KR20040012012A - An electro-rheological fluid comprising polyaniline particles and preparation method thereof - Google Patents

Abstract

PURPOSE: Provided is electrorheological (ER) fluids which have effective ER effect over a broad range of temperature, showing stable Bingham behavior per changes in temperature and electric field, by having semiconducting polyaniline particles dispersed in a non-conductive medium such as silicone oil. CONSTITUTION: The electrorheological fluids wherein 10-20 % by volume of polyaniline particles at pH 7.5-10.0 are dispersed in a non-conductive medium, are prepared by a method comprising: (1) carrying out polymerization of aniline in 1M aqueous hydrochloride solution at -10 to 5 deg.C to provide polyaniline particles; (2) milling the polyaniline obtained from the step (1), and selecting particles of 1-10 micrometer by sieving; (3) adjusting the pH of the resulted particles to 7.5-10.0 with aqueous sodium hydroxide solution; and (4) dispersing the obtained particles into a non-conductive solvent selected from a group consisting of silicone oil, transformer oil, transformer insulating solution, mineral oil, olive oil, and mixtures thereof.

Description

Electro-modified fluid containing polyaniline particles and a method of manufacturing the same {AN ELECTRO-RHEOLOGICAL FLUID COMPRISING POLYANILINE PARTICLES AND PREPARATION METHOD THEREOF}

The present invention relates to an electromodified fluid comprising polyaniline particles.

The term "electromodified fluid" is a generic term for fluids whose mechanical and physical properties change depending on the applied electric field. Generally, a solution in which electrically polarizable particles are dispersed in an electrically insulating solvent. In particular, the electrodenatured fluid increases the viscosity due to the electric field being loaded, exhibits a Bingham behavior showing yield stress, and the reaction is very fast and reversible to the electric field load. This phenomenon is referred to as the "electrodegeneration effect (ER effect)".

The first electromodified fluid developed at the end of the 19th century consisted of liquid only, but it did not provide a satisfactory effect (Duff, A. W., Physical Review, Vol. 4, No. 1, 23 (1986)). The solid dispersion system first proposed by Winslow has made significant progress over the past (Winslow, WH, J. of Applied Physics, Vol. 20, 1137 (1949)), and subsequently contains conductive particles and nonconductive solvents. Research on the system continues.

Most of the electromodified fluids were corn starch or activated silica gel particles dispersed in mineral oil, zeolite particles dispersed in silicone oil, etc., all of which were aqueous fluids. That is, the particle surface is hydrophilic, and the moisture absorbed in the fluid plays a very important role in the ER effect. However, when applied to a system requiring a high temperature or high shear rate, the electromodified fluid not only degrades the ER effect but also causes the risk of short circuit due to water vapor being separated from the particles. . Therefore, it is urgent to develop a non-aqueous electro-modified fluid that does not need moisture fundamentally.

One way to solve this problem is to produce a particle (such as a zeolite) that causes moisture to exist only inside the particle, or to polarize due to an induced dipole moment due to electron transfer in the particle. A method of developing a non-aqueous electromodified fluid exhibiting polarization phenomenon has been proposed.

Accordingly, it is an object of the present invention to provide a non-aqueous electromodified fluid which does not require moisture and a method for producing the same.

1 is a schematic diagram of a reactor for synthesizing polyaniline particles.

2 is a flow chart illustrating a method of producing an electromodified fluid of the present invention.

3 is a distribution of polyaniline particle sizes.

4A and 4B are microscopic micrographs showing that the electromodified fluid of the present invention exhibits an ER effect under electric field load.

5a and 5b show the results of measuring the shear stress and shear viscosity according to the change in the electric field of the electromodified fluid in which the polyaniline particles adjusted to pH 9 in 20% by volume in silicone oil.

Figure 6 shows the shear stress of the electromodified fluid in accordance with the volume ratio of the polyaniline particles contained in the fluid (E = 3.0kV / mm, pH 9.0).

Figure 7 shows the shear stress according to the volume ratio of the polyaniline particles in the electro-modified fluid containing polyaniline particles synthesized at different polymerization temperatures (E = 3.0kV / mm, volume ratio 20%, pH 9.0).

8A and 8B show the static yield stress of the electromodified fluid according to the volume ratio and the electric field of the polyaniline particles contained in the fluid, respectively (pH 9.0).

