# US 4,391,492 A · Thermally addressed cholesteric-smectic liquid crystal device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,391,492 A - Document ID: US4391492A - Status: Granted - Kind: A - Application number: 06/251,247 - Filed: 1981-04-06 - Granted: 1983-07-05 - Earliest claimed: 1981-04-06 - Assignees: Minnesota Mining and Manufacturing Company - Inventors: Sun Lu; David B. Chung - Web page: https://patentgrep.com/patent/US4391492A ## CPC - G02F 1/132: {Thermal activation of liquid crystals exhibiting a thermo-optic effect} - Y10S 359/90: Methods - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract A visual display device is featured which uses a new thermal addressing technique to provide a dark image upon a lighter background. The display is capable of being multiplexed to a large number of rows. The device comprises a cholesteric-smectic liquid crystal material mixed with a pleochroic dye of high order parameter. When the material experiences a transition from a higher to a lower, smectic thermal phase, two different textures or light states are developed; a transparent state and a light absorbing state. The transparent state is developed by applying a sensitizing voltage to certain portions of the medium. The pleochroic dye absorbs the light passing through the unsensitized portions of medium to provide the dark image. The row electrodes are made diffusely reflective so as to provide a double light pass through the medium to improve contrast. ## Claims ### Claim 1 A thermally addressed visual device which provides a dark image against a lighter background comprising: A liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one pleochroic dye of high order parameter and having dielectric anisotropy, said medium being thermally sensitive and having a transition between at least two thermal phases, an upper thermal phase being a cholesteric phase and a lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase, a first light state being normally substantially light absorbing and a second light state being substantially transparent; and means to apply a sensitizing voltage to address portions of said medium to develop said second light transparent state when said medium passes rapidly into said smectic phase, the remaining portions of said medium developing said first substantially light absorbing state. ### Claim 2 (depends on 1) The thermally addressed visual device of claim 1, wherein said pleochroic dye is light stable. ### Claim 3 (depends on 1) The thermally addressed visual device of claim 1, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 4 (depends on 1) The thermally addressed visual device of claim 1, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 5 (depends on 1) The thermally addressed visual device of claim 1, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 6 (depends on 1) The thermally addressed visual device of claim 1, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and further comprising means for passing said medium between a lower and an upper phase including at least one heating electrode disposed adjacent said medium. ### Claim 7 (depends on 6) The thermally addressed visual device of claim 6, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 8 (depends on 1) The thermally addressed visual device of claim 1, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said addressed portions of said medium. ### Claim 9 (depends on 1) The thermally addressed visual device of claim 1, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 10 A thermally addressed visual device which provides a dark image against a lighter background, said dark image being observable from the same side as a light source passing light through said device, comprising: a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent and having dielectric anisotropy, said medium being thermally sensitive and having a transition between at least two thermal phases, an upper thermal phase being a cholesteric phase and a lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase, a first light state being normally substantially light absorbing and a second light state being substantially transparent; means disposed adjacent said medium for diffusely reflecting light passing through said medium back through said medium; and means to apply a sensitizing voltage to address portions of said medium to develop said second light transparent state when said medium passes rapidly into said smectic phase, the remaining portions of said medium developing said first substantially light absorbing state. ### Claim 11 (depends on 10) The thermally addressed visual device of claim 10, wherein at least one coloring agent comprises a pleochroic dye. ### Claim 12 (depends on 11) The thermally addressed visual device of claim 11, wherein said pleochroic dye is of high order parameter. ### Claim 13 (depends on 11) The thermally addressed visual device of claim 11, wherein said pleochroic dye is light stable. ### Claim 14 (depends on 10) The thermally addressed visual device of claim 10, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 15 (depends on 10) The thermally addressed visual device of claim 10, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 16 (depends on 10) The thermally addressed visual device of claim 10, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and between cholesteric and smectic "A" phases. ### Claim 17 (depends on 10) The thermally addressed visual device of claim 10, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and between cholesteric and smectic "A" phases, and further comprising means for passing said medium between a lower and an upper phase including at least one heating electrode disposed adjacent said medium. ### Claim 18 (depends on 17) The thermally addressed visual device of claim 17, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 19 (depends on 10) The thermally addressed visual device of claim 10, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said portions of said