Ferroelectric nematic liquid crystal gel

Abstract

An aspect of the invention relates to liquid crystal gels (liquid-crystalline gels) exhibiting a ferroelectric nematic liquid-crystalline phase over a substantial range of temperatures, preferably at ambient temperature. The gels are physical gels based on liquid crystal material. In addition, the present invention relates to electric and electronic elements which contain the ferroelectric liquid crystal gels.

Description

[0001] Ferroelectric nematic liquid crystal gel An aspect of the invention relates to liquid crystal gels (liquid-crystalline gels) exhibiting a ferroelectric nematic liquid-crystalline phase over a substantial range of temperatures, preferably at ambient temperature. In addition, the present invention relates to electric and electronic elements which contain the ferroelectric liquid crystal gels according to the invention. Energy harvesting is becoming more important in various situations, such as wearable devices. See Xu, C., Song, Y., Han, M. et al., Portable and wearable self-powered systems based on emerging energy harvesting technology, Microsyst Nanoeng 7, 25 (2021), (https: / / doi.org / 10.1038 / s41378-021-00248-z) for an overview of technologies. Further, see Mishra, S., Unnikrishnan, L., Nayak, S. K., Mohanty, S., Macromol. Mater. Eng.2019, 1800463, (https: / / doi.org / 10.1002 / mame.201800463) for an overview of current technologies using piezoelectric polymer composites in comparison to conventional solid state piezo-ceramics. Utilising the properties of some ferroelectric materials such as piezoelectricity is a recognized method to achieve energy harvesting and these properties can also be used for mechanical sensors and sound generation. Piezoelectricity is exhibited by some non-centrosymmetric crystal structures and poled polymers. However suitable materials are limited. Gels, which are materials consisting of a 3D-network of chains that trap a liquid phase to form a semi-solid, often elastic, structure, have been investigated for many systems including liquid crystals combined with organic gelators. A tutorial article on nematic gels can be found in Liquid- crystalline physical gels, T. Kato, Y. Hirai, S. Nakaso, M. Moriyama, Chem. Soc. Rev.2007, 36, 1857 (https: / / pubs.rsc.org / en / content / articlelanding / 2007 / cs / b612546h). As supported by Kato. et al. liquid-crystalline physical gels are obtained by the self-assembly of fibrous solid networks of gelators in liquid crystals. Liquid crystals are transformed into gels with chemical or physical 3D network structures. The LC chemical gels are prepared by polymerisation of LC or non-LC monomers in liquid crystals. Liquid-crystalline physical gels are obtained by the self-assembly of fibrous solid networks of gelators in liquid crystals. Typically these networks employ H-donor-acceptor bonds or other reversible molecule interactions between gelator molecules. In previous years, the areas of application for liquid crystal compounds have been considerably expanded to various types of display devices, electro-optical devices, electronic components, sensors, etc. For this rea- son, a number of different structures have been proposed, in particular in the area of nematic liquid crystals. The nematic liquid-crystal mixtures have to date found the broadest use in flat-panel display devices. They have been employed, in particular, in passive TN or STN matrix displays or sys- tems having a TFT active matrix, including the well-known TN, IPS, FFS and VA systems. Most of these devices employ the nematic liquid crystal phase, including all common LCD television sets, LCD desktop monitors and mobile LCD devices. Some alternative liquid-crystalline phases are known, like ferroelectric smectic phases or blue phases. However, a ferroelectric nematic phase (NF-LC phase) had been postulated by theory for decades only, without finding a suitable liquid-crystalline material with such property. Only recently, a few chemical structures have been reported to show ferroelectric nematic behaviour at certain temperatures. Firstly, Hiroya Nishikawa, Kazuya Shiroshita, Hiroki Higuchi, Yasushi Okumura, Yasuhiro Haseba, Shin-ichi Yamamoto, Koki Sago, and Hirotsugu Kikuchi, Adv. Mater. (2017), 29, 1702354, describe a compound of formula A to have a ferroelectric nematic behaviour at temperatures between about 45°C to 68°C. Further, Nerea Sebastián, Luka Cmok, Richard J. Mandle, María Rosario de la Fuente, Irena Drevenšek Olenik, Martin Čopič and Alenka Mertelj, Physical Review Letters (2020), 124, 037801, describe a compound of formula B with similar behaviour between about 120°C to 133°C. Further comparison of the two only available substances for NF-LC phases is presented by Xi Chen et al., PNAS (June 23, 2020), 117 (25) 14021- 14031. The high significance of the advent of the new NF-LC phase underlines O. D. Lavrentovich, ProcNatAcadSciUSA (2020), 117(26), 14629-14631. Very high values of the dielectric susceptibility of these substances and some structural variations thereof is reported in the publication Li et al., Sci. Adv.2021, 7. A further ferroelectric nematic substance of formula C is published by Atsutaka Manabe, Matthias Bremer, Martin Kraska (2021): Ferroelectric phase at and below room temperature, Liquid Crystals, 48, 1079-1086 (DOI 10.1080 / 02678292.2021.1921867), which is described to have a ferroelectric nematic liquid-crystalline phase (NF-LC phase) close to ambient temperature. Ambient temperature, also sometimes called room temperature, means in a narrower sense a temperature of 20°C here. Ferroelectric nematic mixtures for room temperature application have been disclosed in WO2022117552 A1. There is a need for piezoelectric materials that are easy to provide and which are easily formed into any desired shape. They should have a strong response to pressure or shape change. An object of the present invention is to provide new polar materials with a combination of physical and electric properties for fulfilling technical needs in applications like harvesting mechanical or thermal energy, sensors, piezoelectric devices, semi-solid forms of liquid crystals, actuators and other new applications of liquid crystals. In addition, it is an aim for the materials to be thermally and photochemically stable under the conditions prevailing in the areas of application, in particular at room temperature and 10 K, 20 K or more above and / or below. Short description of the invention Surprisingly, it has been found that a piezoelectric gel having the NF-LC phase can be made without losing the ferroelectric behaviour. The material is suitable for piezoelectric applications. In one aspect the invention relates to a novel liquid crystal gel that comprises a ferroelectric nematic liquid crystal and a suitable gelator with a molecular weight between 250 and 1000 g / mol. The gels according to the invention are sufficiently stable and colourless. In particular, they are distinguished by extraordinarily high dielectric constants and in particular by very high dielectric anisotropies (Δε), owing to which they are sensible to external electrical fields. In addition, the gels used according to the present invention have suitable working temperatures and high clearing points. The liquid crystal gel exhibits a ferroelectric nematic liquid-crystalline phase over a significant range of temperatures, including ambient temperature. The liquid crystal gels according to the invention exhibit outstanding dielectric properties. The ferroelectric nematic liquid crystal gel not only provides improved properties for energy harvesting and electromotoric devices but also has potential uses in other electric and electronic devices. Due to their outstanding properties the gels can perform in many new areas of technology and may have use for electro-optical purposes, for capacitors including supercapacitors, non-linear optic elements, mechanical sensors, sensors for electrical fields, memory devices and electro-mechanic devices, including electric generators (i. e. energy harvesting devices, microphone) and actuators (including e.g. loudspeaker). The materials may for example enable unconventional modes of energy harvesting from vibrational motion. The second aspect of the invention involves a piezoelectric element comprising the ferroelectric nematic liquid crystal gel described above. Specifically, the piezoelectric element includes a mechanical substrate that may impart mechanical stress to the gel or which may receive forces from the gel. This