KR102463829B1 - Dispersing agent for high-concentration aqueous carbon nanotubes and carbon nanotube dispersion containing the same - Google Patents

Abstract

The present invention relates to dispersion for high-concentration aqueous carbon nanotubes, which contains carbon nanotubes (CNT), a dispersant, and an aqueous solvent, wherein the dispersant contains polyvinylpyrrolidone and a styrene-acrylic copolymer. The dispersant of the present invention can improve the dispersibility of the carbon nanotubes to prepare the carbon nanotube dispersion with low viscosity by improving the dispersibility of the carbon nanotubes.

Description

Dispersing agent for high-concentration aqueous carbon nanotubes and carbon nanotube dispersion containing the same

The present invention relates to a high concentration aqueous carbon nanotube dispersant and a carbon nanotube dispersion containing the same, and more particularly, to a dispersing agent containing polyvinylpyrrolidone and a styrene-acrylic copolymer and a carbon nanotube dispersion containing the same. it's about

Carbon nanotubes are typically classified into multi-walled carbon nanotubes and single-walled carbon nanotubes. According to the number of walls, it is also divided into double-walled carbon nanotubes and thin-walled carbon nanotubes. It is composed of several bundles, and each of the hexagons composed of 6 carbons form a tubular shape with each other, thereby exhibiting excellent physical and chemical performance.

Although carbon nanotubes have some performance differences depending on diameter and length, they have very good tensile strength and high thermal and electrical properties. It is a material that is expected to grow continuously over the years. If carbon nanotubes are used instead of the existing carbon materials currently used in secondary batteries, weight can be reduced and charging efficiency can be greatly increased.

However, carbon nanotubes have the disadvantage of being difficult to handle and expensive, and have a very stable structure at room temperature and pressure due to the strong Van der Waals bonding energy between carbon nanotubes. Therefore, dispersion is difficult and the exact length is also difficult to measure, so it is limited to high-tech fields. These problems can be solved through chemical surface modification and advanced dispersion technology, and through this, the carbon nanotube dispersion in a stable state can be used for secondary batteries and other applications, so that it can be recognized as an important material.

In this regard, as a technology related to the dispersion of carbon nanotubes, Korean Patent Registration No. 10-1471044 forms a dispersion by mixing a phthalocyanine compound containing a metal ion at the synergistic center of the carbon nanotube. Patent Publication No. 10-2011-0126998 tried to improve the dispersibility of carbon nanotubes by using a polymer dispersant having a polar reactive functional group.

Korean Patent No. 10-1471044 (Registered on Dec. 3, 2014) Korean Patent Publication No. 10-2011-0126998 (published on November 24, 2011)

The carbon nanotube dispersion of the present invention has been devised to solve the above problems, and includes carbon nanotubes (CNT), a dispersing agent, and an aqueous solvent, and the dispersing agent is polyvinylpyrrolidone and a styrene-acrylic copolymer. An object of the present invention is to provide a carbon nanotube dispersion comprising a.

The present invention may also have the object of achieving these objects and other objects that can be easily derived by a person skilled in the art from the general description of the present specification in addition to the above clear objects.

The carbon nanotube dispersion of the present invention includes carbon nanotubes (CNT), a dispersing agent, and an aqueous solvent, and the dispersing agent includes polyvinylpyrrolidone and a styrene-acrylic copolymer characterized in that

In addition, the styrene-acrylic copolymer may have a weight average molecular weight of 10,000 to 40,000, 12,000 to 35,000, or 15,000 to 30,000.

In addition, in the styrene-acrylic copolymer, a molar ratio of the styrene monomer to the acrylic monomer may be 75:25 to 25:75.

And, in the styrene-acrylic copolymer, the styrene monomer may be selected from the group consisting of styrene, styrene derivatives having 8 to 10 carbon atoms, and mixtures thereof.

And, in the styrene-acrylic copolymer, the acrylic monomer is acrylic acid, methacrylic acid, acrylic acid or methacrylic acid derivative having a linear or branched alkyl group having 1 to 32, 1 to 22, or 1 to 12 carbon atoms, and these may be selected from the group consisting of a mixture of

In addition, the dispersant may be included in an amount of 10 to 500 parts by weight, 10 to 100 parts by weight, or 10 to 30 parts by weight based on 100 parts by weight of the carbon nanotubes.

