JP2007231127A - Liquid crystalline compound-carbon nanotube composite material and method for producing the same composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystalline compound-carbon nano tube composite material excellent in electric conductivity and mechanical properties and capable of controlling orientation state of a carbon nanotube in a desired direction and to provide a method for producing the composite material. <P>SOLUTION: In the liquid crystalline compound-carbon nanotube composite material in which a carbon nanotube is dispersed into a crystalline compound having a lyotropic liquid crystallinity and used as a matrix, peak of fluorescence intensity appears in 1,110-1,150 nm fluorescence wavelength in near infrared fluorescence measurement. The composite material can be produced by mixing a dispersion in which carbon nanotube is dispersed with a liquid crystalline compound having lyotropic liquid crystallinity in a weight ratio of the dispersion/liquid crystalline compound of (50/50) to (30/70) and then allowing the mixture to stand for a prescribed period. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal compound-carbon nanotube composite material and a method for producing the composite material. More specifically, the present invention relates to a liquid crystal-carbon nanotube composite material in which carbon nanotubes are uniformly dispersed in a liquid crystalline compound having lyotropic liquid crystallinity, and a method for producing the composite material.

  A carbon nanotube is a carbon allotrope having a structure in which a graphite sheet (also called a graphene layer) having a hexagonal network of carbon atoms arranged in a cylindrical shape or a tube shape, and its diameter is on a nanometer scale. The structure has a graphite structure. In addition, there are two known types of carbon nanotubes: single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Single-walled carbon nanotubes are made of graphite sheets. Whereas only one sheet is wound in a cylindrical shape, the multi-walled carbon nanotube is a graphite sheet in which the graphite sheets are concentrically stacked and overlapped at substantially equal intervals. Carbon nanotubes can be either a metal or a semiconductor depending on the diameter and how the carbon is wound (chirality), and thus have excellent electrical characteristics and high mechanical properties that are lighter and stronger than steel.

  Since carbon nanotubes have geometrical and physical properties not found in conventional materials, they represent the nanotechnology field, and have the highest current density, antistatic properties, electrical conductivity, thermal conductivity, electromagnetic waves. As a new material having excellent functions such as shielding properties, Young's modulus, and tensile strength, it is expected to be applied in various fields such as electronic materials, medical care, and energy. In particular, various materials such as polymer materials and inorganic materials are used as matrices, and carbon nanotubes are dispersed as fillers in these matrices to obtain functional composite materials having the above-mentioned characteristics. (For example, see Patent Documents 1 to 4).

JP 2005-14332 A JP 2005-122930 A JP 2005-326825 A Japanese Patent No. 3665969

  By the way, in order to take advantage of the structural characteristics of carbon nanotubes, which have a large aspect ratio and a small diameter, it is necessary to disperse carbon nanotubes uniformly in the matrix. However, the high functions of the carbon nanotube can be exhibited efficiently. On the other hand, carbon nanotubes are extremely stable because they have a surface in which carbon π-electrons are conjugated for a very long distance, and the surface of the π-electrons is difficult to wet and difficult to mix with other substances. Have. And since van der Waals force works between the carbon nanotubes, the cohesive force is very strong, resulting in a bundle in which dozens of carbon nanotubes are randomly aggregated in the matrix. For this reason, it is difficult to produce a composite material in which carbon nanotubes are uniformly dispersed in a matrix, and improvement has been desired.

  The present invention has been made in view of the above problems, and since carbon nanotubes are uniformly dispersed in a liquid crystal compound serving as a matrix, the electrical conductivity and mechanical properties are excellent, and the orientation state of the carbon nanotubes Is to provide a liquid crystal compound-carbon nanotube composite material that can be controlled in a desired direction, and a method for producing the composite material.

  In order to solve the above-described problems, the liquid crystal compound-carbon nanotube composite material according to the present invention is a liquid crystal compound-carbon nanotube composite material in which carbon nanotubes are dispersed using a lyotropic liquid crystal compound as a matrix. Thus, a fluorescence intensity peak appears when the fluorescence wavelength in the near infrared fluorescence measurement is 1110 to 1150 nm.

