Enhanced scattering in voltage sensitive encapsulated liquid crystal

• US 4,606,611 A
• Filed: 03/21/1983
• Issued: 08/19/1986
• Est. Priority Date: 09/16/1981
• Status: Expired due to Term

• Current Assignee: Manchester R & D Partnership
• Original Assignee: Manchester R & D Partnership
• Inventors: Fergason, James L.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Gallivan, Richard F.
• Application Number:
  US06/477,138
• Time in Patent Office: 1,247 Days
• Field of Search: 350/331 R, 350/334, 350/344, 350/345
• US Class Current: 349/90
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/1335 Structural association of cells with optical devices, e.g. polarisers or reflectors
• CPC Class Codes: G02F 1/137 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
• CPC Class Codes: G02F 2202/043 pleochroic

Abstract

In the present invention encapsulated liquid crystal material in a support medium illuminated from the viewing side or direction will appear bright or white relative to background when in distorted alignment, e.g. in the absence of an electric field. Incident light impinging on the liquid crystal material is isotropically scattered thereby into the support medium, and using the principle of total internal reflection a relatively large part of the isotropically scattered light is reflected back to illuminate the distorted liquid crystal material tending to brighten the same so that light it scatters back to the viewing direction out of the support medium causes the liquid crystal material to appear relatively light or bright as compared to the background where there is no liquid crystal material or where the liquid crystal material is in parallel alignment in field-on condition, i.e. aligned with respect to an electric field, and, thus, substantially transmissive. Original incident light where there is no liquid crystal material, that light which is isotropically scattered toward the back or non-viewing side of the display and within a certain cone or solid angle, and that light passing through aligned (field-on) liquid crystal material will tend not to be totally internally reflected; such light will pass through the support medium and may be absorbed by a remote black or colored material.

Claims

1. Liquid crystal apparatus comprising liquid crystal means for selectively primarily scattering or transmitting light in response to a prescribed input, said liquid crystal means comprising operationally nematic liquid crystal material having positive dielectric anistropy, a support medium means for supporting said liquid crystal means, and reflecting means for effecting total internal reflection of light scattered by said liquid crystal means.

2. The apparatus of claim 1, said liquid crystal means comprising at least one layer of encapsulated operationally nematic liquid crystal material in said support medium means, said liquid crystal material having an ordinary index of refraction substantially matched to that of said support medium means to maximize optical transmission in the presence of an electric field and to effect substantial isotropic scattering in the absence of an electric field.

3. The apparatus of claim 1, wherein the dielectric constant of said support medium means is at least about as large as the lower dielectric constant of said liquid crystal means.

4. The apparatus of claim 1, said support medium means having a viewing side and an opposite side, respective media at said viewing and opposite sides, and the index of refraction of said support medium means being greater than the index of refraction of the medium at one of respectively such viewing and opposite sides, said reflecting means comprising an interface of such one of said sides with the medium thereat to effect total internal reflection of light in said support medium means incident on such interface at an angle exceeding a predetermined cone of light angle at which light would be transmitted through such interface.

5. The apparatus of claim 4, wherein said liquid crystal means is operative in the absence of an electric field to scatter a substantial amount of light at an angle exceeding the total internal reflection angle of said support medium at such interface.

6. The apparatus of claim 5, said support medium means comprising containment medium means for containing said liquid crystal material in volumes, said volumes including walls for distorting the natural structure of the liquid crystal material in the absence of an electric field, the ordinary index of refraction of said liquid crystal material being substantially matched to the index of refraction of said containment medium means to maximize transmission of light in the presence of an electric field that causes generally parallel alignment of the liquid crystal structure and the extraordinary index of refraction of said liquid crystal material when in such distorted structure alignment being different from that of said containment medium means to effect scattering of light in the absence of an electric field.

7. The apparatus of claim 6, wherein said plural volumes of liquid crystal material in said containment medium means cover a substantial portion of the surface area of said support medium means.

