JPH0841476A - Liquid crystal electrorheological fluid - Google Patents

Abstract

(57) [Summary] [Structure] A liquid crystal compound in which a non-liquid crystal side chain and two or more liquid crystal groups are bonded to one molecular chain, and a molecular chain of the liquid crystal compound containing no liquid crystal group An electrorheological fluid composed of a mixture of a non-liquid crystalline compound having a strong affinity with and a weak affinity with a liquid crystalline group. [Effect] It is possible to provide a stable electrorheological fluid that does not cause phase separation even when left standing for a long period of time, temperature change, or voltage application.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniform electrorheological fluid which is stable against temperature changes and long-term storage, and is used as an actuator for vibration absorption, torque transmission, servo control and the like.

[0002]

2. Description of the Related Art Electro-rheological fluids whose viscosity changes remarkably instantaneously and reversibly when a voltage is applied are so-called Winslow fluids (US Pat. 241
7850).

Thereafter, a method of using ion exchange resin particles (Japanese Patent Laid-Open No. 50-92278) or zeolite particles (Japanese Laid-Open Patent Publication No. 2-3711) as water-containing fine particles, and organic semiconductor particles (British Patent No. 2170510). , Surface-insulated conductive particles (JP-A-64-6093), liquid crystal polymer particles (Proceedings t)
he2nd Int'l Conf. on ERF,
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 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, a liquid crystalline substance has been attracting attention as a homogeneous electrorheological fluid that does not cause the problems of particle sedimentation and aggregation. The liquid crystal substance undergoes molecular orientation when a voltage is applied and its viscosity increases. Particularly in a liquid crystal substance in which two or more liquid crystal groups are bonded to one molecular chain, the domains formed by the liquid crystal groups are bonded to each other, so that the increase in viscosity due to voltage application is remarkable. Further, by diluting the liquid crystal compound with the non-liquid crystal compound (2) having 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. Performances such as expansion of operating temperature range and reduction of base viscosity are improved (JP-A-5-51590).

[0005]

However, it is composed of a mixture of a liquid crystal compound and a non-liquid crystal compound (2) having a strong affinity for the molecular chain of the liquid crystal compound but a weak affinity for the liquid crystal group. In the electrorheological fluid, when the mixing ratio of the non-liquid crystal compound (2) exceeds a certain amount, there is a problem that the two undergo phase separation. Therefore, in order to improve the compatibility between the liquid crystal compound and the non-liquid crystal compound (2) which has a strong affinity for the molecular chain of the liquid crystal compound but a weak affinity for the liquid crystal group, it is possible to The purpose is to prevent phase separation due to temperature change and voltage application.

[0006]

[Means for Solving the Problems] When a liquid crystal compound is compatible with more non-liquid crystal compounds without phase separation, the response to voltage application is improved, the operating temperature range is expanded, and the base viscosity is reduced. The performance of is improved. The present inventors have examined the molecular structure of a liquid crystalline substance in which the domain does not grow significantly even when left for a long period of time or when the temperature changes. It was found that the growth of a liquid crystal domain can be inhibited by bonding a group, and the present invention could be reached.

That is, according to the present invention, a liquid crystal compound (1) in which two or more liquid crystal groups and a non-liquid crystal group are bonded to one molecular chain and a liquid crystal compound containing no liquid crystal property The liquid crystalline group having a strong affinity is an electrorheological fluid composed of a mixture with the non-liquid crystalline compound (2) having a weak affinity. The liquid crystalline groups bonded to a certain molecular chain are aggregated with the liquid crystalline groups bonded to the same molecular chain or another molecular chain to form a domain. When this domain grows large, the non-liquid crystal compounds are eliminated and phase separation occurs because the liquid crystal compounds aggregate with each other as schematically shown in FIG. Therefore, in order to prevent phase separation, it suffices if domain growth can be inhibited. The present invention has found that the growth of liquid crystal domains can be inhibited as shown schematically in FIG. 1 by attaching a bulky non-liquid crystalline group as a side chain to the molecular chain in addition to the liquid crystalline group. It is a thing.

