Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-12-23
2001-08-07
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S089000
Reexamination Certificate
active
06271898
ABSTRACT:
FIELD OF THE INVENTION
This application is a continuation application of co-pending application Ser. No. 08/704,316 which is a non-provisional application of provisional application Ser. No. 60/005,269. The present invention relates to a method for forming, in an aqueous medium, particles and droplets containing liquid domains. In particular, the present invention relates to a method for forming, in an aqueous medium, particles containing liquid crystal domains and having a narrower particle size distribution than liquid crystal domains prepared from conventional processes. The present invention also relates to liquid crystal-containing particles formed by the disclosed method, and to films containing the liquid crystal-containing particles. Liquid-crystal containing particles made according to the present method exhibit improved electro-optic properties over conventional liquid crystal particles when incorporated into polymer dispersed liquid crystal films.
BACKGROUND OF THE INVENTION
Materials other than liquid crystals may be contained within droplets formed according to the method of the present method. Such material may be any organic liquid and preferably has a low water solubility, as discussed herein below. The liquid material may also be a solution of a material which is normally a solid at room temperature. One or more materials may be used in combination with, or in place of, a liquid crystalline material. As used herein, the term “organic liquid” includes reagents, adjuvants, and other chemically or biologically active species. Examples include inks, toners, dyes, flavors and fragrances. Other examples include biocides such as pesticides, herbicides, mildicides, insecticides and fingicides, marine anti-fouling agents, pharmaceutically acceptable agents, and the like. The organic liquids used in this manner according to the present invention may be pure liquids, mixtures or solutions of solid or liquid species in organic solvents. The organic liquid may be removed by evaporation, for example during film formation, leaving a void, or air or another gaseous material, within the particle.
Alternatively, material contained within the droplets may be inorganic or partially inorganic in nature, or may be comprised of precursors of inorganic species. For example, appropriately functionalized organic species could be chemically, or otherwise, converted to inorganic salts or complexes while in the droplet. Such appropriately functionalized organic species could themselves be part of a mixture or solution with one or more additional liquid or solid species. Complexes of organic ligands with metals may also be incorporated into the droplets. As discussed herein, the method of the present invention, is particularly useful in forming uniformly sized polymer particles containing liquid crystal material.
Applications for liquid crystals include: computer display screens; wristwatches; architectural windows; privacy windows; automotive windows; automobile sunroofs; switching devices such as for optics systems, projection display devices; reflective display devices; hand-held paging devices; cellular phones; laptop computers; television screens including car-mounted television screens; automotive displays including radio, dashboard, and on-board navigation systems; helmet displays such as “heads-up” displays; cockpit displays; imaging devices; virtual reality devices; simulation devices; electronic gating devices; diffraction gratings; and calculators. In these applications and others, the liquid crystal devices may be monochromatic or polychromatic.
Common liquid crystal materials are rod-like molecules which can be aligned by an electric or magnetic field, or by a surface. Conventional liquid crystal display (LCD) devices rely on the ability of liquid crystal molecules to align with electric fields and surfaces. Polymer dispersed liquid crystal (PDLC) devices, discussed below, rely upon the ability of liquid crystal (LC) molecules to align with electric fields and with surfaces, and also upon the fact that the extent to which the liquid crystal molecules refract, or bend, light is dependent upon the orientation of individual molecules with respect to incident light. An indicator of the capacity of the molecules to refract light is the index of refraction, or refractive index, discussed below.
Liquid crystal devices, or LCDs can contain a range of liquid crystal types that include but are not limited to nematic, twisted nematic, super twisted nematic, cholesteric, ferroelectric liquid crystals. Such types are well known in the art.
Another type display utilizing liquid crystals relies on liquid crystal domains dispersed within a polymer matrix. A liquid crystal domain is a region occupied exclusively or predominantly by liquid crystal molecules. This type of liquid crystal display is known as a polymer dispersed liquid crystal display (PDLC). PDLCs are often used in the form of thin films, meaning films having a thickness of up to about 200 microns, typically a thickness of between 2 microns and 50 microns. The ability of the PDLC device to transmit light, (“on state”) or scatter light (in the opaque “off state”) is dependent upon the relative ability of the LC domain and the polymeric phase to refract light, as indicated by the so called refractive index. The refractive index of a material is the ratio of the velocity of light in a vacuum to the velocity of light in the material. The angle of refraction varies with the wave-length of the light used. The refractive index is typically represented by h, with a superscript usually added to indicate the temperature at which a measurement is made and a subscript is used to indicate the wavelength of the light source. (The Chemist's Ready Reference Handbook, G. J. Shugar and J. A. Dean, McGraw-Hill, Inc., New York, 1989). For a typical organic material, the refractive index may range from about 1.4 to about 2, and is calculated by the formula
h=c/v
where h is the refractive index, c is the speed of light in a vacuum and v is the speed of light in a given material.
The ability of an electric field to influence the extent of refractive index matching is due to the fact that liquid crystals exhibit differing indices of refraction, dependent upon their orientation with respect to incident light. When light passes through a liquid crystal medium along the long axis of the molecules, the refractive index measured is called its ordinary refractive index. When light passes through a liquid crystal molecule perpendicular to its long axis, the refractive index measured is defined as its extraordinary refractive index. In a PDLC device, the orientation of the liquid crystal molecules with respect to incident light is affected by the presence or absence of an electric, or alternatively magnetic, field such that the liquid crystals will express an ordinary refractive index or an extraordinary refractive index as a function of the applied field being either on or off, respectively. In the instance where the ordinary refractive index of the liquid crystal droplets is matched closely with the refractive index of the surrounding polymer matrix, light incident on a film comprising liquid crystal droplets and polymer is not refracted and the film is substantially transparent. In the instance where the extraordinary refractive index of the liquid crystal droplets does not match the refractive index of the surrounding polymer matrix, and the LC droplets are provided with the correct size and geometry, light incident on a film comprising liquid crystal droplets and polymer is refracted and the film is substantially opaque.
The size of the LC droplets, or alternatively referred to herein as LC domains, also has a profound effect upon the electro-optical characteristics of PDLC films. When LC and surrounding polymeric matrix have the same refractive index, the film will be transparent regardless of the size of the domains. When the refractive indecies of the LC droplets and the polymer matrix are not matched, however, domain size, domain size distr
Clikeman Richard Roy
Lau Willie
Sperry Peter Reeves
Vogel Martin
Wills Morris Christopher
Cairns S. Matthew
Dudek James A.
Frickey Darryl P.
Lemanowicz John L.
Nguyen Dung
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