DE19644726A1 - See-through body - Google Patents

Abstract

The invention relates to a transparent body comprising two attaching external transparent bodies which surround a volume of liquid crystals placed between them and intercalated colorants (guest-host cells), having an orientation layer of organic molecules or polymers respectively on the inner surface of the attaching bodies. According to the invention, the orientation layers consist of photochromic molecules or polymers, which regulate the liquid crystal volume following the command-surface effect (specially with cis-trans isomerization). Colorant molecules have also been dissolved in the liquid crystals. Said molecules match the sunlight spectrum and the visual spectral sensitivity of the human eye or the spectral sensitivity of an apparatus placed behind the transparent body.

Description

The invention relates to see-through body with two outer transparent end bodies, which one between them arranged volume with liquid crystals and embedded Enclose dyes, and one orientation layer each from organic molecules or polymers on the inner Finishing surfaces.

Transparent body with liquid crystals in between well known and are particularly popular with LCD screens used. But it is also known, such Transparent body in windows of buildings, cars, trains Airplanes as well as in sunglasses. The See-through bodies are used in sunglasses for their transmission to changing light conditions change so that the eye is too exposed to radiation protect.

Sunglasses are known which have the electrochromic effect exploit and need a battery as a voltage source.

Sunglasses are also known which are electro-optical Use the effect of liquid crystals (LC or FK). Since there smaller voltages and powers are sufficient than with Electrochromic effect extends the energy supply through one or several photocells. To the visible part of the To weaken the spectrum of sunlight, several need Dyes in an LC matrix (guest-most principle / cell) be stored. The application of a voltage leads to a Reorientation of the LC molecules from homogeneous planar to homeotropic (or vice versa, depending on the cell type), whereby by the Interaction with the LC molecules also the dyes in their spatial location can be changed. This changes the absorption of the cell. This is the well-known electro-optical Principle of the guest host cell. The orientation layers are  either built up from polymers (e.g. polymide), whereby by Brushing a preferred direction is created, or from organic Molecules which (by themselves) are vertical or with a Are inclined to the surface.

Phototropic come without any voltage and energy supply Glasses out. The sun's radiation is caused by the photochromic effect a photochemical change in the volume of the Glasses, which manifests itself in the change in absorption.

From US 5,211,876 is a liquid crystal arrangement for a Windshield or sunroof of a car known which is an additional voltage source for changing the Need transmission.

From US 5,298,732 is a windshield for one Passenger cars are known, in which with an LCD arrangement a transmission-reducing area only between drivers and sun is generated. Again, an additional one Voltage source needed to change the transmission.

From US 4,765,977 and US 5,041,244 are liquid crystals Lenses known for sunglasses that have an additional Need voltage source to change the transmission.

It is the object of the invention to provide a see-through body create which by means of liquid crystals (in particular natural light or sunlight) a change in transmission even without applying voltage or a stream, as well as without the imperative of electronic components.

This task is accomplished by the characteristic part of the first claim.

The invention is essentially based on a combination of Guest host cells with orientation layers that the command Show surface effect. By exposure to light, the  Orientation layer orientation changed. This changes the orientation of the liquid crystals and the dyes. This causes a change in the transmission. This process is reversible.

The principle effect of the "command surface" was published in 1989 by T.Seki and K.Ichimura. Numerous other publications were subsequently published on this effect (e.g. BTSeki, K.Ichimura, Thin Solid Films 179 ( 1989 ) 77; K.Aoki, A.Hosoki, K.Ichimura, Langmuir 8 ( 1992 ) 1007; dissertation by M. Büchel at the University of Mainz from 1995; etc.). In the publication by T.Seki et al., Langmuir 1993 , Vol. 9, 211-218 it is mentioned that the orientation of the command surface layer was verified by the addition of a dye.

The see-through body according to the invention has two outer ones transparent shells as a final body, with at least one of the two shells preferably on the outer side the shell curvature can produce an optical effect (but not necessary, see sunglasses).

