KR102266526B1 - Polyvinylidene fluoride complex - Google Patents

Abstract

A polyvinylidene fluoride composite comprising an inorganic oxide doped with fluorine is provided. The polyvinylidene fluoride composite provided in one aspect of the present invention is optically stable and has the effect of exhibiting a strong piezoelectric effect.

Description

Polyvinylidene fluoride complex {Polyvinylidene fluoride complex}

The present invention relates to polyvinylidene fluoride composites.

Recently, many studies have been conducted on the development of high-performance energy harvesters in various fields such as self-driven sensors, smart skins and wearables, and portable electronic devices. In particular, energy harvesting, ultrasound, and body movement due to abnormal airflow/vibration have been significantly explored because of their common occurrence and prevalence in daily life. Among these energy harvesting systems, piezoelectric devices are attracting attention due to their easy and efficient application to electronic, mechanical and other industrial equipment, and this interest is supported by overall advances in microelectronic technology. In particular, poly(vinylidene fluoride) (PVDF) has excellent mechanical properties such as flexibility, durability, and low density, as well as excellent thermal expansion, piezoelectricity and ferroelectric properties. And these properties can be easily processed due to high thermochemical stability and biocompatibility.

It is well known that PVDF has five microcrystals (ie, α-, β-, γ-, δ- and ε-phase PVDF). Among them, β- and γ-phase PVDF seems to have the strongest piezoelectric effect. For this reason, β- and γ-phase PVDFs are commonly referred to as electroactive phase PVDFs. In general, the electroactive phase PVDF is treated with several processing methods, including naturally stable non-electroactive phase PVDF (α-, δ- and ε-phase stretching, heat treatment, polling (high electric field application), and filler addition). However, inducing the crystallinity of the film through an external treatment method has the disadvantage that it may cause undesirable structural deformation and incomplete crystalline phase, but the method of adding a filler prevents the formation of a uniform electroactive phase PVDF over a large area. not only induces, but also retains the robust mechanical properties of PVDF due to the absence of strong stimuli (ie, stretching, heat treatment and palling).

As such a filler material, recently anatase TiO ₂ nanoparticles (a-TiO ₂ particles) are widely used as a filler material, but in spite of high efficacy, a-TiO ₂ particles have significant disadvantages. A phenomenon in which the piezoelectric PVDF matrix is decomposed by the strong photoactivity of a-TiO _{2 particles appears.} Therefore, there is an urgent need to find a light inert filler as an alternative to the a-TiO _{2 filler.}

It is an object of the present invention to provide a polyvinylidene fluoride composite that is optically stable and can induce the formation of an electroactive phase PVDF.

For this purpose, in one aspect of the present invention

A polyvinylidene fluoride composite comprising an inorganic oxide doped with fluorine is provided.

In addition, in another aspect of the present invention

doping the inorganic oxide with fluorine; and

dispersing the fluorine-doped inorganic oxide and polyvinylidene fluoride in an organic solvent;

There is provided a polyvinylidene fluoride composite manufacturing method comprising a.

In addition, in another aspect of the present invention

A piezoelectric element including the polyvinylidene fluoride composite is provided.

Furthermore, in another aspect of the present invention

preparing a polyvinylidene fluoride composite by the method for preparing the polyvinylidene fluoride composite; and

There is provided a method for manufacturing a piezoelectric element comprising; manufacturing a piezoelectric element including the polyvinylidene fluoride composite.

The polyvinylidene fluoride composite provided in one aspect of the present invention is optically stable and has the effect of exhibiting a strong piezoelectric effect.