  In the liquid crystal compound-carbon nanotube composite material according to the present invention, the liquid crystal compound is preferably hydroxypropyl cellulose.

  In the liquid crystal compound-carbon nanotube composite material according to the present invention, the viscosity of the liquid crystal compound is preferably 2.0 to 10.0 mPa · s.

  In the method for producing a liquid crystal compound-carbon nanotube composite material according to the present invention, a dispersion liquid in which carbon nanotubes are dispersed and a liquid crystal compound having lyotropic liquid crystallinity are dispersed in a weight ratio / liquid crystal compound = 50 / 50-30. The mixture is mixed at / 70 and then left for a predetermined period.

  In the method for producing a liquid crystal compound-carbon nanotube composite material according to the present invention, the dispersion contains one or more selected from the group consisting of carboxymethyl cellulose, chitosan, gellan gum, hyaluronic acid, sodium dodecyl sulfate, and dodecyl trimethyl ammonium bromide. It is preferable to do.

  In the liquid crystal compound-carbon nanotube composite material according to the present invention, carbon nanotubes are dispersed using a liquid crystalline compound having lyotropic liquid crystal properties as a matrix, and a fluorescence intensity peak appears at a fluorescence wavelength of 1110 to 1150 nm in near infrared fluorescence measurement. Therefore, the carbon nanotubes are uniformly dispersed in the liquid crystal compound, and a composite material having the electrical characteristics and mechanical characteristics of the carbon nanotubes is obtained. In addition, since the carbon nanotubes are uniformly dispersed in the liquid crystalline compound having lyotropic liquid crystallinity, the carbon nanotubes can be aligned with the alignment of the liquid crystalline compound, and the alignment state of the carbon nanotubes can be set in a desired direction. Can be controlled.

  The liquid crystalline compound-carbon nanotube composite material according to the present invention can effectively exhibit lyotropic liquid crystallinity by using hydroxypropyl cellulose as the liquid crystalline compound constituting the composite material. In addition, hydroxypropylcellulose is a substance that is soluble in a solvent at room temperature and has a wide pH range, and when a polysaccharide is used as a carbon nanotube dispersant, Good compatibility.

  The liquid crystal compound-carbon nanotube composite material according to the present invention can improve the dispersibility of carbon nanotubes by setting the viscosity of the liquid crystal compound constituting the composite material to 2.0 to 10.0 mPa · s. Moreover, the obtained composite material can also confirm the fluorescence intensity peak of a carbon nanotube reliably.

  In the method for producing a liquid crystal compound-carbon nanotube composite material according to the present invention, a dispersion in which carbon nanotubes are dispersed is prepared, and the dispersion and the liquid crystal compound are dispersed in a weight ratio of dispersion / liquid crystal compound = 50/50. Since the composition is mixed at ˜30 / 70 and then allowed to stand for a predetermined period, a liquid crystal compound-carbon nanotube composite material in which carbon nanotubes are uniformly dispersed in a liquid crystal compound as a matrix can be easily and It can be prepared efficiently.

Further, in the method for producing a liquid crystal compound-carbon nanotube composite material according to the present invention, the dispersion is at least one selected from carboxymethyl cellulose and the like.
A liquid crystal compound-carbon nanotube composite in which carboxymethylcellulose and the like are spirally wound around carbon nanotubes when forming a composite material, and CH-π interaction is generated, thereby stably dispersing and isolating carbon nanotubes. Material can be obtained.

  Hereinafter, the liquid crystal compound-carbon nanotube composite material of the present invention (hereinafter sometimes simply referred to as “composite material”) is formed by dispersing carbon nanotubes using a liquid crystal compound having lyotropic liquid crystallinity as a matrix. The

  As the carbon nanotubes constituting the composite material of the present invention, both single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) can be used. Here, as described above, the carbon nanotube is one of carbon allotropes having a structure in which a graphite sheet is wound in a cylindrical shape or a tube shape and having a diameter of the order of nanometers.

