio of the oxidizer to the amount of graphene or graphite microplatelets (hereinafter referred to as c-graphene, 10 layers or more) was adjusted to 0.15, 0.3, 0.5, 0.7, and 0.8. Purified SEO-graphene and SEO-c-graphene were freeze-dried at -90 °C using a freeze dryer (Mareuda, MLB-9003) before application.

[0292]

[0293] Example 3: Synthesis of SEO-graphene using commercial graphene flakes.

[0294] Commercial graphene flake powder (c-graphene) was processed in the same manner as graphene flakes produced by FLPE, except that the ratio of graphene to oxidant was adjusted to 0.1 to 0.7 parts by weight.

[0295]

[0296] Example 4: Preparation of inkjet printing ink

[0297] Edge-mounted graphene oxide particles were washed three times in distilled water using a centrifugal method and then redispersed in distilled water. The edge-mounted graphene oxide dispersion in distilled water was centrifuged at 1,000 rpm for 30 minutes to separate the edge-mounted graphene particles in the supernatant from the larger particles in the sediment. The concentration of the aqueous edge-mounted graphene oxide ink for inkjet printing was prepared at 1 g / L. The aqueous edge-mounted graphene oxide ink for inkjet printing was loaded into an inkjet cartridge (Dimatix DMC-11610 cartridge, 10 pL) and printed on photographic paper using a Dimatix printer (DMP-2831). The photographic paper was used as purchased, and the printed pattern was dried in air at room temperature for 12 hours.

[0298]

[0299] Example 5: Preparation of dispenser printing ink

[0300] The edge-on graphene oxide particle dispersion was vacuum filtered using a 0.45 μm polytetrafluoroethylene (Hydrophilic membrane, HP020047D) filter to produce an edge-on graphene oxide particle filter cake. 0.21 g of edge-on graphene oxide particles were taken from the resulting filter cake, immersed in 2 mL of a 1:1 mixture of distilled water and ethanol, and then mixed to produce a high-concentration / high-viscosity ink for dispenser printing. The ink was filled into a dispenser printing syringe, printed on a PET substrate (request information on printing conditions), and then dried in air at room temperature for 12 hours. Before printing, the PET substrate was treated with UV / ozone to render it hydrophilic.

[0301]

[0302] Example 6: PEDOT:PSS / 0.3-SEO-c-graphene nanocomposite ink and transparent film

[0303] 0.3-SEO-c-graphene was dispersed in PEDOT:PSS in IPA solvent by sonication for 5 min, and then centrifuged at 1,000 rpm for 30 min. The supernatant after centrifugation was used as a nanocomposite ink. The weight ratio of PEDOT:PSS to 0.3-SEO-c-graphene was adjusted by changing the concentration of PEDOT:PSS while maintaining the amount of 0.3-SEO-c-graphene. The weight ratios (w / w) of PEDOT:PSS to 0.3-SEO-c-graphene were measured to be 0.10, 0.15, 0.25, 0.50, 1.10, 1.90, and 2.70. The nanocomposite ink was spin-coated on a glass substrate using a spin coater (Dong Ah, ACE-200). 100 μL of the solution was initially cast onto the substrate and spun at 2 k rpm for 1 min. The glass substrate was UV / ozone treated to render it hydrophilic before coating.

[0304]

[0305] Comparative Example 1: Synthesis of SEO-graphene manufactured using the Hummer method

[0306] 150 mg of graphene and 75 mg of NaNO3 were added to 20 ml of sulfuric acid and sonicated for 5 minutes. 50 mg of KMnO4 was added to the solution and reacted at 0°C. When the solution changed from green to black, it was poured into 100 ml of a water:ethanol (1:1) solution. 3 ml of hydrogen peroxide was added. The washing process was then repeated four times in the same manner.

[0307] The differences from the SEO-graphene manufactured by Example 2 include the presence or absence of phosphoric acid and sodium nitrate and the need for cooling during the reaction time.

[0308]

[0309] Comparative Example 2: Synthesis of SEO-graphene manufactured using the Hummer method

[0310] The SEO-graphene prepared in Comparative Example 1 was sonicated for 5 minutes, dispersed in PEDOT:PSS in an IPA solvent, and then centrifuged at 1,000 rpm for 30 minutes. The supernatant after centrifugation was used as a nanocomposite ink. The weight ratio of PEDOT:PSS to SEO-graphene was adjusted by changing the concentration of PEDOT:PSS while maintaining the amount of SEO-graphene. The weight ratios (w / w) of PEDOT:PSS to SEO-graphene were measured to be 0.10, 0.15, 0.25, 0.50, 1.10, 1.90, and 2.70. The nanocomposite ink was spin-coated on a glass substrate using a spin coater (Dong Ah, ACE-200). 100 μL of the solution was initially cast on the substrate and spun at 2 k rpm for 1 minute. The glass substrate was UV / ozone treated to render it hydrophilic before coating.