medium. ### Claim 20 (depends on 10) The thermally addressed visual device of claim 10, wherein said means for diffusely reflecting said light comprises at least one light diffusing reflective electrode. ### Claim 21 (depends on 10) The thermally addressed visual device of claim 10, wherein said means for diffusely reflecting said light and said means for heating said medium are comprised in at least one diffusely reflective heating electrode. ### Claim 22 (depends on 10) The thermally addressed visual device of claim 10, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 23 A thermally addressed visual device which provides a dark image against a lighter background, comprising: a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one pleochroic dye of high order parameter and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase characterized by development of respective light absorbing and homeotropic textures in said medium, said light absorbing texture being normally substantially light absorbing and said homeotropic texture being substantially transparent, and means to apply a sensitizing voltage to address portions of said medium to develop said light transparent texture when said medium passes rapidly into said smectic phase, said unaddressed portions of said medium developing said light absorbing texture wherein said dye absorbs light passing through said unaddressed portions of said medium. ### Claim 24 (depends on 23) The thermally addressed visual device of claim 23, wherein said pleochroic dye is light stable. ### Claim 25 (depends on 23) The thermally addressed visual device of claim 23, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 26 (depends on 23) The thermally addressed visual device of claim 23, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 27 (depends on 23) The thermally addressed visual device of claim 23, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 28 (depends on 23) The thermally addressed visual device of claim 23, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and further comprising means for passing said medium between a lower and an upper phase including at least one heating electrode disposed adjacent said medium. ### Claim 29 (depends on 23) The thermally addressed visual device of claim 23, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said addressed portions of said medium. ### Claim 30 (depends on 23) The thermally addressed visual device of claim 23, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 31 (depends on 23) The thermally addressed visual device of claim 23, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 32 A thermally addressed visual device which provides a dark image against a lighter background, comprising: a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase, characterized by development of respective light absorbing and homeotropic textures in said medium, said light absorbing texture being normally substantially light absorbing and said homeotropic texture being substantially transparent; means disposed adjacent said medium for diffusely reflecting light passing through said medium back through said medium; and means to apply a sensitizing voltage to address portions of said medium to develop said homeotropic texture when said medium passes rapidly into said smectic phase, said unaddressed portions of said medium developing said light absorbing texture wherein said coloring agent absorbs light passing through said unaddressed portions of said medium. ### Claim 33 (depends on 32) The thermally addressed visual device of claim 32, wherein at least one coloring agent comprises a pleochroic dye. ### Claim 34 (depends on 33) The thermally addressed visual device of claim 33, wherein said pleochroic dye is of high order parameter. ### Claim 35 (depends on 33) The thermally addressed visual device of claim 33, wherein said pleochroic dye is light stable. ### Claim 36 (depends on 32) The thermally addressed visual device of claim 32, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 37 (depends on 32) The thermally addressed visual device of claim 32, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 38 (depends on 32) The thermally addressed visual device of claim 32, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 39 (depends on 32) The thermally addressed visual device of claim 32, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and further comprising means for passing said medium between a lower and an upper phase including at least one heating electrode disposed adjacent said medium. ### Claim 40 (depends on 39) The thermally addressed visual device of claim 39, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 41 (depends on 32) The thermally addressed visual device of claim 32, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said portions of said medium. ### Claim 42 (depends on 32) The thermally addressed visual device of claim 32, wherein said means for diffusely reflecting said light comprises at least one light diffusing reflective electrode. ### Claim 43 (depends on 32) The thermally addressed visual device of claim 32, wherein said means for diffusely reflecting said light and said means for heating said medium are comprised in at least one diffusely reflective heating electrode. ### Claim 44 (depends on 32) The thermally addressed visual device of claim 32, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 45 A thermally addressed visual device which provides a dark image against a lighter background, said dark image being observable from the same side as a light source passing light through said device, comprising: a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one pleochroic dye of high order parameter and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase, characterized by development of respective light absorbing and heomeotropic textures in said medium, said light absorbing texture being normally substantially light absorbing and said homeotropic texture being substantially