Electrocaloric devices using ferroelectric nematic materials.

Abstract

An electrocaloric device is provided that uses a ferroelectric nematic material. The present invention provides an electrocaloric device based on a liquid material suitable for cooling and thermal management. The liquid crystal material specified for the device is operated in or near the ferroelectric nematic phase. The device has a wide operating temperature range and a high induced temperature change, while requiring only modest electric field strengths.

Description

[Technical Field]

[0001] An electrocaloric device based on a liquid dielectric material suitable for cooling and thermal management. The liquid crystal material specified for the device is operated in or near the ferroelectric nematic phase. The device has a wide operating temperature range and a high induced temperature change, while requiring only modest electric field strengths. [Background technology]

[0002] The electrocaloric effect (EC effect) induces a reversible temperature change in a material by adiabatically applying and removing an electric field. The EC effect, which is based on a change in electric field across an active material, has long been considered a potential cooling technology. However, conventional electrocaloric materials (EC materials) either provide only a small induced temperature change (ΔT) or require the application of a relatively large voltage.

[0003] Some EC materials with larger temperature changes are found in the classes of ferroelectric ceramics and ferroelectric polymers, as reviewed by X. Moya et al., Nature Materials, 2014, Vol. 13, pp. 439-450. Most effective research on materials and applications has been conducted using thin films of the materials rather than bulk materials. Because EC materials are primarily solids, building a practical heat pump requires heat exchange between the active material and the surrounding material.

[0004] Liquid crystals (LCs) have also been found to exhibit the electrocaloric effect, which is enhanced by the selection of ferroelectric smectic LC materials (PJ Tipping, HF Gleeson, Crystals 2022, 12, 809 (Non-Patent Document 2)).

[0005] The temperature range where EC efficiency is highest is often limited to around a specific temperature. Different EC materials have widely varying operating temperatures, some close to room temperature, others well above or below room temperature. Different EC materials also have widely varying operating temperature ranges. The choice of material is crucial to the desired temperature of the cooling application.

[0006] In a typical cooling process (Figure 1), an electric field is applied adiabatically to a working material (electrocaloric material) while the material is isolated from a load. The temperature of the material increases as a result of the electric field (adiabatic temperature change, ΔT). While the electric field is maintained, the material is placed in thermal contact with a heat sink. The material transfers thermal energy to the heat sink, resulting in a decrease in the material's temperature and entropy. The material is then isolated from the heat sink and the electric field is removed, resulting in a decrease in the material's temperature by ΔT. The material is then exposed to a cooling load, where the material absorbs thermal energy from the load, increasing its temperature. The material is then isolated from the load, and the process repeats (the reverse Brayton cycle). ΔS and ΔT are performance parameters of the dielectric material used in the cooling process.

[0007] In recent years, the field of application of liquid crystal compounds has expanded considerably to various types of display devices. Most of these devices employ the enantiotropic nematic liquid crystal phase, including common LCD televisions, LCD desktop monitors, and mobile LCD devices. Alternative liquid crystal phases, such as ferroelectric smectic phases and blue phases, are also known. However, the ferroelectric nematic phase (N fThe ferroelectric nematic phase (N-LC phase) has been proposed only by theory for decades, without the discovery of a suitable liquid crystal material with such nematic and ferroelectric properties. More recently, some chemical structures have been reported to exhibit ferroelectric nematic behavior. For example, Atsutaka Manabe, Matthias Bremer, and Martin Kraska (2021): Ferroelectric phase at and below room temperature, Liquid Crystals, Vol. 48, pp. 1079-1086 (DOI 10.1080 / 02678292.2021.1921867) (Non-Patent Document 3) published a ferroelectric nematic material of formula C, which exhibits a monoclinic ferroelectric nematic liquid crystal phase (N-LC phase) near ambient temperature. f -LC phase).

[0008] [ka]

[0009] A drawback of conventional solid-state electrocaloric materials is that their solid nature makes the thermal effect immobile, and the effect is lost in thick layers. Solid-state materials are also susceptible to material fatigue, which accumulates with repeated cooling cycles.

[0010] Electrocaloric materials experiencing a change in electric field at a given starting temperature can be measured by evaluating the adiabatic temperature change (ΔT), the isothermal entropy change ΔS, and the isothermal heat Q. Direct measurements remain difficult. Indirect measurements use an iterative Maxwell approach to determine the temperature change. An expression for the isothermal entropy change (per unit volume), ΔS / V, as a function of electric field can be derived using the Maxwell relationship between electric field and temperature.

[0011]

number

[0012] where E1 and E2 are the initial and final field strengths,

number

[0013] An indirect measurement of Q is given by the relationship Q=T·ΔS.

[0014] Assuming that the initial temperature and volumetric heat capacity are unchanged by the applied electric field, an estimate of the induced temperature change ΔT is:

[0015]

number

[0016] T1: initial temperature at which the electric field is applied;

number

number

[0017] The temperature change induced by the electrocaloric effect in conventional liquid crystals is typically small. Furthermore, the known operating temperature range of the electrocaloric effect in conventional LC materials is limited to below 1 K and is fixed near the isotropic liquid crystal phase transition temperature. To date, no materials have been found that meet the minimum criteria for each relevant parameter required for application in electrocaloric devices. [Prior art documents] [Non-patent literature]

[0018] [Non-Patent Document 1] X. Moya et al., Nature Materials 2014, Vol. 13, pp. 439-450 [Non-patent document 2] PJ Tipping, HF Gleeson, Crystals 2022, Volume 12, Page 809 [Non-patent document 3] Atsutaka Manabe, Matthias Bremer, Martin Kraska (2021): Ferroelectric phase at and below room temperature, Liquid Crystals, Volume 48, Pages 1079-1086 (DOI 10.1080 / 02678292.2021.1921867) DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0019] The present invention aims to alleviate these drawbacks and combine all practical requirements in a single electrocaloric material and device. [Means for solving the problem]

[0020] In a first aspect, the present invention provides an electrocaloric device comprising two or more electrodes for generating an electric field in a spatial volume distributed between the at least two electrodes, and a liquid dielectric material at least partially disposed within the spatial volume, However, the dielectric material relates to electrocaloric devices that include one or more liquid crystal (LC) materials having a ferroelectric nematic phase.

