KR20130103014A

KR20130103014A - Surface modification of carbon nanotubes using ultrasound

Info

Publication number: KR20130103014A
Application number: KR1020120024310A
Authority: KR
Inventors: 심상은; 김영선
Original assignee: 인하대학교 산학협력단
Priority date: 2012-03-09
Filing date: 2012-03-09
Publication date: 2013-09-23

Abstract

The present invention relates to a method for modifying the surface of carbon nanotubes using ultrasonic waves. In the present invention, the step of cleaving the polymer by applying ultrasonic waves to the suspension in which the polymer and carbon nanotubes are dispersed, grafting the polymer on the surface of the carbon nanotubes by the reaction of the radicals and carbon nanotubes formed at the end of the cut polymer Provided is a method for surface modification of carbon nanotubes comprising the step of. According to the present invention, the surface modification of the carbon nanotube can be performed simply and effectively by grafting a desired polymer onto the surface of the carbon nanotubes simply by ultrasonic waves without damaging the carbon nanotubes more than necessary.

Description

Surface modification of carbon nanotubes using ultrasound

The present invention relates to a method for surface modification of carbon nanotubes, and more particularly, to a method for modifying the surface of carbon nanotubes using ultrasonic waves.

Carbon nanotube (CNT) refers to a nanostructure in which a two-dimensional graphene is rolled up in a tube shape in which one carbon atom is formed by sp ² bonds with three other carbon atoms. Single Wall Carbon Nanotubes (SWCNTs) and Multi-walled Carbon Nanotubes (MWCNTs) consisting of a set of concentric cylindrical graphene shells, depending on the number of graphenes forming the walls of the nanostructures. Nanotube). Carbon nanotubes, on the other hand, are related to sp ² bonds of carbon as fullerene-related structures. The carbon nanotubes were introduced by an electric discharge method by Ijima (Ijima S et al., Nature 354 (1991) 56).

In general, carbon nanotubes have a diameter in the range of 1 to 100 nm, and their lengths can be synthesized up to several hundred to produce various types of structures. This unique structure of carbon nanotubes has about twice the thermal conductivity of diamond, about 1000 times higher electrical conductivity than copper, high heat resistance, and 200 times stronger mechanical properties than steel due to the high carbon-carbon bond strength. It provides unique properties and characteristics that are not easily found in conventional materials such as modulus of elasticity and large aspect ratio.

From the above excellent physical properties, carbon nanotubes can be applied as an additive used in a heat dissipating polymer composite, an electrically conductive polymer composite, and a high strength polymer composite. This means that practical development and expansion in flagship industries is possible, including display panels, cell phone enclosures, EMI shielding materials for the microelectronics industry, and conductive materials for the automotive industry. In addition, its applicability and value are considered to be very high in materials and engineering.

When carbon nanotubes are used as an additive of the composite material, the extent to which the bundles of carbon nanotubes are dispersed is very important. In the case of the polymer / carbon nanotube composite, the physical properties of the composite vary depending on the degree of dispersion of the carbon nanotubes in the polymer matrix.

However, since carbon nanotubes are relatively longer than diameter and many or all of their members are surface atoms, aggregation is likely to occur due to van der Waals forces, which are mutual attraction between carbon nanotubes. It is often formed into bundles or agglomerates, which are entangled like a net. In conclusion, there is a fatal problem that carbon nanotubes have very low dispersion in the polymer matrix. This is a great obstacle to the industrial application of the carbon nanotube dispersed polymer composite material, the situation that the development of technology for the method of dispersing the carbon nanotube aggregate is increasing.

The interfacial interaction between the carbon nanotubes and the polymer matrix is directly related to the compatibility of the carbon nanotubes with the matrix and directly affects the dispersion stability of the carbon nanotubes in the matrix. Therefore, both the carbon nanotube reforming method and the polymer matrix reforming method for imparting functionalities to these interfaces are used to promote the dispersion of the carbon nanotubes. In addition, dispersing carbon nanotubes in a solution is similar to the above mechanism.

