Thermally addressed cholesteric-smectic liquid crystal device

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.

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.

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.

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.

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.

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.