And, the carbon nanotube is a multi-walled carbon nanotube,

The dispersant may include 10 to 500 parts by weight, 30 to 300 parts by weight, or 50 to 150 parts by weight based on 100 parts by weight of the carbon nanotubes.

And, the carbon nanotube is a single-walled carbon nanotube,

The dispersant may include 10 to 500 parts by weight, 50 to 400 parts by weight, or 100 to 300 parts by weight based on 100 parts by weight of the carbon nanotubes.

In addition, the dispersant may include 100 parts by weight of polyvinylpyrrolidone and 1 to 100 parts by weight, 5 to 80 parts by weight, or 10 to 50 parts by weight of the styrene-acrylic copolymer.

In addition, the dispersant may include an anionic surfactant.

In addition, the dispersant may include 10 to 100 parts by weight, 10 to 50 parts by weight, or 10 to 20 parts by weight of an anionic surfactant based on 100 parts by weight of polyvinylpyrrolidone and the styrene-acrylic copolymer.

In addition, the anionic surfactant may be a sulfonic acid-based anion or a phosphate-based anionic compound.

In addition, the anionic surfactant may have a molecular weight of 1,000 or less, 900 or less, or 800 or less.

In addition, the anionic surfactant may be disodium distyrylbiphenyl disulfonate.

In addition, the carbon nanotube may be included in an amount of 0.01 to 10 wt%, 0.01 to 9 wt%, or 0.01 to 8 wt%, based on the total weight of the carbon nanotube dispersion.

In addition, the carbon nanotubes may be single-walled carbon nanotubes, double-walled carbon nanotubes, thin multi-walled carbon nanotubes, multi-walled carbon nanotubes, bundled carbon nanotubes, or a mixture thereof.

And, the carbon nanotube is a multi-walled carbon nanotube, and may contain 0.01 to 10 wt%, 0.1 to 9 wt%, or 0.5 to 8 wt% based on the total weight of the carbon nanotube dispersion.

In addition, the carbon nanotube is a single-walled carbon nanotube, and may contain 0.01 to 3 wt%, 0.01 to 2 wt%, or 0.01 to 1 wt%, based on the total weight of the carbon nanotube dispersion.

In addition, the carbon nanotube dispersion may have a viscosity (cps) of 1700 or less, 1100 or less, or 800 or less.

The carbon nanotube dispersion according to the present invention can be applied to secondary batteries, hydrogen storage materials, electrochemical sensors, electromagnetic wave shielding, antistatic and the like due to high thermal and electrical properties. In particular, when applied to the secondary battery field, the equivalent performance is obtained even when used in a small amount compared to carbon black, so that the additional use of an active material is possible, thereby improving battery performance. In addition, the use of carbon nanotubes has an advantage in that it is possible to secure stability by suppressing the volume expansion of silicon, which is recently pointed out as a cause of fires in electric vehicles.

In addition, according to the present invention, the characteristics of carbon nanotubes can be maximized by using a dispersion technique that secures dispersibility and dispersion stability by weakening the van der Waals bond between carbon nanotubes. Through these results, product performance in various fields such as electromagnetic wave shielding and heat dissipation/heat generation as well as secondary battery field can be greatly improved.

Hereinafter, preferred embodiments of the present invention will be described in detail.

However, the present invention is not limited to the specific exemplary embodiments, since the following is merely a detailed description by exemplifying specific embodiments, and since the present invention may be variously changed and may have various forms. It should be understood that the present invention includes all modifications, equivalents and substitutions included in the spirit and scope of the present invention.

In addition, in the following description, many specific details such as specific components are described, which are provided to help a more general understanding of the present invention, and it is common in the art that the present invention can be practiced without these specific details. It will be self-evident to those who have the knowledge of And, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

And, the terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In this application, the singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present application, terms such as 'comprise', 'contain' or 'have' are intended to refer to the presence of a feature, component (or component), etc. described in the specification, but one or more other features or It does not mean that the component etc. are not present or cannot be added.

