Nov. 5, 1968 J. L. FERGASON 3,409,404 ANALYTICAL METHODS AND DEVICES EMPLOYING CHOLESTERIC LIQUID CRYSTALLINE MATERIALS Filed Nov. 13, 1963 2 Sheets-Sheet 1

4/70 M j

20 2/

26 22

INVENTOR. JAMES L . FEQGASO/V

A 77'ORNEY.

1 3,409,404 United States Patent 0 1C@ Patented Nov. 5, 1968

1 2 It is optically negative, while smectic and nematic struc ' ' 3,409,404 ' ANALYTICAL METHODS AND DEVICES EM tures are optically positive. (2) The structure is opti PLOYING 'CHOLESTERIC LIQUID CRYSTAL cally active. It shows strong optical rotatory power. (3) LINE MATERIALS When illuminated with white light, the most striking James , L. Fergason, Verona, Pa., assignor to Westing property of the cholesteric structure is that it scatters house Electric Corporation, Pittsburgh, Pa., a corpora light selectively to ‘give vivid colors. A cholesteric mate tion of Pennsylvania ‘ rial exhibits a scattering peak having a bandwidth of Filed Nov. 13, 1963, Ser. No. 323,341 about 200 angstroms that occurs in or between the infra 19 ‘Claims. (Cl. 23-230) red and ultraviolet portions of the spectrum. (4) In the 10 cholesteric structure, one circular polar component of the incident beam is completely unaffected. For the dextro ABSTRACT OF THE DISCLOSURE cholesteric structure, it is only the circular. polarized The optical properties of a chloresteric liquid crystal beam with counter-clockwise rotating electric vector line material are changed when the cholesteric material which is re?ected. (The sign of ‘rotation refers to an ob is contacted with another material. A variety of mate 15 server who looks in the direction of the incident light.) rials, particularly vapors, are identi?ed by observing their Levo cholesteric structures have the reverse effect. (5) effect on cholesteric liquid crystalline materials. The most When circular polarized light is scattered from these ma convenient observable effect is a change in the color of terials, the sense of polarization is unchanged. In ordi the cholesteric material and, if necessary, comparing the nary materials, the sense of circular polarization is re change to the change effected by a known standard ma— versed. (6) The mean ‘wave length of the re?ection band terial. An analytical device may comprise one or more depends upon the angle of incidence of the beam. The distinct elements of cholesteric liquid crystalline mate relationship can be roughly approximated by the Bragg rial. Suitable cholesteric liquid crystalline materials in diffraction equation for a birefringent material. These enu clude a wide variety of compounds, and mixtures thereof, merated properties effectively de?ne cholesteric liquid derived from cholesterol. 25 crystals. A review of existing knowledge of liquid crystal line materials is found in an article by G. H. Brown and W. G. Shaw entitled “The Mesomorphic State—Liquid - This invention relates to the detection and analysis of Crystals,” Chemical Reviews, v. 57, No. ‘6, December matter, for example, gases and in particular concerns 1957, beginning on p. 1049. methods, articles of manufacture and apparatus particu 30 It has now been discovered, and it is on this discovery larly adapted to analysis on a qualitative and quantitative that the present invention is in large part predicated, that basis. gases, liquids and solids can affect the structure of cho It is a primary object of the present invention to pro lesteric liquid crystals so that one or more optical prop vide a novel method of analysis of both a quantitative erties thereof is at least temporarily changed. It has and qualitative nature, that is easily practiced, and is ‘further been discovered that, upon providing a compa highly sensitive to small concentrations of the materials rable basis, the resultant change is speci?c for the un to be detected. known involved which is thereby determined. By utiliz 7 Another object of the invention is to provide a novel ing these general principles an utterly new mode of analy method of identifying an unknown material. sis is provided. It is a further object of the invention to provide a The optical property most readily utilized in the prac method in which an unknown is brought into contact tice of this invention is that of selective scattering since with a new detector material and the character and it requires no polarizers or analyzers for observation. As amount of the unknown are indicated upon observing beforementioned, each cholesteric liquid crystal, at 1a an optical change in the system contacted. , given temperature and composition, exhibits, 'when ex An additional object of the invention is to provide a posed to white light, a scattering peak. In accordance novel detector, responsive by changes in an optical prop with this invention, the shift in the scattering peak may erty brought about by contact of the detector with an ‘be utilized for the analysis of unknown materials since unknown material. _ the direction of shift is a qualitative indication of the Other and further objects will be apparent from the unknown and the extent of shift is an indication of the following detailed description and discussion of the in quantity of the unknown. However, it is also possible to vention. utilize changes in other optical properties of the liquid Liquid crystalline materials have properties that are crystals. intermediate those of a true liquid and a true crystal since For example, it has also been found that the circular -_they have an ordered structure while also having ?uidity. dichroism and optical rotation of cholesteric materials Liquid crystalline materials are also referred to as mate are similarly affected by foreign matter. The component ' rials in the mesomorphic state. Liquid crystalline mate of circularly polarized light that is affected by the choles rials are known and are characterized or identi?ed by teric material ‘has a waveband of minimum transmission. one of three phases or structures. One is the smectic This waveband shifts in the same direction and to the structure, which is characterized by its molecules being same extent as the scattering peak. Similarly, the wave arranged in layers vwith the long axis approximately nor 60 band of peak optical rotation exhibits such a shift. Since mal to the plane of the layers. The second is the nematic cholesteric liquid crystalline materials have negligible structure, which is characterized by thread like molecules optical absorption, the transmitted radiation may be uti that tend to be and remain in nearly parallel orientation. lized for the purposes of this invention as well as the The third is known as the cholesteric phase the molecu scattered radiation. 