JPH06136344A - Electroviscous fluid - Google Patents

Abstract

(57) [Summary] [Structure] A single molecular species or a mixture of multiple molecular species whose viscosity changes with the application of voltage or the direction of the electric field, and the rate of change of the viscosity is three times or more uniform. An electrorheological fluid consisting of a phase fluid, particularly preferably, the fluid is represented by the following general formula 1 or 2 [Chemical 2] (In the formula, n is a natural number of 1 to 14, X is a single bond or an ether bond, m is 2 or 3, and y is 1 or 2). [Effect] A conventional dispersion stability problem of electrorheological fluid can be essentially solved, and it can be used in a narrow gap such as 10 μm or less. Moreover, the viscosity change is large and a practical homogeneous phase electricity can be obtained. It can be made as a viscous fluid. Therefore, it can be effectively used for a power transmission device, a valve, a vibration absorber, a pressure conversion device, an actuator, etc., which is used in a small machine generally called a micromachine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniform-phase electrorheological fluid whose viscosity changes by applying a voltage or changing the direction of an electric field. Such an electrorheological fluid can be used in various applications such as a power transmission device, a valve, a vibration absorber, a pressure conversion device, and an actuator.

[0002]

2. Description of the Related Art Mineral oil, silicone oil, fluorine-based synthetic oil,
Water-containing fine particles such as silica, starch, ion exchange resin (Japanese Patent Laid-Open No. 50-92278) or surface conductive particles having an insulating film on the outermost surface (Japanese Patent Laid-Open No. 1-260710) are used in an electrically insulating liquid such as chlorinated paraffin. It is known that when a voltage is applied to the dispersed fluid, the viscosity changes reversibly and rapidly. This phenomenon has been known for a long time as the Winslow effect, and most of the electrorheological fluids proposed so far apply the Winslow effect. To disperse the particles, a dispersant such as sorbitan fatty acid ester, amine derivative, and nitrogen-based polymer surfactant is generally used.

The electric double layer theory is the most effective mechanism for developing the Winslow effect. That is, water existing on the particle surface dissociates the dissociation agent on the solid surface to form an electric double layer, and this electric double layer causes the movement of free ions by the application of a voltage from the outside to cause polarization.
The polarized particles are bound to each other by electrostatic attraction, resulting in crosslinking of the particles between the electrodes. It is believed that this crosslinking increases the flow resistance parallel to the electrode, that is, perpendicular to the crosslinking, and increases the viscosity.

Most of the conventionally proposed electrorheological fluids are dispersion type electrorheological fluids in which fine particles are dispersed in an electrically insulating liquid as described above. Therefore, the dispersion stability of the particles due to the difference in the density of the liquid and the particles is a problem, the dispersed particles are likely to aggregate and settle during storage to easily cause phase separation, and long-term storage is difficult, which poses a major problem in practical application. Has become. Therefore, use of particles having a small density difference from the liquid or dispersion stabilization by adsorbing a dispersant on the particle surface has been attempted, but these are not essential solutions.

In many electrorheological fluids of dispersed system, the dispersed particles contain water, which promotes dielectric polarization. There is a problem in that the water content of the particles causes a transition to a liquid, evaporation, electrolysis, and the like, thereby deteriorating the characteristics of the electrorheological fluid. To solve this, using particles that are essentially free of water
(For example, Japanese Patent Laid-Open No. 1-260710) has been proposed, but it is not realistic.

Furthermore, the Winslow effect is a structural viscosity that increases the viscosity by arranging particles at right angles to the flow direction of a fluid when a voltage is applied. Therefore, it is necessary to arrange at least several particles in series between the electrodes in order to obtain the viscosity increase using this electrorheological fluid of the dispersion system, and to obtain the electrorheological effect up to a narrow gap where it cannot be realized. That is essentially impossible. Moreover, 1 μm is required to effectively develop the Winslow effect.
It is said that the above particles are good, the larger the particle size, the greater the electrorheological effect, and particles of about 100 μm are desirable. Therefore, in order to obtain an effective electrorheological effect, it is desirable that the electrodes are separated by 10 μm or more, and it is considered that it is extremely difficult to apply them in a narrow gap below that.

