KR100559492B1 - Electrorheological fluid consisting of polyaniline derivatives as a conducting particle - Google Patents

Abstract

The present invention relates to an electrorheological fluid comprising a polyaniline derivative as conductive particles. Unlike the aqueous electrorheological fluid using natural starch or cellulose that is not chemically treated, the electrorheological fluid of the present invention does not require water or an additive, and exhibits a high electrorheological effect due to polarization of particles. Can work without obstacles. In addition, the electrical stability is better than the non-aqueous fluid rheology using polyaniline can be usefully used in the robot industry, such as automobile and aviation industry.

Electrical conductivity, polymers, rheology, polyaniline derivatives.

Description

ELECTRORHEOLOGICAL FLUID CONSISTING OF POLYANILINE DERIVATIVES AS A CONDUCTING PARTICLE}             

1 is a graph showing the FT-IR spectrum of the polyaniline derivative of the present invention,

2 is a graph showing the results of TGA thermal analysis of the polyaniline derivative of the present invention,

Figure 3a shows a SEM (3000 times) photograph of the polymethylaniline of the present invention,

Figure 3b shows a SEM (3000 times) photograph of the polymethoxyaniline of the present invention,

Figure 3c shows a SEM (1000 times) photograph of the polyethylaniline of the present invention,

Figure 3d shows a SEM (3000 times) photograph of the polyethoxyaniline of the present invention,

4 is a graph showing the shear stress in the electric field of 3 ㎸ / ㎜ of the electrorheological fluid using the polyaniline derivative particles (15% by weight) of the present invention,

5 is a graph showing the static yield stress according to the electric field of the electric rheology using the polyaniline derivative particles (15% by weight) of the present invention,

Figure 6 is a graph showing the shear stress (electric field 3.0 ㎸ / ㎜) according to the particle weight fraction of the electrorheological fluid using the polymethyl aniline particles (Example 1) of the present invention,

7 is a graph showing the static yield stress according to the particle weight fraction or the electric field of the electrorheological fluid using the polymethylaniline particles (Example 1) of the present invention,

8 is a graph showing the current density according to the electric field of the electrorheological fluid using the polymethylaniline particles of the present invention (Example 1, 15% by weight).

The present invention relates to an electrorheological fluid, and more particularly to an electrorheological fluid comprising a polyaniline derivative as conductive particles.

Electro-fluidic fluid is a general term for fluids whose mechanical and physical properties change depending on the applied electric field. Generally, electro-polarized particles (conductive particles) are dispersed in an electrically insulating solvent (non-conductive solvent). Solution. In particular, the rheological fluid exhibits an increase in viscosity and yield stress behavior due to an electric field being loaded, and the reaction is very fast and exhibits a reversible reaction to the electric field load, which is called an electrorheological effect (ER).

Essentially, the application of electrofluidic fluids consists of devices that use a sharp increase in viscosity with the strength of this electric field. As the electric field is applied, the fluid changes from the liquid phase to the solid phase. This process is reversible, and returns to the original liquid phase without loading the electric field. This property has many advantages in device design since it has the advantages of fluid permanence and torque transfer of solids to the fatigue limit pointed out as a disadvantage in conventional solids. In addition, these reactions are very fast at 10 ^-3 seconds and appear as reversible reactions, enabling continuous variable real-time operation. In addition, the electric field required for the phase change is high, but the current is very low, which has the advantage of low power consumption. These advantages can solve the degradation of precision due to the nonlinear friction problem, which is caused by various factors such as wear, temperature, humidity, etc. in the conventional mechanical system, and the corresponding reaction according to the applied external force can be controlled electronically. As a new concept intelligent system, it is in the spotlight.

By using these characteristics, the electro-fluidic fluid can be applied to variable damping mechanisms that can control brakes, engine mounts, dampers, etc., or to power devices such as brakes and clutches. have.

For the first time, the rheological fluid was developed in the late 19th century in liquid form only, but it did not provide satisfactory results [Duff AW, Physical Review, Vol. 4, No. 1, 23 (1986)]. However, after the development of the first solid dispersion system proposed by Winslow, it has made significant progress in this field [Windslow WH, J. of Applied Physics , Vol. 20, 1137 (1949)]. The application possibilities of the brake and clutch system were introduced. Since then, studies on systems containing conductive particles and non-conductive solvents have been continued (US Pat. Nos. 3,397,147, 4,493,788, 4,502,973, 4,668,417). Since there is no need for a physical exercise device to simplify the design of the application device, various applications due to the characteristics of the electrorheological fluid are attracting attention as a new functional fluid and are being activated.

