JPH0388896A - Electro rheology liquid and manufacture of useful particles for said fluid - Google Patents

Abstract

PURPOSE: To provide a fluid with a low D.C. conductivity at room temp. and electrorheological effect over a wide temp. range consisting of a continuous liq. phase and a dispersed fine particle phase prepd. by coating a particle main body having a conductive surface with an electrically insulating control material.

CONSTITUTION: The objective fluid comprises a continuous phase of a carrier liq. and a discontinuous phase of dispersed composite fine particles and wherein the fine particle phase has a conductive surface being polarizable in the particle and an electrically controlled coating film furthermore on the surface and the particle main body from which the conductive surface and the controlled coating film are excluded has lower density than the density of the carrier liq. and the thicknesses and densities of the conductive surface and the controlled coating film has the same mean density as the density of the carrier liq. As the examples of the fine particles, Ni fine spheres coated with a carboxylated polyethylene, Al-coated hollow fine spheres coated with an insulative silicate layer, etc., are cited.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to fluid compositions whose rheological properties change significantly in the presence of an electric field, and in particular the invention is particularly suitable for use in so-called KR fluids. The present invention relates to composite particles having such properties, and methods for preparing such fluids and particles for use in the fluids.

[Conventional technology]

Fluids that significantly change their fluidity, or rheology, in the presence of an electric field have been known for decades. Early studies of such fluids were carried out by Winslow (W, M.

Wlnslow), some of which are published in U.S. Pat.
It is reported in issue 07. Today, darning fluids are commonly referred to as “
electrorheology
l) It is called (ER)J fluid.

Winslow describes solids (separation,
It has been demonstrated that some suspensions (fine particles, dispersed or discontinuous phases) exhibit large reversible electrorheological effects. These ER actions (or effects) are generally as follows:
In the presence of an electric field, electrorheological fluids exhibit f9 Newtonian behavior, and in particular, the shear stress (force applied per unit area) of RE fluids is directly proportional to the shear rate (relative velocity per unit thickness). do. When an electric field is applied, it exhibits a yield stress phenomenon, and at 1, where the shear stress exceeds the yield value, which increases with increasing electric field strength, no shear occurs. This phenomenon appears as an increase in viscosity by several orders of magnitude or more. Therefore, although the ER fluid is initially a liquid, when an electric field is applied to it, it behaves as if it were a solid.

ER fluids can change their properties very quickly, in very short times, on the order of one millisecond (msao), when an electric field is applied or released.

ER fluids that respond quickly to electrical signals can take advantage of their unique properties to replace mechanical systems where response time is limited by the inertia of moving machine parts. Therefore, electrical rheology machine systems requiring particularly rapid response can be interfaced between electronic control equipment and mechanical equipment.

A variety of devices have been provided that utilize electrorheological fluid action for their ability to provide a rapid response interface between electronic controls and machine tables. Accordingly, ER fluids have been suggested for various mechanical devices such as electromechanical clutches, fluidic optical engine mounts, high speed valves with no moving parts, active dampers for vibration control, and the like. Examples of mechanical devices designed to operate with BR fluids include the mounts disclosed in commonly owned U.S. Pat. Nos. 4.720,087 and 4,733,758. Imprisoned.

A wide range of combinations of fluids and suspended particles can exhibit electrorheological effects. For example, as disclosed in the following US patent: March Neck (T.

No. 3.397.147 of August 13, 1968 by W, 'Martinak;
.

No. 4.502,973, March 5, 1985 by 8tafigrOOm; Gossen, J.
s) dated May 26, 1987, No. 4,668,4
No. 17 of Niblock et al.
No. 4,687.589 dated August 18, 987;
No. 1 4,744,914, dated May 17; and Carlson, J.D.

Carlson) dated September 20, 1988 is No. 4,77
No. 2,407. ! T, 5asada*
T, K15hi and K, Kamij O) research [
EntIZled, aOn the Elozrovi
scous Effect on Co11oi
dal Liquids”.

pp, 229-231. ] is also related. Bengami dated October 14, 1986 is patent application No. 61-241,
No. 929 [Title of invention: Electrically conductive viscous fluid] is also relevant.

[Problem to be solved by the invention]

Current ER raw fluids have several drawbacks. For example, many of them exhibit high or 0° conductivity even at room temperature.

This conductivity generally increases rapidly with increasing temperature, thus significantly limiting the usable temperature of the fluid. Also, many of them have relatively low dielectric strength and produce sparks.

