CN110066484B - A carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties and preparation method thereof - Google Patents

Abstract

The invention discloses a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties and a preparation method thereof. The composite material is formed by uniform composite of carbon nanotubes, graphite and polyvinylidene fluoride; The total mass of nanotubes and graphite accounts for 16% to 20% of the mass percentage of the ternary composite material, and the balance is polyvinylidene fluoride; wherein, the mass ratio of carbon nanotubes and graphite is (1:1)～( 1:10). The method of the present invention comprises the following steps: step (1), respectively weighing carbon nanotube powder, graphite powder and polyvinylidene fluoride powder; step (2), mixing and dispersing the powders uniformly; step (3), Put the mixed powder into a mold for cold pressing. The "ternary" composite material of the present invention introduces a new functional body variable on the basis of the traditional binary composite material, so that the composite material has weak negative dielectric properties, and the value of the negative dielectric constant is easier to control.

Description

A carbon nanotube-graphite-polyvinylidene fluoride ternary composite with negative dielectric properties Materials and methods of making the same

technical field

The invention relates to the fields of composite material technology, metamaterial, radio frequency electromagnetic material technology, wireless power transmission and the like, in particular to a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties and a preparation method thereof.

Background technique

The dielectric constant is a basic parameter to characterize the physical properties of electromagnetic materials. When the dielectric constant is negative, it has important development in the fields of electromagnetic shielding and absorption. Moreover, when the material with negative permittivity is combined with the material with negative magnetic permeability, it has many novel electromagnetic properties, such as inverse Doppler effect, inverse Guss-Hans shift effect, negative refraction effect, etc. Microwave absorption and wireless power transmission have broad prospects and have become a research boom in recent years.

There are two preparation methods for negative dielectric materials: one is a material composed of artificial periodic arrays, also known as metamaterials, through resonance to achieve negative dielectric constant; the other is by changing the chemical composition and microstructure of the material. To achieve and control the negative dielectric constant, also known as supercomposite materials, which are generally composed of conductors and insulators, and belong to percolation composite materials.

Theoretical analysis shows that the negative permittivity is formed due to the plasmonic oscillation of delocalized electrons. When the conductive phase content is low, the isolated conductive phases are randomly distributed in the matrix, and the dielectric constant of the composite material is positive at this time, and increases slowly with the increase of the conductive phase content. When the content of the conductive phase is further increased to a critical value (that is, the percolation threshold), most of the conductive phase particles are gradually connected together, but some particles are still dispersed in the matrix in an isolated state. At this time, the dielectric constant of the composite material is given by Positive values turn into negative values, a phenomenon called percolation. The negative dielectric materials prepared in the past are often binary composite materials composed of a conductor and an insulator, and the negative dielectric constant can be achieved by controlling the content of the conductor. Binary composite materials have the disadvantages of unstable dielectric properties and excessively high absolute value of negative dielectric. At present, there are few reports on "ternary" composite materials. On the basis of the original "binary" composite material, another conductor is added in a certain proportion, which is the so-called "ternary" conductor 1-conductor 2- Insulator composites. Compared with binary composite materials, the use of ternary composite materials to achieve negative dielectric constant has obvious advantages. For example, the value of negative dielectric constant is easier to control in a smaller range, that is, the control is more precise. This ternary composite material with negative dielectric properties can have important research value and broad application prospects in applications such as communications, microwave absorption, wireless power transmission, and metamaterials.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the shortcomings of the existing binary composite materials such as unstable dielectric properties and too high absolute value of negative dielectric, and to provide a ternary composite with weak negative dielectric and the value of negative dielectric constant that is easier to control. Material.

In order to achieve the above purpose, the present invention provides a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties. The ternary composite material is composed of carbon nanotubes, graphite and polyvinylidene fluoride. Composite formation; the total mass of carbon nanotubes and graphite accounts for 16% to 20% of the mass percentage of the ternary composite material, and the balance is polyvinylidene fluoride; wherein, the mass ratio of carbon nanotubes and graphite is (1: 1) to (1:10).