The present invention provides a dispersing agent for carbon nanotubes having a low viscosity and high dispersion stability, a carbon nanotube dispersion containing the same, and a method for preparing the same. The carbon nanotube dispersion of the present invention is characterized in that it contains carbon nanotubes (CNT), a dispersant, and an aqueous solvent such as ion-exchanged water. In particular, the dispersant of the present invention contains a polymer dispersant containing polyvinylpyrrolidone and a styrene-acrylic copolymer, so that the CNT concentration is high and the viscosity (cps) is 1700 or less, 1100 or less, or 800 or less carbon nanotube dispersion of low viscosity. can provide

On the other hand, the method for producing a carbon nanotube dispersion of the present invention comprises the steps of preparing a mixture by mixing carbon nanotubes, a dispersing agent, and ion-exchanged water as a solvent, and dispersing the mixture under high pressure conditions after stirring the mixture characterized in that At this time, the agitation may use an impeller, and in particular, a propeller type impeller may be used, and may be treated at 900 to 1500 rpm, 1000 to 1400 rpm, or 1100 to 1300 rpm for 10 to 30 minutes or 15 to 25 minutes. can In addition, the dispersion treatment may use a high-pressure homogenizer, and may be repeatedly processed under pressure conditions of 1000 to 2000 bar, 1100 to 1800 bar, or 1300 to 1500 bar.

Hereinafter, the carbon nanotube dispersion according to the present invention will be described in detail.

carbon nanotube

The carbon nanotubes may be classified into single-walled carbon nanotubes, double-walled carbon nanotubes, thin multi-walled carbon nanotubes, multi-walled carbon nanotubes, and bundled carbon nanotubes according to the number of walls, and the carbon nanotube of the present invention may be in any form consisting of single-walled, double-walled, thin multi-walled, multi-walled, bundled, and mixtures thereof, and may be appropriately selected according to the use of the dispersion. In addition, the carbon nanotube may be included in an amount of 0.01 to 10 wt%, 0.01 to 9 wt%, or 0.01 to 8 wt%, based on the total weight of the carbon nanotube dispersion.

The content of the carbon nanotube may be appropriately adjusted according to the type of carbon nanotube. For example, when using multi-wall carbon nanotubes, the carbon nanotube dispersion may contain 0.01 to 10 wt%, 0.1 to 9 wt%, or 0.5 to 8 wt% based on the total weight of the carbon nanotube dispersion. In addition, when single-walled carbon nanotubes are used, 0.01 to 3% by weight, 0.01 to 2% by weight, or 0.01 to 1% by weight based on the total weight of the carbon nanotube dispersion may be included.

dispersant

The dispersant of the present invention is for enabling the carbon nanotubes to be uniformly dispersed without agglomeration in the carbon nanotube dispersion, and from 10 to 500 parts by weight, 10 to 100 parts by weight, or 10 to 500 parts by weight based on 100 parts by weight of the carbon nanotubes. It may be included in 30 parts by weight, but may be appropriately adjusted depending on the type of carbon nanotube. For example, when using multi-walled carbon nanotubes, the dispersant may be included in an amount of 10 to 500 parts by weight, 30 to 300 parts by weight, or 50 to 150 parts by weight based on 100 parts by weight of the carbon nanotubes. In addition, when single-walled carbon nanotubes are used, the dispersant may be included in an amount of 10 to 500 parts by weight, 50 to 400 parts by weight, or 100 to 300 parts by weight based on 100 parts by weight of the carbon nanotubes. If the content of the dispersant is less than the above range, the dispersion performance may be insufficient and the viscosity of the dispersion may increase. If the content of the dispersant exceeds the above range, the dispersant may act as an impurity and cause deterioration of product performance.

In addition, the carbon nanotube dispersion of the present invention is characterized in that polyvinylpyrrolidone and a styrene-acrylic copolymer are used together as a dispersant. The viscosity of the carbon nanotube dispersion can be reduced by using a dispersing agent including polyvinylpyrrolidone and two types of styrene-acrylic copolymer.

