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BACKGROUND OF THE INVENTION
This invention relates to liquid crystalline imaging, and more
particularly, to providing an electrohydrodynamic induced texture
transformation from the Grandjean to focal-conic texture in liquid
crystalline compositions.
Cholesteric liquid crystals are known to exhibit various observable
textures. For example, cholesteric liquid crystals may adopt a
homeotropic, a focal-conic, or a Grandjean plane texture as modifications
of the cholesteric mesophase itself, as described in Gray, G.W., Molecular
Structure and the Properties of Liquid Crystals, Acadamic Press, London,
1962, pp. 39-54.
U.S. Pat. No. 3,704,056 to J. J. Wysocki, J. E. Adams and R. W. Madrid
discloses that the Grandjean texture of a cholesteric liquid crystalline
material can be transformed into the focal-conic texture by application of
an electrical field. The electrical field induced texture transformation
is indicated therein as also occurring with liquid crystalline
compositions comprising a cholesteric liquid crystalline material and a
nematic liquid crystalline material.
It is known that the application of a D.C. electrical stimulus can cause a
hydrodynamic effect converting an initially clear Grandjean texture to the
scattering focal-conic texture.
In new and growing areas of technology such as liquid crystalline imaging,
new methods, apparatus, compositions, and articles of manufacture are
often discovered for the application of the new technology in a new mode.
The present invention relates to a novel method of providing an
electrohydrodynamic induced texture transition from the Grandjean to the
focal-conic texture.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to provide a novel imaging
method.
It is another object of this invention to provide a novel method for
providing an electrohydrodynamic induced texture transformation.
It is another object of this invention to provide a novel imaging method.
It is yet a further object of this invention to provide a novel method for
imagewise providing an electrohydrodynamic induced texture transformation
from the Grandjean to the focal-conic texture.
It is yet a further object of this invention to provide increased
sensitivity to the imagewise transformation of the Grandjean texture to
the focal-conic texture.
The foregoing objects and others are accomplished in accordance with this
invention by providing a liquid crystalline composition comprising
optically active material and a nematic liquid crystalline material having
negative dielectric anisotropy, and optionally an ionizable salt, between
two electrodes, said liquid crystalline composition capable of undergoing
an electrohydrodynamic induced transformation from the Grandjean to the
focal-conic texture; applying a voltage across said liquid crystalline
composition at a voltage magnitude and for a period of time such that the
voltage-time product is insufficient to initiate substantial texture
transformation; subsequently applying a voltage of a magnitude and for a
period of time such that the voltage-time product is sufficient to bring
said liquid crystalline composition at least into its region of maximum
response to electrical stimulus thereby causing substantial texture
transformation.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as other objects and
further features thereof, reference is made to the following detailed
disclosure of the preferred embodiments of the invention taken in
conjunction with the accompanying drawings thereof, wherein:
FIG. 1 is a graphic representation of the dependence of electrohydrodynamic
induced texture transformation of an exemplary liquid crystalline
composition upon the magnitude and time of application of voltage.
FIG. 2 is a graphicc representation of the dependency of complete
electrohydrodynamic induced texture transformation of an exemplary liquid
crystalline composition upon voltage and time.
FIG. 3 is a schematic illustration of one embodiment of the invention.
FIG. 4 is a schematic illustration of another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The exemplary composition in FIG. 1 is a liquid crystalline composition
comprising about 80 weight percent MBBA
(p-methoxybenzilidene-p-n-butylaniline) and about 20 percent by weight COC
(cholesteryl oleyl carbonate). This liquid crystalline composition is
exemplary of those which are capable of undergoing an electrohydrodynamic
induced texture transformation from the Grandjean to the focal-conic
texture. By "electrohydrodynamic induced texture transformation" is meant
a texture transformation in which turbulent motion occurs. On the x-axis
is plotted the pulse time of applied voltage, i.e., the duration of
applied voltage. On the y-axis is plotted the relative transmission of
white light through the liquid crystalline composition as detected by a
Leitz microscope with an attached photodiode, at a numerical aperture of
0.1. Unity transmission (that is, the value of 0.1) is arbitrarily taken
for the white light transmission through the liquid crystalline
composition in the Grandjean texture. It has been experimentally
determined that the relative transmission can be correlated to the amount
of the liquid crystalline composition that has been transformed to the
focal-conic texture from the Grandjean texture.