Conventionally, a technique of increasing the dispersion stability of carbon nanotubes, oxidizing the surface by supporting the carbon nanotubes in nitric acid, sulfuric acid or a mixed solution thereof, and then using a water or low acid solvent There was a technique involving a series of operations to reduce the elevated acidity by repeated filtration. However, this technology has not only functional problems that cause excessive damage to the surface of carbon nanotubes due to the use of strong acids, but also safety and environmental problems of acid reagents themselves. Had a difficult problem to secure.

Conventionally, as a method of dispersing carbon nanotubes in a solution, there is a method of physically dispersing in a solution by putting carbon nanotubes in a solution and applying ultrasonic waves for a short time. This method simply disperses carbon nanotubes in solution without introducing functional groups, and is also used to disperse carbon nanotubes in carbon nanotubes in a technique for grafting polymers to carbon nanotubes. 0689866). In addition to the sonication or alone, in order to increase the dispersibility of the carbon nanotubes, a surfactant is added to the suspension containing the carbon nanotubes to increase the solubility of the carbon nanotubes. However, these dispersion methods have a problem that the dispersion effect of carbon nanotubes is insignificant as well as a short time to maintain the dispersion stability.

Korean Patent Laid-Open Publication No. 10-2010-0003777 describes a method of grafting vinyl monomers on the surface of carbon nanotubes by generating radiation by irradiating radiation. Korean Patent Laid-Open Publication No. 10-2011-0124008 discloses a method of modifying the surface of carbon nanotubes by generating radiation containing oxygen on the surface of the carbon nanotubes by directly irradiating the carbon nanotubes with radiation in an oxygen atmosphere. . Korean Patent Laid-Open Publication No. 10-2009-0006912 describes a method of modifying carbon nanotubes by irradiating plasma to the carbon nanotubes.

The present invention is intended to modify the surface in a simpler and more effective way without damaging the carbon nanotubes more than necessary, and in particular, an object of grafting the polymer on the surface of the carbon nanotubes in a simple manner using ultrasonic waves. The present invention seeks to obtain high dispersibility and dispersion stability of carbon nanotubes by grafting polymers using ultrasonic waves, and also to solve safety and environmental problems of surface modification methods of conventional carbon nanotubes.

In the present invention,

Cutting the polymer by applying ultrasonic waves to a suspension in which the polymer and carbon nanotubes are dispersed;

Provided is a method for surface modification of carbon nanotubes, comprising the step of grafting a polymer onto a surface of carbon nanotubes by reacting radicals formed on the cleaved polymer terminals with carbon nanotubes.

In addition, the present invention provides a carbon nanotube having a surface modified by the surface modification method of the carbon nanotube.

The surface modification method of the carbon nanotubes of the present invention is a form in which a functional group is introduced into the surface of a carbon nanotube simply and effectively by simply grafting a desired polymer onto the surface of the carbon nanotube by only ultrasonic waves without damaging the carbon nanotubes more than necessary. Surface modification can be done. The carbon nanotube surface modification method of the present invention can be carried out under safer and milder conditions by not using chemicals such as acids or strong oxidizing agents. According to the present invention, the surface-modified carbon nanotubes can maintain the dispersion stability for a necessary time or semi-permanently.

1 is a schematic diagram showing a carbon nanotube surface modification method according to the present invention.
2 is a Turbiscan result of the carbon nanotube dispersion aqueous solution whose surface is modified according to the intensity and intensity of the ultrasonic wave.
FIG. 3 is an FT-Raman spectrum result showing the degree of damage in water of carbon nanotubes whose surface is modified by sonication (300W).
4 is an FT-Raman spectrum result showing the degree of damage in water of carbon nanotubes whose surface is modified by sonication (500W).
5 shows Fourier Transform Spectroscopy (FT-IR) results of carbon nanotubes whose surfaces are modified according to the intensity and intensity of ultrasonic waves.
6 is a result of thermogravimetric analysis (TGA) of carbon nanotubes whose surfaces are modified according to the intensity and intensity of ultrasonic waves.
FIG. 7 is a scanning electron microscope (SEM) photograph of carbon nanotubes whose surface is modified according to the strength and intensity of ultrasonic waves.

Preparation of suspension

First, a suspension in which carbon nanotubes and a polymer is dispersed in a solvent is prepared. The carbon nanotubes used in the present invention may use single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), and may be manufactured and used in a conventional manner or may be used to purchase a commercially available product. It is not particularly limited. For example, the carbon nanotubes may be selected from arc discharge, laser deposition, plasma chemical vapor deposition, microwave chemical vapor deposition, and the like.