[0311]

[0312] Experimental Example 1: Measurement of the properties of graphene produced by FLPE and SEO-graphene.

[0313] Transmission electron microscopy images were obtained using an advanced TEM operating at an acceleration voltage of 10 kV. The graphene dispersion was dropped onto a holey carbon grid (400 mesh gold) and dried in a furnace at 80 °C. Raman spectra were obtained using a Raman spectrometer (Nanophoton) equipped with a RAMANtouch 532.07 nm laser. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were performed using a Nexsa (ThermoFisher Scientific) and a D8 Advance A25 (BRUKER), respectively. Field emission scanning electron microscopy (FE-SEM) images and optical microscopy (OM) images were obtained using a FE-SEM (JEOL JSM-7610F) and an OM (Olympus U-MSSP4), respectively. Samples were prepared by dropping the graphene dispersion onto a Si / SiO2 wafer and drying it at 80 °C. Sheet resistance was obtained using a Source Measure Unit (KEITHLEY, SMU-2450). To prepare a sheet resistance sample, the SEO-graphene dispersion was vacuum filtered using a hydrophilic membrane with a pore size of 0.45 μm, and the SEO-graphene filter cake was dried overnight.

[0314]

[0315] Experimental Example 2: Raman Scattering Analysis of SEO-Graphene

[0316] The amount of oxidant was varied so that the Ox / G ratio was between 0.3 and 1.7 at a fixed amount of pure graphene. The Raman scattering data of SEO-graphene samples obtained with different Ox / G ratios are compared in Fig. 4(a). Like pure graphene, all SEO-graphene samples showed a G band (1353.12 cm -1 ), D band (1538.82 cm) -1 ) and 2D band (2703.36 cm -1) exhibit three main peaks. However, the peak intensity and broadening vary with the Ox / G ratio. Compared to the G band of graphene, the G band peak of SEO-graphene with a 0.3 ratio (0.3-SEO-graphene) is broader due to the combination with the D' band. The D band is more intense in 0.3-SEO-graphene, and the 2D band is broader than that of pristine graphene. These results demonstrate a higher oxidation degree of 0.3-SEO-graphene than that of pristine graphene.

[0317] A similar Raman scattering pattern is observed for SEO-graphene with an Ox / G ratio of 0.7. As the amount of oxidant increases further, when the ratio is 1.0 (1.0-SEO-graphene), the D-band peak becomes much stronger, while the 2D-band peak weakens. Additionally, the G-band peak tends to be broader. SEO-graphene samples with an Ox / G ratio greater than 1.0 also show a similar trend of an intensified D-band peak, a broadened G-band peak, and a decreased 2D-band peak. Since the G-band, D-band, and 2D-band represent the graphitic structure, lattice disorder, and c-axis stacking order of graphene, respectively, the Raman scattering results indicate that the higher the Ox / G ratio, the higher the oxidation level of SEO-graphene.

[0318] To investigate this further, we analyzed 20 SEO-graphene flakes from each Ox / G ratio sample and plotted the ID / IG values ​​as a function of the full-width at half-maximum (FWHM) value of the G band peak, as shown in Fig. 4(b). As expected, both the ID / IG ratio and the FWHM values ​​increase with increasing Ox / G ratio. It appears that SEO-graphene can be divided into two categories based on their degree of oxidation. Those with an Ox / G ratio less than 7 have a similarly low degree of oxidation, whereas those with a ratio greater than 1.0 exhibit a similarly high degree of oxidation. Overall, the Raman scattering patterns of 0.3- and 0.7-SEO-graphene differ significantly from that of GO in terms of the high intensity of the 2D band peak and the lower ID / IG and FWHM(G) values, indicating that SEO-graphene is only partially oxidized with a low degree of oxidation.

[0319]

[0320] Experimental Example 3: XRD Pattern Analysis of SEO-Graphene

[0321] Figure 4(c) shows a comparison of the XRD patterns of SEO-graphene with respect to the Ox / G ratio. Pure graphene flakes exhibit a strong peak at 24º and a weak peak at 43º, corresponding to the (002) basal plane diffraction and (101) planes, respectively. Similarly, SEO-graphene with Ox / G ratios of 0.3 and 0.7 also exhibit a strong graphite structure peak at 26.30º. However, in the case of 0.7-SEO-graphene, the graphite peak is slightly broadened, as evidenced by the FWHM values ​​of the graphite peak, which are 1.06 and 1.59 for 0.3-SEO-graphene and 0.7-SEO-graphene, respectively. A weak peak at 13.82º, indicating the oxidation state, begins to appear in 1.0-SEO-graphene, along with the broadening of the graphite peak due to the lattice distortion arising from the AB stacking sequence of the graphite lattice. The oxidation peak becomes stronger in 1.3-SEO-graphene and shifts to a lower 2θ value of 12.96º. For 1.7-SEO-graphene, the peak corresponding to the graphitic structure becomes significantly weaker, while the peak corresponding to the oxidation state becomes sharper and shifts further to a lower value of 12.14º.