65 lar con?guration of which has not yet been determined. _ In general, a material that is at least partially inter The present invention is concerned with materials ex soluble with the cholesteric liquid crystalline material hibiting a cholesteric liquid crystalline phase. will affect the optical properties of the liquid crystal in The cholesteric phase has certain characteristics which a reversible manner. Also it is the case that a material are markedly different from either the smectic or the 70 that chemically reacts with the cholesteric liquid crystal nematic phase. The characteristic properties of the ch0 line material will affect its optical properties in an ir lesteric structure may be summarized as follows: (1) reversible manner. In instances in which the effect is re a... versible, the liquid crystal provides an optical indication speed with which these changes occur also differ sub of the nature and quantity of the foreign material present stantially in many of the crystals. In instances, the gas at that instant. Because of the reversible nature of the permeating the crystal causes a vivid color change in but effect, the liquid crystal may‘ be continually reused. In seconds, or fractions of seconds. With the reversible sys instances in which they effect‘ is irreversible, thev liquid tems, the effect usually dissipates almost as rapidly, ap crystal provides ranloptica‘l indication of‘the same type parently as the volatile gas diffuses‘ back'»toiand'through that is cumulativeQHenée, each type of effect has ‘ad the atmosphererOther cholesteric liquid ‘crystals appear var'rt'ageous applications - and the j present‘ invention 'is con to have a “memory” and "the"resulttbropght'abotit' by,'\f'or cerhed‘with both reversible'and" irreversible effects. example, solubilizatiorfof gasz‘therei'n may remairr‘af'least ‘The present‘ invention permits identi?cation of a variety 10 partially for periods of hours apparently dueto ‘the; ‘forma of materials by reason of-their affect on cholesteric’liq'uid tion of relatively weak bond'slin theliquid crystal. crystalline materials-For example, reversible effects on Where the unknown to be determined is in the liquid the liquidcrystar optical properties‘have been observed or solid state, contact with thecholesteric liquid crystal withcommon'prganic solvents, amines, simple alcohols material generally diifersyfrom ‘that, employed with gaseous and’organic acids while irreversible ‘effects have been ob-' unknowns.- In these instances, it is‘ useful to‘ incorporate served'with-halogens, oxidizing agents,‘ alcohols,‘ amines, the unknown liquid or solidv in the liquid crystal material acids,‘ bases and'r‘educin'g agents.‘ ‘ while-‘the latter- is dissolved in a‘suitable solvent-There; ' By way of ‘example'and more 'speci?cally'in accordance upon, the-resulting mixture can be poured to-the" sub-: with this invention, vaporsor'gases'are detected and de strate. When the solvent evaporates, thereremains ‘the termined by‘contact thereof with a cholesteric liquid 20 liquid crystal having incorporated therein the added~un—> crystal.‘ In instances,‘ this contact ‘results ‘in a chemical known, either by reactionwith the crystal or by being reaction thatiis irreversible. Consequently, there is brought dissolved therein. Since the resulting cholesteric liquid about a change in the ‘contacted liquid crystal 'so that the crystal is intrinsically different from that which would resultant material'(vapor plus crystal) has diiferent'optical ' result-from the liquid crystal material solution alone, i.e. properties from1' the original or uncontacted cholesteric without the unknown added to the solution. It will be liquid crystal and these optical properties can be meas-‘ evident from what has ‘already beensaid that the, resulting ured. Moreover, the change,‘ being irreversible, remains optical properties, for example color, also will bediiferent, and the contact of additional vapor' “adds” thereto or is with the change being characteristic of the unknown em cumulative, and this may be employed for quantitative ployed. Further, because each cholesteric liquid crystal, determination of the gas involved. By measuring the re is itself unique, the ‘change brought aboutby a given sultant optical properties and comparing these with stand unknown will be unique in each different crystal’. ' _ _ ards, it is possible to determine, in this simple fashion, In addition to contact or interaction of’, a gas, liquid the speci?c gas brought into contact with the cholesteric or solid with a cholesteric liquid crystal, ‘mixtures liquid crystal as well as the amount thereof. can be used.v Accordingly, . two or.’ more gases or_ The absorption of certain gases in the cholesteric phase liquids. or solids may ‘be used with a liquid crys has an in?uence on the forces existing within that phase. tal composed of two or more cholesteric liquid crystals. For example, gas absorption can affect the packing forces Much information has already been determined with within the crystal. These changes are converted to changes binary and ternary cholesteric liquid crystals, and of course i in optical characteristics, for example color changes. ‘even more complex cholesteric liquid crystals can be... Moreover since these are speci?c for the particular gas 40 used. Mixtures can be employed to obtain properties, involved and the material used in the cholesteric ‘phase, such as sensitivity or breadth of operability or the like, there is provided an easily used detection system even in that may be inconvenient or vuneconomic to attain by a the absence of permanent change. single cholesteric liquid crystal. _ _ , v i . The manner by which contact or interaction of the un For use in the present invention, the cholestericliquid known and the liquid crystal is brought about may be 45 crystals can be disposed on any desired support and in determined largely by the state of the unknown. For ex any desired con?guration. The support can be ‘a plastic, ample, simply exposing the cholesteric liquid crystal to glass, ’ metal or the like. A film of polyethylene the vapor or gas has been sufficient, for the gas readily terephthalate that is blackened on one side has been found 7 permeates the crystal, changing its optical properties. A to be useful. The naturegof, the blackening material is great number of laboratory"determinations have been not at all critical since the liquid crystalline material made as follows: A liquid crystal was disposed on ‘a suita need not be in contact with it. Frequently, the crystals ble substrate or holder, for example a plastic or glass are prepared by simply pouring a solution thereof to surface, the crystal being of any diameter but usually 2 the substrate, and allowing the solvent to evaporate. That or 3 inches and 5 to 200 microns thick. Then materials generally results in a more or less circular crystal having to be tested, which very regularly were common laboratory a diameter dependent largely on the quantity of material liquid reagents, were brought close to the crystal. In the used. Such circular crystals normally are ‘of substantially, usual instance with, for example, chloroform, a bottle uniform thickness over most of their area and have containing it would be unstoppered and held in tilted posi thicker zones towards the edges. They can be used,as tion so that vapor in the vbottle above the liquid therein such, or trimmed to some other desired size. For some could‘?ow to