1 is a schematic diagram of a manufacturing method of _{fluorine-doped rutile TiO 2} particles (F-doped r-TiO ₂ particles) according to an embodiment of the present invention;
_{2 is a (a) SEM photograph of general rutile TiO 2} particles according to a comparative example of the present invention and (b) SEM and (c) EDS photographs of fluorine-doped rutile TiO _{2 particles according to an embodiment;}
3 is (a) XRD and (b) XPS graphs of _{general rutile TiO 2} particles according to a comparative example of the present invention and fluorine-doped rutile TiO _{2 particles according to an embodiment;}
4 is a schematic diagram showing an electron-density map of Ti-F bonds in _{fluorine-doped rutile TiO 2} particles according to an embodiment of the present invention;
5a and 5e are FT-IR graphs according to the ratio of inorganic oxide and fluorine-based polymer used during heat treatment according to an experimental example of the present invention;
6 is a graph showing the ratio of the electroactive phase according to the mass fraction of the inorganic oxide according to an experimental example of the present invention,
Figure 7 is a pure PVDF film according to a comparative example of the present invention, 5wt% r-TiO ₂ particles, and fluorine-doped rutile TiO ₂ particles according to an embodiment Output in Forward Connection of a composite film prepared using particles It is a graph showing output voltage in voltage and reverse connection.
8 is a SEM image showing the shape of the film according to the UV exposure time of a PVDF film prepared by fluoride using an TiO ₂ particles doped with bases according to an anatase TiO ₂ particles with an embodiment according to the comparative example of the invention and a graph showing the ratio of the electroactive phase according to the UV irradiation time.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is those well known and commonly used in the art.

In the present specification, polyvinylidene fluoride has the same meaning as Poly(vinylidene fluoride) or PVDF,

In the present specification, TiO ₂ having a rutile structure is r-TiO ₂ , and TiO ₂ having an anatase structure has the same meaning as a-TiO _{2 .}

In one aspect of the invention

A polyvinylidene fluoride composite comprising an inorganic oxide doped with fluorine is provided.

Hereinafter, the polyvinylidene fluoride composite provided in one aspect of the present invention will be described in detail. The contents described in the description of the method for manufacturing the polyvinylidene fluoride composite to be described later are applicable even if not described repeatedly in the following polyvinylidene fluoride composite.

First, the polyvinylidene fluoride composite provided in one aspect of the present invention includes an inorganic oxide doped with fluorine.

The inorganic oxide may be any material that can be etched by HF, for example, SiO ₂ , TiO ₂ , Al ₂ O ₃ , BaTiO ₃ , Pb[Zr _x Ti _1-x ]O ₃ (PZT), ZnO , ZnSnO ₃ or GaN, but is not limited thereto.

In addition, the inorganic oxide is preferably a material having no photoactivity.

Preferably, the inorganic oxide may be TiO ₂ , specifically TiO ₂ (r-TiO ₂ ) having a rutile structure.

The inorganic oxide may be doped with fluorine by HF gas, and the HF gas may be derived from a fluorine-based polymer or may directly supply HF gas.

The fluorine-based polymer may be any fluorine-based polymer capable of forming HF gas through firing, for example, Poly (vinylidene fluoride), Poly (vinylidene fluoride - co - hexafluoropropylene), Poly (vinylidene fluoride - co - trifluoroethylene) , Poly(vinylidene fluoride-co-chlorotrifluoroethylene), Poly(hexafluoropropylene), or Poly(hexafluoro isobutylene), but is not limited thereto.

In the case of doping using HF gas, it is preferable to doping in a solvent in that a large amount of doping is possible.

As the inorganic oxide is doped with fluorine, strong polarity can be induced by forming electron withdrawing groups on the surface of the inorganic oxide.

The fluorine-doped inorganic oxide may induce a phase transition of poly(vinylidene fluoride) (PVDF) into an electroactive phase.

Since fluorine has a strong electronegativity, the fluorine-doped inorganic oxide is preferable in that it can sufficiently induce an electroactive phase of polyvinylidene fluoride with a small amount of particles, and when doped with fluorine, polyvinylidene fluoride It is preferable in that it has good compatibility with the F (fluorine) group and excellent dispersion stability.

In general, the induction of the electroactive phase of PVDF by an inorganic oxide is initiated by hydrogen bonding between the OH group present on the surface of the inorganic oxide and F of PVDF. After that, as the hydrogen bonding between F and H inside the PVDF proceeds, electricity An active phase is induced.

In the polyvinylidene fluoride composite provided in one aspect of the present invention, hydrogen bonding between fluorine (F) present on the surface of the initial inorganic oxide and hydrogen (H) of PVDF is induced to form an electroactive phase, Since the reaction of δ- of inorganic oxide surface F and δ+ of H in PVDF is stronger than the reaction of δ+ of oxide surface H and δ- of F in PVDF, even the same amount of particles can be effective in inducing the electroactive phase.

