JPH05194974A - Electric-field-responsive fluid - Google Patents

Abstract

PURPOSE:To obtain the subject fluid which is stable as a fluid and shows remarkably the Winslow effect by using a molar ratio of the constituent Ba to the constituent Ti in which the constituent Ti predominates and is present in an amount at most 10 times as large as the amount of the constituent Ba. CONSTITUTION:In the objective electric-field-responsive fluid, wherein the dispersing medium is an organic solvent, the dispersoid is ultramicroparticulate amorphous or tetragonal barium wherein the constituent Ti predominates and is present in an amount at most 10 times as large as the amount of the constituent Ba in a molar ratio of the constituent Ba to the constituent Ti. This fluid is stable as a fluid and has a feature of being thickened when an alternating or direct electric field is applied thereto, namey it markedly shows the so-called Winslow effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric field responsive fluid (= electrorheological fluid, hereinafter referred to as "electrorheological fluid", which has a characteristic of increasing viscosity when an alternating electric field or a direct electric field is applied) ER fluid).

[0002]

2. Description of the Related Art Conventionally, ER fluids have been attempted to be put to practical use in various applications such as automobile engine mounts, shock absorbers, dampers, etc., because they exhibit the Winslow effect. As the above-mentioned ER fluid, a fluid in which fine particles having a ferroelectricity such as barium titanate are dispersed in a solvent (Japanese Patent Publication No. 2-38538) or a fluid in which silica fine particles are dispersed in a solvent (Japanese Patent Laid-Open No. 2004-38538) 61-449
98), fluids in which fine particles of aluminum silicate are dispersed in a solvent (JP-A-62-95397), and the like are known.

[0003]

However, in order to produce the above-described fine particle-dispersed fluid, it is necessary to stably disperse the fine particles as a dispersoid in the dispersion medium. Here, in order to disperse the fine particles in the dispersion medium in consideration of Brownian motion, the limit particle diameter is approximated by the following expression (1). 4πr ^3/3 = kT / in _{[(ρ n -ρ 1) g} ] ... (1) the above equation, r is the radius of the particle, k is the Boltzmann constant, T is the absolute temperature, g is the gravitational acceleration, [rho _n the microparticles , Ρ ₁ is the density of the dispersion medium. Where ρ _n ≈500
0 kg / m ^3, when the _{ρ n -ρ 1 ≒ 4000kg / m} 3, the influence of Brown und when the radius r of the fine particles below 20nm is larger than the influence of gravity, the microparticles is estimated that does not settle It Therefore, from the balance of Brownian motion and sedimentation, 20 nm or less, preferably 10 nm
It is necessary to prepare ultrafine particles having the following particle sizes.

However, it is difficult to form ultrafine particles having a particle size of 20 nm or less by, for example, a method of pulverizing a ferroelectric substance, and in addition, there is an example in which such ultrafine particles having a relatively high dielectric constant are produced. Absent. Therefore, this 2
A method for preparing ferroelectric ultrafine particles having a particle size of 0 nm or less and an ER fluid in which the particles are stably dispersed have been desired.

[0005]

The present invention has been proposed in view of the above, and an ER fluid in which the dispersion medium is an organic solvent and the dispersoid is ultrafine particles of amorphous or tetragonal barium titanate. In the above E, the molar ratio of barium to titanium, which is its constituent component, is larger in titanium and is in a range not exceeding 10 times that of barium.
It relates to the R fluid. Further, the present invention also proposes an ER fluid in which, in the above-mentioned ultrafine particles of barium titanate, barium which is a constituent component thereof is partially replaced with one or more of strontium, calcium and magnesium.