  As the single-walled carbon nanotube that can be used in the present invention, for example, those having a fiber diameter of about 1 to 1000 nm, a fiber length of about 0.1 to 1000 μm, and an aspect ratio of 10 to 10,000 are preferable.

  On the other hand, the multi-walled carbon nanotubes that can be used in the present invention are preferably those having a fiber diameter of about 1 to 1000 nm, a fiber length of about 0.1 to 1000 μm, and an aspect ratio of 10 to 10,000.

  Known methods for producing carbon nanotubes include arc discharge methods, laser vapor deposition methods, and catalytic chemical vapor deposition (CVD) methods. For example, non-patent literature (“Basics of Carbon Nanotubes”, ) Corona Publishing, co-authored by Saihachi Hachihachi and Itato Toshiharu). Although not particularly limited, among these, the CVD method, particularly the thermal CVD method can be continuously produced in the gas phase, and therefore the process proceeds smoothly. In that case, if the catalyst is continuously supplied by a method in which the catalyst and the carbon source are brought into contact at a high temperature of 600 ° C. to 1200 ° C., the carbon nanotubes can be continuously recovered. Also, carbon nanotubes produced by other means such as carbon monoxide thermal decomposition method, template method in which organic molecules are inserted into fine pores for thermal decomposition, and fullerene / metal co-evaporation method can be used. no problem.

Specific carbon nanotubes include graphite fibril (registered trademark) (manufactured by Hyperion), vapor grown carbon fiber (registered trademark) (manufactured by Showa Denko KK), and more. Examples include Pyrograph III (trade name) (manufactured by ASIS).

  The carbon nanotubes may be modified on the surface of the carbon nanotubes in order to improve the dispersibility in the liquid crystal compound. The means for modifying the surface of the carbon nanotube is not particularly limited, and for example, a method disclosed in JP-A-2005-14332 can be used.

  Next, as the liquid crystalline compound that becomes a matrix in the composite material of the present invention, a material having lyotropic liquid crystallinity can be used, and for example, hydroxypropyl cellulose or the like is preferably used. Such hydroxypropyl cellulose is a substance that is soluble in a solvent at room temperature and has a wide and stable pH range. Furthermore, when a polysaccharide is used as a carbon nanotube dispersant, Compatibility is also good. The lyotropic liquid crystallinity means that the liquid crystal phase is obtained by interaction with a solvent (generally a change in the concentration of the solution).

  The viscosity of the liquid crystal compound is preferably 2.0 to 10.0 mPa · s. By setting the viscosity of the liquid crystal compound in such a range, the dispersibility of the carbon nanotube can be improved, and the obtained composite material can surely confirm the fluorescence intensity peak of the carbon nanotube. On the other hand, if the viscosity exceeds 10.0 mPa · s, the lyotropic liquid crystallinity may not be exhibited with certainty. The viscosity of the liquid crystal compound is particularly preferably 3.0 to 6.0 mPa · s.

Further, the content of carbon nanotubes in the composite material is preferably 0.001 to 50% by mass, and particularly preferably 0.01 to 30% by mass with respect to the entire composite material. By setting the content of the carbon nanotubes within such a range, various characteristics of the carbon nanotubes can be exhibited to the maximum, and the dispersion with respect to the liquid crystal compound as the matrix is efficiently performed.

  In order to produce the liquid crystal compound-carbon nanotube composite material of the present invention, a dispersion in which carbon nanotubes are dispersed is prepared, and the dispersion and the liquid crystal compound are dispersed in a weight ratio of dispersion / liquid crystal compound = 50/50. It is sufficient to mix at ~ 30 ~ 70 and then leave it for a predetermined period of time. By using this method to produce a composite material, carbon nanotubes are uniformly dispersed in the liquid crystalline compound as a matrix. The liquid crystal compound-carbon nanotube composite material can be easily and efficiently prepared.