The polymer is not particularly limited, and may be used by selecting a polymer having a desired property to be introduced to the surface of the carbon nanotubes. For example, polyvinyl alcohol, polystyrene, polymethyl methacrylate, or the like may be used.

The solvent used to disperse the polymer and the carbon nanotubes may be a material having a specific property and / or functional group which binds to the radicals of the carbon nanotubes described below, for example, a polymer resin, an organic material, an inorganic material, or a mixture thereof. A solvent capable of dissolving or dispersing one or more chemicals selected from among them should be used. The solvent is a hydrophilic or hydrophobic material, more specifically, water, methanol, ethanol, benzene, toluene, tetrahydrofuran and the like can be used. The solvent should be able to dissolve and disperse as much as possible chemicals that can impart functionality to the surface of the carbon nanotubes. For example, when the polyvinyl alcohol (PVA) is to be bonded to the surface of the carbon nanotubes, a solvent such as water or ethanol may be used.

The suspension is a polymer material to be bonded to the surface of the carbon nanotubes and carbon nanotubes is dispersed in a solvent, but is not particularly limited, it is preferable to add carbon nanotubes 0.1 to 30 parts by weight based on 100 parts by weight of the polymer, More preferably, 5 to 30 parts by weight of carbon nanotubes are added. If the amount of carbon nanotubes is too low compared to the polymer, the productivity of the surface-modified carbon nanotubes decreases. On the contrary, if the amount of carbon nanotubes is excessively large compared to the polymer, the surface of the carbon nanotubes cannot be sufficiently modified.

Ultrasonic application and response

By applying ultrasonic waves to the suspension prepared as described above, the polymer is cut to form radicals, and the formed radicals react with the carbon nanotubes to graf the polymer onto the surface of the carbon nanotubes.

When ultrasonic waves are applied to liquid materials, cavitation occurs due to microbubbles. The microbubble increases and decreases in size while repeating expansion and contraction, and when the critical size is reached, energy is dissipated and collapses in the form of a shock wave. When strong cavitation occurs in the polymer chain during this process, the middle part of the bond is usually cut, and radicals are formed at the ends of the cut chain. The present invention focuses on being able to cut the chain of the polymer present in the liquid material by using ultrasonic waves and to form radicals at the cut ends. More specifically, cavitation occurs in the suspension by ultrasonic waves, from which the bonds of the polymer chains are cleaved, and radicals are formed at the ends of the cleaved polymer chains, and a reaction occurs between the radicals and the carbon nanotubes. It is grafted on the surface of carbon nanotubes.

As the frequency, intensity, and application time of the ultrasonic wave applied to the suspension increase, the cavitation inside the suspension increases, thereby increasing the amount of polymer bonded to the carbon nanotubes. In the present invention, as the ultrasonic wave is applied, the chain of the polymer is broken to decrease the molecular weight, and more specifically, the molecular weight of the polymer is further reduced as the frequency, intensity, and application time of the applied ultrasonic wave are increased. The frequency range of the preferred ultrasonic wave usable in the present invention is 1 KHz to 900 MHz, the intensity is 4 W / cm ² to 10000 W / cm ² , and the application time is 3 to 300 minutes. Ultrasound may be performed by a conventional ultrasonic application method, preferably a horn method or a bath method.

Separation of Surface Modified Carbon Nanotubes

Only carbon nanotubes grafted with polymer are separated. Conventional methods used for separation of mixtures can be used, preferably filter filters or thimble filters. In addition, the process of circulating water using soxhlet extraction may be additionally performed to increase purity.

In drying the obtained surface-modified carbon nanotubes, a conventional drying apparatus such as a vacuum oven, a micro oven, or the like may be used.

Hereinafter, an Example is given and this invention is demonstrated in detail. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited by the following examples.

