WO2008147080A1 - Magnetic composite particles and magnetorheological fluid using the same - Google Patents
Magnetic composite particles and magnetorheological fluid using the same Download PDFInfo
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- WO2008147080A1 WO2008147080A1 PCT/KR2008/002905 KR2008002905W WO2008147080A1 WO 2008147080 A1 WO2008147080 A1 WO 2008147080A1 KR 2008002905 W KR2008002905 W KR 2008002905W WO 2008147080 A1 WO2008147080 A1 WO 2008147080A1
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- magnetorheological fluid
- magnetic
- composite particles
- particles
- magnetic composite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
- H01F1/447—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids characterised by magnetoviscosity, e.g. magnetorheological, magnetothixotropic, magnetodilatant liquids
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
- H01F1/442—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids the magnetic component being a metal or alloy, e.g. Fe
Definitions
- the present invention relates to magnetic composite particles formed by coating carbonyl iron particles with polyvinyl butyral, and magnetorheological fluid prepared by dispersing the magnetic composite particles in a nonmagnetic solvent.
- Magnetorheological fluid which is a material having the rheological properties which rapidly change in a magnetic field, changes into a solid having high yield strength from a freely flowable fluid in a magnetic field.
- Such magnetorheological fluid which is a suspension in which magnetic particles are dispersed in a nonmagnetic solvent, exhibits a magnetorheological phenomenon in which rheological behavior and electrical, thermal, mechanical and physical properties are changed depending on the strength of a magnetic field.
- this magnetorheological fluid can control a mechanical force, for example, has a high yield stress of 10 ⁇ 100 kPa when an external magnetic field is applied thereto, and can also control a mechanical force merely through the application of a magnetic field without any additional apparatus, the design of application apparatuses can be simplified. Further, since the fluid properties of this magnetorheological fluid are changed depending on the strength of an external magnetic field, rheological properties can be changed by controlling a magnetic field, thus precisely controlling rheological characteristics.
- shear stress that is, yield stress, which is minimum stress necessary for causing flow in materials.
- the chain bundles formed by the interaction between particles are broken by external force, and particles constituting chain structures resist shear velocity to thus maintain the chain structure, so that the force for restoring the particles to the original chain structure is repeatedly applied, thereby changing rheological properties. That is, in a low shear velocity region, the interaction between particles is activated by an electric field, and thus the attractive force between particles, which can maintain the chain structure, is increased. In contrast, in a high shear velocity region, the chain structure between particles is broken by hydrodynamic force. Base on the difference between these two forces, rheological behavior can be explained.
- the phenomenon in which particles in magnetorheological fluid are arranged in the direction of a magnetic field and shear resistance is increased is attributable to the magnetic force between polarized particles.
- yield stress and rheological properties relating thereto are essentially important to the evaluation of the performance of actual processes and products.
- stable dispersion of particles is also important.
- the shear stress of magnetorheological fluid is measured depending on shear velocity in steady-state shear flow fields, and the yield stress thereof is obtained by extrapolating the shear velocity as zero from this stress behavior.
- the value of the shear stress in this case is defined as dynamic yield stress.
- particles or media can act in a manner dependent on each other due to their magnetic polarizing characteristics.
- magnetorheological fluid has many advantages in the design of apparatuses in that its fatigue limit, which has been pointed out as a disadvantage of solids, can be overcome by the permanence of fluid and it has a good torque transfer function. Furthermore, magnetorheological fluid is also advantageous in that, since the magnetic polarizing phenomenon occurs very rapidly at a level of 10 ⁇ 3 sec, and is reversible, continuously variable real-time operations can be conducted.
- magnetorheological fluid Due to the advantages of magnetorheological fluid, the decrease in precision attributable to problems with nonlinear friction changed by several factors, such as wear, temperature, humidity, and the like, occurring in conventional mechanical systems, can be solved, and reactions corresponding to applied external force can be controlled in a magnetic field through electrical control, and thus magnetorheological fluid can be used in new kinds of intelligent systems.
- Magnetorheological fluid which is an important component of application apparatuses, has low initial viscosity and dispersion stability, and satisfies the requirements of high shear stress and low power consumption in an external magnetic field, and thus can be variously put to practical use. Due to these characteristics of magnetorheological fluid, the size and weight of a conventional complicated mechanical system can be decreased, and the structure thereof can be simplified. In addition, magnetorheological fluid can also be put to practical use in various engineering fields, such as a damper system, shock absorber, engine mount and flow control valve system for vehicles, and positioning systems, robots, actuators, etc.
- magnetorheological fluid which is a Bingham model, exhibits yield stress, which becomes a standard for evaluating the degree of transfer of stress induced by a magnetic field. That is, magnetorheological fluid has a solid property, for example, constant shear stress in a low shear rate when a strong magnetic field is applied thereto. Further, as the strength of a magnetic field is increased, solid chains are formed, and thus the shapes of the solid chains can be maintained. Since most magnetorheological fluids are suspensions having a high particle volume fraction, they do not always exhibit Newtonian fluid behaviors even when no magnetic field is applied, but they have low viscosity in a relatively high shear velocity region. In this case, when an external magnetic field is applied to the magnetorheological fluid, its viscosity and stress are rapidly improved.
