Electro-optical Dipolar Material

Abstract

An article of manufacture is provided as a matrix having dispersed substantially uniformly therethrough a plurality of electro-optically responsive dipole particles selected from the group consisting of electrically conductive and semi-conductive material and dichroic crystals, the matrix being a transparent medium capable of being in the fluid state during the initial orientation of the dipoles, whereby the dipoles are capable of rotation to a desired preferred orientation upon the application of a force field, the medium being thereafter solidified. A method of applying the force field is disclosed.

Parent Case Text

This application is a continuation-in-part of U.S. application Ser. No. 378,836, filed June 29, 1964, in the name of Alvin M. Marks, now U.S. Pat. No. 3,572,876.

Description

This invention relates to conducting dipole polarizers and articles, products, devices, and the like, produced therefrom having preferred optical properties, the conducting dipoles being advantageously formed of metals, non-metals, or semi-conductive materials capable of forming whiskers by vapor deposition or capable of forming submicron rod-like shapes by using metallurgical melting and controlled freezing techniques, growth from a vapor, or other known techniques. The dipoles are suspended in a transparent layer of material capable of being congealed or hardened after the dipoles have been oriented in the desired direction.

RELATED APPLICATION

In related application Ser. No. 378,836, now U.S. Pat. No. 3,512,876 methods and apparatus are disclosed for controlling light and related forms of electromagnetic radiation using dipole particles suspension in transparent media. By employing an external electrical or magnetic field, the optical properties of the media can be varied by orienting and disorienting the dipolar particles in suspension in accordance with the field applied, the media being a fluid in which Brownian movement aids in randomizing the dipole particles upon removal of the external field. In its broad aspects, the related application provides a light-controlling device comprising in combination a fluid suspending medium and a plurality of minute dipole particles rotatably carried in the medium, the particles advantageously having a long dimension of the order of about .lambda./2n and at least one other dimension preferably not exceeding about .lambda./10n (where .lambda. is the wavelength of light and "n" is the index of refraction of the suspending medium). The disposition of the particles in the medium is controlled by applying an electric, magnetic or mechanical shear force field to the suspension. One example of a light-controlling device is an electro-optical shutter. The related application goes into great detail in the technical aspects of dipole particles, which disclosure is wholly incorporated into this application by reference.

BACKGROUND OF THE INVENTION

In the prior art, it is known to produce metal polarizers by the reduction of metal salts in stretched polymers, such as cellulose hydrate, gelatin, polyvinyl alcohol, and the like. The metals so reduced form aggregates within the interstices of the polymer. Such aggregates are usually relatively uncontrolled as to length and diameter. Since most polymers have disordered regions, irregularly shaped metal deposits were often formed which detracted from the transmittance and polarization characteristics. The polymers employed, were capable of swelling or dissolving in water, and were generally sensitive to ambient atmospheric conditions.

Elongated silver particles having a maximum ratio of three to one in the form of ellipsoid of silver, have been produced in glass by strong stretching. For a given mass per unit area of absorbent material, the absorption obtained by such particles is greater than that of an ordinary colorant, such as cobalt dissolved in the glass, by a factor of about 3,000 to one.

The prior art methods of stretching to deform particles do not enable control of particle ratio of length/width, nor do they result in optimum length/width ratios required for strong polarization.

Another polarizer described in the prior art consists of minute wires or conductors on a glass surface or within a glass structure. However, no practical means for the production of such structures have been disclosed. Very long thin conductors are not as efficient for producing a high degree of polarization and transmittance in a specific wavelength range. The dipoles herein disclosed may be fabricated by incorporation into a suitable stable polymer or a glass melt and aligned by mechanical shear forces, or an electric or magnetic field. It would be desirable to have a dipole particle which is inert and which will resist degradation during use in the ambient environment.

OBJECTS OF THE INVENTION

It is an object of the invention to provide conductive and semi-conductive dipole particles which are substantially inert to the ambient environment and which resist degradation.

Another object is to provide as an article of manufacture a transparent material, such as a solid material made of glass or transparent plastic, characterized by a dispersion of microscopic, inert, dipole particles oriented to confer light polarizing properties on the material.

A further object is to provide a solid transparent substrate having a transparent coating thereon containing a dispersion of submicron, inert, conductive, dipole particles having a preferred orientation, whereby to provide predetermined optical properties to the coated substrate.

A still further object is to provide a composition of matter for optical use, said composition comprising a suspending medium containing a plurality of dipole particles, the medium being one capable of being converted to the fluid or soft state to enable orientation of the particles and capable of being solidified to permanently fix the position of oriented dipole particles.

The invention also provides as an object a method of producing dipole particles of relatively controlled sizes.

These and other objects will more clearly appear when taken in conjunction with the disclosure and with the accompanying figures of the drawing which are summarized as follows:

IN THE DRAWING

FIG. 1 illustrates the three fundamental attributes of light;

FIG. 2 is a polar graph showing relative response versus the angle of a dipole to a constant signal intensity;

FIG. 3 shows the relative response of a dipole antenna versus polarization direction;

FIG. 4 depicts a half-wave dipole with a characteristic load resistor tuned to absorb maximum power;

FIG. 5 illustrates diagrammatically the effective cross section of a dipole antenna as compared to the actual physical cross section;

FIG. 6 is a graph showing the relative power absorbed or re-radiated as a function of the wavelength of light for thick and thin half-wave dipoles;

FIG. 7 depicts a transparent substrate, e.g. glass or plastic, having a transparent coating, e.g. of plastic, in which dipoles are dispersed and oriented normal to the surface of the coating;

FIG. 8 is similar to FIG. 7 except that the dipole particles are oriented parallel to the surface to provide polarization effects, whether the coated article is a lens, a coated windshield for automobiles, coated sheet material, and so forth; and FIG. 8A shows flake orientation;

FIG. 9 is similar to FIGS. 7 and 8 except that the dipoles in the coating are randomly oriented;

FIG. 10 is a diagrammatic cross sectional view of a machine for the continuous production of polarizing film or sheet utilizing dipoles which are electrically aligned;

FIG. 11 is a detailed fragment of the electrical aligning section of the device of FIG. 10; and

FIG. 12 is a vertical cross section of a high pressure spin coating device for producing high field orientation dipole suspension coatings.

GENERAL STATEMENT OF THE INVENTION

The present invention overcomes the deficiencies of the prior art by providing metal whisker dipoles or submicron rod-like dipoles of relatively inert material such as chromium, aluminum nickelide, platinum or other conducting metal; or alternatively, by utilizing semi-conductors which are advantageous for certain other characteristics, such as silicon, germanium, or zinc sulfide whiskers, and having a selected length, and length to width ranges.

These are preferentially incorporated in a readily meltable glass, thermoplastic or plastic solution, and orientated by means well known to the art, such as by the application of an electrical or magnetic field or by the application of stretching where differential shear is produced during stretch causing the parallel orientation of the particles, and subsequently solidified by cooling or evaporation of solvent.

Thus, as one broad aspect of the invention, a composition of matter is provided for optical use comprising a plurality of conductive or semi-conductive asymmetric particles (e.g. dipoles) suspended in a transparent medium which is substantially a solid at ambient temperatures but which can be melted or softened to a fluid state at an elevated temperature to form any desired shape, the particles being then oriented to a preferred direction by an electrical or magnetic field before allowing the shaped body to solidify.

Another aspect of the invention resides in an article of manufacture in the form of a polarizer comprising a layer of transparent material having a dispersion of inert conductive or semi-conductive dipole particles therein having a length of .lambda./2n .+-. 50 percent, and preferably having an average diameter of at least about .lambda./10n, where "n" equals the index of refraction of the transparent medium, the long axis of particles being oriented in the plane of the transparent medium.

