DE102009035363A1 - Piezochromic material, piezochromic composite and piezochromic sensor - Google Patents

Abstract

The present invention relates to a piezochromic material consisting essentially of a matrix of a polymer or copolymer in which a liquid crystal and a chirally optically active substance are distributed. Likewise, the present invention relates to a piezochromic composite material in which a layer of the aforementioned piezochromic material is embedded between two polymer films. The piezochromic material or the composite material are used primarily in the field of sensors.

Description

The The present invention relates to a piezochromic material which, in the Substantially consists of a matrix of a polymer or copolymer, wherein a liquid crystal and a chirally optically active substance distributed. Likewise, the present invention relates to a piezochromic composite, in which a layer of the aforementioned piezochromic Material embedded between two polymer films. The piezochrome Material or the composite material find especially in the sensor area Application.

Of the Demand for geometrically deformable sensors for the visualization of low pressure changes in the real life area, d. H. below 50 bar, is enormous and continues to increase steadily. Piezochrome effects based on changeable grid structures, in inorganic crystals or absorption effects in organic Systems offer so far no solution approach.

Piezochromes by modification changes in inorganic crystals, such as. B. with LiF or NaCl monocrystals are known phenomena for decades. The required high pressure changes open up no perspective for use as pressure sensors in everyday areas of life. Thus, for the transition of the green a-modification of CuMoO ₄ into the red γ-modification, a pressure of 2.5 kbar is required or for palladium complexes 1.4 to 6.5 GPa. [ Rodriguez, Physical Review B, 61 (2000) respectively. Tagaki, Platinium Metals Rev. 48 (2004) .]

Hints for switching the wavelength by pressure change in organic polymer structures have not yet been systematically described in the literature. [They have been observed in a few systems, but have not been exploited in any commercial way "[ Bamfield, Chromic Phenomena, The Royal Soc. of Chem. 2001) ]. For poly (3-dodecylthiophene), a bathochromic shift is observed at a pressure change of 8 kbar. In [ Sato, Reactive and Functional Polymers, 68, (2008) ] is given a required pressure change of 10.71 GPa for a likewise bathochromic shift from 605 nm to 672 nm (Δλ = 67 nm) in poly (3- (1-dodecylnyl) thiophene-2,5-diyl). The piezochromic effect is based on an absorption effect. Currently, new piezochromic materials based on oligo (p-phenylene-vinylene) are discussed. To trigger the optical effect, a pressure of 1500 psi (103 bar) is needed [ Kunzelmann, Advanced Materials, 20 (2008) ]. The required pressure changes of 100 bar and orders of magnitude above are also outside of this practice-relevant area for the organic systems.

In the patent literature, which claim piezochromic materials for a wide variety of applications, as a rule no numerical information is given on the necessary pressure for the optical signal. It is generally described a change in color when force. In WO / 2003/089227 a roller with thermochromic and piezochromic properties is discussed. Here, components with piezochromic properties are doped in a polymer matrix. This consists z. As polyurethane, silicone, natural rubber or blends of PVC. Among others, liquid crystals such as biphenyls or cholesterol derivatives are used as thermochromic components and xanthenes, diflavines, dianthrones, phthalocyanine-cobalt complexes or spiropyranes are used as the piezo-chromic components. Pressures between 1450 psi (99.9 bar) and 15000 psi (1034 bar) should be detectable. Other patents relating to the use of piezochromic materials relate to use as a security feature in banknotes such as WO 2005/092995 A1 respectively. FR 2698390 A1 or as an optical signal transmitter in a toothbrush as in US 6,389,636 B1 ,

In WO / 2005/092995 For example, the piezochromic system consists of an ionochromic substance and a developer, forming an electron-donor system. The piezochrome material can be applied as a color print on banknotes and serves accordingly as a security feature. As ionochromic substances pH-sensitive dyes or leuco dyes are used. Specifically mentioned are substances such as phthalide derivatives, derivatives of imidazole, pyrrole, bianthrone, xanthylidenanthrone, dixanthylene or helianthrone. In US 5,320,784 are favored piezochrome substances based on hydroxycarboxylic acids or indolinospirobenzo-thiopyran derivatives.