8. The apparatus of claim 7, further comprising plural electrode means for applying electric field to selected portions of said liquid crystal means, said electrode means comprising plural electrodes positioned over relatively smaller areas of said support medium means and liquid crystal means than such substantial portion size of said liquid crystal means covering said support medium means.

9. The apparatus of claim 6, said support medium means further comprising a support for supporting said volumes of liquid crystal material in said containment medium means.

10. The apparatus of claim 6, wherein the index of refraction of said support medium means is greater than the indices of refraction of the media at both of said viewing and opposite sides, and said reflecting means comprises the interfaces of said sides with such media to effect such total internal reflection.

11. A display device formed of the liquid crystal apparatus of claim 4.

12. The display of claim 11, said liquid crystal means comprising at least one layer of liquid crystal material in a containment medium that tends to distort the structure of at least some of the liquid crystal material to align generally with respect to a wall of such containment medium when in the absence of an electric field, and said liquid crystal material being responsive to an electric field to tent to effect generally parallel alignment of the liquid crystal structure.

13. The display device of claim 11, said reflecting means comprising means for reflecting light scattered by said liquid crystal means back to said liquid crystal means to display relatively bright characters or the like on a relatively dark background.

14. The apparatus of claim 4, wherein the index of refraction of said support medium means is greater than the indices of refraction of the media at both of said viewing and opposite sides, and said reflecting means comprises the interfaces of said sides with such media to effect such total internal reflection.

15. The apparatus of claim 14, said liquid crystal means comprising a layer of encapsulated liquid crystal, and further comprising electrode means positioned between said support medium means and said layer of encapsulated liquid crystal for applying an electric field to align said liquid crystal with respect thereto.

16. The apparatus of claim 15, said encapsulated liquid crystal comprising an emulsion of liquid crystal material and a containment medium, said liquid crystal material having an ordinary index of refraction substantially matched to that of said containment medium to maximize optical transmission in the presence of an electric field and to effect substantial isotropic scattering in the absence of an electric field.

17. The apparatus of claim 4, said medium means at such one of said sides comprising air.

18. The apparatus of claim 4, further comprising light director means for directing incident light into said support medium means at said opposite side thereof.

19. An optical shutter formed of the apparatus of claim 18.

20. The apparatus of claim 18, said director means comprising a louvered light control film.

21. An optical shutter formed of the apparatus of claim 20.

22. The apparatus of claim 18, said director means comprising means for directing such incident light into said support medium means at a direction substantially out of the usual viewing line of sight from said viewing side.

23. The apparatus of claim 18, said director means comprising a light control film having light transmitting and light absorbing portions, and means for coupling said film to said opposite side of said support medium means to form an interface therewith.

24. The apparatus of claim 2, said support medium means having a viewing side and an opposite side, and further comprising a tuned dielectric interference layer on said opposite side of said support medium means for effecting optical constructive interference of at least some of the light in said support medium means incident on said interference layer or the interface thereof with said support medium means at an angle exceeding a predetermined cone angle and destructive interference of light incident at an angle within such cone angle.

25. The apparatus of claim 24, said layer comprising means for forming an interface therewith to effect total internal reflection of light in said support medium means incident on such interface at an angle exceeding a further predetermined cone angle at which light would be transmitted through such interface, such further predetermined cone angle being larger than such predetermined cone angle.

26. A display device formed of the liquid crystal apparatus of claim 25.

27. The apparatus of claim 2, said encapsulated liquid crystal material in a support medium means comprising an emulsion of said liquid crystal material and a containment medium.

28. The apparatus of claim 2, said support medium means comprising containment means for containing discrete quantities of operationally nematic liquid crystal material to distort the same when in random alignment and to permit parallel alignment thereof in the presence of an electric field.

29. The apparatus of claim 28, further comprising additive means in said operationally nematic liquid crystal material for expediting such distorting and return to random alignment upon the removal of such electric field.

30. The apparatus of claim 29, said additive means comprising a chiral additive.

31. The apparatus of claim 1, said support medium means having a viewing side for emitting at least some light isotropically scattered by said liquid crystal means.