The dipole particles can be produced by various methods. Thus, metal dipoles can be produced by vapor deposition in a partial vacuum to produce metal whiskers which can be sized in a blender and the sizes separated by centrifuging or by differential settling.

Another method is to produce a eutectic of a binary alloy which, by directional freezing, produces a rod-like structure, the size of the rod-like structure being determined by the velocity of the plane of soldification and temperature gradient. After selectively dissolving away the matrix metal, the residue of rod-like material is washed and then suspended in an inert liquid for sizing in a blender, the sized material being thereafter selectively separated using differential settling or centrifuging techniques. The foregoing and other methods will be described in more detail hereinafter.

The dipole particles useful in the present invention are characterized in that they have at least one dimension large relative to at least one other dimension, that is to say, they are in the form of flakes, needles or the like. The dipole particles should have at least one dimension equal to one-half of the wavelength of the radiation to be controlled, (normally, visible light, but in some cases, infrared, ultraviolet, microwave, or other portions of the electro-magnetic spectrum) and at least one other dimension substantially smaller than one-half of said wavelength. The magnitude of the third dimension, that is, whether the particle is a needle or a flake, depends on the requirements of the specific embodiment of the invention, as more fully discussed below.

For purposes of brevity, the term "light" is used throughout the present specification and claims in a generic sense and is intended to encompass not only visible light but also infrared and ultraviolet "light," as well as microwave radiation in the neighboring portions of the electromagnetic spectrum.

In addition to the dimensional requirements herein disclosed, the electrical or magnetic properties of the dipolar particles, i.e. the conductivity, should be such as to facilitate orientation in an electric or magnetic field, and strong interaction with electromagnetic radiation.

The suspending medium is a fluid, non-reactive with the dipole particles, or is a substance capable of being converted to a fluid, at a temperature sufficiently low to avoid any adverse effect on the dipole particles.

It is not in all cases necessary that the suspending medium be in the liquid state during the first stage of orienting the particles. Providing the applied torque is sufficiently strong to orient the dipole particles against a certain amount of plastic resistance of the suspending medium, it is sufficient if the suspending medium is in a highly deformable plastic state. The term "fluid" as used herein should therefore be understood to encompass such a plastic or soft condition. For most applications of the present invention, the suspending medium is present as a liquid during alignment or disorientation of the dipole particles. The dipole particles must also be of such a nature that they are capable of being oriented by an applied electric, magnetic or, in certain cases, a mechanical shear force field.

Some particles have an inherent dipole moment by reason of their internal structure in which the effective center of positive charge in the molecule or crystal is spaced from the center of positive charge. Such an inherent dipolar character, if present, is effective to some degree in augmenting the tendency of the particles to orient themselves in an applied force field. Inherent dipolarity is, however, neither essential nor a major factor in determining the effectiveness of the dipole particles.

As stated hereinbefore, the preferred dimensions of the particles above referred to may be characterized by .lambda./2n where .lambda. is the wavelength of the light to be polarized and "n" is the index of refraction of the medium in which the particles are suspended and oriented.

For example, if a suspension of dipole particles is to polarize light at 5,600A, and the index of refraction of the transparent suspending medium is 1.5, the optimum length for the dipole whisker is 5,600/2 .times. 1.5= (5600/3) = 1,860 A. The length to diameter ratio should be not less than three, and preferably greater; that is, from 10 to 100. The percentage of polarization increases with the length/width ratio, and the width of absorption or reflectance band decreases. Where dipole particles are highly conducting, such as with silver, gold or copper whiskers, the polarizer acts as a beam splitter, and the radiation is partly transmitted and partly reflected. The transmitted radiation is polarized with good image resolution. The reflected radiation, however, is scattered, and polarized in a plane at 90.degree. to that of the plane of polarization of the transmitted light.

A beam splitting polarizer of this type is particularly useful where polarization of intense light beam sources is required. In the case of the absorption polarizer, the temperature of the polarizing element rises perhaps to cause destruction. However, with the beam splitting polarizer, the radiation is mostly reflected and transmitted, and the temperature rise is minimized.

The most efficient sheet polarizer is that which requires the smallest number of particles per unit area to accomplish a given percent polarization. The most efficient sheet polarizer is obtained by selecting particles within a narrow size range, about the optimum .lambda./2n dimension. For example, for most efficient polarization in the range from 4,500A to 6,600A, dipole particles having length ranges between 1,500A to 2,200A, are selected. For a still narrower range of polarizing characteristics, then a still narrower range of dipole particle lengths is employed. For example, for a narrow frequency band which might characterize a laser, then a single length with close tolerances is employed.

Stable chemical structures are relatively rare. Most chemical structures are relatively easily deteriorated by ultraviolet, visible and infrared light, heat and chemical action.

Light is an electromagnetic wave having three fundamental attributes, which are: amplitude or intensity, wavelength or color; and polarization or the vibration direction at right angles to the ray.

These three fundamental attributes of light are shown in FIG. 1.

A half-wave dipole antenna, which is normally used for television reception, has interesting properties.

The half-wave dipole is capable of controlling all three attributes of light, by varying its length, thickness, resistivity and angular position.

The electric power absorbed from the radiation by the half-wave dipole depends upon two orientation angles of the dipole. The first angle, .theta., is that between the length of the dipole and the signal path. The second angle, .phi., is that between the length of the dipole and the direction of polarization of the signal.

FIG. 2 shows a polar graph of radiant power absorbed versus angle .theta..

In FIG. 3, the radiation ray path is normal to the plane of the diagram, and there is shown the angle .phi. versus the power absorbed by the dipole.

A maximum response is obtained when the antenna is aligned parallel to the polarized electric vector of the radiation and at right angles to the signal path (.phi. = 0, and .theta. = 90.degree.). The antenna absorbs no power when it is placed at right angles to the polarized electric vector of the radiation; or arranged parallel to the ray path.

When adjusted for a maximum response, a half-wave or .lambda./2 antenna is then said to become resonant to the particular wavelength .lambda..

The power absorbed by the dipole from the radiant energy may be re-radiated, or absorbed and dissipated as heat, depending on the electrical resistance of the half-wave dipole antenna.

If power is to be absorbed from the dipole antenna and utilized in an outside electric circuit, as for example in a television set, a matched or characteristic resistance of 73 ohms must be inserted at its center of the half-wave dipole antenna, as shown in FIG. 4.

An antenna may be made of such material, thickness and length as to achieve full power absorption, or nearly total reflection.

In FIG. 4, there is also shown a half-wave (.lambda./2) antenna 2; in which the central resistor is replaced with a single rod having a distributed resistance of approximately 80 ohms, which results in the absorption of radiation in the wavelength range .lambda..

Now, if instead of a half-wave antenna with a central resistor or an equivalent distributed resistance, a half-wave antenna of low resistance is employed, then the half-wave dipole antenna becomes reflective for the full wavelength. The radiant power may be said to be absorbed by the half-wave dipole and then re-radiated in all directions, with the intensity direction pattern shown in FIG. 2. Thus, the resistivity characteristics of the materials, together with the length and width, controls the distributed resistance of the half-wave antenna. These factors may be adjusted so that the half-wave dipole antenna has high absorptivity or high reflectivity for incident radiation of a given wavelength band.

FIG. 5 shows another very important property of the half-wave dipole antenna, the "effective cross section."

