CA1106955A - Materials, methods and suspensions for light valves - Google Patents

Abstract

Abstract of the Disclosure Polymeric materials which are used to stabilize particles includ-ing colloidal size particles, particularly particl?s which polarize light or other radiation and include halogen in their composition. The materials are long chain molecular copolymers having available functional groups such as OH or acidic groups in their structure and are soluble in liquids in which the colloidal particles are suspendable. At least one monomer of those used to form the copolymer has a branched structure, which may include more than one branch. Some of the materials are copolymers of 3,5,5-trimethylhexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; and bis-2-ethylhexyl fumarate/3,5,5-trimethyl hexyl acrylate/vinylidene chloride/mesaconic acid. The materials retard or prevent the suspended particles in light valve suspensions from grouping together when a voltage is placed across the suspension containing these particles. The materials also reduce the voltage and electrical power needed to achieve a given change in light transmission for a light valve. They also enable suspensions to be used at elevated temperatures without signifi-cant degradation.

Description

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~' . ' This invention relates to p~lymeric materials which stabilize particles including particles of colloidal size to ~ ' ~;

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.` ~ prevent them from grouping together, i.e., agglomerating, when the particles axe ln suspension. In colloidal systems and especially liquid colloidal suspensions, the particles in sus-pension tend to ~roup or stick together to form large groups of particles. This phenomenon is often re~erred to as agglomeration The formation of large groups of particles destroys the sub-stantially homogeneous distribution of the particles in suspen-sion and essentially renders the suspension useless. This prob-lem is particularly acute in suspensions which are used in light ~alves. In the operation of the light valve, a voltage is applied across the suspension. ~his voltage, because of the relative charges on or associated with the particles, can cause the particles to group together and rorm large groups of agglomerates. These masses prevent the proper functioning of the l-ght valve and thereby destroy its utility.
There has been a need, therefore, to develop a materizl which would effectively act to prevent the suspended colloidal particles in a light valve from agglomerating. ¦ -Although the prior art is replete with patents per-~ taining to dispersants including polymeric materials for main-taining particles in suspension, these materials are either unsuitable for use in a light valve suspension or greatly ¦ inferior for such purpose to the polymers of the present inven-I tion. Descriptions of light valves that use a liquid suspen-¦ sion are given in U.S. Patent No. 1,955,923 (Land), and in j U.S. Patent No. 3,708,219 (Forlini et al-). Basically they ¦ are devices which control the transmission of light.
In order to be suitable for use in a light valve suspension, a polymer should be soluble in the liquid suspend- ¦
iDg med um of the suspension. The pol~mer should furthermore Il .

~ 59~j5 `") l-i be capable of associating with the surfaces of the suspended particles in order effectively to furnish steric protection from agglomeration particularly when particles are aligned under influence of an electric field,(a condition which drastically increases the tendency to agglomerate)~ Also the polymer should associate with the particles so that if the polymer is present when the particles are initially formed it will prevent the particles from growing too large and help to minimize formation of aggregates of particles during formation.
.~ The polymer should not attack the suspended particles so as to cause them to degrad-e and should not itself degrade at the temperature of use or at temperatures at which the sus-pension may be stored, lest its degradation products attacX the suspended particles, Degradation causes a loss of the polymer's ability to impart steric protection and other benefits herein described. The polymer should preferably have a wide range of solubility so that, if desired, it can be dissolved in the polar liquids in t~hich many of the particles used in light valves are initially formed, and also be solu~le in relatively non-polar and low conductivity li~uids used in operating light valves. The polymer should not coat the walls or the electrodes on t.e walls of the light valve, because a polymer that sticks to them creates a ha~y appearance that destroys the clear view through the light valve and reduces the - ?5 maximum light transmission or change of transmission attainable from the light valve.FUrtherthe polymer should improve the voltage characteristics of the suspension in that it should enable one to obtain a greater change in light transmission for a given voltage gradient applied across the suspension, than is ~ ¦; possib e if one employed nitrocellulose, the prior art polymer _3_ I . i liO6955 u~ed in light valve suspensions by others. In this connection it is especially important and preferable to be able to do so at low frequencies e.g. 1000 Hertz or less, because electrical power usage is very much lower at low frequency than at higher activatins ~requencies.

Nitrocellulose, as previously mentioned, has been in use for a considerable length of time and does work to a certain extent in light valv,e suspensions. Although it does somewhat prevent agglomeration, nitrocellulose has the significant dis-advantage of being highly subject to degradation at only moder-ately high temperatures. For example, nitrocellulose will ¦ degrade at or below 150F. At such temperatures nitrocellulose can break down and form nitrous and nitric acid and other degra-dation products and these can attack the particles in suspension.
I~ the particles degrade when attacked by such acid or other 2a degradation products the suspension will be destroyed. Nitro-cellulose al'so has a further major disadvantage in that there are !
¦ a limited nu~ber of suspending media in which it can be dissolved !
when it is used in light valves. These media are essentially . li~ited to organic esters. ~or many functions esters are not the most desirable liquids in which to suspend the particles.
Therefore, nitrocellulose has very serious chemical and physical drawbacks which are overcome by the polymeric materials of this invention. These polymers have much greater thermal stability than nitrocellulose and will not generally break down unless ~ temperatures are reached that are far above the Point at which ; ~ 6~55 J. nitrocellulose will form nitrous and nitric acid. In addition, they are soluble in many relatively nonconductive liquid suspend-ing media in additi.on to esters.
SUM~ARY OF THE I~VENTION
. It is an object of this invention to provide a novel and improved pol~ner ~o stabilize liquid suspensions.
It is another object of this invention to provide such a polymer for use in liquid suspensions for light valves.

I . It is another object of this invention to provide iO such a polymer which prevents or retards agglomeration of the particles in suspension. .
It is another object of this invention to provide such a polymer which reduces the voltage and electrical po~er needed to achieve a given change in light transmission for a light valve. ~
It is another object of this invention to provide such a polymer which is a long chain molecular copolymer having ~ ¦available functional groups such as O~ or acidic groups in its i structure.

It is another object of this invention to provide l such a polymer t~herein at least one of its monomers has a branched i structure. . .
It is another object of this invention to provide l such a polymer which imparts thermal stability to a liquid ! 2~ suspension.
I . ~ It is another object of this invention to provide ¦such a polymer having a wide range of solubility in both polar and non-polar liquids.
It is still another object.of this invention to provide 1 3~ such a polymer that will not coat the walls or electrodes of a light valve.

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1 It is still another object of this invention to provide¦
a light valve suspension including such a polymer.
It is still another object of this invention to provide.
a stabilized light valve suspension by adding such a polymer.
In carrying out the objects of this invention a polymeric material is provided which stabilizes ~ suspensions . including colloidal particles and especially halogen-containing light polarizing particles e.g., herapathite, purpureocobalt-chloridesulfateperiodide, and cupric bromide.
The materials are long chain molecular copolymers having available functional groups suc~
as OH or acidic groups in their structure and are solublé in ¦ Iiquids in wh7ch the colloidal particles are suspendable.
¦ At least one monomer of those used to form the copolymer lS I has a braslched structure, which may include more than one branch.
I! Some of the m~terials ar~ cop~lymer-. of ~,5,5-trimethylheY~yl I¦ ~crylate~2~hydroxypropyl acrylate/~umaric acid; 5,5-diethyl i! hexyl acrylate/2-hydro~xypro~yl acrylate/fu~aric acid;and bis-,1 2-ethylhex~l fur~arat.e/3,5,5--trimethyl he.Yyl acr~la~e/vinylidene 1, chlori.de/mesaconic acid. ! The polymers act to prevent or retard ! agglomeration of the particles in suspension especially when the ¦ suspension is in use in a light valve and a voltage is placed !¦ across the suspension. The polymers also make it possible for l; suspensions to be used at elevated temperatures without signifi-1l cant degradation, and reduce the voltage gradient and electricalpower needed to achieve a given change in light transmission for the light valve.l . . ' 1.~ 5 PREFERRED EI~IBODIMENT OF THE INVErJTION
This invention relates to polymeric materials which stabilize colloidal particles and particularly to polymeric materials which associate with these particles to maintain the stability of the particles and prevent them from agglomerating to form large groups of pa~ticles. A principal purpose of the invention and polymeric materials is to maintain a substantially homogeneous distribution of these colloidal particles in a suspending medium. In liquid suspensions it is most important that the suspended particles be substantially uniformly distri-buted throughout the suspension. This uniform distribution is especially important when the liquid suspensions are used in light valves. The materials of this invention comprise copolymers , and in particular copoiymers which include at least one type of . , .'' ,.