Specifically, the dispersant may include 100 parts by weight of polyvinylpyrrolidone and 1 to 100 parts by weight, 5 to 80 parts by weight, or 10 to 50 parts by weight of the styrene-acrylic copolymer. Compared to polyvinylpyrrolidone, when the content of the styrene-acrylic copolymer is less than or exceeding the above range, the viscosity of the dispersion may increase, thereby decreasing the viscosity increase rate and fairness.

The dispersant including the styrene-acrylic copolymer is for reducing the viscosity of the carbon nanotube dispersion, and in the styrene-acrylic copolymer, the molar ratio of the styrene monomer to the acrylic monomer is 75:25 to 25:75, or about 30: 70, which may be a copolymer. More specifically, the molar ratio of the styrene monomer to the acrylic monomer may be 25:75 to 60:40, 30:70 to 50:50, or 35:65 to 40:60.

The styrene-acrylic copolymer is a copolymer composed of a hydrophobic styrene-based monomer and an acrylic-based monomer having hydrophilicity due to a carboxyl group, an ester group, or a carbonyl group. The properties of the styrene-acrylic copolymer are determined by the chemical structure of the hydrophilic part and the hydrophobic part and the ratio thereof. The effect of reducing the viscosity of the carbon nanotube dispersion is excellent. The styrene-acrylic copolymer may be an alternating copolymer, a block copolymer, a graft copolymer, or a random copolymer.

The styrene-acrylic copolymer may have a weight average molecular weight of 10,000 to 40,000, 12,000 to 35,000, or 15,000 to 30,000. When the weight average molecular weight of the styrene-acrylic copolymer is less than the above range, the dispersion performance is deteriorated. On the other hand, when the weight average molecular weight exceeds the above range, the viscosity of the carbon nanotube dispersion increases, thereby reducing the viscosity increase rate and fairness.

The styrene monomer used in the present invention may include one selected from the group consisting of styrene, styrene derivatives having 8 to 10 carbon atoms, and mixtures thereof. For example, styrene, α-methylstyrene, α-ethylstyrene, p-methylstyrene, p-ethylstyrene, halogenated styrene compounds, o-methoxystyrene, chlorostyrene, etc. may be included, and these may be used alone or in combination. can

The acrylic monomer used in the present invention is acrylic acid, methacrylic acid, acrylic acid or methacrylic acid having a linear or branched alkyl group having 1 to 32, 1 to 22, or 1 to 12 carbon atoms, and derivatives thereof, and mixtures thereof. It may include one selected from the group. For example, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, octyl (meth) acrylate, 2-ethyl hexyl (meth) acrylate, hydroxyethyl (meth) acrylate, 2 -Hydroxypropyl (meth)acrylate and the like may be included, and these may be used alone or in combination.

The dispersant may further include an anionic surfactant. In this case, the dispersant may include 10 to 100 parts by weight, 10 to 50 parts by weight, or 10 to 20 parts by weight of an anionic surfactant based on 100 parts by weight of polyvinylpyrrolidone and styrene-acrylic copolymer. If the content of the anionic surfactant is less than the above range, the viscosity increase rate over time may increase, and if it exceeds the above range, bubbles may be generated, thereby reducing coating properties and processability.

The anionic surfactant may have a molecular weight of 1,000 or less, 900 or less, or 800 or less, and may be used by combining a sulfonic acid-based anion or a phosphate-based anion, preferably disodium distyrylbiphenyl disulfonate (Disodium distyrylbiphenyl disulfonate) can be When it exceeds the above range, the viscosity of the carbon nanotube dispersion may increase, thereby reducing the viscosity increase rate and processability.

water-based solvent

The present invention relates to an aqueous carbon nanotube dispersion, characterized in that it contains an aqueous solvent. The aqueous solvent may be ion-exchanged water, but is not limited thereto.

Hereinafter, the present invention will be described in more detail through specific examples.