The polyvinylidene fluoride composite provided in one aspect of the present invention may include 0.1 wt% to 20 wt% of the inorganic oxide. Preferably, it may contain 0.2 wt% to 15 wt% of the inorganic oxide, and more preferably 0.5 wt% to 10 wt% of the inorganic oxide.

When the inorganic oxide is included in less than 0.1 wt%, there is a problem that the phase transition of polyvinylidene fluoride cannot be sufficiently induced, and when the inorganic oxide is added in excess of 20 wt%, the flexibility of the polyvinylidene fluoride composite is lowered. If the inorganic oxide does not have piezoelectric properties, there is a problem that the piezoelectric properties may be deteriorated. However, since an inorganic oxide such as PZT itself has piezoelectric properties, the piezoelectric effect may increase as the content of the inorganic oxide increases.

The sum of the proportions of β-type and γ-form crystal structures may be 50 wt% or more with respect to the total α-type, β-type, γ-type, δ-type, and ε-type crystal structures included in the polyvinylidene fluoride. Preferably, it may be at least 60 wt%, more preferably at least 70 wt%, and most preferably at least 80 wt%.

The polyvinylidene fluoride composite may be in any form used in the art, for example, may be in the form of a film or fiber.

By applying a strong electric field to the polyvinylidene fluoride composite to perform a poling process, the piezoelectric effect may be increased by aligning the dipoles in the composite.

In another aspect of the invention

doping the inorganic oxide with fluorine; and

dispersing the fluorine-doped inorganic oxide and polyvinylidene fluoride in an organic solvent;

There is provided a polyvinylidene fluoride composite manufacturing method comprising a.

Hereinafter, the polyvinylidene fluoride composite manufacturing method provided in another aspect of the present invention will be described in detail for each component. The content described in the description of the polyvinylidene fluoride composite described above is applicable even if it is not described repeatedly in the following polyvinylidene fluoride composite manufacturing method.

First, the method for preparing a polyvinylidene fluoride composite provided in another aspect of the present invention includes doping an inorganic oxide with fluorine.

The inorganic oxide may be any material that can be etched by HF, for example, SiO ₂ , TiO ₂ , Al ₂ O ₃ , BaTiO ₃ , Pb[Zr _x Ti _1-x ]O ₃ (PZT), ZnO , ZnSnO ₃ or GaN, but is not limited thereto.

In addition, the inorganic oxide is preferably a material having no photoactivity.

Preferably, the inorganic oxide may be TiO ₂ , specifically TiO ₂ (r-TiO ₂ ) having a rutile structure.

The step of doping the inorganic oxide with fluorine may be performed by contacting the inorganic oxide with HF gas.

The step of doping the inorganic oxide with fluorine may include mixing the inorganic oxide and the fluorine-based polymer and heat-treating the mixture.

The mixing of the inorganic oxide and the fluorine-based polymer may be performed by a simple mixing method in a powder form or a method of dispersing in a solvent and then mixing the solvent by removing the solvent.

In the step of heat-treating the mixture, the fluorine-based polymer may be decomposed at a high temperature to generate fluorine gas, and the fluorine gas may come into contact with the inorganic oxide and react on the surface of the inorganic oxide to fluorinate the surface of the inorganic oxide.

The fluorine-based polymer may be any fluorine-based polymer capable of forming HF gas through firing, for example, Poly (vinylidene fluoride), Poly (vinylidene fluoride - co - hexafluoropropylene), Poly (vinylidene fluoride - co - trifluoroethylene) , Poly(vinylidene fluoride-co-chlorotrifluoroethylene), Poly(hexafluoropropylene), or Poly(hexafluoro isobutylene), but is not limited thereto.

In the case of doping using HF gas, it is preferable to doping in a solvent in that a large amount of doping is possible.

The weight ratio of the inorganic oxide and the fluorine-based polymer may be 3:1 to 1:10, preferably 2:1 to 1:8, and more preferably 1:1 to 1:6.