  In order to prepare a dispersion liquid in which carbon nanotubes are dispersed, for example, carbon nanotubes and a predetermined dispersant are put in a solvent such as pure water, acetic acid solution, and heavy water, and these are mixed to disperse the carbon nanotubes in the solvent. You can do it. The amount of the dispersant is, for example, preferably 5 times or more, and particularly preferably 10 times or more, by weight ratio with respect to the carbon nanotube. When preparing a dispersion, in order to improve the dispersion state of carbon nanotubes, ultrasonic treatment is performed using an ultrasonic device such as an ultrasonic container, an ultrasonic cleaner, or an ultrasonic homogenizer. And uniformly dispersed. Various conditions such as the magnitude of the voltage and the treatment time in the ultrasonic treatment may be appropriately determined according to the content of the carbon nanotubes, the types of the dispersant and the solvent, and the like.

  Furthermore, the carbon nanotubes are more efficiently dispersed in the aqueous solution by subjecting the dispersion after ultrasonic treatment to centrifugation or ultracentrifugation. Centrifugation can be carried out by using a known centrifuge such as a centrifuge, a centrifuge, or an ultracentrifuge. Various conditions such as the number of rotations and processing time in the centrifugal treatment may be appropriately determined according to the content of the carbon nanotubes, the types of the dispersant and the solvent, and the like.

  As the dispersant, polysaccharides such as carboxymethyl cellulose, chitosan, gellan gum, hyaluronic acid and surfactants such as sodium dodecyl sulfate (SDS), dodecyl trimethyl ammonium bromide (DTAB) are used. be able to. As the dispersant, one of these may be used alone, or two or more of these may be used in combination. When these dispersants are used, carboxymethylcellulose and the like are spirally wound around the carbon nanotubes when forming a composite material, so that a CH-π interaction is generated to stably disperse the isolated and isolated carbon nanotubes. A liquid crystal compound-carbon nanotube composite material can be obtained. In particular, it is preferable to use carboxymethylcellulose or chitosan as the dispersant.

  And this dispersion liquid and a liquid crystalline compound are mixed so that it may become a dispersion liquid / liquid crystalline compound = 50 / 50-30 / 70 by weight ratio. By mixing the liquid crystalline compound with the dispersion in the above weight ratio, the liquid crystalline compound having lyotropic liquid crystallinity contains a solvent to be in a liquid crystal state, and the carbon nanotubes are well dispersed in the matrix. The weight ratio of the dispersion to the liquid crystal compound is particularly preferably dispersion / liquid crystal compound = 45/55 to 35/65.

  The mixed liquid is allowed to stand for a predetermined period, for example, 1 day or more, preferably 3 days or more, more preferably 5 days or more, particularly preferably 7 days or more, so that the dispersion of the carbon nanotubes in the matrix is ensured. In addition, liquid crystal compounds also exhibit liquid crystal properties with certainty. Such standing is preferably performed in a room temperature environment.

  The composite material of the present invention includes, in addition to the carbon nanotubes and lyotropic liquid crystalline compounds as essential components described above, dispersants and flame retardants other than those described above within a range not hindering the object and effect of the invention. , Heat stabilizers, conductivity enhancers, flame retardant aids, pigments, dyes, lubricants, mold release agents, compatibilizers, crystal nucleating agents, plasticizers, antioxidants, anti-coloring agents, UV absorbers, fluidity Additives such as a modifier, a foaming agent, an antibacterial agent, a vibration damping agent, a deodorant, a slidability modifier, and an antistatic agent can be added as necessary.

In the composite material of the present invention obtained as described above, the carbon nanotubes are uniformly dispersed in the liquid crystal compound as a matrix. As a result, the fluorescence wavelength in the near infrared fluorescence measurement is 1110 to 1150 nm. A peak of fluorescence intensity will appear.