32. The apparatus of claim 1, said support medium means comprising a containment medium means for holding discrete quantities of such liquid crystal means in respective capsule-like volumes.

33. The apparatus of claim 32, said support medium means further comprising a substantially optically transparent support.

34. The apparatus of claim 33, said substantially optically transparent support comprising a polyester or polycarbonate material.

35. The apparatus of claim 33, further comprising electrode means for applying an electric field to said liquid crystal means to cause the latter to change from a random alignment condition distorted in configuration or shape by the wall of such respective capsule-like volumes for scattering light incident thereon to generally parallel alignment condition to transmit light incident thereon.

36. A display device formed of the liquid crystal apparatus of claim 35.

37. The display device of claim 36, said reflecting means comprising means for reflecting light scattered by said liquid crystal means back to said liquid crystal means to display relatively bright characters or the like on a relatively dark background.

38. The apparatus of claim 32, further comprising means reactive with said containment medium means for tending to force at least a portion of at least some of said liquid crystal means into substantially normal alignment with the wall of such capsule-like volumes.

39. The apparatus of claim 1, said support medium means comprising a containment means for forming a stable emulsion with said liquid crystal means and mounting means for supporting said emulsion, and said reflecting means comprising means for forming an interface with said support medium means to cause total internal reflection of light thereat.

40. The apparatus of claim 39, further comprising electrode means between said mounting means and said emulsion for applying an electric field to effect alignment of such liquid crystal means.

41. The apparatus of claim 39, said liquid crystal material having an ordinary index of refraction substantially matched to said containment means.

42. A display device formed of the liquid crystal apparatus of claim 1.

43. The display device of claim 42, said reflecting means comprising means for reflecting light scattered by said liquid crystal means back to said liquid crystal means to display relatively bright characters or the like on a relatively dark background.

44. The display of claim 42, said liquid crystal means comprising at least one layer of liquid crystal material in a containment medium that tends to distort the structure of at least some of the liquid crystal material to align generally with respect to a wall of such containment medium when in the absence of an electric field, and said liquid crystal material being responsive to an electric field to tend to effect generally parallel alignment of the liquid crystal structure.

45. A display device formed of the liquid crystal apparatus of claim 2.

46. The display device of claim 45, said reflecting means comprising means for reflecting light scattered by said liquid crystal means back to said liquid crystal means to display relatively bright characters or the like on a relatively dark background.

47. The display of claim 45, said liquid crystal material comprising at least one layer of liquid crystal material in a containment medium that tends to distort the structure of at least some of the liquid crystal material to align generally with respect to a wall of such containment medium when in the absence of an electric field, and said liquid crystal material being responsive to an electric field to tend to effect generally parallel alignment of the liquid crystal structure.

48. An optical shutter formed of the liquid crystal apparatus of claim 1.

49. The apparatus of claim 1, said liquid crystal means comprising plural volumes of liquid crystal material in a containment medium and covering a substantial portion of said support medium means.

50. The apparatus of claim 49, further comprising plural electrode means for applying an electric field to selected portions of said liquid crystal means, said electrode means comprising plural electrodes positioned over relatively smaller areas of said support medium means and liquid crystal means than such substantial portion size of said liquid crystal means covering said support medium means.

105. The method of claim 107, said mixing comprising mixing a chrome alkyl complex with such liquid crystal material.

107. The method of claim 10, said providing a further medium comprising providing an air interface between such support medium and such light absorbing medium.

51. A liquid crystal display for displaying bright characters or the like on a dark background, comprising liquid crystal means for substantially isotropically scattering of light incident thereon, said liquid crystal means including plural volumes of operationally nematic liquid crystal material having positive dielectric anisotropy in a containment medium, said volumes being defined by walls of said containment medium, said walls being operative in the absence of an electric field to distort the natural structure of said liquid crystal material to effect scattering of light, and said liquid crystal material being responsive to application of an electric field to align with respect thereto thereby to reduce the amount of such scattering, and reflection means for reflecting light so isotropically scattered by said liquid crystal means back to said liquid crystal means for further scattering thereby.