The non-liquid crystalline side chain in the present invention is a group having a weak affinity with a liquid crystalline group and having a bulkiness capable of inhibiting the growth of domains by the liquid crystalline group. For example pentyl group, a -C _n H _{2n +} 1 _(n octyl group 3
Represents an integer of 18. ) A linear alkyl group represented by
_{C n H 2n OC m H 2m} + 1 (n + m represents. An integer of 3-18) alkyl group containing an ether structure represented by,
—C _n H _2n OPhR (n represents an integer of 1 to 5, R is H
Alternatively, it represents an alkyl group. ) An alkyl group containing an aromatic ring represented by the formula, —CH ₂ CR ¹ R ² R ³ (R ¹ , R ² , R ³
Represents an alkyl group or H. However, R ¹ , R ² , R ³
At least two of them are alkyl groups. ), A branched alkyl group represented by the formula:-(SiR ¹ R ² O) _n R
³ (R ¹ , R ² and R ³ represent an alkyl group, and n is 1 to 5
Represents an integer of 0. ) And the like, such as a siloxane group. On the other hand, when n is 1 or 2 in the linear alkyl group, the bulkiness is small and the growth of the domain cannot be hindered, which is not preferable.

When the introduction ratio of the non-liquid crystal side chain is defined by the following mathematical formula (I), the introduction ratio of the non-liquid crystal side chain in the present invention is preferably 1 to 100%, more preferably 5 to 50. %. Introduction rate of non-liquid crystal side chains = (non-liquid crystal side chains bonded to one molecular chain / number of liquid crystal groups bonded to one molecular chain) × 100 (%) (I) The present invention The liquid crystalline group referred to in 1. is 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, strong type. A liquid crystal exhibiting structure (generally called a mesogen) of a generally known general low-molecular liquid crystal such as a dielectric liquid crystal (for example, a representative example is described in Akio Sasaki, "Liquid Crystal Electronics", Ohmsha). .) Is a linking group containing a moiety. This is a flexible chain called a spacer in the binding group part,
For example, alkylene, oxyalkylene, or siloxane can be interposed.

The molecular chain referred to in the present invention is 1) alkylene represented by -Cm H2m- (m represents an integer of 1 to 20) such as methylene, ethylene and propylene,
2) oxyalkylene represented by —OC _m H _2m — (m represents an integer of 1 to 5) such as oxyethylene, oxypropylene, and oxybutylene; 3) —SiR ¹ such as dimethylsiloxane and phenylmethylsiloxane. R
^It is a monomer or homopolymer or copolymer having 1 unit of siloxane represented by ² O- (R ¹ and R ² represent an alkyl group or a phenyl group), and the degree of polymerization thereof is 2 to 100, more preferably 2 to 30. These molecular chains have, in the units shown in 1) and 2) above, -C for introducing a side chain group such as a methyl group, an ethyl group, a phenyl group or a liquid crystalline group instead of a part of H. _n H _2n −
(N represents an integer of 1 to 20), -O-, -COO-.
In the unit shown in 3), some or all of R ¹ and R ² may have the same bonding groups as described above. This molecular chain needs to have at least two or more bonding groups capable of chemically bonding to the liquid crystal group at one end, both ends or side chains. Further, the above-mentioned molecular chain may have an ester group, an amide group, a phenylene group or the like interposed in the middle thereof, if necessary.

Further, the definitions of strong affinity and weak affinity according to the present invention are as follows. 2 kinds of substances a and b
When mixed at 5 ° C, the weight ratio is 1:10 to 10 :.
The two substances a and b have a strong affinity if they do not separate into two layers at some mixing ratio between 1. On the other hand, 1: 1
When the two layers are separated at any mixing ratio between 0 and 10: 1, the two substances a and b have weak affinity.

Therefore, the non-liquid crystal compound (2) means a molecular chain in which the non-liquid crystal side chain and the liquid crystal group are removed from the liquid crystal compound (1) at a temperature of 1:10 to 10: 1 at 25 ° C. When mixed at a certain mixing ratio, they do not separate into two phases, and the mesogen corresponding to the liquid crystalline group of the liquid crystalline compound (1) and 25 ° C.
It is a substance that separates into two phases when mixed at any mixing ratio of 1:10 to 10: 1.

For example, in the case of a liquid crystal compound in which a benzoic acid ester type liquid crystal group is bound as a side chain of dimethyl silicone, toluene or dichloromethane has too strong an affinity with the liquid crystal group and dissolves the liquid crystal compound to form a liquid crystal. However, dimethyl silicone, phenylmethyl silicone having a small phenyl group content, alkyl-modified silicone, fluorine-modified silicone, mineral oil and the like are preferable, and these correspond to the compound (2) in this case.