the surface of the crystal. Vapors of chloro 60 purposes part or all of the crystal can be givenva regular formv are heavier than air and therefore readily ?ow shape, as by trimming, and then be transferred to other downwardly. For gases that are lighter than air, condi locations or substrates by careful stripping from their tions of upward ?ow can be used. Another convenient zone of deposition. Neither shape nor thickness‘ has been procedure is to‘ project the gas to the crystal surface, for found to be critical in the present invention. However,‘ example by using a syringe or similar means. For more‘ for standardization purposes, it is useful to employ crys- . complex practice as, for example, in using the discovery tals of uniform size and shape. A thickness of about 5 to monitor a room, a chemical reaction ‘or the like, other to 200v microns has been found to be satisfactory, but arrangements to secure the necessary contact may be thicker or thinner crystals can be used as well. With. used. In instances such practice may involve applying thin crystals, it is possible to use transparent supports and heat, or using shielding means, or other conditions that 70 substrates and observe, visually or by measurement, may be determined by the circumstances encountered in changes through the substrate. > " use and the liquid crystal that is to be used. The detector element, comprising the substrate and As already noted each cholesteric liquid crystal is the cholesteric liquid crystalline material, may be dis unique, and the response to any given material will be posed for use in numerous suitable ways. For some unique in the change ‘wrought in opticalproperties. The purposes, it is advantageous to employ an adhesive back; 3,409,404 5 6 ing on the substrate to permit application of the detector it is to be used. For example, cholesteryl caprate ex element to another object in any desired position. In hibits the phase from 82° to 89° C.; for cholesteryl instancesin which the substrate is a ?exible member, the myristrate, the range is 78° to 83° C.; for cholesteryl detector r'nay be formed as a tape thus permitting it to cinnamate, the range is about 161° to 197° C.; for cho be disposed for its end use even on non-planar surfaces. lesteryl propionate, the range is about 98° to 113° C.; .The active or operational detector element of this in for cholesteryl nonanoate, it is 79° to 90° C.; for choles vention is the cholesteric liquid crystal. As is known, the teryl arachidonate, the liquid crystalline phase occurs term cholesteric has been used because this state is ex below 0° C.; for cholesteryl p-nitro benzoate, the liquid hibited by compounds derived from cholesterol. Whereas crystalline phase occurs in the range from about 189° C. those derivatives constitute the most substantial class of 10 to 250° C. at which latter temperature it decomposes. known compounds exhibiting the cholesteric liquid crys Many mixtures of compounds forming the cholesteric talline phase, that phase is by no means limited thereto liquid crystalline state form cholesteric liquid crystal and, of course, cholesteric liquid crystals without regard phases at room temperature and below. Considering the to chemistry'can be employed in the present invention. compounds and mixtures as a whole, detectors are thus ‘Cholesteric liquid crystalline materials which are suit now available to operate for ranges of 5° to 100° C. at able for use in the invention include derivatives of delta any center temperature of minus 20° 'C. to in excess of 5-cholestene S-beta amino as well as compounds de 150° C. As is apparent, in using these materials in this rived‘ fromcholesterol. Some examples of suitable ma invention, the materials will be used at the appropriate terials include mixed esters of cholesterol and in temperature to secure the cholesteric liquid crystalline organic acids such as cholesteryl chloride, choles 20 phase. teryl bromide, cholesteryl nitrate, etc.; organic esters _Many of the foregoing compounds are available com of cholesteryl such as cholesteryl crotonate, choles mercially, having substantial commercial uses. Others terylnonanoate, cholesteryl formate, cholesteryl acetate, are disclosed in the literature to which reference can be cholesteryl propionate, cholesteryl valerate, cholesteryl made for details of preparations as well as general prop hexanoate, cholesteryl docosonoate, cholesteryl vaccenate, 25 erties. Some methods of synthesis found to be especially cholesteryl ,chloroformate, .cholesteryl linolate, choles~ useful are as follows: Cholesteric liquid crystals compris teryl linolenate, cholesteryl oleate, cholesteryl erucate, cho ing carboxylic acid esters of cholesterol can be prepared lesteryl butyrate, cholesteryl caprate, cholesteryl laurate, by heating cholesterol and a carboxylic acid to the boiling cholesteryl myristrate, and cholesteryl clupanodonate, point of the acid, or, in the case of high molecular weight etc.; ethers of cholesterol such as cholesteryl decyl ether, 30 acids, to about 200° C. After thorough reaction, the mix cholesteryl lauryl ether, cholesteryl dodecyl ether, etc.; ture is cooled to handling temperature. Cholesterol and carbonates and carbamates of cholesterol such as cho carboxylic acids can also be made to react in a benzene lesteryl decyl carbonate, cholesteryl methyl carbonate, solution or in other volatile hydrocarbon solvent upon the cholesteryl ethyl carbonate, cholesteryl butyl carbonate, addition of a catalyst, for example, para-toluene sulfonic cholesteryl docosonyl carbonate, cholesteryl cetyl car acid. Another useful method comprises reaction of an bonate, cholesteryl oleyl carbonate, cholesteryl heptyl acyl halide with cholesterol in the presence of a suitable carbamates, etc.; alkyl amides and aliphatic secondary proton acceptor, for example pyridine or analogous com amines derived from 3-beta-amino delta-S-cholestene, the pound. This latter reaction can be performed in the pres corresponding esters noted above of cholestanol, etc. The ence of a solvent if desired though none is needed. corresponding derivatives of beta sitosterol as well as Using the latter process, cholesterol and pyridine can active amyl ester of cyano benzilidene amino cinnamate be dissolved in equal amounts in benzene. The acyl are effective. chloride being used is also dissolved in a similar amount The alkyl portion of the above compounds comprises of benzene and in a like molar quantity. Then this latter at least one compound selected from the group consisting solution is added dropwise to the cholesterol-pyridine of saturated and unsaturated fatty acids and alcohols benzene solution. The reaction proceeds spontaneously, having from 1 to 27 carbon atoms per molecule, the usually with the evolution of heat and the formation of a unsaturated members having from 1‘ to 6 ole?nic groups ?ne white precipitate of pyridine hydrochloride. After per chain. Aryl substituents generally comprise a single complete addition of the acyl chloride, the mixture is re benzene ring that may have