  FIG. 1 is a diagram schematically showing the fluorescence intensity of the composite material of the present invention when the near infrared fluorescence measurement is performed and the fluorescence wavelength is around 1124 nm. When the carbon nanotubes are uniformly dispersed in the matrix, as shown by the solid line in FIG. 1, a fluorescence intensity peak appears at a fluorescence wavelength of 1110 to 1150 nm, for example, 1124 nm ± 14 nm, particularly 1124 nm ± A peak appears at 10 nm. That is, the appearance of a fluorescence intensity peak in the range of the fluorescence wavelength is one of the indicators that the carbon nanotubes are uniformly dispersed in the matrix, and the fluorescence intensity at the peak is determined by the content of the carbon nanotubes. In the case of 0.5 to 1.0 mass of the entire composite material, approximately 6000 to 14000 a. u. It will be about. On the other hand, if the carbon nanotubes in the matrix have a bundle structure and the carbon nanotubes are not uniformly dispersed, the fluorescence intensity will be small, and no clear peak of fluorescence intensity will appear as shown by the dotted line in FIG. become. Moreover, as shown in FIG. 1, the peak of the fluorescence intensity of the dispersed carbon nanotube is often observed also at 1180-1220 nm and 1270-1300 nm.

  In addition, near-infrared fluorescence measurement can be performed using apparatuses, such as a near-infrared spectrofluorometer FP-6600 (made by JASCO Corporation), for example. In addition, since carbon nanotubes have a structure with a small diameter and a large aspect ratio, the optical characteristics vary greatly depending on the deflection direction (light vibration direction), and the length direction is longer than the diameter direction (axial direction) of carbon nanotubes. It is said that light absorption and light emission are likely to occur.

  In a composite material in which carbon nanotubes are dispersed in a matrix, it is considered that the characteristics of the carbon nanotubes change depending on the orientation state due to the large anisotropy of the carbon nanotubes. In the case where carbon nanotubes are uniformly dispersed in a lyotropic liquid crystal compound having a certain molecular orientation while having liquid fluidity, the application of voltage causes the liquid crystal compound to be dispersed. The carbon nanotubes that are aligned in the molecular arrangement and uniformly dispersed in the liquid crystal compound are also aligned in response thereto. Therefore, the orientation of the carbon nanotubes can be controlled by applying a voltage.

  In confirming the relationship between the voltage application and the alignment of the liquid crystal compound and the carbon nanotube, the voltage may be applied using the liquid crystal cell shown in FIGS. 2 is a perspective view of the liquid crystal cell 1, FIG. 3 is a sectional view taken along the line III-III of FIG. 2, and FIG. 4 is a sectional view taken along the line IV-IV of FIG. (Tin Oxide: Indium Tin Oxide) A DC voltage is applied vertically (in the vertical direction in FIGS. 2 and 3) to the ITO electrode substrate 11 with the composite material 12 of the present invention to be tested sandwiched between the electrode substrate 11. What is necessary is just to confirm the time-dependent change of the fluorescence intensity in the case of applying. 2 to 4, the periphery of the composite material 12 to be examined is surrounded by a glass substrate 13. Further, as described above, in consideration of the fact that light absorption and light emission are more likely to occur in the length direction than the diameter direction (axial direction) of the carbon nanotubes, The fluorescence measurement may be performed by applying light (in the vertical direction in FIGS. 2 and 3).

  The relationship between the voltage application and the alignment state of the liquid crystalline compound and the carbon nanotube can be confirmed by measuring the change in fluorescence intensity with time when a DC voltage is applied to the composite material. That is, when the liquid crystal compound is used as a matrix and the carbon nanotubes are uniformly dispersed in the matrix as in the composite material of the present invention and no voltage is applied, near infrared fluorescence measurement A peak of fluorescence intensity appears at a predetermined wavelength (for example, 1110 to 1150 nm, etc.), but when a voltage is applied, the fluorescence intensity decreases with time and tends to become a substantially constant value thereafter. .

