KR101465656B1 - Method of alignment of graphene oxide, Method of moving of graphene oxide and optical device using the same - Google Patents

Abstract

The present invention relates to a method of aligning graphene oxide, a method of moving the graphene oxide and an optical device using the same. More particularly, the present invention relates to a method of aligning graphene oxide to easily control the concentration of the graphene oxide, a method of moving the graphene oxide and an optical device using the same. a method of aligning graphene oxide according to an embodiment of the present invention includes a step of applying an AC electric field to at least one graphene oxide solution among (1-1) biphase (B), isotropic (I), and nematic (N) phase. According to an embodiment of the present invention, the frequency of the AC electric field is 100Hz to 7MHz.

Description

TECHNICAL FIELD The present invention relates to a graphene oxide alignment method, a graphene oxide migration method, and an optical device using the graphene oxide graphene oxide.

The present invention relates to a graphene oxide alignment method, a moving method and an optical device using the same.

Recently, graphene oxide and functionalized graphene oxide based on graphene or graphene structures have been attracting attention. This is because these materials have excellent mechanical and electro-optical characteristics, respectively. In general, it has a two-dimensional molecular structure with an area of several um or more in comparison with a thickness of about 1 nm, so that there is a wide variety of applications using the same. On the other hand, as is well known in the case of graphene, pure carbon-to-carbon sp2 bonds have been attracting attention as a next-generation material that can be used in various fields of devices because of its excellent electrical and thermal conductivity as well as mechanical stiffness characteristics. The possibility of application as a biosensor or a filter has been attracting attention.

Unlike graphene, graphene oxide is well dispersed in common distilled water, and it can be produced in large quantities from graphite by a relatively easy chemical method. Graphene oxide has attracted attention as a precursor of graphene because graphene can be produced through appropriate reduction process based on these advantages.

These materials have recently been found to have liquid crystals on their respective suitable solvents (Graphene raphene Oxide Liquid crystals, Angew. Chem. Int. Ed., 2011, 50, 3043-047). Generally, when a liquid crystal phase is generated, various applications are possible in terms of control of materials, and thus, it presents new possibilities in terms of application using the above materials.

As mentioned above, graphene oxide can be used as a precursor of graphene. At present, graphene fabrication is considered to include deposition using CVD, which requires large equipment, and methods using tape, which have limitations in large area manufacturing. Graphene oxide is easy to fabricate, and it is easy to control using the characteristics of the liquid crystal phase, so one direction can be presented for graphene production.

Up to now, there have been proposed methods using graphene oxide liquid crystals using a magnetic field or spraying at a constant pressure, or using graphene oxide flakes aligned at the interface between water and air. On the other hand, the method of controlling the alignment of the liquid crystal phase using the electric field is easily used in various devices using conventional liquid crystals. However, as mentioned in the reference document, when DC voltage is used, graphene oxide flakes It has a disadvantage in that it is difficult to use in an aqueous solution because the flakes are aligned using a high voltage in a nematic state even when an AC voltage is applied.

Materials such as graphene oxide are generally classified as lyotropic liquid crystals because of their anisotopic structure, and nematic liquid crystals appear at higher concentrations. In the case of graphene oxide, (flake) interaction is so large that it does not react easily to the electric field.

Graphene raphene Oxide Liquid crystals ", Angew. Chem. Int. Ed., 2011, 50, 3043-047

It is an object of the present invention to provide a method of aligning graphene oxide in a predetermined direction in a low-magnitude electric field.

It is a further object of the present invention to provide a method of transferring graphene oxide in a desired direction.

It is another object of the present invention to provide a method for easily controlling the concentration of graphene oxide.

It is still another object of the present invention to prepare an optical device having various structures by easily controlling the directionality or concentration of graphene oxide.

In order to achieve the above object, the graphene oxide aligning method of the present invention comprises the steps of: (1-1) applying an alternating electric field to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) And a step of applying

The concentration of the graphene oxide in the graphene oxide solution may be 0.007 to 5 wt%.

The frequency of the alternating electric field may be 100 Hz to 7 MHz.

The alternating electric field may have a spatially non-uniform distribution.

After the step (1-1), (2-1) evaporating the solvent in the graphene oxide solution may be further included.

In the step (2-1), the solvent may be evaporated in the graphene oxide solution to obtain a nematic phase having refractive index anisotropy or graphene oxide aligned in a desired direction.

In the step (1-1), the graphene oxide solution includes a photo-reactive monomer, and after applying the alternating electric field, light is applied to the graphene oxide solution to form graphene oxide-polymer Complex can be formed.

