JPH086090B2 - Ferroelectric liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferroelectric liquid crystal composition.
More specifically, it relates to a mixed liquid crystal composition capable of forming a thermodynamically stable ferroelectric phase near room temperature.

[Prior Art] Smectic C liquid crystals composed of chiral molecules are
It is known as a liquid crystal exhibiting ferroelectricity. A typical ferroelectric liquid crystal that is a chiral smectic C liquid crystal is p-decyloxybenzylidene-p′-amino-2.
-Methylbutyl cinnamate (p-decyloxybenzyliden
e-p'-amino-2-methylbutylcinnamate) (hereinafter referred to as "DOBAMBC").

The spiral pitch of the ferroelectric liquid crystal is usually about several microns, but when the thickness of the liquid crystal layer becomes thinner than this spiral pitch, the spiral structure is eliminated and the liquid crystal molecules are aligned in one direction. By applying a direct current to the liquid crystal in such a state, the direction of the dipole, that is, the direction of the liquid crystal molecules can be switched depending on the positive or negative polarity of the voltage. The time required for this switching is extremely short as compared with that in the nematic liquid crystal element which is most widely used as a liquid crystal display, and a response time shorter than 1 second per 1 million minutes can be obtained. Even if the voltage application is turned off, the orientation of the liquid crystal molecules is maintained as it is, so that the bistable effect and the memory characteristic can be realized.

Such a chiral smectic C liquid crystal has excellent advantages not found in nematic liquid crystals and cholesteric liquid crystals, but has not been practically used so far. This is because no chiral smectic liquid crystal having thermodynamically stable ferroelectricity near room temperature has been found, such as nematic liquid crystal. For example, the above-mentioned DOBA MBC has a ferroelectric phase region of 64-92 ° C.
, Which is considerably higher than room temperature.

On the other hand, an ester-based liquid crystal known as a kind of ferroelectric liquid crystal shows ferroelectricity at around room temperature, unlike DOBAMBC, but has a drawback that it is thermodynamically unstable.

[Problems to be Solved by the Invention] Under the circumstances, the present inventors have earnestly studied for the purpose of providing a chiral smectic C liquid crystal capable of forming a thermodynamically stable ferroelectric phase near room temperature. As a result, they have found that this object can be achieved by mixing a specific ester liquid crystal with a chiral smectic C liquid crystal represented by DOBAMBC, and completed the present invention.

[Means for Solving the Problems] However, the gist of the present invention is to select from two groups of an azomethine liquid crystal group represented by the general formula I and an ester liquid crystal group represented by the general formula III. And a ferroelectric liquid crystal composition comprising a mixture of liquid crystals.

General formula I: [In the general formula I, A is hydrogen, halogen atom, C N
-, An atom or a group selected from a hydrocarbon group having 1 to 5 carbon atoms, B represents a halogen atom, an atom or a group selected from a hydrocarbon group having 1 to 5 carbon atoms, and n is 1 to 20. Represents the integer. ] General formula III: [In the general formula III, n represents an integer of 1 to 20. The present invention will be described in detail below.

In the present invention, the azomethine series liquid crystal group refers to the liquid crystal represented by the general formula I. Specific examples thereof include the following compounds.

p-decyloxybenzylidene-p′-amino-2-methylbutylcinnamate (DOBAMBC), p-hexyloxybenzylidene-p′-amino-2-chloro-α-propylcinnamate (HOBACPC), p-octyloxybenzylidene -P'-amino-2-methylbutyl-α-
Chlorocinnamate In the present invention, the ester-based liquid crystal group means the above-mentioned general formula II
A liquid crystal represented by I. Specific examples thereof include the following compounds.

pn-hexyloxybenzic acid-p'-
(2-methylbutoxycarbonyl) phenyl ester,
pn-octyloxybenzoic acid-p'-
(2-Methylbutoxycarbonyl) phenyl ester, pn-nonanooxybenzoic acid-p '-(2
-Methylbutoxycarbonyl) phenyl ester, p-
n-octyloxybenzoic acid-p '-(2-
Methylbutoxycarbonyl) phenyl ester, pn
-Decaoxybenzoic acid-p '-(2-methylbutoxycarbonyl) phenyl ester, pn-dodecaoxybenzoic acid-p'-(2-methylbutoxycarbonyl) phenyl ester, pn-tetradecaoxy Benzoic acid-p '-(2-methylbutoxycarbonyl) phenyl ester, pn-hexadecaoxybenzoic acid-p'-(2-methylbutoxycarbonyl) phenyl ester Compounds included in each liquid crystal group of the present invention Is not limited to the compounds exemplified above.