[0021] The ferroelectric nematic LC material preferably comprises at least two compounds having the molecular structure of formula I:

[0022] [ka]

[0023] During the ceremony, A 1 teeth, [ka] represents A 2 teeth, [ka] represents A 3 teeth, [ka] or a single bond, R 1 represents an alkyl group having 1 to 12, preferably 1 to 8, more preferably 1 to 6, most preferably 1 to 5 C atoms (provided that in addition, one or more CH groups in these groups may be in each case independently of one another, such that O / S atoms are not directly linked to one another, e.g., -C≡C-, -CF-O-, -OCF-, -CH=CH-, [ka] or represents H, X is CN, F, CF3, -OCF3, -NCS, Cl, preferably CN or F; L 1 is H or CH3, Z 1 is CFO or -(CO)-O- or a single bond, Z 2 is CFO or -(CO)-O- or a single bond.

[0024] The present invention further relates to methods of cooling objects using the electrocaloric response of ferroelectric nematic liquid crystals, and to methods of cooling objects using the electrocaloric devices described throughout this disclosure.

[0025] The present invention further relates to the use of liquid crystal materials having a ferroelectric nematic liquid crystal phase as electrocaloric dielectric materials in heat pumps or cooling devices, and to the use of electrocaloric devices described throughout this disclosure as cooling devices, i.e. cooling devices for electronic devices, preferably processors, transistors, integrated circuits.

[0026] A further aspect of the invention is a method for manufacturing an electrocaloric device comprising two or more electrodes for generating an electric field within a spatial volume distributed between the two or more electrodes, the method comprising inserting at least partially within said spatial volume a dielectric material comprising a ferroelectric nematic liquid crystal material.

[0027] In one aspect of the invention, an electrocaloric device induces, or can be configured to induce, a temperature change in a dielectric material in response to a change in an electric field across a volume between electrodes.

[0028] One aspect of the present invention relates to the use as dielectric material a liquid crystalline medium which exhibits a ferroelectric nematic liquid crystalline phase over a substantial temperature range, preferably at ambient temperature.

[0029] Ambient temperature is often also called room temperature and here more narrowly means a temperature of 20° C. More generally, it means the starting temperature of an electrocaloric process.

[0030] The present disclosure includes stable compounds that are particularly suitable for application as component(s) of ferroelectric nematic liquid crystal media in the electrocaloric devices of the present invention.

[0031] Surprisingly, it has been found that ferroelectric nematic liquid crystal materials can achieve strong electrocaloric behavior over a very advantageously wide temperature range, preferably above 10 K. The operating range is N f -LC phase upper transition temperature and may extend above and below this transition temperature (e.g., by more than + / - 10 K). The electrocaloric response is distributed over this range. If the transition range is narrow, the electrocaloric response will be relatively high. Ferroelectric nematic liquid crystal materials have a high spontaneous polarization P Sand the electrocaloric efficiency of the material ΔT max The compounds can be used as LC media with unprecedented properties, including liquid crystal media for electrocaloric devices utilizing / ΔE.

[0032] The media and compounds used according to the invention are sufficiently chemically stable. In particular, they are distinguished by very high dielectric constants, especially very high dielectric anisotropy (Δε). These compounds have reasonably good solubility with respect to compounds with comparable properties and can be mixed with similar compounds. Related compounds also have relatively low melting points or can be kept stable below their melting point as supercooled melts. The invention provides N in the advantageous operating range. f This allows the formation of an LC phase and any adjacent transition phases. The operating range can be advantageously adapted to the required temperature and range by varying the liquid crystal medium.

[0033] Liquid crystal phases are inherently stable within their preferred temperature range, which differs from solid crystals, whose macroscopic lattices are prone to mechanical collapse and material fatigue due to accumulated irreversible disorder in the lattice. While damage accumulates in solid systems, liquid systems can always return to their initial order as long as their molecules are stable.

[0034] Surprisingly, N f It was found that LC materials respond to relatively weak electric fields, typically between 0.5 and 5 V / μm. Compared to prior art materials, such as polymers and ceramics, the polarization saturates already at very low electric fields.

[0035] The moderate volumetric heat capacity allows for excellent physical performance. Furthermore, the medium has very low electrical conductivity and is an insulator, unlike conventional high ε rThey have unique properties that are different from materials (e.g., lead zirconate titanate ceramics). The combination of low electrical conductivity and the low required electric field strength results in low electrical losses. Ferroelectric nematic materials are more fluid than highly viscous smectic materials, allowing the current material to move through the device's pipes as a heat carrier. [Brief explanation of the drawings]

[0036] [Figure 1] Figure 1 shows a schematic diagram of a typical electrocaloric cooling process in an electrocaloric device. The cooling process involves two constant-entropy transitions, (a) to (b) and (c) to (d), and two constant-field transitions, (b) to (c) and (d) to (a). The arrows within the boxes indicate the orientation of molecular dipoles within the system. The material begins (a) at ambient temperature T1 with no applied electric field, E1 = 0, and initial entropy S(T1,E1). When an electric field E2 is applied adiabatically to the material (b), the caloric temperature increases by ΔT to T2. Excess heat is transferred to the heat sink while the electric field is maintained, resulting in a temperature return to T1 (c) and a decrease in entropy to S(T1,E2). When the electric field is removed adiabatically, the caloric temperature decreases by ΔT to T3 (d), at which point the material absorbs thermal energy from the heat load and returns to its original state (a).

[0037] [Figure 2] Figure 2 shows a graph of the spontaneous polarization (PS) (nC cm-2) of a ferroelectric nematic LC mixture (M-9) measured at a constant electric field strength (1.0 V / µm) versus temperature (30–80 °C). Further details are provided in the relevant examples.

[0038] [Figure 3]Figure 3 shows a first graph (dotted line) of the electrocaloric temperature change ΔT (K) of the ferroelectric nematic LC mixture M-9 versus reduced temperature T-TF (K), where ΔT is derived from the integral over dE of the slice function of dP / dT in a varying electric field E (Equation 2). The second graph (crosses) shows the ΔT of the comparative ferroelectric smectic LC material "LC1." TF is the upper edge transition temperature of the ferroelectric nematic phase.