one or more lower alky ?uxed for about one hour to insure complete reaction. groups attached thereto. - ' Then the mixture is cooled to room temperature, the pre ‘The foregoing compounds exhibit a cholesteric liquid cipitate is ?ltered, washed with benzene and discarded. crystalline state over a given range of temperature. These The ?ltrate and washings are then treated with a lower temperature ranges in instances are small, and large in alkyl alcohol, for example methyl or ethyl alcohol. other instances for vthe list of materials given, the Crystallization is promoted by slow addition of the alco temperatures may be as low as about minus 20° C. to hol while constantly stirring. Recrystallization can be prac as high as about 250° C. The determination of the range ticed to obtain the pure product. Cholesteryl alkyl or for each material is easily made by heating the compound aryl carbonates can be readily made by ?rst reacting (or mixture) and noting the appearance of turbidity or phosgene with cholesterol, and reacting the product with possibly a color. After a further rise and at a de?nite the appropriate alcohol, in the presence of a proton ac temperature, the material clears to a true liquid and is 60 ceptor, to produce the mixed ester carbonate. Suitably a no longer in the cholesteric liquid state. Upon cooling solvent such as benzene is used as the reaction medium. from the true liquid state, the action is reversed, though Other suitable methods of synthesis can be used as desired. supercooling may'depress the ?rst noted temperature. The Reference will now be made to the attached drawing, consistency of the various materials may range from a in which: thick paste to a freely ?owing liquid, while in the liquid FIGURE 1 shows, in elevation, a cholesteric liquid crys crystalline state. The materials can be used in this state. tal disposed on a substrate; Some suitably are dissolved in a solvent, for example, FIG. 2 is a top view of FIG. 1; chloroform, ether, benzene, petroleum ether, carbon FIG. 3 shows, diagrammatically, a top view as in FIG. tetrachloride, common saturated hydrocarbon mixtures 2 and the effect of allowing a vapor to permeate part of such as kerosene, and carbon disul?de, or other common the liquid crystal; organic solvents, and then poured to a ?lm from which the FIG. 4 is a second view corresponding to that of FIG. solvent evaporates. These films frequently can be sep 3 showing further permeation by the added vapor; arated from the support and located where desired. FIG. 5 is a top plan view of an array of cholesteric Accordingly, each of the materials used in this in liquid crystals to be used in accordance with the inven vention has a characteristic temperature range at which tion; 7 FIG. 6 is a representation of a packed column having crystals, but any larger or smaller number of crystals cholesteric liquid crystals disposed vertically along the can be used as well. inside surface of the column; and As indicative of the results that can be achieved in FIG. 7 is a graph of data of the temperature versus accordance with the present invention, the following dem wave length characteristics of a cholesteric liquid crystal 01 onstration was made: All percents given are by weight. to which various oils have been added. 7 Y I . Ten liquid ‘crystalline*compositions were made,'~e'ach>con' Referring now to the drawing, numeral 10,.indicates a sisting of‘ afmixture vof cholesteryl ‘chloride and choles support orsubstrate member upon which a cholesteric teryl’ nonanoate: The amount off-cholesteryl 'chloride'in liquid crystal can be deposited and supported. Generally, the compositions vari'edfr'om 18% .to ‘311%. Films, or sub-l the__crite_rion for the use of any material as a substrate 10 stantially'. uniform thickness, fo'f each 'compositioqwere is only that it not interfere, as by‘reacting with the crystal made’ by mixing the constituents in .a1solyent_,of.“,20,% that is to be deposited thereon or masking the optical prop. chloroform and 80% petroleum ether. The solutions were erties of the crystal. Typical materials that have been poured onpolyethylene .terephthalate-?lm having a.black used include halogenated hydrocarbon resins such as poly coating on the opposite surface formed~by spraying with tetrafluoroethylene, polyethylene terephthalate and the a black‘ acrylic lacquer available under thenarne “Kry like, glass, methyl methacrylate resins, ceramics generally, lon” from Krylon, Inc., Norristown, Pennsylvania. The‘ etc. The substrate 10 may be any thickness desired. In in solvent was then permitted to evaporate. Each ?lm was stances where transparent substrates are used, it may be then exposed, at 27° C., to a'g'rou'p of common organic useful to limit the thickness so that the substrate does not solvents including acetone, butyl acetate,_benz_ene, chloro contribute unnecessary scattering of light that may be‘ 20 form, trichloroethylene, n-heptane and pyridine. The sol employed. On the upper surface 12 of the substrate 10 vent concentration varied‘from about 1 part per thousand is shown a cholesteric liquid crystal 14. As is evident from to ‘about 50 parts per million. The concentration was s'ui? the wide number of materials that have, a cholesteric cient to produce ‘color changes readily apparent'to the hu'-" liquid crystalline phase and therefore can be used in the man eye. Where no color change was observed, the de invention, it will be evident that a wide variety of ways tecting element eventually became colorless due to a phase of applying the liquid crystal to the substrate is possible. change. These solvents reversibly ‘affected the ?lm color For example, the crystal can be cast thereon, “buttered (i.e., the scatteredwaveband with the ?lm exposed t thereon,” applied from a dropper, painted, sprayed or white light) in the following manner: ~

PERCENT CHOLESTERYL CHLORIDE IN CHOLESTERYL NONANOATE

Solvents 18% t 19% 20% 21% 22% 23% 24% 25%‘ 27% 30% Aeetone______Red to Red to Green to Green to Green to Green to Green to Green to vGreen to Red (no blue. green. blue. slightly slightly slightly slightly slightly slightly change) . - red. red. red. ‘ . red. 1 red. ' . 'red. "w Butyl acetate ______d0_____ Red to _._..do__... Green to Green to . Green to Green to Green (no Green to Do. blue. blue. lue. blue. blue. change). red. ‘ Benzene ______(lo ______.do___...--__do ...... "do ...... do_._-. Green (no Green (no Green to ._‘___do_.... Do. . , change) change). , red. , Chloroiorm ______do ______do_ .__- Green to Green to Green to Green to Green to ' _-.._do_' ______do___-_ ’ Do. red. red. red. ‘ red. red . ' - " I Trichloroethylene ______._do ...... __do_ . . . . Ggien to Green to _ . _.. do. _ .y ..... _ .dop...... -.do ...... -do ______"do. _ _ . _ Do. ue ue. ' N-heptane ______do ______“do ______do ...... "do"... Green to Green to Green to Green to Green to Red to blue. blue. lue. . blue. lue. . blue. Pyridine ______do ______do ...... __do-____ Green to Green to Green to Green to Green to ' Green to Red (no red. red. red. red. r red. d. change) .