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..~ . `. - I . .~.j . ~l~J69:~;5 1 monomer havinq an available OH group or acidic group which is sterically unhindered and in a position to associate or bond with an element or part of the particles beinq stabilized. The ¦ remaining part of the copolymer is preferably a monomer which I is soluble in the liquid mediu~ in whicll the particles are sus-¦ pended. The polymeric stabilizing material thus has to be a material ~hich both strongly bonds the copolymer to the particles and also must be soluble in the suspending medium. If neither part of the copolymer were soluble in the suspending mediu~, the polymer chains associated with particles would not be in a state or condition to extend a substantial distance outward rom the particles to ~revent agglomeration effectively. The materials .
of this invention are particularly suited for the suspensions which are used in light valves.
Briefly, a light valve consists of two sheets of _ usually transparent material such as glass or p~s~c which are spaced apart a very small distance such as 1 to 50 mils and are connected around their periphery by an adhesive or other suitable sealing material. The sheets have transparent electric~lly conductive coatings of a material such as tin oxide or indium oxide on their inner facing surfaces and the coatings are con-nected via leads such as conductive silver paint and wiring to a source of po~er, preferably a source of AC voltage. Tne space .
between the transparent sheets is filled with a suspension such ¦ as a suspension of herapathite particles in a suspendiny mediwm ¦ such as amyl acetate or isopentyl acetate.
The herapathite (or other) particles used in a light valve are small, preferably colloidal sized and are aniso- ¦
! metrically shapea, preferably lath-liXe, rod-shaped or needle-shaped p rticles having an aspect ratio pr-erably ranSing rcm ., .

~ ) t ;9S5 i , ,, 1 I S to 1 to 20 to 1. These anisometric particles, which are pre-ferà~ly light polarizing, polyhalide particles, are normally ¦ unaligned, that is randomly oriented (i.e., totally disoriented) in the suspension. Provided that there is a sufficiently high concentration of unaligned crystals in suspension, light cannot easily pass through the suspension because it is absorbed o~
blocked by the plurality of particles. The suspension will appear very dark. However, when an electric field is applied across the suspension, the particles align parallel to the field (perpendicular to the transparent light valve walls). This is ! accomplished by placing a voltage across the leads that are connected to the thin transparent conductive coatings which are l applied on the inside facesof the walls of the cell. The voltage ¦ ~ is thus placed across the transparent walls or sheets so the I is field passes through the suspension When a voltage exists throush the suspension, the herapathite or other suitable polar-izing particles become aligned as aforesaid so that their long axes are perpendicular to the transparent coatings i.e., parallel to the electric field between the coatings. In this position the particles will block very little of the light passing through the suspension since the particles will generally have their . long axes parallel to the direction of the light passing through.
Thus, when an electric field is placed across the cell, or in other words, when the cell is placed in the "on" condition, 1 25 ¦ light can readily pass the~ethrough. The suspending medium in l which the particles are suspended is preferably transparent so i ' that once the particles are aligned there is little to block i I the transmission of visible light or other radiation throu~h the j ¦~ suspension. However, once the voltage is removed, Brownian j movement quic~ly disaligns the particles so hat their longer ' . !
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11~ 5 axes will be at angles to the direction of the light in many cases and therefore, light will not be able to readily pass through the suspension.
A major problem as aforementioned with these and other ¦
S colloidal particles is that they tend to be attracted to each other. This is especially true when a voltage is placed across the suspension. Under the influence of an electric field the particles are thought to act like induced dipoles and the attraction between the positive and negative ends of proximate particles is sufficient so that once the voltage is placed across the suspension, they will start grouping rapidly together to form large groups of particles. This will defeat the purpose of the light valve since in the "on" condition it should pre-ferably remain uniformly transparent. However, there will be relatively large black areas where the particles have grouped together and where the suspension is no longer transparent.
What is needed therefor is a material which will prevent the ¦ particles from grouping together or will essentially keep them in their normal properly dispersed suspended relationsh-p. The new materials of this 1nvention achieve this result. These materials readily associate with and stabillze the herapathite ¦ or other halogen-contain~ng light polarlzing ~articles The particles being stabilized are preferably ones that contain ~' ¦ iodine, such as herapathite - or ones that contain other halogen }
25- j elements in their structure, such as cupric bromide. The polymeric stabilizing materials not only assoclatë ~Jith the ~ polarizing particles but also contain components in their str~c- !
¦I ture which permit them to readily dissolve in the liquids in ¦I which polarizing particles are suspended. Some of the polymeric 1I materials that are used include copolymers of 2-ethylhe Ii . I

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~ ~L1''3695~ l acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/
acrylic acidi 2-ethylhexylacrylate/2-hydroxypropyl acrylate/
fun~aric acid; 2-ethylhexyl acrylate/2-hydroxy~,opyl acrylat~/
vinylidene chloride~fumaric aci-di 3,5,5-trLmethyl hexyl acrylate~

2-hydroxypro2yl methacrylate; 3,5,5-triTnethyl ~lexyl acrylate/
2-hydr~xy~rop~!l acry]ate/fumarlc acid; bis-2-ethylhexyl fumarate/
2-hydroxypropyl acrylate/acrylonitrile; 5,5-diethyl hexyl acrylate 2-hydrox~propyl acrylate/fumaric acid; ar.d bis-2-eth~lhexyl fumarateJ3,5,5-trimethyl hexyl acrylate/vinylidene chloride/
mesaconic acid. A11 of these materials have a functional group of a polar character such as an OH and/or an acidic group in a position to readily associate with and form a bond with the particle, probably with the halogen, such as iodine in the 1~ structure or herapathite particles being stabilized but possibly also or alternatively with another part of the particle. The association or bond formed by this OH or acidic group is thought to be a hydrogen bond but may possibly be another type of bond or be in addi~ion to another type of bond such as a ~0 coordinate covalent bond. However, it appears that the O~ or acidic group and not the hydrogen alone is needed for the bonding. It is also t~ousht that the hydrogen bonding and/or coordinate covalency through the oxygen leads to the effective-, ness of the bond. These bonds between polymer and particles are extremely strong bonds. It is noted that in the case of certain substances, acrylic acid, for example, there is a I _ _ . . . . . ._ COO~ group available. It is thought that the OH is probably the prlmary reason for its effective action. However, the CO
¦may also be active. It will be appreciated that in all the 30 ~ caseS some available i.e., free OH or acidic group is present I ~ s~ I .
L in a copolymer. By "free" it is meant that the OH or acidic group is in a position that makes it availabl~ for bonding, that is, it is sterically unhindered by the remaining structure of the molecule of which it is a part, so that it can readi}y act to form the hydrogen bond and/or coordinate covalent bond with halogen, or for particles that do not contain halosen in their moIecular structure with the attracted atom or group. If the OH or acidic group were not in this position, for example if in a copolymer it was constricted by rigid groups in close prox-imity to it, it would not be in as good a position to readily combine and therefore the material involved ~ould not be one that would be an effective bonding or stabilizing agent. It will be appreciated then that in the copolymer materials listed : above, the acid or acidic monomers or monomers ~hich include 15, functional groups e.g., acrylic acid, fumaric acid, mesaconic ¦ acid, maleic acid or acrylonitrile, or one o the hydroxyalkyl _ ester_monomers e.g., hydroxyethyl acrylate, hydrox'yethyl~'~'~''~~~~
. ~ methac'rylate,''or 2-hyd'rox'ypropyl'acrylate are the substances j which include available acidic or OH groups and act to combine I with the halogen element or other part of the ~article to form ' the association or bond. These monomers, depending upon choice of monomer may or may not be ~ranched, and may or may not be .
soluble in the sùspending''medium''depending upon choice of - j¦ monomer and medium. ~nother part of these copolymers, that if, 1! for example, 2-ethylhexyl acrylate, bis-2-ethylhexyl f~marate, 5,5-diethylhexyl acrylate or 3,5,5--trimetilyL he~yl acrylate, i?_acts to dissolve the copolymers in the susEer~ding lisuid medi~m.
j It is preferably a branched monomer, and more pre- ' ¦ ferably has two or more branches. Branching ! greatly enhances the ability of the copolymer to retard asglomer-I