- soft magnetic materials such as carbonyl iron, having high polarity and magnetism
- soft magnetic materials are disadvantageous in that they have high density and unstable surface properties.
- the fact that soft magnetic materials have high density prevents magnetorheological fluid from existing in a stable state, and causes a problem in that it is difficult to re-disperse magnetorheological fluid when a magnetic field is removed or its strength is decreased.
- the magnetorheological properties of fluid are very greatly influenced by the size of magnetic particles.
- Large magnetic particles having a particle size on the micrometer scale have a higher yield stress than that of small magnetic particles having a particle size on the nanometer scale. If the particle size is greater than 10 ⁇ m, magnetic particles are precipitated due to the weight thereof, thus preventing magnetorheological fluid from maintaining its dispersion stability. Even so, when magnetic particles having a small particle size are used in order to solve the dispersion problem caused by the difference in specific gravity between magnetic particles and a nonmagnetic solvent, there is a problem in that yield stress is rapidly decreased.
- an object of the present invention is to provide magnetic composite particles of carbonyl iron coated with a polymer, and magnetorheological fluid having inherent magnetorheological effects and high dispersion stability, prepared using the magnetic composite particles.
- the present invention provides magnetic composite particles which are formed by coating carbonyl iron particles with polyvinyl butyral and have a particle size of 3 ⁇ 10 pan.
- the present invention provides magnetorheological fluid, formed by dispersing the magnetic composite particles of claim 1 or 2 in a nonmagnetic solvent such that the volume ratio of the magnetic composite particles to the magnetorheological fluid is 20 ⁇ 40 vol%.
- the magnetic composite particles according to the present invention are advantageous in that they are formed by coating magnetic carbonyl iron particles with polyvinyl butyral, so that the magnetic properties thereof are maintained and simultaneously the density thereof is decreased, thereby increasing the dispersibility thereof.
- the magnetorheological fluid according to the present invention is advantageous in that the phase transition between a fluid phase and a solid phase can be reversed. Due to these characteristics, the present invention can be put to practical use in mechanical devices, such as clutches, brakes, valves, and the like, through the control of a magnetic field, can be used in connection parts, and can also be used in latent control fields, such as vibration control, mechanical energy control, and the like. [Description of Drawings]
- FIG. 1 is a 30000-times magnified SEM (Scanning Electron Microscope) photograph of pure carbonyl iron which is not coated with polyvinyl butyral;
- FIG. 2 is a 30000-times magnified SEM photograph of magnetic composite particles according to the present invention.
- FIG. 3 is a 9000-times magnified SEM photograph of magnetic composite particles according to the present invention.
- FIG. 4 is a graph showing the particle size distribution of pure carbonyl iron which is not coaled with polyvinyl butyral;
- FIG. 5 is a graph showing the particle size distribution of magnetic composite particles according to the present invention.
- FIG. 6 is an FTIR (Fourier Transform Infrared Spectroscopy) graph showing the chemical structure of magnetic composite particles according to the present invention
- FIG. 7 is a graph showing the relationship between shear viscosity and a magnetic field in magnetorheological fluid including the magnetic composite particles according to the present invention.
- FIG. 8 is a graph showing the relationship between shear stress and a magnetic field in magnetorheological fluid including the magnetic composite particles according to the present invention
- FIG. 9 is a photograph showing the state of magnetorheological fluid immediately after it is put into a reagent bottle in order to observe the dispersion stability of the magnetorheological fluid including the magnetic composite particles according to the present invention.
- FIG. 10 is a photograph showing the state of magnetorheological fluid 2 days (48 hours) after it is put into a reagent bottle in order to observe the dispersion stability of the magnetorheological fluid including the magnetic composite particles according to the present invention.
- the present invention relates to magnetic composite particles formed by coating carbonyl iron particles with polyvinyl butyral.
- the magnetic composite particles of the present invention are dispersed in a nonmagnetic solvent, thus obtaining magnetorheological fluid having low particle density and high dispersion stability.
- carbonyl iron that is used in the present invention has high magnetic dipole properties and is formed in a spherical shape, it is generally used as the magnetic material in magnetorheological fluid.
- Carbonyl iron has an average particle size of 3 ⁇ 10 ⁇ sa, which is suitable for use in magnetorheological fluid.
- the average particle size of carbonyl iron is less than 3 ⁇ m, there is a problem in that yield stress is greatly decreased.
- the average particle size thereof is more than 10 //in, there is a problem in that particles may be precipitated due to their weight.
- Polyvinyl butyral has excellent rubber-like properties and polymeric properties, and is a polymeric material which is effective in the control of energy and is widely used for exterior walls of a building, roofs, floors, interior windows, show windows, display stands, and the like.
- Magnetic carbonyl iron particles are coated with polyvinyl butyral using a phase separation method(e.g., coacervation).
- the phase separation method is a method of forming particles by dissolving a material in a solvent having higher solubility among two different solvents and then removing the solvent therefrom.
- a solvent that can dissolve polyvinyl butyral and water are used, and the solvent is vaporized, thus completing magnetic composite particles.
- the magnetic composite particles, formed by coating magnetic carbonyl iron particles with polyvinyl butyral maintain magnetic properties and simultaneously have lower particle density than carbonyl iron particles.