FIG. 5 shows a half-wave dipole antenna having a thickness of one twenty-fifth its length. Its length is .lambda./2 and its thickness .lambda./50. The physical cross section of this half-wave dipole at right angles to the light ray is:

(.lambda./2) (.lambda./50) = .lambda..sup.2 /100. However, it is known that the effective cross section of a half-wave dipole antenna is much larger. The cross section from which the half-wave dipole appears to absorb power is approximately .lambda..sup.2 /8. A rectangle of this size is shown in dotted lines surrounding the antenna rod, the radiant power actually funnelling into the dipole. In this example, the effective area of the antenna has been increased by a factor of .lambda..sup.2 /8 divided by .lambda..sup.2 /100 or 12.5 times.

Dipole antennas have been employed for the electro-magnetic spectrum all the way from long wave radio down through the television range into the microwave and millimeter wave spectrum.

Dipoles have been observed which are resonant in the range of the wavelength of visible light. Yellow light at the peak sensitivity of the human eye has a wavelength of 0.565 microns (yellow). Elongated metal rods of submicron dimensions in colloidal suspension in a transparent medium, results in myriads of light-responsive dipoles. The transparent medium keeps the dipoles in spaced relation.

The index of refraction "n" of a given medium may be defined as the ratio of the speed of light in free space, to the speed of light in the medium. Since the speed of light in all substances is less than in free space, "n" is always greater than one. The wavelength of light in a given medium is inversely proportional to the index of refraction "n" of the medium.

Because the index of refraction of transparent media is approximately 1.5, the dimensions of a half-wave dipole must be decreased in inverse proportion; that is, for n = 1.5, the actual resonant length of a half-wave dipole in such a medium becomes (1/2) .lambda./1.5 = .lambda./3.

For example, in a medium having an index of refraction of 1.5, a half-wave dipole should have a length of (0.565/3) = 0.188 microns (or 1880A) of yellow light for 0.565 microns wavelength (or 5650A).

The .lambda./3 dimension, of course, is correct only for n = 1.5 and will vary with the index of refraction of the medium.

Another interesting property of the dipole is that the sharpness of its tuning, or the wavelength range over which it will absorb or reflect, depends on the ratio of the length to the thickness of the dipole, as well as on the resistivity of the dipole material.

FIG. 6 refers to the reflection or absorption of radiant energy by a half-wave antenna showing the relative power absorbed or re-radiated, versus the ratio of length to thickness of the antennae.

A. for thin dipole antenna (25/1)

B. for a thick dipole antenna (10/1)

We now come to the application of these basic concepts to light control; that is, control of all three basic attributes of light, intensity, color and polarization, by dipoles in suspensions in a transparent medium.

Pigments formed from dipolar materials are visually indestructable. The polarization, reflectivity or absorptivity characteristics of the dipole suspensions are predetermined by the appropriate selection of length, width and resistivity of the dipoles, together with their concentration and orientation.

Such a dipole suspension has the property of absorbing or reflecting specified wavelength ranges. Since a specific resonance characteristic is obtainable from the same material merely by changing its length to width ratio, very pure colors can be obtained by transmission or reflection from coatings formed from such suspensions. When oriented, the dipole suspension has strong polarizing properties.

The substances chosen to form the dipoles are preferably chemically stable materials, which remain permanently within the suspension, and which are not subject to chemical destruction by ordinary atmospheric agents or by exposure to light. However, dichroic crystalline needles, such as herapathite dipoles, may be employed as dipoles.

The dipoles may be formed of metals, such as gold, platinum, palladium, chromium, tin, or metal compounds such as Al.sub.3 Ni, and the like, which are known to grow submicron crystal-whiskers, under appropriate conditions, such as from the vapor phase. Semi-metals, such as carbon, silicon and germanium, are also known to form crystal-whiskers. These crystal-whiskers may then be incorporated in a fluid to form a dipole suspension.

A crystal-whisker made of a single substance of the utmost permanence, may be predetermined in its properties; a perfect black, a perfect white diffuse reflector, or having sharp absorptivity or reflectivity bands in the yellow, green, blue or other regions of the spectrum. When oriented, these result in polarizing these characteristics.

The effective cross section per particle oriented normal to the light ray and parallel to the electric vector of the light in a medium of index of refraction "n" is:

.lambda..sup.2 /8n.sup.2 (1)

This property is useful in calculating the number of particles required for substantially complete light absorption or reflection as follows:

Assuming no aggregation of particles, the concentration of a suspension of submicron dipolar particles per square centimeter in a medium having an index of refraction of 1.5 is determined as follows:

N = (8n.sup.2 /.lambda..sup.2).about.8 .times. (1.5).sup.2 /(0.565 " 10.sup..sup.-.sup.4).sup.2 (2)

= 6.25 .times. 10.sup.9 particles/cm.sup.2.

It is possible to obtain the interparticle spacing between dipoles oriented in the same direction, the interparticle spacing for substantially parallel dipoles being the center to center distance between the longitudinal axis of the particles taken at right angles to each other. The interparticle spacing for substantially complete light absorption or reflection does not substantially exceed the width of the effective cross section.

The derivation of the interparticle spacing, d.sub.p, for the polarizing case is determined where the dipoles are all parallel and disposed in the plane of the sheet. The details are disclosed in copending application (Ser. No. 378,836, filed June 29, 1964, and need not be repeated here. Simply stated, the interparticle spacing may be determined as follows:

N.sub.v = the number of diples per unit volume of suspension

V.sub.p = volume of cube occupied by one dipole = 1/N.sub.v

d.sub.p = interparticle spacing = .cuberoot.V.sub.p = .cuberoot.1/N.sub.v

The concentration of dipole particles required to provide effective surface coverage is generally very low as will be apparent from the following:

Assuming a square cross section for the particle having a width "a," the mass per particle is

m.sub.p = .delta.(.lambda./2n).sup.3 b.sup.2

where

b = width (a) to length ratio and (4)

.delta.= density in gms./cm..sup.3 of the dipole.

Thus, the mass m.sub.p per dipole particle of gold for length to width ratio of 25 where .delta. of gold equals 19 and b = 1/25 is:

m.sub.p = 19(0.565 .times. 10.sup..sup.-.sup.4 /3).sup.3 /25.sup.2

m.sub.p of gold = 2 .times. 10.sup..sup.-.sup.14 gms./particle.

The mass m.sub.d of dipoles per unit area is then determined as follows:

m.sub.d = Nm.sub.p = (8n.sup.2 /.lambda..sup.2)[.delta.(.lambda./2n).sup.3 b.sup.2 ]

m.sub.d = (.lambda./n)b.sup.2 .delta. (5)

Thus, (.lambda./n) b.sup.2 = (particles/cm..sup.2) .times. (mass/particle)

or

6.25 .times. 10.sup.9 .times. 2 .times. 10.sup..sup.-.sup.14 .times. 1.25 .times. 10.sup..sup.-.sup.6 gms./cm..sup.2

As will be noted, very small concentrations of dipole particles of the order of about 2 micrograms/cm..sup.2 are sufficient to provide effective surface coverage.

For a film of 10.sup..sup.-.sup.3 cm.(0.4 mil) thickness, and density = 1 gm./cm..sup.2, this corresponds to a dipole concentration of only 0.125 percent of the solid film.

Because their effective cross section is much greater than the physical cross section, the dipolar particles may be very sparsely distributed in space. The dipolar particles are sufficiently far apart from each other so as to have no physical interaction. Each dipolar particle acts independently of the other.

FIG. 7 shows a film containing dipole particles with their length oriented normal to the surface. The film is transparent because the cross section particles present to the radiation is so small that substantially no light scatter and no light absorption occurs.

FIG. 8 shows a film in the XY plane in which the dipole particles are aligned in the OX direction. Light transmitted along the Z axis into the surface emerges from the other side plane polarized with the electric vector E.sub.Y in the ZY plane. Reflected light is plane polarized with the electric vector E.sub.x in the ZX plane. Reflected light is polarized and scattered.