In the weight ratio of the inorganic oxide and the fluorine-based polymer, if the fluorine-based polymer is mixed in a ratio of less than 3:1, there is a problem that the inorganic oxide may not be sufficiently coated with fluorine, and if the fluorine-based polymer is mixed in a ratio of more than 1:10, the inorganic oxide There is a problem that it can be decomposed by HF.

In the step of doping the inorganic oxide with fluorine, HF gas may be directly supplied without using a fluorine-based polymer to contact the inorganic oxide with HF.

As the inorganic oxide is doped with fluorine, strong polarity can be induced by forming electron withdrawing groups on the surface of the inorganic oxide.

The fluorine-doped inorganic oxide may induce a phase transition of poly(vinylidene fluoride) (PVDF) into an electroactive phase.

Since fluorine has a strong electronegativity, the fluorine-doped inorganic oxide is preferable in that it can sufficiently induce an electroactive phase of polyvinylidene fluoride with a small amount of particles, and when doped with fluorine, polyvinylidene fluoride It is preferable in that it has good compatibility with the F (fluorine) group and excellent dispersion stability.

In general, the induction of the electroactive phase of PVDF by an inorganic oxide is initiated by hydrogen bonding between the OH group present on the surface of the inorganic oxide and F of PVDF. After that, as the hydrogen bonding between F and H inside the PVDF proceeds, electricity An active phase is induced.

In the polyvinylidene fluoride composite provided in one aspect of the present invention, hydrogen bonding between fluorine (F) present on the surface of the initial inorganic oxide and hydrogen (H) of PVDF is induced to form an electroactive phase, Since the reaction of δ- of inorganic oxide surface F and δ+ of H in PVDF is stronger than the reaction of δ+ of oxide surface H and δ- of F in PVDF, even the same amount of particles can be effective in inducing the electroactive phase.

Next, the method for preparing a polyvinylidene fluoride composite provided in another aspect of the present invention includes dispersing the fluorine-doped inorganic oxide and polyvinylidene fluoride in an organic solvent.

The organic solvent may be at least one selected from the group consisting of DMF, DMAc, Acetone and NMP, but is not limited thereto, and may be any organic solvent that can be generally used.

In the above step, 0.1 to 20 parts by weight of the inorganic oxide may be dispersed based on 100 parts by weight of the total of the inorganic oxide and polyvinylidene fluoride dispersed in the organic solvent. Preferably, 0.2 to 15 parts by weight of the inorganic oxide may be dispersed, and more preferably, from 0.2 to 15 parts by weight of the inorganic oxide may be dispersed.

When the inorganic oxide is dispersed in less than 0.1 parts by weight, there is a problem that the phase transition of polyvinylidene fluoride cannot be sufficiently induced, and when the inorganic oxide is dispersed in excess of 20 parts by weight, the flexibility of the polyvinylidene fluoride composite may be reduced. Also, if the inorganic oxide does not have piezoelectric properties, there is a problem that the piezoelectric properties may be deteriorated. However, since an inorganic oxide such as PZT itself has piezoelectric properties, the piezoelectric effect may increase as the content of the inorganic oxide increases.

As described above, by adjusting the ratio of the inorganic oxide and polyvinylidene fluoride, it can be dispersed in the solvent.

In addition, the method for preparing a polyvinylidene fluoride composite provided in another aspect of the present invention may further include obtaining a polyvinylidene fluoride composite from a mixed solution in which the inorganic oxide and polyvinylidene fluoride are dispersed.

The step of obtaining the polyvinylidene fluoride composite from the mixed solution in which the inorganic oxide and polyvinylidene fluoride are dispersed may be performed using bar doping, spin doping, or a simple drying method. could be Through the above methods, a polyvinylidene fluoride composite in the form of a film may be prepared.

In the above step, the solvent of the mixed solution may be evaporated.

The step may be performed at a temperature of 20 °C to 200 °C.

In addition, the step of obtaining the polyvinylidene fluoride composite from the mixed solution in which the inorganic oxide and polyvinylidene fluoride are dispersed may be performed by electrospinning, thereby preparing a polyvinylidene fluoride composite in the form of fibers. .

The sum of the proportions of β-type and γ-form crystal structures may be 50 wt% or more with respect to the total α-type, β-type, γ-type, δ-type, and ε-type crystal structures included in the polyvinylidene fluoride. Preferably, it may be at least 60 wt%, more preferably at least 70 wt%, and most preferably at least 80 wt%.