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1 ation of a light valve suspension under the influence of an electric field and is necessary to be ef~ective against agglomer-ation. Although even one branch, such as the ethyl group of the monomer 2-ethylhexyl acrylate is helpful in this resard and considerably more effective than an unbranched monomer such as octyl acrylate, it is much more useful to have a pIurality of branches. Although the precise reason why branching impedes agglomera~tion is not known, one possible theoretical reason may be that, pro~ided the branches do not block bonding groups fro~
bonding to the particles to be stabilized, the space occupied by the branch may convey steric protection by preventing two particles from approaching one another too closely. If this theory is correct it woùld be reasonable to expect that a plurality of branches will be more effective than one branch of lS about the same size, as one finds experimentally. For reasons ` ¦l that are as yet unknown the presence of a branched monomer in the copolymer also reduces the voltage gradient needed to achieve ' ~ ¦ a given change in light transmission for a light valve, as -`~ _ hereinafter discussed.
1 Preferably at least one monomer, such as the aforesaid -- branched monomer,.which serves, it is thought, a steric blocking ¦
, function, should possess no functional bonding groups. Pre-ferably also such monomer or monomers should constitute a majorlty of the copolymer by weigh~_percent and should be the largest monomer or monomers therein in terms of the comparative molecular weights of the monomers. The branches may themselves be branched i.e. have sub-branches attached thereto.
- 1 Although the branched monomers and many of the other monomers given in the preceding examples are esters, they may be of numerous other types. Por example, the copolymers may `' ~ 55 :. include monomers such as ethers or cyclic monomers, and may include monomers h~ving particularly useful substituent groups such as halogenated monomers, in particular fluorinated monomers which aid the copolymer in the attainment of solubility in fluorinated liquids which may be useful suspending media.
- If desired, two or more copolymers of similar or dif- ¦
fering characteristics may be used in a suspension simultaneously.¦
.The suspending medium, which for light valves is pre-ferably electrically nonconductive, can be such diverse fluids as aliphatic or aromatic hydrocarbons, silicones, esters and non-polar ethers, and particularly halogenated chemically s~able solvents such as fluorinated alkanes, fluorinated esters and fluorinated ethers and mixtures thereof.
When using a fluorinated liquid in a suspending medium it may be necessary to include with it a more polar but relatively nonconductive liquid such as an ester e.g., isopentyl acetate as part of the suspending medium of a suspension in order to get alignment of the particles at moderate voltages. ~oreover, the weight percent or mole percent of each type of monomer cr the weight percent of OH or acidic groups used in a copolymer can be tailored and adjusted to make pcssible solu~ility in a particular liquid or liquids. Thus, the copolymers combine the effectlve bo~ding action with the ability to dissolve in màny types of I liquid suspending media. The part of these polymeric materials -- I~that dissolves in the suspending medium should be suff ciently soluble that the copolymer as a whole can substantially dissolve in the suspending medium. It will be appreciated that in the ! operation of light vaives the more nonconductive the suspending ¦ medium is, the better the light valve ~ill function and perform.
j That is, the less conductive the liquid medium, the less electric Il I
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~ ;`', ~ C~5 power and voltage are usually required to cause the alignment or the particles, and hence the more readily operable the light valve will be. Thus, it is one of the advantages of the present Copolymers thatk they /
¦ -wil-l readily dissolve in very nonconductive suspending media.
Some of these relatively nonconductive suspending media have been mentioned previously but it will be noted that there are ! . many of them and it could be said that suspending media having ~ an electrical resistivity of approximately 5 x 107 ohm-cm or 1~ i more, and preferably 5 x 109 ohm-cm or more, will be operable with the present materials. A suspension (which includes the suspended particles and copolymer) will be somewhat less resistiv than the suspending medium alone. _~
, -- The polymeric materials of the in~ention have particu-lS larly good thermal characteristics, that is, the copol;~mers can generally withstand a temperature ranging from as low as the freezing point of suspending medium to temperatures in excess of :
100C without breaking down. This permits the liqht valveq to - operate over a wide range of temperatures and patijc~ulariy with nonconductive suspending media. :
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~` Nitrocellulose, which was used in prior art light `~ valve suspensions, has very poor thermal properties as aforesaid.
~ At temperatures at or below about 150F nitrocellulose soon begins to brea~ dOWII and form nitrous acid, nitric acid and other degradation products. Formation of such degradation pro-ducts reduces the amount of nitrocellulose available to retard agglomeration, and degradation products also attack and can substantially ruin a suspension. The new materials described herein, however, overcome these disadvantages.
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Nitrocellulose, further, has the dis-advantage that it can only be dissolved in certain liquid suspending media. Obviously, the medium must be one that nitrocellulose will dissolve in. These are essentially organic esters such as isopentyl acetate and amyl or ethyl acetate.- The non-viscous types of esters, which have a viscosity at 25C of 5 centipoises or less, are not particularly nonconductive. They generally have a resistivity of 2 x 108 ohm-cm, or less. Such non-viscous media are desirable when rapid alignment and dls-alignment of particles is sought. However, with the present copolymers, resistivities one or more orders of magnitude greater can be readily achieved because suspending media can be used with these copolymers that have higher resistivities i.e., lower ¦ conductivity at the same viscosity, and thus lower conductivity suspensions can be achieved at the same viscosity.
These copolymeric materials can be used initially during the formation of the particles so that the particles do not agglomerate and group together during their formation and can be left bonded to the particles so that the material con-tinues to prevent agglomeration during all stages of the particles' life and their use or operation. However, they also can be used subsequent to particle formation when they are about ¦ to be used in a suspension. A polymer may also ~e added to a ¦¦ suspension which already includes some of the same polymer or of a different polymer.
j Some e~mples of polyhalide materials that will form ¦l the suspended particles and ~re capable of polarlzing light ¦ and useable in light valves include the aforementioned herapathit~, i ., I! ' ' . ~
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' ~ g~5 1 I purpureocobalt:chloridesulfateperiodider and cupric bromide.
The following are examples of the production of suspen- !
sions for light -~alves and other particles using herapathite and using various copolymers~ In examples 1 to 9 and example 12 the copolymer is used during the formation of particles used in the suspension and is retained in association with the particles when the suspension is made and actually put in opera- ¦
tion. In examples L0 and 11 the copolymer is added to the particles after the particles are formed, and the polymer-bonde~
particles then placed in suspension and then operated in a light valve.
The copolymers used are preferably ones havins an extended chain length of approximately 600 to 4,200 angstroms or more. Although they may be of random structural composition, alternating,block,or graft copolymers may also be used advan-tageously. The following are examples of the present invention.
EXA~LE 1 ....
42.5 grams of a 33 1/3% solution of the copolymer 2-ethylhexyl acrylate/acrylic acid, 75~/25% by weight, in 2-ethoxyethanol is combined with 3.75 grams of quinine bisulphate and 0 50 grams of fluoroalcohol. Then, 8.5 grams of methanol and 10 grams of additional 2-ethoxyethanol are added. An alcoholic solution of a plasticizer (optional), iodine and hydriodic acid (HI) is reacted with the above inyredients I by mixing to form a wet paste of herapathite. The paste is then dried to remove the volatile solvents.
At this point a liquid suspending medium is added to the paste which is dispersed therein by continuous mixing and grinding.
rn this test the c ntent of acid including mono~er ~ ` ~ I ' ? ~ ~
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1 in the copolymer as noted ahove was only 25% by weight ln order to enhance the chance for the copoly~er to dissolve in the suspending medium of a light valve in order to effect dispersion of the dried paste. Favorable results occured. The optical S density of the resulting suspension in isopentyl acetate in a li~ht valve was observed to change from 3.0 to approximately 0.85 when activated, indicating a substantial opening.