transparent; means for passing said medium through said transition between said upper and said lower phase; and means to apply a sensitizing voltage to address portions of said medium to develop said homeotropic texture when said medium passes rapidly into said smectic phase, said unaddressed portions of said medium developing said light absorbing texture wherein said dye absorbs light passing through said unaddressed portions of said medium. ### Claim 46 (depends on 45) The thermally addressed visual device of claim 45, wherein said pleochroic dye is light stable. ### Claim 47 (depends on 45) The thermally addressed visual device of claim 45, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 48 (depends on 45) The thermal addressed visual device of claim 45, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 49 (depends on 45) The thermally addressed visual device of claim 45, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 50 (depends on 45) The thermally addressed visual device of claim 45, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and said means for passing said medium between a lower and an upper phase comprises at least one heating electrode disposed adjacent said medium. ### Claim 51 (depends on 50) The thermally addressed visual device of claim 50, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 52 (depends on 45) The thermally addressed visual device of claim 45, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said addressed portions of said medium. ### Claim 53 (depends on 45) The thermally addressed visual device of claim 45, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 54 (depends on 45) The thermally addressed visual device of claim 45, wherein said means for passing said medium through said thermal transition comprises at least one electrode. ### Claim 55 A thermally addressed visual device which provides a dark image against a lighter background, said dark image being observable from the same side as a light source passing light through said device, comprising: A liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase characterized by development of respective light absorbing and homeotropic textures in said medium, said light absorbing texture being normally substantially light absorbing and said homeotropic texture being substantially transparent; means disposed adjacent said medium for diffusely reflecting light passing through said medium back through said medium; and means to apply a sensitizing voltage to address portions of said medium to develop said homeotropic texture when said medium passes rapidly into said smectic thermal phase, said unaddressed portions of said medium developing said light absorbing texture wherein said coloring agent absorbs light passing through said unaddressed portions of said medium. ### Claim 56 (depends on 55) The thermally addressed visual device of claim 55, wherein at least one coloring agent comprises a pleochroic dye. ### Claim 57 (depends on 56) The thermally addressed visual device of claim 56, wherein said pleochroic dye is of high order, parameter. ### Claim 58 (depends on 56) The thermally addressed visual device of claim 56, wherein said pleochroic dye is light stable. ### Claim 59 (depends on 55) The thermally addressed visual device of claim 55, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 60 (depends on 55) The thermally addressed visual device of claim 55, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 61 (depends on 55) The thermally addressed visual device of claim 55, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 62 (depends on 55) The thermally addressed visual device of claim 55, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and further comprising means for passing said medium between a lower and an upper phase including at least one heating electrode disposed adjacent said medium. ### Claim 63 (depends on 62) The thermally addressed visual device of claim 62, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 64 (depends on 55) The thermally addressed visual device of claim 55, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said addressed portions of said medium. ### Claim 65 (depends on 55) The thermally addressed visual device of claim 55, wherein said means for diffusely reflecting said light comprises at least one light diffusing reflective electrode. ### Claim 66 (depends on 55) The thermally addressed visual device of claim 55, wherein said means for diffusely reflecting said light and said means for heating said medium are comprised in at least one diffusely reflective heating electrode. ### Claim 67 (depends on 55) The thermally addressed visual device of claim 55, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 68 A thermally addressed visual device which provides a dark image against a lighter background, said dark image being observable from the same side as a light source passing light through said device, comprising: a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase, characterized by development of respective light absorbing and homeotropic textures in said medium, said light absorbing texture being normally substantially light absorbing and said homeotropic texture being substantially transparent; means for passing said medium through said transition between said cholesteric and said smectic phase; means disposed adjacent said medium for diffusely reflecting light passing through said medium back through said medium; and means to apply a sensitizing voltage to address portions of said medium to develop said homeotropic texture when said medium passes rapidly into said smectic phase, said unaddressed portions of said medium developing said light absorbing texture wherein said coloring agent absorbs light passing through said unaddressed portions of said medium. ### Claim 69 (depends on 68) The thermally addressed visual device of claim 68, wherein at least one coloring agent comprises a pleochroic dye. ### Claim 70 (depends on 69) The thermally addressed