[0322] The overall trend of the XRD patterns is as follows. When the Ox / G ratio is less than 0.7, SEO-graphene still maintains the graphitic structure, but when the ratio exceeds 1.0, the graphitic structure begins to decrease and an oxidation state appears. These results are consistent with the Raman scattering analysis results of SEO-graphene. The oxidation peak becomes more distinct and its position shifts to lower 2θ values ​​as the Ox / G ratio increases. The interlayer spacings are 6.40 Å, 6.80 Å, and 7.28 Å for Ox / G ratios of 1.0, 1.3–1.7, respectively, indicating that SEO-graphene is functionalized with different levels of oxygen-containing groups. These results clearly indicate that SEO-graphene tends to be more oxidized as the Ox / G ratio increases. However, the interlayer spacing of 7.28 Å for 1.7-SEO-graphene is lower than that of GO (9.5 Å), indicating that the oxidation degree is not as significant as that of GO.

[0323]

[0324] Experimental Example 4: XPS Spectral Analysis of SEO-Graphene

[0325] As shown in Fig. 4(d), the chemical composition of SEO-graphene was analyzed using XPS spectroscopy. As shown in Fig. 4(d), the graphene flakes were confirmed to be composed of 81 to 90% carbon and 10 to 19% oxygen. Figure 5 shows the survey scans of pure graphene and SEO-graphene, indicating high purity with only carbon and oxygen present. The platinum (Pt) peak detected in the survey scans originates from the substrate used to prepare the XPS specimen. The high purity SEO-graphene confirms that our simple purification process is effective in producing high-purity SEO-graphene. As the Ox / G ratio increases, the carbon content gradually decreases from 89.37% in graphene to 81.13% in 1.7-SEO-graphene, while the oxygen content increases in proportion to the decreased carbon content.

[0326] The high oxidation level of SEO-graphene with increasing Ox / G ratio is consistent with the results of Raman scattering and XRD data. As shown in Figure 6, the C1s peak of SEO-graphene was resolved into six major oxygen-containing functional groups: C=C (284.6 eV), C-C (285.5 eV), C-OH (286.3 eV), C-O-C (287.4 eV), C=O (287.7 eV), and C(O)OH (288.6 eV). The C-OH group was found to be the most dominant oxygen-containing group in all SEO-graphene samples. At an Ox / G ratio of 1.7, SEO-graphene begins to exhibit more intense peaks of C=O and C-O-C groups. These results are consistent with those of GO in the reference.

[0327]

[0328] Experimental Example 5: Dispersibility of SEO-graphene in various solvents

[0329] As shown in Fig. 4(e), the dispersibility of SEO-graphene with different Ox / G ratios was evaluated by measuring the zeta potential of aqueous SEO-graphene samples. All SEO-graphene samples exhibited zeta potential values ​​more negative than -35 mV, with the 0.7-SEO-graphene and 1.7-SEO-graphene samples exhibiting highly negative values ​​of -41 and -45 mV, respectively. The negative charge of SEO-graphene flakes is the result of ionization of oxygen-containing functional groups. According to the ASTM standard for the stability of colloidal suspensions, zeta potential values ​​between |31| and |40| mV indicate moderate stability without aggregation, and values ​​between |41| and |50| mV indicate good stability. According to these criteria, all SEO-graphene can be dispersed in water without aggregation, and the 0.7-SEO-graphene and 1.7-SEO-graphene samples are highly dispersed. The 0.7-SEO-graphene sample is more interesting because it maintains a higher graphitic structure than the 1.7-SEO-graphene sample according to Raman scattering, XRD, and XPS data.

[0330] Therefore, as shown in Fig. 4(e), the zeta potential values ​​were measured in relation to the pH value. As is typically observed in GO samples, the aqueous dispersibility of 0.7-SEO-graphene was found to be pH-sensitive. 0.7-SEO-graphene can be stably dispersed in the pH range of 5–8. The highest dispersibility is likely around pH 9, above which the dispersibility decreases due to compression of the double layer at high ionic strength.

[0331] As shown in Figure 7, to further investigate the solvent dispersibility of SEO-graphene, the dispersibility of pure graphene and SEO-graphene with different Ox / G ratios in nine different solvents was compared. All tested graphene dispersions at a concentration of 0.5 mg / mL were initially well dispersed in all solvents and then allowed to settle for a week. The pure graphene dispersions began to settle immediately and mostly completely settled in MeOH, IPA, 2ME, DMF, and ACN after a week. In solvents such as water, EtOH, NMP, and H2O / EtOH, pure graphene exhibited better dispersibility, but most of the graphene sheets still settled. Meanwhile, 0.3-SEO-graphene exhibited excellent dispersibility in water, 2ME, NMP, and H2O / EtOH, and slightly dispersibility in ACN. In addition to these solvents, IPA was found to be a dispersing solvent for 0.7-SEO-graphene. Adding additional oxidized EtOH to the list of good solvents with an Ox / G ratio of 1.0 resulted in six out of nine dispersible solvents. However, 1.7-SEO-graphene recovered its universal dispersibility, exhibiting excellent dispersibility in all solvents except DMF. The excellent dispersibility of all aqueous SEO-graphene dispersions was expected based on their zeta potential values. Notably, IPA and 2ME, widely used in industry, were also found to be excellent dispersing solvents for SEO-graphene. Furthermore, fine-tuning the edge oxidation level provides flexible options for selecting good dispersing solvents, potentially enabling the use of SEO-graphene in a wider range of solvents.