- the magnetic composite particles have improved surface properties, such as an increase in resistance to the oxidation or corrosion due to iron particles, a decrease in surface energy, and the like.
- the magnetorheological fluid of the present invention can be prepared by dispersing the magnetic composite particles, formed by coating magnetic carbonyl iron particles with polyvinyl butyral, in a nonmagnetic solvent.
- the magnetic composite particles be dispersed in the nonmagnetic solvent such that the volume ratio of the magnetic composite particles is 20 ⁇ 40 vol% based on the volume of final magnetorheological fluid.
- the volume ratio of the magnetic composite particles to the final magnetorheological fluid When the volume ratio of the magnetic composite particles to the final magnetorheological fluid is less than 20 vol%, the flow characteristics of the prepared magnetorheological fluid are excessively strong, and thus it cannot be used as suitable magnetorheological fluid. In contrast, when the volume ratio of the magnetic composite particles to the final magnetorheological fluid is more than 40 vol%, particle weight is excessively large, so that initial viscosity is increased, thereby deteriorating dispersibility. More preferably, the volume ratio of the magnetic composite particles may be 20 ⁇ 30 vol% based on the volume of the final magnetorheological fluid.
- nonmagnetic solvent used to prepare the magnetorheological fluid of the present invention various solvents can be used as long as magnetic composite particles are stable in the solvents. Therefore, it is preferred that oils having a low oxidative property be used.
- an effective nonmagnetic solvent exhibits excellent dispersion, has low initial viscosity and high initial density, has a high boiling point and low volatility, is chemically stable, and has suitable stability within a normal operating temperature range. Therefore, in the following Examples of the present invention, mineral oil has been used as the nonmagnetic solvent.
- the nonmagnetic solvent may be selected from the group consisting of transformer oil, halocarbon oil, paraffin oil, mineral oil, olive oil, corn oil, soybean oil, and mixtures thereof.
- Example 1 Preparation of magnetic composite particles in which carbonyl iron particles are coated with polyvinyl butyral Based on the weight of final magnetic composite particles, 5 wt% of polyvinyl butyral was dissolved in 100 ml of chloroform, and then 2 wt% of carbonyl iron, having an average particle size of 3 ⁇ 10 ⁇ m, 400 ml of distilled water, 2 wt% of polyvinyl alcohol (PVA), 0.5 wt% of sodium lauryl sulfate, serving as an emulsifier, and 1 wt% OfPEGi S PPG 53 PEGi 5 , which is a three-block copolymer, were added thereto and were then mixed, so as to form a dispersed solution.
- PVA polyvinyl alcohol
- PEGi S PPG 53 PEGi 5 which is a three-block copolymer
- the dispersed solution was stirred for 2 days using a mechanical overhead stirrer. Thereafter, when chloroform was mostly volatilized, polyvinyl butyral was adsorbed on carbonyl iron particles, and thus the carbonyl iron particles were coated with polyvinyl butyral. Subsequently, the carbonyl iron particles coated with polyvinyl butyral were washed using distilled water, thereby preparing magnetic composite particles.
- the magnetic composite particles, prepared in this way were spherical, and had an average particle size about 100 ⁇ 200 ran, which was greater than that of conventional magnetic composite particles.
- Example 2 Preparation of magnetorheological fluid using magnetic composite particles of polyvinyl butyral/carbonyl iron
- the magnetic composite particles of polyvinyl butyral/carbonyl iron, prepared in Example 1 were mixed with mineral oil such that the volume ratio of the magnetic composite particles to final magnetorheological fluid was 30 vol%, and were then dispersed therein by radiating strong ultrasonic waves using a homogenizer, thereby preparing magnetorheological fluid.
- MR magnetic resonance
- FIG. 1 is an SEM (Scanning Electron Microscope) photograph of pure carbonyl iron
- FIG. 2 is an SEM photograph of magnetic composite particles of polyvinyl butyral/carbonyl iron. From FIGS. 1 and 2, it was found that the pure carbonyl iron and the carbonyl iron coated with polyvinyl butyral were different from each other in surface shape, and thus it can be seen that the carbonyl iron was well coated with polyvinyl butyral. Further, it can be seen that the particle size of the carbonyl iron coated with polyvinyl butyral was increased to some degree compared to that of the pure carbonyl iron.
- FIG. 3 is a 15000-times magnifi ed SEM photograph of magnetic composite particles prepared in Example 1.
- FIGs. 2 is graphs showing the particle size distribution of the pure carbonyl iron before and after it is coated with polyvinyl butyral respectively. From this graph, it can be seen that the average particle size of carbonyl iron is relatively increased after it is coated with polyvinyl butyral.
- Experimental Example 2 Observation of chemical structure of magnetic composite particles of polyvinyl butyral/carbonyl iron
- FIG. 6 is an FTIR graph showing the chemical structure of magnetic composite particles of polyvinyl butyral/carbonyl iron, prepared in Example 1.
- carbonyl iron, polyvinyl butyral and magnetic composite particles thereof are represented by CI, PVB and Cl-PVB, respectively. From FIG. 6, it can be seen from the molecular motion characteristic peak of the magnetic composite particles that carbonyl iron and polyvinyl butyral are mixed with each other.