In many ER raw fluids, the particulate phase settles quickly creating thick muddy deposits, rendering the fluid useless for many applications.

Therefore, the main objective of the present invention is to provide a superior ER raw fluid.

Another object of the present invention is to provide a method for producing particles useful in superior gR fluids.

Another object of the present invention is to provide an ER raw fluid having at least one, preferably all, of the following properties: low conductivity at room temperature; Low or virtually no increase in conductivity; ability to exhibit ER effects over a relatively wide temperature range; and substantially no particle settling.

[Means to solve the problem]

The novel gR fluids of the present invention are characterized by a continuous liquid phase and a dispersed particulate phase, the dispersed particulate phase being prepared by coating a particulate body having at least an electrically conductive surface with an electrically insulating control material; and the electrically insulating control coating is selected to provide composite particles having an average density essentially the same as the density of the liquid phase.

〔Example〕

Referring to the drawings, FIG. 1 shows a composite particle P that is particularly suitable for use as an ER raw fluid. The illustrated composite particle P has four different regions. Although it will become clear later, it will break in even fewer areas.

In FIG. 1, reference number 1 indicates the outermost region providing the electrical control layer. The region 1 is a thin electrically relatively non-conducting tU
=Or preferably provided by an insulating film! Yes. Reference numeral 2 designates the electrically conductive layer underlying the electrical control layer 1. Reference number 3 is a shell surrounding the core 4. Core 4 is surrounded 1 by upper layers 1.2 and 3.

As we will discuss later, each area has a specific effect. To summarize, core 4 (or ff when core 4 is hollow)
3) provides the body of the composite particle and adjusts the buoyancy of the composite particle P; The conductive layer 2 quickly polarizes the composite particles.

The control layer l isolates the conductive layers of adjacent particles P from each other since the particles P are rapidly polarized by the applied electric field.

The core 4 can be any material, for example a gas such as air; a liquid such as paraffin oil or other low-density oils; a solid such as plastic or rubber, or even a vacuum 1. The core 4 should have a low density, lower than the density of the continuous phase carrier liquid in which the composite particles are suspended. This is necessary so that the buoyancy of the core 4 balances the weight of the other components of the particle to render the composite particle essentially neutrally buoyant in the continuous liquid phase. The maximum dimension of the core is approximately o, ooi~
It is necessary to make it as small as within the range of about 10μ.

And it is desirable that it be spherical.

The shell 3 in the embodiment of FIG. 1 forms a container for the core 4 and provides most of the structural strength of the composite particle.

The shell 3 provides a means of defining the core 4 when it is hollow and serves as a base for the remaining layer.

The shell 3 can be made from a wide variety of materials, such as glass or polymers in the case of microballoons, and ceramics, metals or polystyrene in the case of solid or hollow microspheres. When the core 4 is a hollow microsphere, metal is preferable to ceramic because ceramic microspheres tend to break when used for purposes other than rheological studies of ER raw fluid and RR fluid.

The conductive layer 2 polarizes the composite particles P. The core layer can be made from a wide variety of conductive materials, but metals such as copper, silver, aluminum, nickel, etc. are preferred.

The conductive layer 2 can be made of a metalloid, such as graphite, or a semiconductor, such as silicon or germanium. The core layer 2 can then be provided by various means such as electroless plating. Layer 2 is denser than core 4, but relatively thin, so
When combined with other layers, it becomes a floating equilibrium. The conductive layer 2 adds to the mechanical strength of the composite particles P.

The main function of the outer control layer l is to control the electrical interaction between the conductive layer 2 of one composite particle P1 and another adjacent composite particle P (FIG. 4). The outer control layer 1 also serves to control the electrical interaction between the ER raw fluid liquid phase and the shell 3. The control layer l conducts electricity to the carrier fluid but insulates it to the conductive layers of adjacent particles P. control layer l
It has high resistivity and high electrical breakdown strength, and is also hydrophobic.

The outer control layer l can be composed of a wide range of materials depending on the nature of the conductivity 2. The outer control layer is conductive like the carrier liquid, but preferably more conductive. Both are relatively electrically non-conductive. For example, when the conductivity 2 is aluminum, the outer control layer 1 can be aluminum oxide prepared by oxidizing the surface of the aluminum layer by boiling it in water. On the other hand, the outer control layer 1 is provided by deposition from a solution of a material having the required electrical properties. A preferred coating material for control layer 1 is applied by a solution of tetraethyl orthosilicate (TE01) as described in the Examples below. Other silane-based coating materials include tetramethyl orthosilicate and tetrabutyl orthosilicate. Other metal alkoxide based coating materials include titanates, chromates and aluminum zirconates. These groups are considered to be hydrolyzable metal complexes.