The polyvinylidene fluoride composite may be in any form used in the art, for example, may be in the form of a film or fiber.

After obtaining the polyvinylidene fluoride composite from the mixed solution in which the inorganic oxide and polyvinylidene fluoride are dispersed, the method may further include heating to evaporate the residual solvent.

In addition, by applying a strong electric field to the polyvinylidene fluoride composite to further perform a poling process, the piezoelectric effect can be increased by aligning the dipoles in the composite.

In another aspect of the present invention

A piezoelectric element including the polyvinylidene fluoride composite is provided.

The contents described in the description of the polyvinylidene fluoride composite and its manufacturing method are applicable even if the description is not repeated in the piezoelectric element.

The β- and γ-phase polyvinylidene fluoride included in the polyvinylidene fluoride composite may be included in the piezoelectric element because polarization is made by pressure.

The piezoelectric element may be used in a piezoelectric ultrasonic sensor, a pressure sensor, a knocking sensor, a safety actuator, an ultrasonic application device, and the like.

In another aspect of the invention

preparing a polyvinylidene fluoride composite by the method for preparing the polyvinylidene fluoride composite; and

There is provided a method for manufacturing a piezoelectric element comprising; manufacturing a piezoelectric element including the polyvinylidene fluoride composite.

The contents described in the description of the polyvinylidene fluoride composite and its manufacturing method are applicable even if the description is not repeated in the piezoelectric element manufacturing method.

Hereinafter, the present invention will be described in more detail through Examples, Comparative Examples and Experimental Examples. The scope of the present invention is not limited to specific embodiments, and should be construed by the appended claims. In addition, those skilled in the art will understand that many modifications and variations are possible without departing from the scope of the present invention.

<Preparation Example 1> Preparation of fluorine-doped inorganic oxide (PVDF: r-TiO ₂ = 1:1)

1 g of rutile TiO ₂ particles (R960, Dupont Co.) and 1 g of PVDF powder (K-761, Elf Atochem of North America Inc.) were simply mixed.

In order to dope the surface of the rutile TiO _{2 particles with fluorine, the powder mixed with the simple mixed rutile TiO 2} particles and PVDF was heat-treated in an air atmosphere at a temperature of 500° C. for 6 hours using a kiln.

The resulting product was purified by successive steps of ethanol treatment, cross-flow filtration and drying under nitrogen (10 hours at 50°C). This purification step was repeated three times to completely remove residual PVDF.

<Preparation Example 2> Preparation of fluorine-doped inorganic oxide (PVDF: r-TiO ₂ = 2:1)

It was prepared in the same manner as in Preparation Example 1, but 2 g of PVDF powder was mixed.

<Preparation Example 3> Preparation of fluorine-doped inorganic oxide (PVDF: r-TiO ₂ = 3:1)

It was prepared in the same manner as in Preparation Example 1, but 3 g of PVDF powder was mixed.

<Preparation Example 4> Preparation of fluorine-doped inorganic oxide (PVDF: r-TiO ₂ = 4:1)

It was prepared in the same manner as in Preparation Example 1, but 4 g of PVDF powder was mixed.

<Example 1-1> PVDF composite preparation (fluorine-doped r-TiO ₂ 0.5 wt%)

0.005 g of the fluorine-doped r-TiO ₂ particles of Preparation Example 1 were placed in 9 g of DMF (>97%, Sigma-Aldrich) and dispersed using an ultrasonic disperser. After that, 0.995 g of PVDF was added to the mixed solution and dispersed using an ultrasonic sprayer. Finally, using a stirrer, at room temperature, the mixture was mixed at a speed of 600 rpm for 30 minutes.

After spraying 2 ml of the mixture on the PET film, it was doped using a bar coater, and then heat-treated at 80° C. for 5 minutes.

<Example 1-2> PVDF composite preparation (fluorine-doped r-TiO ₂ 1.0 wt%)

It was prepared in the same manner as in Example 1-1, except that _{0.01 g of fluorine-doped r-TiO 2} particles and 0.99 g of PVDF were dispersed.

