JPH08176585A - Electroviscous fluid of uniform system - Google Patents

Abstract

PURPOSE: To obtain the subject fluid useful as an actuator for vibration absorption, torque transmission, etc., having excellent stability at a low temperature without causing phase separation even by leaving it to stand for a long period of time, change in temperature and impression of voltage, comprising a mixture of a specific liquid crystal compound and an aromatic oil. CONSTITUTION: This fluid comprises a mixture of (A) a liquid crystal compound [e.g. a liquid crystal compound of the formula ((m) and (n) are those that m+n is 30 and m/n is 1, 4 on the average, respectively] obtained by bonding plural liquid crystal groups to one molecular chain directly or through a space such as a bond chain of the formula (SiR<1> R<2> O) (R<1> and R<2> are each an alkyl or phenyl) and (B) an aromatic oil which does not show liquid crystal properties by itself and provides a mixed solution having liquid crystal properties when mixed with the component A. The component B contains >=10% aromatic carbon in ring analysis and comprises two or more aromatic oils.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniform electrorheological fluid and is used as an actuator for vibration absorption, torque transmission, servo control and the like.

2. Description of the Related Art An electrorheological fluid whose viscosity changes remarkably instantaneously and reversibly when a voltage is applied is a so-called Winslow fluid (US Pat. No. 2417) in which water-containing fine particles such as silica and starch have been dispersed in insulating oil since the 1940s.
850). Thereafter, a method of using ion-exchange resin particles (JP-A-50-92278) or zeolite particles (JP-A-2-3711) as the water-containing fine particles, and organic semiconductor particles (UK Patent 2170).
510 specification), surface-insulated conductive particles (JP-A-64-6093), liquid crystal polymer particles (Proc).
feedings the2nd Int'l Con
f. on ERF, P.P. Many improvements have been proposed, including methods using non-hydrated particles such as H. 231 (1989)). However, the method using these particles shows excellent performance in the short term, but in the long term, sedimentation and separation of particles and agglomeration of precipitated particles into coagulated clay are unavoidable, which is a major obstacle to practical use. On the other hand, liquid crystalline substances are attracting attention as a uniform electrorheological fluid that does not cause the problems of particle settling and aggregation. The liquid crystal substance undergoes molecular orientation when a voltage is applied and its viscosity increases. In particular, in a liquid crystal compound in which a plurality of liquid crystal groups are bound to one molecular chain, the domains formed by the liquid crystal groups are bound to each other, so that the increase in viscosity due to voltage application is remarkable. Furthermore, by diluting a liquid crystal compound with a compound that has a strong affinity for the molecular chain of the liquid crystal compound but a weak affinity for the liquid crystal group, the response to voltage application is improved and the operating temperature range is expanded. , Performance such as reduction of base viscosity is improved (JP-A-5-51590).

An electrorheological fluid composed of a liquid crystal compound in which a plurality of liquid crystal groups are bonded to one molecular chain as described above is different from the liquid crystal compound in terms of the molecular chain of the liquid crystal compound. When the diluent comprising a compound having a strong affinity but a weak affinity for the liquid crystalline group exceeds a certain amount, the liquid crystalline compound and the diluent tend to undergo phase separation at low temperature or room temperature. It is an object of the present invention to solve these problems and to provide a more practical electrorheological fluid that operates stably without phase separation of a liquid crystalline compound and a diluent even at low temperature or room temperature. .