Preferably, in the ternary composite material, the total mass of carbon nanotubes and graphite accounts for 16% of the mass percentage of the ternary composite material, and the balance is polyvinylidene fluoride; The mass ratio is (1:1) to (1:3).

Preferably, the carbon nanotubes have a diameter of 12-30 nm and a length of 0-6 μm.

The present invention also provides the above-mentioned preparation method of carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties, the method comprises the following steps:

In step (1), the carbon nanotube powder, the graphite powder and the polyvinylidene fluoride powder are respectively weighed, so that the total mass of the carbon nanotube powder and the graphite powder accounts for 16% of the mass of the ternary composite material. %～20%, the balance is polyvinylidene fluoride; the mass ratio of carbon nanotube powder and graphite powder is (1:1)～(1:10);

In step (2), the weighed carbon nanotube powder, graphite powder and polyvinylidene fluoride powder are poured into the grinding tank for random mixing and grinding, and then the powder is poured into the mortar for carrying out. Artificial shear mixing until all the agglomerated small particles of the powder are uniformly dispersed;

In step (3), the mixed powder is put into a mold and cold-pressed to obtain the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material.

Preferably, in step (1), the total mass of carbon nanotube powder and graphite powder accounts for 16% of the mass percentage of the ternary composite material, and the balance is polyvinylidene fluoride; carbon nanotube powder and graphite The mass ratio of the powder is (1:1) to (1:3).

Preferably, in step (2), the powder is mechanically centrifuged and mixed in a grinding tank for 15-25 min, and the rotating speed is 1000-2000 r.

Preferably, in step (2), the order in which the carbon nanotube powder, the graphite powder and the polyvinylidene fluoride powder are poured into the grinding tank is: first add the carbon nanotube powder and the graphite powder, and then add the polyvinylidene fluoride powder. Vinylidene fluoride powder.

Preferably, in step (3), the mixed powder is sieved through a 200-mesh sieve, and then put into a mold for cold pressing.

Preferably, the cold-press forming conditions are as follows: the forming pressure is 20-30 MPa, and the pressure-holding time is 15-20 min.

Compared with the prior art, the present invention can have the following beneficial effects:

(1) The design idea of the present invention is novel, breaking the preparation thinking of the original "binary" composite material, introducing a new functional body with strong electrical conductivity on the basis of the original "binary" composite material, and introducing a new functional body by changing The proportion of the dielectric constant is more controllable in a small range, that is, the control is more precise.

(2) The present invention fully considers the influence of the mixing uniformity on the negative dielectric constant, so the combination of mechanical grinding and manual grinding is used to make the obtained powder more uniform and easier to form a conductive grid.

(3) The preparation process of the present invention is simple, the cost is low, the mass production of products can be realized, and the present invention has a good market prospect. In this way, materials with negative dielectric properties can be obtained.

(4) By adjusting the content of carbon nanotubes and graphite in the functional body, a tunable negative dielectric constant can be obtained, which makes the dielectric constant selectable.

Description of drawings

FIG. 1 is a schematic structural diagram of a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material prepared by the present invention.

FIG. 2 is a graph showing the detection results of the dielectric constants of the composite materials prepared in Comparative Example 1, Example 1 and Example 2. FIG.

Detailed ways

In order to make the specific process and advantages of the present invention clearer, the following will be described in detail with reference to specific embodiments. It should be understood that these examples are intended to illustrate the present invention and not to limit the scope of the present invention. The implementation conditions used in the examples can be further adjusted according to specific conditions, and the unremarked implementation conditions are usually the conditions in routine experiments.

Materials, reagents, etc. used in the following examples can be obtained from commercial sources. Among them, the diameter of the carbon nanotubes used is 12-30 nm and the length is 6 μm.

In the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties of the present invention, carbon nanotubes and graphite are selected as functional bodies, that is, as conductive phases, because the free electrons of carbon nanotubes and graphite are The concentration is high, and the chemical stability of the carbon material is good. Use insulating polyvinylidene fluoride as the substrate. Polyvinylidene fluoride has a good process, and has excellent corrosion resistance, flexibility, and excellent high temperature color change resistance, which can make the ternary composite material simple to manufacture, excellent in performance, and conducive to multi-functionalization. The schematic diagram of the structure of the ternary composite material prepared by the present invention is shown in FIG. 1 .

