JPH0134369B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to light valves and, more particularly, to improvements in liquid suspensions of particles contained within light valve cells. Light valves have been used for over 40 years for light modulation. In U.S. Pat. No. 1,955,923 to Dr. Edwin Land, a light valve is made of two transparent sheets of insulating material separated by a small distance and is used to suspend small particles in a liquid suspending medium. It is defined as a cell containing a turbid liquid. In practice, suspensions also include polymeric stabilizers dissolved in the liquid suspending medium to prevent particle agglomeration.
Early in the development of light valves, nitrocellulose was proposed as a polymeric stabilizer. Recently, U.S. Patent No.
No. 4,164,365 discloses polymeric stabilizers in the form of copolymers. In the absence of an applied electric field, the particles in a liquid suspension have a random Brownian motion, and therefore the light rays passing through the cell will be reflected, depending on the quality and concentration of the particles and the energy content of the light. transmitted or absorbed. When an electric field is applied through the suspension in the light valve, the particles are aligned and, for many suspensions, most of the light can pass through the cell. Light valves have been extensively described in the literature. See US Patent Nos. 1955923, 1963496, 3512876 and 3773684. Donal, Langmuir and Goldmark in early television
thoroughly investigated the use of light valves in black-and-white and color television. US Patent No.
No. 2290582, No. 2481621, No. 2528510 and No.
Please refer to No. 2645976. A more modern use of light valves is as alphanumeric displays. Light valves have also been proposed for use in windows, glasses, etc. to regulate the amount of sunlight that passes through them. Certain esters, nitrobenzene, oils,
Various liquids have been proposed, such as other liquids. See US Pat. No. 1,961,664, US Pat. No. 2,290,582, and others. Similarly, a wide variety of inorganic and organic particles have been proposed for use in light valves, such as mica, aluminum, graphite, metal halides, perhalides of alkaloid salts. Although prior art light valves have had varying degrees of success in modulating light and preventing particle agglomeration during repeated on-off cycles, to date light valve liquids that are in gravitational equilibrium have not been tested. No suspension was obtained. Therefore, prior art light valves exhibit settling of particles over long periods of time. This creates a density gradient within the cell, with the top of the cell being less dense than the bottom. In extreme cases, there is not enough particle density in the top of the cell to provide sufficient contrast between the on and off states. The present invention provides a light valve comprised of cells containing a gravity stable light valve suspension. In particular, the light valve suspension of the present invention comprises particles of an alkaloid salt perhalide or polarizing metal halide or perhalide suspended in a liquid suspension medium and particles of an alkaloid salt perhalide or polarizing metal halide or perhalide dissolved in the liquid suspension medium. and a polymeric stabilizer effective to inhibit particle agglomeration, the liquid suspending medium comprising:
an electrically resistive, incurable, low molecular weight fluorocarbon liquid (described in more detail below) having a specific gravity of at least about 1.5 at room temperature (20°C) and an electrically resistive organic liquid miscible with the fluorocarbon liquid. Thus, the suspension is substantially in gravitational equilibrium. The inventor's “Light Valve Containing Improved Light Valve
Valve Suspension)” in October 1978.
Halogenated liquids are proposed for use in light valves in US patent application Ser. No. 956,417, dated 31st.