In FR 2698390 A1 will be like in WO / 2005/092995 also described a piezochromic material as a security feature for banknotes. The films with a layer thickness of 0.8-2 mm consist of a polymer matrix and a liquid crystal. Suitable matrix components are polyester, cellulose, polyurethane, polyacrylic acid or butadiene-styrene copolymer. The liquid crystal has a cholesterol structure. Numerical values for the pressure are not specified. The same applies to US 6,398,636 ; here too, no numerical values are given for the pressure required to trigger the optical effect. A toothbrush signal indicates when the user is applying excessive force. The piezochromic materials used are cholesteric liquid crystals from Hallcrest LC Technology.

It can be concluded that the known inorganic but also organic Materials can not be used as piezochromic sensors under realistic conditions under pressure changes well below 50 bar. The previously known piezochromic materials are therefore not usable as a security feature in banknotes or in medical technology as a visual pressure sensor for prostheses, dialysis machines, decubitus prophylaxis or compression bandages. The same applies to the simplest visual color sensors which are intended to detect pressure or mechanical deformation (destruction) in packaging materials or in smart labels (Security-ID).

task It is therefore a piezochromic material of the present invention to develop, which at low pressure - below 50 bar - a clear to the human eye provides optical signal and which is mechanically deformable, thus an application in the o. g. Areas is possible.

These The object is with respect to the piezochromic material Features of claim 1, with respect to the piezochromic Composite material with the features of claim 10 and concerning the piezochromic sensor with the features of Patent claim 16 solved. In claim 17 are Uses of both the piezochromic material and the piezochromic composite. The respective dependent claims are advantageous Further developments.

According to the invention thus providing a piezochromic material that is a matrix of at least one polymer and / or copolymer, wherein at least a liquid crystal and at least one chirally optically distributed active substance.

According to the invention all known liquid crystals are used. Under a chirally optically active substance according to the invention is a component understood with chiral (helical) properties. The resulting continuously twisted optical medium acts as a one-dimensional photonic crystal.

In a preferred embodiment, the at least one Liquid crystal thereby selected from the group consisting of N- (p-ethoxybenzylidene) -p-n-butylaniline, N- (p-methoxybenzylidene) -p-n-butylaniline, 4-n-alkylbenzoic acid (4-alkylphenyl ester), cholesteryl benzoate, Cholesterol, tolane, alkanoic acids, stilbene, azobenzene, 4-phenylcinnamic acid, p-terphenyl, 1,2-bisbenzoethylene and / or mixtures thereof.

For the at least one chirally optically active substance are in particular Compounds selected from the group consisting of 4- (4-hexyloxybenzoyloxy) benzoate, Cholesteryl derivatives and / or mixtures thereof in question.

preferred Polymers or copolymers are poly (meth) acrylates and / or Copoly (meth) acrylates. The aforementioned copoly (meth) acrylates are preferably from at least one monofunctional monomer and / or at least built a multi-functional crosslinker.

Advantageous is the monomer selected from the group consisting from benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, methoxyethyl (meth) acrylate, Octadecyl (meth) acrylate and / or mixtures thereof.

preferred Crosslinkers, on the other hand, are selected from the group of 1,4-butanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, Bisphenol A-glycerolate (1-glycerol) phenol diacrylate and / or mixtures thereof.

advantageous Material properties are obtained when the weight ratio between crosslinker and monomer between 0.01 and 0.8, preferably between 0.1 and 0.6, more preferably between 0.2 and 0.4.

In terms of of the piezochromic material, it is preferred if the weight fraction of the liquid crystal, based on the polymer matrix until at 90% by weight, preferably between 15 and 60% by weight, more preferably between 25 and 32 wt .-% is. The content of the optical active substance, based on the matrix is thereby preferably up to 10% by weight, preferably between 0.1 and 2.5% by weight, especially preferably between 0.15 and 0.55% by weight.

In a further advantageous embodiment is the piezochrome material in the form of an elastic and highly ordered System is present, which preferably has a helical structure.

The Draws invention piezochrome material more preferably characterized in that one for the human Eye perceptible piezochromic color change on pressure changes less than 100 bar, preferably less than 50, particularly preferably less 10 bar occurs.