- Example 2 including 30 vol% of the magnetic composite particles of polyvinyl butyral/carbonyl iron, the change in shear viscosity was measured depending on the change in magnetic field, and the results thereof are shown in FIG. 7. From the results, it can be seen that the shear viscosity of the magnetorheological fluid was increased as the strength of the magnetic field was decreased. Further, it can be seen that the shear viscosity thereof was decreased as the shear rate was increased.
- FIG. 8 is a graph showing the change in the shear stress of the magnetorheological fluid depending on the change in the magnetic field. From FIG. 8, it can be seen that the shear stress of the magnetorheological fluid was increased depending on the increase in the strength of a magnetic field, and that the shear rate did not influence the shear stress thereof even though the shear rate increased.
- FIG. 9 is a photograph showing the state of the magnetorheological fluid prepared in
- FIG. 10 is a photograph showing the state of the magnetorheological fluid prepared in Example 2 and the conventional magnetorheological fluid including pure carbonyl iron 2 days (48 hours) after each of them was put into a reagent bottle. From FIGS. 9 and 10, it was found that the magnetorheological fluid prepared in Example 2, which is located at the left side of FIGS. 9 and 10, was slightly precipitated, but the conventional magnetorheological fluid including pure carbonyl iron, which is located at the right side of FIGS. 9 and 10, was mostly precipitated after 48 hours. Therefore, it can be seen that the dispersion stability of carbonyl iron particles was greatly improved by applying polyvinyl butyral thereon.
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Abstract
The present invention relates to magnetic composite particles, which are main raw materials dispersed in magnetorheological fluid, the magnetorheological properties of which change depending on the strength of a magnetic field, and magnetorheological fluid including the magnetic composite particles. The magnetic composite particles are formed by coating carbonyl iron particles with polyvinyl butyral, and have a particle size of 3 ~ 10 μm. The magnetorheological fluid includes the magnetic composite particles. An organic/inorganic hybrid of carbonyl iron having excellent magnetic properties and polyvinyl butyral, which is a synthetic resin having low density and high impact resistance, has excellent dispersibility in fluid and excellent surface properties, compared to pure carbonyl iron, which has been used as conventional magnetic particles.
Description
[DESCRIPTION]
[Invention Title]
MAGNETIC COMPOSITE PARTICLES AND MAGNETORHEOLOGICAL FLUID USING THE SAME [Technical Field]
The present invention relates to magnetic composite particles formed by coating carbonyl iron particles with polyvinyl butyral, and magnetorheological fluid prepared by dispersing the magnetic composite particles in a nonmagnetic solvent.
[Background Art] Magnetorheological fluid, which is a material having the rheological properties which rapidly change in a magnetic field, changes into a solid having high yield strength from a freely flowable fluid in a magnetic field. Such magnetorheological fluid, which is a suspension in which magnetic particles are dispersed in a nonmagnetic solvent, exhibits a magnetorheological phenomenon in which rheological behavior and electrical, thermal, mechanical and physical properties are changed depending on the strength of a magnetic field.
Since this magnetorheological fluid can control a mechanical force, for example, has a high yield stress of 10 ~ 100 kPa when an external magnetic field is applied thereto, and can also control a mechanical force merely through the application of a magnetic field without any additional apparatus, the design of application apparatuses can be simplified. Further, since the fluid properties of this magnetorheological fluid are changed depending on the strength of an external magnetic field, rheological properties can be changed by controlling a magnetic field, thus precisely controlling rheological characteristics.
Under the magnetorheological phenomenon, magnetic particles dispersed in a solvent are polarized by a magnetic field applied to the dispersed solution, so that an attractive force is applied between magnetic dipoles, and thus chain structures are formed in the direction of an
applied magnetic field, with the result that these chain structures resist fluid flow or external shear force, thereby increasing viscosity and yield stress, which are rheological properties. As long as a magnetic field is maintained, the chain structures between magnetic particles are reversibly formed again. The lower the flow rate, the more the chain structures are formed. When it is in the still state without application of external force, the chain structures do not break but well develop. For this reason, in order to induce initial flow, shear stress, that is, yield stress, which is minimum stress necessary for causing flow in materials, is required. The chain bundles formed by the interaction between particles are broken by external force, and particles constituting chain structures resist shear velocity to thus maintain the chain structure, so that the force for restoring the particles to the original chain structure is repeatedly applied, thereby changing rheological properties. That is, in a low shear velocity region, the interaction between particles is activated by an electric field, and thus the attractive force between particles, which can maintain the chain structure, is increased. In contrast, in a high shear velocity region, the chain structure between particles is broken by hydrodynamic force. Base on the difference between these two forces, rheological behavior can be explained. That is, the phenomenon in which particles in magnetorheological fluid are arranged in the direction of a magnetic field and shear resistance is increased is attributable to the magnetic force between polarized particles. With the improvement of viscosity, yield stress and rheological properties relating thereto are essentially important to the evaluation of the performance of actual processes and products. Further, since the magnetorheological fluid must have stable dispersed fluid characteristics when no magnetic field is applied thereto, stable dispersion of particles is also important.