[0332]

[0333] Experimental Example 6: Analysis of Pristine and SEO-Graphene Filter Cake Samples

[0334] As shown in Fig. 2(f) and Fig. 8, since the structural integrity of graphene is directly related to its electrical properties, the electrical properties of the pure and SEO-graphene samples were evaluated by measuring the sheet resistance of graphene filter cakes made with each sample. The graphene filter cakes were prepared by vacuum filtration of 60 mL of graphene dispersion (1 mg / mL) on a membrane filter. Pure graphene exhibits a sheet resistance of 25 Ω / sq. Interestingly, 0.3-SEO-graphene exhibits improved electrical properties compared to pure graphene, with a sheet resistance of 14 Ω / sq. 0.7-SEO-graphene also exhibits the same sheet resistance as 0.3-SEO-graphene, which is reasonable considering the similar Raman scattering, XRD, and XPS results for the two samples. However, the improved electrical properties compared to pristine graphene are remarkable because pristine graphene has better structural integrity than 0.3- and 0.7-SEO-graphene. We will later discuss how the thinner and higher purity characteristics of SEO-graphene flakes, ensured by edge oxidation, contribute to their superior electrical properties. The sheet resistances of 1.0- and 1.3-SEO-graphene increase to 141 Ω / sq and 159 Ω / sq, respectively, indicating that higher levels of edge oxidation degrade the electrical properties at Ox / G ratios above 1.0. Furthermore, the sheet resistance values ​​show greater variation than those of 0.3- and 0.7-SEO-graphene, indicating that a lower level of edge oxidation is more advantageous for producing more uniform SEO-graphene. 1.7-SEO-graphene causes cracks in the filter cake, making the sheet resistance unmeasurable. These findings demonstrate that the optimal level of selective edge oxidation of graphene produces graphene sheets with high dispersibility and excellent electrical properties in various solvents, even superior to those of pristine graphene.

[0335]

[0336] Experimental Example 7: Confirmation of Selective Edge Oxidation of Graphene

[0337] As shown in Figures 9(a) and (b), 0.7-SEO-graphene flakes were characterized using HRTEM to confirm selective edge oxidation of graphene. As can be seen from the structural characterization results, the entire area of ​​the 0.7-SEO-graphene flakes exhibits high crystallinity with bright spots in the FFT image, indicating well-structured graphene flakes. However, as shown in Figure 9(c), the HRTEM image of the edge of the flakes shows a somewhat amorphous phase compared to the interior region. Comparison of the FFT images between the edge and interior regions also suggests different degrees of crystallinity, with bright diffraction spots in the interior region and broad spots at the edge, indicating that the edge of the flakes is selectively more oxidized than the interior region. The EEL spectrum of the 0.7-SEO-graphene flakes scanned across the surface region further confirms that the edge region has a higher content of oxygen-containing functional groups than the interior region. These results provide clear evidence that SEO-graphene flakes undergo selective edge oxidation along the edge region while maintaining excellent structural integrity in the remaining region.

[0338]

[0339] Experimental Example 8: Characterization of c-graphene and SEO-c-graphene

[0340] To evaluate the general applicability of the SEO-graphene process to commercial graphene powder, we performed edge oxidation on commercial graphene flakes (c-graphene) using an approach similar to that used for FLPE-produced graphene. Figure 10 compares the sheet resistance values ​​between pristine c-graphene and c-SEO-graphene with different Ox / G ratios. The initial sheet resistance of pristine c-graphene was measured at 76 Ω / sq. However, after edge oxidation at an Ox / G ratio of 0.12, the sheet resistance significantly decreased to 7 Ω / sq. Similar sheet resistance values ​​were observed up to an Ox / G ratio of 0.7, above which the sheet resistance increased substantially to 49 K Ω / sq. This edge oxidation trend for c-graphene is consistent with that observed for FLPE-produced graphene, indicating that our SEO-graphene process is generally applicable regardless of the graphene production method. One interesting finding is that c-graphene exhibits an order of magnitude decrease in sheet resistance after edge oxidation, which is much larger than the two-fold decrease in graphene produced by FLPE. To investigate the reason for the significant improvement in electrical properties, we compared the structural and chemical properties of pristine c-graphene and c-graphene oxidized to an Ox / G ratio of 0.3 (0.3-SEO-c-graphene). As shown in Figure 10, a comparison of Raman scattering data reveals a slightly broadened G-band peak and a higher intensity in the D-band peak in 0.3-SEO-c-graphene compared to pristine c-graphene. Similarly, a comparison of XRD patterns indicates a higher degree of oxidation in 0.3-SEO-c-graphene (1.07), as evidenced by a marginal peak shift to 0.44º and a slightly higher FWHM value for 0.3-SEO-c-graphene compared to pristine c-graphene (0.784). These comparisons suggest that 0.3-SEO-c-graphene exhibits greater oxidation than pristine c-graphene, even though the oxidation state is minimal. The characterization techniques mentioned above are comparable to those of c-graphene and 0.Although TEM analysis did not provide any distinct differences between 3-SEO-c-graphene and 0.3-SEO-c-graphene, it provides clear evidence for improved electrical properties in 0.3-SEO-c-graphene.