Example 1 was repeated except that the ingredients were as follows: 42.5 grams of a 30% by weight solution of 2-ethylhexyl acrylate/acrylic acid in 2-ethoxyethanol as in Example No. 1, 2.68 grams of quinine bisulphate, 7.30 grams of -methanol and 10 additional grams of 2-ethoxyethanol.

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Example 2 was repeated except that the 10 additional grams of 2-ethoxyethanol were omitted and 0.50 grams of chloro- S
form added to the contents prior to reaction.
EXA*IPLE 4 A copolymer of 2-ethylhexyl acrylate/acrylic acid~

50%/50% by weight was prepared. 42.5 grams of the solution of the copolymer was prepared as a 25% by weight solution in 2-ethoxyethanol to which was added 3.75 grams of quinine bi-¦ sulphate and 8.50 grams of methanol. As in Example 1, an ¦ alcoholic solution of a plasticizer, iodine, and hydriodic acid was reacted with the above ingredients to form a wet pas,e. The dried paste, using heat to aid dispersion, was then suspended in decyl alcohol. The substance was placed in a light valve and ¦¦ satis~actory operation was achieved.
I XX~PLE 5 I
3C I Example 1 was repeated except that an 85~/15% by weight i !
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;955 i ¦ copolymer of 2-ethylhexyl acrylate~acrylic acid was substituted for the 75~/25% copolymer. The dried paste, unlike the paste in Example 1, was dispersible-in the aromatic hydrocarbons, toluene, and, as in EY~ample 1, displayed substantial opening in a light valve. Toluene has the advantages of having a high electrical resistivity, and a low viscosity and therefore a fast response in 2 light valve.
E ~ ~PLE 6 Example 1 is repeated but n-propanol is substituted ~0 for 2-ethoxyethanol to enhance copolymer solubility, and a 93.5%~
6.5~ by weight copolymer of 2-ethylhexyl acrylate/acrylic acid - substituted for the copolymer of Example 1. The resulting dried -paste of hera~athite was dispersible in an aliphtic hydrocarbon, hexane. Aliphatic hydrocarbons have lo~7 viscosities and are generally less conductive at low viscosities than esters. Ali-phatic hydrocarbons are therefore desirable suspending media for : certain light valves.
EXA~IPLE 7 Approximately 0.2 grams of purpureocobaltchloridesulfato _ periodide, an inorganic polyiodide, was mortared in 1 gram of a 75%~25% by weight copolymer of 2-ethylhexyl acrylate/acrylic acid as a 33 1/3~ solution in 2-ethoxyethanol. After drying to evaporate the 2-ethoxyethanol, the particles were suspended in isopentyl acetate and the resulting suspension in a light valve ~ had a gray appearance. Using a voltage gradient of between 30 and 90 volts per mil, in a pulsed mode of operation, the suspen-sion was observed to pulse open and closed continuously in response to the applied voltage without noticeable significant agglomeration. Under a continuous voltage gradient of ap~ro~i-j¦ mately 30 olts per mil and greater a continuous opening of the . .
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Il :. ¦ suspension was observed for several seconds without significant , agglomeration.
EX.~MPLE 8 ' ,1 ! Approximately .04 grams of cupric bromide, a polyhalide ~¦ 5 I material in which the halogen is bromine, was mortared in 1 gram ¦ of a 75%/25g by weight copolymer of 2-ethylhexyi acrylate/
~ acrylic acid as a 33 1/3% solution in 2-ethoxyethanol. After ¦ drying to,evaporate the 2-ethoxyethanol, the resulting suspension , was suspended in isopentyl acetate in a light valve and had a , 10; greenish-yeliow appearance. Repeated pulsing was observea at a voltage gradient of 30 volts per mil or greater without signi-~A ' ficant aggIomeration. Particles appeared to be in the size range of 1-15 microns when observed through a microscope. Lower i ' vQltage gradients also produced good opening. , , ~5 EX~`~PLE 9 ' In order to demonstrate that o,,ther,polar materials can ! also be used instead of acid in a copolymer formulation and still ¦¦ work, a 75~/25~ by weight copolymer of 2-ethylhexyl acrylate/
: , I hydroxyethyl methacrylate was tested. The hydroxyethyl methacry-2,0 late monomer contains an OH functional group in each molecule.
The hydroxyethyl methacrylate is also called ethylene glycol i monomethacrylate. Using the method of Example 1, a successful well-protected suspension resulted. ~lowever, the 75%/25% compo-sition of the copolymer prevented it from being completely llsoluble in isopentyl acetate alone, and hence it was necessary ¦Ito use a 2:1 mixture of isopentyl acetate and chloroform as the ,suspending medium for test purposes. It was observed in the ~ jitest cell that the electrical resistivity of the resulting suspen-! j~ sion (approximately 1.5 x 108 ohm-cm) was an order of magnitude l¦ greater than in cases where acid groups were present in the !
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! -copolymer used to protect the suspended crystals.
Many of the aforesaid tests were conducted more than once using copolymers of various viscositites i.e. molecular weights. In general, it is best to use the lowest molecular weight polymer possible consistent with anti-agglomeration objectives and other purposes, because higher molecular weight ¦ polymers incr,ease viscosity of the suspension and reduce the rise and decay (response) times of light valve suspensions.
. Alternatively, the molecular weight of-the copolymer , can be chosen, if known, so that the length of the extended copolymer chain would be at least 600 angstroms and preferably 2,000 to 4,200 angstroms or greater.
In order to avoid contamination of the final suspen-sion, particularly in the case of a light valve suspension, 15- the copolymer used should be as pure as possible. This is help-ful in that it will prevent unnecessary conductivity in the final suspensions.
In the copolymer systems previously described, L~ has been established that the portion of the copolymer that las not of high polarity primarily affected the solubility of the copolymer.
¦ ~ In several of the aforesaid examples copolymers of 2-ethylhexyl acrylate/acrylic acid resulted in good protection , , I for crystals of herapathite and other materials that were formed , ¦ 25 ¦ or comminuted therewith. As a result of these tests the con-¦ clusion was reached that probably the polàr OH or acid function-¦ ality is responc.ible for the protection and that the non-polar ¦ ~roups in the copolymer serve the function of permitting the ¦ copolymer to be soluble in non-polar solvents or solvents of intermediate polarity depending upon chemical nature and . ..
! -19-. . .
.

~ fi~S~ `
..
:. quantities of the simple molecules contained in the copolymers.
. However, in order to be sure that the 2-ethylhexyl acrylate .... alone was not, by some chance, responsible for furnishi.ng some ~, , ~ or all of the protection, a homopolymer (not a copolymer) of.
~ ,. ¦ 2-ethylhexyl acrylate was made, substituted for the copolymer . I in Example .l, and a paste of herapathite made in accordance with ¦
. the method of Example 1. .As expected, poly(2-ethylhexyl acrylate) . did not prevent agglomeration of particles either during the . . reaction, during drying, or in a light valve suspension of the :10 dried herapathite paste. Accordingly, the conclusion that the ~:~ . OH or acid functionality was responsible for the favorable

3 results previously observed was confirmed. : .
In the case of a colloidal fluid suspension, whether being stored for future use or actually in an unactivated light . :~5 valve (power off), a copolymer used therein can be said to . adequa~ely physically protect the suspended crystals if no sig-. . . nificant noticeable agglomeration takes place over a long period . -. of time - at least days and preferably years. As a quick ~est ~ . of the efficacy of a polymer, a colloidal fluid sus~ension with 1~0 ~ the polymer is placed in a light valve having a low viscosity . suspending medium (approximately 5 centipoises or less) and . the light valve activated by a 10 Kilohertz AC co~tinuously applied electrical field (power on) having a continuous sinus-. ~ oidal wa~eform and a voltage gradient strong enough to orient .25 acicular crystals suspended therein, a copolymer used therein i I can be said to adequately physically protect the suspended } li crystals if the crystals do not noticeably agglomerate signi-ficantly for at least two seconds~ and prefera~ly for at least.
20 seconds. If the field is applied in a pulsed mode using short pulses e.g., 20 milliseconds with relatively longer . . ~ -20-. . ' . I

. , i , .,;, ~- . . ~lr~fi9~ .