The shear stress of magnetorheological fluid is measured depending on shear velocity in steady-state shear flow fields, and the yield stress thereof is obtained by extrapolating the shear velocity as zero from this stress behavior. In a test for measuring shear stress by
controlling shear velocity, strictly speaking, since only the shear stress in a limited shear velocity region in which the shear velocity does not include zero can be measured, the value of the shear stress in this case is defined as dynamic yield stress. In order to form a chain structure of particles and increase viscosity and yield stress under a magnetic field, particles or media can act in a manner dependent on each other due to their magnetic polarizing characteristics. For this reason, magnetorheological fluid has many advantages in the design of apparatuses in that its fatigue limit, which has been pointed out as a disadvantage of solids, can be overcome by the permanence of fluid and it has a good torque transfer function. Furthermore, magnetorheological fluid is also advantageous in that, since the magnetic polarizing phenomenon occurs very rapidly at a level of 10~3 sec, and is reversible, continuously variable real-time operations can be conducted. Due to the advantages of magnetorheological fluid, the decrease in precision attributable to problems with nonlinear friction changed by several factors, such as wear, temperature, humidity, and the like, occurring in conventional mechanical systems, can be solved, and reactions corresponding to applied external force can be controlled in a magnetic field through electrical control, and thus magnetorheological fluid can be used in new kinds of intelligent systems.
Magnetorheological fluid, which is an important component of application apparatuses, has low initial viscosity and dispersion stability, and satisfies the requirements of high shear stress and low power consumption in an external magnetic field, and thus can be variously put to practical use. Due to these characteristics of magnetorheological fluid, the size and weight of a conventional complicated mechanical system can be decreased, and the structure thereof can be simplified. In addition, magnetorheological fluid can also be put to practical use in various engineering fields, such as a damper system, shock absorber, engine mount and flow control valve system for vehicles, and positioning systems, robots, actuators, etc.
Generally, magnetorheological fluid, which is a Bingham model, exhibits yield stress, which becomes a standard for evaluating the degree of transfer of stress induced by a magnetic field. That is, magnetorheological fluid has a solid property, for example, constant shear stress in a low shear rate when a strong magnetic field is applied thereto. Further, as the strength of a magnetic field is increased, solid chains are formed, and thus the shapes of the solid chains can be maintained. Since most magnetorheological fluids are suspensions having a high particle volume fraction, they do not always exhibit Newtonian fluid behaviors even when no magnetic field is applied, but they have low viscosity in a relatively high shear velocity region. In this case, when an external magnetic field is applied to the magnetorheological fluid, its viscosity and stress are rapidly improved.
According to a general magnetic dipole mechanism, soft magnetic materials, such as carbonyl iron, having high polarity and magnetism, must be used. However, most soft magnetic materials are disadvantageous in that they have high density and unstable surface properties. In particular, the fact that soft magnetic materials have high density prevents magnetorheological fluid from existing in a stable state, and causes a problem in that it is difficult to re-disperse magnetorheological fluid when a magnetic field is removed or its strength is decreased.
In order to solve the above problems, various research has been conducted. In particular, attempts to solve the problems by increasing the density of fluid and adding various dispersants have been made, and technologies of preparing polymer gel by dissolving polymer in fluid for the purpose of causing the steric hindrance between particles in order to increase dispersion force have been disclosed ["Development and characterization of hydrocarbon polyol polyurethane and silicone magnetorheological polymeric gels", Journal of Applied Polymer Science 2003, Vol. 92 (2), p. 1176]. However, such conventional technologies are problematic in that, since magnetorheological fluid exhibits very high viscosity of 104~ 106 cP
even when no magnetic field is applied thereto, it is difficult to control the viscosity range of magnetorheological fluid.
Further, as a method of increasing dispersion stability, a method of forming a dual stability layer by mixing water in oil and then collecting magnetic particles has been researched. That is, in the method, attractive force acts between hydrophilically-surface-treated magnetic particles and water, so that magnetic particles are present in emulsified water, thereby improving dispersion ["Rheological properties and stabilization of magnetorheological fluids in a water-in-oil emulsion", Journal of Colloid and Interface Science 2001, Vol. 241 (1) p. 349]. However, this method is problematic in that it is difficult to maintain stability for a long time, and reversible actions cannot be performed according to a magnetic field when this method is put to practical use.
The magnetorheological properties of fluid are very greatly influenced by the size of magnetic particles. Large magnetic particles having a particle size on the micrometer scale have a higher yield stress than that of small magnetic particles having a particle size on the nanometer scale. If the particle size is greater than 10 μ m, magnetic particles are precipitated due to the weight thereof, thus preventing magnetorheological fluid from maintaining its dispersion stability. Even so, when magnetic particles having a small particle size are used in order to solve the dispersion problem caused by the difference in specific gravity between magnetic particles and a nonmagnetic solvent, there is a problem in that yield stress is rapidly decreased. In order to solve this problem, when magnetic particles having a particle size on the nanometer scale are mixed with magnetic particles having a particle size on the micrometer scale in an amount of about 20%, the magnetorheological properties of fluid are improved, and the stability of magnetorheological fluid can be maintained. However, these conventional technologies are limited in that the above problems are solved in consideration of external effects, rather than by the density of magnetic particles.