The four regions l-4 of the composite particle cooperate to provide a composite particle P that solves the main problems with ER raw fluids.

The main problem with conventional ER raw fluids is the settling of particles due to the difference in density between the particles and the insulating liquid that causes them to form a suspended enclosure. The present invention compensates for said density differences by selecting the materials constituting the different regions and their amounts to provide composite particles P having an overall average density essentially the same as the density of the liquid in which they are suspended. It's resolved. This is generally achieved by providing a core region 4 that is substantially lighter, ie of lower density, than the density of the continuous phase suspending liquid medium.

Previous attempts to achieve density matching have been made by selecting different suspension liquids for different types of particles. This is difficult to achieve and at the very least extremely inconvenient. The difficulty arises from the fact that the particles exhibiting the best combination of properties are also dense in the cheapest and most easily used suspending liquids, such as hydrocarbons and silicone oils. More dense suspension fluids have been used, but these have problems such as extremely high cost, toxicity (PCBs and brominated fluids), and incompatibility with other materials typically present in equipment containing ER raw fluids. suffering from

The present invention solves these problems by selecting the material and its amount for each region according to the purpose. Therefore,
For the core 4 and the conductive layer 2 (which tends to be the densest component of the composite particle), the size and density of the core 4, such that the density of the composite particle P matches the density of the suspending liquid; By adjusting the thickness of each layer, the amount constituting each layer is selected in advance.

Another major problem with conventional ER raw fluids is that the discovery of ER effects in a system is almost always done by testing it at room temperature, which means that they cannot be used within a narrow temperature range centered around 25°C. generally works best. As the KR phenomenon is currently understood, traditional ER
The basic mechanism is the same at both extremes, although there are insufficiencies at both the raw fluid high and low temperature extremes. At low temperatures, conventional ER fluids react very slowly to the electric field, which is unsatisfactory because they cannot react fast enough. At high temperatures, conventional ER raw fluids become very conductive, which is bad, and sometimes they lose their KER effect altogether.

The reason why conventional ER fluids fail at these temperature extremes is believed to be that the charge carrier conductance within the particles and suspension or carrier liquid varies depending on temperature. It is believed that the conductance at low temperatures decreases, gradually polarizing the particles and thus slowly exhibiting the effects of ER. Two things occur at high temperatures.

First, since the conductance becomes extremely high, a di-arc is likely to occur where the total conductivity of the fluid is high. Second
If the particles require an activator, the activator (e.g., water) is driven off at high temperatures, rendering the fluid inert in terms of ER balance.

The present invention solves these temperature-related problems as a result of the control layer 1 and conductive layer or conductor 20 composition and thickness. For example, conductor 2 is made significantly more conductive than necessary to rapidly polarize the composite particles. Therefore, temperature-dependent changes in the conductivity of the conductor 2 do not affect the reaction rate of the ER fluid. Since the control N11 is made highly insulating, it prevents hopping of large numbers of charge carriers in the conductive layer 2 from composite particle to composite particle. It is desirable that the insulating or control layer 1 has a high electric breakdown strength in view of the high electric field drop therebetween. High electrical breakdown strength for ER fluids is at least about 4. Q taken as kv/wm.

The strength of the BR effect in ER fluids utilizing these composite particles is directly proportional to the breaking strength of the rising edge control layer l. The test is based on silicates and tetraethyl orthosilicate (TE01).
The dielectric breakdown strength of the ER fluid containing coating particles mainly composed of
It was shown to increase with the number of TE01-based coatings to 4.0 kv7wm for coats. Such particles can be prepared according to Examples I-W.

Another embodiment of particles useful in ER fluids is shown in FIG.

As shown, reference numeral 11 represents the control region or relative insulating layer, 12 represents the conductive layer, and 14 represents the core. Regions 11, 12 and 14 in this embodiment will be described with respect to regions 1, 2 and 4 of FIG. However, in the embodiment shown in FIG. 2, the conductive layer 12 can be a gas, liquid or solid core 14.
form a shell or container. Various coatings are applied as described in Examples 1-6.

In another embodiment shown in FIG.
i represents the control region or relative insulating layer, and reference numeral 22 represents the electrically conductive region which also forms the core of the composite particle. Coated particles having the structure shown in Figure 3 can be used to seal microdroplets of a highly ionic conductor such as water in an insulating skin or shell, or to coat zerolite particles with a protective P3 edge layer. Prepared by. Such composite particles are made by applying a silicate coating onto aluminum particles as described in Example 3. Silicate coatings are applied from silicon or metal alkoxides under acidic or rIi basic conditions. The coating may include substituents from polyfunctional alkoxides.

