JP2949597B2 - Ferroelectric fluid and method of manufacturing the same - Google Patents

Description

The present invention relates to a ferroelectric fluid and a method for producing the same.

(Prior art) A magnetic fluid is a magnetic fluid in which ferromagnetic fine particles are stably dispersed as a dispersoid in a dispersion medium, and exhibits a unique behavior in a magnetic field as a magnetic substance having fluidity, so that it is used for various applications. Have been.

However, the magnetic fluid as described above needs to generate a magnetic field by arranging permanent magnets or electromagnets according to various applications and devices, but when applying a force to the fluid,
Magnetic fluid cannot be applied to a magnetic fluid that is shielded by a ferromagnetic material, and levitation force cannot be applied by applying a magnetic field to a ferromagnetic material in a magnetic fluid. Was.

On the other hand, a ferroelectric substance is a substance in which the dielectric constant increases at a certain temperature and the state where dielectric polarization occurs without applying an electric field exists as a stable state, and is used for audio equipment and small capacitors. It is. If a ferroelectric fluid can be produced by stably dispersing the ferroelectric as a dispersoid in a dispersion medium, that is, a ferroelectric fluid, by generating an electric field,
It is expected that the ferroelectric material having fluidity can be applied to various uses, and it is expected that the above-described drawbacks associated with the generation of a magnetic field in the magnetic fluid will not occur.

In order to produce the above ferroelectric fluid, it is necessary to stably disperse ferroelectric ultrafine particles as a dispersoid in a dispersion medium. The critical particle size for dispersing ultrafine ferroelectric particles in a solvent in consideration of Brownian motion is given by the following equation [1].
Is approximated by

^{4πr 3/3 = kT [(} ρ n -ρ 1) g] [1] ultrafine particles of the radius of the above formula r is ferroelectric, k is the Boltzmann constant, T is the absolute temperature, g is the gravitational acceleration, [rho _n Is the density of the particles, and ρ ₁ is the density of the dispersion medium. Where ρ _n ≒ 50
00kg / m ^3, when the _{ρ n -ρ 1 ≒ 4000kg / m} 3, the strength at the radius r of the ultrafine particles dielectric 20nm or less, the influence of Brownian motion becomes greater than the influence of gravity, the particles unless settle Presumed.

Therefore, the balance between Brownian motion and sedimentation is 20
It is necessary to prepare ferroelectric ultrafine particles having a particle diameter of not more than nm, preferably not more than 10 mn.

<Problems to be solved by the invention> However, for example, in a method of pulverizing a ferroelectric,
It is difficult to make ultrafine particles having a particle size of 20 nm or less, and there is no example of producing such ferroelectric ultrafine particles.

Therefore, a method for preparing the ferroelectric ultrafine particles having a particle diameter of 20 nm or less and a ferroelectric fluid obtained by stably dispersing the method have been desired.

<Means for Solving the Problems> The present invention has been proposed in view of the above, wherein the dispersion medium is an organic solvent, and the dispersoid is amorphous or tetragonal barium titanate ultrafine particles of 20 nm or less. The molar ratio of barium to titanium, which is a constituent of titanium, is larger than titanium and does not exceed twice the barium, and the dispersoid performs Brownian motion in the dispersion medium. And a method for manufacturing the same.

The present invention also proposes a ferroelectric fluid in which the barium titanate ultrafine particles are partially substituted with at least one of strontium, calcium, and magnesium.

As mentioned above, to make a ferroelectric fluid,
It is necessary to produce ultrafine particles of barium titanate having a particle diameter of 20 nm or less and having a high dielectric constant.

First, as a first method for preparing barium titanate, a titanium alkoxide, for example, titanium isopropoxide is added to an alkali solution containing barium ions, for example, an aqueous barium hydroxide solution, and the barium titanate is adjusted by hydrolysis. Method.

 This hydrolysis reaction is considered as the following reaction.