[0039] [Figure 4] FIG. 4 shows the graph of FIG. 2 and two curves at lower field strengths (0.4 and 0.8 V / μm). DETAILED DESCRIPTION OF THE INVENTION

[0040] In one main aspect of the present invention, the electrocaloric device functions as a heat pump or cooling device (electrocaloric cooling device, ECC device). Therefore, the present invention also relates to an electrocaloric heat pump or electrocaloric cooling device. The electrocaloric device has a means for dissipating heat from a medium (liquid dielectric material) to a heat sink (heat exchanger). The heat sink can be a conventional cooling system, such as a connection to the outside air, a second cooling medium, a thermally conductive material (preferably a metal, e.g., copper, silver, etc.), or a combination thereof.

[0041] The present invention also relates to an electrocaloric device in which a dielectric material is used as a heat exchange fluid. In a preferred embodiment of the present invention, the dielectric material is a liquid. The electrocaloric device preferably includes a channel for exchanging the liquid dielectric medium. Preferably, the device further includes a pumping mechanism for exchanging the dielectric medium in the spatial volume between the electrodes. The liquid dielectric medium can be guided in a loop through the electrocaloric device and other areas to be cooled or heated. Preferably, the device according to the present invention includes a loop for the liquid medium, which includes the spatial volume of the electric field between the electrodes. The loop preferably includes one or more heat exchange zones. Preferably, the loop volume is thermally connected or configured to be connected to a heat load, which is the object to be cooled, typically attached to the loop via a heat exchange zone. In this embodiment, optionally, one or more pumps for the liquid medium are connected to the loop to circulate the liquid medium. Optionally, one or more heat exchangers are connected to the closed loop. In a preferred operating mode, a voltage between the electrodes causes a temperature rise in the medium, which is absorbed by a heat sink corresponding to the electrode volume.

[0042] Preferably, the electrocaloric device includes a pumping mechanism for transporting a dielectric medium within the spatial volume between the electrodes. In a more preferred mode of operation, the pump transports a volume of medium between the electrodes to another volume outside the electrode volume, thereby removing the electric field from the first volume of medium and thereby causing a temperature drop. The transported, cooler volume of medium can be used for cooling purposes, while the next volume of medium enters the electrode volume and transfers some of its heat to a heat sink, and so on. By circulating the medium, continuous mode operation of the cooling device is achieved. Devices can be cascaded, with the heat sink of one device being provided by the cooling medium of another device. The spatial separation of the heat sink and the cooled medium is an advantage of this invention. Prior art stacked multilayer electrocaloric devices inherently have limited distance between the cooling zone and the hot zone, making them prone to detrimental heat flow between the zones.

[0043] The electrocaloric device according to the invention preferably has a controlled voltage source connected to the electrodes. The electric voltage can be applied constantly or at intervals depending on the operating mode of the device. The voltage control is preferably adapted to the pumping mechanism. Preferably, the voltage and pumping mechanism are in continuous mode during operation. The interaction of the voltage and pumping at the electrodes can be controlled by a microprocessor.

[0044] Liquid crystal media for use in a device according to the invention are preferably operated at or near the temperature at which the medium has a ferroelectric nematic phase. f - Up to 20 K, more preferably 10 or 5 K, above the upper transition temperature of the LC phase. The choice of medium determines the temperature range in which the electrocaloric effect is most efficient. The best effect can be expected in a temperature range close to the upper transition temperature of the ferroelectric nematic phase range, preferably within + / - 3 K of the transition temperature. Often, at the upper transition temperature of the ferroelectric nematic phase, a transition from the ferroelectric nematic phase to another ferroelectric or nematic phase (transition phase) is observed. Preferably, the electrocaloric device is operated with an LC material having a ferroelectric nematic phase within or near the operating temperature of the electrocaloric device's operating range. Also, a temperature range of 1000 nC cm within the operating temperature range of the electrocaloric device is required. -2 More P s Also preferred are media with a spontaneous polarization of 0.01 . Suitable ferroelectric materials exhibit a ferroelectric response to an applied electric field within the operating temperature range of the device. The ferroelectric response is defined as the spontaneous polarization P (or relative permittivity ε r ) is altered (respectively increased) by a change (respectively increased) in the electric field. Preferably, the electrocaloric material increases in temperature upon application of a voltage and decreases in temperature upon removal of the voltage.

[0045] Electrocaloric devices preferably have an operating temperature of 15°C or higher, more preferably 20°C or higher, most preferably 30°C or higher, and preferably 60°C or lower, preferably 50°C or lower, more preferably 45°C or lower. The temperature of maximum electrocaloric efficiency can be adjusted by using an appropriate LC medium with an appropriate transition temperature of the ferroelectric nematic phase to the adjacent phase (usually N, N, or isotropic phase). Preferred devices therefore have an operating temperature range located within the range of 15-60°C, more preferably within the range of 20-50°C.

[0046] In the following, dielectric media including ferroelectric nematic liquid crystal media are further described.

[0047] Ferroelectric nematics (N f A liquid crystal (LC) material in the (I) phase preferably comprises at least 20% by weight, preferably 50% by weight or more, more preferably 60% by weight or more, and even more preferably 65% ​​by weight or more of compounds selected from compounds having a molecular structure of formula I. The material or medium preferably comprises three, four, five or six or more compounds of formula I. Preferably, the compounds of formula I are selected from compounds of formulae IA, IB and IC below, preferably in the percentages given for each formula independently for each formula. Preferably, the LC medium comprises one or more compounds of formula I, more preferably each of formulae IA and IB and one or more compounds of IC-1 to IC-3 as defined below. Alternatively, the medium comprises one or more compounds of formula IB and each of formula IC.

[0048] Preferably, the liquid crystal medium used in the electrocaloric device has an enantiotropic ferroelectric nematic phase. The liquid crystal medium preferably has a ferroelectric nematic phase at a temperature within the operating temperature of the electrocaloric device, which may preferably be below 30°C. Preferably, the liquid crystal medium has a ferroelectric nematic phase in a temperature interval of at least 10K.