As can be seen from FIG. 1, liquid crystalline compositions capable of
undergoing the electrohydrodynamic induced texture transformation from the
Grandjean texture to the focalconic texture, of which the composition of
FIG. 1 is exemplary, exhibit a region of maximum response to electrical
stimulus. For example, as can be seen from the curve plotted for the
application of 50 volts, the portion of the 50 volt curve between points A
and B indicates the region of maximum response for the exemplary
composition wherein greatest change in relative transmission occurs. Since
change in relative transmission is indicative of change in the amount of
the liquid crystalline composition undergoing the electrohydrodynamic
induced texture transformation, the A to B portion of the 50 volt curve
defined the region where the greatest amount of texture transformation
occurs.
It has been found that the electrohydrodynamic induced texture
transformation from the Grandjean to the focalconic texture is
substantially additive. That is, on the 50 volt curve, one can reach point
B by applying 50 volts for approximately 0.2 seconds, removing the
voltage, and subsequently applying 50 volts for another 0.2 seconds at
which time one is substantially at point B. The 50 volt curve is used for
purposes of illustration only, and it will be understood that any curve of
FIg. 1, whether depicted therein or not, which exhibits a region of
maximum response can be utilized in accordance with the practice of the
present invention. As a matter of practical convenience, applied voltage
curves such as, for example, the 50 volt curve of FIG. 1 which are more or
less in the shape of a reverse "S" are preferred. However, the invention
can be practiced with any liquid crystalline composition capable of
undergoing an electrohydrodynamic induced texture transformation from the
Grandjean to the focal-conic texture. In FIG. 1, the lowest transmission
of about 0.1 relative transmission is indicative of a fully transformed
focal-conic texture for the exemplary composition notes therein. It is
apparent from FIG. 1 that the lower voltages require disproportionally
longer times to achieve the fully transformed focal-conic texture. Thus,
nonlinearity in voltage is a characteristic of the electrohydrodynamically
induced texture transformation to the focal-conic texture from the
Grandjean texture.
The transformation nonlinearity between voltage and time has also been
found through experimentation to apply to current and time. This
nonlinearity in voltage and current can be represented in the form of a
reciprocity relationship of electrical stimulus and time. FIG. 2 is a plot
of this relationship for the complete Grandjean-focal-conic
transformation. The abscissa chosen is the applied voltage. The
voltage-time product to complete the transformation from Grandjean to
focal-conic texture is shown on the left ordinate and the current-time
product (or change) on the right ordinate. If the transformation were a
linear process, a straight horizontal line would be obtained. However, as
seen from FIG. 2, the transformation is not a linear process. FIG. 2 shows
that high voltages and high currents require disproportionally less time
to achieve a transformation. Indeed, it has been found through
experimentation that the magnitude of applied voltage and the time during
which it is applied has a characteristic relationship of E.sup.2 .times. t
where E is the electrical field strength across the liquid crystalline
composition resulting from the application of voltage and t is the
duration of voltage application. It has been found through experimentation
that E.sup.2 .times. t is characteristically of constant value for
complete electrohydrodynamically induced texture transformation for a
particular liquid crystalline composition suitable for use in the practice
of this invention.
The parameter E.sup.2 .times. t characteristically has a different value
for each of the different liquid crystalline compositions suitable for use
in the practice of this invention. It should be noted that the exemplary
liquid crystalline composition for which FIGS. 1 and 2 are plotted had a
layer thickness of about 1 mil. Accordingly, the electrical field strength
across the liquid crystalline composition layer is, in volts per mil, of
the same magnitude as the voltages denoted in FIGs. 1 and 2.