substrate is in contact with the ferroelectric liquid crystal gel, where the gel generates a charge in response to mechanical stress or exhibits a response to an applied electric field. The piezoelectric element can be used in a variety of applications, including in a mechanical sensor or an energy harvesting device. When it makes a response to an electric field it can be used as an actuator, for example as a linear motor or an active element of a (ultra-)sound generator. In summary, this invention provides a solution to the challenges faced by traditional energy harvesting devices and piezoelectric elements by utilizing the unique properties of ferroelectric nematic liquid crystal gels. It represents a significant advancement in the field of energy harvesting and mechanical sensor devices and has potential applications in a variety of electric and electronic devices. The high dielectric permeability enables outstanding physical performance. The high (relative) dielectric permittivity is also especially advantageous for dielectrics in capacitors, since it causes high capacitance on a specific electrode area. In addition, the gels have very low electric conductivity and are unique over conventional high-εrmaterials (e.g. barium titanates) due to their self-generating gel nature. The gel nature of the material discerns them from liquid and solid materials in an advantageous way. Once formed the gel is stable, but can at any time be reformed by a heating-cooling cycle, thus making it damage repairable. In comparison a conventional solid piezoelectric material is prone to cracking under thermal or mechanical stress which is irreversible and cannot be mended. The gel can be formed from the liquid state for coating substrates. The flexible nature allows to adopt its form to any substrate or surface after formation. A very close contact can therefore be formed to electrodes. In a preferred mode of the invention the gel is used to form a capacitor. The liquid crystal gel can in principle be also be used for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases DAP or ECB (electrically controlled birefringence), the IPS (in-plane switching) effect or the effect of dynamic scattering. Ferroelectric nematic liquid crystal gels show unique spontaneous polarization and piezoelectric behaviour, with values not dissimilar or even better than existing poled polymers (e.g. PVDF) or rigid brittle inorganic materials (e.g. zirconium titanate PZT). As all ferroelectric materials, they also show pyroelectricity. The combination of the NFphase with the physical gel network allows to transfer the NFphase into an anisotropic, ferroelectric soft solid. In comparison to the pure NFphase, the FLNC gel shows no flow and is mechanically stable, which allows for easier processing of the liquid ferroelectric LC material. Additionally, the gained elasticity enables reversible deformation and thus makes for a long-lasting mechanical energy harvester. The low elastic modulus of the NF-LC gel in comparison to typical ceramic (PZT) or polymeric (PVDF) ferroelectric materials leads for similar forces to a higher mechanical deformation and thus to a greater change in effective spontaneous polarization. Due to the inverse piezoelectric effect an applied electric field leads to deformation of the NF- LC gel and can as a result act as an electro-mechanical actuator (electrostriction). In comparison to existing pyro- and piezoelectric materials, one main advantage of NF-LC gels is their simple, adaptive and sustainable low-temperature processing via reversible gelation. This invention also includes the use of the gels for electric and electronic elements. Although gelators for liquid crystals have been previously described in other patents and publications, the combination of gelators with ferroelectric nematic liquid crystals has not yet been reported. In summary, the present invention discloses a novel and useful ferroelectric nematic liquid crystal gel and its potential uses in various electric and electronic devices. Repeating the heating and cooling cycle at any time refreshes the gel and resets the alignment. Application of force / movement of the electrodes compresses the gel leading to movement of charge and hence energy harvesting. In a preferred embodiment the ferroelectric gel is aligned by external means (electric field, alignment layers) while it is made, preferably under slow temperature change, in order to impose a directional order in the gel network and / or in the director of the LC phase. The gel with a poled and uniform alignment of the gel fibrous structures or the liquid crystal director has improved poling (asymmetry of alignment relative to the elecrodes). The resulting piezoelectric effect can be thereby improved further. A piezoelectric element is preferred wherein the liquid crystal gel is aligned with a preferred direction of the orientation of at least one of its components from the group of gelator and ferroelectric nematic liquid crystal, preferably the gelator. The gel in the piezoelectric element more preferably comprises a gelator having a fibrous structures and an orientation of said fibrous structures in a preferred direction relative to the electrodes. Short description of the drawing(s): Fig.1 shows a graph where the effective spontaneous electric polarization PS,eff is measured for gels from Base Mixture 1 gelled with different concentrations of the gelator 1 (12-HOA) and in comparison to the non- gelled reference sample over a range of temperature of 20 to 80 °C. The T / Psgraph (measured at 70 Hz) and a voltage of 200 V / mm shows the values of the effective spontaneous polarization Ps,eff upon cooling. The value of Ps,eff has a maximum (plateau shape) for the liquid crystal gel in the same order of magnitude as for the non-gelled reference liquid crystal material. Fig.2 shows the current response of the Base Mixture 1 gelled with 0.5 wt% 12-HOA upon application and release of slight pressure. The isotropic sol mixture of both components was filled in a 1.6 µm thick LC testing cell with ITO coating on both sides covered with Nylon insulating layers. Upon pressing lightly with an insulated glass rod on top of the cell an effective change of spontaneous polarization of around 35 nC / cm² is recorded. An inverted current response of similar size and shape is recorded upon release of the pressure. Detailed description of the invention The invention thus in one main aspect relates to a liquid crystal gel comprising 91% by weight or more of a ferroelectric nematic liquid crystal mixture and 0.1 to 9 % by weight of a gelator having a molecular weight between 250 and 1000 g / mol (based on 100 % of the mixture in total). Preferably the gel according to the invention comprises 0.15 or more, more preferably 0.2 % by weight or more of a gelator (plural included). The gel contains preferably 7 % by weight of the gelator or less, more preferably 5% or less. Most preferably the gel is used in an amount of 0.2 to 1.0 % by weight. The liquid crystal gel is preferably piezoelectric. Use for higher frequencies (e.g. above 102Hz, sound / ultrasound) may usually require higher amounts of gelator, preferably 0.5 to 5 % by weight. Suitable gelators used in the present invention, generally have a linking group capable of forming intermolecular hydrogen bonds in the molecule, like the partial groups -OH, -NHCO-,-NH- or -CO-, optionally aromatic groups like phenyl for pi-bonding, and preferably combinations of such groups. Preferably the liquid crystalline gel according to the invention comprises a gelator having at least one -OH or -NH- group and at least one structural element selected from -(CO)-, -(CO)O- or -(CO)NH- group, where the groups are capable of building intermolecular hydrogen bonds. Gelators preferably comprise any of the following partial formulae wherein RG1is an alky group with 1 to 18, preferably 2 to 5 carbon atoms, and n is a number between 5 and 15, preferably between 7 and 12. The dotted line indicates the single bond connecting the fragment with the remaining parts of a single gelator molecule. The gels according to the invention are preferably liquid crystalline physical gels. Liquid crystal physical gels are by definition gelled with non-polymer additives in contrast to liquid crystal chemical gels. In the following the ferroelectric nematic LC mixture used as basis for the gels is described in more detail. Said ferroelectric nematic LC material preferably comprises at least two compounds with a molecular structure of formula I,