_{Ti ((CH 3) 2 CHO} ) 4 + 4H 2 O + Ba 2+ +2 (OH) - → Ti (OH) 6 2+ Ba 2 +4 (CH 3) 2 CHOH → BaTiO 3 +4 (CH 3) 2 CHOH + 3H 2 O The above FIG. 1 shows the results obtained by adjusting barium titanate having a molar ratio of barium to titanium of 1: 1 at a reaction temperature of 313 to 353 K in the above method. As is clear from the figure,
The average diameter of the adjusted barium titanate is 5 to 20 nm,
The particle diameter decreased as the reaction temperature decreased, and the barium titanate ultrafine particles reacted at 333 K or higher were confirmed to be cubic by X-ray diffraction, and did not exhibit ferroelectricity. Further, the ultrafine particles of barium titanate reacted at 333 K or lower became amorphous, but did not show a sufficiently high dielectric constant.

As a second method for adjusting barium titanate, titanium alkoxide and barium alkoxide,
For example, there is a method in which a mixed solution of titanium isopropoxide and barium isopropoxide is heated in a nitrogen atmosphere and adjusted by adding distilled water.

In the above method, the molar ratio of barium to titanium is adjusted to 1: 1 barium titanate at a reaction temperature of 350K, and further, the barium titanate is placed in an air atmosphere at 1073K.
For 5 minutes. The initially adjusted barium titanate had a particle size of about 20 nm, but did not exhibit ferroelectricity in a cubic system. The barium titanate sintered at 1073 K for 5 minutes changed from a cubic system to a tetragonal system. However, no change was observed in the dielectric constant at 1 kHz, and the particle size was 80 nm.

As mentioned above, the molar ratio of barium to titanium is 1: 1
Is adjusted by the first method,
Even if adjusted by the second method, ultrafine particles having a particle size of 20 nm or less and having a high dielectric constant will not be obtained.

Next, by the first method or the second method described above,
When barium titanate was prepared by increasing the ratio of titanium to the ratio of barium, the obtained barium titanate was X-ray amorphous and was ultrafine particles having an average particle size of 5 to 10 nm. In particular, barium titanate, in which the proportion of titanium was slightly greater than the proportion of barium, showed a high dielectric constant. Further, as the proportion of titanium was increased, it was found that barium titanate having a molar ratio of barium to titanium of up to 1: 2 exhibited a sufficiently high dielectric constant.

On the other hand, barium titanate produced by reacting with the barium ratio being greater than the titanium ratio exhibited only a low dielectric constant, similarly to the barium titanate having a molar ratio of barium to titanium of 1: 1.

As described above, in the composition of barium titanate, when the ratio of barium is larger than the ratio of titanium or the molar ratio is 1: 1, the barium titanate shows only a low dielectric constant. In terms of molar ratio, titanium is larger and exhibits a high dielectric constant in a range not exceeding twice that of barium, for example, in a range of 1: 1.01 to 1: 2.

As described above, the first method or the second method
When the barium titanate having a molar ratio of barium to titanium is larger than that of barium and not more than twice as large as barium using the method described above, a particle size of 20 nm or less and a high dielectric constant are obtained. It is possible to obtain ultrafine particles having a high efficiency.

The barium titanate ultrafine particles thus prepared can be stably dispersed in an organic solvent such as kerosene, for example, by adding a surfactant as a dispersing aid and stirring with an ultrasonic or homogenizer. A ferroelectric fluid sensitive to an electric field can be produced.

As described above, since the ferroelectric substance has a characteristic that the dielectric constant increases at a certain temperature, for example, the molar ratio of barium and titanium is 1: 1.07, barium titanate fine particles,
The dielectric constant shows a maximum value at about 353K, and the ferroelectric fluid in which the barium titanate ultrafine particles are dispersed also shows a high dielectric constant at about 353K, that is, 80 ° C.

In addition, 5 to 10 of barium titanate described above is used.
By replacing% with one or more of strontium, calcium, and magnesium, a ferroelectric fluid exhibiting a high dielectric constant even at room temperature can be produced.

<Example> [Preparation of barium titanate ultrafine particles] In order to prepare barium titanate particles, the following reagents were prepared.

0.3 to 0.4 mol / l titanium isopropoxide in isopropanol 0.2 to 0.4 mol / l barium hydroxide in heated distilled water 0.3 to 0.4 mol / l obtained by dissolving barium metal in isopropanol at about 350 K in a nitrogen atmosphere Barium isopropoxide of 0.4 mol / l A reagent was added to the above reagent, and heated to 320 K to prepare barium titanate.