According to the invention, a piezochromic composite material is likewise provided which comprises a layer of the piezochromic material according to any one of the preceding claims, wherein on at least one side, preferably on both sides of the Layer of the piezochromic material is applied to a polymer film, which is preferably formed of polyolefins, polyesters, polyvinyl chloride and / or polyamides.

The Piezochrome material preferably has a composite material Layer thickness of the piezochromic material between 5 microns to 1 mm, more preferably between 5 microns to 100 microns on.

preferred Layer thicknesses of the polymer film used lie between 5 μm and 100 μm, preferably between 10 μm and 30 μm.

In a further advantageous embodiment, the Polymer film at least on the side, with the piezochromic material is contacted, one for liquid crystals suitable orientation layer.

This can also be monomolecular. This is a mature technology used for decades in the manufacture of LCDs. This is state of the art, US 4,278,326 ; US 4,472,028 ; DD 22 10 24 ; DE 2 635 630 ; DE 2 406 350 or US 4,842,375 , For the specific design possibilities of the orientation layer, reference is therefore made to the aforementioned publications. Polyamide, silanes and MSA copolymers have been the mainstays of such orientation layers in the past 20 years. The polymer layer is applied by a simple dipping method; then the solvent evaporates. An additional rubbing of the coated films in the same direction as the dipping process can be done optionally. The production of LC orientation layers by oblique evaporation in vacuo z. B. with SiO or SiO ₂ is no longer practiced today. The orientation layer stabilizes the supramolecular helical structure during the polymerization; it should be applied to at least one of the two polymer layers. The formation of a stable lattice structure, which is achieved by the crosslinking between the monomers and crosslinkers in the system, is a prerequisite for long-term stability and high switching numbers between the different pressure states. After the light-initiated crosslinking, the polymer film with its orientation layer is no longer absolutely necessary for the mode of operation. It can, if that is technologically advantageous, be removed. This may be the case if the layer thickness is to be further reduced or the adhesiveness to an adjacent material verified.

• a) eine Mischung aus dem mindestens einen Flüssigkristall und der mindestens einen chiral optisch aktiven Substanz mit
• b) mindestens einem monofuntktionalen (Meth)acrylat-Monomer, mindestens einem mehrfachfunktionalen (Meth)acrylat-Vernetzer und/oder Mischungen hieraus sowie
• c) mindestens einem Initiator

vermischt und durch Beaufschlagung mit Temperatur und/oder Licht und/oder durch chemische Initiierung polymerisiert wird.According to the invention, there is also provided a method for producing a previously described piezochromic material, in which

• a) a mixture of the at least one liquid crystal and the at least one chirally optically active substance
• b) at least one monofuntional (meth) acrylate monomer, at least one multifunctional (meth) acrylate crosslinker and / or mixtures thereof and
• c) at least one initiator

is mixed and polymerized by exposure to temperature and / or light and / or by chemical initiation.

The piezochrome composite system can be easily and well reproduced produce. As a rule, the mixture is first of all Liquid crystal and optically active substance produced, which already leads to the formation of a helical structure, which can be well characterized in polarized light. To this ordered system, the addition of the monomer and the Crosslinking agent. The addition can be done in succession or as a mixture of monomer and crosslinker. In this case is on one to pay attention to unwanted, premature polymerization, on the other hand but can also be advantageously already an order between form two components. The initiator is usually called last component added. Finally, the composite material between two polymer films in the desired layer thickness polymerized with light. As polymer films are preferably polyolefins (PE and PP, also the cyclic form Zeonor), polyester, polyvinyl chloride or polyamide used.

at the process according to the invention for the preparation of the above-described piezochromic composite is in Connection to the mixing steps a) to c) of the method described above the resulting mixture layered on a polymer film applied, preferably introduced between two polymer films and following exposure to temperature and / or light and / or polymerized by chemical initiation.

Further According to the invention, a piezochromic sensor is provided, the above-mentioned piezochromic material or a piezochromic composite material includes.

use find the piezochromic materials and / or the piezochromic composites in particular as a security feature in banknotes; as a pressure sensor, in particular in medical technology; as part of an optical, electrical, opto-electric piezochromic and / or chromogenic module.

The present invention will be explained in more detail with reference to the following information and the accompanying examples, without the invention to the specifically mentioned substances or parameters to be limit.