[0002] R1is an alkyl radical having 1 to 12 C atoms, preferably 1 to 8, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, X is CN, F, CF3, -OCF3, -NCS, Cl, preferably CN or F, L1is H or CH3, Z1is CF2O or -(CO)-O- or a single bond, preferably CF2O or -(CO)-O-, most preferably -(CO)-O-, and Z2is CF2O or -(CO)-O- or a single bond, preferably -(CO)-O- or a single bond. The ferroelectric medium for use in gels preferably comprises at least 30 % of compounds of formula I, more preferably 40 %, more preferably 50 % and most preferably 90%, 95% or 98 % or more by weight of compounds of formula I. More preferably the invention uses as the ferroelectric nematic liquid crystal mixture a mixture comprising 15 % by weight or more of one or more compounds of formula IA, 15 % by weight or more of one or more of compounds of formula IB, and 15%, preferably 20 % by weight or more of one or more compounds selected from formula IC-1 to IC-3 in which X1Bdenotes -CN or -NCS, preferably -CN, X1Cdenotes -CN, F, CF3, -OCF3, -NCS, SF5 or O-CF=CF2, preferably -CN or F, most preferably CN, Z1Aand Z1Bindependently of one another denote -(CO)-O- or -CF2-O- or a single bond, preferably -(CO)-O- or -CF2-O-, Z2Aand Z2Bindependently of one another denote a single bond, -(CO)-O- or -CF2-O-, preferably a single bond, Z1Cand Z2Cone of the both groups denotes -(CO)-O- or -CF2-O- and the other a single bond, preferably Z1Cis -(CO)-O- or -CF2-O-and Z2Cis a single bond, L1A, L1Band L1Cindependently of each other denote H or CH3, preferably H, L2Ais F or H, preferably F, L2Cis F or H, preferably F, A1Adenotes A1Bdenotes wherein L8Bdenotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3or CH2CH2CH2OCH3, A1Cindependently denotes A2Cdenotes preferably m, n 0, 1 or 2, where (m + n) is 2,

[0003] R1A, R1 Band R1 Cindependently of each another denote an alkyl radical having 1 to 12 C atoms, preferably 1 to 8, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2 groups in these radicals may in each case be replaced, independently of one another, by -C=C-, -CF2-O-,

[0004] -OCF2-, -CH=CH-

[0005] , -O-, -S-, -(CO)-O- or -O-(CO)- in such a way that O / S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, preferably R1A, R1 Band R1 Cindependently are a halogenated or unsubstituted alkyl radical having 1 to 10 C atoms, where, in addition, one or more CH2 groups in these radicals may be replaced by -O-, -(CO)-O- or -CH=CH- in such a way that O atoms are not linked directly.

[0006] The percentages are provided under the circumstance that the whole medium makes up 100% by weight of the medium.

[0007] The radicals R1A, R1 Band R1 Cin the respective formulae IA, IB and IC-1 to IC-3 and their respective sub-formulae preferably denote alkyl having 1 to 8 carbon atoms, alkoxy having 1 to 8 carbon atoms or alkenyl having 2 to 8 carbon atoms. These alkyl chains are preferably linear or they, preferably in case of R1 C, are branched by a single methyl or ethyl substituent, preferably in 2- or 3-position. R1A, R1 Band R1 Cparticularly preferably denote a straight-chain alkyl radical having 1 to 7 C atoms or an unbranched alkenyl radical having 2 to 8 C atoms, in particular unbranched alkyl having 1 to 5 C atoms. Alternative preferred radicals R1A, R1Band R1Care selected from cyclopentyl, 2-fluoroethyl, cyclopropylmethyl, cyclopentylmethyl, cyclopentylmethoxy, cyclobutylmethyl, 2-methylcyclopropyl, 2- methylcyclobutyl, 2-methylbutyl, 2-ethylpentyl and 2-alkyloxyethoxy. Compounds of the formula IA, IB and IC1 to IC-3 containing branched or substituted end groups R1A, R1Band R1C, respectively, may occasionally be of importance owing to better solubility in the liquid-crystalline base materials. The groups R1A, R1Band R1C, respectively, are preferably straight chain. The radicals R1A, R1Band R1C, respectively, particularly preferably selected from the moieties: CH3C2H5n-C3H7n-C4H9n-C5H11C2H5CH(CH3)CH2n-C6H13n-C7H15n-C3H7CH(C2H5)CH2n-C8H17c-C3H5c-C3H5CH2c-C4H7c-C5H7c-C5H9c-C5H9CH2CH2=CH CH3CH=CH CH2=CH(CH2)2CH3O C2H5O n-C3H7O n-C4H9O n-C5H11O CH3OCH2C2H5OCH2CH3OCH2CH2C2H5OCH2CH2CH3(CO)O C2H5(CO)O n-C3H7(CO)O n-C4H9(CO)O n-C5H11(CO)O H wherein the following abbreviations for the end groups are used: c-C3H5c-C3H5CH2c-C4H7c-C5H7 c-C5H9 and c-C5H9CH2 A preferred embodiment of the invention is directed to a ferroelectric nematic liquid-crystalline medium comprising one or more compounds selected from formulae IA, IB, IC-1, IC-2 and IC-3 as defined above. A further embodiment of the invention is directed to a ferroelectric nematic liquid-crystalline medium comprising one or more compounds of formula IC-1 as defined above, preferably in the percentages and preferred formulae as provided throughout this disclosure. A further embodiment of the invention is directed to a ferroelectric nematic liquid-crystalline medium comprising one or more compounds of formula IC-3 as defined above, preferably in the percentages and preferred formulae as provided throughout this disclosure. In a preferred embodiment, the media according to the present invention preferably comprise one, two, three or more compounds of formula IA-1 preferably selected from the group of formulae IA-1 to IA-3, preferably of formula IA-1: in which the parameters have the respective meanings given above and preferably Z1Adenotes -CF2-O-. In a preferred embodiment, the media according to the present invention preferably comprise one, two, three or more compounds of formula IB-1 and / or IB-2, preferably of formula IB-1,

[0008] R1Bdenotes an alkyl radical having 1 to 12 C atoms, preferably 1 to 7, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, -OCF2-, -CH=CH-, , -O-, -S-, -CO-O- or -O-CO- in such a way that O / S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, preferably R1Bis a halogenated or unsubstituted alkyl radical having 1 to 12 C atoms, where, in addition, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C- or -CH=CH-, A1Bdenotes preferably and Z1B, Z2Bindependently denote -(CO)-O- or -CF2-O-, preferably selected from the group of the following formulae, formulae IB-1- 1 to IB-2-3,: in which the parameters have the respective meanings given above and, in particular, in formula IB-1-1 to IB-1-3, Z1Bpreferably denotes -CF2-O- and, in particular, in formula IB-2-1 and IB-2-2, Z2Bdenotes preferably -CF2-O-; and, in particular, in formula IB-2-3, Z2Bdenotes preferably -C(O)O-. In a preferred embodiment, the media according to the present invention preferably comprise one, two, three or more compounds selected of formulae IC-1-1 to IC-3-5:

[0009] wherein A1Cis defined as above, preferably selected from the group of formulaeIC-1-1-1 to IC-3-5-2, more preferably selected from the group of formulae IC-1-1-1, IC-1-1-2, IC-1-1- 3, IC-1-1-4, IC-3-1-1 and IC-3-2-1:

[0010] in which the parameters have the respective meanings given above and preferably L1Cdenotes H, Z1Cdenotes -CF2-O- or -(CO)-O-, and X1Cdenotes -CN or F, preferably -CN. Particularly preferred compounds of the formula IC-1-1 to IC-1-4 used in the media are the compounds of the formulae below: wherein the parameters are defined as above, preferably L1Cis H. In a preferred embodiment of the present invention the media comprise up to 100 % of one or more compounds, preferably of three, four, five, six or more, compounds selected from group 1 of compounds, the group of compounds of formulae IA, IB and IC-1 / -2 / -3. In this embodiment the media preferably predominantly consist of, more preferably they essentially consist of, and most preferably, they virtually completely consist of these compounds. For the present invention, the following definitions apply in connection with the specification of the constituents of the compositions, unless indicated otherwise in individual cases: - "comprise": the concentration of the constituents in question in the com- position is preferably 5 % or more, particularly preferably 10 % or more, very particularly preferably 20 % or more, - "predominantly consist of": the concentration of the constituents in question in the composition is preferably 50 % or more, particularly preferably 55 % or more and very particularly preferably 60 % or more, - "essentially consist of": the concentration of the constituents in question in the composition is preferably 80 % or more, particularly preferably 90 % or more and very particularly preferably 95 % or more, and - "virtually completely consist of": the concentration of the constituents in question in the composition is preferably 98 % or more, particularly preferably 99 % or more and very particularly preferably 100.0 %. Preferably the media according to the present application fulfil one or more of the following conditions. They preferably comprise: - 20 % or more of compounds of formula IA, more preferably 25 %, more preferably 27 % or more and most preferably 32 % by weight or more of compounds of formula IA, - 17 % or more of compounds of formula IB, more preferably 20 % or more, more preferably 22 % or more and most preferably 25 % by weight or more of compounds of formula IB, - 40 % or more of compounds selected from formula IA and IB, more preferably 45 %, more preferably 50 % or more and most preferably 55 % by weight or more of compounds selected from formula IA and IB, i. e. the sum of compounds of formula IA and IB preferably is at least of the above values, - 40 % or more of compounds selected from the group of formula IB, IC- 1, IC-2 and IC-3, more preferably 50 %, more preferably 60 % or more and most preferably 70 % by weight or more, i. e. the sum of compounds of formula IB, IC-1, IC-2 and IC-3 preferably is at least of the above values, - 20% or more, preferably 25 % or more of compounds selected of formula IC-1, IC-2 and IC-3, more preferably 28 %, more preferably 32 % or more and most preferably 34 % by weight or more, - 40% or more, preferably 60 % or more of compounds selected of formula IC-1 more preferably 70 %, more preferably 80 % or more and most preferably 90 % by weight or more, - optionally 2 % or more of compounds of formula ID (ID-1, ID-2, ID-3, ID- 4), more preferably 5 %, more preferably 10 % or more and most preferably 15 % by weight or more of compounds of formula ID, - one, two, three or more, preferably three or more, compounds of the formula IA-1-1, preferably of formula DUUQU-n-F, most preferably selected from the group of the compounds DUUQU-2-F, DUUQU-3-F, DUUQU-4-F and DUUQU-5-F and DUUQU-6-F, - one, two, three or more, preferably three or more, compounds of the formula IB-1, preferably of formulae GUUQU-n-N and / or DUUQU-n-N, most preferably selected from the group of the compounds GUUQU-2- N, GUUQU-3-N, GUUQU-4-N, GUUQU-5-N, GUUQU-6-N, GUUQU-7- N, DUUQU-2-N, DUUQU-3-N, DUUQU-4-N, DUUQU-5-N and DUUQU- 6-N, - one, two, three or more compounds of the formula IA-1-3, preferably of formula GUUQU-n-F, more preferred selected from the group of the compounds GUUQU-3-F, GUUQU-4-F and GUUQU-5-F, - one, two, three or more compounds of the formula IB-1-3, preferably of formula DUUQU-n-N, more preferred selected from the group of the compounds DUUQU-3-N, DUUQU-4-N and DUUQU-5-N, - one, two, three or more compounds of the formula IC-1-1, preferably of formula MUZU-n-N or MUQU-n-N, more preferred selected from the group of the compounds MUZU-2-N, MUZU-3-N, MUZU-4-N and MUZU-5-N, - one, two, three or more compounds of the formula IC-3, preferably selected from the formulae MUU-n-N or UMU-n-N, more preferably selected from the group of the compounds MUU-3-N, MUU-4-N, MUU- 5-F, UMU-3-N, UMU-4-N and UMU-5-N, - one, two, three or more compounds of the formula IC-1-1, preferably selected from the formulae GUZU-n-N or GUQU-n-N, more preferably selected from the group of the compounds GUZU-3-N, GUZU-4-N, GUZU-5-F, GUQU-3-N, GUQU-4-N and GUQU-5-N, - one, two, three or more compounds of the group of formulae IC-1-1-3 and IC-1-1-4, preferably IC-1-1-3-1 and IC-1-1-4-1, preferably of formulae UUZU-n-N and / or UUQU-n-N, most preferably selected from the group of the compounds UUZU-2-N, UUZU-3-N, UUZU-4-N, UUZU- 5-N, UUZU-6-N, UUQU-2-N, UUQU-3-N, UUQU-4-N, UUQU-5-N and UUQU-6-N, - and / or one or more compounds selected from the group of compounds DUZGU-1- F, DUZGU-2-F, DUZGU-3-F, DUZGU-4-F, or DUZGU-5-F, wherein n is 1, 2, 3, 4, 5, 6 or 7. In another preferred embodiment of the present invention said compounds of formulae IA, IB and IC-1 / -2 / -3 are a first group of compounds, group 1, of compounds. In this embodiment the concentration of the compounds of this group 1 of compounds preferably is in the range from 70 % or more, preferably 80 % or more, more preferably 90 % or more to 100 % or less. In addition to the compounds of formulae IA, IB and IC-1 / -2 / -3 the media according to the invention optionally, preferably obligatory, comprise one, two, three or more compounds selected from formula ID-1 to ID-4