Most electrorheological fluids are aqueous fluids, which are mainly composed of corn starch or activated silica gel particles dispersed in mineral oil, or zeolite particles dispersed in silicone oil. The aqueous fluid absorbs moisture due to its hydrophilic nature, and the absorbed water plays a very important role in the electrorheological effect. However, when the aqueous fluid is applied to a system requiring high temperature or high strain rate, some of the absorbed water vaporizes to reduce the electrorheological effect, and the current density is high so that it can be used in practical applications. There is no risk of short.

As described above, the electrorheological activity of these fluids is highly dependent on the change in moisture content, so when the water is removed, the electrorheological activity is lost and cannot be used at high temperatures.In terms of engineering, the wear of the machine is large and the operating temperature range is limited. There is a disadvantage. Therefore, in recent years, the development of a non-aqueous electrorheological fluid (dry base electrorheological fluid) that does not require water is active. These efforts produce particles such as zeolites that can limit the presence of moisture only inside the particles, and produce non-aqueous electrorheological fluids in which polarization occurs due to induced dipole moments caused by electron transport within the particles. [ Mangmuir , Vol. 14, Feb. 1998, pp 1236-1263.

Representative non-aqueous electrorheological fluids include polymer particles of polyaniline as conductive particles [ J. Colloid and Interface Science , Vol. 126, No. 1, April 1990, pp. 175-188]. European Patent Publication No. 394,005 discloses the electrorheological effect of polyaniline / silicone oil suspensions with a volume fraction of 30%. US Pat. Nos. 5,595,680 and 5,437,806 use polyaniline polymerized from aniline monomers and mixtures of various monomers. Non-aqueous electrorheological fluids are disclosed.

An object of the present invention is to solve the problems of the above-described water-based electro-fluidic fluid and to improve the properties of the non-aqueous electro-fluidic fluid, by using the polyaniline derivative particles as the conductive particles, there is no need for water or additional additives, It is possible to operate without obstacles to the temperature or the external environment, and to provide an electric rheological fluid having excellent electrical stability than the conventional non-aqueous electric rheological fluid.

In order to achieve the above object, the present invention provides an electrorheological fluid in which the conductive particles are dispersed in a non-conductive solvent, the conductive particles are polyaniline derivative particles.

That is, by using the polyaniline derivative particles as the conductive particles,

Firstly, it does not need moisture or additives, and can operate without any obstacles to temperature or external environment,

Secondly, the present invention provides an electric rheological fluid having better electrical stability than the conventional non-aqueous electric rheological fluid.

Hereinafter, the present invention will be described in detail.

The present invention provides an electrorheological fluid in which conductive particles are dispersed in a non-conductive solvent, wherein the conductive particles are polyaniline derivative particles.

The polyaniline derivative particles are electrically semiconductors, and play a role of charge carriers due to the intrinsic physicochemical properties of the particles, not the polarization caused by the electric field, and as shown in Formula 1 below. Polymer particles having an alkyl group or an alkoxy group are used.

(Wherein R is a C ₁ -C ₅ alkyl group or an alkoxy group, y is the molar ratio of the reduced portion in the polyaniline derivative particles and 1-y is the molar ratio of the oxidized portion, y is 0.1-0.9.)

The polyaniline derivative particles are preferably polymethylaniline, polyethylaniline, polymethoxyaniline or polyethoxyaniline particles wherein R is methyl, ethyl, methoxy or ethoxy. In addition, the number average molecular weight of the polyaniline derivative particles is preferably 5,000 to 100,000.

In this case, when the particle size of the polyaniline derivative is too small, brownian motion interferes with the electric force, and when too large, the response to the electric field is too slow and may cause problems such as precipitation. For this reason, the size of the polyaniline derivative particle of this invention is 5-10 micrometers.

The volume fraction of the polyaniline derivative particles, which are conductive particles for the electrorheological fluid, affects the properties of the electrorheological fluid. Specifically, it is effective to increase the volume fraction of the particles in order to obtain a higher yield stress at the possible electric field strength, but this cannot exceed any maximum value which depends on the viscosity of the non-conductive solvent, the shape and the surface properties of the particles, Concentrated polyaniline derivatives have a disadvantage in that the viscosity is too large in the absence of an electric field and the current flows too much when an electric field is given, resulting in poor controllability and stability. Therefore, in the present invention, it is preferable that the volume fraction of the polyaniline derivative particles is 5 to 30% by weight.