.: periods without an applied field between pulses, but with suf-ficient voltage gradient to orient suspended crystals, suspen-sions in which the particles are adequately physically protected should change optical density repeatedly (i.e., open and close) in response to such pulses for at least 5 cycles, and preferably for thousands of cycles or more without noticeably agglomerating significantly~
- ~ Significant particle agglomeration can be visually noticed as dot-like or clump-like areas in the suspensio;n, as well as by a substantial change in closed and/or open optical density for the suspension.
Suspensions containing a copolymer that does not adequately physi~ally protect the particles will agglomerate substantially and, in many cases, cease to function almost ~5 entirely in less than the lower time intervals cited above ; under the aforementioned test conditions. For an inadequately : protected suspension, upon application of a voltage gradient that would cause the particles to orient ~rithout agglomerating if the copolymer was effective, the poorly protected suspension 2b is generally observed to open but not to close.~ In this case, the "opening" i.e., reduction of optical density and increase of light transmission is in large part caused by i~ediate ¦ agglomeration of the crystals; the agglomerated crystals are thought to be loosely stuck together and therefore cannot dis-~5 1 orient i.e, close through Brownian motion as quic~ly as discrete oriented particles can. Some poorly protected suspensions are so badly agglomerated before being placed in a l1ght valve that the suspensions cannot be made to open at all.
It is thought that a copolymer that is effective in preventing or reducing agglomeration of particles in a suspension r : ~ ( /~ 3 I

t does so because part of the copolymer coils outward in solution in the suspending medium, possibly around the particles, there~y preventing or making difficult the _lose approach of another particle to ~le first particle. .
In order that a material adequately physically protect suspended particles from agglomerating, two things are thought necessary, namely, that the material at least partially bond to or associ~te with the particles and, secondly, that the material by forming a thick enough barr,ier around the particles and/or extending part of itself~into solution prevents the close approach and agglomera'Lion of two particles. Any material that - bonds to or associates with the particles and has a long average length in solution relative to the average diameter of the particles might meet these requirements, but polymers have been ¦- 15 found most effective, and the branched copolymers of the present invention particularly e~ficacious and useful. .
- In order for a poly~er to be useful in a light valve . suspension as a stabilizer or for other purposes describ~d herein, it is imperative that the polymer not coat ~,e ~alls of the i 2~ li.ght valve and not coat the tra~.~parent electrically ~onductive ~ .~ ~
: I coatings (i.e. the electrodes) that may cover all or part of the surfaces of ~he walls. IL the polymer does coat the ~lalls ¦ or electrodes they will become hazy in appearance and will limit , the maximum light transmission. I have discovered that in order '~ 25 ¦ to prevent the polymer from forming s~ch an un~Janted coating ¦ one must select the monomers in the copolymer so that in a copolymer thereof, assuming all chains and branches fully extende~
and perpendicular to their source, functional bonding groups e.g. the 0~1 and acidic groups will be closer, preferably much ! closer, to the polymer backbone than non-bonding groups on at ' 11 ' I
j -22- 1 , ~i~6!~55 - least one monomer that includes no functional bonding groups therein. Thus, if 3,5,5-trimethyl hexyl acrylate or 2-ethylhexyl acrylate is copolymerized in a random terpolymer with fumaric acid and 2-hydroxypropyl acrylate, it is apparent from the known structures of these monomers that the terminal groups of the first named monomer, which has no bonding groups therein, will extend further from the backbone than either the carboxyl groups in the fumaric acid monomer or the OH group in the 2-hydroxy-propyl acrylate monomer. The same principle should be applied to polymers covered by this invention other than random copolymers eOg., for any part of a graft copolymer than has bonding groups therein even if such part is itself a polymer. Failure to follow the above-prescribed rule can lead to the undesirable result that the walls and electrodes become coated. It is theorized that this occurs because it becomes possible for the bonding groups to bond thereto. By following the aforesaid rule, the polymers can bond to the suspended particles but not bond to the cell walls and electrodes.
In addition to retarding agglomeration and permitting use of suspensions at relatively high temperatures, the polymers of the present invention are especially valuable in that they make it possible to use low activating voltages and small electric field gradients to operate light valve suspensionsO
In the prior art relating to light valves, it has been suggested to use voltages at frequencies of 1 Kilohertz and higher. Use of lower frequencies would h~ve resulted in the extremely rapid onset of agglomeration, This led to difficulty because low frequency power sources and outlets, such as 50 Hertz and 60 Hertz are commonly available throughout the industrialized world and use of low frequencies would eliminate ` ~ 6~55-- I
I I
the need for expensive high frequency power supplies, and would drastically reduce the amount of power required as well as the attendant cost of power.
The present invention enables low frequencies to be used without a~glomeration or with only slight agglomeration.
A factor'that determines whether a suspension agglomer-ates, and affects the rate of agglomeration if agglomeration does take place, is the voltage gradient applied across the suspension.
Voltage gradient is here defined as the voltage across the suspension, divided by the thickness of the suspension; i.e., $n an ohmic cell the voltage applied between the two electrodes in the cell, divided by the distance between the electrodes. An ohmic cell is one in which the electrodes are in direct contact with the suspension. For example, when a voltage of 600 volts is applied across an ohmic cell in which the thickness of the suspension is 20 mils, i.e. .020 inch, the voltage gradient is 30 volts per mil. When an alternating voltage is used, it ¦ should be specified whether the stated voltage is peak-topeak, ' I or whether the stated voltage is a root-mean-square, i.e."R~lS, a;o value for a sine wave alternating Yoltage. A capacitative cell is one in which the electrodes are not in contact with the suspension, i.e. a cell in which an insulating or capacitative ¦ layer is placed between the electrodes and the suspension.
- ¦ Large voltage gradients are known to cause agglomera-¦ tion and to accelerate agglomeration; ~thereas small voltage ¦¦ gradients eliminate or retard agglomeration. Ho~tever, prior to this invention, small voltage gradients ~tere not useful because ¦ they did not open the light valves sufficiently for any 5 I practical application. ~he present invention enables small ~ voltage gradients to be useful hecause they open the light valves .1 . I

Il -24-il. . , ! ~
~1 I

11~;9~ I
1 to appreciable values of light transmission without agglomera-tion or with only small amounts of agglomeration.
Further advantages of small voltage gradients are:
, reduced electric power required to operate the light valve, with consequent savings of energy and cost; low voltage wiring, thereby requiring less electrical insulation around the electrica leads and terminals associated with the light valve; smaller power supplies, and power supplies of less weight; use o~ compact, mass produced solid state electrical and electronic components;
reduction of the electric current that passes through the suspen-sion, with consequent reduction of the heat ge~erated in the suspension. ~his last mentioned advantage accrues from the observation that heat generated in the cell tends to degrade ! and decompose the suspension, and can deteriorate the seals of the cell that contains the suspension within the light valve.
Another advantage of the this inventlon is that it enables liquid suspension light valves to be used to construct sunglasses and variable optical density spectacles e.g., welding goggles. Prior to this invention, such applications of liquid susp~nsion light valves were not practical because they req~ired high voltages, e.g. hundreds of volts, and such voltages carried close to the eyes and head of the wearer constituted a personnel safety hazard. The present invention enables said sunglasses, spectacles and goggles to be worn safely because the voltages are low e.g. 4 volts.
Prior to this invention, a polymer was used to protect the suspended particles in the light valve, but such prior-art . polymer had only relatively little effect in preventing agglom-eration, and rel~tively high voltacJe gradients were required to open the light valve when the prior art polymer was used.
Nitrocellulose is representative of the prior art.