In the step (1-1), the graphene oxide solution may include PVA (polyvinylalcohol), and in the step (2-1), a graphene oxide-polymer complex may be formed.

In order to achieve the above object, the graphene oxide transfer method of the present invention comprises the steps of: (1-2) applying a graphene oxide solution to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) And moving graphene oxide in a desired direction.

The concentration of the graphene oxide in the graphene oxide solution may be 0.007 to 5 wt%.

The frequency of the alternating electric field may be 100 Hz to 7 MHz.

The alternating electric field may have a spatially non-uniform distribution.

The concentration of the graphene oxide can be controlled by the dielectrophoresis effect generated by the alternating electric field having the spatially nonuniform distribution.

After the step (1-2), (2-2) evaporating the solvent in the graphene oxide solution may be further included.

In step (2-2), the solvent may be evaporated in the graphene oxide solution to obtain a nematic phase having refractive index anisotropy or graphene oxide aligned in a desired direction.

In the step (1-2), the graphene oxide solution may include a photo-reactive monomer. After application of the alternating electric field, light is applied to the graphene oxide solution to form graphene oxide- Polymer complex can be formed.

In step (1-2), the graphene oxide solution includes polyvinylalcohol (PVA), and in step (2-2), a graphene oxide-polymer complex may be formed.

According to an aspect of the present invention, there is provided an optical device comprising: a graphene oxide cell; An electrode for applying a non-uniform electric field to the graphene oxide cell so that the induced birefringence phenomenon occurs in the graphene oxide cell; And an optical device disposed above and below the graphene oxide cell to utilize the induced birefringence phenomenon generated in the graphene oxide cell.

The optical device may include at least one of a display, a retarder, and an optical film or a polarization controller.

In order to accomplish the above object, the optical device of the present invention may include an optical grating according to a periodic change in graphene oxide concentration.

In order to accomplish the above object, the electric device of the present invention can be used by reducing graphene oxide, which is uniformly aligned in a desired direction or moved to a desired position, to graphene.

According to the present invention, graphene oxide can be aligned in a low electric field by using a graphene oxide solution having a low concentration.

Further, the present invention has an advantage in that an optical device having various structures can be manufactured by easily controlling the concentration or directionality of graphene oxide.

1 is a graphite oxide solution divided into nematic and isotropic states,
FIG. 2 is a graph showing the calculation of the volume fraction of a nematic portion as a function of graphene oxide concentration dispersed in distilled water,
FIG. 3 is a graph showing the isotropic (I), ideality (B) and nematic (N) phases of graphene oxide depending on graphene oxide concentration and average grain size dispersed in distilled water,
FIG. 4 is a graph showing the isotropic (I), ideality (B), and nematic (N) phases of the graphene oxide according to the graphene oxide concentration and pH,
FIG. 5 is a photograph of a state of a graphene oxide cell with a thickness of 0.3 mm,
FIG. 6 is a photograph of a state in which no electric field is applied to the graphene oxide solution,
FIG. 7 is a photograph of a state in which an electric field is applied to a graphene oxide solution,
8 is a graph showing induced birefringence (Induced? N) according to graphene oxide concentration,
9 is a graph showing the relationship between the concentration of graphene oxide and the Kerr coefficient value,
10 is a graph showing the induced birefringence (Induced? N) according to the frequency change of the alternating electric field applied to the graphene oxide solution,
11 is a photograph showing an alignment structure of graphene oxide according to a frequency change of an alternating electric field applied to a graphene oxide solution,
12 is a photograph showing the arrangement of graphene oxide according to the voltage arrangement of the electrodes arranged in a cross,
13 (a) is a photograph showing a before voltage before applying a voltage to the graphene oxide cell,
FIG. 13 (b) is a graph showing a photograph of a graphene oxide cell of FIG. 13 (a)
Fig. 13 (c) is a photograph obtained by disposing a polarizing plate having polarization axes perpendicular to each other above and below the graphene oxide cell in the state of Fig. 13 (b)
14 (a) is a photograph showing that the electric field is not applied to the low-concentration graphene oxide solution before evaporating the solvent,
14 (b) is a photograph showing the graphene oxide solution at a high concentration by evaporating the solvent without applying an electric field to the low-concentration graphene oxide solution of FIG. 14 (a)
15 (a) is a photograph showing an electric field applied to a low-concentration graphene oxide solution before evaporating the solvent,
15 (b) is a photograph showing the graphene oxide solution at a high concentration by evaporating the solvent in the graphene oxide solution in the state of Fig. 15 (a).