These coatings are applied from solvents such as ethanol.

The explanation of the theoretical demonstration of the composite particles of the present invention is simple. First, the particles must have high intraparticle conductivity,
This is because, if combined, a large amount of particle FIE can be induced to polarize extremely quickly.

At the same time, it is necessary to limit intraparticle conduction since it results in total current and detrimental power consumption. The present invention solves these problems by inserting an electrically insulating barrier between particles.
The solution is to limit conduction between particles by coating each particle with an electrically insulating layer, thereby providing internally highly conductive composite particles. Such an insulating layer needs to obtain the attractive forces between the particles that result in the field-induced yield stress in the BR fluid, and the insulating layer should be as thin as possible, preferably around the longest axis of the particle, e.g. the diameter of a spherical composite particle. It is desirable to reduce it to about 1% or less! Yes.

How to solve the particle sedimentation problem. It is desirable to provide composite particles with as close to neutral buoyancy as possible in the carrier fluid. This is distantly related to separating the roles of each part of the particle, i.e., one region of the particle controls the density or buoyancy, another region controls the conductivity within the particle, and yet another region controls the internal conductivity of the particle. control the insulation.

By splitting these functions, the areas they serve can be independently controlled and optimized without compromise. Therefore, the core region, which constitutes the majority of the particle's volume, controls structural matters such as shape and mechanical strength, as well as density and electrical properties. Similarly, the regions that control conductivity within the particle only need to perform their function, since any excess mass imparted due to higher density is balanced out by providing a lighter core. It is from. The regions controlling conduction within the particles need only electrically isolate the particles from each other.

The physical properties of ER fluids made in accordance with the present invention can be best observed from the simple system shown schematically in Figures 4-6, in which the composite particles of the present invention are shown in Figure 1. Dew. 4-6 represent the conductive layers and 3i represents the shell defining the core 42. In FIGS. Reference numbers 6 and 7 are electrodes, respectively.

The system consists of two composite particles quadrupled by an insulating suspension 8 and each placed between two electrodes 6.7.

When a potential difference is applied between electrodes 6 and 7 as shown in FIG. 5, the apparent charge within the conductor p@2a of each composite particle is redistributed. This redistribution occurs where the potential within each conductor layer 22 reaches equilibrium. When this is happening,
Equipotential lines can be drawn as shown in FIG. The equipotential lines are the insulating coating 15 of each composite particle and the suspension liquid 8
is drawn assuming that it has a conductivity equal to zero and a dielectric constant equal to one. Since the local electric field is proportional to the potential gradient, the electric field distribution around the composite particle can be determined from the equipotential lines. In other words, the electric field shown in FIG. 6 is high where the equipotential lines are wide and narrow. As shown in Figures 6 and 7, the composite particles are close packed where they contact each other and the electrodes. Therefore, the electric field is highest near these contact points.

Once the distribution of the electric field is known, the electric force acting on the particle boundary can be found by integrating the Maxwellian stress tensor of the closed surface shown in Figure 8 (F = 0
．． 5 f sε, E2ds) 6 In the structure shown,
The forces in each direction on the composite particle should be balanced, and there should be a net force on the composite particle.

When an electric field is applied, the particles do not move.

The yield stress found in ER fluids occurs after applying an electric field and the fluid is either sheared perpendicular to the electric field or pulled parallel to the electric field. The yield stress points can be seen from FIGS. 4-8. When the electrodes are sheared together, cased or pulled apart, the highest forces between the composite particles or between the composite particles and the electrode must be overcome before the electrodes can move. When that force is overcome, the electrode moves and the force required to move the plate does not increase. In an actual ER fluid mixture, a chain of composite particles is a chain of many composite particles, and there are many chains. The yield stress found in actual ER fluid mixtures is a measurement of many chain breaks and reformations. Because the suspension liquid has a certain viscosity! As the pole moves faster, the force required to move the electrode actually becomes higher because viscous drag adds to the electrical force.

The thickness of the control coating la determines the magnitude of the force acting on the composite particles and electrodes. If the coating is very thin, the equipotential lines between the composite particles will be very close. The electric field is very high.