The nonconductive solvent of the present invention is electrically almost insulative and serves to improve the stability of the conductive particles. An effective non-conductive solvent should have excellent dispersibility, low viscosity and electrical conductivity, high boiling point and low freezing point, and should be chemically stable and have high dielectric strength. transformer oil, transformer insulating solution, mineral oi, olive oil, corn oil and soybean oil. It is preferable.

The electrorheological fluid composed of polyaniline derivative particles of the present invention results in a change in rheological properties when an electric field is applied. The rheological fluid exhibits the same behavior as a normal Newtonian fluid in the absence of an electric field, but solidifies under an electric field, indicating a strong resistance to flow. The large increase in viscosity seen in the rheological fluid is caused by changes in the microstructure of the polyaniline derivatives. When an electric field is applied to a stationary polyaniline derivative, particles are rearranged by a polarization phenomenon occurring inside or on the surface of the particles to form a fibrous structure to connect the electrodes. Vertically straining the electric field distorts the fiber structure of the particles. As a result of the energy consumed in these deformations, an increase in viscosity occurs, whereby the yield stress increases as the strength of the electric field increases, and the fluid flows when the applied shear stress is greater than the yield stress of the fluid.

On the other hand, the electrorheological fluid of the present invention is prepared by a conventional method. Specifically, the non-conductive solvent is stirred using a stirrer and prepared by dispersing the polyaniline derivative of the present invention. At this time, the stirrer may use all that can be commonly used in the art.

In addition, the polyaniline derivative of the present invention is synthesized by chemical oxidation polymerization. At this time, the reaction conditions of the oxidative oxidation polymerization can be variously adjusted to show the optimum physical properties.

For example, the aniline derivative represented by the following formula (2) is stirred in an aqueous HCl solution, and oxidatively polymerized by dropping an aqueous HCl solution in which (NH ₄ ) ₂ S ₂ O ₈ is dissolved. The resulting product is adjusted to pH 9 with HCl or NaOH solution for optimum electrorheological effect, and unreacted monomers, oligomers and residual initiators of the prepared polyaniline derivatives are removed by washing with distilled water. Then wash once more with methanol and cyclohexane for hydrophobization of the particle surface. Finally, the polyaniline derivative particles thus prepared are dried in a vacuum oven to remove residual moisture in the particles. At this time, the average diameter of the obtained particles is about 1 to 20 ㎛.

(Wherein, R is a C ₁ ~C ₅ alkyl group or an alkoxy group.)

Thus obtained electric rheological fluid of the present invention has a current density of from 0.007 to 0.003 mA / cm 2 from 25 to 100 ° C. up to 1 to 5 mA / mm.

Hereinafter, the present invention will be described in more detail with reference to Examples.

However, the following examples are illustrative of the present invention and the scope of the present invention is not limited by these examples.

Example 1 Preparation of an Electrorheological Fluid Using Polymethylaniline

(Step 1) Preparation of Polymethylaniline

Methylaniline was added to 400 mL of 1M HCl aqueous solution, followed by stirring, and 240 mL of 1M HCl aqueous solution containing (NH ₄ ) ₂ S ₂ O ₈ was added dropwise to polymerize polymethylaniline. The polymerization was carried out for 2 hours at a stirring speed of 400 ~ 500 rpm at 0 ℃. The resulting product was adjusted to pH 9 with HCl or NaOH solution for optimum electrorheological effect. The product was washed with distilled water to remove unreacted monomers, oligomers, residual initiators and the like. Thereafter, the resultant was washed once more with methanol and cyclohexane for hydrophobization of particle expression to obtain polymethylaniline particles. Finally, the obtained polymethylaniline particles were dried in a vacuum oven for 2 days in order to remove residual moisture in the particles.

As a result of analysis with a particle size analyzer, the average diameter of the polymethylaniline particles was 10-20 탆.

(Step 2) Preparation of the electrorheological fluid 1

1.5 g, 4.5 g, and 9.0 g of polymethylaniline particles obtained in the above steps were added to 28.5 g, 25.5 g, and 21.0 g of silicone oil, respectively, and stirred and mixed at 25 ° C. for 30 minutes. 30 g of 5% by weight, 15% by weight, and 30% by weight of the electrorheological fluids were prepared through this step.

Example 2 Preparation of an Electrorheological Fluid Using Polymethoxyaniline

Polymethoxyaniline particles were prepared in the same manner as in Example 1, except that methoxyaniline was used as the monomer in Step 1 of Example 1.