<Example 1-3> PVDF composite preparation (fluorine-doped r-TiO ₂ 2.0 wt%)

It was prepared in the same manner as in Example 1-1, but fluorine-doped r-TiO ₂ particles of 0.02 g and 0.98 g of PVDF were dispersed.

<Example 1-4> PVDF composite preparation (fluorine-doped r-TiO ₂ 5.0 wt%)

It was prepared in the same manner as in Example 1-1, except that _{0.05 g of fluorine-doped r-TiO 2} particles and 0.95 g of PVDF were dispersed.

<Examples 2-1 to 2-4>

Examples 1-1 to 1-4 were prepared in the same manner as, but the fluorine-doped r-TiO ₂ particles of Preparation Example 2 were used.

<Examples 3-1 to 3-4>

Prepared in the same manner as in Examples 1-1 to 1-4, fluorine-doped r-TiO ₂ particles of Preparation Example 3 were used.

<Examples 4-1 to 4-4>

Prepared in the same manner as in Examples 1-1 to 1-4, fluorine-doped r-TiO ₂ particles of Preparation Example 4 were used.

<Comparative Example 1-1>

A pure PVDF film was prepared.

<Comparative Examples 2-1 to 2-4>

It was prepared in the same manner as in Example 4, but r-TiO ₂ particles not doped with fluorine were used.

The weight of the non-fluorine-doped r-TiO ₂ particles was 0.005 g (Comparative Example 2-1), 0.01 g (Comparative Example 2-2), 0.02 g (Comparative Example 2-3), 0.05 g (Comparative Example 2-4) ) to prepare a PVDF composite.

<Comparative Example 3>

It was prepared in the same manner as in Example 4, but 0.05 g of _{a-TiO 2 particles not doped with fluorine were used.}

<Experimental Example 1> Fluorine-doped r-TiO ₂ analysis

Non-fluorine-doped r-TiO ₂ (FIG. 2a) and r-TiO ₂ (FIG. 2b, 2c) of Preparation Example 4 were analyzed through a scanning electron microscope (Hitachi, S-4300) and EDS, and SEM and EDS pictures are shown in FIG. 2 . It can be seen that F is doped through the fact that the positions of Ti and F in the EDS picture are the same.

The XRD and XPS graph with respect to the fluorine is not doped TiO ₂ and r-from preparation 4 r-TiO ₂ is shown in Figure 3b and Figure 3a, respectively. It can be seen that both particles are in a rutile phase through XRD, and F peak appears only _{in r-TiO 2 of Preparation Example 4 through XPS.}

Table 1 shows the surface charges according to the ratio of _{r-TiO 2} and PVDF mixed before heat treatment for undoped r-TiO ₂ and Preparation Examples 1 to 4, respectively.

Primary measurement (mV) Secondary measurement (mV) Third measurement (mV) Average (mV) r-TiO ₂ 3.81 4.28 5.38 3.81 Preparation Example 1 -5.26 -6.41 -5.81 -5.29 Preparation 2 -6.5 -6.52 -6.67 -6.5 Preparation 3 -9.97 -10.3 -10.5 -9.97 Preparation 4 -11.5 -11.5 -12.0 -11.5

From Table 1, it can be seen that as the ratio of PVDF increases, the doping of F increases as the negative charge value of the surface charge increases.

<Experimental Example 2> Phase analysis of PVDF composite

FT-IR analysis was performed on Examples 1 to 4 and Comparative Examples 2-1 to 2-4, and is shown in FIG. 5 .

5A is for Comparative Examples 2-1 to 2-4, FIG. 5B is for Examples 1-1 to 1-4, and FIG. 5C is for Examples 2-1 to 2-4. FIG. 5D shows Examples 3-1 to 3-4, and FIG. 5E shows FT-IR analysis of Examples 4-1 to 4-4.

Referring to FIG. 5A , it can be seen that Comparative Examples 2-1 to 2-4 have high-strength peaks in the region corresponding to the α phase, which is the non-electroactive phase, regardless of the amount of _{r-TiO 2 used.} That is, this means that r-TiO ₂ not doped with fluorine does not affect the phase transition of PVDF.