A ferroelectric liquid crystal composition according to the present invention comprises an azomethine-based liquid crystal group represented by the general formula I (hereinafter referred to as a group I),
It is a mixture of liquid crystals selected from each liquid crystal group of the ester liquid crystal group represented by the general formula III (hereinafter referred to as group III).

When one of these liquid crystal groups is selected and used alone, the above-mentioned drawbacks are exhibited and the object of the present invention is not achieved. When one of the liquid crystal groups is selected and mixed and used, the object of the present invention is achieved.

According to the experiments by the present inventors, when one kind is selected from both liquid crystal groups and mixed, the liquid crystals to be mixed are combined such that the molecular chain lengths of the molecules in the long axis direction are close to each other. When,
It has been found that the objects of the invention are effectively achieved. In particular, it has been found that those in which the molecular chain lengths are within the range of 10 nm are selectively combined are suitable. According to the experiments conducted by the present inventors, it was further found that the object of the present invention can be effectively achieved when the ratio of the liquid crystal to be mixed is 20 mol% or more in the small group.

The ferroelectric liquid crystal composition according to the present invention may be added with a polar surfactant in order to assist the alignment of liquid crystal molecules, or may be added with a dichroic dye for displaying in color.

The ferroelectric liquid crystal composition according to the present invention is directly injected into a liquid crystal cell or mixed with an organic polymer to form a film,
Electro-optical element, large liquid crystal display, temperature sensor,
It can be applied to liquid crystal optical shutters, optical modulators and the like.

[Advantageous effects of the invention] The present invention has the following particularly remarkable effects, and its industrial utility value is extremely large.

1. The ferroelectric liquid crystal composition according to the present invention forms a ferroelectric phase at around room temperature and achieves excellent brightness when used for display applications. This is a remarkable effect that could not be achieved when the group I liquid crystal was used alone.

2. When the liquid crystal of Group III alone was used, the crystal structure tended to change with a slight temperature change, but the ferroelectric liquid crystal composition according to the present invention is thermodynamically stable at around room temperature. The crystal structure does not change with a slight temperature change.

[Examples] Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but the present invention is not limited to the following description examples as long as the gist thereof is not exceeded.

Examples and Comparative Examples (1) Preparation of Ferroelectric Liquid Crystal Composition As liquid crystals, p-decyloxybenzylidene-p′-amino-2-methylbutyl cinnamate (DOBAMBC) belonging to Group I and a group III P-n-alkoxybenzoic acid-p '-(2-methylbutoxycarbonyl) phenyl ester to which the alkoxy group has a different number of carbon atoms 6 (having a carbon number of 6, 8, 10, 12, 14, 16
Stuff. Hereinafter, this is collectively referred to as "Cn". n means the number of carbon atoms of the alkoxy group), and DOBAMBC and Cn were mixed in a molar ratio of 50:50 to obtain a ferroelectric liquid crystal composition.

(2) Temperature dependence of permittivity About 5 m wide on each side of two slide glasses
Aluminum was vacuum-deposited in a strip shape at m and used as an electrode. While facing the electrode surface, the thickness of the spacer is approx.
A 25 to 30 μm polyester film was sandwiched, and the central portion was cut out in a size of 5 mm × 5 mm to obtain a cell. The cell was filled with liquid crystal in the state of an isotropic liquid, taking care not to let air bubbles enter the cell. The electrode surfaces were assembled at right angles to each other, and the ends of the slide glass were fixed with an epoxy adhesive to prevent contact between the liquid crystal and the outside air.