[0049] In a more preferred embodiment, the invention uses a liquid-crystalline medium comprising at least 10% by weight, preferably at least 15% by weight, of one or more compounds of formula IA, at least 10% by weight, preferably at least 15% by weight, of one or more compounds of formula IB and at least 10% by weight, preferably at least 15% by weight, more preferably at least 20% by weight of one or more compounds selected from the formulae IC-1 to IC-3.

[0050] [ka]

[0051] [ka]

[0052] [ka]

[0053] During the ceremony X 1B represents -CN or -NCS, preferably -CN, X 1C represents -CN, F, CF3, -OCF3, -NCS, SF5 or O-CF=CF2, preferably -CN or F, most preferably CN, Z 1A and Z 1B represent, independently of one another, -(CO)-O- or -CF-O- or a single bond, preferably -(CO)-O- or -CF-O-, Z 2A and Z 2B represent, independently of one another, a single bond, —(CO)—O— or —CF—O—, preferably a single bond, Z 1C and Z 2C One of the two groups represents -(CO)-O- or -CF2-O-, and the other represents a single bond, and preferably Z 1C is -(CO)-O- or -CF2-O-, and Z 2C is a single bond, L 1A , L1B and L 1C each independently represents H or CH3, preferably H, L 2A is F or H, preferably F, L 2C is F or H, preferably F, [ka] represents [ka] represents In the formula, L 8B represents alkyl, alkoxy or alkoxyalkyl having 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, [ka] represents [ka] represents m and n are 0, 1 or 2, provided that (m+n) is 1 or 2, preferably 2; R 1A , R 1B and R 1C are each independently an alkyl group having 1 to 12, preferably 1 to 8, more preferably 1 to 6, most preferably 1 to 5 C atoms (provided that in addition, one or more CH groups in these groups may in each case be independently -C≡C-, -CF-O-, -OCF-, -CH=CH-, -C≡C-, -CF≡C-, -CF≡O-, -OCF≡-, -CH=CH-, -C≡C-, -CF≡O-, -OCF≡-, -CH=CH-, -C≡C-, -CF≡O-, -OCF≡-, -C≡C ... [ka] -O-, -S-, -(CO)-O- or -O-(CO)-, provided that in addition one or more H atoms may be replaced by halogen; Preferably R 1A , R 1B and R 1C are independently halogenated or unsubstituted alkyl groups having 1 to 10 C atoms, provided that in addition, one or more CH groups in these groups may be replaced by -O- or -CH=CH- in such a way that no O atom is directly connected.

[0054] Percentages are provided in the context that the entire medium constitutes 100% by weight of the medium, which typically represents 100% of the liquid portion of the dielectric material.

[0055] The group R in each of the formulae IA, IB and IC-1 to IC-3 and their respective sub-formulae 1A , R 1B and R 1C preferably represents 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 are preferably 1C In the case of R, it is preferably branched with a single methyl or ethyl substituent at the 2- or 3-position. 1A , R 1B and R 1C particularly preferably denotes a linear alkyl group having 1 to 7 C atoms or an unbranched alkenyl group having 2 to 8 C atoms, in particular an unbranched alkyl group having 1 to 5 C atoms.

[0056] Alternatively preferred groups R 1A , R 1B and R 1Cis selected from cyclopentyl, 2-fluoroethyl, cyclopropylmethyl, cyclopentylmethyl, cyclopentylmethoxy, cyclobutylmethyl, 2-methylcyclopropyl, 2-methylcyclobutyl, 2-methylbutyl, 2-ethylpentyl and 2-alkyloxyethoxy.

[0057] Branched or substituted end groups R 1A , R 1B and R 1C Compounds of formulae IA, IB and IC1 to IC-3 containing, respectively, the group R 1A , R 1B and R 1C are each preferably linear.

[0058] base R 1A , R 1B and R 1C are each particularly preferably selected from the lower moiety.

[0059] [ka]

[0060] However, the following abbreviations are used for the end groups:

[0061] [ka]

[0062] In a preferred embodiment, the medium according to the invention preferably comprises one, two or more compounds of formula IA-1, preferably selected from the group of formulae IA-1 to IA-3, preferably of formula IA-1.

[0063] [ka]

[0064] [ka]

[0065] where the parameters have the respective meanings given above, preferably Z 1A represents -CF2-O-.

[0066] In a preferred embodiment, the medium according to the invention preferably comprises one, two or more compounds of formula IB-1 and / or IB-2, preferably of formula IB-1, preferably selected from the group of the following formulae, formulae IB-1-1 to IB-2-3:

[0067] [ka]

[0068] R 1B represents an alkyl group having 1 to 12, preferably 1 to 7, more preferably 1 to 6, most preferably 1 to 5 C atoms (provided that in addition, one or more CH groups in these groups may in each case independently be -C≡C-, -CF-O-, -OCF-, -CH=CH-, -C≡C-, -CF≡ ... [ka] -O-, -S-, -CO-O- or -O-CO-, provided that in addition one or more H atoms may be replaced by halogen; Preferably R 1B is a halogenated or unsubstituted alkyl radical having 1 to 12 C atoms, with the proviso that in addition, one or more CH groups in these radicals may in each case be replaced independently by -C≡C- or -CH=CH-, [ka] represents, and Z 1B , Z 2Bindependently represent -(CO)-O- or -CF2-O-.

[0069] [ka]

[0070] where the parameters have the respective meanings given above, and in particular in formulae IB-1-1 to IB-1-3, Z 1B preferably represents —CF—O—, and in particular in formulae IB-2-1 and IB-2-2, Z 2B preferably represents —CF—O—, and in particular in formula IB-2-3, Z 2B preferably represents —C(O)O—.

[0071] In a preferred embodiment, the medium according to the invention preferably comprises one, two or more compounds selected from the group of formulae IC-1-1-1 to IC-3-5-2, 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.

[0072] [ka]

[0073] In the formula, A 1C and A 2C is defined as above.

[0074] [ka]

[0075] [ka]

[0076] [ka]

[0077] where the parameters have the respective meanings given above, preferably L 1C represents H, Z 1C represents -CF2-O- or -(CO)-O-, and X 1C represents —CN or F, preferably —CN.

