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A practical camouflage system whose colors and color patterns can be continuously, controllably and reversibly varied on command would be of great tactical importance to mobile army units. In the study described a number of possible approaches were researched, an extensive literature search was carried out, and some laboratory investigations performed. From considerations of each of these approaches, the state-of-the-art in materials technology, and of the requirements of the program, a liquid crystal approach was deemed to have the best potential for demonstrating the feasibility of a variable camouflage system. By electrically varying the temperature of a cholesteric liquid crystal, the color is also varied. The concept has been demonstrated to be reversible, controllable and reproducible, even though the colors and color ranges obtained are not ideal.

The report encompasses efforts directed toward the evaluation and validation of the Master Monitor concept developed during conduct of a previous program. Specifically, a series of laboratory studies were conducted which encompass the following: (1) mechanization and evaluation of candidate flat panel display devices for use as the Master Monitor display media, (2) display alerting techniques for alerting the pilot to a system failure, and (3) validation of the MMD information processing system concept.

The development of a new type of large area infrared detector cell with visible light readout is studied in which a liquid crystal layer is electro-optically activated by a pyroelectric film. These studies include the evaluation of pyroelectric films and their poling techniques, the evaluation of liquid crystals for use with pyroelectric currents, analysis of thermal time constants in various cell layers, evaluation of signals obtained with test cells, and the development of prototype detectors. Polyvinylidene fluoride (PVF2) is selected as the best large area pyroelectric material available. In operation with 10.6 micrometer laser exposures, the effects of the pyroelectric generated voltage across the liquid crystal are obscured by thermal flow effects. However, a revised design is recommended in which a conductive faceplate is used to thermally isolate the pyroelectric film from the liquid crystal layer.

Several new stable nematic liquid crystals were synthesized for possible use in dynamic scattering, and the threshold for scattering in an azoxy-type liquid crystal was lowered significantly by the use of charge-transfer acceptors as dopants. The effect of large changes in dielectric anisotropy on twisted nematic devices has been examined, and significant improvements in the decay times for this effect were achieved by using a two-frequency addressing mode. Studies on the electric field-induced cholesteric-nematic transition have shown that a non-uniform distortion of the cholesteric helix occurs under certain conditions. An o-hydroxy substituted analog (OHMBBA) of the room temperature nematic N-(p-methoxybenzylidene)-p-n-butylaniline (MBBA) was prepared. Two broad temperature range binary systems were also examined consisting of OHMBBA mixed with N-(p-ethoxybenzylidene)-p-n-butylaniline (EBBA), and OHMBBA mixed with N-(p-methoxybenzylidene)-p-n-pentylaniline (MPBA).

A semiempirical SCF MO treatment (MINDO/3) has been developed which for the first time seems to allow mechanisms of organic reactions to be predicted in greater detail and with more certainity than could be achieved by experiment, and at much less cost. Calculations for a number of reactions have already led to novel and unexpected mechanism conclusions of major importance. In this connection experimental work has also been carried out on the Cope and Cornforth rearrangements. A high resolution photoelectron spectrometer has been constructed and used to study a variety of organic and organometallic compounds. A number of new nematic liquid crystals have been prepared and novel conclusions reached concerning the effect of structure on mesophase stability.

The fluid flow and forced convective heat transfer characteristics of a uniformly heated right circular cylinder resting on a flat plate in a crossflow of air were experimentally investigated. The circumferential variation of the Nusselt number on the cylinder surface was obtained at Reynolds numbers ranging from 53,000 to 153,000 using a liquid crystal thermographic technique. Pressure coefficients were obtained at five-degree intervals around the cylinder circumference at Reynolds numbers of 105,000 and 156,000. Flow visualization was conducted at a Reynolds number of 10,000 in order to qualitatively examine the flow field. A qualitative theory based upon a compilation of previous results reported for flow around a 'free' cylinder and flow over forward and rear-facing steps was developed.

The program was divided into three separate technical efforts, (1) the mechanical packaging, (2) the electronic circuitry and (3) the liquid crystal plates. The packaging and circuitry efforts proceeded quite smoothly. There were some modifications in both areas due to the desire for interchangeability of L.C. panels for evaluation purposes and variations in lighting schemes but the basic packaging and circuitry concepts proved satisfactory. The liquid crystal plates proved a difficult matter. Because of the subjective evaluation required of the L.C. panel, it was impossible to ascertain the best L.C. cosmetic arrangement. Rather, a series of various combinations of L.C. materials, backplates and lighting systems were assembled and tried. Parallax-face scales combined with effective glass seals also required extensive experimentation.

A thermographic technique is presented that allows visual determination of both qualitative and quantitative heat transfer and fluid flow information to be obtained on heated objects placed in forced convection environments. The technique employs cholesteric liquid crystals as the temperature sensing agent. The liquid crystals indicate temperature by exhibiting brilliant changes in color over discrete, reproducible temperature ranges. The technique has been used to quickly and easily obtain information on the variation of the Nusselt number on a right circular cylinder placed in a crossflow of air. In addition to yielding precise quantitative heat transfer information the liquid crystal thermographic technique afforded the opportunity to visually observe the effects of flow separation, the separation bubble region, the turbulent boundary layer, and the turbulent wake on the surface temperature of the heated cylinder.