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

Figure 1 shows a graphene oxide solution divided into nematic and isotropic phases. When the graphene oxide solution is left in a small bottle for one week as shown in FIG. 1, it is divided into a nematic portion at the lower part of the bottle and an isotropic state at the upper part of the bottle. This overall condition is defined as a biphase.

FIG. 2 shows the result of calculating the volume fraction of a nematic portion as a function of graphene oxide concentration dispersed in distilled water. Although the concentration can be changed according to the quality of the prepared graphene oxide, in the case of the graphene oxide used in the present invention, an isotropic (I) phase is obtained at a concentration of about 0.007 wt% or less, and more than 2 wt% A nematic (N) is obtained. Biphase is obtained between these two concentrations.

5 is a microscopic observation of a state of a graphene oxide cell with a thickness of 0.3 mm. Referring to FIG. 5, an isotropic (I), an ideal (B), and a nematic (N) phase can be obtained according to a graphene oxide liquid crystal phase. The graphene oxide solution according to an embodiment of the present invention may mainly use the concentration of the ideality (B), and may use isotropic and nematic phase concentrations close to the concentration of the ideality.

FIG. 3 is a graph showing the isotropic (I), ideality (B) and nematic (N) phases of graphene oxide according to graphene oxide concentration and average grain size dispersed in distilled water, (I), the ideality (B) and the nematic (N) phase of graphene oxide in accordance with the concentration of graphene oxide and pH.

The graphene oxide alignment method according to an embodiment of the present invention may preferably include applying an alternating electric field to an isotropic phase or an ideal phase (B) phase graphene oxide solution. And applying an alternating electric field to the graphene oxide solution on a nematic (N) phase that is imperfectly close to the ideal. Here, the graphene oxide solution has a concentration before the visible nematic phase is visible, and the macroscopic refractive index anisotropy of the graphene oxide can be easily induced even in a low magnitude electric field. The concentration of the graphene oxide solution according to one embodiment of the present invention can be determined as a median value of the concentration at which the ideality (B) is generated. Preferably, the concentration of graphene oxide in the graphene oxide solution may be 0.007 to 0.5 wt%, when the average particle size of graphene oxide dispersed in distilled water having a pH of 7 is 0.15 to 0.25 m. When the concentration of graphene oxide in the graphene oxide solution is less than 0.007 wt%, the concentration of graphene oxide is too low and the effect of alignment by the electric field is insignificant. When the concentration of graphene oxide is more than 0.5 wt% In this case, unlike ordinary liquid crystals, the interactions between graphene oxide particles are so large that alignment by the electric field is not impossible but not easy.

The liquid crystalline phase of graphene oxide may vary in phase depending on the density or particle size of the functional group attached to the graphene structure, and in some cases, a complete nematic liquid crystal phase may not appear up to 5%.

The macroscopic alignment effect of graphene oxide can be confirmed by induced birefringence due to external stimuli. FIGS. 6 and 7 are graphs showing induced birefringence of graphene oxide contained in an aqueous solution having an average particle size of 0.2 .mu.m and pH7 in order to confirm the alignment effect according to application of an electric field. FIG. It is shown that the electric field is not applied to the oxide solution, indicating that the induced birefringence phenomenon does not occur. Fig. 7 shows that induced birefringence phenomenon occurred when an electric field was applied to the graphene oxide solution. 6 and 7, it can be seen that alignment of graphene oxide occurs when an electric field is applied to the graphene oxide solution.

FIG. 8 is a result of measuring the induced birefringence (Induced? N) according to the concentration based on the results of FIG. 6 and FIG. Referring to FIG. 8, it can be seen that graphene oxide is produced by applying an electric field from a relatively low concentration of 0.025 wt%, which corresponds to an isotropic phase, to a 0.4 wt% (It is confirmed that the graphene oxide concentration can be aligned to 0.5 wt%, though it is not shown in the results). However, if the concentration of graphene oxide is more than 1 wt%, the nematic phase becomes stronger, and the alignment effect due to the electric field is not easily seen. Based on this, the Kerr coefficient corresponding to the induced birefringence that is proportional to the square of the electric field can be calculated. Referring to FIG. 9, when the concentration of graphene oxide is higher than a certain concentration, the Kerr coefficient value suddenly decreases.