[0078] Particularly preferred compounds of the formulae IC-1-1 to IC-1-4 to be used in the medium are compounds of the following formulae:

[0079] [ka]

[0080] where the parameters are defined above, preferably L 1C is H.

[0081] In a preferred embodiment of the present invention the medium comprises up to 100% by weight of one or more compounds, preferably 3, 4, 5 or 6 or more compounds selected from compound group 1, the group of compounds of formulae IA, IB and IC-1 / -2 / -3. In this embodiment the medium and / or LC material preferably consists mainly of, more preferably it consists essentially of and most preferably it consists substantially completely of these compounds.

[0082] For purposes of the present invention, unless otherwise indicated in particular cases, the following definitions apply in connection with the identification of the components of the compositions.

[0083] "Consists mainly of": The concentration of the component in question in the composition is preferably 50% by weight or more, particularly preferably 55% by weight or more, very particularly preferably 60% by weight or more.

[0084] "Consists essentially of": The concentration of the component in question in the composition is preferably 80% by weight or more, particularly preferably 90% by weight or more, very particularly preferably 95% by weight or more.

[0085] "Consists essentially completely of": The concentration of the component in question in the composition is preferably 98% by weight or more, particularly preferably 99% by weight or more, very particularly preferably 100.0% by weight.

[0086] Preferably, the liquid-crystalline medium and / or the dielectric material applied according to the invention fulfill one or more of the following conditions: The liquid-crystalline material, in particular the liquid-crystalline medium, preferably:

[0087] 20% by weight or more of compounds of formula IA, more preferably 25% by weight or more, more preferably 27% by weight or more, most preferably 32% by weight or more of compounds of formula IA,

[0088] 17% by weight or more of compounds of formula IB, more preferably 20% by weight or more, more preferably 22% by weight or more, most preferably 25% by weight or more of compounds of formula IB,

[0089] 20% by weight or more, preferably 25% by weight or more, of compounds selected from the formulae IC-1, IC-2 and IC-3, more preferably 28% by weight or more, more preferably 32% by weight or more, most preferably 34% by weight or more,

[0090] optionally 2% by weight or more of compounds of formula ID (ID-1, ID-2, ID-3, ID-4), more preferably 5% by weight or more, more preferably 10% by weight or more, most preferably 15% by weight or more of compounds of formula ID,

[0091] one, two or more, preferably three or more, compounds of formula IA-1-1, preferably of formula DUUQU-nF, most preferably selected from the group of compounds DUUQU-2-F, DUUQU-3-F, DUUQU-4-F and DUUQU-5-F and DUUQU-6-F,

[0092] one, two or more, preferably three or more, compounds of formula IB-1, preferably of formula GUUQU-nN and / or DUUQU-nN, 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,

[0093] one, two or more compounds of formula IA-1-3, preferably of formula GUUQU-nF, more preferably selected from the group of compounds GUUQU-3-F, GUUQU-4-F and GUUQU-5-F,

[0094] one, two or more compounds of formula IB-1-3, preferably of formula DUUQU-nN, more preferably selected from the group of compounds DUUQU-3-N, DUUQU-4-N and DUUQU-5-N,

[0095] one, two or more compounds of formula IC-1-1, preferably of formula MUZU-nN or MUQU-nN, more preferably selected from the group of compounds MUZU-2-N, MUZU-3-N, MUZU-4-N and MUZU-5-N,

[0096] one, two or more compounds of formula IC-3, preferably selected from the group of formulae MUU-nN or UMU-nN, more preferably selected from the group of compounds MUU-3-N, MUU-4-N, MUU-5-F, UMU-3-N, UMU-4-N and UMU-5-N,

[0097] one, two or more compounds of formula IC-1-1, preferably selected from the group of formula GUZU-nN or GUQU-nN, more preferably selected from the group of compounds GUZU-3-N, GUZU-4-N, GUZU-5-F, GUQU-3-N, GUQU-4-N and GUQU-5-N,

[0098] and / or containing one, two or more compounds selected from the group of formulae IC-1-1-3 and IC-1-1-4, preferably compounds of formulae UUZU-nN and / or UUQU-nN, most preferably compounds UUZU-2-N, UUZU-3-N, UUZU-4-N, UUZU-5-N, UUQU-2-N, UUQU-3-N and UUQU-4-N,

[0099] wherein n is 1, 2, 3, 4, 5, 6, or 7.

[0100] By varying the amounts of compounds of formulae IA, IB and IC, different upper transition temperatures of the ferroelectric nematic phase can be achieved, and thus different electrocaloric effect temperatures.

[0101] In another preferred embodiment of the present invention, the compounds of formulae IA, IB and IC-1 / -2 / -3 are a first group of compounds, compound group 1. In this embodiment, the concentration of the compounds of compound group 1 is preferably 70% or more, preferably 80% or more, more preferably in the range of 90% or more to 100% or less.

[0102] In addition to the compounds of formulae IA, IB and IC-1 / -2 / -3, the media according to the invention optionally, preferably essentially, comprise one, two or more compounds selected from the formulae ID-1 to ID-4.

[0103] [ka]

[0104] X Drepresents CN, F, CF, -OCF, NCS, SF or O-CF=CF, preferably -CN, F, -CF, -OCF, -Cl or -NCS, most preferably F or CN, L 1D , L 2D , L 3D , L 4D , L 5D , L 6D and L 7D independently represent F, H, alkyl, alkoxy or alkoxyalkyl, each having 1 to 7 C atoms, preferably H, F, CH3, OCH3, OCH2CH3, CHOCH3, CHOCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, Z 1D and Z 2D are each independently -(CO)-O-, -CF2-O-, a single bond, and preferably both are -(CO)-O-, R 1D represents an alkyl group having 1 to 12 C atoms, preferably 1 to 7, more preferably 1 to 6, most preferably 1 to 5 C atoms (provided that in addition, one or more CH groups in these groups may in each case independently be -C≡C-, -CF-O-, -OCF-, -CH=CH-, -C≡C-, -CF≡ ... [ka] -O-, -S-, -(CO)-O- or -O-(CO)-, provided that in addition one or more H atoms may be replaced by halogen; Preferably R 1D is a halogenated or unsubstituted alkyl radical having 1 to 12 C atoms, with the proviso that in addition, one or more CH groups in these radicals may in each case be replaced independently by -C≡C- or -CH=CH-, R 2Drepresents alkyl, alkoxy or alkoxyalkyl, each having 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, [ka] represents L 8D represents alkyl, alkoxy or alkoxyalkyl, each having 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3.