..,..., I ,,j I l~L~fi95 The following further examples especially indicate the advantages of the polymers of this in~ention for the use ¦of low voltages in light valves.

EX~MPLE lOA
Step 1: Dissolve the polymer in an alcohol such as n-propanol or methanol, or an ether alcohol such as 2-ethoxy-, ethanol. Pour this solution into a high speed mixer, add 16.6 grams of tricresyl phosphate (TCP), and mix thoroughly. (Optionally, the TCP need not be added.) Step 2: Add 7.3 grams of methyl alcohc,l to 3.7 grams of quinine bisulphate (QBS), and stir until the QBS is dissolved. Add this solution to the mixture made in ' Step 1, and mix thoroughly in the high speed mixer.
,Step 3: Make a solution of 20 percent iodine crystals in " n-propanol which should age about 20 days. Take 8 grams ¦ of this solution and add 4 grams of n-propanol in which .27 grams of calcium iodide has been dissolved.
Shake until well mixed.
Step 4: The mixture of Step 3 is poured into the mixture of Step 2 while the latter mixture is in the mixer operating at hign speed. The mixer remains at high - speed for approximately 35 seconds, and is then stopped.
Step 5: ~ The resulting mixture is spread on a glass plate to dry for approximately 90 minutes in an atmosphere of 78 degrees F and SO percent relative humidity.
Step 6: ,The paste that results from Step 5 is scraped from the glass plate with a sharp blade. This paste is ¦ then ground in an electric mortar grinder for approx-~ imately 30 minutes. 90 grams of isopentyl acetate (IP~) Il -26~
! I .
!
! ' .

_ r ~
10~95~ ~

is then added to the mortar bowl. This mixture is the~
adaed to a jar containing 33 milliliters of chlorofor~
(CHCL3) and placed on a shaker for about one hour.
. ¦ Step 7~ The mixture resulting from Step 6 is diluted with I~
~ until it has an optical density of about 3 when place~ !
in a light valve cell with a spacing of 33 milS,i.e.
¦ .033 inch.
Step 8: The suspension resulting from Step 7 is centrifuged for 4 to 7 hours at a speed of 2500 revolutions per minute at a radius of about 3.5 inches. -;
Step 9, The supernatant from Step 8 is discarded; IPA is added to the sediment; and the diluted sedi~ent is treated in an ultrasonic gene-ator at a frequency ;t of 47 KH2 for 1 to 2 hours.
Step 10: Cent-ifuge again for 2 to 3 hours . Step 11: Repeat Step 9. . --Step 12: Centrifuse again, for 20 to 30 minutes, and discard : . the supernatant. `
Step 13: Dilute the sediment ~ith IPA to give a suspension Oc the desired optical density. -The following are specific examples of the polymers of this invention, and the methods of making suspensions with these pol~ners.

. EXAMPLE 10 Tetrapolymer: 3,5,5 trimethyl-l-hexyl acrylate/ ~`
2-hydroxy propyl acrylate/di-2-ethylhexyl maleate/fumaric acid, in the monomer percenta~es by weight 37.5/22/37.5/~.
A suspension was made in accordanc~ with the method in thc thirteen steps described above, with the following quan-tities used or excepti~ns. In Step 1, a solution of 2 grams o~

1~ llf~69~5'j 1 a the tetrapolymer in 20 grams of alcohol was used. In Step 6, the mortar grinder is not used. After Step 7, and before Step 8, the diluted mixture is placed in an ultrasonic genera- _ tor operating at about 47 KHz for about 17 hours.
'I Instead of Step 13, proceed as follows. Dilute the j sediment with IPA and the tetrapolymer to give a suspension that contains 8 percent of the tetrapolymer. Thereafter dilute further with an 8 percent tetrapolymer solution in IPA, to give s a suspension of ~he desired optical density.
1 0 ! E~r~lP LE 11 ¦ Tetrapo~ymer: 3,5,5 trimethyl-l-hexyl acrylate/
2-hydroxy propyl acrylate/vinylidine chloride/fumaric acid, in the monomer percent~es by weight 75/10/15/3.
A suspensic.~ was made in accordance with the method of ~15 Example 10, with the c~110wing exceptions. In Step 1, the ¦¦ polymer of Example 11 was used instead of the polymer of Example I! 10. - .
EXA~SPLE 12 .
Te~rapolymer: 3 ~,5 trimethyl-l-hexyl acrylate/
f20 2-hydroxy propyl acrylate/di-2-ethylhexyl fumarate/fumaric acid, in the monomer percentages by weight 37.5/22/37.5/3.
; ¦ ~ suspension was made as in Example 11, except that ¦I the polymer of Example 11 is re~laced by the polymer of Example 12.
EXA~IPLE 13 ¦ A suspension was prepare~xact~ as in the 13-step procedure above, using the homopoly~r of the prior art, nitro-¦ cellulose (NC) instead of the copolyrn~rs of this invention.
¦ In Step 1, 6.6 ~ra~s of HA 1~ NC and 7.5 grams of 1 21.6 centipoise NC (E.I. du Pont de Nemo~s & Co.) were "

i dissolved in 2 -ethoxyethanol. _ Suspensions made with the tetrapolymers in three of the preceding four examples, given above, do not agglomerate, or agglomerate very little compared to suspensions made with polymers of the prior art, when used in light valves. Further-more, light valves made with the suspensions in the aforesaid three new polymer examples open much more, i.e. transmit much more radi^ation, than suspensions`of prior art, for the same voltage gradient.
Suspensions made with the new polymers in the three aforesaid examples were tested and compared with a suspension made with nitrocellulose (NC). The tests were as follo-ls.
An ohmic light-valve cell, that provided a 33 mil thickness for a suspension, was filled successively with a suspension made ~lS with NC and with suspensions of the three examples. Each time ; the cell was filled, it was activated successively by alter-nating voltages at frequencies of 40, 60, 100 and 1000 ~Iz.
the ~olymer of In addition, 500 ~z was used for/Example 12. At each of the ~ aforesaid frequencies, voltages of 0, 100, 200, 300, 400, 500 and 600 volts peak-to-peak were applied successively. At each and every combination of the aforesaid frequencies and voltages, the optical transmission of the cell ~as measured in the visible portion of the spectrum, with an RCA photomultiplier No. 931-~ manufactured by Padio Corporation of America. The results are given in the following tables. The headings "NC" ' ¦'"
in the tables means the transmissions of suspension made with NC. The headinss' "new polymer" means the transmissions of the suspensions made with the polymers of the present invention in accordance with each respective example. The ratio of trans- j mission in each case is the quotient of the transmission of the n I

~ . I ~.~r~g~S' ~

:! suspension made with a new polymer divided by the transmission . of the suspension made with NC.
USING COPOLYI~ER OF EXAMPLE 10 FR~QUENCY: 40 Hz 5,~pplied Voltage Transmission Ratio of Voltage Gradient In Percent Trans-Peak-to-Peak Volts Per Mil NC New Polymer missions-0 ,. 0 .977.955 .971 100 3.03 1.02 1.32 1.29 0 200 6.06 1.26 3.47 2.75 ` 300 9.09 1.74 6.Çl . 3.79 400 12.12 2.51 10.23 4.07 500 15.15 3.98 12.59 . 3.16 . 600 18.18 6.17 14.13 2.29 .
1~5 USING COPOLYMER OF EXAMPLE 10 .
FREQUENCY: 60 Hz .
Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans-Peak-to-Peak . Volts Per Mil NC New Polymer missions .... .
.. 0 0 .977 .955 .977 100 3.03 1.02 1.32 1.29 200 6.06 . 1.35 3.31 2.45 300 ~ g.og 2.00 6.61 3.30 . ! 400 ~ 12~12 2.~5 10.47 3.54 ! 5oo 15.15 4.47 12.~8 2.75 1 -' 600 18.18 6.46 14.79 2.28 , . USING COPOLY~'ER OF EX~ ~LE 10 FREQUENCY: 100 Hz !! _30_ I