Carbon nanotubes (CNT) and graphite are used as functional bodies, and polyvinylidene fluoride (PVDF) is used as the matrix. Since carbon nanotubes (CNT), graphite and polyvinylidene fluoride (PVDF) are all nano-scale powders, they are extremely easy to agglomerate. . The theory shows that the smaller the particle size and the lighter the mass, the more difficult it is to mix uniformly, so it is a difficult problem to make it evenly dispersed. In the invention, the carbon nanotube-graphite-polyvinylidene fluoride "ternary" composite material is prepared by using mechanical and manual grinding and cold-pressing forming processes.

Example 1

A method for designing a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties, comprising the following steps:

In step (1), 0.32 grams of functional body powder and 1.68 grams of polyvinylidene fluoride powder are respectively weighed with an electronic balance, so that the mass fraction of functional bodies in the composite material is 16%; the functional bodies contain 0.16 grams of carbon nanotubes Powder and 0.16 grams of graphite powder, that is, the mass ratio of carbon nanotubes and graphite is 2:2.

Step (2), put the powder weighed in step (1) into a ball mill tank for mechanical centrifugation and mixing for 20min, the rotating speed is 1500r, and then manually grind and mix at room temperature, and the feeding sequence is to add carbon nanotubes first. and graphite, and then add polyvinylidene fluoride. Considering that the three powders are light, and the proportion of carbon nanotubes and graphite is small, if carbon nanotubes and graphite are added at the end, some of them will stick to the grinding cover during mechanical grinding, which makes the results greatly different. Error, so first add carbon nanotubes and graphite, and finally add polyvinylidene fluoride. All materials are added after one piece is ground.

Then put the mixed powder into a mortar and perform artificial shear mixing until all the agglomerated small particles of the powder are uniformly dispersed.

In step (3), the mixed powder is sieved through 200 meshes to obtain a uniform functional body (carbon nanotube, graphite)/polyvinylidene fluoride "ternary" composite powder.

In step (4), the sieved mixed powder is uniformly stirred, and then weighs 1 gram of powder into a mold for cold pressing. Among them, the molding pressure was 25MPa, the pressure holding time was 15min, and after demolding, it was a circular sheet with a diameter of 20mm, and after grinding with 1500-grit sandpaper, it was used as a further dielectric property test.

Results: The ternary composite material prepared in Example 1 was tested for negative dielectric constant, and the results are shown in Figure 2. When the mass ratio of carbon nanotubes and graphite is 2:2, and the total mass of carbon nanotubes and graphite accounts for 16% of the mass percentage of the composite material, the dielectric constant of the ternary composite material is in the 100MHz-1GHz frequency band. is a negative value, and the value of the negative dielectric constant is below 100.

Example 2

A method for designing a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties, comprising the following steps:

In step (1), 0.32 grams of functional body powder and 1.68 grams of polyvinylidene fluoride powder are respectively weighed with an electronic balance, so that the mass fraction of functional bodies in the composite material is 16%; the functional bodies contain 0.08 grams of carbon nanotubes Powder and 0.24 grams of graphite powder, that is, the mass ratio of carbon nanotubes and graphite is 1:3.

Step (2), put the powder weighed in step (1) into a ball mill tank for mechanical centrifugation and mixing for 20min, the rotating speed is 1500r, and then manually grind and mix at room temperature, and the feeding sequence is to add carbon nanotubes first. and graphite, and then add polyvinylidene fluoride.

Then put the mixed powder into a mortar and perform artificial shear mixing until all the agglomerated small particles of the powder are uniformly dispersed.

In step (3), the mixed powder is sieved through 200 meshes to obtain a uniform functional body (carbon nanotube, graphite)/polyvinylidene fluoride "ternary" composite powder.