  This means that the carbon nanotubes are oriented perpendicular to the electrode substrate. When light is applied perpendicularly to the electrode substrate and the fluorescence measurement is performed, the fluorescence intensity decreases with the lapse of time due to the application of a voltage, and after a while, settles to a substantially constant value. As a result, the liquid crystal compound is aligned perpendicularly to the substrate, and the carbon nanotubes are also aligned vertically, and the number of carbon nanotubes that are exposed to light in the diameter direction (axial direction) increases. Conceivable. Then, since most of the orientations of the carbon nanotubes in the composite material are aligned in the direction perpendicular to the substrate, the decrease in the fluorescence intensity is settled and settled to a substantially constant value. Thus, utilizing the fact that the molecular arrangement of the liquid crystal compound is aligned and aligned by applying a voltage, the carbon nanotubes uniformly dispersed in the liquid crystal compound can be aligned in response thereto. Therefore, in the composite material of the present invention, the orientation of the carbon nanotubes can be controlled in a desired direction by applying a voltage.

  In the case where carbon nanotubes are uniformly dispersed in the liquid crystalline compound as in the composite material of the present invention, the fluorescence intensity at which a peak can be confirmed at a predetermined fluorescence wavelength is applied by applying a predetermined voltage. Although the fluorescence intensity decreases, the fluorescence intensity tends to increase again by opening without applying a voltage thereafter.

  This is because by applying a predetermined voltage to the composite material, the liquid crystalline compound as a matrix was aligned in the vertical direction with respect to the electrodes, and the carbon nanotubes were also aligned in the vertical direction accordingly, and the fluorescence intensity was reduced. Thereafter, the alignment state of the liquid crystal is broken by leaving it open for a while without applying voltage. As a result, the orientation of the carbon nanotubes collapses and becomes a random dispersion state again, and the number of carbon nanotubes that are exposed to light in the length direction in the composite material increases compared to the orientation state, so that the fluorescence intensity increases again. This is thought to be caused by this. Note that if the carbon nanotubes form a bundle in the matrix and the dispersibility is poor, the fluorescence intensity will decrease, so the fluorescence intensity of the carbon nanotubes will increase again after voltage is applied. It can be seen that it is randomly distributed in the matrix.

  In the liquid crystal compound-carbon nanotube composite material of the present invention, carbon nanotubes are dispersed using a liquid crystalline compound having lyotropic liquid crystal properties as a matrix, and a peak of fluorescence intensity appears at a fluorescence wavelength of 1110 to 1150 nm in near infrared fluorescence measurement. Therefore, the carbon nanotubes are uniformly dispersed in the liquid crystalline compound, and the maximum current density, antistatic property, electrical conductivity, thermal conductivity, electromagnetic wave shielding property, Young's modulus and tensile strength of the carbon nanotubes are provided. It becomes a high-performance composite material having electrical and mechanical properties such as

  In addition, by adopting a configuration in which carbon nanotubes are uniformly dispersed in a lyotropic liquid crystalline compound having a certain molecular orientation while having liquid flowability, the orientation of the liquid crystalline compound is improved. Accordingly, the carbon nanotubes can also be oriented. For example, the orientation of the carbon nanotubes can be controlled in a desired direction by applying a voltage. As described above, when the alignment state of the carbon nanotubes is aligned in a predetermined direction, vibration energy from an arbitrary direction can be efficiently piezoelectrically converted, resulting in excellent piezoelectricity, polarized light emission and polarization absorption in the alignment direction. Further, it is possible to apply to various fields by utilizing the behavior showing optical anisotropy such as birefringence.