Therefore, the above-mentioned essential solution such as dispersion stability requires the use of a uniform phase electrorheological fluid.

On the other hand, it was found that the flow rate of the nematic phase of the thermotropic liquid crystal flowing between the electrodes can be changed by applying a voltage perpendicular to the flow direction, suggesting the use as a uniform phase electrorheological fluid. Sasada et al., "Study on Machinery", Vol. 33, No. 3, page 96 and No. 4, page 81 (1981)]. Here, as the n-type nematic liquid crystal, MBBA (p-methoxybenzylidene) is used.
pn-butylaniline) was used to measure the apparent viscosity using DPM-4 as a p-type nematic liquid crystal, and
It has been reported that there is a 3-fold change in viscosity.

The above research is a pioneering study of the electrorheological effect of the nematic phase of thermotropic liquid crystals, but when considering that liquid crystals are actually used as electrorheological fluids, there are the following problems. In other words, this apparent viscosity measurement is not a direct measurement of the change in resistance due to the viscosity acting between the electrodes when there is relative motion between the electrodes, that is, the electrorheological effect is not directly measured. It is necessary to compare the measured viscosity changes, but when the present inventors measured MBBA, the viscosity change was only 1.85 times, and the performance as an electrorheological fluid was insufficient.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above problems, and an object of the present invention is to provide a practical electrorheological fluid of uniform phase which can be used even in a narrow gap and has a large viscosity change. Especially.

[0011]

The electrorheological fluid of the present invention is a single molecular species or a mixture of plural molecular species whose viscosity changes with the application of a voltage or a change in the direction of an electric field. It is composed of a fluid having a uniform phase with a rate of change of 3 times or more, and particularly preferably, the fluid has the following general formula 3 or formula 4

[Chemical 3]

[Chemical 4] (Wherein, n is a natural number of 1 to 14, X is a single bond or an ether bond, m is 2 or 3, and y is 1 or 2), or a liquid crystal containing the compound represented by the above A liquid crystal composition that reduces the viscosity by the use of a liquid crystal composition, particularly a composition having a ferroelectric liquid crystal phase or a smectic A phase liquid crystal phase.

The voltage application or the change in the direction of the electric field referred to in the present invention means that the voltage is applied or cut perpendicular to the flow direction of the fluid, or the direction and strength of the applied electric field. It means changing.

The viscosity referred to in the present invention is the change in resistance due to the viscosity acting between the electrodes when there is relative motion between the electrodes, and indicates the viscosity measured in an actual shear field.
It is measured by applying a constant torque to a fluid such as a rotational viscometer and observing the change in the torque. The absolute value of this viscosity is appropriately selected depending on the application of the electrorheological fluid, but unless the rate of change of this viscosity is at least 3 times, it will not function as an effective electrorheological fluid. That is, the viscosity of the liquid crystal is sensitive to temperature changes, and when the temperature changes by 10 ° C., the viscosity changes by about 4 to 10 times. By the way, when the electrorheological fluid is applied to an actual device, the accuracy of temperature control is generally about ± 1 ° C., and even in such a temperature range, the liquid crystal undergoes a maximum double viscosity change. Therefore, unless the electro-viscosity change of at least about 3 times can be expressed, it does not function as an effective electro-viscous fluid.

For example, when configuring a microtorque converter with a lockup function for power transmission of a small machine, it is necessary to change the viscosity of the liquid to be enclosed. The electrorheological fluid of the present invention can be used for such applications, but in such a case, a viscosity change rate of at least about 3 times is required.

The rate of change in viscosity as used herein means the viscosity A when no electric field is applied, the viscosity B when an electric field is applied or changed so that the reading of the viscometer is maximized, or the viscosity of the viscometer. When the viscosity C when an electric field is applied or changed so that the reading is minimized, the value is B / A or A / C.