However, neither this inventor's application nor any prior art known to the inventor describes the use of a light valve liquid suspension as defined in the claims of the present invention. It does not imply, nor does it imply. The particles in the liquid suspension are preferably perhalides of alkaloid acid salts, preferably polarizing alkaloid acid acid halides [as used herein, the term "alkaloid" refers to Hackh) Chemical Dictionary (Chemical
4th Edition, McGraw-Hill Book Company, New York, 1969]. Preferably, the alkaloid moiety is
quinine alkaloids as defined in "Dictionary" (above). U.S. Patent No. 2,178,996,
No. 2289712 details the use of perhalides of quinine alkaloid salts, and these perhalides are useful in the present invention. Examples of useful alkaloid acid perhalides include heterocyclic organic nitrogen bases such as pyridine, picoline, diphenyloxazole, quinoline, quinaldine; quinine, cinchonidine, hydrocinchonidine, hydrocinchonine and other quinine alkaloids. and perhalides of acid acids such as toluidine. Most preferably, the quinine alkaloid is 1978
Hydrogenated quinine alkaloid acid salt perhalides such as dihydrocinchonidine sulfate periodide described in U.S. Pat. Quinine bisulfate periodide (herapathite) is also useful. Alternatively, the particles may be polarizing metal halides or perhalides, such as cupric bromide and purpureocobalt chloride sulfate periodide as described in Land US Pat. No. 1,956,867. The shape of the particles used in the light valve suspension must be such that the particles block more light in one orientation than in another orientation. Particles in the form of needles or rods or in the form of small pieces or thin flakes are suitable. Preferably the particles are polarizing crystals. This is because a relatively small concentration of polarizing crystals in suspension provides a relatively large change in optical density between the activated and inactivated states of the light valve. The fluorocarbon liquid used in this invention is a liquid low molecular weight fluorocarbon polymer. In order to obtain the polymer in liquid state, the polymer is usually an oligomer, which can be a homopolymer or a copolymer or a telomer. Suitable fluorocarbon liquids include low molecular weight homopolymers of chlorotrifluoroethylene, bromotrifluoroethylene, hexafluoropropylene, copolymers of tetrafluoroethylene and hexafluoropropylene, backbones consisting of _-CF2- units and pendant -OC _o F _2o+1 groups, where n is generally 1 to 4, and the like. In each case,
The fluorocarbon liquid is comprised of at least about 50% of its total atoms, preferably at least about 60% halogen atoms, and preferably at least about 75% of its halogen atoms are fluorine atoms, with the balance being chlorine atoms and/or bromine atoms. It is. To provide the basis for providing a suspension in substantial gravity equilibrium, the fluorocarbon liquid must be electrically resistive and have a specific gravity at room temperature of at least about 1.5, preferably greater than about 1.7. It has to be something. The final adjustment of the specific gravity of the liquid suspending medium is as detailed below.
This is accomplished through the use of an organic liquid that is miscible with the fluorocarbon liquid. Additionally, the fluorocarbon liquid must be chemically inert so as not to adversely affect particles in suspension or parts of the light valve such as spacers, sealants, and coatings on the walls of the light valve cells. In addition to these requirements, the fluorocarbon liquid must have a high boiling point, exceeding 100°C;
It is therefore desirable for the light valve cell to have a low vapor pressure so that it does not "swell" due to increased internal pressure at high temperatures. Fluorocarbon liquids must be safe for use. Therefore, it is preferred that the fluorocarbon liquid be nonflammable and have little or no toxicity. Additionally, the fluorocarbon liquid remains in a liquid state over an operating range of -40°C to 85°C, a temperature range that includes almost all light valve applications, so that the fluorocarbon liquid remains below -50°C, preferably above about -50°C. It is advantageous to have a lower pour point. For certain applications, such as displays for indoor use only, a narrower range may be acceptable. In most cases, fluorocarbon liquids have low viscosities at room temperature, especially when intended for use in low temperature light valves, such as outdoor displays and windows. This allows the light valve to respond fairly quickly when turned on and off, even at the lower end of the desired temperature range.
In some cases, high viscosities may be appropriate. Generally, fluorocarbon liquids are polymers having only a few monomeric fluorocarbon repeating units, such as dimers or trimers or tetramers. In some cases, more than 4 units of polymer may be present, and the number of repeating units is not critical as long as the polymer is in the liquid state. Often, polymerization methods give mixtures of oligomers, such as mixtures of dimers and trimers, but
If the mixture has the desired properties, the mixture can be used as is without separation into individual polymer species. As is known, the higher the degree of polymerization, the more
Molecular weight, boiling point, viscosity, and pour point increase. Also,
The more carbon atoms in the monomer, the more rapidly these properties increase with increasing degree of polymerization. Given these trends and the preferred properties of fluorocarbon liquids, a particular liquid can be selected empirically without undue experimentation. Presently preferred for use as fluorocarbons are bromotrifluoroethylene and oligomers of chlorotrifluoroethylene. These low molecular weight polymers are odorless, non-flammable, inert, electrically resistive, low toxicity, non-corrosive liquids; these polymers are polymerized from bromotrifluoroethylene or chlorotrifluoroethylene and are completely halogen-free. are produced by stabilizing the polymer to provide modified end groups. Halocarbon Products Corporation of Hatsukensatsu, New Jersey, U.S.A.