&Lt; Example 1-5 >

A suspension was prepared by dissolving polyvinyl alcohol (Mw 89,000 to 98,000, 99%, Aldrich) in 95 g of distilled water and mixing with 0.25 g of carbon nanotube (10-20 nm in diameter, 10-50 μm, 95%, Hanwha Nanotech). Thereafter, the suspension was mounted on a horn type ultrasonic processing apparatus, and 0 minutes (control 1), 10 minutes (Example 1), 20 minutes (Example 2), and 30 minutes at room temperature at a frequency of 20 kHz and an intensity of 300 W, respectively. (Example 3), ultrasonic waves were applied every 40 minutes (Example 4) and 50 minutes (Example 5).

Thereafter, a highly purified surface-modified carbon nanotube slurry obtained by circulating water for 4 days by filtering using a thimble filter having a filter diameter of 8.0 μm, and then dried in a vacuum oven at 50 ° C. for 48 hours. It was.

<Example 6-10>

Except that the ultrasonic wave was applied at a strength of 500W was carried out in the same manner as in Example 1-5 to obtain a carbon nanotube with a modified surface.

Specifically, depending on the ultrasonic application time, 0 minutes (control 2), 10 minutes (Example 6), 20 minutes (Example 7), 30 minutes (Example 8), 40 minutes (Example 9) and 50 minutes ( Example 10) Ultrasonic waves were applied.

<Example 11>

Polystyrene (average Mw 90,000, Aldrich) was dissolved in 95 g of toluene and mixed with 0.25 g of carbon nanotubes (10-20 nm in diameter, 10-50 μm, 95%, Hanwha Nanotech) to prepare a suspension. The suspension was mounted on a treatment apparatus, and ultrasonic waves were applied at 0 and 0 minutes (control 3) and 30 minutes (Example 11) at room temperature at a frequency of 20 kHz and an intensity of 300 W, respectively. Thereafter, a highly purified surface-modified carbon nanotube slurry obtained by circulating toluene for 4 days by filtering using a thimble filter having a filtration pore diameter of 8.0 μm and then circulating toluene for 4 days was dried at 50 ° C. in a vacuum oven for 48 hours. It was.

Example 11 to which ultrasonic waves were applied was found to increase the amount of polystyrene bound to the surface of the carbon nanotubes compared to the control group 3 to which ultrasonic waves were not applied.

&Lt; Example 12 >

Except that the ultrasonic wave was applied at a strength of 500W it was carried out in the same manner as in Example 11 to obtain a carbon nanotube with a modified surface. In detail, ultrasonic waves were applied for 0 minutes (control 4) and 30 minutes (Example 12), respectively, according to the ultrasonic application time.

As compared with the control group 4 without applying the ultrasonic waves, the amount of polystyrene bonded to the surface of the carbon nanotubes was increased as compared to the control example 4 without the ultrasonic wave.

[Experimental Example]

Determination of Carbon Nanotube Damage by Ultrasonic Application

In Example 1-10, as the ultrasonic wave was applied to a solution of 0.25 g of carbon nanotubes dispersed in 95 g of distilled water, the degree of damage of the carbon nanotubes was confirmed using the FT-Raman spectrum.

3 shows that the intensity of the ultrasonic wave is 300W, and FIG. 4 shows that the surface damage caused by the ultrasonic waves of the carbon nanotubes is insignificant regardless of the application time of the ultrasonic waves.

Qualitative analysis of surface-modified carbon nanotubes by ultrasonic application

The presence and qualitative analysis of functional groups on the carbon nanotubes whose surface prepared in Example 1-10 was modified by poly (vinyl alcohol) were used by FT-IR, and the results are shown in FIG. 5.

As shown in FIG. 5, the amount of poly (vinyl alcohol) bound to the surface of the carbon nanotubes increases as the intensity of the ultrasonic waves is increased from 300W to 500W than when the ultrasonic waves are not applied (controls 1 and 2). have.

Likewise, as the ultrasonic application time increases to 50 minutes, the amount of poly (vinyl alcohol) bound to the surface of the carbon nanotubes increases.

Quantitative Analysis of Surface-Modified Carbon Nanotubes by Ultrasonic Application

For the carbon nanotubes prepared by Examples 6, 8, and 10, the quantitative analysis of the polymer bound to the surface of the carbon nanotubes was performed using thermogravimetric analysis (TGA). Indicated.

As shown in Figure 6, when the intensity of the ultrasonic wave 500W, it can be seen that the amount of poly (vinyl alcohol) bound to the surface of the carbon nanotubes is significantly increased than when the ultrasonic wave is not applied (control group 2). .