As described above, in order to produce an ER fluid, it is necessary to produce ultrafine particles of barium titanate having a particle size of 20 nm or less and a high dielectric constant. First, as the first method for adjusting barium titanate,
A method in which a titanium alkoxide, for example, titanium isopropoxide is added to an alkaline solution in which barium ions are present, for example, a barium hydroxide aqueous solution, and the mixture is hydrolyzed is used. The hydrolysis reaction is considered to be 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 FIG. 1 shows the result of adjusting barium titanate having a molar ratio of barium to titanium of 1: 1 at a reaction temperature of 313 to 353 K by the above method. As is clear from the figure, the average particle size of the adjusted barium titanate is 5
At ~ 20 nm, the particle size decreased as the reaction temperature decreased, and the ultrafine particles of barium titanate reacted at 333 K or higher were confirmed to be cubic by X-ray diffraction and showed ferroelectricity. There wasn't. Further, the ultrafine particles of barium titanate reacted at 333 K or less became amorphous, but did not show a sufficiently high dielectric constant.

As a second method for adjusting barium titanate, a titanium alkoxide and barium alkoxide, for example, a mixed solution of titanium isopropoxide and barium isopropoxide is heated in a nitrogen atmosphere and distilled water is added. The method of adjusting by doing. In the above-mentioned method, barium titanate having a molar ratio of barium to titanium of 1: 1 was adjusted at a reaction temperature of 350K, and the barium titanate was further sintered in an air atmosphere at 1073K for 5 minutes. The barium titanate prepared at the beginning had a grain size of about 20 nm, but did not exhibit ferroelectricity in the cubic system, and barium titanate sintered for 5 minutes at 1073 K showed a cubic to tetragonal system. However, no change was observed in the dielectric constant at 1 kHz.
The particle size was 0 nm. As described above, barium titanate having a molar ratio of barium to titanium of 1: 1 can be prepared by either the first method or the second method.
Ultrafine particles having a particle size of nm or less and a high dielectric constant cannot be obtained.

Next, barium titanate was prepared by the above-mentioned first method or second method so that the proportion of titanium was higher than the proportion of barium. The obtained barium titanate was non-radioactive. Crystalline, average particle size 5-10n
It was ultrafine particles of m. In particular, barium titanate having a titanium content slightly higher than that of barium exhibited a high dielectric constant. It was also found that barium titanate having a molar ratio of barium to titanium up to 1:10 exhibited a sufficiently high dielectric constant as the proportion of titanium was increased.
On the other hand, the barium titanate produced by reacting with the barium ratio higher than the titanium ratio showed only a low dielectric constant as in the barium titanate in which the molar ratio of barium to titanium was 1: 1.

As described above, barium titanate has a low dielectric constant when its composition is such that the ratio of barium is higher than that of titanium or the molar ratio thereof is 1: 1, but barium titanate is Regarding the molar ratio with respect to titanium, titanium is larger and shows a high dielectric constant in a range not exceeding 10 times that of barium, for example, in a range of 1: 1.01 to 1:10.

As described above, by using the above-mentioned first method or second method, the molar ratio of barium to titanium is larger in titanium and is larger than that in barium.
If barium titanate is prepared in a range not exceeding twice,
Ultrafine particles having a particle size of 0 nm or less and a high dielectric constant can be obtained.

The ultrafine particles of barium titanate thus prepared are kerosene, alkylnaphthalene and poly-α.
-In organic solvents such as olefins, silicone oils, esters, ethers, other petroleum solvents, mineral oils and vegetable oils, for example, sodium oleate, alkylammonium acetate, alkylsulfosuccinate, n-acyl as a dispersion aid Amino acid and its salt, n-alkyltrimethylene diamine derivative, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl ether acetate, alkyl phosphate, alkali acetate, etc. Stirring with a homogenizer enables stable dispersion, and an ER fluid sensitive to an electric field can be produced.

Since the above-mentioned dielectric has a characteristic that the permittivity increases at a certain temperature, fine particles of barium titanate having a molar ratio of barium to titanium of 1: 1.07 are about 353K. Shows the maximum value of the dielectric constant, and the ER fluid in which the ultrafine particles of barium titanate are dispersed also shows a high dielectric constant at about 353K, that is, at 80 ° C.

By substituting 5 to 10% of barium in the above barium titanate with one or more of strontium, calcium and magnesium, an ER fluid exhibiting a high dielectric constant even at room temperature can be produced.