[0105] Preferably, it comprises one or more of formulae ID-1-1 to ID-3-1.

[0106] [ka]

[0107] where the variable group R 1D and L 8D is defined as above.

[0108] The corresponding starting materials can generally be readily prepared by those 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.

[0109] In the present disclosure, the 2,5-disubstituted dioxane ring of the formula: [ka] Preferably, the dioxane ring is in the 2,5-trans configuration, i.e., the two substituents are both equatorial in the preferred chair conformation. 2,5-disubstituted tetrahydropyrans of the formula: [ka] Likewise, it preferably represents a tetrahydropyran ring in the 2,5-trans configuration, ie, the two substituents are preferably both equatorial in the preferred chair conformation.

[0110] The liquid crystal media used according to the invention have a wide temperature range of the ferroelectric nematic phase. They exhibit a ferroelectric nematic phase range of 20°C and above (ambient temperature). They cover the range of most technical interest, 10-30°C and above, as well as lower and / or higher temperatures. They are therefore highly suitable for a wide range of cooling operations in various applications.

[0111] The liquid crystal media used according to the invention preferably exhibit a temperature range of the ferroelectric nematic phase that is at least 20 degrees wide, which preferably spans a range of at least 40 degrees, more preferably at least 60 degrees.

[0112] Preferably, the liquid crystal medium used according to the present invention exhibits a ferroelectric nematic phase at temperatures of 10°C to 30°C, more preferably 10°C to 40°C, more preferably 10°C to 50°C, more preferably 0°C to 50°C, and most preferably -10°C to 50°C.

[0113] In another preferred embodiment, the liquid crystal medium used according to the present invention exhibits a ferroelectric nematic phase preferably at 10°C to 40°C, more preferably at 10°C to 50°C, more preferably at 10°C to 60°C, and most preferably at 10°C to 70°C.

[0114] These advantageous electrocaloric properties are primarily achieved above the temperature at which the medium is in the ferroelectric nematic phase. Dielectric and thermotropic properties may exhibit hysteretic behavior, particularly with changes in temperature, in which case the value obtained at a given temperature may depend on the history of the material, i.e., whether it is being heated or cooled.

[0115] The liquid-crystalline media according to the invention preferably contain from 2 to 40, particularly preferably from 4 to 20, compounds as further components in addition to one or more compounds according to the invention. In particular, these media may contain from 1 to 25 components in addition to one or more compounds according to the invention. These further components are preferably selected from ferroelectric nematic or nematogenic (monotropic or isotropic) substances.

[0116] Prior art ferroelectric materials and similar compounds with high dielectric constants for combination with the present material are selected, for example, from the following structures:

[0117] [ka]

[0118] The medium used according to the invention preferably comprises from 1% to 100% by weight, more preferably from 10% to 100% by weight, particularly preferably from 50% to 100% by weight, of the compounds of the formulae IA and / or IB and / or IC-1 / IC-2 / IC-3 which are preferably used according to the invention.

[0119] 1000 nC cm at the upper transition temperature of the ferroelectric nematic phase range -2 More than 2000 nC·cm -2 More than 3000 nC cm, most preferably -2 Preferably, the electrocaloric device according to the present invention has a liquid crystal material exhibiting a spontaneous polarization Ps of 15,000 or more at 20°C and 10 Hz. r , and more preferably ε of 20,000 or more r , most preferably ε of 30,000 or more r Further preferred is an electrocaloric device according to the invention, wherein the liquid crystal material exhibits:

[0120] The term "alkyl" embraces unbranched and branched alkyl radicals having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, particularly preferably the unbranched radicals methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl and n-heptyl, and also the radicals n-butyl, n-pentyl, n-hexyl and n-heptyl, which are alternatively substituted by one methyl, ethyl or propyl. Radicals having 1 to 5 carbon atoms are generally preferred.

[0121] The term "alkenyl" embraces unbranched and branched alkenyl groups having up to 12 carbon atoms, in particular 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 preferred 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, etc. Groups having 2 to 5 carbon atoms are generally preferred.

[0122] The expression "halogenated alkyl group" preferably includes mono- or polyfluorinated and / or chlorinated groups. Perhalogenated groups are included. Fluorinated alkyl groups are particularly preferred, in particular CF3, CH2CF3, CH2CHF2, CHF2, CH2F, CHFCF3 and CF2CHFCF3. The expression "halogenated alkenyl group" and related expressions are explained accordingly.

[0123] The terms liquid crystal medium (LC medium) and liquid crystal material are used synonymously throughout this disclosure.

[0124] Above and below, percentage data are expressed as % by weight. Unless otherwise specified, for example, melting point T(C,N), smectic (Sm) to nematic (N) phase transition T(S,N) and clearing point T(N,I), respectively, T(N f All temperature values ​​given in this application, such as (°C), (°F), ...

[0125] The physical, physicochemical and electro-optical parameters are determined in a generally known manner, as described, inter alia, in the document "Merck Liquid Crystals - Licristal® - Physical Properties of Liquid Crystals - Description of Measurement Methods", 1998, Merck KGaA, Darmstadt.

[0126] The appearance of the ferroelectric nematic phase in the material is identified using differential scanning calorimetry (DSC) and by observing the texture under a polarized light microscope equipped with a hot stage for controlled cooling or heating, respectively, and also by the temperature dependence of the dielectric properties. The transition temperature is primarily determined by detecting the optical behavior under a polarized light microscope.

[0127] The dielectric anisotropy Δε of the individual substances is determined at 20 °C and 1 kHz. For this purpose, 5-10% by weight of the substance to be examined and measured is dissolved in the dielectrically positive mixture ZLI-4792 (Merck) and the measured value is extrapolated to a concentration of 100% by weight. The optical anisotropy Δn is determined at 20 °C and a wavelength of 589.3 nm.