[0011] XDdenotes CN, F, CF3, -OCF3, NCS, SF5 or O-CF=CF2, preferably -CN, F, -CF3, -OCF3, -Cl or -NCS, most preferably F or CN, L1D, L2D, L3D, L4D, L5D, L6Dand L7D, independently denote F, H, alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably H, F, CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3or CH2CH2CH2OCH3, Z1DandZ2Dindependently of one another denote -(CO)-O-, -CF2-O-, a single bond, and preferably both -(CO)-O-, R1Ddenotes an alkyl radical having 1 to 12 C atoms, preferably 1 to 7, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, -OCF2-, -CH=CH-, , -O-, -S-, -(CO)-O- or -O-(CO)- in such a way that O / S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, preferably R1Dis a halogenated or unsubstituted alkyl radical having 1 to 12 C atoms, where, in addition, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C- or -CH=CH-, R2Ddenotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3or CH2CH2CH2OCH3, A1Ddenotes a single bond, wherein L8Ddenotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3or CH2CH2CH2OCH3, preferably it comprises one or more of formulae ID-1-1 to ID-2-1: wherein the variable groups R1Dand L8Dare defined as above. The media optionally comprise additionally one or more compounds selected from the following groups of compounds: Preferred are media comprising one or more compounds of groups 1 and 2. Additional ferroelectric substances and similar compounds with high dielectric permittivity for combination with the current substances are selected from e.g. the following structures: Corresponding starting materials can generally readily be prepared by the person skilled in the art by synthetic methods known from the literature or are commercially available. The reaction methods and reagents used are in principle known from the literature. Further reaction conditions are exemplified by the working examples. Further preferred process variants, not mentioned above, are revealed by the examples or the claims. In the present disclosure, the 2,5-disubstituted dioxane ring of the formula preferably denotes a 2,5-trans-configured dioxane ring, i.e., the substituents are preferably both in the equatorial position in the preferred chair conformation. The 2,5-disubstituted tetrahydropyran of the formula likewise preferably denotes a 2,5-trans-configured tetrahydropyran ring, i.e., the substituents are preferably both in the equatorial position in the preferred chair conformation. The liquid-crystalline medium used according to the invention has a broad temperature range of the ferroelectric nematic phase. It exhibits the ferroelectric nematic phase ranges at 20 ° and above and below (ambient temperature). It covers the technically most interesting range from at least 10 to 50°C and significantly beyond to lower and / or higher temperatures. So it is highly suitable for all kind of household or industry use, and with some limitations even outdoors. The medium exhibits a ferroelectric nematic phase at least over a temperature range of 20 Kelvin or more, more preferably over 30 K or more, and most preferably over a range of 40 K or more. The achievable combinations of temperature range of the ferroelectric nematic phase, clearing point, low-temperature stability (LTS), (relative) dielectric permittivity, dielectric anisotropy and optical anisotropy containing the compounds of formulae IA, IB and IC-1 / -2 / -3 are far superior to previous materials of such kind from the prior art. Previously only single compound materials were available with limited choice, which have a limited ferroelectric nematic phase range. In addition, the mixtures according to the invention generally exhibit very broad nematic phase ranges having clearing points of 65°C or more. The liquid crystal media according to the invention preferably exhibit a temperature range of the ferroelectric nematic phase which is 20 degrees wide or more, preferably it extends over a range of 40 degrees or more, more preferably of 60 degrees or more. Preferably the liquid crystal media according to the invention preferably exhibit the ferroelectric nematic phase from 10°C to 30°C, more preferably from 10°C to 40°C, more preferably from 10°C to 50°C, more preferably from 0°C to 50°C and, most preferably, from -10°C to 50°C. In another preferred embodiment the liquid crystal media according to the invention preferably exhibit the ferroelectric nematic phase from 10°C to 40°C, more preferably from 10°C to 50°C, more preferably from 10°C to 60°C and, most preferably, from 10°C to 70°C. Preferably the media according to the invention have values of εrof 700 or more, more preferably of 800 or more, more preferably 15000, even more preferably 30000 or more, and more preferably 35000 or more (at 20 °C and 10 Hz). These dielectric properties are achieved at temperatures at which the media are in the ferroelectric nematic phase. The dielectric characteristics may show a hysteresis behaviour, particularly over varying temperature, and in that case the values obtained at a certain temperature may depend on the history of the material, i.e. whether the material is being heated up or cooled down. This effect enables, amongst others, the operation of devices e.g. in bistable modes, which may be used beneficially in electro-optical devices, as e.g. known from ferroelectric smectic devices. The liquid crystal media according to the invention preferably comprise 2 to 40, particularly preferably 4 to 20, compounds as further constituents besides one or more compounds according to the invention. In particular, these media may comprise 1 to 25 components besides one or more compounds according to the invention. These further constituents are preferably selected from ferroelectric nematic or nematogenic (monotropic or isotropic) substances, The media according to the invention preferably comprise 1 % to 100 %, more preferably 10 % to 100 % and, particularly preferably, 50 % to 100%, of the compounds of formulae IA and / or IB and / or IC-1 / IC-2 / IC-3 preferably used according to the invention. The invention also relates to a method of preparation of a liquid-crystalline gel described herein, wherein 91% by weight or more of a ferroelectric nematic liquid crystal mixture and 0.1 to 9 % by weight of a gelator having a molecular weight between 250 and 1000 g / mol are combined and mixed with each other and with any other optional components or additives. The resulting mixture amounts to 100 % by weight. The liquid-crystal mixtures and gels according to the invention are prepared in a manner which is conventional per se. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, preferably at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing. It is furthermore possible to prepare the mixtures in other conventional manners, for example by using premixes, for example homologue mixtures, or using so-called “multi-bottle” systems. The liquid-crystal mixtures and gels may also comprise further additives known to the person skilled in the art and described in the literature. For example, 0 to 15%, preferably 0 to 10%, of pleochroic dyes, chiral dopants, stabilisers or nanoparticles can be added. The individual compounds added are employed in concentrations of 0.01 to 6%, preferably 0.1 to 3%. However, the concentration data of the other constituents of the liquid- crystal mixtures, i.e. the liquid-crystalline or mesogenic compounds, are given here without taking into account the concentration of these additives. The invention also relates to electro-optical displays (in particular TFT dis- plays having two plane-parallel outer plates, which, together with a frame, form a cell, integrated non-linear elements for switching individual pixels on the outer plates, and a ferroelectric nematic liquid-crystal gel having positive dielectric anisotropy and high specific resistance located in the cell). The expression "alkyl" encompasses unbranched and branched alkyl groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, in particular and preferably the unbranched groups methyl, ethyl, n-propyl, n- butyl, n-pentyl, n-hexyl and n-heptyl and further, alternatively, the groups n- butyl, n-pentyl, n-hexyl and n-heptyl substituted by one methyl, ethyl or propyl. Groups having 1-5 carbon atoms are generally preferred. The expression "alkenyl" encompasses unbranched and branched alkenyl groups having up to 12 carbon atoms, in particular the unbranched groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E- alkenyl, C5-C7-4-alkenyl, C6-C7-5-alkenyl and C7-6-alkenyl, in particular C2-C7-1E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4-alkenyl. Examples of pre- ferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E- hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having 2 to 5 carbon atoms are generally preferred. The expression "halogenated alkyl radical" preferably encompasses mono- or polyfluorinated and / or -chlorinated radicals. Perhalogenated radicals are included. Particular preference is given to fluorinated alkyl radicals, in par- ticular CF3, CH2CF3, CH2CHF2, CHF2, CH2F, CHFCF3and CF2CHFCF3. The expression "halogenated alkenyl radical" and related expressions are explained correspondingly. Above and below, percentage data denote per cent by weight. All temperature values indicated in the present application, such as, for example, the melting point T(C,N), the smectic (Sm) to nematic (N) phase transition T(S,N) and the clearing point T(N,I) are indicated in degrees Celsius (°C) and all temperature differences are correspondingly indicated in differential degrees (° or degrees), unless explicitly indicated otherwise. Furthermore, C = crystalline state, N = nematic phase, NF= ferroelectric