[0014]

【Example】

(Preparation of Barium Titanate Ultrafine Particles) The following reagents were prepared to prepare barium titanate particles. 0.3-0.4 mol / l in isopropanol
Titanium isopropoxide 0.2-0.4 mol / l barium hydroxide in heated distilled water 0.3-0.4 mol / l obtained by dissolving metal barium in isopropanol at about 350 K in nitrogen atmosphere.
l barium isopropoxide

A reagent is added to the above-mentioned reagents, and 32
Barium titanate was prepared by heating to 0K.

Further, a mixed solution of the above reagents and reagents was heated at 350 K in a nitrogen atmosphere, distilled water was added to prepare barium titanate, and calcium carbonate was removed by acid washing.

With respect to the barium titanate fine particles prepared by the above-mentioned two methods, the average particle diameter and the molar ratio of the constituents were measured by the following measuring methods.

(Measurement of average particle size) From the measurement using a pycnometer, the density of the ultrafine particles of barium titanate was about 5000 k.
It was determined by using the measurement result of the specific surface area by the BET method assuming that it is g / m ³ .

(Measurement of Molar Ratio of Constituents) After fine particles of barium titanate were alkali-melted, the molar ratios of barium and titanium which were the constituents were determined by a gravimetric method and a colorimetric method, respectively.

The prepared barium titanate was X-ray amorphous and had an average particle size of 5 to 10 nm.

FIG. 2 shows the results of measuring the dielectric constant. The volume fraction of ultrafine particles was about 40% when measuring the dielectric constant. Among these ultrafine particles, barium titanate with a molar ratio of barium to titanium of 1: 1.17 was used at a low frequency AC voltage. Shows a higher dielectric constant, eg Lichtene
From the Cker equation [f (ε) = logε], the dielectric constant is
It was calculated to be 2300 at 1 kHz.

FIG. 3 shows the effect of temperature on the permittivity of this adjusted barium titanate. The dielectric constant of barium titanate in which the molar ratio of barium to titanium is 1: 1.07 is 4 at a volume fraction of 40% at 1 kHz and 353K.
0, and the Lichtenecker formula [f (ε) =
log ε] was calculated to be 10,000 or more.

(Preparation of ER fluid) Of the barium titanate fine particles prepared as described above, the particle size is 8 nm.
And 10 g of kerosene containing 1 g of barium titanate having a molar ratio of barium to titanium of 1: 1.17 and 1 g of sodium salt of polyoxyethylene (6) alkyl ether acetate.
It was added to the inside and dispersed by stirring with a homogenizer. The dispersion rate calculated by measuring the weight of the precipitated particles was 60%, and it was observed by a transmission electron microscope that fine particles of barium titanate in this ER fluid exhibited a good dispersion state. In addition, ER in which 2% by volume of barium titanate was dispersed in kerosene
When the dielectric constant due to the temperature change of the fluid was measured, when the measurement frequency was 500 Hz, the dielectric constant suddenly increased at 353 K and reached 300 at about 383 K. The increase of the dielectric constant was remarkable when the low frequency AC voltage was applied. The measurement voltage is 1 V, and the temperature at which the maximum permittivity of this ER fluid is
It was slightly different from the measurement result of the fine particles alone.

(Winslow effect measurement) Particle size is 8 nm
Then, an ER fluid in which barium titanate having a molar ratio of barium to titanium of 1: 1.17 was dispersed in paraffin and dodecane was prepared, and an alternating electric field was applied to the ER fluid to measure shear stress and shear rate. The relationship was measured. The results are shown in FIGS. 4 and 5. A yield value occurred for the ER fluid of the present invention and behaved like a Bingham fluid. In addition, it was confirmed that the shear stress was increased in accordance with the strength of the electric field to be an ER fluid.