Examples of the fluid whose viscosity change rate is three times or more include a liquid crystal compound or a ferroelectric liquid crystal compound having a structure represented by the general formula 1 or 2, but the ferroelectric liquid crystal When a liquid crystal is used, the viscosity is reduced by applying a voltage. This is because the ferroelectric liquid crystal compound has spontaneous polarization, and when a voltage is applied by this spontaneous polarization, the molecular long axis of the liquid crystal molecule is aligned parallel to the electrode surface. It is presumed that the structure is oriented in the shearing direction due to the shearing force applied to, which causes the action of decreasing the viscosity. Therefore, it is clear that a ferroelectric liquid crystal having spontaneous polarization causes a similar decrease regardless of the type of compound.

The present inventor has also found that even if the liquid crystal phase is not the ferroelectric liquid crystal phase, the smectic A phase causes a similar decrease in viscosity.

Specific examples of the compound that can be used as the electrorheological fluid of the present invention include:

Embedded image (in the formula, R represents an alkyl group having 1 to 20 carbon atoms) and the like. These compounds may be used as a single compound or a mixture of a plurality of compounds.

Further, as a concrete example of the ferroelectric liquid crystal compound which can be used as the electrorheological fluid of the present invention,

Embedded image (in the formula, R ₁ represents an alkyl group or an alkoxy group having 1 to 20 carbon atoms, R ₂ represents an alkyl group having 1 to 20 carbon atoms), etc., and these compounds may be used alone. Alternatively, it may be mixed with a phenylpyrimidine-based or ester-based nonchiral liquid crystal composition and used.

The electrorheological fluid of the present invention can be used in the same form as an ordinary electrorheological fluid of a dispersion system, and as described above, it is also used in a place having an extremely narrow gap as compared with a disperse electrorheological fluid. be able to. Further, since the electrodes are kept at a narrow interval, the change in viscosity can be further increased by applying a low voltage or slightly changing the electric field.

[0021]

【Example】

(Example 1) The measurement of electroviscosity was performed using a rotational viscometer modified so that an electric field could be applied. This rotational viscometer is the concentric cylindrical rotational viscometer shown in FIG. 1, and the rotor 1 is a cup type. The rotor 1 also serves as a rotating electrode when an electric field is applied, and a coupling made of a polyacetal-based copolymer is interposed between the viscometer body and the rotor 1 for electrical insulation.

The stator 2 has a concentric cylindrical shape, and a fixed electrode processed into a ring shape is inserted into the stator 2 so as to concentrically surround the inner side and the outer side of the rotor 1. The outer and inner diameters of the rotor 1 were 56.0 mm and 54.0 mm, respectively, and the clearance between the rotor 1 and the stator was 0.4 mm both on the outside and inside of the rotor 1.

The electric field was applied between the rotor, which is a rotating electrode, and the lower fixed electrode. The rotor was energized using a slip ring 3 made of phosphor bronze whose surface was plated with gold. In the figure, 4 is a rotary shaft, 5 is a measurement control unit,
6 represents an XYZ table, and 7 represents a base. In this example, a DC voltage of 0 to 1000 V was applied.

The measurement was carried out by injecting a 3.00 cc sample from the cell gap while rotating the rotor 1 using a syringe after adjusting the zero point of the device, and gradually increasing from the lowest rotational speed at which torque can be read without an electric field. The electric field strength was increased stepwise, and the torque change and temperature at that time were read and recorded. When the electric field was applied, the electric field strength was maintained for 2 to 3 minutes, and it was confirmed that there was no sudden change in torque and temperature, and then the measurement was performed again. After increasing the electric field strength at a constant speed and the torque reading reaches the upper limit of the measurement range,
On the contrary, the electric field strength was gradually decreased stepwise and the same measurement was performed.

