KR100659590B1 - Electrorheological fluids using carbon nanotube-adsorbed polystyrene and poly(methyl methacrylate) microsphere and methods of use thereof - Google Patents

Abstract

Provided are an electrorheological fluid, its preparation method, a surface conductive microsphere used in the electrorheological fluid which can be prepared more simply and whose conductivity can be controlled, and its preparation method. The surface conductive microsphere comprises a core which comprises polystyrene or PMMA; and a shell which is formed by adsorbing a carbon nanotube on the surface of the core. Preferably the polystyrene or PMMA core has a diameter of 1-29 micrometers; and the carbon nanotube has a diameter of 8-40 nm. The electrorheological fluid comprises a nonconductive solvent; and the surface conductive microsphere which is dispersed in the nonconductive solvent. Preferably the nonconductive solvent is at least one selected from a vegetable oil, polydimethylsiloxane, a silicone oil and a mineral oil.

Description

Electrorheological Fluids Using Carbon Nanotube-adsorbed Polystyrene and Poly (methyl methacrylate) Microsphere and Methods of Use Thereof}

1 is a result of observing PS microsphere particles and PMMA microsphere particles obtained in one embodiment of the present invention by field-emission scanning electron microscopy (FESEM), where a and b are PS and PMMA microsphere particles, respectively.

Figure 2 is a simplified view showing a process for producing a polymer microspheres (surface conductive microspheres) in which carbon nanotubes are adsorbed on the surface according to the present invention.

3 to 5 are the results of observing the surface conductive microspheres prepared in one embodiment of the present invention by field-emission scanning electron microscop (FESEM). 3A and 3B show surface conductive microspheres formed by mixing PS microspheres in a carbon nanotube aqueous solution dispersed using CTAB and NaDDBS as surfactants, respectively. 4A and 4B show surface conductive microspheres formed by mixing PS microspheres in a carbon nanotube aqueous solution dispersed using SDS and Triton X-100 as surfactants, respectively. 5, a, b, c, and d are surface conductive microspheres formed by mixing PMMA microspheres in carbon nanotube aqueous solution dispersed using CTAB, NaDDBS, SDS, and Triton X-100 as surfactants, respectively.

Figure 6 shows the microsphere dispersion and settled state prepared in one embodiment of the present invention, a is PS microsphere dispersion and PMMA microsphere dispersion from the left, b is from the left CTAB, NaDDBS, SDS and Triton X- It is a carbon nanotube dispersion dispersed in each of 100 aqueous solution, c is a PS microsphere colloidal aqueous solution is added to the carbon nanotube dispersion dispersed in each aqueous solution of CTAB, NaDDBS, SDS and Triton X-100 from the left side and mixed.

FIG. 7 illustrates the results of observing the microstructure with an optical microscope before and after applying an electric field after dispersing PMMA microspheres (using CTAB surfactant) in which carbon nanotubes are adsorbed in silicone oil in one embodiment of the present invention.

8 is a result of dispersing the PS and PMMA microspheres adsorbed with carbon nanotubes of the present invention in a non-conductive solvent by sonication and then separating and observing them with FESEM, where a and b are PS and PMMA microsphere particles, respectively.

The present invention relates to a polymer microsphere with carbon nanotubes adsorbed, an electric field fluid using the same, and a method for manufacturing the same. In particular, a surface conductive microsphere formed by adsorbing carbon nanotubes on a polymer (polystyrene, PMMA) microsphere surface and its vision It relates to an electric field fluid dispersed in a solvent.

Carbon nanotubes have been in the spotlight as one of the most interesting new materials since their invention in 1991. These excellent properties have attracted considerable attention in the scientific and industrial fields. Currently, abundant experimental results on excellent properties such as mechanical, electrical and thermal properties of carbon nanotubes have been reported. Most of these superior properties can be exploited by introducing carbon nanotubes into the form of polymer matrices. Research into the preparation of such compositions containing carbon nanotubes is currently rapidly increasing. Many studies have used carbon nanotubes as fillers for polymer sheets and fibers. Polymers reinforced with carbon nanotubes are believed to have many potential engineering uses, from battery electrodes and electronics to much stronger composites.