The relationship of applied voltage and time and total current and time for
electrohydrodynamically induced texture transitions to the focal-conic
from the Grandjean texture is indeed surprising and unexpected. Moreover,
this discovery together with the substantially additive effect previously
mentioned allows one to sensitize the liquid crystalline composition prior
to causing texture transformation. This will become more evident as the
discussion proceeds.
In FIG. 3, a typical liquid cystalline imaging member 10, sometimes
referred to as an electroded imaging sandwich, is shown in partially
schematic cross-section where a pair of transparent plates 11 having
substantially conductive coating 12 upon the contact surface, comprise a
parallel pair of substantially transparent electrodes. An imaging member
wherein both electrodes are transparent is preferred where the imaging
member is to be viewed using transmitted light; however, a liquid
crystalline imaging member may also be viewed using reflected light
thereby requiring only a single transparent electrode while the other may
be opaque. The transparent electrodes are separated by spacing member 13
which contains voids which form one or more shallow cups which contain the
liquid crystalline composition layer which comprises the active element of
the imaging member. A voltage is applied between the electrodes by an
external circuit 15 which typically comprises a source of potential 16
which is connected across the two electrodes through leads 17. The circuit
15 may also contain suitable switching means. The potential source may be
either D.C., A.C. or a combination thereof.
In the liquid crystal imaging member described in FIG. 3 the electrodes may
be of any suitable transparent conductive material. Typical suitable
transparent conductive electrodes include glass or plastic substrates
having substantially transparent and continuously conductive coatings of
conductors such as tin; indium oxide, indium, aluminum, chromium, tin
oxide, or any other suitable conductor. These substantially transparent
conductive coatings are typically evaporated onto the more insulating,
transparent substrate. NESA glass, a tin oxide coated glass manufactured
by the Pittsburgh Plate Glass Company, is a commercially available example
of a typical transparent, conductive electrode material.
The spacer, 13 in FIG. 3, which separates the transparent electrodes and
contains the liquid crystal film between said electrodes, is typically
chemically inert, transparent, substantially insulating and has
appropriate dielectric characteristics. Material suitable for use as
insulating spacers include cellulose acetate, cellulose triacetate,
cellulose acetate butyrate, poly urethane elastomers, polyethylene,
polypropylene, polyesters, polystyrene, polycarbonates, polyvinyl
fluoride, polytetrafluoroethylene, polyethylene terephthalate, and
mixtures thereof.
Such spacers, which also approximately define the thickness of the imaging
layer or film of liquid crystals, are preferably of a thickness in the
range of about 100.mu. or less. Preferred results are typically attained
with spacers in the thickness range between about 1.mu. and about 100.mu..
Layer 14 of the liquid crystalline composition may comprise any suitable
liquid crystalline composition capable of undergoing an
electrohydrodynamic induced texture transformation from the Grandjean
texture to the focal-conic texture. Typical suitable liquid crystalline
compositions comprise an optically acrive material and a nematic liquid
crystalline material, and, optionally, an ionizable salt.
Typical suitable optically active materials include non-mesomorphic
optically active materials and mesomorphic optically active materials.
Typical suitable non-mesomorphic optically active materials include:
derivatives of alcohols such as 1-methol, 1-linanool, d-mannitol,
d-borneol and d-quercitol; derivatives of ketones such as d-camphor,
d-3-methylcyclohexanone, 1-methone and 1-6-isopropyl-3-cyclohexanone;
derivatives of carboxylic acid, 1-campholic acid, 1-arabonic acid,
d-tartaric acid, and 1-ascorbic acid; derivatives of aldehydes such as
d-citronellal; derivatives of alkenes such as 1-B-pinane, d-silvesterene,
and d-linonene; derivatives of amines such as 1-2-methylpiperidine;
derivatives of nitriles such as d-mandelonitrile; derivatives of amides
such as d-hydrocarbamide; and mixtures thereof.