visual device of claim 69, wherein said pleochroic dye is of high order, parameter. ### Claim 71 (depends on 69) The thermally addressed visual device of claim 69, wherein said pleochroic dye is light stable. ### Claim 72 (depends on 68) The thermally addressed visual device of claim 68, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 73 (depends on 68) The thermally addressed visual device of claim 68, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 74 (depends on 68) The thermally addressed visual device of claim 68, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 75 (depends on 68) The thermally addressed visual device of claim 68, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and said means for passing said medium between an upper and a lower phase comprises at least one heating electrode disposed adjacent said medium. ### Claim 76 (depends on 75) The thermally addressed visual device of claim 75, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 77 (depends on 68) The thermally addressed visual device of claim 68, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said portions of said medium. ### Claim 78 (depends on 68) The thermally addressed visual device of claim 68, wherein said means for diffusely reflecting said light comprises at least one light diffusing reflective electrode. ### Claim 79 (depends on 68) The thermally addressed visual device of claim 68, wherein said means for diffusely reflecting said light and said means for heating said medium are comprised in at least one diffusely reflective heating electrode. ### Claim 80 (depends on 68) The thermally addressed visual device of claim 68, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 81 (depends on 68) The thermally addressed visual device of claim 68, wherein said means for passing said medium through said thermal transition comprises at least one electrode. ### Claim 82 A thermally addressed, multiplexed, visual device which provides a dark image against a lighter background, said dark image being observable from the same side as a light source passing light through said device, comprising: a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said smectic phase, characterized by development of respective homeotropic and light absorbing textures in said medium, a first light state being normally substantially light absorbing and a second light state being substantially transparent; means for passing said medium through said transition between said cholesteric and said smectic phase; means disposed adjacent said medium for diffusely reflecting light passing through said medium back through said medium; and means to sequentially apply sensitizing voltages to address portions of said medium to develop said second substantially light transparent state when said medium passes rapidly into said smectic phase, said medium developing said homeotropic texture in said addressed portions, the remaining unaddressed portions of said medium developing said first substantially light absorbing state, said unaddressed portions of said medium developing said light absorbing texture wherein said coloring agent absorbs light passing through said unaddressed portions of said medium. ### Claim 83 (depends on 82) The thermally addressed visual device of claim 82, wherein at least one coloring agent comprises a pleochroic dye. ### Claim 84 (depends on 83) The thermally addressed visual device of claim 83, wherein said pleochroic dye is of high order, parameter. ### Claim 85 (depends on 83) The thermally addressed visual device of claim 83, wherein said pleochoric dye is light stable. ### Claim 86 (depends on 82) The thermally addressed visual device of claim 82, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 87 (depends on 82) The thermally addressed visual device of claim 82, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 88 (depends on 82) The thermally addressed visual device of claim 82, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 89 (depends on 82) The thermally addressed visual device of claim 82, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and said means for passing said medium between a lower and an upper phase comprises at least one heating electrode disposed adjacent said medium. ### Claim 90 (depends on 89) The thermally addressed visual device of claim 89, wherein said heating electrodes are disposed adjacent said medium and diffusely reflect light passing through said medium back through said medium. ### Claim 91 (depends on 82) The thermally addressed visual device of claim 82, wherein said means for sensitizing portions of said medium comprises at least one electrode for applying a sensitizing voltage to said portions of said medium. ### Claim 92 (depends on 82) The thermally addressed visual device of claim 82, wherein said means for diffusely reflecting said light comprises at least one light diffusing reflective electrode. ### Claim 93 (depends on 82) The thermally addressed visual device of claim 82, wherein said means for diffusely reflecting said light and said means for heating said medium are comprised in at least one diffusely reflective heating electrode. ### Claim 94 (depends on 82) The thermally addressed visual device of claim 82, wherein said liquid crystal medium comprises a mixture of at least two liquid crystal compounds. ### Claim 95 (depends on 82) The thermally addressed visual device of claim 82, wherein said means for passing said medium through said thermal transition comprises at least one electrode. ### Claim 96 A thermally addressed, multiplexed, visual display device which provides a dark image against a lighter background comprising: A liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one pleochoric dye of high order parameter and having dielectric anisotropy, said medium being thermally sensitive and having a transition between at least two thermal phases, said medium having two possible light modulating states in a lower thermal phase, an upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, a