otherwise applied. A quite common method of application The data in the table illustrates that each solvent had a is to pour a solution containing the liquid crystal thereon unique effect on the set 'of ten liquid crystals. Thus if an‘ and allow the solvent to evaporate. unknown solvent of the group described were exposed to the set of liquid crystals, it could be readily identi?ed. When the crystal is deposited from a solvent as just 50 indicated, an irregular shape normally occurs and such For example: acetone isv unique in producing a red to is shown in the top view thereof in FIG. 2. In FIG. 2, the green shift in the 19% crystal; butyl acetate is unique in irregular shape 14 is the cholesteric liquid crystal and the producing no-change in the-green color of the 25% circular shape 12 is the surface of the substrate 10. crystalg'benzene is unique in causing no change in the As noted hereinbefore optical properties, such as color, green color‘of the 23% or 24%‘ crystals; chloroform is‘ of a liquid crystal change when a vapor is allowed to unique in producing a green to red shift in the 20% permeate the crystal. In FIG. 3, there 18 shown a small crystal; trichloroethylene is unique in producing di?erent’? irregular shape 16 within the irregular shape 14 which effects in the 21% crystal (green to blue) and the 22% constitutes the liquid crystal supported on the surface 12 crystal (green to red); n-heptane is unique in turning all of the substrate. 10. The irregular shape 16 constitutes a of the liquid crystals blue; and pyridine is unique in pro color area brought about by permeation by a vapor into ducing a green to red shift in the 21% vcrystal that is the cholesteric liquid crystal 14".1As more of that vapor readily distinguished from the slightly red appearance of‘ is added, the irregular shape 16 expands correspondingly that crystal when exposed to acetone. ' ’ as is shown at 16 in FIG. 4. v - Consequently, an array of the seven compositions hav ing from 19% to 25 % cholesteryl chloride in cholesteryl Since each liquid crystal is distinct and its reaction. or 65 response to an unknown is.distinct, an array of liquid nonanoate permits‘the speci?c identi?cation of‘the above crystals can be devised to give an immediate determina me‘ntioned seven solvents. ' . ‘ ‘ ' tion of the unknown. Such an array is shown in FIG. 5. The foregoing demonstrates the feasibility of forming Thus three distinct liquid crystals 20, 21 and 22 are sup an array of cholesteric liquid crystals that have a unique pattern in response to any of the materials that alter the ported on a substrate 26. The liquid crystals being of 70 known characteristics and known response to a given optical properties of the liquid crystals, thus providing a vapor, can be simultaneously exposed to an unknown “?ngerprint” of each of those materials. vapor. Observation of all crystals will, upon comparison Another application of this invention is in gas with standard information, indicate through optical chromatography, to which reference can be made in con change the identi?cation of the unknown. Of course, such junction with FIG. 6. There a vertically disposed trans an array need not be limited to three cholesteric liquid parent tube 30 can be adapted to have a plurality of 3,409,404 9. 10 liquid crystals of predetermined composition along its presence of any foreign material, e.g., a vapor, in the inside surface. In the embodiment shown three ‘liquid cholesteric liquid crystal affects the interaction of those crystals 34, 35 and 36 are used, though any other number forces and thus the scattering characteristics of the re could be employed. Within the tube 30 is a mass of gas sulting material. For the same reasons, other optical absorbents 38. At its lower end, tube 30 is provided with properties are similarly affected, such as optical rotation, a gas inlet 39 and a gas outlet 40‘ extends from the upper shift of circular dichroism, birefringence, and the like, end of the tube. Upon passing a gas into the system, it is and changes in those properties can be used in the analysis absorbed on the absorbent until the latter is saturated, system. Conventional optical instruments, recorders and at which time it passes onwardly. By appropriate place the like, such as a photomultiplier, a photocell and so on ment of speci?ed liquid crystals lengthwise or vertically 10 can be used also to read out the detector in addition to along the tube 30, the effective absorbency, or more cor direct visual observation. These may indeed be necessary rectly the failure to absorb possibly due to saturation, is for remote operations. promptly indicated because the gas would pass by that Mixtures of compounds also can be used. For example, portion of the absorbent, permeate the liquid crystal, for one such mixture was 45 percent of cholesteryl acetate example liquid crystal 34, and thereby change its optical and 55 percent of cholesteryl benzoate. It had a deep red properties which would be visible through the transparent color at room temperature. The composition of this mix tube, or could be measured. Similar action in due course ture was varied in ?ve percent steps in both directions. will be evidenced by crystals 35 and 36 vertically disposed It was found that the color was shifted further toward from crystal 34. Consequently, the liquid crystals can the red for either direction of composition change. Other be used to indicate absorbent effectiveness, and visually i mixtures were 50 percent each of cholesteryl acetate and show when regeneration or replacementshould take place. cholesteryl cinnamate; cholesteryl cinnamate and choles The cholesteric liquid crystals as such can be employed teryl benzoate; cholesteryl palmitate and cholesteryl ace as the packing for a gas chromatograph column. This is tate; cholesteryl palmitate and cholesteryl benzoate; cho— possible for gases to permeate and diffuse through each lesteryl chloroformate and cholesteryl palmitate; cho crystal in a distinct manner. This property permits gas lesteryl chloroformate and cholesteryl acetate; cholesteryl resolution; and the conditions at all times in the column chloroformate and cholesteryl benzoate. would be directly observable because of the light scatter In FIG. 7 there are plotted data obtained on a cho ing effects accompanying the diffusion. lesteryl liquid crystal varied by the presence of a small In another contemplated use for the present invention, amount of different commercial oils. The various liquid a cholesteric liquid crystal would be disposed within a 30 crystals were illuminated with a helium lamp. The color controlled atmosphere reaction zone. If the reaction to of maximum re?ected