Between these two shells, which in a certain Are spaced from each other, there is a volume. In this volume there are liquid crystals and embedded ones Contain dyes, which through the two shells before Leakage are prevented.

There is one on the inner surface of each of the two shells Orientation layer made of organic molecules or polymers attached, which is in direct contact with the liquid crystals stands.

The orientation layers are according to the invention photochromic molecules or polymers, which according to the command Surface effect switch the volume of liquid crystals. This are especially molecules and polymers with cis-trans Isomerization. Furthermore according to the invention are in the Liquid crystals dissolved dye molecules, which on the  Sunlight spectrum and visual spectral sensitivity of the human eye or on spectral sensitivity of a device behind the see-through body.

This combination according to the invention makes it possible to create sun-sensitive see-through bodies (sunglasses lenses, panes for various vehicles or buildings, etc.), which are much less expensive than the previously known solutions
An insulation layer is advantageously arranged between the transparent conductive electrode and the orientation layer. This insulation layer is preferably made of SiO ₂ .

The orientation layer is preferably made of azobenzenes or molecules containing stilbene (or polymers).

The liquid crystals are preferably nematic Liquid crystals.

The final body is preferably made of plastic or of glass.

It is advantageous if below the orientation layer a coupling layer with anchor groups is attached. Thereby the orientation layer becomes more secure on the shells of the See-through body anchored.

The preferred area of use for the see-through body is this Use as a lens for sunglasses.

The invention in the following by way of example with reference to Drawings explained, with other essential features as well explanation for better understanding and Design options of the inventive concept described are.  

Show:

Fig. 1 shows a first view of the body according to the invention; and

Fig. 2 shows a further variant of a see-through body according to the invention.

The see-through bodies shown in FIGS. 1 and 2 are drawn purely theoretically, so that the size relationships shown are unrelated to the real size relationships. The see-through bodies can in particular be lenses for sunglasses, windows for buildings, cars, trains, airplanes, etc., the lenses in particular being able to have one or no dioptric effect.

The structure of the see-through body is quickly explained. The first see-through body ( 1 ) according to the invention shown in FIG. 1 shows a feasible minimal solution. It has two cover layers ( 1 a, 1 b) which create a cavity and which consist of a transparent hard or soft material. This material can e.g. B. glass, on which one can apply the command surface layers by means of chemisorption or the Langmuir-Blodgett technique. It can also be applied to plastic using the Langmuir-Blodgett technique. However, it is also possible, in particular, to first apply a thin SiO ₂ layer to plastics, to which the command surface layers can be applied.

An orientation layer ( 2 a, 2 b) is in each case applied to the inner surface of these cover layer bodies ( 1 a, 1 b). The cavity between the two cover layer bodies ( 1 a, 1 b) with the orientation layer ( 2 a, 2 b) on its inner surface is filled with rod-shaped liquid crystals ( 3 ) which have a dye admixture according to the prior art, so that the guest-host principle is used.

The orientation layer ( 2 a, 2 b) is the essential part of the invention. It consists of molecules that undergo cis-trans isomerization under the influence of UV radiation and thus change geometrically. The geometric change leads to a change in the position of the liquid crystals ( 3 ) lying on the orientation layer ( 2 a, 2 b), which ultimately leads to an adjustment of the position of all liquid crystals ( 3 ) between the two orientation layers ( 2 a, 2 b). The switching speed of such an alignment layer (2 a, 2 b) is in the previously known molecules currently in seconds / minutes range and the longer the molecules depends on the length of the molecules (the faster they go from one state to the different condition over). (B 2 a, 2) as molecules of the orientation layer come photochromic molecules having the above-described isomerization in question. Examples include azobenzenes and stilbenes.