Electric field fluid (electrorheological fluid, ER fluid) is a general term for fluids whose mechanical and physical properties change depending on the applied electric field. Generally, electric polarized particles are dispersed in electrically insulating solvents. Solution. In particular, the electric field fluid exhibits an increase in viscosity and yield stress behavior due to an electric field being loaded. The reaction is very fast and exhibits a reversible reaction to the electric field load, which is called an electrorheological effect (ER). A system containing conductive particles and non-conductive solvents after Winslow in 1947 discovered that the fluid's viscosity increased significantly when an external electric field was applied to a fluid made from a mixture of mineral oil and fine solid starch powder. Research is ongoing.

Most ER fluids have suspended particles with higher dielectric constant and conductivity in suspension mediated fluids with low dielectric constant and low viscosity. Because ER particles attract others to form aligned fibrous structures in the direction of the applied electric field, ER fluids exhibit a violent and reversible change in their rheological properties as a result of the applied electric field. Suspension microstructure transition from a liquid-like state to a solid-like state can be obtained by controlling the strength of the applied electric field. According to the polarization model, the suspended particles become polar due to inadequate dielectric bonds between the particles and the suspension fluid under the applied electric field. The interaction between the polarized particles causes them to line up themselves in the direction of the electric field.

Many electric field fluids are aqueous fluids that induce polarization through water, such as corn starch or active silicagel particles dispersed in mineral oil, and zeolite particles dispersed in silicone oil. Such aqueous field fluids, when applied to systems requiring high temperatures or high strain rates, separate water from the particles, vaporize some of them, resulting in poor ER effects, and short circuit risks. There is a need for the development of dry-base electric fluids that do not require moisture in recent years. In order to solve this problem, a method of preparing particles (eg zeolite) capable of confining the presence of moisture inside the particles, and a method of preparing a dry base electric field fluid in which the polarization phenomenon is caused by the induced dipole moment caused by electron transport in the particles Development has been proposed.

The general polymer is not electrically conductive, but if the conductive material is coated on the polymer particles, the surface is conductive. The surface conductive polymer particles may be dispersed in a nonconductive solvent to prepare an ER fluid. Korean Patent Laid-Open Publication No. 2003-0095544 discloses a method of preparing ER fluid by polymerizing and coating polyaniline, which is a conductive polymer, on polymethylmethacrylate (PMMA) particles to make surface conductive polymer particles, and then dispersing them in a non-conductive solvent. It is describing.

Today ER fluids are used in many applications using electromechanical devices because of their attractive characteristics such as short reaction times, low power consumption, ease of action, and simple mechanical structure. However, despite extensive research and development efforts, devices using ER fluids are still in very early stages of commercialization due to a number of unresolved issues such as colloidal instability and inadequate yield stress.

The present invention provides a new surface conductive particles obtained by adsorption coating of carbon nanotubes with a conductive material on polymer particles such as polystyrene (PS) and polymethyl methacrylate (PMMA), and a method of manufacturing the same. In the present invention, carbon nanotubes are combined by a very simple and measurable process on the microsphere surface of PS and PMMA. That is, the present invention provides a surface conductive microsphere consisting of a shell formed by adsorbing a PS or PMMA core and carbon nanotubes. The microspheres may be prepared through a simple process including mixing two colloidal aqueous solutions, that is, a carbon nanotube aqueous solution dispersed by a surfactant and a microsphere colloidal aqueous solution of PS or PMMA.

 Since the surface conductive microspheres of the present invention generate electrical conduction primarily from the conductive carbon nanotube layer coated on the surface, the surface conductive microspheres exhibit properties of ER fluid when dispersed in a non-conductive solvent. It is another object of the present invention to provide an ER fluid using the surface conductive microspheres of the present invention and a method for producing the same.

Other objects and advantages of the present invention will be described below and will be better understood by practice of the present invention.

In the present invention,

A surface conductive microsphere comprising a core made of polystyrene or PMMA and a shell formed by adsorption of carbon nanotubes on the surface of the core and an electric field fluid dispersed in the nonconductive solvent are provided.