[0341] As shown in Figure 11, TEM analysis reveals a range of thicknesses from few-layer graphene to thick graphite microplatelets. In addition, spherical impurities were observed on the surface of the c-graphene flakes. In contrast, as shown in Figures 10(d–e) and 12, the 0.3-SEO-c-graphene flakes exhibit much thinner dimensions and higher purity without spherical impurities, and oxidized zones ∼3 nm wide are observed along the edges, similar to those observed in the FLPE-produced graphene flakes. This suggests that the impurities were dissolved during the synthesis and purification of SEO-graphene. The observed thinning of the flakes is very intriguing, as no intentional exfoliation process was performed. This suggests that the c-graphene underwent exfoliation due to repeated sonication during the purification process. To support this hypothesis, SEM characterization of 0.3-SEO-c-graphene flakes obtained after a single sonication is shown in Figure 13. Edge expansion was observed at the flake edges, which is due to the selective attachment of oxygen-containing functional groups to these regions. The expanded edge layer facilitates exfoliation during subsequent sonication. Atomic force microscopy (AFM) analysis showed that the average thickness of c-graphene decreased from 68.1 nm to 1.5 nm after selective edge oxidation. A more strategic sonication process could produce multi-layer graphene flakes. For graphene flakes produced by FLPE, selective edge oxidation did not significantly improve the electrical properties because the flakes were already few-layer graphene flakes.

[0342] As shown in Figure 14, the dispersibility of 0.3-SEO-c-graphene flakes was tested in H2O, IPA, 2ME, NMP, and H2O / EtOH (5:5) solvents. These solvents, which showed good dispersibility for 0.7-SEO-graphene flakes, were also found to be good solvents for 0.3-SEO-c-graphene flakes. These results demonstrate that selective edge oxidation can produce high-quality graphene flakes with improved dimensions and purity along with improved dispersibility.

[0343] As shown in FIGS. 15 to 17, the AFM analysis results of commercial graphene all showed that the thickness was 3 nm or more, and that it was in fact graphite microplatelets with a thickness of 10 or more sheets, whereas SEO-c-graphene was found to be few-layer graphene with a thickness of 1.5 nm or less.

[0344]

[0345] Comparative Experimental Example 1: Measurement of the Characteristics of SEO-Graphene Manufactured Using the Hummer Method

[0346] The characteristics of Indian graphene (Graphene), SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method are shown in Fig. 18.

[0347] FIG. 18 shows the FWHM(G) according to the Raman scattering ID / IG of (a) Indian graphene, SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method according to a comparative experimental example of the present invention, (b) XRD of Indian graphene, SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method, (c) filter cake photograph and measured sheet resistance of SEO-c-graphene produced by the traditional Hummer method, (d) Raman scattering of Indian graphene, SEO-c-graphene (I-SEO) synthesized by the improved Hummer method, and SEO-c-graphene (H-SEO) produced by the traditional Hummer method, (e) Indian graphene and SEO-c-graphene synthesized by the improved Hummer method. Comparison of the sheet resistance values ​​of SEO-c-graphene (I-SEO) and SEO-c-graphene (H-SEO) produced by the traditional Hummer method.

[0348]

[0349] Experimental Example 9: Characteristic Analysis of Inkjet Printing Ink and Dispenser Printing Ink

[0350] As shown in Fig. 19(a), 0.3-SEO-GM was dispersed in H2O at a concentration of 1.0 mg / mL without a dispersant for pure aqueous inkjet printing. The UV-vis spectrum of the ink exhibited an absorption peak at 269 nm. Stable droplet release was achieved without secondary droplets. A rectangular graphene pattern (1 mm wide, 3 mm long) was printed on photographic paper after 50 passes. The pattern was air-dried for 12 h without post-processing. As shown in Fig. 19(c), the cross-linked network of graphene flakes resulted in a sheet resistance of 1.46 kΩ / sq, which surpassed the printed rGO and graphene patterns.

[0351] The present invention pioneers the application of pure aqueous graphene dispersions to inkjet printing, enabling the environmentally friendly and efficient production of graphene patterns. Optimizing parameters and substrates can improve electrical conductivity. As shown in Figure 19(e)d, the successful printing of the university logo confirmed stable jetting performance.