Hackensack has released liquid oligomers of bromotrifluoroethylene and chlorotrifluoroethylene as BFC Fluid, respectively.
and Halocarbon Oil
It is sold under the product name. Low molecular weight liquid oligomers of chlorotrifluoroethylene having a specific gravity of about 1.6 to about 2.0 at room temperature and suitable chemical and physical properties are prepared by polymerizing chlorotrifluoroethylene to the desired extent. be able to. The terminal groups must be fully halogenated and inert to provide maximum stability. Halo Carbon Products Corporation is 0.8/
Halocarbon oils sold under the names 100, 1.8/100, 4-11, 11-14, and 11-21 have relatively low viscosity. Such polymers are also high boiling, with initial boiling points of 135°C to 260°C, and therefore low vapor pressures. A more complete description of the relevant properties of these preferred polymers is in the table below. High molecular weight liquid polymers of chlorotrifluoroethylene are also commercially available and these polymers have higher viscosities.

[Table] Among the halocarbon oils shown above, the one currently preferred for use is halocarbon oil 0.8/100. Low molecular weight liquid polymers of bromotrifluoroethylene generally have a specific gravity ranging from approximately 2.2 to 2.4 or more at room temperature, depending on the degree and temperature of polymerization. Liquids with high specific gravity are advantageous when using relatively high specific gravity particles in the light valve suspension or when it is desired to use less fluorocarbon liquid. When using liquid polymers of bromotrifluoroethylene, the thermal stability of the telomer is improved if the end groups of the polymer contain only chlorine and fluorine, preferably only fluorine, as halogen atoms. Mixtures of fluorocarbon liquids can be used, such as mixtures of chlorotrifluoroethylene oligomers and bromotrifluoroethylene oligomers. The light valve suspension of the present invention includes a protective polymer to prevent particle agglomeration during light valve use. As is known, the protective polymer must be soluble in the liquid suspension medium and must be capable of binding to the particles. In some cases, the first polymer is bound to the particles but insoluble (or less soluble than desired) in the liquid suspension medium, and the second polymer is bound to the first polymer and insoluble in the liquid suspension medium. 2, which is sufficiently soluble to provide good dispersion of the particle-protected polymer complex in the liquid suspending medium.
Species protective polymers can be used. The protective polymer forms a large sterically protected area around the particles, thus acting to inhibit agglomeration. Copolymers of the type described in U.S. Pat. No. 4,165,365 are
Can be used as a protective polymer. These copolymers are copolymers of at least two different monomers, at least one of the monomers
the species has sterically unhindered functional hydroxy and/or acidic groups, and at least one of the monomers has a branched group, the unhindered species furthest from the backbone of the copolymer. The distance to the hindering functional group is less than the distance from the backbone to the end group of the branched group, and the branched groups of the copolymer are sufficiently soluble that the copolymer as a whole is substantially present in the liquid suspension medium of the light valve suspension. It has become soluble in The functional groups carried by the copolymer are provided by copolymerizable monomers containing such groups. Thus, acidic groups are provided by using ethylenically unsaturated acids such as acrylic acid, methacrylic acid, fumaric acid, mesaconic acid, maleic acid, etc. or acrylonitrile and other acidic monomers. Hydroxy groups can be provided by hydroxyalkyl esters of ethylenically unsaturated acids, such as hydroxyalkyl acrylates or hydroxyalkyl methacrylates. Similarly, other acidic groups such as sulfonic acid groups, functional groups such as cyano groups, isocyanato groups, etc. can be provided by using suitably substituted ethylenically unsaturated monomers. Basic groups can be provided by amine or amide groups if they are compatible with the particles. Branching monomers for the copolymer are selected as described in my US Pat. No. 4,164,365. Preferably, the branching monomer does not contain functional groups that bind to the particles. It is also preferred that the branching monomer make up the majority of the copolymer by weight and be the highest molecular weight monomer.