nematic phase, Sm = smectic phase (more especially SmA, SmB, etc.), Tg = glass-transition temperature and I = isotropic phase. The data between these symbols represent the transition temperatures. ^n denotes optical anisotropy (589 nm, 20°C), ^ ^ the dielectric anisotropy (1 kHz, 20°C). The physical, physicochemical and electro-optical parameters are deter- mined by generally known methods, as described, inter alia, in the bro- chure "Merck Liquid Crystals - Licristal® - Physical Properties of Liquid Crystals - Description of the Measurement Methods", 1998, Merck KGaA, Darmstadt. The occurrence of the ferroelectric nematic phase of the materials is identified using differential scanning calorimetry (DSC), via observation of the textures under a polarising microscope equipped with a hot-stage for controlled cooling resp. heating and additionally confirmed by temperature dependent determination of the dielectric properties. Transition temperatures are predominantly determined by detection of the optical behaviour under a polarising microscope. The dielectric anisotropy ^ ^ of the individual substances is determined at 20°C and 1 kHz. To this end, 5 to 10 % by weight of the substance to be investigated are measured dissolved in the dielectrically positive mixture ZLI-4792 (Merck KGaA), and the measurement value is extrapolated to a concentration of 100%. The optical anisotropy ^n is determined at 20°C and a wavelength of 589.3 nm by linear extrapolation. The relative dielectric permittivity (εr) of the materials, especially in the ferroelectric nematic phase is directly determined by measuring the capacitance of at least one test cell containing the compound and having cell thickness of 250 µm with homeotropic and with homogeneous alignment, respectively. Temperature is controlled by a Novocontrol Novocool system set to temperature gradients of + / -1 K / min; + / -2 K / min; + / - 5 K / min; + / - 10 K / min applied to the sample cell. Capacitance is measured by a Novocontrol alpha-N analyzer at a frequency of 1 kHz or 10 Hz with a typical voltage < 50 mV down to 0.1 mV in order make sure to be below the threshold of the investigated compound. Measurements are performed both upon heating and upon cooling of the sample(s). In the present application, unless explicitly indicated otherwise, the plural form of a term denotes both the singular form and the plural form, and vice versa. Further combinations of the embodiments and variants of the inven- tion in accordance with the description also arise from the appended claims or from combinations of a plurality of these claims. Examples The present invention is described in detail by the following non-restrictive examples. Further combinations of the embodiments of the current invention and variants of the invention are also disclosed by the claims. The following examples explain the invention without intending to restrict it. The person skilled in the art will be able to glean from the examples working details that are not given in detail in the general description, generalise them in accordance with general expert knowledge and apply them to a specific problem. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. This applies both to the media as compositions with their constituents, which can be groups of compounds as well as individual compounds, and also to the groups of compounds with their respective constituents, the compounds. Only in relation to the concentration of an individual compound relative to the medium as a whole does the term “comprise” mean: the concentration of the compound or compounds in question is preferably 1% or more, particularly preferably 2% or more, very particularly preferably 4% or more. For the present invention, " ^" means less than or equal to, preferably less than, and " ^" means greater than or equal to, preferably greater than. For the present invention denote trans-1,4-cyclohexylene, denotes a mixture of both cis- and trans-1,4-cyclohexylene and denote 1,4-phenylene. For the present invention, the expression "dielectrically positive com- pounds" means compounds having a Δε of > 1.5, the expression "dielectri- cally neutral compounds" means compounds having -1.5 < Δ ε < 1.5 and the expression "dielectrically negative compounds” means compounds having Δ ε < -1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10% of the compounds in a liquid-crystalline host and determining the capacitance of the resultant mixture in each case in at least one test cell having a cell thickness of 20 µm with homeotropic and with homogeneous surface alignment at 1 kHz. The measurement voltage is typically 0.5 V to 1.0 V, but is always lower than the capacitive threshold of the respective liquid-crystal mixture (material) investigated. The host mixture used for dielectrically positive and dielectrically neutral compounds is ZLI-4792 and that used for dielectrically negative com- pounds is ZLI-2857, both from Merck KGaA, Germany. The values for the respective compounds to be investigated are obtained from the change in the dielectric constant of the host mixture after addition of the compound to be investigated and extrapolation to 100% of the compound employed. The compound to be investigated is dissolved in the host mixture in an amount of 10%. If the solubility of the substance is too low for this purpose, the concentration is halved in steps until the investigation can be carried out at the desired temperature. The liquid-crystal media according to the invention may, if necessary, also comprise further additives, such as, for example, stabilisers in the usual amounts. The amount of these additives employed is preferably in total 0 % or more to 10 % or less, based on the amount of the entire mixture, particularly preferably 0.1 % or more to 6 % or less. The concentration of the individual compounds employed is preferably 0.1 % or more to 3 % or less. The concentration of these and similar additives is generally not taken into account when specifying the concentrations and concentration ranges of the liquid-crystal compounds in the liquid-crystal media. For the purposes of the present invention, all concentrations are, unless explicitly noted otherwise, indicated in per cent by weight and relate to the corresponding mixture as a whole or mixture constituents, again a whole, unless explicitly indicated otherwise. In this context the term “the mixture” describes the liquid-crystalline medium. The following symbols are used, unless explicitly indicated otherwise: T(N,I) or clp. clearing point [°C], Dielectric properties at 1 kHz and preferably at 20°C or at the respective temperature specified: dielectric susceptibility perpendicular to the director, dielectric susceptibility parallel to the director, Δ ε dielectric anisotropy and especially for the screening data of single compounds. And, in particular for the data from the screening of the respective compounds in the nematic host mixture ZLI-4792,: neextraordinary refractive index measured at 20°C and 589 nm, noordinary refractive index measured at 20°C and 589 nm and Δnoptical anisotropy measured at 20°C and 589 nm. The following examples explain the present invention without limiting it. However, they show the person skilled in the art preferred mixture con- cepts with compounds preferably to be employed and the respective con- centrations thereof and combinations thereof with one another. In addition, the examples illustrate the properties and property combinations that are accessible. Definitions of structural elements by abbreviations for use in acronyms for chemical compounds: Table A: Ring elements Table B: Bridging units Table C: End groups in which n and m are each integers, and the three dots "…" are place- holders for other abbreviations from this table. Besides the compounds of formulae IA, IB and IC-1 / -2 / -3 the mixtures according to the invention preferably comprise one or more compounds of the compounds mentioned below. The following abbreviations are used: (n, m, k and l are, independently of one another, each an integer, pref- erably 1 to 9 preferably 1 to 7, k and l possibly may be also 0 and preferably are 0 to 4, more preferably 0 or 2 and most preferably 2, n preferably is 1, 2, 3, 4 or 5, in the combination “-nO-” it preferably is 1, 2, 3 or 4, preferably 2 or 4, m preferably is 1, 2, 3, 4 or 5, in the combination “- Om” it preferably is 1, 2, 3 or 4, more preferably 2 or 4. The combination “- lVm” preferably is “2V1”.) For the present invention and in the following examples, the structures of the liquid-crystal compounds are indicated by means of acronyms, with the transformation into chemical formulae taking place in accordance with Tables A to C above. All radicals CnH2n+1, CmH2m+1and ClH2l+1or CnH2n, CmH2mand ClH2lare straight-chain alkyl radicals or alkylene radicals, in each case having n, m and l C atoms respectively. Preferably n, m and l are independently of each other 1, 2, 3, 4, 5, 6, or 7. Table A shows the codes for the ring elements of the nuclei of the compound, Table B lists the bridging units, and Table C lists the meanings of the symbols for the left- and right-hand end groups of the molecules. The acronyms are composed of the codes for the ring elements with optional linking groups, followed by a first hyphen and the codes for the left-hand end group, and a second hyphen and the codes for the right-hand end group. Table D shows illustra- tive structures of compounds together with their respective abbreviations. Table D Exemplary, preferred compounds of formula IA Exemplary, preferred compounds of formula IC-1 Exemplary, preferred compounds of formula IC-3 Further compounds optionally used