[0352] For dispenser printing, continuous filament ink and paste graphene ink with a high graphene content are required to obtain precise patterns. Dispersants are typically used to achieve stable dispersion of graphene flakes, but we developed dispenser graphene ink using only EtOH / H2O solvent (5:5) and 0.3-SEO-GM at a high concentration of 105 mg / mL. As shown in Figure 21(a), the ink exhibits shear-thinning behavior, with the viscosity decreasing with increasing shear rate. As shown in Figure 21(b), the storage modulus (G') is higher than the loss modulus (G'') across the entire angular frequency range, indicating suitable rheological properties. As shown in Figure 21(c), line patterns of various widths and heights were successfully printed on a PI substrate by adjusting the printing speed and pressure. The printed line patterns were air-dried for 12 hours without post-processing. As shown in Fig. 21(c), a 1200 μm line pattern formed by densely interconnected graphene flakes exhibited a sheet resistance of 250 Ω / sq. As shown in Fig. 20(c), a university logo was printed on a PET substrate to demonstrate the ability to print large-area graphene patterns using dispenser printing. The successful application of this ink for dispenser printing highlights the excellent dispersibility of 0.3-SEO-GM in EtOH / H2O solvents. This ink formulation holds great potential for various applications, particularly in industrial fields.

[0353]

[0354] Experimental Example 10: Characterization of Nanocomposite Ink and Transparent Film

[0355] As shown in Fig. 22, the nanocomposite ink was confirmed to be stably dispersed at all mass ratios of PEDOT:PSS to 0.3-SEO-c-graphene. Fig. 23 shows that the nanocomposite ink exhibits absorption peaks at 205 nm and 230 nm, corresponding to 0.3-SEO-c-graphene and PEDOT:PSS, respectively. As shown in Fig. 23, increasing the amount of PEDOT:PSS in the nanocomposite ink broadens the absorption peak at 230 nm, while the 205 nm peak decreases. This observation suggests that the stability of the nanocomposite ink is maintained over all weight ratios of PEDOT:PSS. The sheet resistance of the nanocomposite film fabricated by repeated spin-coating for 15 cycles using 0.5 w / w ink was significantly reduced to 120 kΩ / sq. The sheet resistance was further reduced to 15 kΩ / sq when using a higher weight ratio nanocomposite ink of 2.70 w / w. Increasing the spin-coating cycle to 50 times resulted in a sheet resistance of 3.4 kΩ / sq. As shown in Figure 24, the transmittance of all films exceeded 80% at 550 nm. The sheet resistance of the pure PEDOT:PSS film was 1,000 kΩ / sq, which was 10 times higher than that of the nanocomposite ink prepared with the same amount of PEDOT:PSS. This difference in sheet resistance can be attributed to the difference in film morphology.

[0356] As shown in Figure 25, the pure PEDOT:PSS film exhibits irregularity with void regions on the film surface, whereas the nanocomposite film exhibits relatively high uniformity in coverage. The pure PEDOT:PSS film exhibits a sheet resistance of 1,000 kΩ / sq, while the nanocomposite film has a sheet resistance of 100 kΩ / sq. The pure PEDOT:PSS film was prepared from a 0.1 w / w PEDOT:PSS solution (PEDOT:PSS / IPA), and the nanocomposite film was prepared by mixing 0.3 mg of 0.3-SEO-c-graphene into a 0.1 w / w PEDOT:PSS solution. Both films were air-dried at room temperature for 12 h before measuring the sheet resistance and AFM characterization. The root-mean-square (RMS) surface roughness was measured to be 1.224 nm and 2.450 nm for the pure PEDOT:PSS and nanocomposite films, respectively.

[0357] As shown in Figure 26, the transmittance and sheet resistance performances of the nanocomposite film are similar to those of reported transparent graphene films. The nanocomposite film comprising PEDOT:PSS / 0.3-SEO-c-graphene corresponds to a sample fabricated with 2.70 w / w ink and 50 spin-coating cycles. The post-treatment methods used for the reported films were as follows: [1], [2], [8],

[0015] thermal reduction at 1100 °C, [3] annealing at 250 °C for 2 h in argon / hydrogen atmosphere, [4] thermal reduction at 200 °C or 400 °C in hydrazine or argon / hydrogen atmosphere, [5] vacuum annealing at 1100 °C or a combination of hydrazine treatment and annealing at 400 °C in argon atmosphere, [6] heating at 2250 °C for ~ 4 h, [7] thermal reduction at 600-1,000 °C in argon, hydrazine or hydrogen atmosphere, [9] heating at 500 °C for 2 h,