9 shows shear stress values of electromodified fluids having a volume ratio of 10% of polyaniline particles having different pHs (3kV / mm).

Figure 10 shows the yield stress value for the electric field of the electro-modified fluid containing polyaniline particles having different pH (volume ratio 10%).

FIG. 11 shows changes in current density and yield stress values according to external temperature change of an electromodified fluid including polyaniline particles (volume ratio 10%, pH 8.5).

The object of the present invention is achieved by providing an electromodified fluid in a form in which semiconducting polyaniline particles are dispersed in an electrically insulating medium, i.e., a nonconductive solvent.

Polyaniline, which has attracted much attention as a conductive polymer, has been studied as a non-aqueous ER fluid because it is easy to synthesize and has an advantage of controlling electrical properties through changing oxidation states.

Semiconducting polyaniline particles according to the present invention are prepared by the following method.

The aniline monomer was polymerized in 1M aqueous hydrochloric acid solution by stirring for 2 hours using (NH ₄ ) ₂ S ₂ O ₈ as an initiator while keeping the temperature of the aqueous solution low, that is, in the range of -10 to 5 ° C. In order to complete the polymerization reaction, the whole solution may be further stirred for about 2 hours while maintaining the above temperature range. It is preferable to adjust the temperature during superposition | polymerization to -10-5 degreeC. The time required for the total polymerization is preferably 4-5 hours, but may be stirred for about 24 hours if necessary in order to complete the polymerization.

It is preferred to use a prefabricated 2 liter reactor to keep the polymerization temperature constant, and to use a peristaltic pump to keep the amount of initiator and feed rate constant (see FIG. 1). After the polymerization is completed, the precipitate is filtered and washed 2-3 times with distilled water. The precipitated product particles are milled and then the sieve is used to select the particle size. The size of the polyaniline particles suitable for use in the electromodified fluid according to the present invention is preferably 1 µm or more and less than 50 µm.

The resulting polyaniline is doped with acid because it is polymerized in a strong acidic solution, and consequently has high electrical conductivity. Therefore, it is necessary to lower the electrical conductivity in order to use the electro-denatured fluid. That is, to find the fluid is shown an electrical effect including a modified polyaniline particles of polyaniline particles conductivity ^10-12 - should be present in the 10 ^-9 S / cm range, particles of polyaniline conductivity is so adjusted to the pH of the particles, It is preferable to go through the process of controlling the conductivity of the particles by adjusting the pH of the particles (see Figure 2). Thus, the pH of the polyaniline particles polymerized in the acidic solution is adjusted to a pH of 7.5-10.0 using 1M aqueous sodium hydroxide solution. In this case, the conductivity of the particles 10 ^-12 - is a 10 ^-9 S / cm range is markedly reversed the conductivity.

Next, the oligomers and unreacted monomers of polyaniline in the product are removed by washing with distilled water, followed by 3-5 washes with ethanol and cyclohexane and filtered. This process is intended to improve the wetting by making the synthetic polymer particles hydrophobic when the polyaniline particles are dispersed in the dispersion oil. The filtered polyaniline particles are dried in a vacuum oven at room temperature. The molecular weight of the polyaniline particles obtained by such a method is about 20,000 in weight average molecular weight (Mw).

The polymerization reaction to prepare the polyaniline is relatively stable in air, the product is also easy to separate, and in particular the yield is at least as high as 60-80%. Even if the amount of the monomer is increased for the purpose of mass production of the polyaniline compound, the yield does not drop significantly, and there is no significant difference in the properties of the particles.

The electromodified fluid of the present invention is prepared by the same method as described above, by preparing a micro sized polyaniline particles as shown in Figure 3, and then dispersing them in a non-conductive solvent. Figure 3 measures the size distribution of the particles in a state where the polyaniline particles are dispersed in ethanol for 5 minutes.

In the electromodified fluid according to the present invention, polyaniline particles are dispersed at 5-20% by volume with respect to the nonconductive solvent. If the volume ratio of the polyaniline particles in the fluid is 20% by volume or more, the properties as the fluid are lost, which is not preferable.

The non-conductive solvent used in the present invention should not react chemically with other materials included in the electromodified fluid, should have adequate stability within the normal operating temperature range, and have a low viscosity when the electric field is not loaded. Do. Therefore, any solvent may be used as long as such conditions are met. That is, the embodiment of the present invention mainly used a silicone oil, but is not limited thereto, in addition to transformer oil, transformer insulating solution (transformer insulating solution), mineral oil, olive oil, corn oil, soybean Soybean oil or a mixture thereof may be used.