FIG. 9 shows a film having dipolar particles in random orientation. Reflected light is symmetrically scattered in all directions. The transmitted light and the reflected light show no polarization. However, since the dipoles are "tuned" to a particular wave band, the transmitted and reflected rays are complementary in color. Consequently, in the random orientation, the dipoles act as pigments. However, these dipolar pigments are subject to control by variation of physical quantities of dimension resistivity and orientation.

As stated hereinabove, dipoles may be oriented by an electric field, a magnetic field (if the particle is magnetic, diamagnetic or paramagnetic), or by viscous shear forces in the suspending fluid. Dipole particles tend to disorient rapidly in suspending fluids of low viscosity. For low viscosity fluids obtained by heating to a fluid temperature, the disorientation of dipolar particles may occur in milliseconds. The disorientation is due to Brownian movement or the random impact of the fluid molecules on the dipole particle.

However, if the suspending fluid viscosity is high, dipole orientation will persist for a longer time, from seconds to hours. A permanent orientation of dipolar particles may be achieved in a fluid by allowing the solvent, in the case of a plastic composition, to evaporate while maintaining the orientation.

Metallurgical techniques may be employed to produce dipoles. A known eutectic method for the manufacture of metal dipoles has produced chromium rods and aluminum nickelide rods having a length/width ratio of about 100, in a range of diameters from 50A to 300A, and lengths to about 40,000A. The method involves the precipitation of one metal dissolved in another; for example, chromium precipitated from a chromium-copper melt, using a travelling temperature differential, or directional cooling from one end of a melt. The solidification rate may vary from about 0.1 to 10 cm./sec. at a temperature gradient of about 1.degree. to 100.degree. C./cm. Subsequently, the copper is dissolved in acid, leaving long thin chromium metal rods having a submicron diameter, and of various lengths. After the extraction of the metal rods, they can be further decreased in size using acid of controlled concentration. Thus, where the diameter is 500 to 1,000A, acid treatment can further decrease the diameter.

It has been found that long rods may be chopped into shorter lengths in a suitable range by the following procedure. The metal rods are suspended in an inert fluid. The fluid may comprise water, alcohol, or an ester with or without dissolved polymer. The polymer helps to suspend these particles. The suspension is placed in a high speed blender, the revolving metal blades of which cause strong shear and impact forces to occur. Most of the cut rods do not appear to be bent but appear to be cleanly sheared into shorter straight rods.

It is theorized that the particles are cut by high speed impact or possibly torn asunder by opposing turbulent shear forces. Whatever the physical explanation may be, the rod lengths varying from about 700A up to the maximum particle length are placed in suspension. The particles are then separated into size ranges by fractional centrifugation or by electrophoresis. The larger particles, in the case of centrifugation, are thrown down as the first centrifugate and then successively smaller ranges of particles are thrown down into the centrifugate. Finally, there remains only smaller particles of irregular shape of a very small length/width ratio. A suitable intermediate ratio range is selected and the process may be repeated, using a smaller viscosity fluid if required, to get a narrower range of ratios. These particles are then filtered and washed with solvent and vacuum dried.

Where glass is used as the final matrix, the selected dipole rods are then mixed with finely powdered glass frits, of a suitable composition well known in the art. This mix is melted, stirred, debubbled, and cast to form sheets. These sheets, when heated to a high viscosity, may be drawn by stretching to orient the dipolar particles. Alternatively, the sheets may be melted or softened at high temperatures to a low viscosity, and the dipole rods oriented by electrical means. To produce a light polarizing sheet, the orientation is carried out to position the dipoles parallel to the surface.

To produce a uniaxial polarizer of the type described in my U.S. Pats. Nos. 3,205,775 and 3,350,982, the dipole rods are oriented normal to the surface of the sheet. To obtain a wedge-shaped transmission pattern requires a combination of two sheets in which the dipole rods are oriented respectively parallel to, and normal to the surface; that is, a combination of uniaxial and linear polarizing sheets.

Various techniques known in the art of glass making may be employed. For example, continuous drawing methods may be employed using a glass melt containing dipoles, and the drawing and rolling of the glass will cause the orientation of the dipolar particles to produce polarized glass. Various selected size ranges may be employed to produce sharp absorption and reflection bands.

To polarize the entire visible spectrum, selected length ranges of dipole rods varying in length from about 1,000A to 2,500A may be employed. To produce glasses which will polarize the infrared, larger particles are employed from about 2,100A up to about 10,000A in length to polarize infrared in the range of 1 to 30 microns. Thus, broadly speaking, the length of the dipoles may range from 1,000A to 10,000A, the ultimate size being determined by the particular end use.

Polarizers may also be made by incorporating these dipolar rods in the same selected size ranges in polymers normally employed for polarizing materials; i.e. polyvinyl alcohol, polyvinyl butyral, and these subjected to mechanical elongation to orient the particles in a manner well known in the art.

Another method which may be employed advantageously is the incorporation of the particles in a polymer solution, such as a silicone polymer solution, which has a high degree of stability at an elevated temperature. This solution may be employed by flowing or spinning a coating onto a glass surface, for example, a lens, which is subjected to an electrical field just before it dries, while the dipoles are free to turn. The dipole rods may be oriented with their long axes parallel to the surface by applying an electrical field parallel to the surface or the dipoles may be oriented normal to the surface by the application of an electrical field normal to the surface.

The polymeric coating containing the dipoles is set by allowing the fluid to evaporate. The dipoles may be placed in a monomer and oriented by electrical fields while the monomer is setting. Alternatively, the monomer may be stretched when partially polymerized to orient the particles by mechanical shear forces and then finally set by completing the curing process.

As illustrative of the various methods which may be employed in producing conductive dipoles, the following examples are given:

EXAMPLE 1

Flake Dipole Suspensions

To prepare metallic flakes for use as dipole particles, a layer of metal is deposited, for example, by known vacuum deposition techniques, on a film of plastic or other convenient substrate, and the substrate is subsequently dissolved, thus causing the metal film to be suspended as a flake in the solvent. The suspended film is then chopped to flakes of the desired size by using a Waring blender and the desired sizes separated by differential centrifugation.

EXAMPLE 2

Ultrathin Aluminum Flake Suspensions

A novel method of preparing ultrathin aluminum flake suspensions uses aluminum flakes 1-17 microns in diameter, and 0.1 to 1 micron in thickness as the starting point. A suspension is prepared by adding 48 grams of the aluminum flake material to 300 cubic centimeters of di-isooctyl adipate. This mixture is then shaken and poured into a 500 cubic centimeter graduated cylinder and allowed to settle. Most of the aluminum flakes then settle to the bottom of the graduate. However, a small portion of the flakes remains suspended in a thin layer at the top of the graduate. This top layer then comprises ultrathin aluminum flakes, approximately 0.1 micron in thickness, which are then recovered.

Thus, by means of this flotation method, the 0.1 micron thickness flakes are separated from the thicker flakes. These ultrathin flakes may be further separated and concentrated by centrifuging.

Another way to make thin flakes of aluminum or the like is to coat a thin rubber sheet with a film of aluminum by exposing it to aluminum vapor, until a film of approximately 0.01 micron thickness has been built up. This sheet is then stretched to break up the surface into flakes of aluminum. The underlying rubber sheet is next dissolved in order to place the flakes in suspension. Finally, the large flakes are eliminated, and the small flakes in the desired size range are concentrated, by centrifugation. This technique can also be employed using polyvinyl alcohol or polyvinyl chloride sheets by heating the sheets after the coating step, to facilitate their being stretched.