[0012] Table E Exemplary, preferred molecular gelators (mixtures of stereoisomers are included by the drawn structures, but pure stereoisomers are preferred) Mol. Molecular structureNameweight [gmol-1] N,N'-(cyclohexane-1,2- 450.75 diyl)diundecanamide 1,1'-(cyclohexane-1,2- 480.78 diyl)bis(3-decylurea) 2,3-bis(decyloxy)anthracene 490.77 N-(4-butylphenyl)-1-(4- 267.37 methoxyphenyl)methanimine 5-(heptyloxy)-2-((p- 325.45 tolylimino)methyl)phenol N-lauroyl-L-glutamic acid di-n- 453.71 butylamide decyl 2-(5-benzyl-3,6- 402.54 dioxopiperazin-2-yl)acetate

[0013] Mixture Examples Mixtures representing ferroelectric nematic gels are prepared by combining a gelator with suitable mesogens. Generally a ferroelectric nemetic liquid- crystalline mixture is combined with the gelator at a temperature above the gelation temperature and mixed until a homogeneous solution is obtained. Alternatively the components are mixed in any order suitable for handling. The homogenized mixture is cooled swiftly to a temperature below the nematic / ferroelectric-nematic transition temperature (TFerroN). A gel forms spontaneously and reversibly from the mixtures while below the gelation temperature. Alternatively the homogenized mixture is aligned by external means (electric field, alignment layers) and gelled under slow temperature change in order to impose a directional order in the gel network and in the director of the LC phase. The following liquid crystal host mixtures (Base Mixtures) are used for the preparation of gels. Base mixture 1 The following mixture (M-1) is prepared and investigated. c) value upon cooling, Base mixture 2 The following mixture (M-2) is prepared and investigated. c) value upon cooling, Base Mixture 3 The following mixture (M-3) is prepared and investigated. c) value upon cooling, Base Mixture 4 The following mixture (M-4) is prepared and investigated. c) value upon cooling, These is the highest value of the relative dielectric permittivity εr for any physical matter known to the authors so far. Base Mixture 5 The following mixture (M-5) is prepared and investigated. c) value upon cooling, Base Mixture 6 The following mixture (M-6) is prepared and investigated. c) value upon cooling,

[0014] Base Mixture 7 The following mixture (M-7) is prepared and investigated. c) value upon cooling,

[0015] Base Mixture 8 The following mixture (M-8) is prepared and investigated. c) value upon cooling,

[0016] Base Mixture 9 The following mixture (M-9) is prepared and investigated. c) value upon cooling,

[0017] Base Mixture10 The following mixture (M-10) is prepared and investigated.

[0018] Base Mixture 11 The following mixture (M-11) is prepared and investigated. c) value upon cooling, Base Mixture 12 The following mixture (M-12) is prepared and investigated. c) value upon cooling,

[0019] Base Mixture 13 The following mixture (M-13) is prepared and investigated. c) value upon cooling, Base Mixture 14 The following mixture (M-14) is prepared and investigated.

[0020] Base Mixture 15 The following mixture (M-15) is prepared and investigated. c) value upon cooling, Mixture Example 16 The following mixture (M-16) is prepared.

[0021] c) value upon cooling. Mixture Examples Liquid crystal gels are prepared consisting of the foregoing Base Mixtures and a gelator from foregoing Table E or the following Table 1. Table 1. Gelators (Structure, molecular weight):

[0022] Mixtures are prepared from the Base Mixtures 1 to 15 together with the gelators of Table 1. The content of gelator is 0.5 % by weight unless indicated otherwise. To test if the gelation process was successful, a mixture of the NF-LC and an appropriate gelator is filled in a glass tube as an isotropic liquid. After cooling down and waiting for the gelation to finish, the tube is angled at roughly 45° with the opening pointing downwards. Gelation is considered successful when no flow occurs for at least 24 h. The resulting mixtures form gels. Selected results with varying amounts and kinds of gelator and varying Base Mixture are presented according to the following mixture table (Table 2). Table 2. Mixture Examples for liquid crystal gels: Evaluation of gels (methods a) to h)): a) Microscopic studies To study the optical properties of the gelled NF-LCs, the materials were filled in 1.6 µm thick (20 µm for piezoelectric tests) LC cells (purchased from the Military University of Technology in Warsaw, Poland) coated with polyimide, where the director n was aligned with a small to non-existent pre-tilt to the rubbing direction. In addition, both sides of the cell are coated with a conductive ITO layer. The studies were performed with a Leica DM 2700 P polarized light microscope, equipped with an Instec heating stage HCS302 controlled by a mk1000 temperature unit. Pictures were taken by a pixeLink PL-D752CU video camera. b) X-Ray diffraction Small angle X-ray measurements (SAXS) were performed with the SAXSess MC2 system (Anton Paar) and a Mythen 2 K detector (Dectris). The X-ray radiation (Cu-K^, ^ = 0.15418 nm) was generated by an ISO- DEBYEFLEX 3003 X-ray generator (Seifert). Wide angle X-ray measurements were performed with the Bruker AXS NanoSTAR system (Cu-K^ radiation, Goebel mirror monochromator, 100 µm point beam collimator, VÅNTEC-500 detector), equipped with a heating stage controlled by 2216e (Eurotherm) and a cooling unit Unichiller from Huber. The samples were placed in 0.7 mm outer diameter capillaries out of Glas #14 (Hilgenberg). c) Electro-Optic Measurements To measure the response of the gelled NF-LC to electric stimuli, the mixture of NF-LC and gelator was heated into the isotropic sol state and filled into LC testing cells (IPS1000A035uX003) from Instec. These are 3.5 µm thick and are coated with antiparallel rubbed alignment layers. Additionally, two stripes of ITO with a length of 1 cm are aligned in plane to generate an electric field. The gap between these stripes is 1 mm. The temperature was controlled by a TMS 94 (LINKAM) connected to a LTS 350 hot stage (LINKAM). The spontaneous electric polarization was obtained from recording the current response while applying a triangular AC voltage with a frequency of 70 Hz [K. Miyasato, S. Abe, H. Takezoe, A. Fukuda, E. Kuze, Jpn. J. Appl. Phys.1983, 22, L661-L663.]. The voltage was generated with a 33500B waveform generator from KEYSIGHT and amplified with a 7500 amplifier from Krohn-Hite. The voltage response was amplified and the noise reduced with a SR560 Low-Noise preamplifier from STANFORD RESEARCH SYSTEMS. This signal was recorded with a DSO-X 2004A Oscilloscope from KEYSIGHT. To calculate the current from the voltage response a 0.5 kΩ resistor was used. d) Dielectric Measurements The measurements of the dielectric constants were done with a 4192A LF Impedance Analyzer from Hewlett-Packard. The samples were filled in 20 µm thick cells from the Military University of Technology, Warsaw coated with polyimide and rubbed on both sides parallel. The cells have an ITO coating with an active area of 5 mm by 5 mm which was connected via copper wires to the analyzer. For all the measurements a voltage of 0.1 Vrmswas used. The temperature was controlled by a NOVOTHERM temperature controlling unit from Novocontrol. e) Dynamic Scanning Calorimetry The samples were transferred into Perkin Elmer crucibles (part no. B016- 9321) in batches of 3-5 mg. The measurement was performed with a DSC8000 instrument from Perkin Elmer. Heating / cooling rates of 1, 5, and 20 K min-1were used with 2 cycles each. For analysis the software Pyris was used. f) High Resolution FFTEM Freeze fracture electron microscopy replicas of the gels were prepared with the freeze fracture and etching system EM BAF060 from Leica. At room temperature, a small amount of sample was placed on two copper grids (hexagonal 360 mesh) and two copper plates (4.5 mm × 3.0 mm), which were assembled to a sandwich. The sample was then plunged into liquid ethane cooled by liquid nitrogen. The frozen and fractured specimen was quickly transferred into the vacuum chamber of BAF060. At −150 °C, the surface was replicated by a layer of Pt / C (#2 nm) deposited at an angle of 45° and stabilized by a layer of pure carbon (#20 nm) at 90°. The high resolution TEM pictures were taken with the Spectra 300 from Thermo Fisher Scientific. An acceleration voltage of 300 kV was used. g) Piezo-effect Measurement The isotropic sol mixture of a NF-LC with a gelator was filled in a mold to get a disk like shape. After gelation the disk was placed in a custom build device that consists of a stepper motor moving a copper stamp up and down to press on the gel resting on a copper plate. Both of the copper parts are contacted so that the voltage generated via the piezoelectric effect can be measured. h) Inverse Piezo-effect Measurement The gel was prepared similar to g) but instead of applying a force, an electric field was applied while the answer of the gel was measured with a newton-meter. This field was up to 200 V / cm. The voltage was generated with a 33500B waveform generator from KEYSIGHT and amplified with a 7500 amplifier from Krohn-Hite. Result of evaluations: The coexistence of ferroelectric nematic phase and gel (successful gelation) was proven via POM (characteristic textures), SAXS (characteristic scattering profiles, typical scattering maxima from the NFphase as well as from the gel fibers can be observed), FFEM (appearance of gel fibers, optical proof), dielectric spectroscopy (high dielectric constant in the NFphase) and Ps measurements (proof of ferroelectricity of NF-LC gels). In comparison to the non-gelled NF-LC it was shown that the spontaneous polarization decreases with increasing gelator content, but is still present up to very high gelator contents up to 9 wt.%. The broad range of gelator concentration that leads to a ferroelectric gel is advantageous since also the mechanical and thermal properties are altered with changing gelator amount (higher mechanical stability and elastic modulus as well as higher gel-sol transition temperature with increasing gelator concentration). Thus a material with tailored properties for a given application is possible. Device Example 1: Piezoelectric element and its electric response To prove that the gelled NF-LC shows a piezoelectric response the Base mixture 1 was mixed with 0.5 wt% 12-HOA and heated up into the sol- isotropic state (>70 °C). The mixture was then transferred into a 20 µm thick LC testing cell of glass coated with ITO on both sides. After cooling and waiting for 5 min to let the gelation take place, the cell was contacted via copper wires to a preamplifier for noise reduction. The output of the amplifier was then connected to an oscilloscope. Gently pressing on the cell with an insulated glass rod gives rise to a change in voltage over the 0.5 kΩ resistor. From this the current can be calculated (see Fig.2). This current answer is polar and indicates a change in effective spontaneous polarisation of about 35 nC / cm². Device Example 2: Inverse piezoelectric effect (force implied by electric field) In addition the inverse piezo-effect is investigated. While applying an electric field to the gel of the previous Example, a force of up to 0.16 N is exerted by the gel itself. This force is due in part to the electrostatic forces between the copper plates, which are amplified by the high dielectric constant, and in part to the inverse piezoelectric effect. Device Example 3: Inverse piezoelectric effect (sound generation and recording) Base mixture 1 was mixed with 3.5 wt% 12-HOA and heated up into the sol-isotropic state (>70 °C). The mixture was then transferred into a 6 µm thick LC testing cell of glass coated with ITO on both sides and allowed to cool and form the gel phase. An AC power source (100 V, 5 kHz sinus wave) was attached to the cell. An audible sound was generated. In addition, the device was connected face-to-face with a piezoelectric sensor according to Device Example 1 by taping them together. The resulting electrical response of the sensor is matched to the power source with an oscilloscope. The phase and frequency of the sinus waves match.