In the case of the command surface effect, one layer of a molecule or polymer (e.g. azobenzene) is located on the carrier substrate ( 1 a, 1 b). The orientation layer (2 a, 2 b) and with it the liquid crystal (3) changes its orientation from the homeotropic phase in the trans state to the homogeneous planar phase in the cis state, which is oriented along the direction of transmission, with the use of azobenzene molecules (a, 2 b 2) nm at an irradiation having the wavelength of about 360 in the orientation layer. the opposing orientation change occurs at an irradiation having the wavelength of about 440 nm. by modifying the azobenzene derivatives (in particular push-pull groups) However, these absorption ranges can be shifted (to longer wavelengths).

A further variant of the see-through body ( 1 ') according to the invention is shown in FIG. 2, but which has a much more complicated layer structure between the two cover layer bodies ( 1 a', 1 b ').

In the example shown in Fig. 2 phantom body (1 ') on the inner surfaces of the outer layer body (1 a', 1 b ') first, a transparent electrode (5 a, 5 b) (for. Example, an indium tin Oxide, also called ITO). An insulating layer ( 4 a, 4 b) (eg made of SiO ₂ ) is deposited thereon, but this is not mandatory. This is followed by the orientation layer ( 2 a ', 2 b'), which is composed of the molecules already described. However, a coupling layer (not shown in the figure) can also be applied between the orientation layer ( 2 a ', 2 b') and the insulating layer ( 4 a, 4 b) or electrode ( 5 a, 5 b). Between the two alignment layers (2 a ', 2 b') are the liquid crystals (3 ') with the dye admixture (guest-host principle).

With this arrangement there is also one Change in transmission of the see-through body by an energy and power supply possible, which makes sense if the required switching wavelengths (e.g. through discs) are not more are available. This allows the see-through body then also as sunglasses lenses behind lenses (e.g. in in a building or in a car).

As already mentioned, the invention is characterized by a Combination of the guest-host principle with the command surface Effect out. However, the volume of the Liquid crystal cell changed photochemically, like this at phototropic glasses, but only that Orientation layer between the top layer bodies and the Liquid crystals, optionally also an electrode between the orientation layer and the top layer bodies may be appropriate. The orientation layer gives the Liquid crystals have a uniform orientation. From a few special orientation layers described above known that their exposure to UV and their chemical and change physical structure and a liquid crystal cell of can switch homeotropically to homogeneously planar and thus one Can trigger command surface effect.  

The advantage of the inventive solution, especially for Sunglasses are missing or not mandatory Presence of any power supply and electronics. In addition, only an extremely thin layer becomes photochemical changed while the volume of the liquid crystal cell did not is photochemically exposed.

When choosing suitable molecules for building the Orientation layers for the invention The transparent body is in particular its long-term stability, Switching speed and the wavelength dependence of the cis To consider trans isomerization.

The change in transmission in the invention Transparent bodies is less than 40% (but 25-30% are sure) with a maximum transmission of about 75% and fewer.

As photochromic molecules for use as a "command surface layer ", molecules are considered which, when irradiated, have a cis- Trans photoisomerization show that with a change in Geometry of the molecule is connected. The most popular Examples are the stilbene derivatives and the azobenzene derivatives.

Stilbene derivative

R1 benzene ring with carbon atom on (via double bond) Carbon atom on benzene ring R2.

Azobenzene derivative

R1 benzene ring with nitrogen atom on (via double bond) Nitrogen atom on benzene ring R2.

The coupling layer between the surface and the photochromic function is typically integrated into the whole molecule (the R ₁ in the above nomenclature). One therefore does not necessarily speak of individual layers, but of "functions" that are integrated in a molecule. In general, the molecules have the following schematic structure:
Head group, photochromic group, spacer, anchor group.

The anchor group connects the molecule with the Substrate surface. The spacer separates the photochromic group from the surface (since this group needs space to hold the To be able to carry out isomerization). The head group is that free end of the molecule. This serves the photochromic Create space and connect to the groups Ensure liquid crystals in the cell.