Research was conducted toward the syntheses of new organic compounds with a general structure involving two benzene rings joined by a central group, usually polar, and with 4,4'-disubstitution of n-alkyl and n-alkoxyl groups or small polar-functions such as chloro, cyano-aric acyloxy-substituents. Some members of each of the compound series involving central groups including nitrones, azines, esters, and azo- were found to possess nematic liquid crystalline behavior. The azo- and ester series with n-alkyl and n-alkoys 4,4'substituents had temperature ranges just above ambient; binary mixtures of a number of these possessed nematic behavior at ambient temperatures. Several novel compound types with gross overall structures related to the 4,4' disubstituted bisubstituted bisaryl derivatives but with intramolecular ring fusion were also prepared. In general nematic vehavior in these compounds, when present, was exhibited at higher temperatures and over narrower ranges than for the open-ring analogues. (Author)

The patent concerns an imaging system for environments where light scattering reduces image quality. The imaging system comprises a scanning illumination source to illuminate an object field. A first photoelectric transducer converts a focused image of the illuminated object field to an electric analog. A second real-time thresholding photoelectric transducer is physically and electrically connected to the first transducer to recreate an optical image of the object field having electrical analog values in excess of a predetermined value. Utilization of the optical output from the second transducer is by conventional optical or electrooptical systems. This system can be used for remotely controlled unmanned underwater vehicles as well as automatic data gathering packages carried on manned submersible vehicles.

In the patent application an optical transmit-receive coupler includes a first transparent, electrically conductive coating contiguous to a light transmission path. A second transparent electrically conductive coating is disposed relative to the first transparent, electrically conductive coating so that a nematic liquid crystal material is contained therebetween. A source of a.c. potential is connected to the respective electrically conductive coatings to develop an electric field across the nematic liquid crystal material, causing it to be molecularly arranged to give the optical effect of a diffraction grating. Means for varying the frequency of the a.c. potential causes commensurate variation in the periodic vorticity of the nematic liquid crystal material and thereby selectively determines the wavelengths of light energy coupled through the liquid crystal material by diffraction.

This patent application combines liquid crystals with an optical waveguide in order to couple coherent light out of and into the waveguide. The liquid crystal is one of the substances adjacent the waveguide and normally has an index of refraction less than that of the waveguide section. The liquid crystal must be highly aligned to insure guiding. The nature of the alignment i.e., homotropic or homogeneous will affect the index of refraction presented to the incoming coherent light and thus determine whether wave guiding is possible and the number of modes that can be supported. An applied electric field changes the index of refraction of the liquid crystal approximately that of the waveguide, therefore, light may be coupled into or out of the waveguide through the area of the liquid crystal in which the index of refraction has been changed. This effect can be used as an on-off switch but not as a mode selector, since no modes can be supported in the dynamically scattering liquid crystal media.

In the patent application a transmit/receive optical coupler controls the transmission of light energy between first and second optical paths separated by a medium of lower index of refraction for confining at least one of the optical paths to total internal reflection. An anisotropic nematic liquid crystal material which has an index of refraction substantially equal to the separating medium when in a state of homeotropic alignment is positioned between the optical paths, replacing a portion of the separating medium. Electrodes are disposed contiguous to the liquid crystal material and are connectable to a source of electrical potential. Upon the application of the electrical potential, an electric field is impressed upon the liquid crystal material inducing a higher indux of refraction, frustrating the total internal reflection, and coupling light energy between the two optical paths.

The program objective was to determine the feasibility of a reflective liquid crystal display built directly on a silicon substrate containing an MOS memory and ac drivers. To eliminate chip-to-chip interconnections, the substrate was a mosaic of four 1.7-inch IC chips with low circuit density. Extensive packaging development has culminated in techniques for mosaic fabrication and assembly of a complete display panel. These results are applicable to future designs with simpler integrated circuitry for acceptable yield and lower power. They are also useful for field effect liquid crystal displays and for other display technologies. Design and construction of general interface circuitry and of a specific keyboard adaptor were completed. (Modified author abstract), See also report dated Jul 74, AD-782 817.

Brillouin scattering was used to study the hypersonic properties of cholesteryl palmitate in the liquid crystal-liquid phase transition region. Contrary to the results of similar measurements by Durand and Rao, no anomalous change in either the velocity or the attenuation of the hypersonic waves was observed at the transition. (Author)

This paper researches the feasibility for using cholesteric liquid crystals for locating the unbonded areas or voids in adhesively bonded helicopter rotor blades. Results of testing two tail rotors are presented and analyzed. A general review of other nondestructive testing methods for rotor blades and a review of liquid crystals is also included. (Author)

The relationship between a second rank tensor anisotropy and the orientational order in a cholesteric liquid crystal is derived. Experimental results on a mixture of cholesteryl chloride and p-azoxyanisole confirm this relationship and also provide an explanation of the dipolar NMR lineshape of a sample in the cholesteric phase. (Author)

Using the 90 degree scattering geometry, the authors have measured the intensity of four light scattering components, V(v), V(h), H(v) and H(h) in cholesteryl myristate by cooling it from the isotropic liquid to the solid phase. The Krishnan effect is observed in the isotropic liquid as well as in the temperature below the isotropic liquid-mesophase transition temperature. (Modified author abstract), Presented at the International Liquid Crystal Conference (5th), Stockholm, 1947.

The report describes the development of a Liquid Crystal 3-D Display. The display consists of a stack of ten cholesteric-nematic liquid crystal cells. Each cell consists of a matrix of 20 x 40 addressable elements, 0.15 x 0.15 inches per element, with a total active display area of 3 x 6 inches. The modified half select matrix addressing scheme provides for up to four levels of gray scale. Display electronics is designed to accept information formatted by a minicomputer to refresh the display at a 2.5 to 10 hertz rate. Physical and chemical characteristics of the cholesteric nematic liquid crystal are described in detail. (Author)