• – Monomer: Benzylmethacrylat (BzMA, Aldrich), 2-Ethylhexylacrylat (EHA, Aldrich), 2-Methoxyethylacrylat (MEA, Polyscience), Octadecylacrylat (ODA, Aldrich)
• – Vernetzer: 1,4-Butandiol-diaccrylat (BDA, Aldrich), Polyethylenglycol-diacrylat (PEG-DA, M700, Aldrich), 1,10 Decandiol-diacrylat (DDA, Aldrich)
• – Optisch aktive Substanz: 4-(4-Hexyloxybenzoyloxy)benzoat (S811, Merck), Cholesterylderivat (Aldrich)
• – Photoinitiator: Genocure LTM (Rahn), Daracure, Irgacure (Ciba), Lucerin (BASF)
• – Flüssigkristall: BL 037 (Merck), E5 (BDH): beides Mischungen von Alkyl-cyanobiphenylderivaten und Alkoxy-cyanobiphenylderivaten.

In the following preparation examples are preferably used as

• Monomer: benzyl methacrylate (BzMA, Aldrich), 2-ethylhexyl acrylate (EHA, Aldrich), 2-methoxyethyl acrylate (MEA, Polyscience), octadecyl acrylate (ODA, Aldrich)
• Crosslinkers: 1,4-butanediol diaccylate (BDA, Aldrich), polyethylene glycol diacrylate (PEG-DA, M700, Aldrich), 1,10-decanediol diacrylate (DDA, Aldrich)
• - Optically active substance: 4- (4-hexyloxybenzoyloxy) benzoate (S811, Merck), cholesteryl derivative (Aldrich)
• Photoinitiator: Genocure LTM (Rahn), Daracure, Irgacure (Ciba), Lucerin (BASF)
• - Liquid crystal: BL 037 (Merck), E5 (BDH): both mixtures of alkyl-cyanobiphenyl derivatives and alkoxy-cyanobiphenylderivaten.

The Of course, functionality is not on the here mentioned - commercial - substances limited. For the expert is immediate and easy to recognize that a variety of other monomers, crosslinkers, initiators (here also thermal chain starter), optically active substances or Liquid crystals can be used with analogous structural units can. Monomers, crosslinkers, initiators and optically active Of course, substances can also be used as mixtures be used. Instead of liquid crystal mixtures like On the other hand, BL 037 or E5 can also be individual substances such as N- (p-ethoxybenzylidene) -p-n-butylaniline (EBBA, Riedel-De Haen) or N- (p-methoxy-benzylidene) -p-n-butylaniline (MBBA, Riedel-De Haen) or derivatives of 4-n-alkylbenzoic acid (4-alkyl-phenylester) n, Benzoic acid cholesteryl ester, cholesterol, tolane, alkanoic acids, Stilbene, azobenzene, 4-phenylcinnamic acid, p-terphenyl, or For example, 1,2-bis-benzoyläthen.

The Parts by weight of the initiator and the optically active substance in the composite system are preferably below 10%. At this point it is noted that for the operation of the piezochromic Materials the molecular ratio of the individual substances is important to each other. The crosslinker is preferably with up to 20% available; Monomer and liquid crystal preferably each with up to 90%.

Of the piezochrome effect is visible at a pressure already below 50 bar. The composite material consists of at least one Monomer, a crosslinker, a photoinitiator, a liquid crystal and an optically active substance. It is explicitly pointed out that the resulting macroscopic properties are not derived linearly from the respective individual materials used. The newly formed supramolecular elastic system has independent physicochemical properties. Of particular advantage proves a helical structure.

The Switching speed between the different colors depending the pressure change is preferably in the second range. Above all, it can be controlled by the proportion of the crosslinker in the system. At high crosslinker content, the reverse reaction also in the minutes range or even above it.

piezo Chrome Leave layers between 5 μm and 100 μm thick to manufacture as shown above. If necessary can the layer thickness also be larger, but what is not required for the piezochromic effect.