To limit extremely high forces, the coating must be minimally thin. However, if a given potential is applied to the electrodes, there is less limitation on the thickness of the control coating, which is determined by the breaking strength of the coating material. Therefore, a composite particle with a thin control coating at a low applied potential should exhibit the same yield stress as a composite particle with a thick coating at a high applied potential. Electrical rupture of the film mf+g! Depending on the degree
And there is likely an optimum control coating thickness determined by the radius of the composite particles, the dielectric constant of the insulating coating, the dielectric constant of the suspending liquid, and the wear characteristics of the insulating coating. The dielectric constant of the control coating should be at least as high as the dielectric constant of the suspending enclosure or carrier liquid; generally the composite particles are spherical and about o, i to Zo.

μ, WtL<H has a diameter of approximately 0.1 to 2.0 μ.

Although composite particles have been described in terms of spheres, they can also take other shapes, such as spindles.

A method for preparing metal-coated microspheres is, for example, 19
The date of January 15, 1986 is Yorotsuno <Patent Application Publication No. 0.
No. 167.834, and methods for preparing metal-coated particles with various shapes are disclosed in the following publication: RPreparation a
nd Properties of Uniform
yCoated Inorganio Co1Loid
al Particles'by Garg et a
I, in Langmuir, 1988. vol
.

4, 111111. pI), 38-44° The insulating layer should have a thickness of about 1% or less of the total diameter of the spherical composite particles. When the insulating layer is formed by a silicate or TE01 based coating method as described in Example I, the thickness can be in the range of 0.001 to 1.0 microns. The thickness can be controlled by adjusting the number of coats or by adjusting the concentration of TE01 in the coating solution. The insulation coating must be continuous.

The continuous phase liquid can be a fluid used or capable of being used as an electrorheological fluid. Such fluids should have a relatively high dielectric constant, preferably in the range of about 2.0 to 9.0, and a specific gravity of about 0.7 to 2.0. The most common light fluids of this type are hydrocarbon oils and silicone oils, although there are also heavier fluids such as perfluorinated polyethers (sold under the trade name "GALDEND-10" by Monzedison). Liquids disclosed in commonly assigned US Pat. No. 4,772,407 may also be used. The insulating carrier liquid is desirably essentially anhydrous, as the presence of water in the insulating carrier liquid is not required by the present invention.

Although the insulating liquid forming the continuous phase provides insulation between the composite particles, this effect is different from the insulation provided by the insulation layer on the composite particles.

In other words, the insulating layer on the particle is different from the film or coating present on the particle as a result of immersing the particle in an insulating carrier fluid. Therefore, the insulation value of the insulation layer of the composite particles is different from the corresponding value of the carrier fluid.

Evaluation of fluids prepared for ER responses is often performed in a two-step process. In the first step, the fluid is tested at 81
Determine whether an effect exists.

If an 81 effect is observed, a second step test is performed which provides a better basis for comparison of the 81 effect in fluids.

In the first step, a grip probe consisting of a pair of parallel bars extending from the nodule with a spacing of approximately 311 meters is inserted into a volume of prepared ER fluid. About 2500-3000D, O between their parallel bars.

Apply voltage. The probe has a power rating of approximately 6 watts. 81 action is the ER of the surroundings where voltage is applied to the probe.
It is considered to be present when it forms a gel-like mass between and in the ER raw fluid rods when removed from the raw fluid, and when the voltage is interrupted and a gel mass flows from the rod.

In the second step (that is US Pat. No. 4772+!0
7), the KR fluid is passed through channels whose sides form parallel electrodes with constant spacing. A pressure transducer measures the pressure drop between the inlet and outlet ends of the flow channel as a function of applied voltage. By keeping the flow rate low, the viscous contribution to the pressure drop is made negligible. The induced yield stress is calculated according to the formula disclosed in column 12, lines 13-36 of the above patent. The calculated yield stress can be used as a basis for comparing 81 operations in various fluids.

The invention will be more readily understood from the following specific examples, which are given by way of illustration only and are not intended to limit the scope of the invention.

50 g of hollow aluminum silicate microspheres are stirred in a 900 M activated palladium solution at 25° C. for 1 hour.

Activated palladium solution is palladium chloride in hydrochloric acid solution 18
．． 9 l, 100 ml of 37% hydrochloric acid and 200 ml of water
Prepared by mixing. To this was added dihydrate tin chloride (I [12,3811), and the resulting solution was
Stir for a minute. Add dihydrated tin chloride (I[
) 57.1 jl of sodium stannate, 7 OI and 200 at of 37% hydrochloric acid are added. The mixed solution was heated to 49-65°C for 3 hours, followed by tri
Dilute with water in a volume ratio of . The resulting activation solution was 1.0
It is acidic with a pH of:

The treated microspheres are filtered and rinsed with fluoroboric acid.