[Disclosure] [Technical Problem]
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide magnetic composite particles of carbonyl iron coated with a polymer, and magnetorheological fluid having inherent magnetorheological effects and high dispersion stability, prepared using the magnetic composite particles. [Technical Solution]
In order to accomplish the above object, the present invention provides magnetic composite particles which are formed by coating carbonyl iron particles with polyvinyl butyral and have a particle size of 3 ~ 10 pan.
Further, the present invention provides magnetorheological fluid, formed by dispersing the magnetic composite particles of claim 1 or 2 in a nonmagnetic solvent such that the volume ratio of the magnetic composite particles to the magnetorheological fluid is 20 ~ 40 vol%.
[Advantageous Effects]
The magnetic composite particles according to the present invention are advantageous in that they are formed by coating magnetic carbonyl iron particles with polyvinyl butyral, so that the magnetic properties thereof are maintained and simultaneously the density thereof is decreased, thereby increasing the dispersibility thereof. Further, the magnetorheological fluid according to the present invention is advantageous in that the phase transition between a fluid phase and a solid phase can be reversed. Due to these characteristics, the present invention can be put to practical use in mechanical devices, such as clutches, brakes, valves, and the like, through the control of a magnetic field, can be used in connection parts, and can also be used in latent control fields, such as vibration control, mechanical energy control, and the like.
[Description of Drawings]
FIG. 1 is a 30000-times magnified SEM (Scanning Electron Microscope) photograph of pure carbonyl iron which is not coated with polyvinyl butyral;
FIG. 2 is a 30000-times magnified SEM photograph of magnetic composite particles according to the present invention;
FIG. 3 is a 9000-times magnified SEM photograph of magnetic composite particles according to the present invention;
FIG. 4 is a graph showing the particle size distribution of pure carbonyl iron which is not coaled with polyvinyl butyral; FIG. 5 is a graph showing the particle size distribution of magnetic composite particles according to the present invention;
FIG. 6 is an FTIR (Fourier Transform Infrared Spectroscopy) graph showing the chemical structure of magnetic composite particles according to the present invention;
FIG. 7 is a graph showing the relationship between shear viscosity and a magnetic field in magnetorheological fluid including the magnetic composite particles according to the present invention;
FIG. 8 is a graph showing the relationship between shear stress and a magnetic field in magnetorheological fluid including the magnetic composite particles according to the present invention; FIG. 9 is a photograph showing the state of magnetorheological fluid immediately after it is put into a reagent bottle in order to observe the dispersion stability of the magnetorheological fluid including the magnetic composite particles according to the present invention; and
FIG. 10 is a photograph showing the state of magnetorheological fluid 2 days (48 hours) after it is put into a reagent bottle in order to observe the dispersion stability of the
magnetorheological fluid including the magnetic composite particles according to the present invention. [Best Mode]
Hereinafter, the present invention will be described in detail. The present invention relates to magnetic composite particles formed by coating carbonyl iron particles with polyvinyl butyral. The magnetic composite particles of the present invention are dispersed in a nonmagnetic solvent, thus obtaining magnetorheological fluid having low particle density and high dispersion stability.
Since carbonyl iron that is used in the present invention has high magnetic dipole properties and is formed in a spherical shape, it is generally used as the magnetic material in magnetorheological fluid. Carbonyl iron has an average particle size of 3 ~ 10 μsa, which is suitable for use in magnetorheological fluid. When the average particle size of carbonyl iron is less than 3 μm, there is a problem in that yield stress is greatly decreased. In contrast, when the average particle size thereof is more than 10 //in, there is a problem in that particles may be precipitated due to their weight.
Polyvinyl butyral has excellent rubber-like properties and polymeric properties, and is a polymeric material which is effective in the control of energy and is widely used for exterior walls of a building, roofs, floors, interior windows, show windows, display stands, and the like.
Magnetic carbonyl iron particles are coated with polyvinyl butyral using a phase separation method(e.g., coacervation). The phase separation method is a method of forming particles by dissolving a material in a solvent having higher solubility among two different solvents and then removing the solvent therefrom. In the present invention, as the two different solvents, a solvent that can dissolve polyvinyl butyral and water are used, and the solvent is vaporized, thus completing magnetic composite particles. As described above, the magnetic composite particles, formed by coating magnetic
carbonyl iron particles with polyvinyl butyral, maintain magnetic properties and simultaneously have lower particle density than carbonyl iron particles. Further, the magnetic composite particles have improved surface properties, such as an increase in resistance to the oxidation or corrosion due to iron particles, a decrease in surface energy, and the like. Meanwhile, the magnetorheological fluid of the present invention can be prepared by dispersing the magnetic composite particles, formed by coating magnetic carbonyl iron particles with polyvinyl butyral, in a nonmagnetic solvent. In this case, it is preferred that the magnetic composite particles be dispersed in the nonmagnetic solvent such that the volume ratio of the magnetic composite particles is 20 ~ 40 vol% based on the volume of final magnetorheological fluid. When the volume ratio of the magnetic composite particles to the final magnetorheological fluid is less than 20 vol%, the flow characteristics of the prepared magnetorheological fluid are excessively strong, and thus it cannot be used as suitable magnetorheological fluid. In contrast, when the volume ratio of the magnetic composite particles to the final magnetorheological fluid is more than 40 vol%, particle weight is excessively large, so that initial viscosity is increased, thereby deteriorating dispersibility. More preferably, the volume ratio of the magnetic composite particles may be 20 ~ 30 vol% based on the volume of the final magnetorheological fluid.