(Measurement of levitation force) In the apparatus shown in FIG. 6, the levitation force received by the soda lime glass balls in the ER fluid prepared as described above was measured. The glass bulb is hung by a cotton thread on the load cell to measure the weight change. In this case, the measured value is shown with respect to the distance from the point O in FIG. 6, and the levitation force in the insulator is given by Lin et al. F = 2πR ³ ε ₀ ε ₁ (ε ₂ −ε ₁ ) / (ε ₂ + 2ε ₁ ) × ∇E ₀ ² (2) where ε ₁ and ε ₂ are the dielectric constants of the fluid and the object, and ∇E
₀ ² represents the slope of the square of the electric field strength, and ε ₀ is the dielectric constant of vacuum. The ε _{2 of} this glass sphere is 7.5 and the radius R is 0.005 m. The equation of levitation force according to the shape of the electrode reported by Adamson is expressed by the following equation (3). F = (9/2) πR ³ V ² (h) ⁻³ ε ₀ ε ₁ (ε ₂ −ε ₁ ) / (ε ₂ + 2ε ₁ ) ... (3) where V is the voltage between the copper electrodes and h is It is the distance shown in FIG. The levitation force of 30 kg / cm ² acts on the glass ball,
This agrees with the value calculated from the equation (3). If the concentration of dispersoid barium titanate in the fluid is increased or ultrafine particles having a higher dielectric constant are used, the levitation force is further increased.

[0026]

As described above, since the ER fluid of the present invention is obtained by stably dispersing fine particles having a high dielectric constant in an organic solvent, it is not possible to use a conventional dielectric as a fluid dielectric. It is expected to be used in various applications and devices that cannot be applied, and has extremely high practical value and contribution. For example, when the ER fluid is formed into a thin film having a thickness of several μm and an electric field is applied perpendicularly to the thin film, the light passing through the thin film controls the electric field, so that an optical shutter similar to the magneto-optical effect using the magnetic fluid, It is expected to be applied to optical modulators. Further, since the electric field gradient acts on the ER fluid and the pressure acts on it, the force is smaller than that of the magnetic fluid, but the position of the object in the ER fluid can be controlled to some extent. Furthermore, by mixing the ER fluid in the liquid crystal,
A response different from the case where an electric field is applied to a conventional liquid crystal is expected, and when mixed with a magnetic fluid, for example, when using a conventional oil-based magnetic fluid as a printer ink,
Compared with the low dielectric constant, the ER fluid has a high dielectric constant and is easily colored, and the printing speed when an electric field is applied can be made extremely high. Also, the electric field response can be improved. Further, the fact that the permittivity of the ER fluid depends on the temperature and takes the maximum value at a certain temperature is different from the fact that the magnetization of the magnetic fluid decreases as the temperature rises. You can control the movement. The ER fluid of the present invention is expected to be used in various ways as described above. In each use, it is sufficient to apply a voltage to generate an electric field. Does not happen.

The ER fluid of the present invention as described above can be produced very simply, inexpensively, rapidly and with stable quality without requiring complicated steps or special equipment.

[Brief description of drawings]

FIG. 1 is a correlation diagram between a reaction temperature and an average particle diameter in barium titanate having a molar ratio of barium to titanium of 1: 1.

FIG. 2 is a correlation diagram of frequency and dielectric constant in barium titanate prepared at various molar ratios.

FIG. 3 is a correlation diagram between temperature and dielectric constant.

FIG. 4 is a correlation diagram showing the relationship between shear stress and shear rate when an alternating electric field is applied to the ER fluid of the present invention having paraffin as a dispersion medium.

FIG. 5 is a correlation diagram showing the relationship between shear stress and shear rate when an alternating electric field is applied to the ER fluid of the present invention having dodecane as a dispersion medium.

FIG. 6 is a buoyancy measuring device using the ER fluid of the present invention.

Claims (2)

[Claims] 1. An electric field responsive fluid in which a dispersion medium is an organic solvent and a dispersoid is ultrafine particles of amorphous or tetragonal barium titanate in a molar ratio of its constituent components, barium and titanium. , Titanium is larger, and the electric field responsive fluid is characterized in that it does not exceed 10 times that of barium. 2. The electric field response according to claim 1, wherein the barium titanate ultrafine particles are obtained by substituting at least one of strontium, calcium and magnesium for part of barium which is a constituent thereof. Sex fluid.