The microspheres are then added to an electroless nickel plating solution at 25°C with stirring. After 10 minutes, distilled water 100%
The plating rate is increased by adding 25 Jl of hypophosphorous acid bath solution dissolved in d. Those particles are filtered and rinsed with distilled water. Purification of the nickel-coated microspheres is carried out in distilled water, and broken microspheres, precipitated metallic nickel and floating nickel microspheres are collected by filtration. When dried, it becomes particles with a light edge color. Examination of the particles by electron microscopy showed that the thickness of the metallic nickel layer applied by electroless deposition was approximately 2 microns.

The diameter of the particles was approximately 1505 m.

Coating of nickel microspheres with an insulating silicate layer was accomplished by first coating the microspheres at 25° C. with a primer consisting of 3 d% m of ethyl phosphate ethyltriethoxysilane in 210 m ethanol of distilled water and concentrated NH,OH 9 + R1. This is done by stirring the solution for 1 hour. This primer coating ensures satisfactory adhesion between the nickel and the following silicate layer. Those particles were then mixed with 12M tetraethyl orthosilicate, 140M ethanol, 541Lt distilled water and concentrated NH,OH6.
Stir in the at solution for 1 hour. The latter step is repeated to provide a second silicate coating.

Those composite particles were then filtered and rinsed with ethanol.
Filter and dry in the open at 120'C for 1.5 hours. The composite particles are free-flowing. The thickness of the silicic acid coating is approximately 2000X.

A 33% by weight suspension of composite particles is prepared in 50 as silicone oil. This suspension is an ER with low conductivity.
Indicates the response. In control tests, uncoated nickel microspheres show no ER response and are highly conductive as shown by the sparks generated during tests in the same voltage range.

Example π Nickel microspheres are prepared as in Example. Following the steps in the example process, four coats of silicate are applied instead of two coats on the nickel microspheres. The total thickness of the silicate coating is 1000-4000A. A 33% by weight suspension of these heavier coated composite particles in the same silicone oil exhibits ER behavior over a wider voltage range than the silicate coated microspheres of Example I.

Nickel micro EJ10 prepared as in Example work
jl oxidized carboxylated polyethylene notluene 10
Add at 80°C to a stirred solution consisting of 0+jl to 5I. After stirring for 1 hour, the composite particles are collected by filtration, rinsed with toluene, and dried in air. 10 as
It was found that a suspension of 10% composite particles in silicone oil exhibited an ER effect and was capable of generating sparks.

10 liters of aluminum coated hollow microspheres were dissolved in 140-140 ethanol of tetraethyl orthosilicate 121114
, distilled water 54- and concentrated NH, OH 5+J) and stir for 1 hour. The resulting composite particles are filtered, rinsed with ethanol, filtered and dried in the open for 1 hour to remove the ethanol. Those composite particles are free-flowing.

Following the coating step described above, a portion of the composite particles is coated with a second coating.
silicate coating. Another portion of the composite particles is given four more coats using the same coating process.

1 consisting of 33% by weight aluminum coated hollow microspheres treated with 1.2 and 5 coats of tetraethyl orthosilicate to form a silicate coating.
00S silicone oil suspension exhibits ER action. TE01
Suspensions of aluminum-coated microspheres with a 5-coating treatment exhibit ER behavior over a wider voltage range than do aluminum microspheres with even less coating.

Control tests with untreated aluminum coated microspheres show no ER response and are highly conductive as shown by sparks generated over the same voltage range. The thickness of the silicate coating is approximately 500 to 100 OA per coat.
Hollow aluminum microspheres are boiled in distilled water for 1 hour to give an aluminum oxide coating. A suspension of 1'o weight percent of composite particles in 10 cs of silicone oil gives a strong ER response upon generation of an electric spark. In control tests, untreated aluminum microspheres show no ER response and are highly conductive as shown by the electrical sparks generated during the test in the same voltage range.

Add hollow microspheres of mercaptopropyltrimethoxysilane 121d to 280ml of ethanol and stir for 15 minutes. Add 108 WLt of distilled water and concentrated Nu◆0H12- and stir at 1 until the solution becomes clear. Silver coated hollow microspheres are added to the solution and stirred for 1 hour.

The microspheres are then treated twice with tetraethyl orthosilicate (TE01) as in the Example. The so-treated particles are filtered, rinsed in ethanol, filtered and dried overnight in an open oven at 120°C. The resulting composite particles are free-flowing.