As the nonmagnetic solvent used to prepare the magnetorheological fluid of the present invention, various solvents can be used as long as magnetic composite particles are stable in the solvents. Therefore, it is preferred that oils having a low oxidative property be used.
Generally, an effective nonmagnetic solvent exhibits excellent dispersion, has low initial viscosity and high initial density, has a high boiling point and low volatility, is chemically stable, and has suitable stability within a normal operating temperature range. Therefore, in the following Examples of the present invention, mineral oil has been used as the nonmagnetic
solvent. In addition, the nonmagnetic solvent may be selected from the group consisting of transformer oil, halocarbon oil, paraffin oil, mineral oil, olive oil, corn oil, soybean oil, and mixtures thereof.
[Mode for Invention] Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, the scope of the present invention is not limited thereto.
Example 1: Preparation of magnetic composite particles in which carbonyl iron particles are coated with polyvinyl butyral Based on the weight of final magnetic composite particles, 5 wt% of polyvinyl butyral was dissolved in 100 ml of chloroform, and then 2 wt% of carbonyl iron, having an average particle size of 3 ~ 10 μm, 400 ml of distilled water, 2 wt% of polyvinyl alcohol (PVA), 0.5 wt% of sodium lauryl sulfate, serving as an emulsifier, and 1 wt% OfPEGiSPPG53PEGi5, which is a three-block copolymer, were added thereto and were then mixed, so as to form a dispersed solution. The dispersed solution was stirred for 2 days using a mechanical overhead stirrer. Thereafter, when chloroform was mostly volatilized, polyvinyl butyral was adsorbed on carbonyl iron particles, and thus the carbonyl iron particles were coated with polyvinyl butyral. Subsequently, the carbonyl iron particles coated with polyvinyl butyral were washed using distilled water, thereby preparing magnetic composite particles. The magnetic composite particles, prepared in this way, were spherical, and had an average particle size about 100 ~ 200 ran, which was greater than that of conventional magnetic composite particles.
Example 2: Preparation of magnetorheological fluid using magnetic composite particles of polyvinyl butyral/carbonyl iron The magnetic composite particles of polyvinyl butyral/carbonyl iron, prepared in
Example 1, were mixed with mineral oil such that the volume ratio of the magnetic composite particles to final magnetorheological fluid was 30 vol%, and were then dispersed therein by radiating strong ultrasonic waves using a homogenizer, thereby preparing magnetorheological fluid. In order to observe the magnetic composite particles and measure the magnetic resonance (MR) effect of the magnetorheological fluid using the same, experiments were conducted as follows.
Experimental Example 1: Observation of shape of magnetic composite particles of polyvinyl butyral/carbonyl iron
The surface of the carbonyl iron coated with polyvinyl butyral, prepared in Example 1, was observed using an SEM (S-4300, Hitachi, Japan).
FIG. 1 is an SEM (Scanning Electron Microscope) photograph of pure carbonyl iron, and FIG. 2 is an SEM photograph of magnetic composite particles of polyvinyl butyral/carbonyl iron. From FIGS. 1 and 2, it was found that the pure carbonyl iron and the carbonyl iron coated with polyvinyl butyral were different from each other in surface shape, and thus it can be seen that the carbonyl iron was well coated with polyvinyl butyral. Further, it can be seen that the particle size of the carbonyl iron coated with polyvinyl butyral was increased to some degree compared to that of the pure carbonyl iron. FIG. 3 is a 15000-times magnifi ed SEM photograph of magnetic composite particles prepared in Example 1.
Further, FIGs. 2 is graphs showing the particle size distribution of the pure carbonyl iron before and after it is coated with polyvinyl butyral respectively. From this graph, it can be seen that the average particle size of carbonyl iron is relatively increased after it is coated with polyvinyl butyral.
Experimental Example 2: Observation of chemical structure of magnetic composite particles of polyvinyl butyral/carbonyl iron
The chemical structure of the magnetic composite particles of polyvinyl butyral/carbonyl iron, prepared in Example 1, was observed using Fourier transform infrared spectroscopy (FTIR). FIG. 6 is an FTIR graph showing the chemical structure of magnetic composite particles of polyvinyl butyral/carbonyl iron, prepared in Example 1. Here, carbonyl iron, polyvinyl butyral and magnetic composite particles thereof are represented by CI, PVB and Cl-PVB, respectively. From FIG. 6, it can be seen from the molecular motion characteristic peak of the magnetic composite particles that carbonyl iron and polyvinyl butyral are mixed with each other.
Experimental Example 3: Observation of shear viscosity and shear stress of magnetorheological fluid including magnetic composite particles of polyvinyl butyral/carbonyl iron In order to observe the shear viscosity of the magnetorheological fluid, prepared in
Example 2, including 30 vol% of the magnetic composite particles of polyvinyl butyral/carbonyl iron, the change in shear viscosity was measured depending on the change in magnetic field, and the results thereof are shown in FIG. 7. From the results, it can be seen that the shear viscosity of the magnetorheological fluid was increased as the strength of the magnetic field was decreased. Further, it can be seen that the shear viscosity thereof was decreased as the shear rate was increased.
