Liquid crystal switching mechanism

Details Liquid crystal switching mechanism Liquid crystal switching mechanism

2002-09-04

2004-11-30

Wu, Shean C (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C428S001300, C428S001400, C252S299300, C252S299400, C252S299500, C252S299010, C349S041000, C349S123000

Reexamination Certificate

active

06824837

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to switching devices that use liquid crystals. More particularly, the invention relates to switching devices prepared from polymers or self-assembled monolayers containing redox-active groups that induce a shift in the orientation of liquid crystals when the oxidation state of the redox-active group is altered.
BACKGROUND OF THE INVENTION
Various display devices are known in the art. The prior art devices generally require a relatively high voltage or a relatively high current. Because power (Watts) is determined by multiplying current (Amps) by voltage (Volts), P=I*V, such devices generally require relatively high power to operate. For example electrochromic displays exist that have a low switching potential but require a high current. Such devices typically consume too much power to be useful in portable devices. On the other hand, conventional displays use low currents but require high applied potentials such that power consumption is still too high for many applications.
Although suitable switching mechanisms exist, a need remains for switching mechanisms which operate at low power and moderate response times. These types of switching mechanisms might find use in applications such as electronic labels, electronic ink, or electronic paper. There is also substantial interest in finding ways to switch the orientations of liquid crystals using driving circuitry that can be easily fabricated.
SUMMARY OF THE INVENTION
The present invention provides liquid crystal devices in which the orientation of the liquid crystal is altered when the oxidation state of a redox-active group is changed. The invention further provides methods for producing liquid crystal devices, methods for changing the orientation of a liquid crystal, and kits for producing liquid crystal devices.
A liquid crystal switching device includes a first substrate having a first surface; a redox-active material disposed on at least a first portion of the first surface, the redox-active material comprising at least one redox-active group; a liquid crystal disposed above the top of the redox-active material; and a salt dispersed in the liquid crystal. When the oxidation state of the redox-active groups are changed from a first oxidation state to a second oxidation state, such as by electrochemical oxidation, electrochemical oxidation using a redox mediator species, or oxidation using a chemical oxidizing agent, the liquid crystal changes its orientation with respect to the first surface of the first substrate providing a detectable change in the appearance of the liquid crystal.
In some embodiments of the invention, the first surface of the first substrate, or at least one region of the first surface, is electrically conducting. Further liquid crystal devices are provided in which the electrically conducting surface or surface region is a metallized top surface or surface region. Further liquid crystal devices are provided in which the metallized top surface or surface region of the first substrate comprises a metal selected from gold, silver, copper, nickel, palladium, platinum, or combinations thereof. In embodiments where the first surface comprises at least one electrically conducting region, the redox-active material is disposed on at least a portion of the electrically conducting region.
In other provided devices, the redox-active groups are supported on electrically conducting surfaces or surface regions, other than a metallized surfaces or surface regions, such as surfaces or surface regions made from conducting organic materials such as polymers or conducting metal oxides, such as indium tin oxide (ITO) or titanium dioxide. ITO is a substrate in some provided devices because it is optically transparent. Conducting polymers are substrates in other provided devices and may be flexible.
Still other liquid crystal devices are provided in which the metallized top surface or surface region is gold. In some provided liquid crystal devices, the gold is uniformly deposited without any overall azimuthal preference whereas in other devices, the gold or other metal is obliquely deposited. In some provided devices, the gold is obliquely deposited at an angle of from 35° to 60° whereas in other devices the gold is deposited at an angle of at or about 40°. The angle is defined as the angle from the normal of the substrate.
Liquid crystal devices are further provided in which the surface-bound redox-active group is selected from a group that includes ferrocene; a derivatized ferrocene such as nonamethyl ferrocene; a viologen; a pyridine, bipyridine or salts of these; a metal meso porphyrin; a quinone; a hydroquinone; an anthracene and other monocyclic and polycyclic aromatic compounds; or combinations thereof. Still other liquid crystal devices are provided in which the surface-bound redox-active groups attached to a metallized surface or metallized surface region of a first substrate are formed by reacting a compound of formula Fc—(CH
2
)
n
—SH with the first surface or surface region forming a self-assembled monolayer (SAM) where Fc is ferrocene and n has a value ranging from 1 to 20, 3 to 18, 5 to 15, 6 to 14, 8 to 12, 9 to 11, 10, or 11.
Further liquid crystal devices are provided in which surface-bound redox-active groups are attached to one portion of the surface of the substrate and another portion of the surface of the substrate does not contain any of the surface-bound redox-active groups. In still other provided devices, the region of the surface of the substrate with surface-bound redox-active groups has a defined shape such as a number, letter, symbol, circle, triangle, square, pentagon or other polygon.
Other liquid crystal devices are provided in which the surface-bound redox-active groups attached to the surface of the substrate are redox-active groups of a polymer coated on the surface of the substrate. In further provided liquid crystal devices, the redox-active groups of the polymer are ferrocene groups whereas in yet other such devices the polymer is poly(vinylferrocene) or a polymer that incorporates at least some vinylferrocene.
Further liquid crystal devices are provided in which the liquid crystal is a nematic liquid crystal. Still other devices are provided in which the liquid crystal has a dipole moment that is parallel to the long axis of the liquid crystal. Yet other liquid crystal devices are provided in which the liquid crystal is 4-cyano-4′-pentylbiphenyl (5CB). Still other devices are provided in which the liquid crystal is either a cholesteric phase or a smectic phase, including ferroelectric phases (smectic C*).
Yet other liquid crystal devices are provided in which the salt of the device is a tetraalkylammonium salt. In some provided devices, the salt is a tetraalkylammonium tetrafluoroborate, a tetraalkylammonium hexafluorophosphate, or a tetraalkylammonium tetraphenylborate. In other provided devices, the salt is a tetraalkylammonium tetrafluoroborate or a 1-alkyl-4-alkylcarbamoyl-pyridinium tetrafluoroborate. In still other provided devices, the salt is a tetrabutylammonium salt such as tetrabutylammonium tetrafluoroborate. In other devices, the salt is a metal halide, such as, but not limited to, sodium bromide. In other devices, the salts are organic-inorganic hybrids involving organic encapsulated metals such as dicyclohexyl 18-crown-6 potassium tetrafluoroborate (18C-6/KBF
4
), 15-crown-5 sodium tetraphenyl borate (15C-5/NaO
4
B) or cryptofix-2-2-2 potassium tetrafluoroborate (K*/BF
4
).
In still other provided liquid crystal devices, the salt is dispersed in the liquid crystal at a concentration of from 1 &mgr;M to 80 mM assuming perfect dissolution. In still other provided devices, the salt is dispersed in the liquid crystal at a concentration of from 5 mM to 75 mM, of from 10 mM to 60 mM, of from 15 mM to 50 mM, of from 20 mM to 40 mM, of from 25 mM to 40 mM, of from 30 mM to 35 mM, or of about 35 mM.
Other liquid crystal devices are further provided in which the liquid crystal is oriented planar to the surface of

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