intensity, corresponding to the be carried out were, for example, to be accomplished in strong spectral lines of helium, was observed at various the absence of oxygen or air, a liquid crystal particularly temperatures and plotted for each system. The base cho sensitive thereto could be used. Upon observing changes, lesteric liquid crystal in all instances was, by weight, if any, in the liquid crystal an operator would immediately 35 20 parts of cholesteryl propionate and 80 parts Otf cho know if his conditions of oxygen concentration were no lesteryl nonanoate. Data for the ?rst (top) curve were longer tolerable. He could accordingly take appropriate obtained on that mixture free of the oils. Then a crystal action. Where this system is used in connection with a was formed by adding 5 parts by weight of oleic acid to vacuum pump, a photocell can be focused on the crystal the 20:80 mixture of the propionate and nonanoate, and and be adapted to start the pump when the crystal indi 40 pouring to a substrate in the usual manner. The third cated an undesirable oxygen concentration. For example mixture was made by adding 5 parts of acodar (commer a mixture of 30 weight percent of cholesteryl eleosterate, cial oil with high percentage of free fatty acids) to the 20 weight percent of cholesteryl nonanoate and 50 weight base mixture. Number 4 was 5 parts of coconut oil and percent cholesteryl oleyl carbonate, which is red at 24° 100 parts of the base. Similarly, 5 parts of corn oil, of C., would change to a blue color upon absorption of tall oil, of triolen and of methyl oleate were used with oxygen. A typical reaction in which such a system may base .mixes to provide, respectively, the 5th through 8th be particularly useful is that in which organo-metallic liquid crystals. Temperature-wave length data were taken compounds, such as an alkyl lithium, are involved. on each and plotted. It is to be noted that FIG. 7 is sub Numerous similar applications are possible in view of the stantially to scale, and direct reading can be made from it. great number of controlled atmosphere reactions and The curves of FIG. 7 show many of the unique charac processes that are presently practiced. As other control teristics of the discovery. The substantial effect of tem examples, it is noted that very small amounts of gaseous perature on any of the given crystals is plain. The unique hydrogen chloride convert, at about 25° C., a cholesteric effect of any of the additives in the same crystal also is liquid crystal composed of 10 weight percent of cholesteryl plain, and shows at once that these materials, which have 3-beta-amine, 10 weight percent of cholesteryl nonanoate some chemical similarity, can be detected and distin and 80 weight percent of cholesteryl oleyl carbonate from guished. For example, if any of these materials is known blue to red. Similarly the presence of ammonia at room to be present in the base crystal mixture, temperature temperature is indicated by a substantial blue color in a scanning to give a characteristic color will immediately liquid crystal composed, by weight, of 20 percent of show which it is. Or at constant temperature, the maxi chloroformate, 60 percent of cholesteryl oleyl carbonate 60 mum re?ection of helium light can be noted, thereby and 20 percent of cholesteryl. nonanoate. showing which additive is involved. Thus if maximum re Another example of the invention was: A liquid crystal ?ectance of the crystal is red at 26° C., the additive is was made from equal parts by weight of cholesteryl ace coconut oil, while if, at the same temperature, it is yellow, tate and cholesteryl benzoate. At room temperature in the curves show it to be corn oil. ordinary light, a 10 micron thick ?lm ‘of this crystal was Further a constant temperature line can be projected red. Benzene vapors changed it to blue. Chloroform vapors across this graph and the sharply differing colors noted deepened its red color, Trichloroethylene caused a change for several compositions. For example, the 26° C. line to blue. v ‘v ' crosses the curves for mixtures 4, 5, 6, 7 and 8 and the Theoptical property most frequently used to observe colors indicated will range from red to blue. change v(and therefore the presence of an unknown) in 70 The data in FIG. 7 can be replotted. Thus if the ratio a cholesteric liquid crystal has been color. A change in of the slopes of any of the curves 2 through 8 to that of color, of‘ course, is evidence of a change in the scattering curve 1 be replotted versus the wave length, a curve char characteristics of the cholesteric liquid crystal. The acteristic of the effect of the additive in the particular cholesteric phase exists in a balance of short-range van liquid crystal (the base mixture) is found. Any other der Waals and longer range dipole interaction forces. The amount of that additive in this liquid crystal will give an ..11 12 other curve of this type having the same general charac-,-. .:.f0 insurereproducibility.and ‘that the results achieved can teristics as this particular curve. Identi?cation is possible be appropriately interpreted. In this invention, substrates through this, and by standardization procedures quantities can affect the intensity of a'color (dark substrates re?ect eanalso be recognizedrThis same procedure of forming better) and must be considered to that extent. Tempera standard references can be accomplished with any other ture in most instances has..a striking effect (see FIG. 7), cholesteric liquid crystal and, with any other_;series of and canJbring- about a;,color change or change in other chemically similar additives with similar results... 4_ optical property-This can occasionally be utilized to fur Anotherv series ofv mixtures‘. included equal parts of therjre?ne the a'nalylsissystemuGenerally, however, this cholesteryl acetate, cholesteryl benzoate, andcholesteryl mustiim'er‘ely be‘ noted,‘ so that changes‘ resulting will be palmitate. This gave a very stable ,liquid crystal, and its 10 attributed to'the ‘proper in?uence. A ‘dipole ?eld’canq'affect colorv was green at roomtemperature. The color could be the ,dipolar charactero?cholesterol derivatives. A" shear varied toward the red by adding a small ‘amount‘o‘f chow? stress 'applied to a cholesteric ‘ liquid )crystal ‘can ’ change lesteryl benzoate. Cholesteryl cinnamate was added to the optical characteristics.'Radiation'can affect the chemi a mixture of this nature with the result that a highly ' "I cal constitution therebyproviding a different cholesteric stable liquid crystal phase was formed which could be liquid ‘crystal and, consequently, differentv optical proper shifted to the red by adding more ,cholesteryl