KR20170121914A - METHOD FOR PREPARING POLYVINYLIDENE FLUORIDE COMPOSITE USING INFRARED IRRADIATION AND POLYVINYLIDENE FLUORIDE COMPOSITE COMPRISING TiO2 COATED CARBON NANOTUBE - Google Patents

Abstract

The present invention relates to a method of preparing a polyvinylidene fluoride composite, and a polyvinylidene fluoride composite prepared thereby, wherein the method comprises the steps of: preparing a carbon nanotube (CNT) coated with titanium dioxide (TiO_2); adding the CNT coated with titanium dioxide to a polyvinylidene fluoride (PVDF) solution; and irradiating infrared rays to the PVDF solution containing the CNT coated with titanium dioxide. The method of preparing a polyvinylidene fluoride composite according to the present invention can simplify the process by inducing -type crystalline structure of PVDF without a mechanical drawing process. Additionally, by irradiating the infrared rays corresponding to the natural frequency of PVDF, and thereby vibrating the molecules to induce the -type crystalline structure, the method of the present invention can increase reactivity between the CNT coated with titanium dioxide and PVDF molecules, and improve piezoelectric characteristics.

Description

METHOD FOR PREPARING POLYVINYLIDENE FLUORIDE COMPOSITE USING INFRARED IRRADIATION AND POLYVINYLIDENE FLUORIDE COMPOSITE COMPRISING TITANIUM AND METHOD FOR PREPARING POLYVINYLIDENE FLUORIDE COMPOUND COATED CARBON NANOTUBE}

The present invention relates to a method for producing a polyvinylidene fluoride composite material and a polyvinylidene fluoride composite material produced using the same, and more particularly, to a method for producing a polyvinylidene fluoride composite material by irradiating infrared rays corresponding to a natural frequency of polyvinylidene fluoride A method of manufacturing a polyvinylidene fluoride composite material capable of improving the piezoelectric properties by increasing the reactivity between the carbon nanotubes coated with titanium dioxide and the polyvinylidene fluoride molecules by inducing the? -Type crystal phase by vibrating the molecules and Polyvinylidene fluoride composite material.

Polyvinylidene fluoride (PVDF) is a semi-crystalline polymer exhibiting a polymorphism classified into at least four crystal forms such as?,?,?, And? Shows a large spontaneous polarization due to a strong dipole group because it has a plane zigzag type TT type molecular chain.

PVDF, which has a high content of β crystals, is attracting attention as a piezoelectric material for detecting deformation and pressure since it has excellent piezoelectricity and ferroelectricity. Because of its structural flexibility, PVDF can be used as an infrared sensor, an actuator, It is a piezoelectric polymer material widely used in sensor fields such as a transistor.

However, in order to apply PVDF as a piezoelectric material, the β-type crystal content is high and the remanent polarization (Pr) value should be high. In order to produce PVDF having excellent piezoelectric properties, there is a method of applying a process of transferring an? -Type crystal to a? -Type crystal.

In general, post-treatment processes such as mechanical stretching and poling are used as methods for increasing the? -Type crystal phase through? -Type crystal change. However, in such a stretching process, not only the stretching ratio of the polymer itself is limited but also the PVDF molecular chain tends to be roughly oriented to the surface, which is uneconomical from a cost point of view.

It is an object of the present invention to provide a method for producing a polyvinylidene fluoride which can induce a? -Type crystal phase of polyvinylidene fluoride without mechanical stretching process, simplify the process, and irradiate infrared rays corresponding to a natural frequency of polyvinylidene fluoride To provide a method of manufacturing a polyvinylidene fluoride composite material capable of enhancing the reactivity between a carbon nanotube coated with titanium dioxide and a polyvinylidene fluoride molecule to induce a? -Type crystal phase by vibrating molecules to improve piezoelectric characteristics will be.

Another object of the present invention is to provide a polyvinylidene fluoride composite material having excellent piezoelectric properties as produced by the above-described method for producing a polyvinylidene fluoride composite material.