Mixtures of the nematic liquid crystalline substance and the optically
active, non-mesomorphic material can be prepared in organic solvents such
as chloroform, petroleum ether, methylethyl ketone and the like, which are
typically subsequently evaporated from the mixture thereby leaving the
liquid crystalline composition. Alternatively, the individual components
of the liquid crystalline composition can be combined directly by heating
the mixed components to a temperature which is above the isotropic
transition temperature of the nematic liquid crystalline substance and the
melting point of the non-mesomorphic material.
Typical suitable mesomorphic optically active materials include liquid
crystalline optically active materials such as cholesteric liquid
crystalline materials. Typical suitable cholesteric liquid crystalline
materials include derivatives from reactions of cholesterol and inorganic
acids; for example, cholesteryl chloride, cholesteryl bromide, cholesteryl
iodide, cholesteryl nitrate, esters derived from reactions of cholesterol
and carboxylic acids; for example cholesteryl crotonate; cholesteryl
nonanoate; cholesteryl hexanoate; cholesteryl formate; cholesteryl
chloroformate; cholesteryl propionate; cholesteryl acetate, cholesteryl
valerate; cholesteryl linolate; cholesteryl linolenate; cholesteryl
oleate; cholesteryl erucate; cholesteryl butyrate; cholesteryl caprate;
cholesteryl laurate; cholesteryl myristate; ethers of cholesterol such as
cholesteryl decyl ether; cholesteryl oleyl ether; cholesteryl dodecyl
ether; carbamates and carbonates of cholesterol such as cholesteryl decyl
carbonate; cholesteryl oleyl carbonate; cholesteryl methyl carbonate;
cholesteryl ethyl carbonate; cholesteryl butyl carbonate; cholesteryl
docosonyl carbonate; cholesteryl heptyl carbamate; and alkyl amides and
aliphatic secondary amines derived from 3.beta.-amino-.DELTA..sup.5
-cholestene and mixtures thereof; peptides such as
poly-.gamma.-benzyl-l-glutamate; derivatives of beta sitosterol such as
sitosterol chloride; and active amyl ester of cyano benzylidene amino
cinnamate. The alkyl groups in said compounds are typically saturated or
unsaturated fatty acids, or alcohols, having less than about 25 carbon
atoms and unsaturated chains of less than about 5 double-bonded olefinic
groups. Aryl groups in the above compounds typically comprise simply
substituted benzene ring compounds. Any of the above compounds and
mixtures thereof may be suitable for cholesteric liquid crystalline films
in the advantageous system of the present invention.
The liquid crystal imaging layers or films are preferably of a thickness in
the range of about 1 to about 100.mu.. Optimum results are typically
attained with layers in the range of thicknesses between about 1/4 mil and
about 5 mils.
Typical suitable nematics having negative dielectric anisotropy include
N-(p-Methoxybenzilidene)-p-butylaniline (MBBA); p-azoxyanizole (PAA),
N-(p-Ethoxybenzilidene)-p-butylaniline (EBBA);
dl-4-(2-methylhexyl)-4'-ethoxy-.alpha.-chloro-trans-stilbene;
p-methoxybenzilidene-p'-aminophenyl-3-methyl valerate (MBV);
p-ethoxybenzilidene-p'-aminophenyl-3-methyl valerate;
pp'-methoxypentyltolane (MPT); pp'-propoxyheptyltolane (PHT);
pp'-dioctoxytolane (DOT), trans-4-butyl-.alpha.-chloro-4'-ethoxystilbene
and phase IV and phase V of nematic liquid crystalline phases available
under the trademark Licristal from EM Laboratories, Inc. Phase IV is a
eutectic mixture of
##EQU1##
and
##EQU2##
phase V is a mixture of
##EQU3##
and
##EQU4##
With highly resistive compositions, optionally ionizable salts may be added
to the liquid crystalline composition to enhance conductivity in order to
provide current flot. Typical additives include tetraethyl ammonium
bromide, tetramethyl ammonium chloride, tetra-n-butyl ammonium chloride
and tetramethyl ammonium perchlorate.