The resulting suspension is suited for use in those embodiments of the invention which require a suspension of dipoles in the form of flakes, for example, the Reflective-Absorptive devices, discussed in the referenced copending application.

EXAMPLE 3

Needle-like Metal Dipole Suspensions

For the production of a metal rod dipole particle, a convenient method is to dissolve a metal salt in a matrix of polyvinyl alcohol, cast the solution as a polyvinyl alcohol film, soften and stretch the film in known manner, reduce the metal salt to the metal by exposure of the film to a reducing liquid or gas, and finally dissolve the polyvinyl alcohol in a suitable solvent, thereby providing a suspension of metal rods.

Another convenient method of manufacturing minute metallic dipole particles is to employ a soluble thread having a diameter in the submicron range, and deposit a film of aluminum on the thread by passing the thread through a zone or chamber in which it is exposed to aluminum vapor. The thread is then wound on a spool, and sliced with a microtome. Finally, the supporting thread is dissolved in a suitable solvent, leaving the metal coating in the form of thin aluminum strips in colloidal suspension.

EXAMPLE 4

Needle-like Metal Dipoles from "Whiskers"

Needle-shaped metallic dipoles may be formed from a metal, such as gold, platinum, palladium, chromium, tin or the like, which are known to grow submicron-diameter crystal whiskers under appropriate conditions, usually from the vapor phase. These crystal whiskers may then be incorporated into fluid to form a dipole suspension. Such needles, if classified to a uniform length, may be made sharply selective as to the wavelengths of light affected by them. This property results from their large length-to-thickness ratio and resistivity, for reasons which are explained below. Such materials constitute a new class of pigments different in effectiveness and mode of operation from conventional pigments.

The factors controlling the growth of needle-like whisker dipoles are partial pressure and temperature of the metal vapor, temperature and nature of the deposition surface, and time of growth. Usually, the growth occurs best under vacuum, or inert gas such as helium or nitrogen, but, in some cases, as with gold, whiskers can be grown in air. Two gold sheets separated by a few millimeters and by a few degrees temperature difference, held in air at a temperature such as to generate an appreciable gold partial vapor pressure, will cause gold whisker crystals to grow normal to the surface of the cooler gold sheet. The dimensions of the whiskers are such as to fall within the size ranges herein specified. On cooling, the whiskers may be incorporated in a plastic film formed by coating the surface of the gold sheet, encompassing the whiskers. Upon drying, the film may be stripped away and dissolved, leaving the gold dipoles in suspension in the fluid. This process may be performed continuously using an endless belt of a material, such as stainless steel, which is initially provided with active sites for initiation of whisker growth.

EXAMPLE 5

Flat Crystals

Flakes made from crystalline material, such as lead carbonate (pearlescence), may be grown to any desired size by methods well known to the art. These flakes have an index of refraction of about 2.4, and, when placed in a fluid having an index of refraction of about 1.5, are readily aligned by an electric field, and in the equivalent of about 15-20 layers almost totally reflect visible ultraviolet and near infrared radiation, when disoriented or oriented in the plane of the cell wall or sheet; while being almost completely transparent when aligned normal to the sheet surface.

Zinc vapor will deposit submicron flat crystals on a substrate, which can be dissolved away as above described, to yield a metal flake suspension having dipolar characteristics.

Graphite forms flat hexagon flakes which, when suspended in a fluid of low viscosity, show dipolar characteristics.

EXAMPLE 6

Metal Coated Preformed Dipoles

Preformed rods of Boehmite (colloidal alumina) are metal-coated by vapor deposition. The Boehmite is in the form of minute crystalline rods or fibrils having a length of approximately 1,000A and a width of about 5A. In metal coating the fibrils, the Boehmite crystal rods are heated to various elevated temperatures while exposed to the metal vapor.

Another method is to coat Boehmite particles by chemical deposition. For example, Boehmite particles may be soaked in a solution of a metal halide or nitrate, such as gold chloride, gold nitrate or silver nitrate. The particles are washed to remove all but the adsorbed salt. The Boehmite powder is then heated to a temperature of about 300.degree. C to decompose the adsorbed salt and thus produce a coating of silver or gold metal on the Boehmite.

EXAMPLE 7

Production of Dipoles from Binary Eutectics

Metal fibers can be prepared by the unidirectional solidification of binary eutectic alloy. A well known example is the system Al-Al.sub.3 Ni. The alloy containing about 5.7 percent to 6.4 percent by weight of nickel and the balance aluminum is produced by melting together high purity aluminum (99.99 percent) and high purity nickel (99.99 percent). The melts are unidirectionally solidified using induction and resistance heating sources by maintaining a thermal gradient during cooling. Whiskers or rods of Al.sub.3 Ni are formed lying parallel to each other in the direction of solidification and dispersed through an aluminum matrix. By increasing the rate of cooling, the diameter of the needles or rods can be increased. The Al.sub.3 Ni whiskers may be extracted from the aluminum matrix by using a 3 percent solution of aqueous HCl solution. As soon as the whiskers are dislodged, they are removed rapidly from solution and are washed. The whiskers can be graded according to size by differential settling or differential centrifugation as described hereinbefore. Splat cooling may be employed by striking metal droplets against a cold surface of high heat conductivity.

Examples of other eutectic alloys are the following: --------------------------------------------------------------------------- TABLE 1

System Eutectic Comp.* Matrix Fibers* __________________________________________________________________________ Ag-Bi Bi-2.5% Ag Bi Ag-0.83% Bi Ag-Ca Ag-14% Ca Ca Ag.sub.4 Ag Ag-Pb Pb-4.7% Ag Pb Ag-0.8% Pb Ag-Sr Ag-12% Sr SrAg.sub.5 Ag Ag-Ga Ga-6.5% Al Ga Al Al-Sn Sn-2.2% Al Sn Al Au-Be Au-20% Be Be Au.sub.3 Au Au-Ca Au-13.2% Ca Ca Au.sub.4 Au Au-Na Au-17% Na NaAu.sub.2 Au Au-Sb Au-34% Sb AuSb.sub.2 Au-0.64% Sb Au-Te Te-47% Au AuTe.sub.2 Au Au-Tl Tl-27.7% Au Tl Au Au-U Au-12.5% U U Au.sub.3 Au

As will be noted, the fibers contain substantially one metal, that is, some of the compositions yield fibers which at worst contain less than 1 percent of the second metal. Of the 13 systems listed, five may yield fibers of pure or nearly pure metal in a matrix of a second pure metal, such as Ag-Bi, Ag-Pb, Al-Ga, Al-Sn and Au-Tl. There are other systems, among which is included the system Cu-Cr.

The resistivities of some of the metals are given as follows:

TABLE 2 --------------------------------------------------------------------------- Resistivities of Metals

Resistivity Element 0.times.10.sup.- .sup.6 ohm-cm. at 20.degree. C. __________________________________________________________________________ Aluminum 2.62 Antimony 39.0 Cadmium 7.5 Chromium 2.6 Copper 1.69 Gold 2.4 Indium 9.0 Iron 10.0 Lead 21.9 Palladium 10.8 Silver 1.62 Tantalum 13.1 Thallium 18.1 Titanium 3.0 Zinc 6.0

Utilizing the known resistivities of the foregoing metals, the length to width ratios of absorbing and reflecting dipoles can be calculated using equation (57) of parent application Ser. No. 378,836 now U.S. Pat. No. 3,512,876, referred to hereinabove. These calculations are summarized in Table 3 which sets forth the length to width ratios for absorbing and reflecting dipoles utilizing specified metals.