FIG. 8 is a graph showing the change in the shear stress of the magnetorheological fluid depending on the change in the magnetic field. From FIG. 8, it can be seen that the shear stress of the magnetorheological fluid was increased depending on the increase in the strength of a magnetic field, and that the shear rate did not influence the shear stress thereof even though
the shear rate increased.
Experimental Example 4: Observation of dispersion stability of magnetorheological fluid including magnetic composite particles of polyvinyl butyral/carbonyl iron
FIG. 9 is a photograph showing the state of the magnetorheological fluid prepared in
Example 2 and conventional magnetorheological fluid including pure carbonyl iron immediately after each of them was put into a reagent bottle in order to observe the dispersion stability of the magnetorheological fluid prepared by dispersing carbonyl iron particles coated with polyvinyl butyral.
FIG. 10 is a photograph showing the state of the magnetorheological fluid prepared in Example 2 and the conventional magnetorheological fluid including pure carbonyl iron 2 days (48 hours) after each of them was put into a reagent bottle. From FIGS. 9 and 10, it was found that the magnetorheological fluid prepared in Example 2, which is located at the left side of FIGS. 9 and 10, was slightly precipitated, but the conventional magnetorheological fluid including pure carbonyl iron, which is located at the right side of FIGS. 9 and 10, was mostly precipitated after 48 hours. Therefore, it can be seen that the dispersion stability of carbonyl iron particles was greatly improved by applying polyvinyl butyral thereon.
Claims
[CLAIMS] [Claim 1 ]
Magnetic composite particles which are formed by coating carbonyl iron particles with polyvinyl butyral, and which have a particle size of 3 ~ 10 //m. [Claim 2]
The magnetic composite particles according to claim 1, wherein the polyvinyl butyral has a thickness of 100 ~ 200 nm. [Claim 3]
Magnetorheological fluid, formed by dispersing the magnetic composite particles of claim 1 or 2 in a nonmagnetic solvent such that the volume ratio of the magnetic composite particles to the magnetorheological fluid is 20 ~ 40 vol%. [Claim 4]
The magnetorheological fluid according to claim 3, wherein the nonmagnetic solvent is one or more selected from the group consisting of silicon oil, transformer oil, a transformer insulating solution, mineral oil, olive oil, corn oil, and soybean oil.
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| KR1020070050940A KR20080103773A (en) | 2007-05-25 | 2007-05-25 | Magnetic composite particles and magnetorheological fluid using the same |
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Cited By (4)
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| US20150228389A1 (en) * | 2014-02-11 | 2015-08-13 | Hyundai Motor Company | Magneto-rheological fluid composition |
| CN113515868A (en) * | 2021-08-04 | 2021-10-19 | 常熟理工学院 | Chain cluster model construction method and performance estimation method of magnetorheological elastomer |
| CN116313362A (en) * | 2023-04-25 | 2023-06-23 | 重庆大学 | Magnetorheological fluid with irradiation resistance and preparation method thereof |
| WO2023203524A1 (en) * | 2022-04-21 | 2023-10-26 | Multi-Scale Medical Robotics Center Limited | Magnetic slimebot, composition for its manufacture and uses thereof |
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| KR101768711B1 (en) * | 2014-07-21 | 2017-08-17 | 서울대학교산학협력단 | Magnetorheological fluids containing ferro-magnetic compounds wrapped by foamed polymer and their preparation method |
| KR101602315B1 (en) * | 2014-11-19 | 2016-03-10 | 인하대학교 산학협력단 | Magnetorheological fluid comprising plate-like iron particles |
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| US5989447A (en) * | 1996-11-28 | 1999-11-23 | G E Bayer Silicones Gmbh & Co. Kg | Magnetorheological liquids, a process for producing them and their use, and a process for producing magnetizable particles coated with an organic polymer |
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| US5989447A (en) * | 1996-11-28 | 1999-11-23 | G E Bayer Silicones Gmbh & Co. Kg | Magnetorheological liquids, a process for producing them and their use, and a process for producing magnetizable particles coated with an organic polymer |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150228389A1 (en) * | 2014-02-11 | 2015-08-13 | Hyundai Motor Company | Magneto-rheological fluid composition |
| US9449744B2 (en) * | 2014-02-11 | 2016-09-20 | Hyundai Motor Company | Magneto-rheological fluid composition |
| CN113515868A (en) * | 2021-08-04 | 2021-10-19 | 常熟理工学院 | Chain cluster model construction method and performance estimation method of magnetorheological elastomer |
| WO2023203524A1 (en) * | 2022-04-21 | 2023-10-26 | Multi-Scale Medical Robotics Center Limited | Magnetic slimebot, composition for its manufacture and uses thereof |
| CN116313362A (en) * | 2023-04-25 | 2023-06-23 | 重庆大学 | Magnetorheological fluid with irradiation resistance and preparation method thereof |
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| KR20080103773A (en) | 2008-11-28 |
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