[0128] The relative permittivity (ε) of the material, especially in the ferroelectric nematic phase r) is determined directly by measuring the capacitance of at least one test cell containing the compound, with a cell thickness of 250 μm and homeotropic and homogeneous orientation, respectively. The temperature is controlled by a Novocontrol Novocoool system set, with a temperature gradient of + / - 1 K / min; + / - 2 K / min; + / - 5 K / min; and + / - 10 K / min applied to the sample cell. The capacitance is measured with a Novocontrol α-N analyzer at a frequency of 1 kHz or 10 Hz, with a standard voltage stepping down from less than 50 mV to 0.1 mV, below the threshold of the measured compound. Measurements are performed both during heating and cooling of the sample (single or multiple samples).

[0129] In this application, unless expressly stated otherwise, the plural of a term refers to both the singular and the plural, and vice versa. Further combinations of the embodiments and variations of the invention according to the detailed description arise from the appended claims or from multiple combinations of these claims. [Example]

[0130] The invention will now be described in more detail in the following non-limiting examples.

[0131] 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.

[0132] From the foregoing description, those skilled in the art can easily ascertain the essential features of the present invention, and can make various modifications and changes to adapt the present invention to various uses and conditions without departing from the spirit and scope thereof.

[0133] This applies both to the medium as a composition having components which may be groups of compounds and individual compounds of the composition, and also to groups of compounds having their respective components and compounds. As far as the concentration of individual compounds relative to the medium as a whole is concerned, the term "comprising" means that the concentration of the compound(s) or compounds in question is preferably 1% by weight or more, particularly preferably 2% by weight or more, very particularly preferably 4% by weight or more.

[0134] In the present invention, [ka] represents trans-1,4-cyclohexylene, [ka] represents a mixture of both cis- and trans-1,4-cyclohexylene, [ka] represents 1,4-phenylene.

[0135] In the present invention, the expression "dielectrically positive compound" means a compound with Δε > 1.5, the expression "dielectrically neutral compound" means a compound with -1.5 ≦ Δε ≦ 1.5, and the expression "dielectrically negative compound" means a compound with Δε < -1.5. The dielectric anisotropy of a compound is determined herein by dissolving 10% by weight of the compound in a liquid crystal host and determining the capacitance of the resulting mixture at 1 kHz in at least one test cell with a cell thickness of 20 μm and in each case with homeotropic and homogeneous surface alignment. The measurement voltage is typically 0.5 V to 1.0 V, but always lower than the capacitance threshold of the respective liquid crystal mixture (material) under consideration.

[0136] The liquid crystal media and LC materials used according to the present invention may also contain further additives, such as stabilizers, in conventional amounts, if necessary. The total amount of these additives used is preferably from 0 to 10% by weight, particularly preferably from 0.1 to 6% by weight, based on the total amount of the mixture. The concentration of each compound used is preferably from 0.1 to 3% by weight. The concentrations of these and similar additives are generally not taken into account when specifying the concentration and concentration range of the liquid crystal compound in the liquid crystal medium.

[0137] For the purposes of the present invention, all concentrations are given in percent by weight unless expressly stated otherwise and relate to the corresponding mixture as a whole or to the entire mixture components unless expressly stated otherwise. In this context, the term "mixture" describes a liquid-crystalline medium.

[0138] Unless otherwise stated, the following symbols are used: T(N,I) respectively T(N f ,I) (or clp.) Clearing point (℃).

[0139] Dielectric properties at 1 kHz and preferably at 20°C or each specified temperature: Δε for dielectric anisotropy and especially for single compound selection data.

[0140] and specifically for data from screening of the respective compounds in the nematic host mixture ZLI-4792: n e The extraordinary refractive index measured at 20°C and 589 nm, n0Normal refractive index measured at 20°C and 589 nm, and Δn Optical anisotropy measured at 20°C and 589 nm.

[0141] The following examples are illustrative of the present invention and are not intended to limit the present invention. Those skilled in the art can understand from the examples the detailed operations not detailed in the general description, and generalize them based on their general expertise and apply them to specific problems. The examples show those skilled in the art preferred mixing concepts, preferably used compounds, and their respective concentrations. Furthermore, the examples illustrate available properties and property combinations.

[0142] Definitions of structural elements by abbreviation for use in acronyms for chemical compounds are provided in the table below.

[0143] <Table A: Ring elements>

[0144] [Table 1]

[0145] [Table 2]

[0146] <Table B: Crosslinking Units>

[0147] [Table 3]

[0148] <Table C: Terminal group>

[0149] [Table 4]

[0150] where n and m each represent an integer and the three dots "..." are spaces for other abbreviations from the table.

[0151] In addition to the compounds of formulae IA, IB and IC-1 / -2 / -3, the mixtures used in the present invention preferably contain one or more of the compounds described below.

[0152] The following abbreviations are used: (n, m, k and l are each independently an integer, preferably 1 to 9, more preferably 1 to 7; k and l can be 0, preferably 0 to 4, more preferably 0 or 2, and most preferably 2; n is preferably 1, 2, 3, 4 or 5; in the combination "-nO-", it is preferably 1, 2, 3 or 4, more preferably 2 or 4; m is preferably 1, 2, 3, 4 or 5; in the combination "-Om", it is preferably 1, 2, 3 or 4, more preferably 2 or 4. The combination "-lVm" is preferably "2V1".)

[0153] In the present invention and the following examples, the structures of liquid crystal compounds are represented by acronyms, and conversion to chemical formulas is performed according to Tables A to C above. n H 2n+1 , C m H 2m+1 and C l H 2l+1 or C n H 2n , C m H 2m and C l H 2l are linear alkyl or alkenyl groups having n, m and l C atoms, respectively. Preferably, n, m and l are each, independently of one another, 1, 2, 3, 4, 5, 6 or 7. Table A shows the codes for the ring elements of the core structure of the compounds, Table B lists the bridging groups, and Table C lists the meaning of the codes for the left and right terminal groups of the molecule. The initial letter consists of the code for the ring element with any linking groups, followed by a first hyphen and the code for the left terminal group, and a second hyphen and the code for the right terminal group. Table D shows exemplary structures of the compounds with their respective abbreviations.