According to an embodiment of the present invention, there is provided a method of manufacturing a carbon nanotube (CNT) coated with titanium dioxide (TiO ₂ ), a method of manufacturing a carbon nanotube coated with titanium dioxide by using polyvinylidene fluoride (PVDF) And a step of irradiating infrared rays to the polyvinylidene fluoride solution to which the titanium dioxide-coated carbon nanotubes are added. The present invention also provides a method for producing a polyvinylidene fluoride composite material.

The carbon nanotube may be a multiwalled carbon nanotube (MWCNT).

The step of preparing the titanium dioxide coated carbon nanotubes may include treating the carbon nanotubes with O ₃ , HNO ₃ , H ₂ SO ₄ / HNO ₃ , KMnO _4, or a mixture thereof to impart a functional group, Can be coated.

The titanium dioxide precursor used in the step of preparing the titanium dioxide-coated carbon nanotube may be selected from the group consisting of titanium tetrachloride (TiCl ₄ ), titanium tetraisopropoxide (TTIP), tetrabutyl titanate titanate, TBOT), and mixtures thereof.

The polyvinylidene fluoride solution may be dissolved or suspended in a solvent selected from the group consisting of dimethylformamide (DMF), di-methylacetamide (DMAc), tetrahydrofuran (THF), acetone, Wherein the solvent is selected from the group consisting of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and mixtures thereof, polyvinylidene fluoride is added to the polyvinylidene fluoride solution in an amount of 5 By weight to 25% by weight.

The infrared ray irradiation can be performed for 0.1 second to 2 hours with infrared rays having a wavelength range of 2.5 to 25 占 퐉, a power of 10 to 1000 mW and an irradiation distance of 5 to 50 cm.

According to another embodiment of the present invention, there is provided a carbon nanotube (CNT) comprising polyvinylidene fluoride (PVDF) and titanium dioxide (TiO ₂ ) coated carbon nanotube (CNT), wherein the polyvinylidene fluoride Wherein the ratio of the? -Type crystal structure to the entire?,?,?, And? -Type crystal structures is 80% by weight or more.

The polyvinylidene fluoride composite material may include 99.5 to 99.9% by weight of the polyvinylidene fluoride and 0.1 to 0.5% by weight of the titanium dioxide-coated carbon nanotube, based on the total weight of the polyvinylidene fluoride composite material .

The surface of the carbon nanotube may be substituted with any one functional group selected from the group consisting of a hydroxy group, a carbonyl group, a carboxyl group, and combinations thereof.

The method of the present invention for producing a polyvinylidene fluoride composite material can induce a? -Type crystalline phase of polyvinylidene fluoride without mechanical stretching process, simplifying the process, and reducing the natural vibration frequency of polyvinylidene fluoride frequency) to induce the? -type crystal phase to increase the reactivity between the titanium dioxide-coated carbon nanotube and the polyvinylidene fluoride molecule, thereby improving the piezoelectric characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart showing a method for producing a polyvinylidene fluoride composite according to an embodiment of the present invention. FIG.
2 is a diagram schematically showing a method for producing the polyvinylidene fluoride composite material of FIG. 1;
3 is a process flow chart showing a step of producing a carbon nanotube coated with titanium dioxide.
FIG. 4 is a view schematically showing the titanium dioxide-coated carbon nanotube manufactured in FIG.
FIG. 5 is a diagram schematically showing vibration modes of PVDF molecules that can occur upon infrared absorption.
6 is a graph showing the results of surface crystal structure analysis of titanium dioxide-coated carbon nanotubes.
7 is a graph showing the crystal structure analysis results of a polyvinylidene fluoride composite material to which titanium dioxide-coated carbon nanotubes are added.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the specific embodiments but may be embodied in various forms and is intended to be illustrative of the scope of the invention.