Microscopic micrographs of FIGS. 4A and 4B show that the electrodenatured fluid of the present invention actually exhibits an ER effect under electric field load. When the electric field is not loaded, the semiconducting polyaniline particles are dispersed in non-conductive solvent, which shows the characteristics of the Newtonian fluid (Fig. 4a). It can be seen that the formation of the structure exhibits the characteristics of Bingham behavior showing the yield stress (Fig. 4b).

Figures 5a and 5b shows the results of measuring the shear stress and shear viscosity according to the change in the electric field of the electro-modified fluid in which the polyaniline particles adjusted to pH 9 at 20% by volume in silicone oil. It can be seen that the chain-shaped particle structure is well maintained even at high shear stress, and the shear stress value at which the chain structure breaks down varies depending on the size of the electric field.

However, polyaniline-based electromodified fluids also exhibit the behavior of Newtonian fluids at very high shear rates. That is, when the electric field is not applied, the behavior of the Newtonian fluid is shown, but when the electric field is applied, the flow behavior is shown above the shear stress of a certain magnitude. In addition, it can be seen that the values of the shear stress and the shear viscosity increase with the increase of the electric field, and in the case of the electromodified fluid having a pH of polyaniline particles of 9.0 and the content of 20% by volume, the shear stress of about 1250 Pa is shown. You can see that.

Figure 6 shows the relationship between the shear rate and shear stress according to the volume ratio of the polyaniline particles contained in the electromodified fluid. As in the case of the electric field, the shear stress value increases as the volume of the polyaniline particles in the fluid increases, and as the volume ratio of the particles increases, the portion where the chain structure breaks up is shifted toward the higher shear rate. .

FIG. 7 shows the change in shear stress with respect to the shear rate of an electromodified fluid comprising polyaniline particles polymerized at different temperatures. Shear stress was found to be the highest value in the case of the lowest polymerization temperature PA-10, otherwise the shear stress with respect to the temperature difference was not very large. Here, PA-10, PA-5, PA0 and PA5 mean that the polymerization temperatures are -10 ° C, -5 ° C, 0 ° C and 5 ° C, respectively.

8a and 8b show the change in the static yield stress of the polyaniline electro-modified fluid with respect to the volume ratio and the electric field of the polyaniline particles contained in the electro-modified fluid, respectively. It can be seen that the yield stress increases exponentially with respect to the electric field and volume ratio, respectively.

Figure 9 shows the change of the shear stress value of the electro-denatured fluid according to the pH of the polyaniline particles contained in the electro-denatured fluid. It can be seen that the electromodified fluid containing particles of pH 8 to pH 9 shows similar shear stress values.

Figure 10 shows the change in the yield stress value of the electro-denatured fluid, according to the pH change and electric field changes of the polyaniline particles contained in the electro-denatured fluid. In all cases, the yield stress value increases with increasing electric field, showing the best yield stress value near pH 8.5.

11a and 11b show the results of measuring the change of the current density and the change of the stress value, respectively, by raising the external temperature using an electromodified fluid having a pH of 8.5 and a content of 10% by volume of the polyaniline particles. . It is important to keep the current density below the limit value because the value of the current density is a reference for whether or not the electromodified fluid can be actually used. Electromodified fluids produced using polymers exhibit smaller current density values than other materials, and can also control current density values by controlling conductivity through particle modification. When measuring yield stress, the shear yield stress at which the shear deformation occurs while increasing the constant shear stress little by little at a constant temperature is measured. The yield stress value shows an uneven behavior as the current density increases with increasing temperature. However, as can be seen in Table 11b, the electromodified fluid according to the present invention can be used stably up to 100 ° C.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the embodiments are only illustrative of the present invention, and the scope of the present invention is not limited thereto.

Example 1 Preparation of Polyaniline Particles

0.3 mol of aniline monomer was mixed with 200 ml of 1 M hydrochloric acid and placed in a four neck flask. The temperature of the reactor was fixed at 0 ° C. using an external circulating temperature controller, and then stirred using a mechanical stirrer to mix monomers and hydrochloric acid well. 0.36 mol (NH ₄ ) S ₂ O ₈ was added to a 500 ml beaker with 120 ml of distilled water to dissolve well, and then the solution was added dropwise to the flask containing the aniline monomer solution within about 30 minutes. Subsequently, the reaction was carried out for about 2 hours, and after finishing the external temperature control, the mixture was further stirred at room temperature for 2 hours.