In step (4), the sieved mixed powder is uniformly stirred, and then weighs 1 gram of powder into a mold for cold pressing. Among them, the molding pressure was 25MPa, the pressure holding time was 15min, and after demolding, it was a circular sheet with a diameter of 20mm, and after grinding with 1500-grit sandpaper, it was used as a further dielectric property test.

Results: The ternary composite material prepared in Example 2 was tested for negative dielectric constant, and the results are shown in Figure 2. When the mass ratio of carbon nanotubes and graphite is 1:3, and the total mass of carbon nanotubes and graphite accounts for 16% of the mass percentage of the composite material, the dielectric constant of the ternary composite material in the 1GHz frequency band is Negative values, and the value of the negative dielectric constant is below 500.

Comparative Example 1

A method for designing a carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric properties, comprising the following steps:

In step (1), 0.32 grams of functional body powder and 1.68 grams of polyvinylidene fluoride powder are respectively weighed with an electronic balance, so that the mass fraction of functional bodies in the composite material is 16%; the functional bodies contain 0.24 grams of carbon nanotubes The powder and 0.08 g of graphite powder, that is, the mass ratio of carbon nanotubes and graphite, is 3:1.

Step (2), put the powder weighed in step (1) into a ball mill tank for mechanical centrifugation and mixing for 20min, the rotating speed is 1500r, and then manually grind and mix at room temperature, and the feeding sequence is to add carbon nanotubes first. and graphite, and then add polyvinylidene fluoride. Considering that the three powders are light, and the proportion of carbon nanotubes and graphite is small, if carbon nanotubes and graphite are added at the end, some of them will stick to the grinding cover during mechanical grinding, which makes the results greatly different. Error, so first add carbon nanotubes and graphite, and finally add polyvinylidene fluoride. All materials are added after one piece is ground.

Then put the mixed powder into a mortar and perform artificial shear mixing until all the agglomerated small particles of the powder are uniformly dispersed.

In step (3), the mixed powder is sieved through 200 meshes to obtain a uniform functional body (carbon nanotube, graphite)/polyvinylidene fluoride "ternary" composite powder.

In step (4), the sieved mixed powder is uniformly stirred, and then weighs 1 gram of powder into a mold for cold pressing. Among them, the molding pressure was 25MPa, the pressure holding time was 15min, and after demolding, it was a circular sheet with a diameter of 20mm, and after grinding with 1500-grit sandpaper, it was used as a further dielectric property test. Because the cold-formed samples will have some burrs on the edges. The function of grinding is to make the surface of the sample smooth and to have better contact with the instrument during dielectric testing.

Results: The ternary composite material prepared in Comparative Example 1 was tested for negative dielectric constant, and the results are shown in Figure 2. When the mass ratio of carbon nanotubes and graphite is 3:1, and the mass percentage of carbon nanotubes and graphite in the composite material is 16%, the dielectric constant of the ternary composite material is greater than 0.

The above examples show that the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material prepared by the present invention has weak negative dielectric properties, and the value of the negative dielectric constant is below 500. By adjusting the content of carbon nanotubes and graphite in the functional body, the dielectric constant of the composite material is more controllable in a small range, that is, the control is more precise. Compared with the traditional binary composite material, the ternary composite material of the present invention can significantly reduce the value of the dielectric constant, and can be used in communication, wireless power transmission, microwave absorption and other fields and has important applications. The present invention can not only adjust the content of carbon nanotubes and graphite, but also adjust the content of polyvinylidene fluoride in the matrix, that is, the present invention is not limited to the total mass of carbon nanotubes and graphite accounting for the mass of the ternary composite material. The percentage is 16%-20%, the balance is polyvinylidene fluoride, and the mass ratio of carbon nanotubes and graphite is (1:1)-(1:10) "ternary" composite material.