[0010] ,

[0012] chemical reduction (hydrazine monohydrate) 12 h at 80 °C,

[0011] in DCE-PmPV. Thermal exfoliation,

[0013] thermal reduction in a hydrazine atmosphere at 500°C, and

[0014] thermal reduction in a hydrazine atmosphere at 200°C. In particular, the nanocomposite film does not require post-treatment because no additives were used, unlike reported graphene films that often require lengthy post-treatment processes such as thermal or hydrazine reduction. Raman spectra of pure PEDOT:PSS and nanocomposite films are shown in Fig. 27. The vibrational modes of PEDOT:PSS were observed at wavenumbers 1566 cm-1, 1506 cm-1, 1441 cm-1, 1362 cm-1, 1246 cm-1, and 1131 cm-1. The bands at 1566 cm-1, 1506 cm-1, 1441 cm-1, 1362 cm-1, 1246 cm-1, and 1131 cm-1 correspond to the asymmetric stretching of carbon-carbon (C=C) bonds.Asymmetric stretching of carbon-carbon (C=C) bonds, symmetric stretching of C=C bonds, stretching vibration of carbon-carbon (C-C) bonds, inter-ring stretching vibration between carbon atoms (C-C), and stretching of carbon-oxygen (C-O). For the nanocomposite film, the Raman mode appears at 2703 cm-1, which corresponds to the 2D band of graphene. In addition, the mode of the aromatic ring stretching vibration (C-C) is strengthened because this mode overlaps with the G band of the graphite structure. The band at wavenumber 2876 cm-1 indicates the integration of PEDOT:PSS and 0.3-SEO-c-graphene in the PEDOT structure. The Raman spectrum indicates that the nanocomposite film has the combined characteristics of PEDOT:PSS and graphene.

[0358]

[0359] By means of solving the above problem, the present invention can provide an ink composed only of a pure solvent and graphene particles without a dispersant.

[0360] In addition, the present invention can provide ink that can be naturally dried in the air after printing without the existing post-processing process using high temperature and light.

[0361] In addition, the present invention can provide not only low-concentration graphene ink but also high-concentration and high-viscosity water-based graphene ink.

[0362] In addition, the present invention can well maintain the structural, electrical, and chemical properties, which are the inherent characteristics of graphene, through selective edge oxidation of graphene particles.

[0363] In addition, the present invention can stably disperse the polymer in various solvents, including water, for a long period of time by controlling the degree of edge oxidation.

[0364] Additionally, the present invention can improve the production and purity of graphene having a thinner thickness than the initial graphene.

[0365] In addition, the present invention can develop a graphene ink without a dispersant.

[0366]

[0367] In this way, it will be understood by those skilled in the art that the technical configuration of the present invention described above can be implemented in other specific forms without changing the technical idea or essential features of the present invention.

[0368] Therefore, the embodiments described above should be understood as being exemplary and not restrictive in all respects, and the scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A step for preparing a graphene oxide dispersion by dispersing edge-on graphene oxide particles in distilled water; Including an inkjet printing ink manufacturing step of centrifuging the edge oxide graphene dispersion dispersed in the distilled water and then taking the upper liquid; The above edge oxide graphene is, Graphene flake manufacturing step for manufacturing graphene flakes; A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above; A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated; A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent; An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes; An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed in a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed; A SEO-graphene flake precipitation step of centrifuging the above ultrasonically treated oxidized mixture to precipitate SEO-graphene flakes; A method for manufacturing an inkjet printing ink based on edge-oxidized graphene, characterized in that it comprises a SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them by ultrasonic treatment.

2. In paragraph 1, The above graphene flake manufacturing step is, A graphite dispersion preparation step for preparing a graphite dispersion by dispersing graphite powder in deionized water containing sodium dodecyl sulfate (SDS); A graphite dispersion exfoliation step in which the graphite dispersion prepared above is exfoliated after ultrasonic treatment; A method for manufacturing an inkjet printing ink based on edge-oxidized graphene, characterized in that it comprises a graphene flake separation step of manufacturing graphene flakes by centrifuging the above-described exfoliated graphite dispersion.

3. In paragraph 1, In the above graphene flake redispersion step, A method for manufacturing edge-oxidized graphene-based inkjet printing ink, characterized in that the above sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent is mixed in a ratio of 9:

1.

4. In paragraph 1, In the above oxidizing agent addition step, A method for manufacturing edge-oxidized graphene-based inkjet printing ink, characterized in that the oxidizing agent is potassium permanganate (KMnO4).

5. Including an inkjet printing ink manufactured by dispersing the edge oxide graphene particles in distilled water, The above edge oxide graphene is, An edge-oxidized graphene-based inkjet printing ink characterized in that the edges are selectively oxidized by oxidizing graphene flakes using an oxidizing agent.

6. In paragraph 5, An edge-oxidized graphene-based inkjet printing ink, characterized in that the oxidizing agent is 0.3 to 1.7 parts by weight of the graphene flakes.

7. In paragraph 5, An edge-oxidized graphene-based inkjet printing ink, characterized in that the sheet resistance of the oxidized graphene is 14 Ω / sq when the oxidizing agent is 0.3 and 0.7 parts by weight relative to 1 part by weight of the graphene flake.

