US3723346A

US3723346A - Temperature indicator using the smectic c phase of a liquid crystal

Info

Publication number: US3723346A
Application number: US00146520A
Authority: US
Inventors: T Taylor; J Fergason
Original assignee: INT LIQUID XTAL CO
Current assignee: International Liquid Xtal Co; INT LIQUID XTAL CO
Priority date: 1971-05-24
Filing date: 1971-05-24
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27

Abstract

TEMPERATURES MAY SOMETIMES BE QUICKLY AND CONVENIENTLY SENSED AND/OR MAPPED WITH THE USE OF A VARIABLE-TILT COMPOUND OF THE SMECTIC C MESOMORPHIC PHASE. DISCLOSED ARE SEVERAL ORGANIC COMPOUNDS THAT ARE CAPABLE, WITHIN CERTAIN TEMPERATURE RANGES, OF EXHIBITING SUCH A PHASE, SUCH AS TEREPHTHAL-BIS(4-N-BUTYLANILINE) AND OTHER COMPOUNDS RESULTING FROM THE REACTION OF TEREPHTHALDEHYDE WITH AMINES OR AMIDES OF THE FORMULA:

1-R,4-A-BENZENE

WHERE A IS -NH2 OR -CONH2 AND R IS A SATURATED ALKYL OR ALKOXY GROUP CONTAINING 1-12 CARBON ATOMS. THE COMPOUND IS MADE, APPLIED TO A SURFACE THAT HAS BEEN RUBBED UNIDIRECTIONALLY, AND THEN (WHILE THE COMPOUND IS WITHIN ITS SMECTIC C PHASE TEMPERATURE RANGE) VIEWED IN LIGHT THAT IS POLARIZED PLANARLY OR CIRCULARLY. THE TEMPERATURE INDICATION IS SENSITIVE TO CHANGES IN TEMPERATURE THAT ARE QUITE SMALL, AND THE RESPONSE PATTERN IS EXCEPTIONALLY RAPID (BEING ON THE ORDER OF A MILLISECOND AT THE GREATEST), SINCE NO MOLECULAR REARRANGEMENT IS INVOLVED.

Description

United States Patent Int. Cl. G02f 1/16 U.S. Cl. 252-408 Claims ABSTRACT OF THE DISCLOSURE Temperatures may sometimes be quickly and conveniently sensed and/ or mapped with the use of a variable-tilt compound of the Smectic C mesomorphic phase. Disclosed are several organic compounds that are capable, within certain temperature ranges, of exhibiting such a phase, such as terephthal-bis (4-n-butylaniline) and other compounds resulting from the reaction of terephthaldehyde with amines or amides of the formula:

where A is --NH or -CONH and R is a saturated alkyl or alkoxy group containing 1-12 carbon atoms. The compound is made, applied to a surface that has been rubbed unidirectionally, and then (while the compound is within its Smectic C phase temperature range) viewed in light that is polarized planarly or circularly. The temperature indication is sensitive to changes in temperature that are quite small, and the response pattern is exceptionally rapid (being on the order of a millisecond at the greatest), since no molecular rearrangement is involved.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to novel organic chemical compositions that exhibit a variable-tilt Smectic C phase and to a method of sensing or mapping temperatures of an object with the use of such compositions.

(2) Description of the prior art SUMMARY OF THE INVENTION Temperatures may sometimes be quickly and conveniently sensed and/ or mapped with the use of a variabletilt compound of the Smectic C mesomorphic phase. Disclosed are several organic compounds that are capable, within certain temperature ranges, of exhibiting such a phase, such as terephtha1-bis-(4-n-butyl aniline) and other compounds resulting from the reaction of terephthaldehyde with amines or amides of the formula:

Q where A is -NH or CONH and R is a saturated alkyl or alkoxy group containing 1-12 carbon atoms. The compound is made, applied to a surface that has been rubbed unidirectionally, and then (While the compound is within 3,723,346 Patented Mar. 27, 1973 its Smectic C phase temperature range) viewed in light that is polarized planarly or circularly. The temperature indication is sensitive to changes in temperature that are quite small, and the response pattern is exceptionally rapid (being on the order of a millisecond at the greatest), since no molecular rearrangement is involved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been unknown, prior to the instant invention, that there are compounds of the Smectic C phase that exhibit a temperature-dependent tilt angle. These com-' pounds of the Smectic C phase may be used for the measurement of temperature, at least within the temperature domain wherein the compound involved exhibits the Smectic C phase. A prerequisite to the practice of the invention is that the molecules that are within the Smectic C phase are oriented in such a way that the layers are all parallel to the surfaces that contain the liquid-crystal material. This parallelism may be accomplished in various ways, such as by rubbing the containing surfaces with a cotton cloth, or with paper or other material that has an orienting influence on the surface with which the liquidcrystal material is in contact. Liquid-crystal material is then placed between the two rubbed surfaces in such a way that the rubbed directions of the surfaces are parallel. In some instances, a desired parallel orientation of the layers may be achieved by containing the liquid-crystal material between two surfaces, only one of which has been so unidirectionally rubbed. There is thus obtained a liquid-crystal unit, and when circularly polarized light is caused to become incident upon the stratum of liquidcrystal material, the liquid-crystal material gives a uniform retardation thereacross, provided that the temperature is constant across the sample. If the temperature throughout the domain of the stratum of temperaturedependent variable-tilt Smectic C liquid-crystal material is not uniform, the liquid-crystal material then does not have a tilt angle that is uniform, but rather has a tilt angle that varies in accordance with the temperature in various portions of said domain, and there is thus obtained an optical retardation that varies from one location to another within the sample, with the value of said optical retardation depending upon the tilt angle at any particular location within thesample. Thus, if the sample is observed in transmission of a circular polarizer having a sense opposite to that of the incident light, there is observed an interference color that is characteristic of the temperature of the liquid-crystal material at a particular point within the above-mentioned domain.

One example of a material that exhibits the properties that are discussed above is terephthal-bis-(4-n-butyl) aniline, which has a variable-tilt Smectic C phase in the temperature range of 172.5 C. to 144.1 C. In that temperature range, the tilt angle changes from 0 degree to 26 degrees. The rate of change of the tilt angle is not linear over the temperature range. In the temperature range of 172.5 C. to 166 C., the tilt angle changes rather rapidly at a rate exceeding 3 degrees per degree centigrade, and from 166 C. to 144.1 C., the rate of change is on the order of 0.5 degree per degree of centigrade. This change of tilt angle is reversible with temperature, so long as the liquid-crystal material is not allowed to crystallize into a dilferent phase.

Terephthal-bis-(4-n-butyl)aniline may be prepared as follows: One mol of terephthaldehyde in 8 mols of ethanol is mixed with 2 mols butyl aniline. The mixture is refluxed for 16 hours. Terephthal-bis (4-n-butyl)aniline is obtained in percent yield, after recrystallization from ethanol.

We have found, moreover, that the above-mentioned tilt angle is repeatable or reproducible with temperature variations within a range of or 0.2 degree centigrade. The reproducibility may be better than that, since the equipment used to determine such reproducibility was itself only accurate to within or 0.2 degree centigrade. Those skilled in the art will appreciate that liquidcrystal materials of the variable-tilt Smectic C phase comprise exceedingly good temperature indicators, because very small changes in optical retardation may easily be observed with the use of suitably (planarly or circularly) polarized light.

There are other liquid-crystal materials or compounds that have exhibited properties that indicate that they possess a variable-tilt Smetic C phase. Such compounds are terephthal-bis-(4-n-butylaminobenzoate); terephthal bis- (4-n-hexyloxyaniline); and terephthal-bis-(4-n-octyloxyaniline). Their Smectic C temperature ranges are, respectively; 91 C. to 134 C.; 175 C. to 230 C.; and l73.7 C. to 231.5 C.

It may thus be stated that the compounds that exhibit the variable-tilt Smectic C phase appear for the most part to be products of the reaction of one mole of terephthaldehyde with 2 moles of an organic amine or amide of the class having the structure:

where A is an amine (--NH or an amide (-COHN group and R is a saturated and preferably straight-tail aliphatic alkyl or alkoxy group containing 1 to 12 carbon atoms. As will be apparent, the group R is located para to the reactive group A by means of which it is joined to the terephthaldehyde to form the compound in question.

There is thus obtained a compound of the structural formula:

where X is a radical selected from the group consisting of =N and In accordance with the further embodiment of the present invention, a Smectic C variable-tilt liquid-crystal material is caused to be oriented as previously described upon a metallic reflecting surface with the liquid-crystal material then being observed in reflected and circularly polarized light. In this instance, the circularly polarized light that is transmitted through the liquid-crystal material undergoes a phase change upon reflection so that it is converted into circularly polarized light of a sense opposite to its original sense. Thus, when the reflected light is observed through the original circular polarizer, there is obtained a result that is equivalent to the viewing of a sample in transmission that is positioned between two polarizers of opposite sense. Again, as with the viewing of a sample of the liquid-crystal material in question through which light has transmitted, there is an optical retardation that depends upon the tilt angle, and thus within the temperature region involved, upon the temperature. If the temperature is constant throughout the domain of the stratum of liquid-crystal material, the interference color of the sample, viewed in accordance with this embodiment of the invention, is uniformly the same, but, if there is a variation in temperature from one location to another throughout the stratum comprising the domain, there is a corresponding variation of the interference colors observed.