355 i ~ j ~1 I . . I .
.~. ¦ Applied Voltage Transmission Ratio of ¦ - Voltage Gradient In Percent Trans-. ~ Peak-to-Peak Volts Per ~lil NC New Polymer missions . 0 0 .977 .955 .977 . 5 100 3.03 1.05 1.32 1.25 200 6.06 1.41 3.39 2.40 300 ~ 9.09 2.00 6.61 3.30 400 _~ 12.12 .3.16 10.00 3.16 500 15.15 4.90 12.88 2.62 600 18.18 7.08 15.14 2.13 USING COPOLY~ER OF EX~PLE 10 FREQUENCY: 1,000 Hz . Applied Voltage Transmission . Ratio of .
. Voltage Gradient .In Percent Trans-Peak-to-Peak Volts Per ~lil NC New Polymer missions . 0 0 .955 .955 977 . ~ 100 3.031.26 1.45 1.15 200 6.062.51 3.63 1.~4 300 9.095.01 7.59 . 1.51 400 12.128.51 11.22 1.31 . 500 15.1512.59 13.~9 1.07 . 600 1~.1815.85 15.95 1.01 ~ . USING COPOLY~ER OF EXP~IPLE 11 .-~ . FREQUENCY: 40 Hz Applied VoltageTransmission Ratio of Voltage GradientIn Percent Trans-! Peak-to-Peak Volts Per ~il NC New Poly~ missions .977 1.18 l.20 100 3.031.02 2.3~ 2.30 1~ 200 6.061.26 6.31 5.00 . I ~ .

. 300 9.09 1.74 9.77 5.81 400 12.12 2.51 12.59 5.01 500 15.15 3.98 14.79 3.96 i 600 18.18 6.17 15.85 . 2.56 j USING COPOLYL~ER OF EXAMæLE 11 FREQUENCY: 60 Hz Applied Voltage Transmission Ratio of Voltage , Gradient In Percent - Trans-Peak-to-Peak Volts Per Mil . NC New Polymer missions 3~3 lo O o .977 1.18 1.20 ~3 I loo 3.03 1.02 2.2~ 2.19 .
200 6.06 1.35 6.31 4.67 .300 9.09 2.00 10.00 5.00 I 400 12.12 2.95 13.18 4.46 - .
i~ 500 15.15 4.47 15.85 3.54 . I 600 18.18 6.46 17.78 2.75 .
. ¦USING COPOLYMER OF EXAMPLE 11 lPREQUENCY: lC0 Hz ~ -i! Applied Voltage Transmission Ratio of 2~Voltage Gradient In Percent Trans- .
Peak-to-Peak V lts Per Mil NC New Polymer : missions .-0 0 .977 1.18 1.20 . 100 3.03 1.05 2.34 2.22 3200 ~ 6.06 1.41 6.31 4.~7 1300 9.09 2.00 9.55 4-77 400 12.12 3.16 12.88 4.07 j,500 15.15 4.90 15.85 3.23 !1600 18.18 7.08 18.62 2.62 . 30 1, 1' -32- . I

, i, ' ' .i il .

~ ~lnb~sS ~ I

~1 . USING COPOLYMER OF EX~lPLE 11 . FRE.QUENCY: 1,000 T~z Applied VoltageTransmission Ratio of Voltage GradientIn Percent Trans- . ¦
¦ Peak-to-Peak Volts Per Mil _NC New Polymer missions 0 0 .977 1.18 1.20 100 3.031.26 2.51 1.99 . 200 _, 6.062.50 6.31 2.51 300 9.095.01 10.47 2.08 10 400 12.128.51. 14.13 1.66 500 15.1512.59 16.60 1.31 ,600 18.1815.85 19.05 1.20 ¦ USING COPOLY~IER OF EXAMPLE 12 . - .
¦ ~ FREQUENCY: 40 Hz 15Applied VoltageTransmission Ratio of Voltage GradientIn Percent Trans-Peak-to-Peak Volts Per Mil NC New Poly~ missions ~` o o .977 1.02 1.04 100 3.03 1.02 1.86 1.82 .
~20200 6.06 1.26 5.01 3.97 .
300 ~.09 1.74 9.77 5.61 400 12.12 2.51 13.18 5.25 .. j 500 . I5.15 3.98 15.85 3.98 1 600 ; 18.18 6.17 18.20 2.94 11USING COPOLYMER OF EX~IPLE 12 ¦FREQUENCY: 60 ~Iz .
¦ ~o~lied . VoltageTransmission Rati.o of ¦ Voltage GradientIn Percent Trans-. Peak-to-Peak Volts Per Mil NC New Polymer missions !

6gss D ¦ i l 0 0 .977 1.02 1.04 i 100 3.03 1.02 1.86 1.82 ¦ 200 6.0G 1.35 4.68 3.46 300 9.09 2.00 11.22 5.61 Ij 400 12.12 2.95 15.49 5.25 -500 15.15 4.47 18.62 4.16 . I 600 18.18 6.46 19.50 3.01 . USING COPOLYMER OF E~IPLE 12 FREQUENCY: 100 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Tr~ns-Peak-to-Peak Volts Per ~lil NC New Polymer missions . 0 0 .9771.02 1.04 . . 1100 3.03 1.051.95 1.85 .
1200 6.06 1.414.79 3.39 300 9.09 2.0011.22 5.61 j 400 12.12 3.1615.49 4.88 i! 500 15.15 4.90 18.62 3-80 600 18.18 7.08 i9.95 '2.81 20. USING CQPOLY~R OF EXA~IPLE 12 ¦ j ~REQUENCY: 500 Hz Applied Voltage Transmission ~tio of I .j Voltage Gradient In Percent Trans- j i Peak-to-Peak Volts Per Isil NC New Polymer missions 2_ I 0 0 .9771.02 1.04 100 3.03 1.1~ 2.0~ 1.72 j,.200 . 6.06 1.95 5.50 2,~
300 9.09 3.55 10.96 3.08 400 12.12 6.03 15.14 2.51 1,500 15.15 8.91 17.78 1.99 I, -34-, ,1 . I
!
,, 600 18.18 ~2.02 19.05 1.58 USING COPOLYMER OF EX~IPLE 12 FRI:QUENCY: 1,000 ~Iz . ¦ Applied VoltageTransmission Ratio of 5j Voltage GradientIn Percent Trans- ' ¦
¦~ Pea~-to-Peak Volts Per Mil NC New Polymer missions ¦ .l 0 ' 0 .977 1.02 1.04 ~ I , 100 , 3.03 1.26 1.95 1.54 200 6.06 2.51 5.75 2.29 10300 9.09 5.01 11.22 2.23 400 12.12 8.51 15.85 1.86 500 15.15 12.5919.05 1.51 600 , 18.18 15.8520.42 .1.28 Examination of this data reveals the following.
'15 The use of the polymers of this invention results in more than a five-foid increase in the opening of the light valve compared to the use of prior-art polymers. This is for the copolynler of shown / Example 11 at 300 vol,ts and 40 ~z. It is shown also for the copolymer of ~ Example 12 at 300 volts at 40, 60 and 100 Hz.
~ . At all frequencies of the'activating voltage, and at ¦ all voltages, the polymers of this invention give greater value openings i.e. more transmission, than does the polymer of th~
prior art, i.e. NC. This is shown without exception in all rows of ~igures in all examples at all frequencies in all Oc the tables of measurements given above. In all cases, the use of the polymers of this invention enables the light valve to , be cpened more with a lower activating voltage.
The present invention can be used with light valves ! that are used as displays, windows including double glazed units,, ~ windshields, mirrors and many similar devices.

~1 -35-1~ . .
Il t, ~ i 6g~5 ..