By the above-mentioned method, the liquid crystal composition A having the composition shown in Table 1 (this composition takes a nematic liquid crystal phase at a temperature of -10 to 60 ° C.) was measured at the start of 20.6 ° C. Table 2 shows the results measured at 21.2 ° C at the end of the measurement. The electrorheological effect is represented by the following formula as a relative viscosity obtained by dividing the reading of the viscometer when an electric field is applied by the reading of the viscometer when no electric field is applied. Relative viscosity = (reading of viscometer when electric field is applied) / (reading of viscometer when no electric field is applied) Here, the reading of viscometer has a dimension of torque, but the ratio of readings when an electric field is applied is taken. By doing so, it can be made dimensionless and can be expressed as a relative viscosity, and this value as it is or the reciprocal of the viscosity decrease becomes the rate of change of viscosity.

[0026]

[Table 1]

[0027]

[Table 2]

Example 2 Liquid Crystal Composition A of Example 1
In place of liquid crystal composition B shown in Table 3 (this composition is
For a nematic liquid crystal phase at a temperature of 6 to 70 ° C.), the relative viscosity when the electric field strength was increased was similarly measured. The measurement temperature was 26.7 ° C. The results are shown in Table 4.

[0029]

[Table 3]

Comparative Example 1 Liquid Crystal Composition B of Example 2
The same measurement was performed for MBBA. The results are shown in Table 4.

[0031]

[Table 4]

Thus, it can be seen that MBBA has a small change in viscosity in a shear field and is not suitable for practical use.

Example 3 A large number of glass beads 3 having a diameter of 5 μm are sandwiched between two flat substrates 1 and 2 as shown in FIG. 2, and the liquid crystal composition A measured in Example 1 is filled therein.
The force required to move the upper substrate 1 in parallel with the lower substrate 2 was measured under the condition with or without electric field applied. Gold was vapor-deposited on the sides of the upper and lower substrates which were in contact with the liquid crystal composition 4 to form electrodes 5 and 5 '. The parallel movement of the upper substrate 1 was performed by the cantilever 8 via the pusher rod 7 driven by the motor 6, and the force required for the parallel movement was measured by the load cell 9. The force required for displacement and movement of the upper substrate 1 was read by the digital display 10. In this measurement, it was confirmed that the force required for the parallel movement of the electrode increased when an electric field was applied compared to when no electric field was applied, and it was found that the electrorheological fluid works effectively even when used in a narrow gap of about 5 μm. It was

(Comparative Example 2) Instead of the liquid crystal composition A of Example 3, a dispersion type electrorheological fluid in which colloidal silica was dispersed in a silicon type fluid was filled, and the same measurement as in Example 2 was performed. However, no significant difference was observed in the force required to move the measured electrodes regardless of the presence or absence of an electric field. This is probably because the gap between the upper and lower substrates is as narrow as 5 μm and the dispersed electrorheological fluid does not work well.

(Example 4) Instead of the cup-shaped rotor used in the rotational viscometer used in Example 1, the diameter was 10.0 m.
m-type cylindrical rotor with a rotor-stator spacing of 0.7
Using a viscometer consisting of 5 mm, 1.4931 g of 5-nonyl-2- (4-nonyloxyphenyl) pyrimidine and (S) -4 '-(2-methyloctanoyl) were measured in the same manner as in Example 1. ) -4-Biphenyl 3-chloro-4-octyloxybenzoic acid ester 0.7 cc of liquid crystal composition C consisting of a mixture with 0.5066 g was injected into the cell, and at a temperature of 40.3 ° C.
The relative viscosities were measured when the electric field strength was increased with the number of rotations of the rotor being 10 rpm and 50 rpm. The results are shown in Table 5.
It was shown to. The liquid crystal composition C was changed from a crystal phase to a chiral smectic C phase at 30 ° C. at a temperature rise, and from a chiral smectic C phase to a smectic A phase at 60 ° C. at 75 ° C.
It is a ferroelectric liquid crystal composition that undergoes a transition from a smectic A phase to an isotropic phase.