Mixtures of liquid crystals can be prepared in organic solvents such as
chloroform, petroleum ether, methylethyl ketone and others, which are
typically subsequently evaporated from the mixture thereby leaving the
liquid crystalline mixture. Alternatively, the individual liquid crystals
of the liquid crystalline mixture can be combined directly by heating the
mixed components above the isotropic transition temperature.
In accordance with the practice of the present invention, the liquid
crystalline composition layer 14 of FIG. 3 is first provided with a
voltage thereacross of a magnitude and for a duration sufficient to
partially transform layer 14 from the Grandjean to the focal-conic
texture. By "partially transformed" is meant that the region of maximum
response to electrical stimulus of the liquid crystalline composition of
layer 14 is approached. Preferably, but not necessarily, the partial
transformation is up to about the region of maximum response to electrical
stimulus. Subsequent to the partial transformation step, a voltage is
applied of magnitude and for a duration sufficient to transform the liquid
crystalline composition of layer 14 to a point at least within the region
of maximum response to electrical stimulus and, preferably, to the point
of complete transformation to the focal-conic texture.
In operation, the imaging sandwich of FIG. 1 can be utilized to provide the
initial partial transformation step by a uniform application of voltage
between the two electrods. Subsequently, the further transformation step
to either within the region of maximum response to electrical stimulus or
to complete focal-conic texture transformation can be created in imagewise
configuration by applying the subsequent voltage in imagewise
configuration. Alternatively, the subsequent voltage could be applied
uniformly wherein the subsequent transformation is uniform and not in
imagewise configuration. Typically, the application of imagewise
configured voltage in the subsequent transformation is carried out by
utilizing at least one shaped electrode, shaped in imagewise
configuration, in the FIG. 1 embodiment. As will be seen, below, in
connection with the description of FIG. 4, a more versatile imaging method
is provided by the incorporation of a photoconductive layer in the FIG. 1
embodiment wherein the application of voltage across the layer of liquid
crystalline composition is optically controlled.
The Grandjean texture is typically charaterized by reflective dispersion of
incident light around a wavelength .lambda..sub.o (where .lambda..sub.o =
2np where n = the index of refraction of the liquid crystalline film and p
= the pitch of the liquid crystalline film) and optical activity for
wavelengths of incident light away from .lambda..sub.o. If .lambda..sub.o
is in the visible spectrum for normal incidence and normal viewing, the
liquid crystalline film appears to have the color corresponding to
.lambda..sub.o, and if .lambda..sub.o is outside the visible spectrum the
film appears colorless and non-scattering. The Grandjean texture is
sometimes referred to as the "disturbed" texture.
The focal-conic texture is also typically characterized by reflective
dispersion but in addition this texture also exhibits diffuse scattering
in the visible spectrum, whether .lambda..sub.o is in the visible spectrum
or not. The appearance of the focal-conic texture state is typically
milky-white when .lambda..sub.o is for outside the visible spectrum. The
focal-conic texture of cholesteric liquid crystals is sometimes referred
to as the "undisturbed" texture.
For example, in the inventive system when cholesteric liquid crystals are
placed in the electrode sandwich in the Grandjean texture, they initially
appear colored, or colorless and transparent. If the electrode sandwich is
observed between polarizers, the imaging sandwich appears colored or
black. When the voltage is placed across the liquid crystalline film, the
texture change is observable because the liquid crystalline film becomes
white in the image area when the imaging sandwich is observed in
transmitted or reflected light. The described imaging system thereby
produces a white image on a dark or colored background. However, it is
clear that the liquid crystal imaging sandwich may be used to create the
desired image, with or without the use of polarizers or other image
enhancing devices.