The polystyrene (PS) core is preferably spherical particles having a particle size in the range of 1 μm to 20 μm in diameter. When the diameter of the core is 1 µm or less, it is difficult to adsorb carbon nanotubes to the surface of the core, and when the diameter of the core is 20 µm or more, mobility decreases and the characteristics as ER fluid decrease. In a preferred embodiment of the present invention, PS microspheres having an average particle diameter of 3.0 μm were used as the core.

The PMMA core is preferably spherical particles having a particle size in the range of 1 μm to 20 μm in diameter. When the diameter of the core is 1 µm or less, it is difficult to adsorb carbon nanotubes to the surface of the core, and when the diameter of the core is 20 µm or more, mobility decreases and the characteristics as ER fluid decrease. In a preferred embodiment of the present invention, PMMA microspheres having an average particle diameter of 6.5 μm were used as the core.

PS and PMMA microspheres are not particularly limited and can be made by dispersion polymerization which is known to be the most useful method for the production of monodisperse polymer particles (Shen, S .; Sudol, ED; El-Aasser, MS J.). Polym. Sci., Part A: Polym. Chem . 1994, 32 , 1087.).

The carbon nanotubes are not particularly limited, but may be preferably those having a diameter of 8 to 40 nm when considering the degree of adsorption to the polymer microspheres. In one embodiment of the present invention was used MWNT (multiwalled carbon nanotubes) of 8 to 40nm diameter synthesized by CVD (thermal chemical vapor deposition) method. Single-walled carbon nanotubes (SWNTs) may have many uses in the industry but are difficult to commercialize due to their high cost. In comparison, MWNTs are 500 times cheaper than current SWNTs in similar purity. In addition, the electrical properties of the complete MWNT are known to be similar to SWNTs due to the one-dimensional electrical structure and electrical transport properties. Therefore, although both MWNTs and SWNTs can be used as the carbon nanotubes of the present invention, MWNT is preferable in consideration of economical efficiency.

In the surface conductive microsphere of the present invention, electrical conductivity is primarily generated from the conductive carbon nanotube layer adsorbed and coated on the surface. The polymer microspheres on which carbon nanotubes are adsorbed have a monodispersity and have a spherical shape. Suspending and suspending the microspheres of the present invention in a non-conductive solvent has the characteristics of an electric field fluid (ER fluid) which increases in viscosity upon application of electricity. According to the present invention, PS nanospheres or PMMA microspheres on which carbon nanotubes are adsorbed exhibit conductivity at a conductivity range of 2.9 × 10 ⁻⁴ to 6.3 × 10 ⁻⁵ S / cm, which is acceptable for ER fluid. This phenomenon can be explained by the interfacial polarization of carbon nanotubes adsorbed on the surface of the polymer microspheres.

As the non-conductive solvent for dispersing the surface conductive microsphere of the present invention, for example, vegetable oils such as soybean oil, polydimethylsiloxane, silicone oil, mineral oil, other non-polar and hydrophobic organic solvent, etc. can be used. have. The polymeric microspheres are preferably dispersed at a rate of 10 vol% to 40 vol% with respect to the nonconductive solvent. At 10 vol% or less, the characteristics of the ER fluid are weak, and at 40 vol% or more, microspheres may exhibit coagulation, which may cause a problem of reduced ER fluid properties. In one embodiment of the present invention, a dispersion obtained by dispersing PMMA microspheres in which carbon nanotubes were adsorbed on silicone oil showed typical ER (electtrorheological fluid) properties to form a chain structure under an electric field (1.4 kV / mm). (FIG. 7). PMMA microspheres adsorbed with carbon nanotubes form a thin and dense particle chain within 1 second under an electric field, and the structure remains stable while the electric field is applied. A thin fiber chain spans between the two electrodes, which becomes the transport path for the moving carrier and determines the behavior of the ER fluid.

The surface conductive microspheres of PS or PMMA according to the present invention can be prepared through a simple process of mixing two colloidal aqueous solutions, that is, a carbon nanotube aqueous solution dispersed by a surfactant and an aqueous PS or PMMA microsphere colloidal solution.