30 g of 15% by weight of an electrorheological fluid was prepared in the same manner as in Example 1 except that 4.5 g of the polymethoxyaniline particles obtained above were added to 25.5 g of the silicone oil.

Example 3 Preparation of an Electrorheological Fluid Using Polyethylaniline

Polyethylaniline particles were prepared in the same manner as in Example 1, except that ethylaniline was used as the monomer in Step 1 of Example 1.

Except for adding 4.5 g of the obtained polyethylaniline particles to 25.5 g of silicone oil, the same method as in Example 1 was carried out, to thereby prepare 30 g of 15% by weight of the electrorheological fluid.

Example 4 Preparation of an Electrorheological Fluid Using Polyethoxyaniline

Polyethoxyaniline particles were prepared in the same manner as in Example 1 except that ethoxyaniline was used as the monomer in Step 1 of Example 1.

30 g of 15% by weight of an electrorheological fluid was prepared in the same manner as in Example 1 except that 4.5 g of the polyethoxyaniline particles obtained above were added to 25.5 g of silicone oil.

Experimental Example 1 Chemical Structure Analysis of Polyaniline Derivatives by Infrared Spectroscopy

Chemical structures of the polyaniline derivatives obtained in Examples 1 to 4 were analyzed using an infrared spectrometer (IFS48, BRUKER). The results are shown in FIG. 1, which shows the infrared spectral spectral peaks of the polyaniline derivative.

As shown in FIG. 1, the wavenumber 1590 cm ^-1 is the C = C stretch of the quinoid ring, 1490-1500 cm ^-1 is the C = C stretch of the benzoid ring, and 3000-2800 cm ^-1 is -CH ₂ The characteristic peak of CH ₃ .

Experimental Example 2 Thermostability Test of Polyaniline Derivatives by Thermogravimetric Analysis

The thermal stability of the polyaniline derivative of the present invention was tested by thermogravimetric analysis using a thermogravimetric analyzer (PL-TGA, Polymer Laboratories). The temperature range is 20-600 degreeC, and isothermal rate is 20 degreeC / min. The results are shown in FIG.

As shown in FIG. 2, there was a gradual weight loss at 250 ° C., and a more rapid weight loss at 300 ° C. However, even above 600 ° C., the weight loss did not reach 40%. From the above results, it was confirmed that the polyaniline derivative of the present invention has excellent thermal stability.

Experimental Example 3 Morphology Observation of Polyaniline Derivatives by Scanning Electron Microscopy

The polyaniline derivatives obtained in Examples 1 to 4 were observed using a scanning electron microscope (S-420, Hitachi) to observe the form of the polyaniline derivatives. The results are shown in FIGS. 3A to 3D, respectively.

As shown in Figures 3a to 3d, the particle shape is round, but it can be seen that the small particles are aggregated into one mass. The average diameter of the particles was 5-10 μm.

Experimental Example 4 Flow Characteristics Analysis of an Electro-Rheological Fluid Based on Polyaniline Derivatives in Shear Rate Control Mode

When the electro-fluidic fluid consisting of particles of the polyaniline derivatives obtained in Examples 1 to 4 was applied to the electric field 3 kV / mm using a shear force tester (MC-120, PHYSICA), the shear rate was changed from 0.01 to 1000. Shear stress was measured, and the results are shown in FIG.

In the absence of electric field application, the shear stress increases with the increase of shear rate, and the viscosity is almost constant, as with normal Newtonian fluids. However, even in the absence of an electric field, non-Newtonian fluids with a shear stress gradient of less than 1 are seen due to the high particle loading fraction. Therefore, shear thinning phenomenon is observed in which the apparent shear viscosity decreases with increasing shear rate.

Figure 4 shows the flow curve under an electric field of 3 kHz / mm in shear control mode of the electro-fluidic fluid of 15% by weight polyaniline derivative particle concentration. The electric rheological fluid based on polyaniline derivatives shows high shear stress when electric field is applied. Shear stress persists with increasing shear rate. In general, at high shear rates, the movement of the fluid breaks the chain of particles. As a result, the shear stress and shear rate of the rheological fluid show linear behavior. As shown in FIG. 4, different behaviors are shown for each polyaniline derivative. Polymethylaniline exhibits the behavior of a typical electrofluidic fluid and exhibits better electrorheological properties than any other polyaniline derivative. For example, it can be seen that shear stress is maintained even at low shear rates.