52. The display of claim 51, said reflection means comprising a support medium means for supporting said liquid crystal means and carrying out total internal reflection of light therein, said support medium means having a viewing surface through which light isotropically scattered by said liquid crystal means within a prescribed angle can be transmitted to provide such bright character appearance.

53. The display of claim 52, further comprising an area of said support medium means in which light is not reflected through said viewing surface thereby effecting the appearance of a relatively dark background.

54. The display of claim 53, said area comprising an area proximate liquid crystal means that is substantially optically transmissive.

55. The display of claim 51, said liquid crystal means comprising at least one layer of encapsulated liquid crystal material.

56. The display of claim 51, further comprising electrode means for selectively applying an electric field to at least some of said liquid crystal means to cause the same to be substantially optically transparent.

57. A liquid crystal display for displaying bright characters or the like on a dark background, comprising liquid crystal means for substantially isotropically scattering light incident thereon, and reflection means for reflecting light so isotropically scattered by said liquid crystal means back to said liquid crystal means for further scattering thereby, said reflection means comprising a support medium means for supporting said liquid crystal means and carrying out total internal reflection of light therein, said support medium means having a viewing surface through which light isotropically scattered by said liquid crystal means within a prescribed angle can be transmitted to provide such bright character appearance, and said support medium means having an area in which light is not reflected through said viewing surface thereby effecting the appearance of a relatively dark background, said area comprising an area proximate liquid crystal means that is substantially optically transmissive, said liquid crystal means comprising at least one layer of encapsulated operationally nematic liquid crystal material in said support medium means, said liquid crystal material having positive dielectric anisotropy and an ordinary index of refraction substantially matched to that of said support medium means to maximize optical transmission in the presence of an electric field and to effect substantial isotropic scattering in the absence of an electric field.

58. The display of claim 57, further comprising electrode means for selectively applying an electric field to at least some of said liquid crystal means to cause the same to be substantially optically transparent.

59. A liquid crystal display for displaying bright characters or the like on a dark background, comprising liquid crystal means for substantially isotropically scattering light incident thereon, and reflection means for reflecting light so isotropically scattered by said liquid crystal means back to said liquid crystal means for further scattering thereby, said reflection means comprising a support medium means for supporting said liquid crystal means and carrying out total internal reflection of light therein, said support medium means having a viewing surface through which light isotropically scattered by said liquid crystal means within a prescribed angle can be transmitted to provide such bright character appearance, said liquid crystal means having positive dielectric anisotropy and wherein the dielectric constant of said support medium means is at least about as large as the lower dielectric constant of said liquid crystal means.

60. A liquid crystal display for displaying bright characters or the like on a dark background, comprising liquid crystal means for substantially isotropically scattering light incident thereon, and reflection means for reflecting light so isotropically scattered by said liquid crystal means back to said liquid crystal means for further scattering thereby, said reflection means comprising a support medium means for supporting said liquid crystal means, and an interface between said support medium means and a further medium having a smaller index of refraction with respect to that of said support medium means thereby to effect total internal reflection of light incident on such interface at an angle greater than a predetermined one with respect to normal at such interface.

61. The display of claim 60, said further medium comprising a tuned dielectric interference layer of material for effecting selective constructive and destructive optical interference.

62. A liquid crystal display for displaying bright characters or the like on a dark background, comprising liquid crystal means for substantially isotropically scattering of light incident thereon, and reflection means for reflecting light so isotropically scattered by said liquid crystal means back to said liquid crystal means for further scattering thereby, said liquid crystal means comprising at least one layer of encapsulated liquid crystal material, said encapsulated liquid crystal material comprising an emulsion of liquid crystal material and a containment medium therefor.

63. Liquid crystal apparatus comprising liquid crystal means for selectively primarily scattering or transmitting light in response to a prescribed input, said liquid crystal means comprising operationally nematic liquid crystal material having positive dielectric anisotropy, first medium means for containing said liquid crystal means, and second medium means for cooperating with said first medium means to effect total internal reflection of light scattered by said liquid crystal means.