A plurality of liquid crystalline groups bonded to one molecular chain are combined with liquid crystalline groups bonded to the same molecular chain or another molecular chain to form a domain. When this domain grows large, the liquid crystal compounds aggregate with each other, so that the diluent is eliminated and phase separation occurs. Therefore, in order to prevent phase separation, growth of the domain may be inhibited. Keeping in mind that the liquid crystal group generally has a structure having an aromatic ring, the present inventors have conducted various studies on various diluents that do not cause the domain to grow significantly even after being left for a long period of time or when the temperature changes. As a result, if an oil containing a specific amount of an aromatic component is used as a diluent, the liquid crystallinity is not lost, and the aromatic component in the diluent and the aromatic component in the liquid crystalline group constituting the liquid crystalline compound are not lost. It was possible to reach the present invention by finding that the domains of the liquid crystal do not grow due to the affinity. That is, according to the present invention, a liquid crystal compound (1) having a plurality of liquid crystal groups bonded to one molecular chain does not exhibit liquid crystallinity by itself, and when mixed with the liquid crystal compound (1), The mixed liquid is an electrorheological fluid composed of a mixture with an aromatic oil (2) that retains liquid crystallinity. The aromatic oil referred to in the present invention may be any as long as it contains a predetermined amount of aromatic carbon and does not lose the liquid crystallinity of the liquid crystalline compound, for example, mineral oil obtained from coal or petroleum, or alkylbenzene or fluorine atom. Synthetic oils such as included alkylbenzenes, polyphenyl ethers and their derivatives can be mentioned. If the aromatic component of the oil is too large, the liquid crystallinity is impaired, and if it is too small, the compatibility tends to decrease. The oil containing a specific amount of an aromatic component as referred to in the present invention contains 10% or more, preferably 20% or more of aromatic carbon, and when mixed with a liquid crystalline compound, does not lose the liquid crystallinity of the liquid crystalline compound. It is oil. When the aromatic oil is mineral oil, the ratio of the paraffinic component and the naphthene-based component other than the aromatic component may be any. The aromatic carbon component ratio of oil can be determined by ring analysis by the ri-VGC method described in ASTM D2140. The liquid crystallinity and its disappearance are judged by a polarization microscope or a differential calorimeter (DSC), but a simple method depending on the presence or absence of the polarizability when a sample is sandwiched between two polarizing plates can be used. The amount of the aromatic oil used as the diluent is 10 to 300 parts by weight, preferably 10 to 300 parts by weight of the weight of the liquid crystal compound (1) in which two or more liquid crystal groups are bonded to one molecular chain to be diluted. Is 3
The amount is 0 to 150 parts by weight, and more preferably 50 to 100 parts by weight. If it is too small, the effect of reducing the base viscosity due to dilution becomes small, and if it is too large, the effect of electroviscosity becomes small. The aromatic oils used in the present invention may be used alone or in combination of two or more. The liquid crystalline group referred to in the present invention means a Schiff base type, azo type, azoxy type, biphenyl type, terphenyl type, cyclohexyl type, benzoate type, cyclohexylcarboxylic acid type, phenylcyclohexane type, biphenylcyclohexane type, cholesteryl type. , Etc. The core molecular structure that expresses the liquid crystallinity of general low-molecular liquid crystals known in the art (for details, see Shoichi Matsumoto, "Liquid Crystal Electronics", Ohmsha, Ltd.). (Generally called mesogen). This liquid crystalline group is sometimes bonded directly to the molecular chain in the present invention, since generally to facilitate movement and alignment of the liquid crystal groups, -C _m H _2m - or - (Si
R ¹ R ² O) _m- (where m is an integer from 1 to 18, R ¹ ,
R ² represents an alkyl group or a phenyl group. ) And the like, which are conventionally known, so-called spacers. By the way, the molecular chain referred to in the present invention means a chain compound such as alkylene or siloxane containing carbon or silicon as a main component, a benzene ring or glucose.
ose) is a monomer having a molecule composed of a cyclic compound such as a ring as one unit, or a homopolymer or a copolymer,
In the case of a polymer, the degree of polymerization is 2 to 100, more preferably 2 to 50. Further, if necessary, a bonding group such as an ester group, an amide group, a phenylene group, etc. can be interposed in the molecular chain. The molecular chain may be rigid, but one having high flexibility is preferable because it exhibits fluidity even at a relatively low temperature and does not hinder the alignment of the liquid crystalline substance when a voltage is applied. In particular, when an oligomer or polymer is synthesized with units constituting the molecular chain, a flexible molecular chain whose glass transition temperature (Tg) is 25 ° C. or lower, preferably 0 ° C. or lower, more preferably −20 ° C. or lower is , To obtain an electrorheological fluid that can be used from low temperatures. Specific examples of such a flexible molecular chain include 1)
Methylene, ethylene, propylene, -C _m H _2m -
(Where m is an integer from 1 to 18), 2) oxyethylene, oxypropylene, oxybutylene, etc. -OC _m H _2m- (where m is an integer from 1 to 5) Oxyalkylene group 3) dimethylsiloxane, phenylmethylsiloxane, etc. --SiR ¹ R ²
It is a monomer having a unit of siloxane represented by O- (wherein R ¹ and R ² represent an alkyl group or a phenyl group), or a homopolymer or copolymer. In the case of these polymers, the degree of polymerization is 2 to 100, more preferably 2 to 10 for alkylene, 2 to 10 for oxyalkylene, and 2 to 30 for siloxane. These flexible molecular chains are, in the units shown in 1) and 2) above, methylene (having 1 to 18 carbon atoms), amide, urethane, for introducing a liquid crystal group, instead of a part of H. Some or all of the units shown in 3) include divalent linking groups such as esters, ethers, carbonates, ester amides and ether amides, side groups such as alkyl groups (having 1 to 8 carbon atoms) and phenyl groups, and 3). It is possible to carry the above-mentioned linking group instead of R ¹ of The molecular chain may have a liquid crystal group or a spacer at one end or both ends or a side chain.
It is necessary to have at least two or more of the above-mentioned linking groups capable of chemically bonding to the sar. 1) to 3)
Among the molecular chains of 3), siloxane of 3) is particularly preferable because a liquid crystal compound (1) excellent in operability and electrical insulation at low temperature can be easily obtained.