Experimental Example 5 Observation of Yield Stress Changes According to the Electric Field Changes of Polyaniline Derivatives-Based Rheological Fluids

Shear stress at an electric field of 1, 1.5, 2, 2.5, 3, 4, 5 kV / mm using an rheometer (MC-120, PHYSICA) was used for the rheological fluid composed of particles of the polyaniline derivatives obtained in Examples 1 to 4. Shear stress (yield stress) at which the flow (shear rate) starts to occur when the temperature is changed is measured, and the result is shown in FIG. 5.

As shown in Fig. 5, the yield stress is different from the theory that the proportional to the square of the intensity of the electric field. This is because of various reasons such as particle concentration and particle shape.

Experimental Example 6 Analysis of Flow Characteristics and Different Yield Stress Changes in Electric Field Intensity According to Particle Concentration Changes of Polymethylaniline-Based Rheological Fluid in Shear Rate Control Mode

For the rheological fluid having a weight ratio of 5, 15, and 30% by weight based on polymethylaniline obtained in Example 1, the shear stress change according to the shear rate was measured as in Experimental Example 4, and also in Experimental Example 5 and Similarly, the shear stress (yield stress) in which the shear rate occurs when the shear stress is changed is measured, and the results are shown in FIGS. 6 and 7.

FIG. 6 is a flow curve measured while changing particle concentration under an electric field of 3 μs / mm of a polymethylaniline-based electrofluidic fluid in a shear rate control mode. Compared with FIG. 4, the shear stress was increased when the particle concentration was increased. In addition, the critical shear rate at which the change in the chain structure begins is increased to a higher value.

Figure 7 shows the change in yield stress according to the change in the electric field strength at each concentration of the polymethyl aniline-based electro-fluidic fluid. Like Experimental Example 5, it exhibits a different behavior from the theory because of various reasons such as particle concentration and particle shape.

Experimental Example 7 Observation of Current Density Changes According to Temperature, Particle Concentration, and Electric Field Intensity of Polymethylaniline-based Electrorheological Fluids

The current density across the two electrodes was measured as follows. Shear stress 10 s ^{−1 was applied} for 10 minutes to change the temperature to measure the current required at that time. The current density is obtained by dividing the measured current by the area where the actual current flows, and the result is shown in FIG. 8.

Figure 8 shows the current density change according to the temperature change of polymethylaniline-based electro-fluidic fluid of 15% by weight particle concentration. The current density of the polymethylaniline-based electrofluidic fluid increased slightly with increasing electric field. In general, the limit of the current density of an electrorheological fluid for commercial use is from 6 mA / mm to 300 mA / m 2. Therefore, it can be seen that the electrorheological fluid of the present invention exhibits much smaller value than the requirement of commercialization and thus has better electrical stability.

As described above, the present invention relates to a non-aqueous electrorheological fluid in which polyaniline derivative particles are dispersed, and the electrorheological fluid does not need to be separately added to exhibit an electrorheological effect, and can be polarized by itself. It can be seen that it can be used in a wide temperature range of 0 to 100 ℃. In addition, as the particle weight ratio increases as well as the electric field increases, the electric rheological effect increases greatly and shows stable Bingham behavior against temperature and electric field changes, thereby enabling the control of suspensions, vibration dampers, engine mounts, etc. It can be applied to variable damping mechanisms or power devices such as brakes and clutches, and can be applied to automotive and aviation industries.

Claims (5)

In the electrorheological fluid in which conductive particles are dispersed in a non-conductive solvent, The conductive particles are polyaniline derivative particles represented by the following formula (1), An electrorheological fluid, characterized in that the weight ratio of the polyaniline derivative particles is 5% by weight to 15% by weight based on the total weight of the electric rheological fluid: Formula 1

(Wherein R is a C ₁ to C ₅ alkyl group or an alkoxy group, y is the molar ratio of the reduced portion in the polyaniline derivative particles and 1-y is the molar ratio of the oxidized portion, y being 0.1 to 0.9). The electrorheological fluid according to claim 1, wherein R is methyl, ethyl, methoxy or ethoxy. 2. The electrorheological fluid according to claim 1, wherein the polyaniline derivative particles have a particle diameter of 5 to 10 mu m. The method of claim 1, wherein the non-conductive solvent is in the form of a single or a mixture thereof selected from the group consisting of silicone oil, transformer oil, transformer insulating solution, mineral oil, olive oil, corn oil and soybean oil. Electrorheological fluids. delete

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