Suitable branching monomers include branched alkyl esters of ethylenically unsaturated acids, such as 2-ethylhexyl acrylate, bis-2-ethylhexyl fumarate, 5,5-diethylhexyl acrylate, 3,5,5-trimethyl acrylate. It's hexyl. However, one or both of the functional group-containing monomer and the branching monomer can be an ether or a cyclic monomer. Particularly useful monomers are halogenated monomers, especially fluorinated monomers, which can facilitate achieving solubility of the copolymer in a liquid suspension. Particular copolymers useful in the present invention are described in US Pat. No. 4,164,365. When nitrocellulose is used as the protective polymer, as is required for dihydrocinchonidine sulfate periodide particles, the particle-nitrocellulose complex is not dispersed in the liquid suspension medium. In such cases, the nitrocellulose preferably comprises a first pendant, branched, carbon-carbon chain, optionally interrupted with oxygen atoms, and a hydroxy group, optionally interrupted with oxygen atoms. The copolymer should be used with an auxiliary organic copolymer having a second pendant carbon-carbon chain with the most remote hydroxy group being closer to the main chain of the copolymer than the terminal branching group. Useful copolymers include hydroxyalkyl acrylates (where alkyl is an alkyl of 1 to 3 carbon atoms) and sec- and tert-alkyl acrylates (where alkyl is an alkyl of 4 to 12 carbon atoms). It is a copolymer with A third comonomer, such as an unsaturated acid, can be used but is usually unnecessary. Copolymers useful as auxiliary copolymers can be made by the method of US Pat. No. 4,164,365. Particles - Hydroxy groups of the auxiliary copolymer associated with the nitrocellulose complex and the resulting particles -
The nitrocellulose-copolymer ternary complex can be well dispersed in liquid suspension media. Generally, as the hydroxy content of the auxiliary copolymer increases, its affinity for nitrocellulose increases, but the solubility of the protective polymer in the fluorocarbon liquid decreases. The organic liquid that is miscible with the fluorocarbon polymer aids in dissolving the protective polymer into the liquid suspension medium. A useful working range for the auxiliary copolymer is about 10 to about 30% hydroxy monomer and about 90 to about 70% branched monomer. A currently preferred copolymer is a 10-30% 2-hydroxypropyl acrylate/70-90% 2-ethylhexyl acrylate copolymer with a molecular weight of 50,000-300,000. The electrically resistive organic liquid that is miscible with the fluorocarbon liquid serves two primary purposes. The first and most important objective is that through the use of miscible organic liquids, the specific gravity of the liquid suspension medium can be matched to the specific gravity of the particle-protected polymer complex.
Generally, such composites have a specific gravity that is lower than the specific gravity of the fluorocarbon liquid, and the low specific gravity miscible organic liquid serves to lower the specific gravity of the liquid suspending medium. Second, miscible organic liquids can be used, especially when the polymer dissolves poorly in the fluorocarbon liquid, as is the case with nitrocellulose.
Assists in dispersing the particle-protected polymer complex into the liquid suspension medium. Various organic liquids can be used as the miscible organic liquid. Useful liquids include esters of aliphatic and aromatic acids, such as isopentyl acetate,
Included are alkyl or phenyl acetates such as p-nonylphenyl acetate, dioctyl phthalate, diisodecyl adipate, dioctyl sebacate, aromatic hydrocarbons such as benzene, toluene, silicones (organosiloxanes). Generally, the miscible organic liquid is present in an effective amount to provide gravitational balance and aid in dispersing the particle-protected polymer complex into the liquid suspending medium. Using more than this effective amount is unnecessary for solubility and can unduly lower the specific gravity of the fluorocarbon liquid/auxiliary liquid mixture. At present,
It is preferred that the fluorocarbon liquid is at least about 40%, preferably at least about 60%, by weight of the liquid suspending medium, and thus the amount of miscible organic liquid is selected accordingly. Even within these ranges, care must be taken to properly balance solubility and gravity requirements. Thus, when using particle-polymer composites in which the polymer moiety has only marginal solubility in the fluorocarbon liquid, large amounts of the liquid suspending medium may be used, such as to make the specific gravity of the liquid suspending medium too low for gravitational equilibrium purposes. Miscible organic liquids may be required. This means that miscible organic liquids are generally around 0.85
This is possible considering the fact that it has a specific gravity of ~1.2. Generally speaking, each light valve suspension has one specific gravity that reaches gravitational equilibrium. Ideally, a suspension in perfect equilibrium never settles. In reality, small deviations from the ideal values may be allowed, so that small compromises are inevitable. It is also clear that the specific gravity at which gravitational equilibrium is reached for a given suspension depends on the choice of particles, protective polymer, liquid suspending medium and other substances that can be dissolved in the liquid suspending medium. , and therefore the specific gravity for obtaining gravitational equilibrium varies from suspension to suspension depending on the particular parameters of a given suspension. Similarly, if the amount of protective polymer used in the suspension is varied, for example to change the viscosity of a given suspension to increase or decrease the response time, the specific gravity required for gravitational equilibrium will also be varied. The gravitational balance of light valve suspensions is easily determined with a simple test. In this test, 10 ml of light valve suspension is centrifuged for 1 hour at 2500 rpm in a centrifuge tube. Gravity equilibrium has been achieved if less than 10% of the particles settle after the tube is removed from the centrifuge. As is clear, in order to obtain a gravity-stable light valve suspension, the particles and the protective polymer and the fluorocarbon liquid and the miscible organic liquid must be combined not only with respect to their specific gravity, but also with respect to their physical, chemical, and electrical properties. The optical properties and optical properties must also be carefully selected. For example, it makes no sense to provide a gravity-stable light valve suspension where the particles will aggregate after only a few cycles of on-off operation.