According to an embodiment of the present invention, there is provided a method of manufacturing a polyvinylidene fluoride composite material, comprising the steps of: preparing a carbon nanotube (CNT) coated with titanium dioxide (TiO ₂ ) To a solution of polyvinylidene fluoride (PVDF), and irradiating infrared rays to the polyvinylidene fluoride solution to which the titanium dioxide-coated carbon nanotubes are added.

The method for producing the polyvinylidene fluoride composite material can induce the? -Type crystalline phase of polyvinylidene fluoride without mechanical stretching process, simplifying the process, and can reduce the natural frequency of polyvinylidene fluoride, To induce the? -Type crystal phase to increase the reactivity between the titanium dioxide-coated carbon nanotube and the polyvinylidene fluoride molecule, thereby improving the piezoelectric characteristics.

FIG. 1 is a flow chart showing a process for producing the polyvinylidene fluoride composite, and FIG. 2 is a diagram schematically showing a process for producing the polyvinylidene fluoride composite. Hereinafter, a method for producing the polyvinylidene fluoride composite will be described with reference to FIGS. 1 and 2. FIG.

First, a carbon nanotube coated with titanium dioxide is prepared.

FIG. 3 is a process flow chart showing a step of manufacturing the titanium dioxide-coated carbon nanotube, and FIG. 4 is a diagram schematically showing the titanium dioxide-coated carbon nanotube. Hereinafter, the steps of preparing the titanium dioxide-coated carbon nanotube will be described with reference to FIGS. 3 and 4. FIG.

The carbon nanotubes may be added to the PVDF in the form of particles to induce the? -Form crystallization of the PVDF to improve the piezoelectric properties. Although the type of the carbon nanotube is not limited to the present invention, it is preferable to use a multiwalled carbon nanotube (MWCNT) in order to improve the piezoelectric characteristics by inducing the? -Type crystal phase through infrared irradiation desirable.

In addition, the surface of the carbon nanotube may be coated with titanium dioxide. The titanium dioxide exists in the form of three crystal structures of rutile, brookite and anatase, and mainly anatase and rutile crystals can be used. The titanium dioxide can be coated on the surface of the carbon nanotubes by using the carbon nanotubes as a support. Of the crystal structures of titanium dioxide, titanium dioxide having anatase crystal has a large specific surface area and can form a hydrogen bond with the fluorine atoms of the PVDF because the amount of hydroxyl group is large on the surface.

Therefore, when only the carbon nanotubes are used, only physical adsorption due to difference in hydrogen atoms and electronegativity of the PVDF may occur. However, when the titanium dioxide is coated on the surface of the carbon nanotubes, It is advantageous to induce a molecular chain of the? Form because it can bind to the molecular chain of PVDF by hydrogen bonding.

In addition, when titanium dioxide is coated on the carbon nanotube having a high aspect ratio, it can be uniformly bonded to the molecular chains of the PVDF through a wider area.

On the other hand, in order to coat the surface of the carbon nanotubes with the titanium dioxide more effectively, it is preferable that a surface of the carbon nanotube is coated with a hydroxy group, a carbonyl group, a carboxyl group, Can be substituted for any one functional group selected from

For this purpose, the carbon nanotubes may be treated with O ₃ , HNO ₃ , H ₂ SO ₄ / HNO ₃ , KMnO _4, or a mixture thereof to provide a functional group, followed by coating the titanium dioxide.

Accordingly, the physicochemical coupling between the carbon nanotube and the titanium dioxide precursor material can be enhanced through hydrogen bond and van der Waals attraction.

The titanium dioxide-coated carbon nanotube particles can be prepared by a method such as a sol-gel process, a hydrothermal process, a microwave oven, an electrodeposition method, and a chemical vapor deposition Depositon). ≪ / RTI >

The titanium dioxide precursor may be selected from the group consisting of titanium tetrachloride (TiCl ₄ ), titanium tetraisopropoxide (TTIP), tetrabutyl titanate (TBOT), and mixtures thereof. Lt; / RTI >

In order to induce thermal hydrolysis during the reaction of the titanium dioxide precursor and the carbon nanotube into which the functional group is introduced, the reaction can be carried out at a temperature of 70 to 90 ° C or less.