The resulting polyaniline particles are dark blue green, indicating the degree of oxidation due to the acid solution. The reaction was stirred for another 24 hours at room temperature, then waited until a precipitate was produced, filtered using a filter paper, and the filtered particles were milled in an aqueous solution. The particles were washed with distilled water to remove unreacted material, and then washed three times with ethanol and cyclohexane.

The obtained polyaniline particles were adjusted to have a pH in the range of 7.5-10.0 using 1M aqueous sodium hydroxide solution. The color of the particles changed from blue green to brown as the pH changed. This change comes from the difference in the degree of oxidation, as explained earlier.

The weight average molecular weight of the polyaniline particle obtained by such a method was 20,000. The molecular weight was confirmed from GPC measurement results using THF as a solvent.

In the same manner, polyaniline particles were prepared by varying only the temperature of the polymerization reaction at -10 ° C, -5 ° C, and 5 ° C, respectively, which were used in the preparation of the electromodified fluid according to the present invention.

Example 2 Preparation of Electromodified Fluid

Polyaniline particles adjusted to pH 9.0 were sifted to select only particles having a particle size distribution in the range of 1 μm to 50 μm, and then polyaniline such that the volume of the particles was 5, 10, 15 and 20% by volume of the fluid The particles were each dispersed in a 30 cS silicone oil using a mechanical stirrer to prepare an electromodified fluid containing polyaniline particles in different volume ratios.

In addition, the pH was 7.5. Using polyaniline particles adjusted to 8.0, 8.5, 9.0, 9.5 and 10.0, an electromodified fluid containing 10% by volume of polyaniline was prepared in the same manner as above.

Example 3: Electrorheological Characterization

The characteristics of the electromodified fluid prepared in the same manner as described in Example 2 were examined in the following manner, and the results are as shown in FIGS. 4 to 11.

Using a rotary viscometer (PHYSICAMC120 rheometer), the relationship between the shear rate and the shear stress, the relationship between the shear rate and the shear viscosity was measured. The shear rate ranged from 0.0013-1000sec ^-1 and the shear stress ranged from 1 Pa-1312 Pa.

The yield stress at this time was measured by changing the electric field in the range of 0 kV-3 kV with an external high voltage generator (Meyport 230) using Z3-DIN geometry for the electro-modified fluid.

According to the present invention, an electromodified fluid including semiconducting polyaniline particles and a method for preparing the same are provided.

The electromodified fluid of the present invention exhibits an ER effect even in a wide temperature range, and as the volume ratio of the polyaniline particles contained in the fluid increases as well as the electric field, the ER effect appears larger, and the Bingham behavior is stable to temperature and electric field changes. It was confirmed that it has an advantage.

Accordingly, the electromodified fluid of the present invention can be applied to a variable damping mechanism capable of controlling a suspension device, a vibration damper, an engine mount, or a power device such as a brake, a clutch, and the like. Application is possible.

Claims (5)

Electromodified fluid in which polyaniline particles of pH 7.5-10.0 are dispersed in a nonconductive solvent at 10-20% by volume. The electromodified fluid of claim 1, wherein the nonconductive solvent is selected from the group consisting of silicone oil, transformer oil, transformer insulating solution, mineral oil, olive oil, and mixtures thereof. The electromodified fluid of claim 1, wherein the polyaniline particles are polymerized at a temperature in the range of −10 to 5 ° C. 3. The electromodified fluid of claim 1, wherein the polyaniline particles have a size distribution of 1-10 μm. (1) polymerizing aniline under a 1M hydrochloric acid aqueous solution at a temperature range of -10 to 5 ° C to prepare polyaniline particles, (2) milling the polyaniline particles produced in step (1) and sieving them to select particles having a size of 1-10 μm, (3) adjusting the pH of the particles obtained in step (2) to 7.5-10.0 using an aqueous sodium hydroxide solution, and (4) dispersing the particles in a non-conductive solvent selected from the group consisting of silicone oil, transformer oil, transformer insulating solution, mineral oil, olive oil and mixtures thereof, Method of producing an electromodified fluid.