That is, the method for producing a surface conductive microsphere according to the present invention,

(a) obtaining a microsphere colloidal aqueous solution of polystyrene or PMMA by dispersion polymerization;

(b) adding homogenous carbon nanotubes at 0.001 to 1 wt% to 0.01 to 10 wt% surfactant solution to disperse homogeneously;

(c) dispersing the carbon nanotube dispersion of (b) by adding a microsphere colloidal aqueous solution of polystyrene or PMMA obtained in (a);

(d) maintaining the mixed dispersion of (c) while carbon nanotubes are adsorbed on the surface of polystyrene or microspheres of PMMA to precipitate, and then separating the precipitates.

The microsphere colloidal aqueous solution of polystyrene or PMMA may be obtained by using a known method for producing monodisperse polymer particles, and in particular, may be made by dispersion polymerization.

In general, cananotubes form bundles stabilized by van der Waals forces as a result of the formation of hollow ropes. Indeed, low dispersion in water or organic solvents limits the use of carbon nanotubes. Therefore, good dispersion of carbon nanotubes is one of the key. In order to overcome such obstacles, a method of chemically modifying the surface of carbon nanotubes or adding a surfactant to a solvent may be considered. In the present invention, in order to disperse the carbon nanotubes in water, the unique properties of the carbon nanotubes are minimized by chemical modification, and in order to avoid the problem of dissolving PS and PMMA microspheres in an organic solvent, an aqueous solution using an aqueous solution is used. Disperse carbon nanotubes in At this time, preferably, the metal catalyst remaining in the carbon nanotubes is first removed and then dispersed in an aqueous solution, and known methods may be used to remove the metal catalyst.

As surfactant, Preferably it is CTAB (cationic cetyl trimethylammonium bromide); Sodium dodecylbenzene sulfonate (NaDDBS); Sodium dodecyl sulfate (SDS); Triton X-100 may be used alone or in combination of two or more thereof. Especially preferably CTAB or NaDDBS or mixtures thereof can be used. More preferably, carbon nanotubes are sonicated in an aqueous surfactant solution such as SDS, NaDDBS, CTAB, and non-ionic Triton X-100 to stabilize the van der Waals forces. The concentration of each surfactant can be adjusted in the range of 0.01 to 10 wt%, preferably 0.01 to 3 wt%. Depending on the type of surfactant, in general, the critical micelle concentration (CMC) of the surfactant is 0.01 to 3 wt%.

In addition, the concentration of carbon nanotubes in the aqueous surfactant solution is preferably 0.001 to 1wt%. When the concentration of carbon nanotubes is less than 0.001 wt%, the adsorption efficiency of carbon nanotubes to the polymer microspheres is significantly lowered, and when it is 1.0 wt% or more, the stability of the carbon nanotube dispersion solution is significantly reduced.

To obtain a homogeneous dispersion of carbon nanotubes in an aqueous solution, PS or PMMA microsphere colloidal aqueous solution is added at a constant rate to disperse. At this time, preferably, the polymer (PS, PMMA) microsphere colloidal aqueous solution is dispersed in a carbon nanotube dispersion at a rate of 0.1-20 ml / min. Polymer microspheres adsorbed on the surface of carbon nanotubes are slowly settled to the bottom of the reaction vessel (glass vial). The mixed dispersion is kept in the air for a sufficient time to allow the sedimentation to take place sufficiently. As settling, the carbon nanotube dispersion also turns into a clear solution. The precipitated surface conductive polymer microspheres are separated and the separated surface conductive microspheres are washed with distilled water to remove the surfactant and then dried in air or in vacuo to room temperature.

Observing the prepared surface conductive microspheres with field-emission scanning electron microscop (FESEM), the carbon nanotubes are closely adsorbed on the surface of the polymer microspheres. Best results in the present invention were obtained when the carbon nanotubes were dispersed in an aqueous solution of CTBA or NaDDBS (FIGS. 3 and 5).

The polymer microspheres on which the nanotubes were adsorbed maintained the strong adsorption state even after sonication in a solvent (FIG. 8). Adsorption of carbon nanotubes to the surface of polymer microspheres seems to be related to the hydrophobic interaction between polymer and carbon nanotubes. Similar results were obtained for PS microspheres and PMMA microspheres using the same procedure (FIGS. 3-5).