FIG. 10 shows the induced birefringence (Induced Δn) according to the frequency change of the alternating electric field applied to the graphene oxide solution. The voltage magnitude of the alternating electric field applied to the graphene oxide solution is fixed at 10 V, And the induced birefringence value is measured by adjusting the frequency. Referring to FIG. 10, stable birefringence values are induced in the range of 2 kHz to 1 MHz, and birefringence is reduced to about half at 7 MHz. 11 shows the alignment structure of graphene oxide according to the frequency change of the alternating electric field applied to the graphene oxide solution. When the frequency of the alternating electric field applied to the graphene oxide solution is 500 Hz (a), it can be confirmed that the alignment of graphene oxide is stable. However, when the frequency of the alternating electric field applied to the graphene oxide solution is 100 Hz (b), it can be seen that alignment of graphene oxide is unstable. In addition, when the frequency of the alternating electric field applied to the graphene oxide solution is 50 Hz (c), it can be confirmed that electrolysis of the graphene oxide solution occurs. Referring to the results of FIGS. 10 and 11, it is preferable that the frequency of the alternating electric field applied to the graphene oxide solution is within a range of 100 Hz to 7 MHz.

Figure 12 shows that the arrangement of graphene oxide can be controlled according to the voltage arrangement of the electrodes arranged in a cross. Referring to FIG. 12, it can be seen that the direction of the applied alternating electric field varies according to the voltage arrangement applied to the graphene oxide solution, and the arrangement of the graphene oxide is controlled in various ways. By using the phenomenon in which the induced refractive index is generated by the voltage in this way, it can be applied to manufacture of displays and other electric devices.

13 shows an example of an optical grating according to a concentration change as an example of another application possibility according to the application of voltage of graphene oxide. This is due to the ununiformity of the ac electric field distribution applied to the graphene oxide solution and the spatial shift of graphene oxide. 13 (a) and 14 (b) show only a graphene oxide cell without a polarizer. Here, the graphene oxide cell is preferably a graphene oxide solution in a low isotropic or biphase state. 13 (a) shows a before voltage before applying a voltage to the graphene oxide cell, which shows that only the transparent electrode pattern is seen.

Fig. 13 (b) shows application of a non-uniform electric field to the graphene oxide cell of Fig. 13 (a) depending on the position. In one embodiment of applying a non-uniform electric field, different voltages are alternately applied to electrodes formed in a plurality of stripes arranged at regular intervals at a position applied to the graphene oxide cell depending on the position of the graphene oxide cell Lt; / RTI > When a non-uniform electric field is applied to the graphene oxide cell depending on the position, a dielectro-phoretic phenomenon occurs due to the electric field difference depending on the position, and the graphene oxide moves toward the electrode having a strong electric field. Accordingly, a difference in concentration of graphene oxide is generated for each position, so that a periodic pattern as shown in FIG. 13 (b) is formed to form an optical grating.

Fig. 13 (c) is a graph showing the results of indifferent birefringence obtained by arranging a polarizing plate having polarization axes perpendicular to each other above and below the graphene oxide cell in the state of Fig. 13 (b). Inductive birefringence does not occur under two polarizers perpendicular to each other if alignment is not achieved even though graphene oxide is moved to a strong electric field and there is a difference in concentration by position. That is, induced birefringence is generated by two polarizers perpendicular to each other as shown in FIG. 14 (c), which means alignment of graphene oxide occurs at a strong electric field.

In addition, the optical device according to an embodiment of the present invention may use a phenomenon in which different induced birefringence occurs as shown in FIG. 13 (c), and in addition to the optical grating shown in FIG. 13 (b) The birefringence phenomenon can be used. The optical device according to an embodiment of the present invention includes a graphene oxide cell, an electrode for applying an unequal electric field to the graphene oxide cell to cause induced birefringence in the graphene oxide cell, (E.g., a polarizing plate or a reflector) disposed above and below the graphene oxide cell to effectively utilize the induced birefringence phenomenon. Here, the optical device may include a display, a retarder, and an optical film, a polarization controller, and the like.

As shown in FIG. 13 (b), the optical device according to another embodiment of the present invention can generate a lattice structure due to absorption or concentration difference by generating a density difference arbitrarily. That is, according to another embodiment of the present invention, it is possible to manufacture an optical device in which an optical grating is formed according to a periodic change in graphene oxide concentration, without using a refractive index anisotropy or using a polarizing plate.

FIGS. 14 and 15 show the result of rotating the polarizing plate in such a manner that alignment is maintained while evaporating a solvent in a low concentration isotropic or biphase graphene oxide solution.

Figure 14 (a) shows that an electric field is not applied to a low concentration graphene oxide solution (for example, an isotropic phase or an ideal (B) phase) graphene oxide solution before evaporating the solvent, 14 (b) shows a state in which the low-concentration graphene oxide solution shown in FIG. 14 (a) is applied to a solvent (for example, 14 (a) and 14 (b), in which an electric field is not applied to the graphene oxide solution, are induced in graphene oxide solution It can be seen that the liquid crystal phase due to the occurrence of birefringence is not oriented in a certain direction.