On the other hand, in FIGS. 5B to 5E , it can be seen that the peak corresponding to the α phase is decreased, and the peaks corresponding to the β and γ phases are sharply increased. In addition, it can be seen that the peaks corresponding to the β and γ phases gradually increase in intensity according to the amount of _{fluorine-doped r-TiO 2 .}

In addition, as the peaks corresponding to the β and γ phases increase from 5b to 5d, it can be seen that as the ratio of PVDF during fluorine doping increases, the doping degree of F increases, and thus the electroactive phase increases. .

6 is a graph showing the ratio of the electroactive phase according to the mass fraction for Examples 1 to 4 and Comparative Example 2. The ratio of the electroactive phase was calculated as in Equation 1 below.

<Equation 1>

Electroactive phase ratio = X _e /(X _α + X _e ) = A _e /{(K _e /K _α )A _α + A _e }

where X _e and X _α are the mole fractions of the _{electroactive phase and the α phase, respectively, K e} = 0.150 and K _α = 0.365 μm ^-1 are the magnetic permeability coefficients of the electroactive phase and the α phase, respectively, A _e = 840 cm ^-1 and A _α = 764 cm ⁻¹ are the absorption intensities of the electroactive phase and the α phase, respectively.

In the case of the composite including _{r-TiO 2} not doped with fluorine as in Comparative Example 2 in FIG. 6, _{the ratio of the active phase slightly increased only when the amount of r-TiO 2} was increased to 1.0 wt%, and from 1.0 to 5.0 wt% As the % increases, the proportion of the electroactive phase remains almost the same, and it can be seen that the proportion of the active phase is up to 30%.

On the other hand, in the case of the composite including _{fluorine-doped r-TiO 2} as in Examples 1 to 4, as _{the amount of fluorine-doped r-TiO 2} increases, the ratio of the PVDF electroactive phase sharply increases, 2.0 In the case of wt%, it can be confirmed that most of the α phase disappears, and the proportion of the electroactive phase is 90% or more.

In addition, as confirmed above, the PVDF ratio at the time of initial fluorine doping increases from Example 1 to Example 4, and it can be seen that the doping degree of F increases, and thus the ratio of the electroactive phase increases.

<Experimental Example 2> Analysis of piezoelectric effect of PVDF composite

After cutting the 20 μm thick composite film prepared in Examples 4-1 to 4-4, Comparative Example 1 and Comparative Example 2-4 to ^{a size of 2 × 2 cm 2} , the Al foils are placed between the two Al foils. placed out of reach. After that, it was placed between two PET films and sealed, and an electric wire was connected to each Al foil.

In contrast, the output voltage in the forward connection is shown in FIGS. 7A to 7F, and the output voltage in the reverse connection is shown in FIGS. 7G to 7i.

In the case of a pure PVDF film and _{a composite film including r-TiO 2} not doped with fluorine, it can be seen that the voltage output is about 137 mV and 127 mV, respectively ( FIGS. 7a and 7b ). _{In the case of including r-TiO 2} not doped with fluorine, rather a slight decrease in performance is observed because the amount of PVDF decreases. That is, it can be seen that r-TiO ₂ not doped with fluorine has no effect on the improvement of the piezoelectric effect in the PVDF matrix.

On the other hand, in the case of a fluorine-doped r-TiO _2, Examples 4-1, 4-4 (Fig. 7c through 7f) toward and fluorine doping is increased to r-TiO ₂ from, also as a result the output voltage is increased can be known

In order to confirm whether this electrical signal is due to the piezoelectric effect, a polarity reversal test (Reverse Connection) was performed, and it can be confirmed that the output voltage is reversed as shown in FIGS. 7G to 7I .

That is, it can be seen that the fluorine-doped r-TiO ₂ increases the electroactive phase, and as a result, the piezoelectric performance is improved.

<Experimental Example 3> Characteristic analysis according to light irradiation

For Comparative Examples 3 and 4-4, whether photolysis according to the light irradiation time was investigated, and SEM images and graphs thereof are shown in FIG. 8A. Photolysis experiments were performed using a lamp illuminating a wide range of waves in the range of 200 to 1500 nm with an intensity of 0.1 W/cm ^{2 .} Then, the composite film was irradiated using SEM, and the degree of resolution was estimated by measuring the ratio of the resolved PVDF area to the total area before light irradiation using the open-source image analysis program ImageJ.