(Comparative Example 3) In the same manner as in Example 4, using 5-nonyl-2- (4-nonyloxyphenyl) pyrimidine (Compound D), the rotor was rotated at a temperature of 40.9 ° C. Relative viscosity was measured at 10 rpm and 50 rpm. The results are shown in Table 5. This compound is a liquid crystal compound that undergoes a transition from a crystal phase to a smectic C phase at 33 ° C., a smectic C phase to a smectic A phase at 60 ° C., and a smectic A phase to an isotropic phase at 75 ° C. when heated.

[0037]

[Table 5]

Example 5 Using the rotational viscometer used in Example 1, a compound having a phase transition temperature shown in Table 6 was used.
For (1) to (5), the rotation speed of the rotor is 10 rpm, Table 7
At the temperature described in (at which temperature these compounds take a nematic phase), the change in viscosity when no electric field was applied and when the electric field strength shown in Table 7 was applied was measured. The results are shown in Table 7.

[0039]

[Table 6]

[0040]

[Table 7]

Example 6 In the same manner as in Example 1, with respect to the compounds (3) and (6) shown in Table 6,
Rotor speed 10 rpm, temperature measured in Table 8 (at which temperature these compounds take smectic A phase)
Then, the relative viscosity was measured. The results are shown in Table 8.

[0042]

[Table 8]

(Example 7) In the same manner as in Example 4, using (S) -4 '-(2-methyloctanoyl) -4-biphenyl 3-chloro-4-octyloxybenzoic acid ester, The relative viscosity was measured at a rotor rotation speed of 10 rpm and a temperature of 80.3 ° C. (at this temperature, these compounds take a chiral smectic C phase) when no electric field is applied and when an electric field of 160 V / mm is applied. As a result, the viscosity decreased to 0.33 when the electric field was not applied, and the rate of change in viscosity was 3.

(Example 8) In the same manner as in Example 1, for the compounds and mixtures having the phase transition temperatures shown in Table 9, the rotation speed of the rotor was 10 rpm and the temperatures shown in Table 10 were used.
(At these temperatures, these compounds take a nematic phase), and the change in viscosity was measured when no electric field was applied and when the electric field strength shown in Table 10 was applied. The results are shown in Table 1.
It was shown at 0.

[0045]

The electrorheological fluid of the present invention essentially solves the problem of dispersion stability of conventional disperse electrorheological fluids.
It can be used in a narrow gap such as 0 μm or less, and has a large viscosity change, and can be used as a practical homogeneous electrorheological fluid. Therefore, it can be effectively used for a power transmission device, a valve, a vibration absorber, a pressure conversion device, an actuator, etc., which is used in a small machine generally called a micromachine.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a rotary viscometer used to measure a change in viscosity in an example of the present invention.

FIG. 2 is a device for demonstrating that it can be effectively used even in the narrow gap shown in the second embodiment.

[Explanation of symbols]

 1-Rotor 2-Stator 3-Spring 4-Rotating shaft 5-Measurement control section 6, 7-Substrate 8-Glass beads 10 and 10'-Electrode

[Table 9]

[Table 10]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuichi Okubo 3-17-35, Shinzonan, Toda City, Saitama Prefecture Nikko Kyoishi Co., Ltd. No. Stock Company Nikko Kyoishi

Claims (4)

[Claims] 1. A single-phase molecular mixture or a mixture of a plurality of molecular types whose viscosity changes with the application of a voltage or a change in the direction of an electric field, wherein the rate of change of the viscosity is 3 times or more from a homogeneous phase fluid. An electrorheological fluid characterized by: 2. The electrorheological fluid according to claim 1 is represented by the following general formula (1) or (2) [Chemical 2] (Wherein n is a natural number of 1 to 14, X is a single bond or an ether bond, m is 2 or 3, and y is 1 or 2), and a homogeneous electrorheological fluid is contained. . 3. The electrorheological fluid according to claim 1, wherein the viscosity is reduced by applying a voltage. 4. The electrorheological fluid according to claim 3, which is a composition having a ferroelectric liquid crystal phase or a smectic A phase liquid crystal phase.