TABLE 3 --------------------------------------------------------------------------- Length to Width Ratios of Metallic Dipoles

Metal Absorbing Dipole Reflecting Dipole __________________________________________________________________________ Aluminum 23.9 7.6 Antimony 6.2 2.0 Cadmium 14.2 4.5 Chromium 24.1 7.6 Copper 29.2 9.5 Gold 25.1 7.0 Indium 12.9 4.1 Iron 12.3 3.9 Lead 8.3 2.6 Palladium 11.8 3.7 Silver 30.5 9.6 Tantalum 10.7 3.4 Thallium 9.1 2.9 Titanium 22.4 7.1 Zinc 15.9 5.0

In constructing Table 3, the ideal absorbing dipole is assumed to have a distributed R of about 80 ohms and the ideal reflecting dipole is assumed to have a distributed resistance R of 8 ohms. Values of 1.5 for "n" and 0.5 microns for .lambda. were used.

Thus, the properties of the metal dipoles can be determined beforehand, depending upon the length to width ratio and those sizes selected in accordance with the particular property desired.

Having graded the sizes of the metal dipoles, these can then be used to make a wide range of products. In this connection, reference is made to FIGS. 10 and 11 as illustrative of forming polarizer material in sheet form.

In FIG. 10, there is shown a supply roll 1 and a wind up roll 2 for a thin film substrate or web 3 of plastic material, such as cellulose acetate, cellulose acetate butyrate, acrylic, vinyl film or the like, having a thickness, for example of 0.1 to 1 mm. Film 3 passes over roller 4 where it is coated by a polymer solution 5 containing dipoles. The level 6 of the polymer solution is maintained by the feed 7, from a level sensing device such as an inverted bottle (not shown). Evaporation of solvents from the coating is initially prevented by means of the shield 8. The dipole coating layer 9 shown in FIG. 11 remains liquid for a time sufficient to enable orientation of the dipole particles 10 by an electrical field 11. An electric field parallel to the surface of the coating is maintained between a plurality of electrodes 12, 13, 14, 15, 16, etc. in the vicinity of the coating 9. To minimize the effect of the vertical component of the electric field near the electrodes, cool air may be provided in the areas 20 and 21 by ducts 22 and 23 (FIG. 11). This decreases the temperature, and increases the viscosity, of the coating layer 9 thereby preventing the dipoles from being disoriented by the vertical field component. In a similar manner, heated air may be provided in the areas 25 and 26 by the ducts 27 and 28 to decrease the viscosity of the coating 9 where the component of the electric field is most nearly parallel to the surface of the film. This enables the dipoles 10 to be aligned parallel to the surface of the coating 9. The dipoles are fixed by passing the film 3 through the evaporation chamber 30 (FIG. 10) which is provided with the input air duct 31 and the output air duct 32 containing the evaporated solvent. The duct 31 may contain a number of sections. Section 33 may be at a low temperature to freeze the particles into alignment initially while evaporation is occurring. Section 34 may be at ambient temperature to continue the evaporation of solvent and section 35 may be at a higher temperature to evaporate the residual solvent. The film emerging from section 35 over roll 36 is dry.

If an herapathite dipolar suspension is employed, the electric field 11 is preferably AC field having a frequency of 10 to 100 kHz. at an electric field intensity of 1 to 20 kv./cm. The best alignment is obtained at the greatest electric field intensity which is just under the electric breakdown strength of air. Greater electric field strengths may be employed if the entire device is pressurized to several atmospheres.

With metal dipoles in a nonionic fluid, DC or low frequency AC may be employed, in the same electric field strength range.

The herapathite composition which may be employed contains submicron selected particles prepared for example as in Example 1 in the copending application Ser. No. 378,836 previously noted.

Metal dipole suspension may, for example, be prepared as described herein. In this connection, reference is made to a technical paper entitled "Behavior of Unidirectionally Solidified Al-Al.sub.3 Ni Eutectic" by Lemkey, Hertzberg and Ford; Transactions of the Metallurgical Society of AIME, Feb., 1965, Vol. 233, pages 334-341.

In this article, it is shown that at a growth velocity exceeding 3 cm. per hour, a spaced rod-like structure occurs initially. The spacing between the rods, and the rod diameter becomes smaller as the velocity increases. The rod spacing is proportional to the inverse square root of the growth velocity. For example, extrapolation to 300 cm. per hour shows particle separation of 0.2 microns with a rod diameter of about 300A.

The thermal gradient was between 25.degree. and 37.degree. C. per cm. A greater temperature gradient, which results in smaller dipole rods, may be obtained by placing the eutectic in a small diameter tube, such as a quartz tube, having an inside diameter of 1 mm.

To achieve a dipole diameter of 50-300A, a thermal gradient of about 300.degree. C. per cm. may be used at a growth velocity of about 0.13 cm./sec. After the rods are grown, the matrix is then dissolved away utilizing an acid, such as dilute hydrochloric acid. The particles may be further decreased in size by washing them with a suitable acid, such as hydrochloric acid, until the optimum diameter and length has been obtained. The dipole rods remaining undissolved are washed with water, and then with alcohol and acetone and dispersed in a solvent containing a polymer as described above.

The invention may be employed in the coating of lenses using a spin coating technique as follows with particular reference being made to FIG. 12

The object is to apply field of the order of 200 to 300 Kv./cm. across an air gap in which the coating is placed. The purpose of the device is to obtain maximum orientations and extremely large electrodichroic ratios for coatings oriented in the plane of the surface of the lens. The effect is essentially electrostatic and the currents employed would generally be in the microampere range. The electric field is preferably applied across a distance not exceeding about 7 cms. on most lens applications, an electric field of upwards of 1 million volts being contemplated for such a distance, the voltage being AC or DC. Since the gap normally required for a field of 1 million volts is about 33 cms, the electric breakdown strength must be increased by about 5 times. This may be accomplished by placing the element to be coated and aligned in a pressure tank operating at about 5 times atmospheric pressure or approximately 75 p.s.i.

In FIG. 12, a cylindric chamber 40 is provided with a cover 41 sealed by O-rings 42. A shaft 43 passes through cylindrical chamber 40 via a sealed bearing 44, the shaft being inserted into the extending end on insulated body 45. Slip rings 46 and 47 are connected through insulated bushings 48 and 49, respectively, to terminals 50 and 51.

The bushings 48 and 49 should be large enough in diameter so that the path length between the exposed conductors and the walls on the interior is greater than that which would afford a spark breakdown path under the established interior pressure conditions. Exterior atmospheric pressure conditions can be tolerated provided bushings 48 and 49 are extended sufficiently outward to provide at least a 33 cm. total gap or they may be alternatively immersed in an insulating oil bath 52. The dipole fluid 53 is poured on lens 54 held within spin holder 54A and rotated along with electrodes 55 and 56 between which the intense electric field is established. Excess fluid is thrown off and the dipoles are oriented to very nearly parallelism. Provision should be made for the evaporation of the solvent and for the provision of additional air to carry away the evaporated solvent. This may be done with an air source pipe 57 and an exit pipe 58 connected to a valve which controls the flow of air through the chamber.

The interior 59 of the chamber is desirably maintained at a pressure of at least 75 p.s.i. before the application of the voltage. When the operation is complete, the dipolar particles are aligned and evaporation has occurred to solidify coating 53. The voltage is then turned off and the rotation of shaft 43 stopped. The pressure within the chamber is released and the top 41 removed so that the coated lens can be taken out of the spin holder and another inserted.