In the manufacture of surface-conductive microspheres, the adsorption degree of carbon nanotubes has a large difference according to the four surfactants that disperse the carbon nanotubes. However, the mechanism by which microspheres interact with surfactants is not yet clear. However, the hydrophobicity between the surfactant molecules and the surface of the carbon nanotubes is considered to be important. In other words, when PS and PMMA microspheres are added to a carbon nanotube dispersion, the surfactant molecules are thought to provide a link between the carbon nanotubes and the microspheres by providing hydrophobic interactions that can enhance the contact at the interface. do. In addition, the stability of each carbon nanotube in an aqueous solution with a surfactant may be due to the fragmentation of carbon nanotubes adsorbed on the polymer microspheres. Moreover, relatively small diameter carbon nanotubes adsorb better on the surface of PS and PMMA than larger diameters. The diameter of the multiwalled carbon nanotubes used in the present invention ranges from 8 to 40 nm.

On the other hand, the settling time of the PS microspheres on which carbon nanotubes were adsorbed was measured at room temperature for every four different surfactants. SDS and Triton X-100 showed long sedimentation time over 2 days, while CTAB and NaDDBS showed short sedimentation time within 1 hour. This fast settling time indicates a stronger interfacial interaction between these surfactants and the PS microspheres. When the PS microsphere dispersion is added to the carbon nanotube dispersion containing the surfactant, the carbon nanotube containing the surfactant is quickly adsorbed onto the surface of the PS microsphere, so that the precipitation of the carbon nanotube containing the surfactant occurs.

The ER fluid may be prepared by dispersing the PS or PMMA microspheres adsorbed on the carbon nanotubes prepared through the above process, that is, the surface conductive microspheres of the present invention in a non-conductive solvent. That is, in the present invention,

(a) obtaining a microsphere colloidal aqueous solution of polystyrene or PMMA by dispersion polymerization;

(b) adding homogenous carbon nanotubes at 0.001 to 1 wt% to 0.01 to 10 wt% surfactant solution to disperse homogeneously;

(c) dispersing the carbon nanotube dispersion of (b) by adding a microsphere colloidal aqueous solution of polystyrene or PMMA obtained in (a);

(d) maintaining the mixed dispersion of (c) while carbon nanotubes are adsorbed on the surface of the microspheres of polystyrene or PMMA, followed by separation of the precipitates to obtain surface conductive microspheres;

(e) A method for producing an electric field fluid is provided, comprising dispersing the surface conductive microspheres obtained in (d) in a non-conductive solvent.

Preferably the surface conductive microspheres are dispersed by sonication in a non-conductive solvent. It is not necessary to add a stabilizer to disperse the surface conductive polymer microspheres in a non-conductive solvent.

As the non-conductive solvent, vegetable oils such as soybean oil, polydimethylsiloxane, silicone oil, mineral oil, engine oil, and other nonpolar and hydrophobic organic solvents may be used in the hydrophobic liquid.

In one embodiment of the present invention, silicon oil was used as the non-conductive solvent.

In step (e) the microspheres are dispersed at a rate of 10 vol% to 40 vol% with respect to the non-conductive solvent.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the scope of the present invention is not limited by the following examples, and those skilled in the art to which the present invention pertains should be within the equivalent scope of the technical concept of the present invention and the claims to be described below. Of course, various modifications and variations are possible.

Example 1

Fabrication of Surface Conductive Microspheres with Carbon Nanotubes Adsorbed on PS Microspheres

(1) PS microsphere colloidal aqueous solution

PS microsphere colloidal aqueous solution with an average particle diameter of 3.0 micrometers was obtained by the dispersion polymerization method. First, purge the inside of the round bottom flask with nitrogen. Put 351.12 ml of ethanol into the purged flask and add 30 g of styrene, 0.3 g of AIBN, and 3.6 g of PVP while stirring. The stirring speed is maintained at 150 rpm and the temperature is maintained at 70 ° C. for 24 hours. The obtained PS microsphere particles were observed by field-emission scanning electron microscopy (FESEM). The result is the same as a in FIG.

(2) Preparation of Carbon Nanotubes

In this embodiment, MWNTs (multiwalled carbon nanotubes) synthesized by thermal chemical vapor deposition (CVD) were used. First, carbon nanotubes were treated with 3M HNO 3 at 60 ° C. for 12 hours and refluxed at 5 M HCl at 120 ° C. for 6 hours to remove residual metal catalyst before use.