cinnamate. ties. The aii‘gl’e'of incidence-and the character of light used The color of the mixture of cholesteryl acetate, palmitate, cenalso- 12¢ signi?cant; For example, with polarized or and benzoate fell roughly at the wavelength of the 55.40 unpolarized ‘light, the scattering maximum (50%‘). isyall A. line of mercury at room temperature. It was found circularly. dichroic at normal incidence, butdecreases as that 30 percent each of cholesteryl acetate, cholesteryl the angle of incidence increases. Inany of the foregoing benzoate, cholesteryl palmitate plus 10 percent cholesteryl instances~,~;no adverse effects will result, in any analysis cinnamate formed a liquid crystal whose colorwas about procedureif, for example, the-test temperature is the that of the sodium D line at room temperature. It was ‘ ,‘ same asthat at which the standard was determined,_or found that by intermediate mixtures any spectral color ' but a single angle of incidence is used and so on. 7 could be obtained. Iv v 25 From the foregoing discussion, description and data The sensitivity of the analysis procedures made possible it is evident that the present invention constitutes a unique by this invention is considered utterly remarkable when and highly effective analysis discovery. Its sensitivity can compared with any other system presently available to be compared to that of the human nose in scope. Data the analyst. The data in FIG. 7 show this. Other tests of have vshown that with it, changes in‘ concentration on the invention have further con?rmed this unique aspect 30 the‘o'rder of but a few parts per million 'can' be detected, of the invention. For example, tests with a series of tri as well as chain characteristics, isomerism and other slight glycerides provided analogous results to those shown in variations in chemical structure. It may be noted that FIG. 7. In other tests, I have been able to distinguish cis quantities of iriaterial'used are not critical, and are gen and trans isomerism by the difference in degree of effect erally, important onlyfor quantitative analysis. However, produced. In those determinations made to date, cis in'th'e 'practice'of the invention it has been the usual prac isomers have been found to produce a greater shift in color tice to use abou't'one" to 50 parts by weight of the unknown or other optical characteristic than the trans con?guration per I00 parser liquid crystal, though other weight ratios of the same chemical compound. Further, a series of tests could be used aslw'ell. ‘When it is considered that a ‘deter were made with alcohols of varying chain length in cho ‘- mination can‘ be readily made with very minor amounts of lesteryl chloroformate and it was observed that where the 40 the cholesteric" liquid crystal, the economy available with alkyl moiety therein had an even number of carbon atoms ' invention ‘becomes apparent. a lesser effect was present on the temperature vs. wave While theinvention has been disclosed with respect to length characteristics than if the chain had an odd num speci?c materials and conditions it' will be evident that ber of carbon atoms, thereby adding this additional re‘ changesi'can be made in it without departing from its ?nement to the analysis procedures now available. Types scope. ' of steroids are also distinguishable from one another. 'I claim: Further, differences of a C2H5 group in a compound ‘have "'1. A method‘ of identifying an unknown material com been detected. Indeed, I have noted that even the location prising the steps of providing a cholesteric liquid crystal of a double bond gives a characterizing result by changing element, contacting the liquid crystal element with said the slope of a temperature vs. wave length curve. It is 50 unknown‘ material, and observing a change in an‘ optical conceived that re?nements will give characteristics as use property of the cholesteric liquid crystal element in re ful as spectographs presently are in the analysis‘ of some sponse to the presence of said unknown material. materials, but with an ease of practice and an economy ' '2. A method‘ of identifying an unknown vapor com that will be of great advantage. ' prising the steps of obtaining a thin ?lm‘of cholesteric For analysis or detection systems where continuous 55 liquid crystalline material, bringing the unknown vapor ' monitoring is undesirable or not possible, an irreversible into contact With‘the ‘thin ?lm, and observing a change detector may be more useful than those of reversible sys in an optical property of the liquid crystal in response to tems. ‘In the irreversible system, interaction of the cho the presence of the unknown vapor. _ lesteric' liquid crystal and the unknown occurs bringing 3. A method ‘of identifying an unknown'vapor com about a permanent change in optical properties ‘because, 60 prising the steps of obtaining a thin ?lm of ‘a material in in effect a new cholesteric liquid crystal results from the ancholesteric' liquid crystalline phase, exposing ‘the, thin interaction. The effect on optical properties depend‘s'on ?lm to the vapor whose'composition is to be determined the speci?c materials reacted and their concentrations. ' and which is at least partially soluble in the thin ?lm, and In this manner,.vcholesteryl nonanoate, or any cholesterol observingthe color-,changcin the thin ?lm in response to 65 derivative, can be used to detect free halogens suchvas, the presence of the vapor. " . -. I . _ chlorine or bromine. Ozone, oxygen and the halogens ‘can 4. A method of identifying an. unknown material com be detected and determined by cholesteryl allyl ether or prising the steps of mixing ‘a predetermined quantity of the cholesteryl eleostearate. - ‘ H if unknown material and a material capable of exhibiting In the foregoing instances, the mechanism of reaction a cholesteric‘ liquid crystal phase with known optical prop is presently understood 'to be primarily that of addition erties, obtaining a ?lm in a cholesteric liquid crystal phase to double bonds and, in some cases, catalysis of polymer-_ from the resulting mixture and observing a change in ization. In addition, it has been found that alcohols, and amines can be detected by cholesteryl chloroformate in optical property in the ?lm from those of the cholesteric a reaction that forms a'carbonate or urethane. - liquidcrystal in the absence ofthe added unknown ma “ In any analysis procedure, standardization is practiced 75 terial. ' 3,409,404 13 14 5. A method in accordance with claim 4 in which the elements disposed on said substrate so as to permit radia unknown in a liquid. tion and molecules from the surrounding atmosphere to 6. A method for identifying an unknown liquid