The kind of configuration discussed above is especially applicable to thermal imaging. A thin metal film is used as one of the containing surfaces of the liquid-crystal material and thermal radiation is focused upon such a film. The resulting variation in temperature from one point to another throughout the stratum yields a visible and colored image of the thermal-radiation pattern. There is thus contained a thermal-imaging device that corresponds, in a sense, to that disclosed by Fergason in US. Pat. No. 3,114,836, except that the devices made with the use of the variable-tilt Smectic C liquid-crystal material of the present invention has the advantage of responding substantially more rapidly than the cholesteric-phase liquid-crystal material described by Fergason in the above-mentioned patent, since no molecular rearrangement is involved.

Yet another embodiment of the instant invention comprises the observation of the liquid-crystal material by means of transmitted plane-polarized light. In order that plane-polarized light can be used unambiguously, it is essential that the layers of the liquid-crystal material be parallel to the surfaces, and also that the long axes of the molecules be uniformly oriented in one direction. Uniform orientation of the long axes of the molecules is usually more difficult to obtain over large areas than is parallelism of the layers to the surface. If such an oriented variable-tilt Smectic C liquid-crystal material is placed between crossed or parallel polarizers, uniform interference color is observed if the temperature across the sample is constant, but, again, if there is a. variation from one point to another in temperature throughout the domain of the stratum of variable-tilt Smectic C liquid-crystal material, there is a corresponding variation from point to point in the interference color that is observed. When linear polarizers are used, the interference colors that are observed depend upon the orientation of the direction of the long axes of the molecules with respect to the privileged directions of the polarizers.

It is considered that the synthesis and the utilization of the organic-chemical compounds involved lies well within the skill of the art, in view of the disclosure contained hereinabove, and it is further submitted that it will be apparent to those skilled in the art how to construct a liquid-crystal unit wherein a suitable One of such compounds is brought into the form of a stratum of a suitably oriented variable-tilt Smectic C liquid-crystal material. Such stratum may be 0.1 mil to 20 mils in thickness, being produced by applying the organic compound itself or a suitable solution thereof in a volatile organic solvent to the surface with which it is to be in contact.

It will also be apparent to those skilled in the art that the keeping of the liquid-crystal material within the desired temperature range may in some instances be conveniently accomplished by providing one of the strata with which it is in contact with a suitable coating of transparent electroconductive material such as indium oxide doped with tin oxide. Suitable bus bars and leads are provided, and by applying an appropriate amount of electrical power, there is generated enough heat to maintain the variable-tilt Smectic C liquid-crystal material within a desired temperature range. Those skilled in the art will perceive how, by shielding a portion of the domain from incident thermal radiation and using it as a control viewed in monochromatic light, it is possible to control G -aQ-WQ where X is selected from the group consisting of =N- and and R is selected from the group consisting of the aliphatic alkyl and alkoxy radicals that contain 1 to 12 carbon atoms.

2. A composition as defined in claim 1, characterized in that the composition is within a temperature range such that said compound exhibits a temperature-dependent variable-tilt Smectic C phase.

3. A composition as defined in claim 1, characterized in that said compound is terephthal-bis-(4-n-butylaniline).

4. A composition as defined in claim 3, characterized in that the composition is within a temperature range such that said compound exhibits a temperature-dependent variable-tilt Smectic C phase.

5. A composition as defined in claim 1, characterized in that said compound is terephthal-bis-(4-n-butylaminobenzoate).

6. A composition as defined in claim 5, characterized in that the composition is within a temperature range such that said compound exhibits a temperature-dependent variable-tilt Smectic C phase.

7. A composition as defined in claim 1, characterized in that said composition is terephthal-bis-(4-n-hexyloxyaniline).

8. A composition as defined in claim 7, characterized in that the composition is within a temperature range such that said compound exhibits a temperature-dependent variable-tilt Smectic C phase.

9. A composition as defined in claim 1, characterized in that said compound is terephthal-bis-(4-n-octyloxyaniline).

10. A composition as defined in claim 9, characterized in that the composition is within a temperature range such that said compound exhibits a temperature-dependent variable-tilt Smectic C phase.

References Cited UNITED STATES PATENTS 3,655,270 4/1972 Creagh 252408 ROBERT F. BURNETT, Primary Examiner M. E. McCAMISH, Assistant Examiner US. Cl. X.R.

23--230 LC; 16l--1, 5; 260-599; 350P