The mixing weight ratio of the liquid crystal compound (1) and the non-liquid crystal compound (2) in the present invention is preferably (liquid crystal compound) :( non-liquid crystal compound) = 1: 0.4 to 1:
2, more preferably (liquid crystal compound) :( non-liquid crystal compound) = 1: 0.5 to 1: 1.5. Hereinafter, the compatibility between the liquid crystal compound (1) and the non-liquid crystal substance (2) in the present invention will be specifically described with reference to Examples.

[0015]

【Example】

[0016]

Example 1 and Comparative Example 1 The compatibility of 10 g of the liquid crystal compound having the non-liquid crystal side chain shown in Chemical formula 1 below with 10 g of the non-liquid crystal compound shown in Chemical formula 2 below was 96P.
It was HR (Example 1).

[0017]

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[0018]

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On the other hand, the compatibility of the liquid crystal compound shown in Chemical formula 3 below, in which a non-liquid crystalline side chain was not introduced, and the non-liquid crystal compound shown in Chemical formula 2 above was measured and found to be 38 PHR (Comparative Example 1). ).

[0020]

[Chemical 3]

From these results, when the non-liquid crystal side chain is introduced into the liquid crystal compound, the liquid crystal compound (1) of the non-liquid crystal compound (2) is compared with the case where the non-liquid crystal side chain is not introduced. 2) was more than doubled. The compatibility was measured by the following method. 1) Dissolved in tetrahydrofuran (THF) in a mass ratio of 5 times the total mass of the liquid crystal compound (1) and the non-liquid crystal compound (2) having the same mass as the liquid crystal compound. 2) THF is distilled off from the solution of 1). 3) The mixture obtained in 2) is allowed to stand at 25 ° C. for 24 hours. 4) The non-liquid crystal compound (2) separated at the time of 3) is removed, and its mass is measured to calculate the amount of the compatible non-liquid crystal compound (2). 5) Compatibility of non-liquid crystal compound (2) with liquid crystal compound (1) (PHR) = (mass of compatible non-liquid crystal substance /
Mass of liquid crystalline substance) × 100

[0022]

Example 2 and Comparative Example 2 A mixture of the liquid crystal compound (1) and the non-liquid crystal compound (2) prepared in Example 1 (the separated non-liquid crystal compound (2) has been removed).
Was allowed to stand for 1 month at 25 ° C, but no further separation occurred (Example 2). On the other hand, the mixture of the liquid crystal compound (1) and the non-liquid crystal compound (2) prepared in Comparative Example 1 (the separated non-liquid crystal compound (2) has been removed) was kept at 25 ° C. for 1 month. When left to stand, 1.1 g of the non-liquid crystal compound (2) was separated (Comparative Example 2).

[0023]

Example 3 and Comparative Example 3 A mixture of the liquid crystal compound (1) and the non-liquid crystal compound (2) prepared in Example 1 (the separated non-liquid crystal compound (2) has been removed).
Was charged between parallel disk electrodes and a voltage of DC 1 kV was applied for 8 hours, but no separation was observed (Example 3).

On the other hand, the mixture of the liquid crystal compound (1) and the non-liquid crystal compound (2) prepared in Comparative Example 1 (the separated non-liquid crystal compound (2) has been removed) was placed between the parallel disk electrodes. Then, when a voltage of DC 1 kV was applied for 8 hours, a part of the non-liquid crystal compound (2) was separated (Comparative Example 3). Here, the disk electrode diameter is 32 mm, and the inter-electrode distance is 0.5 mm. The parallel disk electrode is installed in an electric furnace equipped with a temperature controller, and the temperature during voltage application is maintained at 60 ° C.

[0025]

EFFECTS OF THE INVENTION It is possible to provide a stable electrorheological fluid that does not cause phase separation even if it is left for a long period of time, the temperature is changed, or a voltage is applied.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing that the growth of liquid crystal domains is inhibited when a non-liquid crystal side chain is introduced into a liquid crystal compound.

FIG. 2 is a schematic diagram showing a state in which a liquid crystal domain grows when a non-liquid crystal side chain is not introduced into a liquid crystal compound.

[Explanation of symbols]

 1 Liquid crystalline group 2 Spacer 3 Molecular chain 4 Non-liquid crystalline side chain

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area // C10N 40:14

Claims (1)

[Claims] 1. A liquid crystal compound (1) having a non-liquid crystal side chain and two or more liquid crystal groups bonded to one molecular chain, and a liquid crystal compound (1) containing no liquid crystal group. An electrorheological fluid composed of a mixture with a non-liquid crystal compound (2) having a strong affinity for a molecular chain but a weak affinity for a liquid crystalline group.