com‘ impinge thereon; said substrate being non-reactive and in prising the steps of dissolving a quantity of a material soluble with said sensitive elements; each of said sensi capable of existing in the cholesteric liquid phase with tive elements comprising a different material, each such known optical properties in a solvent therefor, adding a different material being in a cholesteric liquid crystal~ quantity of the unknown liquid to the resultant solution line phase in a given temperature range and each exhibit to produce a new solution, obtaining a ?lm in a cholesteric ing a sensitivity by which the color of said sensitive ele liquid crystal phase from the new solution and observing ment changes in a predictable and reversible manner the change from the known optical property in a ?lm 10 upon the solution of a‘ material therein, the color changes obtained from the resultant solution. of di?’erent ones of said plurality of sensitive elements 7. A method for identifying an unknown liquid com being dissimilar so that upon exposure of said array to prising the steps of dissolving a predetermined quantity a material to be analyzed while in said temperature range of a material capable of existing in the cholesteric liquid a color pattern is formed in said array that assists in deter phase with known optical properties in a solvent there 15 mining the composition of said material. for, adding a measured quantity of the unknown liquid to 13. A detector element having a cholesteric liquid the resultant solution to produce a new solution, obtain crystalline phase comprising a mixture of compounds, ing a ?lm of the new solution in a cholesteric liquid said mixture containing an alkenyl carbonate of a com crystal phase, adding an additional measured quantity of pound selected from the group consisting of cholesterol the unknown liquid to the said new solution to obtain a 20 and cholestanol. third solution, obtaining a second ?lm of the third solu 14. The detector element of claim 13 wherein said tion in cholesteric liquid crystal phase, observing the carbonate is cholesteryl oleyl carbonate. optical properties of the two ?lms and comparing the 15. The detector element of claim 13 wherein said properties found with standards to identify the unknown carbonate is cholestanyl oleyl carbonate. liquid. 25 16. An analytical device comprising a substrate, a 8. A method for identifying an unknown solid com plurality of distinct sensitive detector elements disposed prising the steps of ‘dissolving a quantity of a material on said substrate, each of said elements containing a ma-. capable of existing in the cholesteric liquid phase with terial in the cholesteric liquid crystalline phase. known optical properties in a solvent therefor, adding a 17. The device of claim 16 wherein said material is a quantity of the unknown solid to the resultant solution to 30 mixture of compounds, said mixture containing an alkenyl produce a new solution, obtaining a ?lm in a cholesteric carbonate of a compound selected from the group con liquid crystal phase from the new solution and observing sisting of cholesterol and cholestanol. a change in color in the ?lm from the new solution com 18. The device of claim 17 wherein said carbonate is pared to the color of a ?lm obtained from the resultant cholesteryl oleyl carbonate. solution. 35 19. The device of claim 17 wherein said carbonate is 9. A method for identifying an unknown solid com cholestanyl oleyl carbonate. prising the steps of dissolving a predetermined quantity of a material capable of existing in the cholesteric liquid References Cited phase with known optical properties in ‘a solvent therefor, UNITED STATES PATENTS adding a measured quantity of the unknown solid to the 40 resultant solution to produce a new solution, obtaining a 3,114,836 12/1963 Fergason et al. ______23-230 ?lm in a cholesteric liquid crystal phase from a portion of 2,785,057 3/1957 Schwab et al. ______23--253 the new solution, adding an additional measured quantity 3,006,735 10/1961 Jordan ______23-253 of the unknown solid to the said new solution to obtain a 3,215,498‘ 11/1965 Schlitt ______23—232 third solution, obtaining a ?lm in a cholesteric liquid 45 crystal phase from the third solution, observing the optical OTHER REFERENCES properties of the two ?lms and comparing the properties Peters, J. P. ‘and Van Slyke, D. D.: Quantitative found with standards to identify the unknown solid. Clinical Chemistry, The Williams and Wilkins Co., Balti 10. In combination: ‘apparatus comprising a column more, 1963, p. 509 relied on. having gas inlet and gas outlet means to said column, a 50 Gray, G. W.: Molecular Structure and the Properties of cholesteric liquid crystal disposed in the column inter Liquid Crystals, Academic Press, New York, 1962, pp. 6, mediate the inlet and outlet means, said column being 11, 12, 47,193, 194 relied on. capable of containing a mass of solid absorbent, the liquid International Critical Tables: vol. I, pp. 314-320 Q199 crystal being capable of solubilizing gas to be absorbed N32 Mar. 10, 1927. by the solid absorbent, whereby the passage of gas through Merck Index: 7th ed., Merck & Co. Inc. RS 356 M524 the column to at least the liquid crystal therein can be 1960 c. 36. ' observed by change in optical properties in the cholesteric Whitaker’s Five-Year Cumulative Book list 1958 liquid crystal. 1962: J. Whitaker & Sons, London, 1963. 11. An article for the analysis of a material comprising: Gilman, H.: Organic Chemistry, An Advanced Treatise, a substrate; a plurality of sensitive elements disposed on vol. 2, J. Wiley & Sons, Inc., New York, 1938 pp. 1271 said substrate, each of said sensitive elements comprising 1272 relied on. a different material, each such diiferent material being Dewey, B. T. & Gelman, A. H; Ind. & Eng. Chemistry, in a cholesteric liquid crystalline phase and each exhibit Anal. Ed. 14, 361 (1942). . ing a sensitivity by which the color of said sensitive ele Kirchner, J. G., Miller, J. M., and Keller, G. 1.: Anal. ment changes upon the solution of a material therein, Chemistry 23, 420 (1951). the color changes of different ones of said plurality of Lederer, E., and Lederer, M.: Chromatography, A sensitive elements being dissimilar so that exposure to a Review of Principles and Applications, Elsevier Pub. Co., material to be analyzed produces a color pattern in said New York, 1957, pp. 172~173 relied on. plurality of sensitive elements that assists in determining the composition of said material. 70 MORRIS O. WOLK, Primary Examiner. 12. An article for the analysis of a material com prising: a substrate; an array of a plurality of sensitive R. M. REESE, Assistant Examiner. “L