The temperature dependence of the permittivity is shown by
It was measured by the bridge method at 0 Hz and an applied voltage of 10V. The measurement results are shown in FIGS. 1 to 6. In these figures, the vertical axis represents permittivity ε ′ and ε ″, the horizontal axis represents temperature (T), and the unit is absolute temperature (K).
In addition, the central arrow in the figure indicates the process of raising and lowering the temperature.

Table 1 below shows the measured data (combination of liquid crystals, cell thickness) and the figure numbers of the measurement results of the temperature dependence.

Fig. 5 shows smectic C in the range of 349K to 367K in the temperature rising process and in the range of 337K to 365K in the temperature falling process.
It shows that a liquid crystal (S ^* _C ) phase appears. What is actually applicable to the electro-optical element is the S ^* _C phase of the temperature decreasing process, and in particular, the range of 349K to 369K where the temperature increasing process and the temperature decreasing process overlap in Fig. 5 is thermodynamically stable. Area. However, this thermodynamically stable S ^* _C phase is in a temperature region considerably higher than room temperature and is not practical.

FIG. 6 shows that the S ^* _C phase appears only in the temperature decreasing process, but is near the room temperature, which is a low temperature region, as compared with the example of DOBAMBC alone shown in FIG. However, this temperature region is a region below the phase transition of the crystalline smectic A liquid crystal. Therefore, if it is stored in this temperature region for a long time, it may crystallize.

On the other hand, in the example shown in FIGS. 1 to 4,
It can be seen that the temperature at which the S ^* _C phase appears is near room temperature, which is a low temperature region, and is in a thermodynamically stable region.

(3) Measurement of Dielectric Constant A mixture of DOBAMBC prepared in (1) above and 6 kinds of pn-alkoxybenzoic acid-p ′-(2-methylbutoxycarbonyl) phenyl ester was prepared as in (2) above. A cell having the same structure as that used in "temperature dependence of dielectric constant" was filled. The cell filled with the mixture was used to measure the increase Δε in the dielectric constant due to the occurrence of spontaneous polarization when the paraelectric phase was transferred to the ferroelectric phase. The results are shown in FIG.

In FIG. 7, the vertical axis is Δε and the horizontal axis is the difference between the molecular chain length of Cn and the molecular chain length of DOBAMBC {(LC-n)-(L
DOBAMBC)}, and the unit is shown in nm.

FIG. 7 shows that in a mixed liquid crystal composition of DOBAMBC and C-n, when combined so that the difference in molecular chain length between the two is within the range of 10 nm, Δε has the maximum value in this range. ing.

[Brief description of drawings]

1 to 4 show the temperature dependence of the dielectric constant of the ferroelectric liquid crystal composition according to the present invention, and FIGS. 5 and 6 show the temperature dependence of the dielectric constant of the comparative example. Showing sex. In these figures, the vertical axis represents the dielectric constants ε ′ and ε ″, the horizontal axis represents temperature (T), and the unit is absolute temperature (K). Regarding the cell filled with the dielectric liquid crystal composition, the increase Δε (vertical axis) of the dielectric constant due to the occurrence of spontaneous polarization and the molecular chain length of Cn when the paraelectric phase is transferred to the ferroelectric phase. The relationship with the molecular chain length of DOBAMBC (horizontal axis) is shown.

Claims (3)

[Claims] 1. An azomethine-based liquid crystal group represented by the general formula I,
And a ferroelectric liquid crystal composition comprising a mixture of liquid crystals selected from two groups of the ester liquid crystal group represented by the general formula III. General formula I: [In the general formula I, A is hydrogen, a halogen atom, C≡
N- represents an atom or a group selected from a hydrocarbon group having 1 to 5 carbon atoms, B represents a halogen atom, an atom or a group selected from a hydrocarbon group having 1 to 5 carbon atoms, and n is 1 to 1 Represents an integer of 20. ] General formula III: [In the general formula III, n represents an integer of 1 to 20. ] 2. A plurality of groups of liquid crystals contained in a liquid crystal composition, wherein the difference between the molecular chain length of one liquid crystal and the molecular chain length of another liquid crystal is within the range of 10 nm. A ferroelectric liquid crystal composition according to claim (1). 3. The ferroelectric liquid crystal composition according to claim 1, wherein the proportion of the liquid crystal of the small group in the liquid crystal composition is 20 mol% or more.