first light state being normally substantially light absorbing and a second light state being substantially transparent; and a matrix of electrodes disposed about said medium, a number of said matrix electrodes defining rows and a number of said matrix electrodes defining columns, said row electrodes heating said medium to cause said medium to pass through a thermal transition between said lower and said upper phase, and said column electrodes for applying sequential sensitizing voltages to address portions of said medium to develop said second light transparent state when said medium rapidly cools and passes into said smectic phase, the remaining unaddressed portions of said medium developing said first substantially light absorbing state. ### Claim 97 (depends on 96) The thermally addressed visual device of claim 96, wherein said pleochroic dye is light stable. ### Claim 98 (depends on 96) The thermally addressed visual device of claim 96, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 99 (depends on 96) The thermally addressed visual device of claim 96, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 100 (depends on 96) The thermally addressed visual device of claim 96, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 101 (depends on 96) The thermally addressed visual device of claim 96, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and wherein said electrodes are disposed adjacent said medium. ### Claim 102 A thermally addressed, multiplexed, visual display device providing a dark image against a lighter background, comprising: A liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one pleochroic dye of high order parameter and having dielectric anisotropy, said medium being thermally sensitive and having a transistion between at least two thermal phases, said medium having two possible light modulating states in a lower thermal phase, an upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, a first light state being normally substantially light absorbing and a second light state being substantially transparent; and a matrix of electrodes disposed about said medium, a number of said matrix electrodes defining rows and a number of said matrix electrodes defining columns, said column electrodes being substantially at right angles to, and disposed in another plane with respect to said row electrodes, said row electrodes for heating said medium to cause said medium to pass rapidly through a thermal transition between said lower and said upper phase, and said column electrodes for applying sequential sensitizing voltages to address portions of said medium to develop said second light transparent state when said medium cools and passes into said smectic phase, the remaining unaddressed portions of said medium developing said first substantially light absorbing state. ### Claim 103 (depends on 102) The thermally addressed visual device of claim 102, wherein said pleochroic dye is light stable. ### Claim 104 (depends on 102) The thermally addressed visual device of claim 102, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 105 (depends on 102) The thermally addressed visual device of claim 102, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 106 (depends on 102) The thermally addressed visual device of claim 102, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 107 (depends on 102) The thermally addressed visual device of claim 102, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases, and wherein said rows are disposed adjacent said medium. ### Claim 108 A thermally addressed, multiplexed, visual display device providing a dark image against a lighter background, said image being observable from the same side as a light source passing light through said device, comprising: A liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent and having dielectric anisotropy, said medium being thermally sensitive and having a transition between at least two thermal phases, said medium having two possible light modulating states in a lower thermal phase, an upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, a first light state being normally substantially light absorbing and a second light state being substantially transparent; and a matrix of electrodes disposed about said medium, a number of said matrix electrodes defining rows and a number of said matrix electrodes defining columns, said column electrodes being substantially transparent to light passing through said medium, said row electrodes being substantially diffusely reflective for heating said medium to cause said medium to pass through a thermal transistion between said lower and said upper phases, said column electrodes for applying sequential sensitizing voltages to address portions of said medium to develop said second light transparent state when said medium rapidly cools and passes into said smectic phase, the remaining portions of said medium developing said first substantially light absorbing state, said row electrodes being disposed behind said medium and having means to diffusely reflect the light passing through the medium back through said medium. ### Claim 109 (depends on 108) The thermally addressed visual device of claim 108, wherein at least one coloring agent comprises a pleochroic dye. ### Claim 110 (depends on 109) The thermally addressed visual device of claim 109, wherein said pleochroic dye is of high order parameter. ### Claim 111 (depends on 109) The thermally addressed visual device of claim 109, wherein said pleochroic dye is light stable. ### Claim 112 (depends on 108) The thermally addressed visual device of claim 108, wherein at least one liquid crystal compound comprises a smectic "A" liquid crystal material in said lower phase. ### Claim 113 (depends on 108) The thermally addressed visual device of claim 108, wherein said liquid crystal medium comprises an alkyl cyano biphenyl. ### Claim 114 (depends on 108) The thermally addressed visual device of claim 108, wherein said