Extreme Thin piezochromic layers / films can be produced in this way are and are suitable for use preferably in safety technology, medical technology and pressure sensors. Of the In addition, piezochrome film can be used as Functional component in any electrical, optical, electro-optical piezoelectric or chromogenic modules. The stable helical Structure embedded in an elastomeric matrix also allows one sustainable deformability of the layers / foils without loss of piezochromic effect.

example 1

component A: To the liquid crystal mixture E5 (mixture consisting from four components Alkylcyanobiphenylderivaten and a component Alkoxycyanobiphenyl derivative) becomes the optically active substance S-811 mixed with a weight of 22%. The mixture is over the clearing point of the E5 component is heated to 58 ° C and then cooled again at room temperature.

component B: 34% by weight DDA is doped to the monomer BzMA. The Mixture is heated to 60 ° C for 25 min.

The Mixtures A and B are in a ratio of 1: 2.4 mixed at a temperature between 50 ° C and 55 ° C. Finally, 0.2 percent by weight of polymerization initiator Genocure LTM added. The piezochrome material comes with a Layer thickness of 25 microns between two each 15 microns thick polypropylene films coated with polyamide (smaller 1 μm) and polymerized for 15 min under UV light.

As a result, a red-reflective film is obtained, which is easily movable and flexible and, when the pressure increases by 0.4 bar, switches to a film which reflects green to the eye. Will the pressure again increased by 0.7 bar, the color is blue. The process is reversible. The circuit takes less than a second. Such a film can be incorporated as a security feature in banknotes.

Example 2

component A: The liquid crystal EBBA becomes the optically active Substance Cholesteryloleylcarbonat doped with 27 weight percent. The mix is over the clearing point of EBBA heated to 52 ° C.

component B: To the monomer ODA, 28% by weight of crosslinker PEG-DA, M70 doped, with the mixture being heated to 55 ° C.

The Mixtures A and B are mixed in the ratio 1: 1.9 at a temperature between 45 ° C and 50 ° C. When Polymerization initiator is used Lucerin (BASF) at 0.45. The piezochrome material is made with a layer thickness of 30 microns mounted between each two 12 μm thick Zeonorfolien. Both Zeonor foils are made with a maleic anhydride-styrene copolymer Orientation layer (less than 1 micron) provided. The system is polymerized for 20 minutes in UV light; then leaves remove the Zeonor foil easily.

in the As a result, a 30 μm thick piezochromic layer is obtained. At a pressure increase of 0.8 bar it changes their color from red to blue in less than a second.

Example 3

component A: To a liquid crystal mixture consisting of EBBA and MBBA in the ratio 3: 1 becomes the optically active substance S-811 (4 - [[4- (hexyloxy) benzoyl] oxy] benzoic acid 2-octyl ester) doped with 30 weight percent, the temperature above 50 ° C is and the duration of at least 8 min. is.

component B: To the monomer MEA 22 weight percent of a crosslinker mixture consisting from BDA: DDA mixed in a ratio of 1: 2.5. The temperature in this case is between 50 ° C and 55 ° C. Daracur 0.4% by weight is used as a photoinitiator for the subsequent polymerization used. The piezochrome Material is interspersed with a layer thickness of 50 μm mounted two 20 micron thick polyethylene films, the previously treated with a lecithin solution (2.5%). The lecithin-coated PE films were added rubbed in the direction of the dipping process.

in the The result is a 90 μm thick piezochromic film. At a pressure of 8 bar changes visibly for the human eye turns the color from red to green. The circuit takes less than a second. After the pressure has dropped, this relaxes System in less than a minute in the initial state.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2003/089227 [0005]
• WO 2005/092995 A1 [0005]
• FR 2698390 A1 [0005, 0007]
• - US 6389636 B1 [0005]
• WO 2005/092995 [0006, 0007]
• - US 5320784 [0006]
• US 6398636 [0007]
• - US 4278326 [0026]
• US 4472028 [0026]
• - DD 221024 [0026]
• DE 2635630 [0026]
• - DE 2406350 [0026]
• US 4842375 [0026]

Cited non-patent literature

• Rodriguez, Physical Review B, 61 (2000) [0003]
• - Tagaki, Platinium Metals Rev. 48 (2004) [0003]
• Bamfield, Chromic Phenomena, The Royal Soc. of Chem. 2001) [0004]
• Sato, Reactive and Functional Polymers, 68, (2008) [0004]
• Kunzelmann, Advanced Materials, 20 (2008) [0004]