  Further, the liquid crystal properties of the present invention exhibiting the above-mentioned effects such as excellent electrical characteristics such as electrical conductivity and mechanical characteristics, and the ability to control the orientation state of the carbon nanotubes in a desired direction by applying voltage or the like. Compound-carbon nanotube composite materials can be applied to various fields of materials using carbon nanotubes. For example, energy materials (secondary cells, fuel cells, hydrogen storage materials, solar cells) such as electric devices and liquid crystal devices. Etc.), optical materials (photolithography, electrophotography, nonlinear optical materials, display devices, liquid crystal elements, fluorescent display tubes, optical recording media, field emission displays, photorefractive materials, photoconductors, etc.), electrical materials (electrical / magnetic)・ Superconductive materials, conductive materials, dielectrics, transistors, emitters, magnetic recording media, etc.), functional materials and sensors Etc. (thermal conductors, lubricants, polymer composites, inorganic composites, inks, electric field sensors, pressure sensors, biosensors, gas sensors, etc.) and polymer nanocomposites using carbon nanotubes can do.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not restrict | limited at all by these Examples.

[Example 1]
Production of hydroxypropylcellulose-carbon nanotube composite:
Using the following methods (1) and (2), a composite material of hydroxypropyl cellulose, which is a liquid crystal compound, and carbon nanotubes was produced.

(1) Production of carbon nanotube-dispersed aqueous solution:
100 mg of carboxymethylcellulose having a molecular weight of about 60,000 (manufactured by Daicel Chemical Industries, Ltd.) and 10 mg of single-walled carbon nanotubes (Hipco (trade name): Carbon Nanotechnologies Inc.) having the following specifications in 10 ml of pure water, Using a sonic cleaner (ultrasonic homogenizer US-300T: manufactured by Nippon Seiki Seisakusho Co., Ltd.), ultrasonic treatment was performed for 60 minutes under the condition of 3.2 V to disperse the carbon nanotubes in the aqueous solution. Next, this dispersion was subjected to ultracentrifugation (small separation ultracentrifuge V-570: manufactured by JASCO) under the conditions of 25 ° C., 60 minutes, 163000 g, and a rotational speed of 60000 rpm, and 4 ml of the supernatant was extracted. This supernatant was used as a carbon nanotube dispersion.

(Specifications of carbon nanotube)
Purity: about 85% by mass
Diameter: 0.4 to 1.5 nm (average diameter about 1.0 nm)
Length: 0.1 μm to 1000 μm
Aspect ratio: 1000 or more

(2) Production of hydroxypropylcellulose-carbon nanotube composite material:
After putting 4 ml (3.6 mg) of the carbon nanotube dispersion prepared in (1) into 6 mg of hydroxypropylcellulose (product name Hydropropylpropyl Cellulose: manufactured by Tokyo Chemical Industry Co., Ltd., viscosity: 3-6 mPa · s) The hydroxypropyl cellulose-carbon nanotube composite material of the present invention was obtained by leaving it to stand for 1 week.

[Test Example 1]
Confirmation of orientation behavior of carbon nanotubes by near infrared fluorescence measurement (1):
The hydroxypropyl cellulose-carbon nanotube composite material obtained in Example 1 was sandwiched between ITO electrode substrates 11 shown in FIGS. 2 to 4 to produce a liquid crystal cell 1 having a thickness of about 1 mm. Then, with respect to the liquid crystal cell 1, the change with time in fluorescence intensity (fluorescence intensity peak) was measured when a DC voltage was applied in the direction perpendicular to the ITO electrode substrate 11 under the following conditions. FIG. 5 shows the measurement results of changes with time in fluorescence intensity when a DC voltage is applied and the fluorescence wavelength is 1124 nm. The fluorescence measurement was carried out under the following conditions by applying light perpendicular to the electrode substrate 11.

(Conditions for applying DC voltage)
Voltage magnitude: 10V
Time: 15 minutes Device: HIOKI 7015 Signal source
(Manufactured by Hioki Electric Co., Ltd.)