The titanium dioxide-coated carbon nanotube particles may have a sintering temperature of 400 to 500 ° C and may be sintered at the above temperature for 1 to 2 hours.

The sintering of the titanium dioxide having the anatase crystal structure may be performed by using an autoclave vessel, a microwave oven, an electric furnace, a vacuum oven, and a chemical vapor deposition May be applied.

More specifically, for example, when the sintering is performed using the microwave oven, the time can be shortened compared to other methods. At this time, the frequency of the microwave at sintering may be 300 to 30,000 MHz, the microwave power may be 100 to 2000 W, and the irradiation time of the microwave may be 5 to 1 hour.

Nitrogen (N ₂ ) or argon (Ar) gas may be used to maintain a stable environment during sintering.

Next, the PVDF is added to a solvent to prepare the PVDF solution, and the titanium dioxide-coated carbon nanotubes prepared above are added to the PVDF solution.

The PVDF refers to a PVDF compound. The PVDF is not only PVDF but also a PVDF copolymer such as poly (vinylidene fluoride-co-trifluoroethylene), P (VDF -TrFE)) and the like.

The PVDF solution is prepared by dissolving PVDF pellets in a solvent such as dimethylformamide (DMF), di-methylacetamide (DMAc), tetrahydrofuran (THF), acetone the solvent may be prepared by adding PVDF to any one solvent selected from the group consisting of acetone, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and mixtures thereof.

At this time, the PVDF content may be 5 to 25% by weight, and preferably 15 to 20% by weight based on the total weight of the PVDF solution. When the content of PVDF is less than 5% by weight, it is difficult to control the solution in the production of the composite material due to low viscosity, and the probability of formation of pores in the composite is increased. When the content exceeds 25% by weight, PVDF is difficult to be dissolved, There may be a problem in uniform dispersibility of the particles.

The titanium dioxide coated carbon nanotubes prepared above are added to the PVDF solution prepared above. At this time, the titanium dioxide-coated carbon nanotube particles may be dispersed using a 3-roll-mill, an ultrasonication, an impeller, a paste mixer, or the like .

Finally, the polyvinylidene fluoride solution to which the titanium dioxide-coated carbon nanotubes are added is irradiated with infrared rays. Irradiation of the infrared ray may be performed in the solution after adding the titanium dioxide-coated carbon nanotube particles to the PVDF solution.

In the infrared ray irradiation process, infrared rays corresponding to the natural frequency of the PVDF are irradiated to the molecules to vibrate the molecules to induce the? -Type crystal phase of the PVDF, whereby the reactivity between the titanium dioxide-coated carbon nanotube and the PVDF molecules So that the piezoelectric characteristics can be improved.

Specifically, the PVDF molecular chain has a specific vibration mode according to the natural frequency, and when the infrared ray is absorbed, the dipole moment changes, so that the vibration due to the resonance phenomenon may occur and the amplitude of the molecular vibration may be changed . This change in amplitude can occur only when the molecule has a dipole moment. In the case of the PVDF, there is a strong dipole moment in the molecule due to a difference in electronegativity between a hydrogen atom having a positive charge and a fluorine atom having a negative charge. Therefore, when excitation is externally performed at the same frequency as the natural frequency for each chemical bond constituting the PVDF molecular chain, the possibility of hydrogen bonding with the titanium dioxide coated carbon nanotube is more likely to be achieved by the resonance phenomenon .

An infrared ray has a frequency band close to the natural frequency of the chemical bond constituting the molecular chain of the PVDF. The infrared ray has a merit that the reflection is good when the wavelength is short, and the absorption is good when the wavelength is long. (Near IR, 0.78 to 2.5 탆), a medium infrared region (IR, 2.5 to 50 탆) and a far infrared region (far IR, 50 to 1000 탆), and a far infrared region .