medium passes rapidly through two transitions between isotropic and cholesteric phases, and rapidly between cholesteric and smectic "A" phases. ### Claim 115 In a thermally addressed visual display device having a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one coloring agent, the method of displaying a dark image against a lighter background, comprising the steps of: (a) passing said medium rapidly through a thermal transition from an upper thermal, cholesteric phase to a lower thermal, smectic phase; (b) sensitizing certain portions of said medium defining a background to develop a substantially light transparent state in said background when said medium passes rapidly into said lower thermal, smectic phase, the remaining unsensitized portions of said medium developing a light absorbing state; (c) passing light through said medium; and (d) absorbing light in said unsensitized portions of said medium to provide a dark image upon said lighter sensitized background. ### Claim 116 (depends on 115) The method of claim 115, wherein said dark image is observable from the same side as the light passing through said medium, and comprising the further step of: (e) diffusely reflecting the light passing through said medium back through said medium. ### Claim 117 (depends on 115) The method of claim 115, wherein said medium has dielectric anisotropy and further wherein the sensitized portions of said medium are sensitized by the further step of: (e) applying a voltage to said certain portions of said medium in order to sensitize said certain portions into developing said light transparent state. ### Claim 118 (depends on 117) The method of claim 117, wherein said voltage is applied in a given chronological sequence to said certain portions of said medium. ### Claim 119 (depends on 115) The method of claim 115, wherein said sensitized portions of said medium are sensitized in chronological sequence. ### Claim 120 (depends on 115) The method of claim 115, further comprising the step of: (e) passing said medium through said transition from said lower thermal, smectic phase to said upper thermal, cholesteric phase prior to step (a). ### Claim 121 (depends on 120) The method of claim 120, wherein said transition step (e) is accomplished by heating said medium. ### Claim 122 (depends on 115) The method of claim 115, wherein said transition step (a) is accomplished by rapidly cooling said medium. ### Claim 123 (depends on 115) The method of claim 115, wherein said medium passes rapidly through two thermal transitions rapidly between an upper isotropic phase, an intermediate cholesteric phase, and a lower smectic phase. ### Claim 124 (depends on 115) The method of claim 115, wherein said light passing through said medium in step (c) comprises ambient light. ### Claim 125 In a thermally addressed visual display device having a liquid crystal medium including at least one liquid crystal cholesteric compound mixed with at least one pleochroic dye of high order parameter and having dielectric anisotropy, said medium being thermally sensitive and having a transition between an upper and a lower thermal phase, said upper thermal phase being a cholesteric phase and said lower thermal phase being a smectic phase, said medium having two possible light modulating states in said lower thermal, smectic phase characterized by development of respective light absorbing and homeotropic textures in said medium, said light absorbing texture being normally substantially light absorbing and said homeotropic texture being substantially transparent, the method of displaying a dark image against a lighter background, comprising the steps of: (a) rapidly passing said medium through said transition from said upper thermal, cholesteric phase to said lower thermal, smectic phase; (b) sensitizing certain portions of said medium defining a background to develop said second substantially light transparent state in said background when said medium passes rapidly into its lower thermal, smectic phase, the remaining unsensitized portions of said medium developing said light absorbing state; (c) passing light through said medium; and (d) absorbing light in said unsensitized portions of said medium to provide a dark image upon said lighter sensitized background. ### Claim 126 (depends on 125) The method of claim 125, wherein said dark image is observable from the same side as the light passing through said medium, and comprising the further step of: (e) diffusely reflecting the light passing through said medium back through said medium. ### Claim 127 (depends on 126) The method of claim 126, wherein the sensitized portions of said medium are sensitized by the further step of: (e) applying a voltage to said certain portions of said medium in order to sensitize said certain portions into developing said light transparent state. ### Claim 128 (depends on 127) The method of claim 127, wherein said voltage is applied in a given chronological sequence to said certain portions of said medium. ### Claim 129 (depends on 126) The method of claim 126, wherein said sensitized portions of said medium are sensitized in chronological sequence. ### Claim 130 (depends on 126) The method of claim 126, further comprising the step of: (e) passing said medium through said transition from said lower thermal, smectic phase to said upper thermal, cholesteric phase prior to step (a). ### Claim 131 (depends on 130) The method of claim 130, wherein said transition step (e) is accomplished by heating said medium. ### Claim 132 (depends on 126) The method of claim 126, wherein said transition step (a) is accomplished by rapidly cooling said medium. ### Claim 133 (depends on 126) The method of claim 126, wherein said medium passes rapidly through two thermal transitions between an upper isotropic phase, an intermediate cholesteric phase, and a lower smectic phase. ### Claim 134 (depends on 126) The method of claim 126, wherein said light passing through said medium in step (c) comprises ambient light.