In addition, it can be seen that the amount of poly (vinyl alcohol) bound to the surface of the carbon nanotubes increases as the time for applying the ultrasonic wave is increased to 50 minutes.

In addition, in the amount of poly (vinyl alcohol) bonded to the surface of the carbon nanotubes, it can be seen that the critical condition is formed from the intensity of the ultrasonic wave 500W and the application time of the ultrasonic wave 30 minutes (Example 8).

Scanning electron microscope analysis of surface modified carbon nanotubes

Surface morphology analysis of surface-modified carbon nanotubes by polymer was performed using scanning electron microscopy (SEM) and the results (control, Example 1, Example 3, Example 5, Example 6, and Example). Example 8 and Example 10) are shown in FIG.

As the intensity and application time of the ultrasonic wave increases, more poly (vinyl alcohol) is bonded to the surface of the carbon nanotubes, and thus, the thickness of the carbon nanotubes can be confirmed to be thicker.

In addition, it can be seen that the poly (vinyl alcohol) is excessively combined with the thickness of the carbon nanotubes from the intensity of the ultrasonic wave 500W and the ultrasonic application time from 30 minutes in relation to the critical condition.

Evaluation of Dispersion Stability of Surface-Modified Carbon Nanotubes

Optical analysis of dispersion stability of the surface-modified carbon nanotubes prepared by Examples 6, 8, and 10 was evaluated using Turbiscan, and the results are shown in FIG. 2.

As shown in FIG. 2, in the case where the intensity of the ultrasonic wave was 500W, the dispersion stability of the carbon nanotubes was increased as the ultrasonic application time was increased from 10 minutes to 60 minutes. That is, the dispersion stability of the carbon nanotubes prepared in Example 10 was found to be the highest.

In addition, optical analysis of the dispersion stability of the surface-modified carbon nanotubes prepared in Examples 11 and 12 was evaluated through the optical image. This image was obtained by dispersing carbon nanotubes modified in each condition in water and photographing one month later. The results are shown in FIG. 8.

As shown in FIG. 8, when the application time of the ultrasonic wave was 30 minutes, the optical dispersion stability of the dispersed carbon nanotubes was higher than that of the 300 W when the intensity of the ultrasonic wave was 500 W.

Therefore, according to the present invention, a surface-modified carbon nanotube may be manufactured using ultrasonic waves to bond a polymer having specific properties and / or functional groups to the surface of the carbon nanotube, and may be semipermanently high in a polymer matrix, an organic solution, and an inorganic solution. Dispersion stability and compatibility can be achieved.

As described above, the present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims

Cutting the polymer by applying ultrasonic waves to a suspension in which the polymer and carbon nanotubes are dispersed;
The method of modifying the surface of the carbon nanotubes comprising the step of grafting the polymer on the surface of the carbon nanotubes by the reaction of the radicals and carbon nanotubes formed on the cut polymer terminal.

The method of claim 1, wherein the suspension is added to the carbon nanotubes in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the polymer.

The carbon nanotubes of claim 1, wherein the suspension is dispersed in the polymer and carbon nanotubes in at least one solvent selected from the group consisting of water, methanol, ethanol, benzene, toluene and tetrahydrofuran. Surface modification method.

The method of claim 1, wherein the ultrasonic wave is applied by a horn method or a bath method.

The method of claim 1, wherein the degree of polymer grafting on the surface of the carbon nanotubes is controlled according to the frequency, intensity, and application time of the ultrasonic waves.

The method of claim 1, further comprising selectively separating only carbon nanotubes grafted with the polymer.

The method of claim 6, wherein the separating of the carbon nanotubes comprises separating using a filter filter paper or a thimble filter.

The carbon according to any one of claims 1 to 7, wherein the ultrasonic waves are applied at 1 KHz to 900 MHz, 4 W / cm ² to 10000 W / cm ² , and an application time of 3 to 300 minutes. Method of surface modification of nanotubes.

The method of claim 8, wherein the ultrasonic wave is applied at 300 to 500 W / cm ² .

A carbon nanotube grafted with a polymer obtained by the method of any one of claims 1 to 7.