10 as silicone oil 17. Composite particles in 411 8.
Suspension No. 81 exhibits an ER response and a low conductivity below the breakdown voltage of the coating. In control tests, untreated hollow microspheres show no ER response and are highly conductive.

0.05~ to aluminum particles with a diameter of 40μ by the following method.
Coat with a 0.25μ thick silicate film.

Ethanol 23Qm/ is added to aluminum particles 60I. To this mixture, water 108+117, concentrated NH, 0H1
z- and tetraethyl orthosilicate 24- are added. After adding each ingredient, shake the mixture for 5 seconds,
The mixture is then stirred for 1 hour after all ingredients have been added. Filter the particles and rinse 5 times in water. The particles are then dried in a vacuum oven at 150°C for 1-3 days. The particles were then cooled to room temperature and exposed to GALDEN for 10 as
(trade name) fluid was mixed with 30% by weight to produce KR fluid. The process was repeated to apply two coatings.

The total thickness of the two coatings is 500 ~ zso
oi (o, os ~ 0.25μ).

It was found that the obtained ER raw fluid was relatively non-conductive and exhibited an RR response. The ER raw fluid becomes essentially anhydrous as a result of prolonged high drying.

Similar effects were obtained using identically sized silicon particles treated in the same way.

2.3 advantages result from applying the electrical control coating from a solution of tetraethyl orthosilicate (TE01). The important point is that the thickness of the coating can be adjusted. Another advantage is that TE01 can be coated on water-absorbing materials to prevent particles from absorbing water and to improve RR.
A desirable contribution of the fluid is that it can also provide an electrical control layer. For example, desirable hydrophobic agents include members of the organometallic alkylsilane group of compounds such as octadecyltrialkoxysilane.

From the above description, it can be seen that the present invention has the drawbacks of known ER fluids.
It is clear that there is a need to provide superior electrorheological fluids, as well as new composite particles for many fluids and methods of making the composite particles and fluids. Although preferred embodiments and methods of manufacturing the same have been described in detail, various improvements, modifications, and changes can be made without departing from the spirit and scope of the invention as defined in the claims.

[Brief explanation of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of a composite particle made according to one embodiment of the invention; FIG. 2 is an enlarged schematic cross-sectional illustration of a composite particle made according to another embodiment of the invention; FIG. An enlarged cross-sectional schematic diagram made in accordance with yet another embodiment; FIG. 4 is a schematic diagram of the device showing the composite particles of FIG. 1 placed between two electrodes; FIG. 4
6 is the equipotential lines induced in the apparatus of FIG. 5; FIG. 7 is the equipotential lines in the particle control coating in the apparatus shown in FIGS. 5 and 6; and The figure is number 5
7 shows the surfaces used to explain the integration of the Maxwellian stress tensor in FIGS. 6 and 7; FIG. Engraving of drawings (no changes to content) 0 Inventor Debra N. Atsukaamen Rika Ormond Beach, Florida, United States. Sure Boulevard 245 Ocean 107'2- Hand (Method) % Formula % (1. Incident Display Flat Bottom 2nd Year Matsutoshi-dono) Application No. 105130 Invention - Ichigen's Name, Guidance = * Classification Method for producing electrorheological fluids and particles useful in the fluids 3. Relationship with the case of the person making the amendment Patent applicant's attorney 6. Number of claims increased by amendment

Claims (30)