When the infrared rays corresponding to the infrared rays of the intermediate region are irradiated to the PVDF molecules, the molecules absorbing the infrared rays may cause molecular motion such as vibration, rotation and translation. The generation of infrared rays should cause a change in the dipole moment caused by the vibration and rotation of the molecule, and the vibration movement may be caused by infrared rays corresponding to a unique vibrational frequency depending on the kind and intensity of the molecular bond and the kind of the bonding atom. And can be absorbed by molecules. In this case, the energy transfer occurs and the amplitude of the molecular vibration changes.

The unique vibration mode of the PVDF molecular chain has various vibration modes and is shown in FIG. FIG. 5 is a diagram schematically illustrating vibration modes of PVDF molecules that may occur upon absorption of infrared rays. Referring to FIG. 5, the PVDF molecular chain may be stretched, inflated by bending vibration, scissoring (~ 1450 cm ^-1 ), rocking (~ 720 cm) ^-1 ), wagging (~ 1250 cm ^-1 ), and twisting (~ 1250 cm ^-1 ).

Energy transfer occurs when infrared rays corresponding to the natural frequency of the PVDF are absorbed and the dipole moment is changed to generate vibration and the amplitude of the molecular vibration becomes larger. The range of the infrared wavelength corresponding to the natural frequency of the PVDF corresponds to the range of 2.5 to 25 μm. The inherent vibration frequency and vibration method of the PVDF can be confirmed by infrared absorption spectroscopy, and the molecular vibration method in the state of the polymer solution before the crystallization can be predicted.

Therefore, the wavelength band of the infrared ray used for the infrared ray irradiation may be 2.5 to 25 占 퐉, preferably 7 to 15 占 퐉. If the wavelength of the infrared light is less than 2.5 μm or more than 25 μm, it corresponds to the infrared region but does not correspond to the vibrational infrared region, so that molecular vibration due to infrared irradiation may not occur.

The power of the infrared rays may be 10 to 1000 mW, and preferably 100 to 500 mW. If the power of the infrared ray is less than 10 mW, the intensity of the infrared ray irradiation is very weak. Therefore, the energy supply necessary for causing the molecular vibration may not be sufficient. If the infrared ray power exceeds 1000 mW, Degradation may occur.

The irradiation distance of the infrared ray may be 5 to 50 cm, and preferably 15 to 30 cm. The thermal energy generated by the infrared irradiation is generated, and the temperature at this time may be increased to 200 DEG C or more. Therefore, when the irradiation distance of the infrared rays is less than 5 cm, the degradation of the sample may occur as the temperature increases to 200 ° C or more, which is higher than the melting temperature of PVDF, which is 165 ° C. When the irradiation distance exceeds 50 cm, May be insufficient to cause molecular vibration due to infrared activity because the applied intensity is weakened.

The irradiation time of the infrared ray may be 0.1 second to 1 hour, preferably 10 seconds to 20 minutes. If the irradiation time of the infrared rays is less than 0.1 second, it is difficult to expect the effect due to the molecular vibration because it is a very short time to cause molecular vibration. If the irradiation time exceeds 1 hour, the temperature rise due to accumulated heat energy causes degradation ) May occur, and deterioration may proceed due to long-term irradiation.

The polyvinylidene fluoride composite material may be in the form of a film, and may further include a step of irradiating the infrared ray to produce a film using the PVDF solution. As a method for producing a film using the PVDF solution, a conventionally known method can be used, so that detailed description thereof will be omitted in the present invention.

However, the PVDF film can be prepared by using, for example, a solvent casting method. For this purpose, the solvent can be evaporated from the PVDF solution coated with the titanium dioxide-coated carbon nanotube. The evaporation of the solvent may be suitably controlled according to the type of the solvent, and may be performed at a temperature of 60 to 120 ° C., for example, and further drying at a temperature of 60 ° C. or more to remove the remaining solvent It can be rough.