To sum up, the carbon nanotube-graphite-polyvinylidene fluoride "ternary" composite material with negative dielectric properties of the present invention introduces a new functional variable on the basis of the traditional binary composite material, so that the negative dielectric The value of the constant can be regulated in a smaller range, that is, the regulation can be more precise. Using carbon nanotubes (CNT) and graphite with good electrical conductivity as the functional body, and polyvinylidene fluoride (PVDF) as the matrix, by determining the proportion of the two conductors in the functional body, the control of the negative dielectric is realized. precision. In the preparation, considering the influence of the powder mixing uniformity on the formation of the conductive mesh and the influence on the negative dielectric constant, a secondary mixing method was adopted, which was firstly mechanically centrifugally mixed, and then manually sheared and mixed to make it The resulting mixed body tends to be more uniform. The preparation process is simple, and through the design idea of the "ternary" composite material, the composite material with negative dielectric constant prepared by the present invention has important practical value and broad application fields in metamaterials, microwave absorption and wireless power transmission. market prospects.

The above description of the embodiments is for those of ordinary skill in the art to understand and apply the present invention. Those skilled in the art can easily modify these embodiments and apply the general principles described herein to other embodiments without inventive step. Therefore, without being limited to the implementation cases herein, improvements and modifications made to the present invention by those skilled in the art according to the disclosure of the present invention should all fall within the protection scope of the present invention.

Claims (9)

1. The carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with the negative dielectric property is characterized in that the ternary composite material is formed by uniformly compounding carbon nanotubes, graphite and polyvinylidene fluoride; the mass sum of the carbon nano tube and the graphite accounts for 16-20% of the mass of the ternary composite material, and the balance is polyvinylidene fluoride; wherein the mass ratio of the carbon nano tube to the graphite is (1:1) - (1: 10).

2. The carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric property of claim 1, wherein the sum of the mass of the carbon nanotube and the graphite in the ternary composite material accounts for 16% of the mass of the ternary composite material, and the balance is polyvinylidene fluoride; wherein the mass ratio of the carbon nano tube to the graphite is (1:1) - (1: 3).

3. The carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric property of claim 1, wherein the diameter of the carbon nanotube is 12-30nm, and the length of the carbon nanotube is 0-6 μm.

4. The method for preparing the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric property as claimed in claim 1, wherein the method comprises the following steps:

step (1), respectively weighing carbon nanotube powder, graphite powder and polyvinylidene fluoride powder, so that the mass sum of the carbon nanotube powder and the graphite powder accounts for 16-20% of the ternary composite material, and the balance is polyvinylidene fluoride; the mass ratio of the carbon nano tube powder to the graphite powder is (1:1) - (1: 10);

step (2), pouring the weighed carbon nano tube powder, graphite powder and polyvinylidene fluoride powder into a grinding tank for disordered random mixing and grinding, then placing the powder into a mortar for artificial shearing and mixing until all agglomerated small particles of the powder are uniformly dispersed;

and (3) putting the uniformly mixed powder into a mould, and carrying out cold press molding to obtain the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material.

5. The preparation method of the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with the negative dielectric property as claimed in claim 4, wherein in the step (1), the mass sum of the carbon nanotube powder and the graphite powder accounts for 16% of the ternary composite material by mass, and the balance is polyvinylidene fluoride; the mass ratio of the carbon nano tube powder to the graphite powder is (1:1) - (1: 3).

6. The preparation method of the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric property as claimed in claim 4, wherein in the step (2), the powder is mechanically centrifugally mixed in a grinding tank for 15-25 min at a rotation speed of 1000-2000 r.

7. The method for preparing the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric property as claimed in claim 4, wherein in the step (2), the carbon nanotube powder, the graphite powder and the polyvinylidene fluoride powder are poured into a grinding tank in the following sequence: firstly adding carbon nano tube powder and graphite powder, and then adding polyvinylidene fluoride powder.

8. The method for preparing the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with the negative dielectric property as claimed in claim 4, wherein in the step (3), the uniformly mixed powder is sieved by a screen with more than 200 meshes, and then is placed in a mold for cold press molding.

9. The method for preparing the carbon nanotube-graphite-polyvinylidene fluoride ternary composite material with negative dielectric property as claimed in claim 4, wherein the cold press molding conditions are as follows: the molding pressure is 20-30 MPa, and the pressure maintaining time is 15-20 min.

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