Thus, the light valve suspension of the present invention provides a gravity stable, non-cohesive light valve suspension with a desired rapid response time and a desired wide range of operating temperatures. , combining the sometimes conflicting requirements of particles, protective polymers, and liquid suspension media. In this specification and claims, all parts and ratios are by weight unless otherwise specified. Example 1 A Dihydrocinchonidine sulfate periodide-
(DCSI) - Production of nitrocellulose composite 1 part dihydrocinchonidine, 1 part methanol,
To this solution was added 0.32 parts of 97% H ₂ SO ₄ and the solution was evaporated to dryness. The obtained dihydrocinchonidine sulfate is in the form of a white powder. Dihydrocinchonidine sulfate 2.12g, 2-ethoxyethanol 10.0g, water 5.0g, CHCl ₃ 3.0
Solution A was prepared by dissolving in g. Solution B was a 33 1/3% 2-ethoxyethanol solution of nitrocellulose. This nitrocellulose has a low viscosity (18-25 cps) type and a high viscosity (15-20 cps) type.
It is a 50:50 mixture of types. Before the nitrocellulose is dissolved in 2-ethoxyethanol, all isopropanol and/or other solvents must be dried off.
Otherwise, later during the method described here
This will generate large DCSI particles. Mix solution A and 20.0g of solution B to make solution C.
I made it. After dissolving 0.3 g of hydrated Cal ₂ in 10.0 g of water, 1.54
Add l ₂ g and 21.0 g of tricresyl phosphate,
Solution D was prepared by shaking for 15 minutes. Solutions C and D were mixed vigorously in a Waring blender and mixed with a polyethylene spatula along the inner wall of the cup, counter to the flow direction of the blender. In 2-4 minutes, a deep blue viscous paste with golden spots was obtained. Add this paste to 0.3048mm (12 mil)
The mixture was stretched as a film and dried in air for several hours until no volatile solvent odor was detected. The dried paste was placed in an electric mortar grinder and ground for about 1/2 hour. Next, 50 g of isopentyl acetate was added while grinding in a mortar grinder, and then mixed in the mortar grinder for an additional hour. Next, the obtained suspension was taken out of the mortar and subjected to ultrasonic stirring treatment for 17 hours. B Production of DCSi suspension 40 g of the suspension from A above was shaken,
It was mixed with 90 g of isopentyl acetate. This diluted suspension was divided into four 50 ml centrifugal sedimentation tubes and centrifuged at 2500 rpm for 10 hours to settle most of the particles near the bottom of the tubes. After discarding the clear liquid above the particles in each tube, 7 g of isopentyl acetate was added to each tube. After stirring the contents of each tube with a spatula, ultrasonic stirring treatment was performed for 17 hours, and then the contents of each tube were divided into two 25 ml centrifugal sedimentation tubes. After centrifuging the 25 ml tube at 2500 rpm for about 6 hours, most of the particles settled near the bottom of the tube again, and the liquid above the particles was discarded. Next, 2 g of isopentyl acetate was added to each centrifuge tube, and the contents were stirred with a spatula. After the centrifuge tubes were subjected to ultrasonic agitation for 17 hours, the contents from the two centrifuge tubes were combined into one 10 ml centrifuge tube and centrifuged at 2500 rpm for about 60 minutes. The top suspension was poured into a vial and stored, and the bottom was discarded. A portion of the stock suspension was injected into a test cell with a 33 mil spacing between opposing walls. This suspension was applied at a frequency of 10KHz to 30 volts/mil peak-peak.