! ¦ The previously described liquid suspe~sions can also be set (hardened) by not adding any plasticizer in their pre-¦ paration. The uses of such set suspensions include using these I thin, hardened films of material as sheet polarizers. -¦1 The polymers of this invention are useful with a variety of kinds of particles including dye particles, dichroic, pleochroic or light polari2ing dye materials.
. It is understood that this invention may be used for a light valve that operates in part or all of the infrared and/or ultraviolet portions of the electromagnetic spectrum as well as the visible part of electromagnetic spectrum depending on the type of light valve and suspension employed.
It is understood that the term "liquid", where ¦ applicable, may include a gel or a thixotropic liquid, or a ¦ plastic liquid provided that the suspended particles can beoriented therein upon application of an electric field.
I Although the polymers of this invention have been dis-¦ cussed herein primarily in terms of their use in a light valve ¦ suspension, it should be understood that they may be employed 1l in any other type of suspension where any of their properties ¦ may be favorably utilized e.g., as binders, in coatings for special papers, and in paints and ink formulations.
¦ While specific cmbodiments of my invention have been ¦ illustrated, it will be appreciated that the invention is not ¦ limited thereto, since many modifications may be made by one skilled in the art which fall within the true spirit and scope or the invention.

Ii ., ' . i 1~ !
'I ~

l! l ~_ I' i

Claims (30)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A light valve for controlling the transmission of radiation, which comprises a cell and a liquid suspension in said cell; said liquid suspension comprising:
an electrically resistive liquid suspending medium;
a plurality of small, anisometrically shaped, light-polarizing, halogen-containing particles suspended in said suspending medium; and a copolymer of at least two different monomers;
at least one of said monomers having a sterically unhindered functional group selected from the group consisting of an OH group and an acidic group, and at least one of said monomers having a branched group, the distance from the backbone of the copolymer to said sterically unhindered functional group most distant from the backbone being less than the distance from the backbone to the terminal group of said branched group, the branched groups in said copolymer being sufficiently soluble so that the copolymer as a whole is substantially dissolved in said liquid suspending medium.

2. The light valve of claim 1 wherein said branched group has a plurality of branches.

3. The light valve of claim 1, wherein said monomer containing said branched group contains none of said functional groups.

4. The light valve of claim 1, wherein said monomer containing said branched group constitutes more than 50%, by weight, of the copolymer.

5. The light valve of claim 1, wherein said monomer containing said branched group has a higher molecular weight than the other monomers.

6. The light valve of claim 1, wherein said monomer containing said branched group is a fluorinated monomer.

7. The light valve of claim 1 wherein the particles are polyhalide particles.

8. The light valve of claim 7 wherein the polyhalide particles are polybromide particles of colloidal size which are orientable upon application of a field to the suspension.

9. The light valve of claim 8 wherein the monomer containing said functional group is a hydroxyalkyl ester.

10. The light valve of claim 9 wherein the hydroxyalkyl ester is a hydroxyalkyl acrylate.

11. The light valve of claim 8 wherein the monomer containing said functional group is a polybasic acid.

12. The light valve of claim 11 wherein the polybasic acid is select-ed from the group comprising fumaric acid, maleic acid, and mesaconic acid.

13. The light valve of claim 8 wherein the monomer containing said branched group is an ether.

14. The light valve of claim 8 wherein the copolymer includes a monomer which is selected from the group comprising a partially esterified polybasic acid and a completely esterified polybasic acid.

15. The light valve of claim 8 wherein the monomer containing said branched group is a halogenated monomer.

16. The light valve of claim 8 wherein the copolymer is selected from the group comprising random, alternating, block, and graft copolymers.

17. The light valve of claim 1 wherein the suspending medium is non-aqueous.

180 The light valve of claim 17 wherein the suspending medium is a non-polar ether.

19. The light valve of claim 17 wherein the suspending medium is a halogenated liquid.

20. The light valve of claim 19 wherein the halogenated liquid is selected from the group comprising fluorinated alkanes, fluorinated esters and fluorinated ethers.

21. The light valve of claim 1 wherein the copolymer permits the suspension to achieve temperature stability above 100°F without significant degradation.

22. The light valve of claim 1 wherein the suspension is stabilized so that an applied voltage of at most 15 volts peak-to-peak per mil of suspension thickness at an AC frequency of 1000 Hertz or less will cause a substantial change in the light transmission of said suspension.

23. The light valve of claim 1 wherein the suspension has a light transmission for visible light of at most one percent, and has a light trans-mission of at least ten times that amount upon the application of at most 12 volts peak-to-peak per mil of suspension thickness at an AC frequency of 1000 Hertz or less.

24. The light valve of claim 1 wherein the particles comprise a material selected from the group comprising herapathite, cupric bromide, and purpureocobaltchloridesulfateperiodide.

25. The light valve of claim 1 wherein the copolymer is a copolymer of monomers selected from the group comprising 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate; ethyl acrylate/hydroxy-ethyl methacrylate; 2-ethylhexyl acrylate/2-hydroxypropylacrylate/acrylic acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 2-ethyl-hexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid;
3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl methacrylate; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl maleate/fumaric acid, 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl fumarate/
fumaric acid; 2,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/

vinylidene chloride/fumaric acid; 5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; bis-2-ethylhexyl fumarate/2-hydroxypropyl acrylate/
acrylonitrile; and bis-2-ethylhexyl fumarate/3,5,5-trimethyl hexyl acrylate/
vinylidene chloride/mesaconic acid.

26. A method of preparing and stabilizing the materials to form the suspended particles in a liquid suspension for a light valve, the suspension including a liquid suspending medium and particles suspended therein, com-prising the steps of:
providing a first material, providing at least one additional material which when combined with the first material forms polyhalide particles, providing a copolymer which includes at least two different monomers at least one of which includes an unhindered functional group, at least one of which is soluble in the suspending medium, and at least one of which is branched, and combining said first and additional materials to form polyhalide particles in the presence of the copolymer, the copolymer stabilizing the polyhalide particles when the polyhalide particles are suspended in the suspending medium.

27. The method of claim 26 wherein the copolymer is a material from the group comprising 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate; ethyl acrylate/hydroxyethyl methacrylate;
2-ethylhexyl acrylate/2-hydroxypropylacrylate/acrylic acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl methacrylate; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxy-propyl acrylate/di-2-ethylhexyl maleate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl fumarate/fumaric acid; 2,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid;

bis-2-ethylhexyl fumarate/2-hydroxypropyl acrylate/acrylonitrile; and bis-2-ethylhexyl fumarate/3,5,5-trimethyl hexyl acrylate/vinylidene chloride/
mesaconic acid.

28. The method of preparing a liquid suspension for a light valve comprising the steps of:
providing a first material, providing at least one additional material which when combined with the first material forms polyhalide particles providing a copolymer which includes at least two different monomers, at least one of which includes an unhindered functional group, at least one of which is soluble in the suspending medium, and at least one of which is branched, combining said first and additional materials to form polyhalide particles in the presence of the copolymer, the copolymer stabilizing the polyhalide particles when the polyhalide particles are suspended in the suspending medium, drying the polyhalide particles and copolymer, and suspending the dried polyhalide particles and copolymer in the suspending medium.

29. The method of claim 28 wherein the copolymer is a material from the group comprising 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/
hydroxyethyl methacrylate; ethyl acrylate/hydroxyethyl methacrylate; 2-ethyl-hexyl acrylate/2-hydroxypropylacrylate/acrylic acid; 2-ethylhexyl acrylate/
2-hydroxypropyl acrylate/fumaric acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl methacrylate; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/
di-2-ethylhexyl maleate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl fumarate/fumaric acid; 2,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid;
5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylatetfumaric acid; bis-2-ethyl-hexyl fumarate/2-hydroxypropyl acrylate/acrylonitrile; and bis-2-ethylhexyl fumarate/3,5,5-trimethyl hexyl acrylate/vinylidene chloride/mesaconic acid.

30. The method of stabilizing a liquid suspension for a light valve comprising the steps of:
providing a liquid suspension including a liquid suspending medium and a plurality of particles therein, and adding a copolymer which includes at least two different monomers, at least one of which includes an unhindered functional group, at least one of which is soluble in the suspending medium, and at least one of which is branched.