(3) Aqueous Dispersion of Carbon Nanotubes

After preparing 0.3 wt% surfactant solution of CTAB, NaDDBS, SDS, and non-ionic Triton X-100, respectively, add 0.02 wt% of carbon nanotube prepared in (2) to each surfactant solution to form homogeneous dispersion. It was.

(4) Surface Conductive Microspheres

2 briefly illustrates this process. Disperse the dispersion of the PS microspheres obtained in (1) at a rate of 0.5 ml / min using a syringe pump to the homogeneous dispersion of the carbon nanotubes obtained in (3) above. Stir slowly. While the dispersion mixture of (1) and (3) was kept in the atmosphere for 48 hours, the PS microspheres with carbon nanotubes adsorbed on the surface were slowly settled to the bottom of the glass tank of the reactor. As the PS microspheres with carbon nanotubes adsorbed on the surface are settled, the mixed dispersion is also changed to a clear solution. PS nanospheres adsorbed with carbon nanotubes were separated, washed with distilled water to remove surfactant, and dried in air.

(5) observation

The surface morphology of the PS microspheres adsorbed with the carbon nanotubes obtained above was observed by FESEM. A case of using CTAB and NaDDBS aqueous solution as a dispersion of carbon nanotubes, respectively, is shown as a and b in FIG. 3, and a case using SDS and non-ionic Triton X-100 aqueous solution is shown as a and b in FIG. 4. As can be seen from the figure, the carbon nanotubes are closely adsorbed on the surface of the PS microsphere. When the carbon nanotubes were dispersed in an aqueous solution of CTBA or NaDDBS, the carbon nanotubes were strongly adsorbed onto the PS microspheres, thereby obtaining better results. On the other hand, when carbon nanotubes were dispersed in an aqueous solution of SDS or Triton X-100, the carbon nanotubes were not strongly adsorbed on the PS microspheres.

Example 2

Fabrication of Surface Conductive Microspheres Adsorbed Carbon Nanotubes on PMMA Microspheres

(1) PMMA microsphere colloidal aqueous solution

PMMA microsphere colloidal aqueous solution of 6.5 micrometers in average particle diameter was obtained by the dispersion polymerization method. First, purge the inside of the round bottom flask with nitrogen. Put 351.12 ml of methanol into the purged flask and add 38.88 g of MMA, 0.53 g of BPO, and 7.16 g of PVP while stirring. At this time, the monomer is maintained at 10% or less with respect to the total amount, and if necessary, 3wt% or less cross linker is added. The stirring speed is maintained at 50 rpm, and the reaction is carried out for 24 hours while maintaining the temperature of 65 ℃. The obtained PMMA microsphere particles were observed by field-emission scanning electron microscopy (FESEM). The result is the same as b of FIG.

(2) Preparation of Carbon Nanotubes

In the same manner as in Example 1, the metal catalyst remaining in the carbon nanotubes was removed.

(3) Aqueous Dispersion of Carbon Nanotubes

0.3 wt% of aqueous surfactant solution of CTAB, NaDDBS, SDS and non-ionic Triton X-100 was prepared in the same manner as in Example 1, and then homogenized by adding 0.02 wt% of the carbon nanotubes prepared in (2). One dispersion was formed.

(4) Surface Conductive Microspheres

The same procedure as in Example 1 was conducted except that the PMMA microspheres obtained in (1) of the present example were used instead of the PS microspheres to precipitate the PMMA microspheres on which carbon nanotubes were adsorbed. PMMA microspheres adsorbed with carbon nanotubes were separated and washed several times with distilled water to remove the surfactant, and dried in a vacuum oven at room temperature.