to−peak) electric field was applied. The optical density of the cell without an electric field was 3.0, and the decay time was 50 milliseconds. Disintegration time 40 to suspension
It is measured by applying an electric field for milliseconds and continuously measuring the optical density from the time the electric field is interrupted until the optical density reaches 3.0 again. The time required for the optical density of the suspension to return to 3.0 is the disintegration time. This suspension tended to settle after long periods of use and was therefore not in gravitational equilibrium. However, this suspension performed perfectly well as a light valve suspension in all other respects. C. Addition of fluorocarbon to the suspension 4 g of the DCSI suspension prepared in B above and 20% adipic acid of a copolymer of 2-ethylhexyl acrylate (85%) and 2-hydroxypropyl acrylate (15%) 4 g of dioctyl solution were mixed with stirring in a 50 ml beaker.
Halocarbon oil 1.8/100 was gradually added to this beaker while stirring, and the specific gravity of the suspension was monitored. Addition of halocarbon oil was stopped when the specific gravity of the suspension reached 1.54. This was equivalent to approximately 31g of halocarbon oil. Other tests have shown that for DCSI-nitrocellulose-2-ethylhexyl acrylate/2-hydroxypropyl acrylate copolymer and halocarbon oil 1.8/100, a specific gravity of the suspension of 1.54 means that gravitational equilibrium has been reached. I understand. Finally, as a preferred technique, the suspension was ultrasonically stirred for at least 17 hours. When the resulting suspension was checked for gravitational equilibrium using the test method described above, less than 5% of the particles were observed to settle. Distance between opposing transparent coatings: 0.127 mm (5
A test cell (Mill) was filled with the suspension and tested for use as a light valve suspension. The results were as follows. Optical density with no voltage applied 2.3 Contrast ratio at 40 volts RMS and 60 Hz 20:1 Decay time <600 ms These results demonstrate that gravity-stable suspensions produce high-density images when the light valve is off. It is very suitable for use in light valves as it gives a high contrast between the on and off states and has an extremely fast response time, thus allowing the light valve to open and close quickly. It is shown that. Example 2 Solution A was prepared by dissolving 1.65 g of quinine bisulfate in a mixture of 5 g of methanol, 5 g of chloroform, and 10 g of n-propanol and stirring until clear. Add 2-acrylic acid to this solution.
A copolymer of ethylhexyl and acrylic acid (monomer weight percent of 90% and 10%, respectively) was added and dissolved into the solution. To prepare solution B, Bil ₃ 0.04g, CaCl ₂ 0.07
g, n-propanol 10 g, 57% HI aqueous solution 0.13
g and the mixture was subjected to ultrasonic stirring for about 15 minutes before adding 1.06 g of iodine and 15 g of dioctyl sebacate. Solution B was prepared by ultrasonically stirring the resulting solution for about 1 hour. Solution A and Solution B were mixed together at high speed in a Waring blender and the resulting quinine bisulfate perhalide paste was recovered and prepared as described in Example 1.
It was spread on a glass plate and dried. 150g of isopentyl acetate from the above dried paste
A concentrated suspension of quinine bisulfate perhalide was prepared by dispersing the quinine bisulfate perhalide in the following manner and further diluted to produce a gravity equilibrium suspension as follows. % Concentrated Suspension 4.50 2-Ethylhexyl 2-cyano-3,3-diphenyl acrylate 2.96 1-phenylheptane 4.70 Halocarbon Oil 1.8/100 87.84 100.00% Tested in a test cell with an electrode spacing of 0.8382 mm (33 mils) When unactivated, this suspension has an optical density of 3.0 and a peak of ~500 volts.
It is 1.0 when activated at peak voltage.
The specific gravity of this suspension is approximately 1.70.