FIG. 4 illustrates another embodiment of the invention, particularly suited
for optically addressing or imaging the liquid crystalline composition
layer 14. In FIG. 4, like numerals refer to like parts of FIG. 3. The only
additional aspect of FIG. 4 is the photoconductive layer 18.
Photoconductive layer 18 may comprise any suitable photoconductive
material. Typical suitable photoconductive materials include
photoconductive inorganic materials and photoconductive organic materials.
Typical suitable inorganic photoconductive materials include sensitized
zinc oxide, for example, sensitized by the addition of Rhodamine dye,
available from Dupont, selenium, selenium alloy with arsenic such as, for
example, arsenic triselenide, tellurium, tellurium antimony or bismuth;
cadmium sulfide, cadmium sulfoselenide, and the many other typical
suitable inorganic photoconductive materials listed in U.S. Pat. No.
3,121,006 to Middleton et al and listed in U.S. Pat. No. 3,288,603, both
of which patents are hereby incorporated by reference. Typical suitable
organic photoconductive materials include, for example, a combination of
2,5-bis(p-aminophenyl)-1,3,4-oxadiazole available under the trademark TO
1920 from Kalle and Co., Weisbaden-Biebrich, Germany and Vinylite VYNS, a
copolymer of vinyl chloride and vinyl acetate, available from Carbide and
Carbon Chemicals Company; and the combination of
2,4,7-trinitro-9-fluorenone to polyvinyl carbazole, available under the
trademark Luvican 170 from Winter, Wolf and Company, New York, New York.
The thickness of the photoconductive layer is not critical to the practice
of the invention and any thickness which provides a sufficiently high dark
resistance ma be utilized. That is, the dark resistance should be
sufficient to provide greater voltage across the photoconductive layer
than across the liquid crystal layer in the dark. When struck by actinic
radiation, the voltage decreases across the photoconductive layer and
increases across the liquid crystalline layer 14. It will be appreciated
that photoconductors having a fundamental absorption band within the
electromagnetic spectrum, including the visible region, the x-ray region,
the ultra-violet region, the infrared region, etc., can be employed. The
radiation used will, of course, be radiation which is actinic to the
photoconductor employed.
The method provided by the practice of the present invention will be
appreciated to be of significance, especially in imaging embodiments
thereof where the imagewise configured transformation is to take place
under conditions of limited imagewise configured stimulus. That is, with
respect to the embodiment of FIG. 1, the imagewise applied voltage across
liquid crystalline composition layer 14 may be from a source of either
limited magnitude or limited duration; similarly, in the embodiment of
FIG. 4, the imagewise configured optical input may be from a source having
a limited optical intensity such as, for example, a cathode ray tube.
In optically imaging the embodiment of FIG. 4, the partial transformation
step to a point prior to, and preferably up to about the region of maximum
response to electrical stimulus, is carried out by either uniformly or in
imagewise configuration impinging the photoconductive layer with radiation
actinic thereto while a voltage is applied across the imaging sandwich.
Similarly the subsequent transformation step in the embodiment of FIG. 4
is carried out with radiation which is actinic to the photoconductor and
which may impinge the photoconductor either uniformly or in imageiwse
configuration. It will be appreciated, of course, that the optical address
in one step is uniform and in the other step imagewise, or vice versa, in
the imaging mode. Of course, when the optical address in both steps is
carried out with radiation uniformly impinging the photoconductor, then
the liquid crystalline composition layer 14 will uniformly transform to
the extent desired.