(5) observation

The surface morphology of the resultant carbon nanotubes adsorbed PMMA microspheres was observed by FESEM, and the results are shown in FIG. 5. 5 is a case where carbon nanotubes are dispersed in CTAB aqueous solution, b is dispersed in NaDDBS aqueous solution, c is dispersed in SDS aqueous solution, and d is dispersed in non-ionic Triton X-100 aqueous solution. . As can be seen from the figure, even in the case of PMMA microspheres, carbon nanotubes were closely adsorbed on the surface. In addition, when the carbon nanotubes were dispersed in the aqueous solutions of CTBA and NaDDBS as in the PS microspheres, the carbon nanotubes were more strongly adsorbed than in the aqueous solutions of SDS and Triton X-100.

Test Example 1

Measurement of conductivity and amount of adsorbed carbon nanotubes on surface conductive microspheres

The electrical conductivity of the surface conductive microspheres on which the carbon nanotubes prepared in Examples 1 and 2 were adsorbed was measured by a four-probe method using a disk-shaped specimen. ^Four -probe electrical measurements of the specimens showed DC conductivity (σDC) of 2.9 × 10 ⁻⁴ to 6.3 × 10 ⁻⁵ S / cm at room temperature. The results are shown in Table 1 below.

The actual amount of adsorbed carbon nanotubes was measured using thermogravimetric analysis (TGA) at 600 ° C. under nitrogen atmosphere. PS and PMMA decompose almost completely at this temperature, so only the weight of carbon nanotubes adsorbed on the surface is measured. The results are shown in Table 1.

Test Example 2

Measurement of Settling Time

In Example 1, the time for the carbon nanotubes to settle while adsorbed on the surface of the polymer particles for each of the four different surfactants was measured at room temperature. In Figure 6, A is a PS microsphere dispersion and PMMA microsphere dispersion from the left, B is a carbon nanotube dispersion dispersed in each aqueous solution of CTAB, NaDDBS, SDS and Triton X-100 from the left, C is a and b Is mixed, that is, mixed by adding a PS microsphere colloidal solution to the carbon nanotube dispersion dispersed in each aqueous solution of CTAB, NaDDBS, SDS and Triton X-100 from the left. When PS microsphere colloid was added, SDS and Triton X-100 showed long sedimentation time of 2 days or more, while CTAB and NaDDBS showed short sedimentation time of less than 1 hour. This fast settling time means that the interfacial interaction between the surfactant of the carbon nanotubes used and the PS microspheres is stronger.

Example 3

Preparation of Electric Field Fluid Using Surface Conductive Microspheres Adsorbed Carbon Nanotubes

PS and PMMA surface conductive microspheres prepared in Examples 1 and 2 were added to silicone oil at 10 vol% and dispersed by sonication to prepare an electric field fluid. At this time, no dispersion stabilizer was used.

On the other hand, the PS and PMMA surface conductive microspheres after the ultrasonic treatment were separated and observed by FESEM, and the carbon nanotubes on the surface maintained the same strong adsorption state as before the ultrasonic treatment. The results are shown in FIG. 8, where a and b are PS and PMMA microsphere particles, respectively.

Test Example 3

Electric field application for ER fluid

After the electric field was applied to the ER fluid of Example 3 in which the carbon nanotubes adsorbed PMMA microspheres (using CTAB surfactant) were dispersed in silicone oil, the microstructures were observed using an optical microscope. A high DC voltage was used to apply the electric field, and the difference between the two electrodes was fixed at 350 μm. First, observe the microstructure image of the ER fluid before applying the electric field using an optical microscope (figure left in Figure 7), and then apply the microstructure with an optical microscope while applying an electric field of 1.4 kV / mm for 5 seconds to the ER fluid. Observation was made (Figure right). As shown in the figure, the ER fluid obtained in the present invention exhibited the properties of a typical ER fluid (electrorheological fluid) to form a chain structure under an electric field. This phenomenon is based on the interfacial polarization of PMMA microspheres adsorbed with carbon nanotubes. The PMMA microspheres adsorbed with carbon nanotubes form thin and dense particle chains within 1 second under an electric field, and the electric field is applied. While the structure remained stable. The thin fibrous chain appeared to span between the two electrodes, which became the transport pathway of the moving carrier and determined the conductive behavior of the ER fluid.