Claims (1)

Claims: 1. A light valve comprising a cell containing a suspension of particles in a liquid suspension medium, wherein the light valve suspension comprises an alkaloid salt suspended in the liquid suspension medium. perhalide or polarizing metal halide or perhalide particles and a protective polymer effective to inhibit agglomeration of the particles dissolved in the suspending medium; the medium has a specific gravity of at least about 1.5 at room temperature and is made up of at least about 50% of its atoms of halogen atoms, at least 60% of the halogen atoms being fluorine and the remainder being chlorine and/or bromine; an electrically resistive, inert, low molecular weight, liquid fluorocarbon polymer and an electrically resistive organic liquid miscible with the fluorocarbon liquid, the fluid suspending medium suspending the particles in substantial gravitational equilibrium; A light valve characterized in that it is effective for causing 2. The light valve of claim 1, wherein the fluorocarbon polymer is an oligomer. 3. The fluorocarbon polymer is a low molecular weight homopolymer of chlorotrifluoroethylene, bromotrifluoroethylene, and hexafluoropropylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, and _-CF2-
Claims 1. Polyfluoroalkoxy polymers having a main chain of units and pendant -OC _o F _2o+1 groups, where n is generally from 1 to 4. The light valve according to item 1. 4. The light valve of claim 3, wherein the fluorocarbon polymer has a pour point of less than about -50°C and a boiling point of greater than about 100°C. 5. The light valve of claim 3, wherein the fluorocarbon polymer is an oligomer of chlorotrifluoroethylene. 6. The light of claim 5, wherein the oligomer has an initial boiling point in the range of about 135°C to about 260°C and a pour point in the range of about -70°C to about -130°C. valve. 7 The oligomer has a molecular weight of at least about 1.7 at room temperature.
6. The light valve according to claim 5, having a specific gravity of . 8. The oligomer has an initial boiling point in the range of about 135°C to about 205°C, a pour point in the range of -130°C to about -93°C, and a specific gravity in the range of about 1.6 to about 2.0 at room temperature. A light valve according to claim 5, characterized in: 9. The light valve of claim 3, wherein the fluorocarbon polymer is an oligomer of bromotrichlorethylene. 10. The light valve of claim 9, wherein said oligomer has a specific gravity of about 2.2 to about 2.4 at room temperature. 11. Claim 1, wherein at least about 60% of the atoms of the fluorocarbon polymer are comprised of halogen atoms, and at least about 75% of the halogen atoms are fluorine and the remainder are chlorine and/or bromine. Light valve as described in section. 12. The method of claim 1, wherein the miscible organic liquid is selected from the group consisting of esters of aliphatic and aromatic acids and alcohols, aromatic hydrocarbons, and silicones. Light valve. 13. The method of claim 12, wherein the miscible liquid is selected from the group consisting of isopentyl acetate, p-nonylphenyl acetate, dioctyl phthalate, diisodecyl adipate, dioctyl sebacate, benzene, and toluene. Light valve. 14. The light valve of claim 1, wherein the liquid fluorocarbon polymer comprises about 40% by weight of the liquid suspending medium. 15. The light valve of claim 1, wherein the liquid fluorocarbon polymer comprises about 60% by weight of the liquid suspending medium. 16. The light valve according to claim 1, wherein the particles are particles of a polarizing quinine alkaloid salt perhalide. 17. The light valve of claim 16, wherein the quinine alkaloid is selected from the group consisting of quinine, cinchonidine, hydrocinchonidine, and hydrocinchonine. 18. The light valve according to claim 1, wherein the particles are particles of dihydrocinchonidine sulfate periodide. 19. The light valve of claim 1, wherein the particles are particles of quinine bisulfate periodide. 20 The protective polymer comprises nitrocellulose;
carrying a hydroxy group, having a first pendant, branched C-C chain, optionally interrupted by an oxygen atom, and a second pendant, branched C-C chain, optionally interrupted by an oxygen atom; , an auxiliary copolymer in which the most remote hydroxy group is closer to the main chain of the copolymer than the terminal branch group. 21 The auxiliary copolymer is composed of a hydroxyalkyl acrylate (where alkyl is an alkyl of 1 to 3 carbon atoms) and a branched alkyl acrylate (where alkyl is an alkyl of 4 to 12 carbon atoms). 21. A light valve according to claim 20, characterized in that it is a copolymer. 22 The protected polymer is a copolymer of at least two different monomers, at least one of which has a non-sterically hindered functional acidic group and/or a hydroxyl group for binding to or associating with the particle. and at least one of the monomers has a branched group, and the distance from the main chain of the copolymer to the non-sterically hindered functional group furthest from the main chain is shorter than the distance from the main chain to the terminal group of the branched group, 2. The light valve of claim 1, wherein the branched groups in said copolymer are sufficiently soluble such that said copolymer as a whole is substantially dissolved in said liquid suspending medium. 23. The light valve of claim 22, wherein the copolymer is a copolymer of a hydroxyalkyl ester of an ethylenically unsaturated acid and a branched alkyl ester of an ethylenically unsaturated acid.