(Near-infrared fluorescence measurement conditions)
Apparatus: Near-infrared fluorescence spectroscopy using Ti / sapphire laser as excitation light source
Stem (InGaAs detector)
Excitation wavelength: 690-830 nm
Fluorescence detection wavelength (fluorescence wavelength): 950-1450 nm
Exposure time: 20 seconds Integration count: 1 time

  As shown in the results of FIG. 5, when the excitation wavelength is 720 nm and the fluorescence wavelength is 1124 nm, the fluorescence intensity of the composite material of Example 1 is about 6000 a. u. However, when a voltage was applied, the fluorescence intensity decreased with time and then settled to a substantially constant value (about 1000 au). From the result that the fluorescence intensity decreases with the application of voltage and then settles down to a certain value, when fluorescence measurement is performed by irradiating light perpendicular to the electrode substrate, hydroxypropyl as a matrix It can be seen that the cellulose was oriented perpendicular to the substrate, and the carbon nanotubes were also oriented along with it, and that the fluorescence intensity settled to a certain value was mostly due to the orientation of the carbon nanotubes in the composite material. This is considered to be because they are aligned in a substantially constant direction (perpendicular to the substrate).

[Test Example 2]
Confirmation of orientation behavior of carbon nanotubes by near-infrared fluorescence measurement (2):
Fluorescence intensity (A) of the composite material of Example 1 before applying voltage in the case of performing near-infrared fluorescence measurement while applying a voltage in the same manner as in Test Example 1, immediately after applying the voltage for 15 minutes FIG. 6 shows the measurement results of the fluorescence intensity (B) of the carbon nanotubes and the fluorescence intensity (C) of the carbon nanotubes opened after B and left for one day.

  From the result of FIG. 6, the composite material of Example 1 has a low fluorescence intensity because the carbon nanotubes are oriented in the vertical direction with respect to the electrodes by applying a voltage (A → B in FIG. 5). Thereafter, the fluorescence intensity increased again by releasing the voltage and leaving it to stand (C in FIG. 5). As a result, the orientation of the carbon nanotubes collapsed and returned to a randomly dispersed state, and as a result, the number of carbon nanotubes that were exposed to light in the length direction in the composite material increased, and the fluorescence intensity increased again. It is considered a thing.

  Since the liquid crystal compound-carbon nanotube composite material of the present invention is excellent in electrical characteristics and mechanical characteristics, it can be advantageously used in various fields such as the electronic material field, the medical field, and the energy field.

It is the figure which showed typically the fluorescence intensity in case the fluorescence wavelength near 1124nm at the time of performing near-infrared fluorescence measurement. It is a perspective view of a liquid crystal cell. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is IV-IV sectional drawing of FIG. It is a figure which shows the measurement result in Test Example 1. It is a figure which shows the measurement result in Test Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal cell 11 ITO electrode substrate 12 Composite material (test object)
13 Glass substrate

Claims (5)

A liquid crystal compound-carbon nanotube composite material in which carbon nanotubes are dispersed using a liquid crystalline compound having lyotropic liquid crystallinity as a matrix,
A liquid crystal compound-carbon nanotube composite material, wherein a fluorescence intensity peak appears at a fluorescence wavelength of 1110 to 1150 nm in near infrared fluorescence measurement.   The liquid crystal compound-carbon nanotube composite material according to claim 1, wherein the liquid crystal compound is hydroxypropyl cellulose.   The liquid crystal compound-carbon nanotube composite material according to claim 1 or 2, wherein the liquid crystal compound has a viscosity of 2.0 to 10.0 mPa · s. A dispersion in which carbon nanotubes are dispersed and a liquid crystalline compound having lyotropic liquid crystallinity are mixed at a weight ratio of dispersion / liquid crystalline compound = 50/50 to 30/70,
A method for producing a liquid crystal compound-carbon nanotube composite material, which is then allowed to stand for a predetermined period. 5. The liquid crystalline compound according to claim 4, wherein the dispersion contains one or more selected from the group consisting of carboxymethylcellulose, chitosan, gellan gum, hyaluronic acid, sodium dodecyl sulfate and dodecyltrimethylammonium bromide. A method for producing a carbon nanotube composite material.

Images