Claims (17)

Piezo-chromic material comprising a matrix of at least one polymer and / or copolymer, and at least a liquid crystal and at least one chirally optically active substance distributed in the matrix. Material according to claim 1, characterized that the at least one liquid crystal is selected is selected from the group consisting of N- (p-ethoxybenzylidene) -p-n-butylaniline, N- (p-methoxybenzylidene) -p-n-butylaniline, 4-n-alkylbenzoic acid (4-alkylphenyl ester), Benzoic acid cholesteryl ester, cholesterol, tolane, alkanoic acids, Stilbene, azobenzene, 4-phenylcinnamic acid, p-terphenyl, 1,2-bisbenzoethylene and / or mixtures thereof. Material according to one of the preceding claims, characterized in that the at least one chirally optically active substance is selected from the group consisting from 4- (4-hexyloxybenzoyloxy) benzoate, cholesteryl derivatives and / or Mixtures of these. Material according to one of the preceding claims, characterized in that the polymer and / or copolymer a Poly (meth) acrylate or a copoly (meth) acrylate, which is preferred from at least one monofunctional monomer and / or at least a multi-functional crosslinker is constructed. Material according to the preceding claim, characterized that a) the monomer is selected from the group consisting of benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, methoxyethyl (meth) acrylate, Octadecyl (meth) acrylate and / or mixtures thereof and / or b) the crosslinker is selected from the group consisting of 1,4-butanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, bisphenol A-glycerolate (1-glycerol) phenol diacrylate and / or mixtures thereof. Material according to one of the two preceding claims, characterized in that the weight ratio between Crosslinker and monomer between 0.01 and 0.8, preferably between 0.1 and 0.6, more preferably between 0.2 and 0.4. Material according to one of the preceding claims, characterized in that the weight fraction a) the liquid crystal up to 90% by weight, preferably between 15 and 60% by weight, especially preferably between 25 and 32% by weight and / or b) the chiral optically active substance up to 10 wt .-%, preferably between 0.1 and 2.5% by weight, more preferably between 0.15 and 0.55% by weight is, in each case based on the matrix. Material according to one of the preceding claims, characterized in that the material in the form of an elastic and highly ordered system, which is preferably a helical structure having. Material according to one of the preceding claims, characterized in that one for the human eye Perceptible piezochromic color change with pressure changes less than 100 bar, preferably less than 10 bar occurs. Piezochrome composite comprising a layer of the piezochromic material according to one of the preceding claims, characterized in that on at least one side, preferred on both sides of the layer of the piezochromic material a polymer film is applied, which preferably consists of polyolefins, polyesters, polyvinyl chloride and / or polyamides is formed. Composite according to the preceding claim, characterized by a layer thickness of the piezochromic material between 5 microns to 1 mm, more preferably between 5 μm to 100 μm. Composite material according to one of the two preceding Claims, characterized in that the polymer film a layer thickness between 5 microns and 100 microns, preferably between 10 microns and 30 microns. Composite material according to one of claims 10 to 12, characterized in that the polymer film at least on the side facing the material one for liquid crystals having appropriate orientation layer. Process for producing a piezochromic material according to one of claims 1 to 9, in which a) one Mixture of the at least one liquid crystal and the at least one chirally optically active substance b) at least a monofuntional (meth) acrylate monomer, at least one multi-functional (meth) acrylate crosslinkers and / or mixtures from this as well c) at least one initiator mixed and by exposure to temperature and / or light and / or is polymerized by chemical initiation. Process for producing a piezochromic composite material according to one of the claims 10 to 13 in which, following the mixing steps a) to c) of the method according to the preceding claim, the resulting mixture is applied in layers to a polymer film, preferably introduced between two polymer films and subsequently by exposure to temperature and / or light and / or by chemical Initiation is polymerized. Piezochrome sensor, comprising a piezochromic Material according to one of claims 1 to 9 and / or a Piezochrome composite material according to one of the claims 10 to 13. Using a piezochromic material after a of claims 1 to 9 and / or a piezochromic composite material according to any one of claims 10 to 13 as a security feature in banknotes; as a pressure sensor, in particular in medical technology; as part of an optical, electrical, opto-electric piezochromic and / or chromogenic module.