According to another embodiment of the present invention, the polyvinylidene fluoride composite material includes polyvinylidene fluoride (PVDF) and carbon nanotube (CNT) coated with titanium dioxide (TiO ₂ ). The polyvinylidene fluoride composite material may be produced using the method for producing the polyvinylidene fluoride composite material according to an embodiment of the present invention.

At this time, the polyvinylidene fluoride composite material is irradiated with infrared rays to induce the? -Type crystalline phase of the molecule by vibration, so that the? -Type,?,?, And? The proportion of the crystal structure may be 80% by weight or more, preferably 85 to 99% by weight, and thus the PVDF composite material has excellent piezoelectric properties.

The PVDF composite material may include 99.5 to 99.9% by weight of the PVDF and 0.1 to 0.5% by weight of the titanium dioxide-coated carbon nanotube, based on the total weight of the PVDF composite material. If the content of the titanium dioxide-coated carbon nanotubes is less than 0.1 wt%, the amount of the carbon nanotubes may be insufficient to increase the? Crystal structure because the amount of the carbon nanotubes is less than the total weight of the carbon nanotubes. If the content of the carbon nanotubes exceeds 0.5 wt% The nanotube particles may aggregate with each other to lower the dispersibility of the particles in the composite, and the crystallinity may also be lowered.

Meanwhile, the surface of the carbon nanotubes may be substituted with any one functional group selected from the group consisting of a hydroxy group, a carbonyl group, a carboxyl group, and combinations thereof. This is for better coating the titanium dioxide on the surface of the carbon nanotubes.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[Manufacturing Example: Production of PVDF Composite]

(Example 1)

1) TiO ₂ Lt; RTI ID = 0.0 > MWCNT < / RTI >

The method of preparing the MWCNT coated with TiO ₂ according to the first embodiment includes a step of reacting with the precursor material of TiO ₂ after the surface treatment of the MWCNT.

The surface treatment of the MWCNT was performed using HNO ₃ and H ₂ O ₂ (30% v / v). The MWCNT was first added to HNO ₃ and stirred, followed by ultrasonic treatment. Thereafter, it was repeatedly washed with ion-exchanged water. The filtered MWCNT was eluted with H ₂ O ₂ After the exchange, the same process as the previous process was repeated. Finally, functionalized MWCNTs with two solvents were dried at 120 ° C for 6 hours. Through the above process, functional groups such as hydroxyl group, carbonyl group and carboxyl group were imparted to the MWCNT surface.

The functionalized MWCNT was added to HCl together with the precursor material of TiO ₂ and then reacted for 2 hours through ultrasonic treatment. Thereafter, it was neutralized by ammonia water and then stirred at a temperature of 70 ° C to 90 ° C to induce thermal hydrolysis. The TiO ₂ -MWCNT particles were then dried at 100 ° C after repeated washing cycles.

Finally, sintering was performed at 500 ° C to form TiO ₂ , which forms the anatase-type crystal structure. The sintering was performed in a microwave oven under a nitrogen atmosphere. The results of the crystal structure analysis of the titanium dioxide-coated carbon nanotubes fabricated through the above process are shown in FIG.

6, peaks corresponding to the anatase type crystal structure were generated. As a result, the surface of the carbon nanotube was coated with anatase type titanium dioxide.

2) TiO ₂ Coated MWCNT-reinforced PVDF solution and solvent evaporation step

The PVDF pellets were dissolved in a DMF solvent at a water bath temperature of 50 ° C to a PVDF content of 20% by weight to prepare a solution.

The TiO ₂ -coated MWCNT particles were added to the PVDF solution and mixed with the PVDF solution through a roll-mill dispersion method.

3) irradiating infrared rays corresponding to the natural vibration frequency band of the PVDF molecular chain

The prepared PVDF solution was irradiated with infrared rays under the following conditions to induce absorption of infrared rays corresponding to the natural frequency of the PVDF to induce molecular vibration.