As in Comparative Example 3, it can be seen that the film is decomposed by UV irradiation only when _{anatase TiO 2} (a-TiO _{2 ) is used.} It can be confirmed through the SEM image that the shape of the PVDF is severely damaged even in a short period of time. In the initial stage, crack propagation on the surface is due to the absorption of light energy on the surface, which generates a significant amount of free radicals from _{a-TiO 2 , which causes surface degradation.} In the case of the PVDF composite film having a-TiO ₂ , 99% of PVDF is decomposed after 64 hours, and it can be seen that only _{a-TiO 2 remains.}

On the other hand, when using fluorine-doped r-TiO ₂ as in Example 4-4, it can be confirmed that excellent light stability is not decomposed (FIG. 8a), and there is no change in the electroactive phase even when the light irradiation time is increased. It can be confirmed that there is no (Fig. 8b).

Claims (12)

A polyvinylidene fluoride composite comprising an inorganic oxide doped with fluorine,
The sum of the proportions of β-type and γ-form crystal structures with respect to the total α-type, β-type, γ-type, δ-type and ε-type crystal structures included in the polyvinylidene fluoride is 50% by weight or more,
The inorganic oxide is at least one selected from the group consisting of SiO ₂ , r-TiO ₂ , Al ₂ O ₃ , BaTiO ₃ , Pb[Zr _x Ti _1-x ]O ₃ (PZT), ZnO, ZnSnO ₃ and GaN. Polyvinylidene fluoride composite, characterized in that.
delete delete According to claim 1,
The polyvinylidene fluoride composite is a polyvinylidene fluoride composite, characterized in that in the form of a film.
doping the inorganic oxide with fluorine; and
dispersing the fluorine-doped inorganic oxide and polyvinylidene fluoride in an organic solvent;
The method for preparing the polyvinylidene fluoride composite of claim 1 comprising:
The inorganic oxide in the fluorine-doped inorganic oxide is SiO ₂ , r-TiO ₂ , Al ₂ O ₃ , BaTiO ₃ , Pb[Zr _x Ti _1-x ]O ₃ (PZT), ZnO, ZnSnO ₃ and GaN. A method for producing a polyvinylidene fluoride composite, characterized in that at least one selected from the group consisting of.
6. The method of claim 5,
The step of doping the inorganic oxide with fluorine is
mixing an inorganic oxide and a fluorine-based polymer; and
heat-treating the mixture;
Polyvinylidene fluoride composite manufacturing method comprising a.
7. The method of claim 6,
The fluorine-based polymer is Poly (vinylidene fluoride), Poly (vinylidene fluoride - co - hexafluoropropylene), Poly (vinylidene fluoride - co - trifluoroethylene), Poly (vinylidene fluoride-co-chlorotrifluoroethylene), Poly (hexafluoropropylene) and Poly (hexafluoro isobutylene) Polyvinylidene fluoride composite manufacturing method, characterized in that at least one selected from the group consisting of.
6. The method of claim 5,
The step of doping the inorganic oxide with fluorine is
Method for producing a polyvinylidene fluoride composite comprising the step of contacting the inorganic oxide with HF gas.
6. The method of claim 5,
The organic solvent is a polyvinylidene fluoride complex manufacturing method, characterized in that at least one selected from the group consisting of DMF, DMAc, Acetone and NMP.
6. The method of claim 5,
The polyvinylidene fluoride composite manufacturing method is after dispersing the fluorine-doped inorganic oxide and polyvinylidene fluoride in an organic solvent.
Polyvinylidene fluoride composite manufacturing method, characterized in that it further comprises the step of obtaining a polyvinylidene fluoride composite from the mixed solution in which the inorganic oxide and polyvinylidene fluoride are dispersed.
A piezoelectric element comprising the polyvinylidene fluoride composite of claim 1.
Preparing a polyvinylidene fluoride composite by the polyvinylidene fluoride composite manufacturing method of claim 5; and
A piezoelectric element manufacturing method comprising a; manufacturing a piezoelectric element including the polyvinylidene fluoride composite.

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