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. The aromatic component of the diluent is ASTM D2
It was determined by a ring analysis method according to the ri-VGC method described in 140. The sample preparation and the compatibility measurement method were as follows. The following compound is used as a liquid crystal compound (1), an aromatic oil (2) as a diluent having the same mass as that of the liquid crystal compound is mixed, kept at 120 ° C. for 5 minutes, and then vigorously stirred for 2 minutes. The diluent was gradually cooled to 25 ° C., and the diluent that had separated at the time of standing for 24 hours was removed, and the mass of the diluent was measured to calculate the amount of the compatible diluent. Amount of compatibility of diluent with liquid crystal compound (1) (parts by weight)
= (Mass of compatible diluent / mass of liquid crystal compound) x 1
The liquid crystallinity was judged by the presence or absence of the polarizability when the sample was sandwiched between two polarizing plates at 25 ° C.

Embedded image

Examples 1 and 2 The compound of Chemical formula 1 was used as a liquid crystalline compound (1), and as an aromatic oil (2), a sample A (aromatic oil rich in aromatic carbon; JSO Aroma 7) was used.
90, manufactured by Nippon San Oil Co., Ltd.) and Sample B (naphtholine oil having a large amount of aromatic carbon; Sirkolite R.P.O. manufactured by Nippon San Oil Co., Ltd.) are shown in Table 1.
The compatibility was good and the liquid crystallinity was maintained well.

Comparative Example 1 The compound of Chemical formula 1 was used as the liquid crystal compound (1),
The results obtained using Sample C (paraffinic oil) are shown in Table 1. The liquid crystallinity was maintained, but the compatibility was insufficient. The basic viscosity of the electrorheological fluid and the electrorheological effect, which are basic characteristics, were measured according to the following methods. Using a plate * plate type rotational viscometer having a pair of parallel disks modified so that the entire plate-opposing surface forms an electrode, the sample was sandwiched between the electrodes, and the shear rate was measured at 30 ° C. 200se
An increase in shear stress due to voltage application when c ^-1 was applied and a DC voltage of 2.0 kv / mm was applied was measured as an electrorheological effect. In this embodiment, the electrode diameter of the facing portion is 32 m.
m, the electrode gap was 0.50 mm. Both Examples 1 and 2 showed an electrorheological effect of about 2500 Pa, but in Comparative Example 1, the base viscosity was not stable, and a stable electrorheological effect was not obtained.

[Table 1]

The present invention provides an electrorheological fluid which is stable even at a low temperature side without causing phase separation even if it is left for a long period of time, the temperature is changed, or a voltage is applied.

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Claims (3)

[Claims] 1. A liquid crystal compound (1) having a plurality of liquid crystal groups bonded to one molecular chain, and a liquid crystal compound (1) which itself does not exhibit liquid crystallinity and is mixed with the liquid crystal compound (1). , An electrorheological fluid whose mixture is a mixture with an aromatic oil (2) that retains liquid crystallinity 2. The electrorheological fluid according to claim 1, wherein the aromatic oil (2) contains at least 10% of aromatic carbon in ring analysis. 3. An electrorheological fluid comprising two or more aromatic oils according to claim 1.