8. In paragraph 5, An inkjet printing ink based on edge-oxidized graphene, characterized in that when the oxidizing agent is 0.3 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, an XRD peak of (002) basal plane diffraction of the edge-oxidized graphene appears at 2θ = 26.10º to 26.40º, and when the oxidizing agent is 1.0 to 1.7 parts by weight relative to 1 part by weight of the graphene flake, a new XRD peak of the edge-oxidized graphene is formed at 13.80º to 12.15º.

9. In paragraph 5, An edge-oxidized graphene-based inkjet printing ink, wherein the graphene flakes are characterized by being composed of 81 to 90% carbon and 10 to 19% oxygen.

10. A step for preparing a graphene oxide dispersion by dispersing edge-on graphene oxide particles in distilled water; A step of producing an edge oxide graphene particle filter cake by vacuum filtering the edge oxide graphene dispersion dispersed in the distilled water using a polytetrafluoroethylene (Hydrophilic membrane, HP020047D) filter; A step for manufacturing ink for Spencer printing, which comprises taking edge oxide graphene particles from the above-mentioned filter cake, immersing them in a mixture of distilled water and ethanol, and then mixing them; The above edge oxide graphene is, Graphene flake manufacturing step for manufacturing graphene flakes; A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above; A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated; A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent; An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes; An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed in a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed; SEO-graphene flake precipitation step of centrifuging the above ultrasonic treated oxidation mixture to precipitate SEO-graphene flakes; A method for manufacturing edge-oxidized graphene-based dispenser printing ink, characterized by comprising an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them through ultrasonic treatment.

11. Including ink for Spencer printing manufactured by taking edge oxide graphene particles from a filter cake obtained by vacuum filtering the edge oxide graphene dispersion dispersed in distilled water, The above edge oxide graphene is, Edge-oxidized graphene-based dispenser printing ink characterized in that graphene flakes are oxidized using an oxidizing agent and edges are selectively oxidized.

12. In paragraph 11, Edge-oxidized graphene-based dispenser printing ink, characterized in that the oxidizing agent is 0.3 to 1.7 parts by weight of the graphene flakes.

13. A step for preparing a graphene oxide dispersion by dispersing edge-oxidized graphene particles in a PEDOT:PSS solution dispersed in IPA; A nanocomposite manufacturing step of centrifuging the above graphene oxide dispersion and then taking the supernatant; A ratio control step for controlling the ratio of PEDOT:PSS to graphene oxide particles (PEDOT:PSS / edge graphene oxide, w / w) in the above nanocomposite; A glass substrate manufacturing step for converting hydrophilicity of a glass substrate to be used as a film substrate through UV treatment and ozone treatment; A nanocomposite deposition step of spin-coating and depositing the nanocomposite with the above-described ratio on the hydrophilic-converted glass substrate; A film manufacturing step of manufacturing a transparent film by drying a glass substrate on which the above nanocomposite is deposited at room temperature; The above edge oxide graphene is, Graphene flake manufacturing step for manufacturing graphene flakes; A graphene flake precipitation step of centrifuging and precipitating the graphene flakes manufactured above; A graphene flake redispersion step in which the above-deposited graphene flakes are redispersed in a sulfuric acid / phosphoric acid (H2SO4 / H3PO4) solvent and then ultrasonically treated; A graphene flake heating and stirring step of heating and stirring graphene flakes redispersed in the solvent; An oxidizing agent addition step of preparing an oxidizing mixture by adding an oxidizing agent to the heated and stirred graphene flakes; An oxidation mixture ultrasonic treatment step in which the above oxidation mixture is mixed with a distilled water / ethanol (DI water / EtOH) solvent, hydrogen peroxide (H2O2) is added, and then ultrasonic treatment is performed; SEO-graphene flake precipitation step of centrifuging the above ultrasonic treated oxidation mixture to precipitate SEO-graphene flakes; A method for manufacturing a transparent film using an edge-oxidized graphene PEDOT:PSS nanocomposite, characterized by including an SEO-graphene flake purification step of redispersing the precipitated SEO-graphene flakes in a distilled water / ethanol (DI water / EtOH) solvent and then purifying them by ultrasonic treatment.

14. A nanocomposite prepared by dispersing the edge-oxide graphene particles in a PEDOT:PSS solution dispersed in isopropyl alcohol (IPA); and A transparent film deposited by spin-coating the above nanocomposite on a glass substrate; including, The above edge oxide graphene is, A transparent film using an edge-oxidized graphene PEDOT:PSS nanocomposite, characterized in that graphene flakes are oxidized using an oxidizing agent and edges are selectively oxidized.

15. In paragraph 14, A transparent film using the above nanocomposite, characterized in that the transparent film using the edge oxide graphene PEDOT:PSS nanocomposite has an optical transparency of 80% or more based on a wavelength of 550 nm.

16. In paragraph 14, A transparent film using edge oxide graphene PEDOT:PSS nanocomposite, characterized in that the transparent film using the above nanocomposite has a sheet resistance of 3.4 Ω / sq or less.

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