Further, the mixed solution of the above-mentioned reagent and the reagent was heated at 350 K in a nitrogen atmosphere, distilled water was added to prepare barium titanate, and calcium carbonate was removed with an acid and washed.

The average particle diameter, dielectric constant, and molar ratio of the constituents of the barium titanate fine particles prepared by the above two methods were measured by the following measurement methods.

(Measurement of Average Particle Size) From the measurement with a specific gravity bottle, the barium titanate ultrafine particles were determined to have a density of about 5000 kg / m ³ , and were determined using the measurement results of the specific surface area by the BET method.

(Measurement of Dielectric Constant) A sample was filled between the circular electrodes, and measured with an LCR meter. Here, the dielectric constant of an irregular mixture of two or three non-conductive components was calculated using the following Lichtenecker equation, which is known to best agree with the experimental results.

f (ε) = δ ₁ f (ε ₁ ) + δ ₂ f (ε) ₂ , δ ₁ + δ ₂ [2] f (ε) = logε [3] (Measurement of Molar Ratio of Constituents) After fine particles of barium titanate were alkali-melted, the molar ratios of the constituents barium and titanium were determined by a weight ratio and a colorimetric method, respectively.

The prepared barium titanate is X-ray amorphous,
Its average particle size was 5-10 nm.

FIG. 2 shows the result of measuring the dielectric constant. The volume fraction of the ultrafine particles is about 40% when measuring the dielectric constant, and among these ultrafine particles, barium titanate with a molar ratio of barium to titanium of 1: 1.17 is higher at low frequency AC voltage The dielectric constant was calculated. For example, the dielectric constant was calculated to be 2300 at 1 kHz from Lichtenecker's equation [3] described above.

FIG. 3 shows the effect of temperature on the dielectric constant of the prepared barium titanate. The dielectric constant of barium titanate with a molar ratio of barium to titanium of 1: 1.07 is 1 kHz, 353 K
Shows 40 at a volume fraction of 40%, and was calculated to be 10,000 or more according to Lichtenecker's equation [3].

[Preparation of Ferroelectric Fluid] Of the barium titanate fine particles prepared as described above, the particle diameter is 8 nm, and the molar ratio of barium to titanium is
1 g of barium titanate of 1: 1.17 was added to 10 g of kerosene containing 1 g of polyoxyethylene (6) alkyl ether acetate sodium salt, and dispersed by stirring with a homogenizer.

The dispersion rate calculated by measuring the weight of the sedimented particles was 60%, and it was observed by a transmission electron microscope that the fine particles of barium titanate of the ferroelectric fluid exhibited a good dispersion state.

In addition, when the dielectric constant of a ferroelectric fluid in which barium titanate having a volume fraction of 2% was dispersed in kerosene due to temperature change was measured, when the measurement frequency was 500 Hz, the dielectric constant suddenly increased at 353K. It was 300 at 383K. The increase in the dielectric constant was remarkable when a low frequency AC voltage was applied. still,
The measurement voltage was 1 V, and the temperature at which the maximum dielectric constant of the ferroelectric fluid was slightly different from the measurement result of the fine particles alone.

[Measurement of Levitation Force] Using the apparatus shown in FIG. 4, the levitation force applied to the soda-lime glass sphere of the ferroelectric fluid produced as described above was measured. The glass sphere is suspended by a cotton thread in a load cell to measure a change in weight. In this case, the measured value is shown with respect to the distance from the point O in FIG. 4, and the levitation force in the absolute body is expressed by Lin et al. By the following equation [4].

F = 2πR ³ ε ₀ ε ₁ (ε ₂ −ε ₁ ) / (ε ₂ + 2ε ₁ ) × ▽ E ₀
² [4] where ε ₁ and ε ₂ are the dielectric constants of the fluid and the body, respectively, ▽ E ₀
² indicates the gradient of the square of the electric field strength, and ε ₀ is the dielectric constant of vacuum. The glass sphere has an ε ₂ of 7.5 and a radius R of 0.005 m. The equation of buoyancy by electrode shape reported by Admson is given by the following equation [5].