64. The apparatus of claim 63, said liquid crystal means comprising encapsulated liquid crystal.

65. The apparatus of claim 63, said first medium means having an index of refraction exceeding the index of refraction of said second medium means.

66. The apparatus of claim 63, said second medium means comprising a tuned dielectric interference layer applied to said first medium means forming an interface therewith to effect optical interference with respect to at least some of the light transmitted at such interface.

67. A display device formed of the apparatus of claim 63.

68. An optical shutter formed of the apparatus of claim 63.

69. In combination an encapsulated operationally nematic liquid crystal comprising liquid crystal material and support medium means for containing such liquid crystal material, said liquid crystal material having positive dielectric anisotropy and ordinary index of refraction substantially matched to the support medium substantially to maximize optical transmission in the presence of an electric field and to effect isotropic optical scattering in the absence of an electric field.

70. The combination of claim 69, further comprising light director means for directing incident light into said support medium means for transmission to said liquid crystal material.

71. The combination of claim 70, said light director means comprising a louvered light control film.

72. The combination of claim 69, wherein the dielectric constant of said support medium means is at least about as large as the lower dielectric constant of said liquid crystal material.

73. The display device formed of the combination of claim 69.

74. The optical shutter formed of the combination of claim 69.

75. The combination of claim 69, said support medium means comprising a containment medium, and said liquid crystal material and containment medium comprising an emulsion.

76. The combination of claim 69, said support medium means comprising containment medium means for containing discrete quantities of liquid crystal material in capsule-like volumes.

77. The combination of claim 76, further comprising means reactive with said containment medium means for tending to force at least a portion of at least some of said liquid crystal material into substantially normal alignment with the wall of such capsule-like volumes.

78. The combination of claim 76, said containment medium means comprising wall means for tending to distort the natural structure of said liquid crystal material into general alignment therewith in the absence of an electric field.

79. The combination of claim 78, further comprising electrode means for applying an electric field to said liquid crystal material to align the latter with respect to such field.

80. The combination of claim 79, further comprising additive means in said liquid crystal material for expediting return to random alignment and such distorting of said liquid crystal material upon the removal of such electric field.

81. The combination of claim 76, said support medium means further comprising a substantially optically transparent support means on both sides of said liquid crystal material in said containment medium means for supporting and containing the same.

82. The combination of claim 81, further comprising a further medium having an index of refraction smaller than that of said support medium means and forming an interface with respect to the latter to cause total internal reflection at said interface of at least some of the light scattered into said support means by said liquid crystal means.

83. The combination of claim 81, further comprising an optical interference layer on a surface of said support medium means remote from said liquid crystal material in said containment medium means.

84. A method of displaying a bright character or other information on a relatively dark background using liquid crystal material contained in volumes formed in a containment medium, such liquid crystal material being operationally nematic, having positive dielectric anisotropy, having an extraordinary index of refraction that is different from the index of refraction of such containment medium and an ordinary index of refraction substantially matched to the index of refraction of such containment medium, comprising distorting the natural structure of such liquid crystal material to effect substantially isotrophic scattering of at least some light incident on such liquid crystal material, reflecting at least some of such scattered light back to such volumes of liquid crystal material for further scattering, and transmitting to a viewing area at least some of the light scattered by such liquid crystal material to form such character or other information.

85. The method of claim 84, said reflecting comprising totally internally reflecting isotropically scattered light back to such liquid crystal material to brighten the same.

86. The method of claim 84, further comprising effecting constructive optical interference with respect to at least some of such isotropically scattered light to direct the same incident on such liquid crystal material.

87. The method of claim 84, further comprising illuminating such liquid crystal material from opposite a viewing side thereof using incident light directed at an angle ordinarily out of the viewing line of sight.

88. The method of claim 84, further comprising selectively applying an electric field to such liquid crystal material to align the same for transparency to form such relatively dark background.