The infrared ray was irradiated for 10 minutes with an infrared ray having a wavelength of 13 μm, a power of 100 mW and an irradiation distance of 30 cm.

4) PVDF composite film formation

Solvent volatilization for film formation can be carried out by solvent casting. The infrared irradiated PVDF solution is poured onto a crystal plate and dried under a hood using a hot plate. Specifically, the solvent was evaporated at a temperature of 60 to 120 DEG C using the hot plate, and further dried at a temperature of 60 DEG C or more to remove residual solvent.

(Comparative Example 1)

The PVDF pellets were dissolved in a DMF solvent at a water bath temperature of 50 ° C to a PVDF content of 20% by weight to prepare a solution.

The infra-red irradiated PVDF solution was poured onto a crystal plate and dried under a hood using a hot plate. Specifically, the solvent was evaporated at a temperature of 60 to 120 DEG C using the hot plate, and further dried at a temperature of 60 DEG C or more to remove residual solvent.

(Comparative Example 2)

Except that in place of the said TiO ₂ coated MWCNT particles in Example 1 was used for MWCNT particles are TiO ₂ coating was not carried out in the same manner as in Example 1.

[ Experimental Example : Manufactured PVDF  Composite XRD  analysis]

XRD analysis was performed on the PVDF composites prepared in the above Examples and Comparative Examples.

7 is a graph showing the results of XRD analysis of the PVDF composite prepared in Comparative Example 1, and a second graph (PVDF / Neat MWCNT) of the PVDF composite prepared in Comparative Example 2 And the third graph (PVDF / TiO ₂ coated MWCNT) is a graph showing the XRD analysis results of the PVDF composite prepared in Example 1. FIG.

Referring to FIG. 7, it can be seen that the PVDF composite prepared in Example 1 showed an increase in β-type crystal content and piezoelectric characteristics also increased from the result of XRD crystallization increase.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments or constructions. Various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention. It will be clear to those who have knowledge.

Claims (6)

Preparing a carbon nanotube (CNT) coated with titanium dioxide (TiO ₂ )
Adding the titanium dioxide coated carbon nanotube to a polyvinylidene fluoride (PVDF) solution, and
Irradiating the polyvinylidene fluoride solution to which the titanium dioxide-coated carbon nanotube is added with infrared light
≪ / RTI > wherein the polyvinylidene fluoride composite material is a polyvinylidene fluoride composite material. The method according to claim 1,
The step of preparing the titanium dioxide coated carbon nanotubes may include treating the carbon nanotubes with O ₃ , HNO ₃ , H ₂ SO ₄ / HNO ₃ , KMnO _4, or a mixture thereof to impart a functional group, ≪ / RTI > wherein the polyvinylidene fluoride composite is coated. The method according to claim 1,
Wherein said infrared radiation is irradiated with infrared rays having a wavelength range of 2.5 to 25 占 퐉, a power of 10 to 1000 mW, and an irradiation distance of 5 to 50 cm for 0.1 second to 2 hours, wherein said polyvinylidene fluoride composite Gt; Polyvinylidene fluoride (PVDF), and
And a carbon nanotube (CNT) coated with titanium dioxide (TiO ₂ )
Wherein the ratio of the? -Form crystal structure to all the? -Form,? -Form,? -Form, and delta -type crystal structures included in the polyvinylidene fluoride is 80% by weight or more. 5. The method of claim 4,
Wherein the polyvinylidene fluoride composite material comprises 99.5 to 99.9% by weight of the polyvinylidene fluoride and 0.1 to 0.5% by weight of the titanium dioxide-coated carbon nanotube, based on the total weight of the polyvinylidene fluoride composite material Polyvinylidene fluoride composite. 5. The method of claim 4,
Wherein the surface of the carbon nanotubes is substituted with a functional group selected from the group consisting of a hydroxy group, a carbonyl group, a carboxyl group, Fluoride composites.

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