F = (9/2) πR ³ V ² (h) ^-3 ε ₀ ε ₁ (ε ₂ −ε ₁ ) / (ε ₂
+ 2ε ₁ ) [5] Here, V is the voltage between the copper electrodes, and h is the distance shown in FIG. A buoyancy of 30 kg / cm ² acts on the glass ball,
It was consistent with the calculated value from equation [5]. The levitation force is further increased by increasing the concentration of barium titanate as a dispersoid in the fluid or by using ultrafine particles having a higher dielectric constant.

<Effects of the Invention> As described above, since the ferroelectric fluid of the present invention is obtained by stably dispersing fine particles having a high dielectric constant in an organic solvent, a conventional ferroelectric material having fluidity is used. It is expected to be used for various applications and devices that cannot be applied with ferroelectrics, and has a very high practical value and contribution.

For example, a ferroelectric fluid is formed into a thin film having a thickness of several μm,
When an electric field is applied perpendicularly to the thin film, the light passing through the thin film controls the electric field, so that it is expected to be applied to an optical shutter, an optical modulator, and the like in the same manner as the magneto-optical effect using a magnetic fluid.

Further, since the pressure acts by applying an electric field gradient to the ferroelectric fluid, the force is smaller than that of the magnetic fluid, but the position of the object in the ferroelectric fluid can be controlled to some extent.

Furthermore, by mixing a ferroelectric fluid in the liquid crystal, a response different from the case where an electric field is applied to the conventional liquid crystal is expected. When mixed with a magnetic fluid, for example, a conventional oil-based magnetic fluid can be used in a printer. When used as an ink for ink, the ferroelectric fluid has a large dielectric constant and is easily colored, as compared with having a small dielectric constant, and can extremely increase the printing speed when an electric field is applied. . In addition, the electric field response can be improved.

Also, the fact that the dielectric constant of the ferroelectric fluid depends on the temperature and has a maximum value at a certain temperature is different from the fact that the magnetization decreases as the temperature rises in the magnetic fluid. Can control the transfer of heat inside.

The ferroelectric fluid of the present invention is expected to be used in various ways as described above. For each use, an electric field may be generated by applying a voltage, and by applying a magnetic field as in the above-described magnetic fluid. No drawbacks.

In addition, the method for producing a ferroelectric fluid of the present invention does not require special raw materials and a production apparatus, and does not require a multi-step production process. can do.

[Brief description of the drawings]

FIG. 1 is a correlation diagram between the reaction temperature and the average particle size in barium titanate in which the molar ratio of barium and titanium is 1: 1.
FIG. 2 is a correlation diagram between frequency and dielectric constant of barium titanate prepared at various molar ratios, FIG. 3 is a correlation diagram between temperature and dielectric constant, and FIG. 4 uses a ferroelectric fluid of the present invention. It is a buoyancy measuring device.

Claims (4)

(57) [Claims] The dispersion medium is an organic solvent, and the dispersoid is amorphous or tetragonal ultrafine particles of barium titanate having a particle size of 20 nm or less. The ferroelectric fluid is larger than the barium and not more than twice as large as barium, and the dispersoid performs Brownian motion in the dispersion medium. 2. The ultrafine particles of barium titanate according to claim 1 are characterized in that a part of barium constituting the barium titanate is replaced by at least one of strontium, calcium and magnesium. Ferroelectric fluid. 3. Titanium alkoxide is added to an alkaline solution in which barium ions are present, and the molar ratio of barium to titanium generated by heating to 303 to 353K is higher in titanium than in barium. A method of producing a ferroelectric fluid, comprising dispersing ultrafine particles of amorphous or tetragonal barium titanate having a size of not more than twice and having a diameter of 20 nm or less in an organic solvent and performing Brownian motion. 4. A mixed solution of a titanium alkoxide and a barium alkoxide is heated to about 353 K in a nitrogen atmosphere, and the molar ratio of barium to titanium produced by adding distilled water is larger for titanium. Production of ferroelectric fluid characterized by dispersing ultrafine particles of amorphous or tetragonal barium titanate of not more than twice as large as 20 nm or less in an organic solvent and performing Brownian motion Method.