The simplest type of head group are alkyl chains different lengths, n. The spacer is in the simplest case also an alkyl chain of length m. The chemistry of the system often requires an alkoxy group as the head group. The Anchor group can chemically surface (typically Glass, quartz, silica). This happens about Silane compounds:  

Table of azobenzene carboxylic acids

To do this, the substrate may need to be pretreated with an appropriate reagent (e.g. glass / quartz surface):

Physical interactions can also occur that bind the molecule to the surface (physisorption). Examples include molecules that can be applied to surfaces as monomolecular films using the Langmuir-Blodgett method. Another possibility is to design the anchor group as a polymer. Then several (spacer photochromic head group) systems are bound to a polymer main chain. This main chain then acts as an anchor group. The connection to the surface takes place via physical effects (example: ionic / electrostatic or Van der Waals interaction). Some representatives of such polymers can also be applied using the Langmuir-Blodgett method. Examples include:

the above azobenzene functionalized polyglutamates

• a) poly (5- (x- (4- (4-hexylphenylazo) phenoxy) ethyl) -L-glutamate, and
• b) Poly (5- (2- (4- (4-decyloxyphenylazo) phenoxy) ethyl) -L- Are glutamate.

The well-known azobenzene derivatives are based on one unidirectional, homeotropic initial orientation of the Orientation layer of the LC cell. You use LC Mixtures with (positive) dielectric anisotropy and pleochroic dyes or dye mixtures, which in the  LC mixture are soluble. Examples of the LC mixture is ZLI1840 from Merck and the dye G313 (2.5%) (manufacturer is z. B. the company Merck), with maximum absorption at 666 nm. In the off state (without exposure) this cell appears bright On state (with exposure) the cell appears green.

Other guest host liquid crystal cells are also possible The above combination is therefore only an example. Mainly by a different dye mixture can change the color impression will. This gives 2.5% of the dye M137 (max. Absorption at 637 nm) (manufacturer is e.g. Merck) in ZLI1840 (Manufacturer is e.g. Merck) a blue one Transmission color. Another combination is use the liquid crystal DON-103 (manufacturer is e.g. the company Rolic) in combination with the dye LCD-118 (manufacturer is e.g. B. the company Merck).

For the highest possible contrast you should use a polarizer use whose orientation is the unidirectional orientation is adapted to the orientation layer.

The switching times of the effect are in the minute range. By changing the molecular parameters, such as the Extension of the spacer or the reinforcement of the Interaction between liquid crystal and the photochromic Unit (polar group in the center of the liquid crystal Molecule), the switching time can be shortened.

Claims (9)

1. see-through body with two outer transparent closure, which enclose a volume arranged between them with liquid crystals and embedded dyes (guest-host cell), and in each case an orientation layer of organic molecules or polymers on the inner surfaces of the closure body, characterized that the orientation layers are composed of photochromic molecules or polymers, which switch the volume of the liquid crystals according to the command surface effect (in particular with cis-trans isomerization), and that dye molecules are dissolved in the liquid crystals, which affect the sunlight spectrum and the visual spectral sensitivity of the human eye or the spectral sensitivity of a device behind the see-through bodies. 2. see-through body according to claim 1, characterized in that that between the transparent electrode and the Orientation layer arranged an insulation layer is. 3. see-through body according to claim 1 or 2, characterized in that the insulation layer is composed of SiO ₂ . 4. see-through body according to one of claims 1-3, characterized characterized in that the orientation layer molecules (or polymers) containing azobenzene or stilbene is constructed. 5. see-through body according to one of claims 1-4, characterized characterized in that the liquid crystals are nematic Are liquid crystals.   6. see-through body according to one of claims 1-5, characterized characterized in that the end body made of plastic are. 7. see-through body according to one of claims 1-5, characterized characterized in that the end bodies are made of glass. 8. see-through body according to one of claims 1-7, characterized characterized that below the orientation layer a coupling layer with anchor groups is attached. 9. see-through body according to one of claims 1-8, characterized characterized in that the see-through body is a lens for is sunglasses.