[Example]

Preparation Example 1: Synthesis of styrene-acrylic copolymer (1)

87 mol parts of styrene monomer, 435 mol parts of isopropyl alcohol, and 145 mol parts of ion-exchanged water were injected into a glass reactor equipped with a thermometer, stirrer, dropping funnel, nitrogen inlet tube and reflux cooling device, and uniformly mixed. The inside of the reactor was replaced with nitrogen, and the temperature was raised to 85°C in a nitrogen atmosphere. Next, 145 mol parts of acrylic acid and 80 mol parts of sodium sulfate aqueous solution (25%) as an initiator were added dropwise over 4 hours. After completion of the dropping of the monomer and initiator, 20 mole parts of a 25% aqueous sodium sulfate solution was added dropwise for 1 hour, and the unreacted monomer was completely polymerized while maintaining 85° C. for 2 hours. The temperature was raised to 101 °C while depressurizing the inside of the reactor to remove isopropyl alcohol. After cooling the reaction mixture to room temperature, 390 mol parts of ion-exchanged water was added, and 150 mol parts of caustic soda (50% aqueous solution) was slowly added to synthesize a copolymer.

Preparation Example 2: Synthesis of styrene-acrylic copolymer (2)

A styrene-acrylic copolymer was synthesized in the same manner as in Preparation Example 1, except that 87 parts of styrene monomer was injected and 90 parts of acrylic acid was added dropwise.

Preparation Example 3: Synthesis of styrene-acrylic copolymer (3)

A styrene-acrylic copolymer was synthesized in the same manner as in Preparation Example 1, except that 87 parts of styrene monomer was injected and 60 parts of acrylic acid was added dropwise.

Preparation Example 4: Synthesis of styrene-acrylic copolymer (4)

A styrene-acrylic copolymer was synthesized in the same manner as in Preparation Example 1, except that acrylic acid and an aqueous sodium sulfate solution as an initiator were added dropwise for 8 hours.

Preparation Example 5: Synthesis of styrene-acrylic copolymer (5)

A styrene-acrylic copolymer was synthesized in the same manner as in Preparation Example 1, except that 130 parts of sodium sulfate aqueous solution was added dropwise over 4 hours, and 20 parts of sodium sulfate aqueous solution was dropped over 1 hour to completely polymerize unreacted monomers.

Preparation Example 6: Synthesis of styrene-acrylic copolymer (6)

A styrene-acrylic copolymer was synthesized in the same manner as in Preparation Example 1, except that 390 parts of ion-exchanged water was added after cooling the reaction mixture to room temperature, and 150 parts of ammonium salt was slowly added.

The molecular weight, polydispersity, and viscosity of the copolymers prepared according to Preparation Examples 1 to 6 are shown in Table 1 below.

Preparation Example 1 Production Example 2 Production Example 3 Preparation 4 Production Example 5 Preparation 6 Molecular Weight (g/mol) 25,000 22,000 18,000 21,000 20,000 26,000 polydispersity 2.1 2.0 1.9 1.7 viscosity
(cps) 320 280 220 270 320

Example 1: Preparation of carbon nanotube dispersion (1)

5% by weight of multi-walled carbon nanotubes (10B, JEIO), 2.25% by weight of polyvinylpyrrolidone (K17, Ashland), 0.75% by weight of the dispersant of Preparation Example 1, and ion-exchanged water as a solvent are mixed in ion-exchanged water After preparing a mixture of 500 g by using a propeller type impeller, it was treated for 20 minutes at 1,200 rpm, and 15 times at a pressure of 1,400 bar using Micronox's PICOMAX equipment (high pressure homogenizer), followed by a carbon nanotube dispersion. was prepared.

Example 2: Preparation of carbon nanotube dispersion (2)

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.75 wt% of the styrene-acrylic copolymer dispersant of Preparation Example 2 was mixed.

Example 3: Preparation of carbon nanotube dispersion (3)

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.75 wt% of the styrene-acrylic copolymer dispersant of Preparation Example 3 was mixed.

Example 4: Preparation of carbon nanotube dispersion (4)

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.75 wt% of the styrene-acrylic copolymer dispersant of Preparation Example 4 was mixed.