89. A method of making a liquid crystal apparatus comprising placing an encapsulated liquid crystal material in a support medium that has an optical internal reflection characteristic, and forming such encapsulated liquid crystal material as operationally nematic material, said forming comprising forming an emulsion of an operationally nematic liquid crystal material and a containment medium to provide capsule-like containment volumes of such liquid crystal material, the walls of such volumes tending to distort the natural structure of such liquid crystal material when generally randomly aligned in the absence of an electric field.

90. The method of claim 89, further comprising providing a further medium at an interface with such support medium and selecting the index of refraction of such support medium to be greater than the index of refraction of such further medium.

91. The method of claim 89, further comprising mixing with such liquid crystal material an additive that expedites return to distorted random alignment upon removal of an electric field.

92. The method of claim 89, further comprising adding a control agent to such liquid crystal material to control the viscosity thereof.

93. The method of claim 92, said adding comprising adding chloroform to such liquid crystal material and mixing the same.

94. The method of claim 89, further comprising adding a surfactant to such liquid crystal material.

95. The method of claim 94, said adding comprising adding a non-ionic surfactant.

96. An emulsion of an operationally nematic liquid crystal material and a containment medium, and further comprising a surfactant mixed therein.

97. The emulsion of claim 96, said surfactant comprising a non-ionic surfactant.

98. An optical display made from the emulsion of claim 96.

99. A method of making a liquid crystal apparatus, comprising forming a plurality of volumes of operationally nematic liquid crystal material in a containment medium such that the walls of such volumes tend to distort the natural structure of such liquid crystal material in the absence of an electric field to scatter light incident on such volumes, placing such volumes of liquid crystal material for support by a support medium that has an optical internal reflection characteristic, providing a further medium at an interface with such support medium and selecting the index of refraction of such support medium to be greater than the index of refraction of such further medium, whereby light scattered by such liquid crystal material at an angle greater than the internal reflection angle at such interface is totally internally reflected back to such liquid crystal material, and such liquid crystal material being responsive to the presence of an electric field to align with respect thereto and thereby to reduce scattering.

100. The method of claim 99, said providing comprising providing an air interface.

101. The method of claim 99, further comprising applying a tuned dielectric interference layer to a surface of such support medium opposite the surface at which such support medium ordinarily is viewed.

102. The method of claim 101, said applying a tuned dielectric interference layer comprising evaporating material onto a surface of such support medium.

103. An article made according to the method of claim 99.

104. The method of claim 99, further comprising mixing an aligning material with operationally nematic liquid crystal material.

106. A method of making a liquid crystal apparatus comprising placing an encapsulated liquid crystal material in a support medium that has an optical internal reflection characteristic, providing a further medium at an interface with such support medium, selecting the index of refraction of such support medium to be greater than the index of refraction of such further medium, and placing a light absorbing medium beyond such further medium for absorbing light transmitted through such further medium, whereby light impinging on such interface at an angle exceeding the total internal reflection angle is totally internally reflected to such liquid crystal material, and light transmitted through such interface is absorbed by such light absorbing medium.

108. A liquid crystal apparatus, comprising plural volumes of liquid crystal material in a containment medium, said liquid crystal material having positive dielectric anisotropy, said containment medium having an index of refraction, and said liquid crystal material having an ordinary index of refraction substantially matched to the index of refraction of said containment medium to maximize transmission of light and an extraordinary index of refraction different from the index of refraction of said containment medium to increase scattering of light transmitted through said containment medium and liquid crystal material.

109. The apparatus of claim 108, wherein the extent of transmission and scattering of light with respect to said containment medium and liquid crystal material is substantially independent of optical polarization direction.

110. The apparatus of claim 109, wherein said containment medium includes surface means for defining the boundaries of said volumes.

111. The apparatus of claim 110, wherein said surface means includes means for distorting the natural structure of said liquid crystal material to increase scattering of light incident on an interface of said liquid crystal material and said containment medium.

112. The apparatus of claim 108, wherein said containment medium and said liquid crystal material comprise an emulsion thereof.