A polarizing medium results after fluid layer shown in FIG 12 has solidified (as by cooling if the fluid is a thermoplastic or a glass). For example, the dipoles may be metal needles, such as platinum, and the medium a low melting point low viscosity glass, such as "solder glass"

The dipole particles utilized in polarizers according to this invention differ from those of prior art polarizers, such as Polaroid "J" polarization which was an oriented herapathite suspension in cellulose acetate butyrate. The dipoles of the present invention are controlled in size and shape to close tolerances, whereas those of the prior art were of random size and shape. Consequently, polarizers produced in accordance with this invention have no perceptible light scatter. Light scatter was a particularly serious disadvantage of prior art polarizers which were a result of the process of manufacturing, which caused larger particles to be produced in situ.

As stated hereinbefore, semiconductors, as set forth, may be employed in the preparation of such dipoles as described.

Preparation of Submicron Herapathite

Crystals

To produce submicron herapathite crystals in high concentration in a low viscosity suspending fluid, which form an optically clear, non-scattering dipole particle suspension of suitable electrodichroic ratio and sensitivity, the reacting solutions should be:

1. miscible

2. near maximum concentration

3. at low viscosity

4. at low temperature

5. rapidly mixed in reacting proportions

6. violently agitated

An example follows: --------------------------------------------------------------------------- EXAMPLE A

No. 1 Parts by Weight __________________________________________________________________________ Iodine 20 Normal propanol 80 100

The iodine is dissolved in the normal propanol by heating and shaking.

No. 2 Quinine Bisulphate 32.5 Methanol 67.5 100.0

For complete solution warm with agitation in a hot water bath to about 70.degree. C.

no. 3 Nitrocellulose, 5-6 second type RS (solids) 12.5 Isopropyl Alcohol 5.5 Isopropyl Acetate 16.0 Toluol 16.0 Methanol 100.0

Solutions Nos. 2 and 3 are then heated to 70.degree. C. and used to prepare No. 4.

No. 4 Material % Solution %Solids No. 2 Quinine Bisulphate 32.5 12.5 4.06 No. 3 Nitrocellulose 12.5 60.5 7.55 Methanol 13.0 Butyl Acetate 14.0 100.0 11.61

This solution is then warmed to 70.degree. C. and pressure filtered at the same temperature to remove any small undissolved crystal which would act as nuclei for crystallization.

Solutions Nos. 1 and 4 are then mixed in proportion and rapidly mixed in a container cooled by an acetone dry-ice bath. The result is: ##SPC1##

While Solution No. 5 is being prepared, alkyl epoxy stearate (Celluflex-23), a high boiling solvent also known as a "plasticizer" is cooled in an ice bath to 0.degree. C., and added in the following proportions to make a paste containing the submicron herapathite particles in suspension: ##SPC2##

No. 6 is then mixed with a mechanical stirrer for about 10 minutes to insure complete reaction and homogenity. After this, to remove the volatile solvents, the suspension No. 6 is placed in a rotating evacuator for about 2 hours and a paste is then obtained which is substantially free from solvents except the plasticizer and which has a resistivity of at least 30 megohm-cm.

The analysis of the paste resulting from No. 6 after the volatiles have been removed is:

No. 7 % by Wt. Iodoquinine Sulphate 13.0 Nitrocellulose 16.3 Celluflex-23 70.7 100.0

As a diluent for the paste, there is then prepared:

No. 8 Xylol 80 parts Butyl Acetate 20 parts 100 parts

No. 9 No. 7 50 parts No. 8 50 parts 100 parts

A solids analysis of No. 9 is as follows:

Solids % Solids __________________________________________________________________________ Iodoquinine Sulphate 6.5 44.3 Nitrocellulose 8.15 55.7 14.65 100.0

% Solids Total 14.65% % IQS in Suspension 6.5%

No. 9 may be used directly or be centrifuged to obtain a supernatent liquid for use in an electrodichroic system.

A herapathite suspension prepared in this manner is characterized by elongated submicron crystals of herapathite, which remain in suspension without settling and which is suitable for use as a dipole particle suspension in the practice of this invention.

Chemically, herapathite is quinine trisulphate dihydroiodide tetraiodide hexahydrate, the chemical name for 4C.sub.20 H.sub.24 O.sub.2 N.sub.2 .sup.. 3H.sub.2 SO.sub.4 .sup.. 2HI .sup.. I.sub.4 .sup.. 6H.sub.2 O. The molecular weight is 2,464.

Stoichiometrically herapathite contains approximately 25.8 percent of iodine which is approximately a ratio of iodine to quinine bisulphate of 1/3.

However, I have found that the proportions can be varied from 1/2 through 1/4. This is apparently due to herapathite being a molecular compound or a mixed crystal in which the proportion of the components may vary.

Moreoever, the HI in the compound is present in the proportion of two moles of quinine to one of HI. The heating of the iodine solution No. 1 usually suffices to provide sufficient HI as set forth in the above example. The presence of HI in stoichiometric quantities is required to form a stable crystalline compound. An additional quantity of HI may be added to achieve the molar ratio set forth.

Generally, I have found the composition of Example A to be satisfactory, and this composition has been used in most of the tests.

As will be appreciated from the foregoing disclosure, the embodiments provided by the invention are many and varied. For example, as one embodiment, an article of manufacture is provided comprising a matrix having dispersed substantially uniformly at least at the surface thereof a plurality of dipoles selected from the group consisting of electrically conductive and semi-conductive material, such as metal or herapathite dipoles, the matrix being a medium capable of being in the fluid state during the initial dispersion of the dipoles whereby said dipoles are capable of rotation to a desired preferred orientation upon the application of a force field. Thus, the liquid state of the matrix may be in the form of a solution that dries during the application of the force field, or the medium forming the matrix may be one which is converted to the fluid state by the application of heat, but which is capable of hardening during the application of a force field. The matrix might be a coating applied to a surface, such as a curable plastic coating; or it might be a coating applied to a transparent substrate, such as glass or a hard plastic.

The dipoles dispersed in the matrix may have an average length of about .lambda./2n .+-. 50 percent and an average diameter ranging up to about .lambda./10n .+-. 50 percent, .lambda. being the wavelength of light and "n"the index of refraction of the matrix medium. Depending on the wavelength of the particular light striking the surface, the dipoles may range in length from about 1,000A to 10,000A.

The number of particles in a unit area of matrix medium may be determined simply by using the formula N = 8n.sup.2 /.lambda..sup.2. The interparticle spacing of the dipoles oriented in the plane of the matrix medium is generally at least about the effective cross section of the dipole divided by its average length, the effective cross section being determined by the formula: Effective cross section = .lambda..sup.2 /8n.sup.2.

Another embodiment provided by the invention is a composition of matter for a light controlling device comprising a transparent suspending medium and a plurality of dipole particles selected from the group consisting of conductive and semi-conductive material suspended in the medium, the medium being one which is capable of being in a fluid state to enable the dipoles to be rotated to a preferred orientation upon the application of a non-constant force field, the medium being then capable of being solidified at ambient temperatures during the application of the force field in order to fix the particular orientation of the dipoles desired. The type of dipole particles employed may be the same as those discussed hereinbefore.

A further embodiment is an article of manufacture in the form of a solid transparent layer of a medium having substantially uniformly dispersed therethrough said dipole particles having a preferred orientation relative to the plane of the transparent layer. The transparent layer may be a material selected from the group consisting of glass and plastic. By glass, is meant any transparent inorganic material capable of being worked into any desired shape, either by melting and shaping the glass, or by forming a coating of the glass-like material onto a transparent substrate, such as with a solution which, upon drying, leaves a glass-like coating. Similarly, by plastic, is meant any transparent organic material which is capable of being softened and shaped into any desired form or which can be employed as a solution which leaves a coating after the solution has been evaporated from a layer deposited by the solution. In any event, it is any material of the foregoing type which is capable of having a fluid state during which dipole particles dispersed through the fluid can be oriented by using a non-constant force field, which force field is maintained until it is caused to harden or cure or form a permanent layer by drying.