15 (a) shows application of an electric field to a low concentration graphene oxide solution (for example, an isotropic phase or an ideality (B) phase) before evaporating the solvent. Referring to FIG. 15 (a), it can be seen that when an electric field is applied to a low concentration graphene oxide solution, graphene oxide is effectively generated without generating a discontinuity constant in the electric field direction in the electric field generation region. FIG. 15 (b) shows a graphene oxide solution at a high concentration by evaporating a solvent (for example, distilled water) in the graphene oxide solution in the state of FIG. 15 (a). Referring to FIG. 15 (b), graphene oxide effectively aligned in a certain direction by an electric field at a low concentration can be seen to be aligned even by evaporation of the solvent. Using this phenomenon, an electric field is applied to a low-concentration graphene oxide solution, and then the solvent is evaporated to obtain a nematic graphen oxide having a refractive index anisotropy or a graphen oxide arranged in a predetermined direction.

In the case of FIG. 15 (b), a polymer-stabilizable substance is added to the graphene oxide solution so as to effectively maintain the arrangement of graphene oxide when the solvent is evaporated, followed by a suitable treatment to form a polymer . In one embodiment, an alternating electric field is applied to a low-concentration graphene oxide solution to which a photo-reactive monomer is added, and then the graphene oxide solution is aligned in a predetermined direction. Then, light is applied to the graphene oxide solution, Oxide-polymer complexes. In another embodiment, an alternating electric field is applied to a low-concentration graphene oxide solution to which PVA (polyvinylalcohol) is added, and the solvent is evaporated to form a graphene oxide-polymer complex aligned in a predetermined direction . The graphene oxide formed by the polymer stabilization method has an advantage that the arrangement by the electric field is effectively maintained even when the solvent is evaporated.

According to an embodiment of the present invention, an electric device can be manufactured by reducing graphene oxide aligned in a desired direction or moved to a desired position. Here, examples of the electric device may include at least one of a light emitting device, a conductive thin film, a substrate, a transistor, a memory device, a solar cell, and an electrode.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions as defined by the following claims It will be understood that various modifications and changes may be made thereto without departing from the spirit and scope of the invention.

Claims (21)

delete delete Applying an alternating electric field to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) phase and a nematic (N) phase,
Wherein the frequency of the alternating electric field is 100 Hz to 7 MHz.
Applying an alternating electric field to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) phase and a nematic (N) phase,
Wherein the alternating electric field has a spatially non-uniform distribution.
delete delete (1-1) applying an alternating electric field to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) phase and a nematic (N) phase; And
After the step (1-1)
(2-1) evaporating the solvent in the graphene oxide solution,
In the step (1-1), the graphene oxide solution includes a photo-reactive monomer, and after applying the alternating electric field, light is applied to the graphene oxide solution to form graphene oxide-polymer ≪ / RTI >
In the step (2-1), the solvent is evaporated in the graphene oxide solution to obtain a nematic phase having refractive index anisotropy or graphene oxide aligned in a desired direction.
delete delete delete (1-2) a step of applying an alternating electric field to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) phase and a nematic (N) phase to move graphene oxide in a desired direction In the pin oxide transfer method,
Wherein the frequency of the alternating electric field is 100 Hz to 7 MHz.
(1-2) a step of applying an alternating electric field to at least one graphene oxide solution of an ideal (B) phase, an isotropic (I) phase and a nematic (N) phase to move graphene oxide in a desired direction In the pin oxide transfer method,
Wherein the alternating electric field has a spatially non-uniform distribution.
13. The method of claim 12,
The graphene oxide transfer method includes:
Wherein the graphene oxide concentration can be controlled by a dielectrophoresis phenomenon generated by an alternating electric field having a spatially nonuniform distribution.
delete delete 13. The method of claim 12,
After (1-2), (2-2) evaporating the solvent in the graphene oxide solution,
In the step (1-2)
Wherein the graphene oxide solution comprises a photo-reactive monomer, and after application of the alternating electric field, light is applied to the graphene oxide solution to form a graphene oxide-polymer complex Graphene oxide.
delete Graphene oxide cell;
An electrode for applying a non-uniform electric field to the graphene oxide cell so that the induced birefringence phenomenon occurs in the graphene oxide cell;
And an optical device disposed above and below the graphene oxide cell to utilize the induced birefringence phenomenon generated in the graphene oxide cell.
19. The apparatus of claim 18, wherein the optical device
A display, a retarder, and an optical film, and a polarization controller.
delete delete

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