Example 5: Preparation of carbon nanotube dispersion (5)

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.75% by weight of the styrene-acrylic copolymer dispersant of Preparation Example 5 was mixed.

Example 6: Preparation of carbon nanotube dispersion (6)

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.75 wt% of the styrene-acrylic copolymer dispersant of Preparation Example 6 was mixed.

Example 7: Preparation of carbon nanotube dispersion (7)

Carbon nanotubes in the same manner as in Example 1, except that 0.75 wt% of the styrene-acrylic copolymer dispersant of Preparation Example 1 and 0.5 wt% of disodium distyrylbiphenyldisulfonate, an anionic surfactant, were mixed. A dispersion was prepared.

Comparative Example 1: Preparation of carbon nanotube dispersion (8)

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the dispersant was mixed at 2.25% by weight of polyvinylpyrrolidone and 0.75% by weight of polyacrylic acid (molecular weight 8,500).

Test Example 1: Viscosity Measurement

The viscosity of the carbon nanotube dispersions prepared in Examples 1 to 7 and Comparative Example 1 was measured. The viscosity was measured at 25° C. and 60 rpm using a viscometer (Dial Viscometer LVT, Brookfield Co.). The measurement results are shown in Table 2 below.

Test Example 2: Absorbance Measurement

The absorbance of the carbon nanotube dispersions prepared in Examples 1 to 7 and Comparative Example 1 was measured. 9.9 g of ion-exchanged water and 0.1 g of the carbon nanotube dispersion were mixed and diluted to 1/100 concentration, and then 10 g of ion-exchanged water was added to 1 g of the diluted carbon nanotube dispersion and diluted once more. The absorbance was measured using an ultraviolet-visible spectrophotometer (UV-1800, SHIMADZU). The measurement results are shown in Table 2 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 viscosity
(cps) 700 1100 1700 800 1500 not measurable absorbance
(1:10) 2.5 2.1 2.2 2.0 2.1 2.0 2.5 1.0

From Table 2, it can be seen that Examples 1 to 7 using a dispersing agent including a styrene-acrylic copolymer showed lower viscosity and higher absorbance than Comparative Examples. In particular, it can be seen that Examples 1 and 7 have the lowest viscosity and high absorbance, and thus have the best dispersion performance. On the other hand, as in Comparative Example 1, when polyacrylic acid, not a styrene-acrylic copolymer, was used as a dispersant, agglomeration occurred and it was impossible to measure the viscosity.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the specific embodiments described above, and those skilled in the art can implement various modifications without departing from the gist of the present invention. Of course it is possible. Therefore, the scope of the present invention should not be construed as being limited to the above embodiments, and should be defined by the claims described below as well as the claims and equivalents.

Claims (7)

As a carbon nanotube dispersion,
Contains carbon nanotubes (CNT), a dispersant, and an aqueous solvent,
The dispersant comprises polyvinylpyrrolidone and a styrene-acrylic copolymer,
The styrene-acrylic copolymer has a molar ratio of styrene monomer to acrylic monomer of 75:25 to 25:75,
In the styrene-acrylic copolymer, the styrene monomer is selected from the group consisting of styrene, α-methylstyrene, α-ethylstyrene, p-methylstyrene, p-ethylstyrene, and mixtures thereof;
The dispersant is included in an amount of 10 to 500 parts by weight based on 100 parts by weight of the carbon nanotubes,
The dispersant comprises 100 parts by weight of polyvinylpyrrolidone and 5 to 80 parts by weight of a styrene-acrylic copolymer,
The carbon nanotube dispersion has a viscosity (cps) of 1700 or less,
Carbon nanotube dispersion. The method according to claim 1,
The styrene-acrylic copolymer has a weight average molecular weight of 10,000 to 40,000, characterized in that the carbon nanotube dispersion. delete delete delete The method according to claim 1,
The dispersing agent, characterized in that it comprises an anionic surfactant, carbon nanotube dispersion. The method according to claim 1,
The carbon nanotube dispersion, characterized in that contained in 0.01 to 10% by weight based on the total weight of the carbon nanotube dispersion.