Of noteworthy significance in the practice of the present invention
according to the optical address imaging embodiment of the sandwich
structure in FIG. 4 is the fact that the sandwich structure can be
sensitized or partially transformed prior to being exposed to the optical
output of a cathode ray tube. Subsequently, when exposed to the optical
output of a cathode ray tube the sensitized structure will sufficiently
transform to provide an image corresponding to the cathode ray tube
optical output and of sufficient contrast from the previously transformed
background areas so as to be distinguishable therefrom. Preferably, the
exposure to the optical output of the cathode ray tube is sufficient to
provide complete transformation to the focal-conic texture. This is
typically occur when care is taken to sensitize the structure by partially
transforming up to about the region of maximum response to electrical
stimulus.
The following Examples further specifically illustrate various preferred
embodiments of the present invention. Parts and percentages are by weight
unless otherwise indicated.
EXAMPLE I
An imaging member according to FIG. 3 is prepared as follows. An about 1
mil thick Mylar spacer is sandwiched between two tin-oxide coated glass
electrodes and filled by capillary action with a liquid crystalline
composition comprising by weight about 80% MBBA and about 20% cholesteryl
oleyl carbonate. The liquid crystalline compositions assume the Grandjean
texture. The imaging member is illuminated with a Spectra Physics 162
Argon ion laser. Light transmitted through the imaging member was detected
with an E.G. and G. SGD-100 photodiode having an active area of about 0.05
cm.sup.2 and located relative to the imaging member such that the
resulting numerical aperture was about 0.006. Since the amount of
transmitted light detected varies with varying numerical aperture values,
this numerical aperture value of about 0.006 was utilized throughout all
of the Examples.
The electrodes are electrically connected to a pulsed D.C. voltage source.
A first pulse of an amplitude of about 60 volts and duration of about 0.34
seconds was applied. The transmitted light detected subsequent to the
pulse is observed to be about 21% less than the transmitted light detected
initially (prior to voltage application) which initial transiitted light
is taken as unity. The member is driven back to its initial unity
transmission level by applying about 400 volts peak to peak A.C. voltage
for about 7 seconds at about 3 KHz.
A second pulse of an amplitude of about 100 volts and duration of about
0.125 seconds is applied. The transmitted light detected subsequent to the
second pulse is observed to be about 12% less than the initial unity
transmission level. The member is again driven back to its initial unity
transmission level. Decreases in transmission are correlated to
transformation from the Grandjean to the focal-conic texture. Then, the
first and second pulses previously described are applied sequentially
without an intervening return to the initial unity transmission level. The
second pulse is applied about 0.1 second after the first pulse terminates.
This sequence of pulses results in a decrease of transmission of about 78%
from the initial unity transmission level.
When the second pulse is in imagewise configuration and applied
sequentially to the uniform application of the first pulse the image area
of the member undergo the 78% decrase of transmission while the background
areas undergo the 21% decrease of transmission.
It is noteworthy that the first voltage pulse obviously sensitized the
imaging member and provided, upon second voltage pulse application, a
greater transmission decrease than results from either the first or second
pulse above, or the mere addition of the first and second pulse
transmission decreases. Thus, the sequential application of the first and
second voltage pulses provide a synergetic effect in transforming the
Grandjean texture to the focal-conic texture.
EXAMPLE II
Example I is repeated except that the first voltage pulse is 50 volts for
about 0.32 seconds, the second voltage pulse is about 100 volts for about
0.05 seconds.
The separate application of the first voltage pulse results in a
transmission decrease of about 16% and the second voltage pulse results in
a transmission decrease of about 10%.
The sequential application of voltage pulses in Example I is followed
except that the second pulse immediately follows the first pulse without
the 0.1 second time delay. The resulting transmission decrease is observed
to be about 50% from the initial unity transmission.
It will be appreciated that other variations and modifications will occur
to those skilled in the art upon a reading of the present disclosure.
These are intended to be within the scope of this invention.
For example, any of numerous cell electrode configurations that allow
selective addressing of the liquid crystalline material may be utilized,
such as the so-called matrix or cross grid electrode configuration, where
non-optical input is provided.
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