As another embodiment, the invention provides a polarizer comprising a solid layer of transparent medium, such as glass or plastic, having a substantially uniform dispersion therethrough of dipole particles oriented in the plane of the layer, selected from the group consisting of electrically conductive and semi-conductive particles, the particles preferably and advantageously having an average length of about .lambda./2n.+-.50 percent and a diameter ranging up to about .lambda./10n.+-.50 percent. As stated above, the dipole particles may advantageously be metallic and be spaced from each other in accordance with the preferred limitations stated hereinbefore.

The invention also provides a composite article of manufacture comprising a substrate of a transparent material having a transparent optical coating thereon, such as glass or plastic, and containing a dispersion of dipole particles similarly as described herein.

The method embodiment of the invention for producing an article of manufacture of a transparent medium having preferred optical properties resides in providing the medium, e.g. glass or plastic, in the fluid state containing a uniform dispersion of dipole particles selected from the group consisting of electrically conductive and semi-conductive material (e.g. metal dipoles), in forming a layer of the material in the fluid state, in subjecting the layer to the action of a force field whereby to orient said dipoles in a predetermined direction, and in maintaining the force field while allowing the layer to solidify. The solidification referred to may be the result of drying the fluid, allowing the fluid to harden or cure which, in the case of glass, would harden by cooling and the same is true for some plastics. However, the plastic might have a curing catalyst which causes hardening to take place while the force field is maintained.

The methods disclosed hereinabove may similarly be employed in producing a coated substrate of transparent material in which the coating may be of glass or plastic containing dipoles which is applied to the substrate in a fluid state and the dipoles similarly oriented in the plane of the coating using the non-constant force field.

A method which may be employed in effecting the orientation of dipole particles in a transparent medium resides in providing the medium as a layer in the plastically deformable state (e.g. glass or plastic) containing a uniform dispersion of dipole particles, in physically stretching the layer unidirectionally so as to orient the dipoles in the plane of the layer in the direction of stretch, and then allowing the stretched layer to congeal or harden to permanently fix the oriented positions of the dipoles dispersed in the layer.

It will be understood that in polarizers made in accordance with this invention, the flakes (e.g. aluminum flakes) are oriented normal to the surface and in parallel planes as shown in FIG. 8A. The orientation shown in FIG. 8A may be obtained by momentarily applying a pulsed electric field along the Z-axis, followed immediately by a pulsed electric field along the X-axis, whereby the particles are oriented along the respective axes. The pulses are applied sufficiently rapidly, for example at a repetition rate of about 1,000 per second so that the flakes do not have a chance to disorient between successive pulses. Thus, the plane of substantially each of the flakes, when oriented, may be parallel to two of the axes. For example, the plane of substantially each of the oriented particles may be parallel to the plane of the layer, or normal thereto.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

Claims

What is claimed is:

1. A film, sheet or block of material comprising a matrix having dispersed substantially uniformly therethrough a plurality of electro-optically responsive dipole particles selected from the group consisting of electrically conductive and semi-conductive material and dichroic crystals, said matrix comprising a medium having separate fluid and solid states and being in the fluid state during the initial orientation of the dipoles, and said dipoles being rotatable to a predetermined desired orientation upon the application of a force field.

2. The material of claim 1, wherein the dipoles are metallic.

3. The material of claim 1, wherein the dipoles have an average length of about .lambda./2 n .+-. 50 percent and an average diameter ranging up to about .lambda./10 n .+-. 50 percent, .lambda. being the wavelength of light and "n" the index of refraction of the matrix medium.

4. The material of claim 3, wherein the dipoles range in length from about 1,000A to 10,000A.

5. The material of claim 4, wherein the number of particles per unit area is at least the reciprocal of the effective cross section per particle.

6. A material in accordance with claim 1, wherein said material comprises a transparent optical coating on a substrate of transparent material, said coating having said dipole particles oriented in the plane thereof, said dipole particles having an average length of about .lambda./2 n .+-. 50 percent and an average diameter ranging up to about .lambda./10 n .+-. 50%, where .lambda. is the wavelength of light and "n" the index of refraction of the transparent coating.

7. The material of claim 6, wherein the substrate and the coating are selected from the group consisting of glass and plastic.

8. The material of claim 6, wherein the dipole particles are metallic.

9. The material of claim 8, wherein the dipole particles have an average length of about 1,000A to 10,000A.

10. The material of claim 9, wherein the number of particles per unit area is at least the reciprocal of the effective cross section per particle.

11. A film, sheet, or block of matter for a light-controlling device comprising a transparent suspending medium and a plurality of dipole particles selected from the group consisting of conductive and semi-conductive material, and dichroic crystals, suspended in the medium, said medium having separate fluid and solid states and being in a fluid state to enable the dipoles to be rotated to a predetermined orientation upon the application of a force field, and said medium being solidified to permanently fix the rotational position of the dipole particles.

12. The matter of claim 11, wherein the transparent suspending medium is selected from the group consisting of glass and plastic.

13. The matter of claim 12, wherein the dipole particles have an average length of about .lambda./2 n .+-. 50 percent, and an average diameter ranging up to about .lambda./10 n .+-. 50 percent, .lambda. being the wavelength of light and "n" the index of refraction of the suspending medium.

14. The matter of claim 13, wherein the dipoles range from about 1,000A to 10,000A in length.

15. The matter of claim 14, wherein the dipole particles are metallic.

16. A film, sheet or block of material comprising a solid transparent layer of a medium having substantially uniformly dispersed therethrough dipole particles selected from the group consisting of conductive and semi-conductive material, and dichroic crystals, said particles having a preferred orientation relative to the plane of the transparent layer, and wherein the dipoles have an average length of about .lambda./2 n .+-. 50 percent, and an average diameter ranging up to about .lambda./10 n .+-. 50 percent, .lambda. being the wavelength of light and "n" the index of refraction of the transparent medium.

17. The material of claim 16, wherein the dipoles are metallic and have an average length falling within the range of about 1,000A to 10,000A.

18. The material of claim 16, wherein the umber of particles per unit area is at least the reciprocal of the effective cross section per particle.

19. A polarizer comprising a solid layer of transparent medium having a substantially uniform dispersion therethrough of dipole particles oriented in the plane of said layer selected from the group consisting of electrically conductive and semi-conductive particles, and dichroic crystals, said dipole particles having an average length of about .lambda./2 n .+-. 50 percent and an average diameter ranging up to about .lambda./10 n .+-. 50 percent, where .lambda. is the wavelength of light and "n" the index of refraction of the transparent material.

20. The polarizer of claim 19, wherein the transparent material is selected from the group consisting of glass and plastic.

21. The polarizer of claim 19, wherein the dipole particles are metallic.

22. The polarizer of claim 21, wherein the dipole particles have an average length of about 1,000A to 10,000A.

23. The polarizer of claim 22, wherein the number of particles per unit area is at least the reciprocal of the effective cross section per particle.

24. A polarizer comprising a layer of transparent material containing a uniform dispersion of flake particles selected from the group consisting of electrically conductive and semi-conductive material, and dichroic crystals, the plane of the layer being referenced to a coordinate system having three mutually perpendicular axes described as the X-, Y- and Z-axes, and the flakes being oriented such that the plane of substantially each of the flakes is parallel to a plane formed by two of said axes.

25. The polarizer of claim 24, wherein the flakes are substantially normal to the plane of the layer.

26. The polarizer of claim 25, wherein the flakes are aluminum.