[Claims] 1. an electrorheological fluid consisting of a continuous phase of a carrier liquid and a discontinuous phase of dispersed particulates, an electrically conductive surface capable of causing rapid intraparticle polarization of said particulate phase;
means for defining a particle body having an electrically controlled coating on said surface that substantially prevents conduction within the particle while permitting said polarization; said particle body excluding said electrically conductive surface and said controlling coating; having a density lower than the density of the carrier liquid; the thickness and density of the conductive surface and control coating being selected to provide a composite particulate body having an average density essentially the same as the density of the carrier liquid; An electrorheological fluid characterized by: 2. The electrorheological fluid of claim 1, wherein the particle body is hollow and sealed by the electrical control coating. 3. The particle body has a core structure, and a shell on the core structure,
The electrorheological fluid of claim 1 including at least one layer of electrically conductive material on said shell. 4. 2. The electrorheological fluid of claim 1, wherein said particle defining means comprises a hollow microsphere having a conductive shell providing said conductive surface. 5. 5. The electrorheological fluid of claim 4, wherein said carrier liquid is relatively non-conductive and said control layer is also relatively conductive. 6. 6. The electrorheological fluid of claim 5, wherein said control coating conducts electricity to said carrier liquid but electrically insulates said shell from said carrier liquid. 7. The electrorheological fluid of claim 1, wherein the control coating is deposited from a solution of a hydrolyzable metal complex. 8. Claim 1, wherein said electrically conductive surface is provided by metal.
Electrorheological fluids as described. 9. The electrorheological fluid of claim 1, wherein the particle body comprises a gas. 10. An electrorheological fluid in which a discontinuous particulate phase is suspended in a continuous liquid carrier phase, wherein said particulate phase comprises particles having a density lower than that of said continuous phase and at least one electrically conductive surface of at least one of the electrically insulating materials.
prepared by coating with a layer, the nature and amount of the electrically insulating material being selected to provide composite particles having an average density essentially the same as that of the carrier liquid with respect to the electrically conductive surface of the particles. An electrorheological fluid characterized by: 11. 11. The electrorheological fluid of claim 10, wherein said electrically insulating layer is formed on said shell by coating from a solution of a hydrolyzable metal complex. 12. 12. The electrorheological fluid of claim 11, wherein the hydrolyzable metal complex is selected from the group consisting of silane-based coating materials and metal alkoxide-based coating materials. 13. 13. The electrorheological fluid of claim 12, wherein the silane-based coating material is selected from the group consisting of tetraethyl orthosilicate, tetramethyl orthosilicate, and tetrabutyl orthosilicate, or other silicone alkoxides. 14. 13. The electrorheological fluid of claim 12, wherein the metal alkoxide coating material is selected from the group consisting of titanates, chromates, and aluminum zirconates. 15. 11. The electrorheological fluid of claim 10, wherein said particles are spherical and hollow and said control coating has a thickness less than about 1% of the diameter of said coated particles. 16. 11. The electrorheological fluid of claim 10, wherein the electrically insulating layer has a thickness of about 10,000 Å or less. 17. 11. The electrorheological fluid of claim 10, wherein the particles have a largest dimension of less than 100 microns. 18. An electrorheological fluid in which a discontinuous particulate phase is suspended in a continuous insulating liquid phase, the particulate phase comprising hollow particle bodies coated with an electrically conductive material and an electrically insulating material, the nature and amount of the electrically conductive material and the electrically insulating material are selected to provide composite particles having an average density essentially the same with respect to each other and the particle body as that of the insulating liquid. 19. 19. The electrorheological fluid of claim 18, wherein said hollow particle body is formed from a ceramic, metal or polymeric material. 20. 19. The electrorheological fluid of claim 18, wherein the hollow particle bodies are spherical and have an overall dimension of less than about 100 microns. 21. 19. The electrorheological fluid of claim 18, wherein the density of the hollow particle body, excluding the conductive and insulating coating, is less than the density of the insulating liquid phase. 22. It consists of a particle having a shell with a hollow core and an electrically conductive surface, and a particulate phase comprising a coating of an electrically insulating material on the electrically conductive surface of the particle, the electrically conductive material and the electrically insulating material and the amount thereof being in the hollow core. said electrically insulating coating is coated on said electrically conductive layer by precipitation from a solution of a hydrolyzable metal selected to provide composite particles having a total density essentially the same as that of the insulating liquid with respect to density; an electrorheological fluid in which a discontinuous particulate phase is suspended in a continuous insulating liquid phase, characterized in that said conductive layer is provided by a metallic material. 23. Particles useful in electrorheological fluids, characterized in that they consist of a core having a metal shell and a layer of electrically insulating material coated onto the core by precipitation from a solution of a hydrolyzable metal complex. 24. 24. The particle of claim 23, wherein the hydrolyzable metal complex is selected from the group consisting of silanes and metal alkoxides. 25. 24. The particle of claim 23, wherein the core is hollow. 26. 24. The particles of claim 23, having a maximum dimension of less than about 100 microns and a dielectric coating thickness of less than about 10,000 angstroms. 27. 24. The particle of claim 23, wherein the core is hollow, the shell is spherical, the conductive layer is metal, and the electrically insulating coating is provided by precipitation from a solution of tetraethyl orthosilicate. 28. 24. The particle according to claim 23, further comprising a hydrophobic coating on the insulating coating. 29. 29. The particle of claim 28, wherein the hydrophobic coating is provided by a compound of organometallic alkyl silane groups. 30. 24. Particles according to claim 23 in association with an insulating liquid carrier.