According to the present invention, a surface conductive microsphere obtained by adsorption coating of carbon nanotubes on PS or PMMA particles is provided. It has a spherical shape, exhibits monodispersity, and electrical conduction occurs from the carbon nanotube layer. The surface conductive microspheres of the present invention exhibit conductivity in the conductivity range that the ER fluid can accommodate, and are dispersed in a non-conductive solvent to exhibit the properties of an electric field fluid (ER fluid). The surface conductive microsphere of the present invention is much simpler and easier to process to have surface conductivity compared to the monodisperse PMMA ER particles previously used to prepare a fluid, and conducts surface conduction with carbon nanotubes such as controlling conductivity. There are several advantages to forming a layer.

Claims (20)

An electric field fluid in which a surface conductive microsphere comprising a core made of polystyrene or PMMA and a shell formed by adsorption of carbon nanotubes on the surface of the core is dispersed in a nonconductive solvent. The total fluid of claim 1, wherein the polystyrene core has a diameter of 1 μm to 20 μm. The full length fluid of claim 1, wherein the PMMA core has a diameter of 1 μm to 20 μm. The electric field fluid of claim 1, wherein the carbon nanotubes have a diameter of 8 to 40 nm. The non-conductive solvent of claim 1, wherein the non-conductive solvent is selected from vegetable oils; Polydimethylsiloxanes; Silicone oil; Full length fluid, characterized in that at least one selected from mineral oil. The full length fluid according to any one of claims 1 to 4, wherein the microspheres are dispersed at a ratio of 10 to 40 vol% with respect to the non-conductive solvent. A surface conductive microsphere comprising a core made of polystyrene or PMMA and a shell formed by adsorption of carbon nanotubes on the surface of the core. The method of claim 7, wherein The polystyrene core is a surface conductive microsphere, characterized in that the diameter of 1 ㎛ to 20 ㎛. The method of claim 7, wherein The PMMA core has a surface conductive microspheres, characterized in that the diameter of 1 ㎛ to 20 ㎛. The surface conductive microsphere according to any one of claims 7 to 9, wherein the carbon nanotubes have a diameter of 8 to 40 nm. (a) obtaining a microsphere colloidal aqueous solution of polystyrene or PMMA by dispersion polymerization; (b) adding homogenous carbon nanotubes at 0.001 to 1 wt% to 0.01 to 10 wt% surfactant solution to disperse homogeneously; (c) dispersing the carbon nanotube dispersion of (b) by adding a microsphere colloidal aqueous solution of polystyrene or PMMA obtained in (a); (d) maintaining the mixed dispersion of (c) while carbon nanotubes are adsorbed on the surface of the microspheres of polystyrene or PMMA, followed by separating the precipitates. The method of claim 11, wherein the polystyrene core has a diameter of 1 μm to 20 μm. The method of claim 11, wherein the PMMA core has a diameter of 1 μm to 20 μm. The method of claim 11, wherein the carbon nanotubes are 8 to 40 nm in diameter. The method of claim 11, wherein the surfactant is selected from the group consisting of CTAB; NaDDBS; SDS; Triton X-100 The production method characterized in that at least one selected from. The method of claim 15, wherein the surfactant is CTAB or NaDDBS or a mixture thereof. (a) obtaining a microsphere colloidal aqueous solution of polystyrene or PMMA by dispersion polymerization; (b) adding homogenous carbon nanotubes at 0.001 to 1 wt% to 0.01 to 10 wt% surfactant solution to disperse homogeneously; (c) dispersing the carbon nanotube dispersion of (b) by adding a microsphere colloidal aqueous solution of polystyrene or PMMA obtained in (a); (d) maintaining the mixed dispersion of (c) while carbon nanotubes are adsorbed on the surface of the microspheres of polystyrene or PMMA, followed by separation of the precipitates to obtain surface conductive microspheres; (e) dispersing the surface conductive microspheres obtained in (d) in a non-conductive solvent. 18. The method of claim 17, wherein the nonconductive solvent is selected from vegetable oils; Polydimethylsiloxanes; Silicone oil; Production method characterized in that at least one selected from mineral oil. 18. The process according to claim 17, wherein in step (e) the microspheres are dispersed at a rate of 10 to 40 vol% with respect to the non-conductive solvent. 20. The method according to any one of claims 17 to 19, wherein ultrasonic waves are applied when the surface conductive microspheres are dispersed in a nonconductive solvent.

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