Claims

Patent Claims 1. A liquid crystal gel comprising 91% by weight or more of a ferroelectric nematic liquid crystal mixture and 0.1 to 9 % by weight of a gelator having a molecular weight between 250 and 1000 g / mol.

2. A liquid crystal gel according to claim 1 which exhibits a ferroelectric nematic phase.

3. Liquid crystal gel according to claim 1 or 2, wherein the gelator has at least one -OH or -NH- group and at least one structural element selected from -(CO)-, -(CO)O- or -(CO)NH-.

4. Liquid crystal gel according to one or more of claims 1 to 3 comprising one or more compounds of formula I,wherein A1denotesA2denotesA3denotes or a singlebond, R1is an alkyl radical having 1 to 12 C atoms, preferably 1 to 8, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, -OCF2-, -CH=CH-,-O-, -S-, -(CO)-O-or -O-(CO)- in such a way that O / S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, X is CN, F, CF3, -OCF3, -NCS, Cl, L1is H or CH3, Z1is CF2O or -(CO)-O- or a single bond, and Z2is CF2O or -(CO)-O- or a single bond.

5. Liquid crystal gel according to any of claims 1 to 4 which exhibits a relative dielectric permittivity εr of 700 or more at 20 °C and 1 kHz.

6. Liquid crystal gel according to one or more of claims 1 to 5, which comprises one, two, three or more compounds selected from formula ID-1 to ID-4,in which XDdenotes CN, F, CF3, -OCF3, NCS, SF5or O-CF=CF2, L1D, L2D, L3D, L4D, L5D, L6Dand L7D, independently denote F, H, alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, Z1Dand Z2Dindependently of one another denote -(CO)-O-, -CF2-O-, a single bond, and preferably both -(CO)-O-, R1Ddenotes an alkyl radical having 1 to 12 C atoms, where, in addi- tion, one or more CH2groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, -OCF2-, -CH=CH-, , -O-, -S-, -(CO)-O- or -O-(CO)- in such away that O / S atoms are not linked directly to one another, and inwhich, in addition, one or more H atoms may be replaced by halogen, N(CH3)2or H, R2Ddenotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3or CH2CH2CH2OCH3, A1Ddenotes a single bond,wherein L8Ddenotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3or CH2CH2CH2OCH3.

7. Liquid crystal gel according to one or more of claims 1 to 6 exhibiting a ferroelectric nematic phase at least at a temperature from 10°C to 30°C.

8. Liquid crystal gel according to one or more of claims 1 to 7 exhibiting a ferroelectric nematic phase at least over a temperature range of 20 Kelvin.

9. Use of the liquid crystal gel according to at least one of claims 1 to 8 for electro-mechanic devices including electric generators, mechanical sensors and actuators, for electro-optical purposes or for capacitors.

10. Use of the liquid crystal gel according to at least one of claims 1 to 8 for energy-harvesting applications.

11. Use of the liquid crystal gel according to at least one of claims 1 to 8 for non-linear optic elements or memory devices.

12. Piezoelectric element comprising a ferroelectric nematic liquid crystal gel between electrodes.

13. Piezoelectric element according to claim 12, wherein the liquid crystal gel is one according to one or more of claims 1 to 8.

14. Piezoelectric element according to claim 12 or 13, wherein the liquid crystal gel is aligned with a preferred direction of the orientation of at least one of its components from the group of gelator and ferroelectric nematic liquid crystal.

15. A method of preparation of a liquid crystal gel according to any one of claims 1 to 8, wherein at least one ferroelectric nematic liquid crystal mixture or its components are combined and mixed with 0.1 to 9% by weight of a gelator having a molecular weight between 250 and 1000 g / mol and with any optional other components or additives.

16. A method of preparation of a liquid crystal gel according to any one of claims 1 to 8 with a direction of the orientation of the gelator, wherein the components of the gel are formed into a gel by cooling below the gelling temperature under the influence of an external electrical field.

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