[0154] Examples of preferred compounds of formula IA

[0155] [Table 5]

[0156] Examples of preferred compounds of formula IB

[0157] [Table 6]

[0158] Examples of preferred compounds of formula IC-1

[0159] [Table 7]

[0160] Examples of preferred compounds of formula IC-3

[0161] [Table 8]

[0162] Optionally used further compounds

[0163] [Table 9]

[0164] [Table 10]

[0165] In the formula, n is 0, 1, 2, 3, 4, 5, 6, 7, etc., and preferably 0, 1, 2, 3, 4, or 5.

[0166] <Mixture example> The following exemplary mixtures are disclosed. The preparation of the compounds is carried out in the same manner as those of the same or similar structure in previous publications. The preparation of the mixtures is carried out in the conventional manner by combining the necessary materials and homogenizing them at an appropriate elevated temperature.

[0167] <Mixture example 1> The following mixture (M-1) is prepared:

[0168] [Table 11]

[0169] <Mixture example 2> The following mixture (M-2) is prepared:

[0170] [Table 12]

[0171] <Mixture example 3> The following mixture (M-3) is prepared:

[0172] [Table 13]

[0173] These are the relative permittivity ε of all physical substances known to the authors so far. r It is the highest value among

[0174] <Mixture example 4> The following mixture (M-4) is prepared:

[0175] [Table 14]

[0176] <Mixture example 5> The following mixture (M-5) is prepared:

[0177] [Table 15]

[0178] <Mixture example 6> The following mixture (M-6) is prepared:

[0179] [Table 16]

[0180] <Mixture example 7> The following mixture (M-7) is prepared:

[0181] [Table 17]

[0182] <Mixture example 8> The following mixture (M-8) is prepared:

[0183] [Table 18]

[0184] <Mixture example 9> The following mixture (M-9) is prepared:

[0185] [Table 19]

[0186] A nematic transition phase (N2) is observed in the temperature range up to 58° C. above the ferroelectric nematic phase, followed by a conventional nematic phase (N1).

[0187] <Mixture example 10> The following mixture (M-10) is prepared:

[0188] [Table 20]

[0189] <Mixture example 11> The following mixture (M-11) is prepared:

[0190] [Table 21]

[0191] <Mixture example 12> The following mixture (M-12) is prepared:

[0192] [Table 22]

[0193] <Mixture example 13> The following mixture (M-13) is prepared:

[0194] [Table 23]

[0195] <Mixture example 14> The following mixture (M-14) is prepared:

[0196] [Table 24]

[0197] The mixture is heated to about 43°C. F The maximum temperature change is ΔT max =3K.

[0198] <Mixture example 15> The following mixture (M-15) is prepared:

[0199] [Table 25]

[0200] The mixture is suitable for high operating temperatures (approximately 76°C) and maximum temperature changes ΔT max = 1.5K. is.

[0201] Reference materials: The ferroelectric materials FELIX-017 / 000 and OB4HOB [Bsaibess, E.; Sahraoui, A.H.; Boussoualem, Y.; Soueidan, M.; Duponchel, B.; Singh, D.P.; Nsouli, B.; Daoudi, A.; Longuemart, S. Study of the electrocaloric effect in ferroelectric liquid crystals. Liq. Cryst. 2019, Vol. 46, pp. 1517-1526] were studied by Bsaibess et al.

[0202] Klemencic et al. induced a temperature change during the transition from the isotropic phase to the SmA phase in 12CB [Klemencic, E.; Trcek, M.; Kutnjak, Z.; Kralj, S. Giant electrocaloric response in smectic liquid crystals with direct smectic-isotropic transition. Sci. Rep. 2019, Vol. 9, p. 1721].

[0203] PST-MLC: Lead scandium tantalate (PST), a ferroelectric ceramic disposed in a multilayer capacitor (MLC) [Nair, B.; Usui, T.; Crossley, S.; Kurdi, S.; Guzman-Verri, G.G.; Moya, X.; Hirose, S.; Mathur, N.D. Large electrocaloric effects in oxide multilayer capacitors over a wide temperature range. Nature 2019, Vol. 575, pp. 468-472] is included for reference.

[0204] The temperature changes of 12CB and PST-MLC are direct measurements, while the other measurements are indirect measurements.

[0205] SCE13 is a ferroelectric chiral smectic C (SmC) * ) liquid crystal mixture (Merck) with the following phase sequence (upon cooling, °C):

[0206] I 100.8 N * 86.3 SmA 60.8 SmC * -20Cr

[0207] LC1 has the following structure:

[0208] [ka]

[0209] LC2 has the following structure:

[0210] [ka]

[0211] Compounds LC1 and LC2 enter a chiral smectic ferroelectric phase (SmC) at a specific temperature. * ) has been reported (Tipping, PJ; Gleeson, HF, Crystals 2022, Vol. 12, p. 809).

[0212] 12CB has the following structure:

[0213] [ka]

[0214] result The mixtures were characterized according to literature methods according to Tipping, PJ; Gleeson, HF, Crystals 2022, Vol. 12, p. 809. Reference data are also taken from this literature. The densities and heat capacities of the mixtures were measured by conventional methods.

[0215] The mixture of Example 9 was subjected to the indirect measurement method, and the applied electric field (0.2 to 1.0 Vμm -1 , 0.2Vμm -1 Spontaneous polarization P as a function of the frequency interval (87 Hz) and temperature from 65 °C to 30 °C s The rate of change of spontaneous polarization is obtained.

number

[0216] An exemplary measurement curve for mixture M-9 is shown in detail in FIGS.

[0217] The material evaluation results and comparison with reference data are summarized in Table 1 below.

[0218] Table 1. Maximum spontaneous polarization (P) in the present material and other systems selected for comparison. S ), volumetric heat capacity (C E ), maximum EC temperature change (T max ), figure of merit ΔT max / ΔE, and the temperature range over which the electrocaloric temperature change continues to exceed 90% of the peak temperature change.

[0219] [Table 26]

[0220] Characterization of Mixture Example 9 (Mixture M-9)

[0221] Key results: Peak electrocaloric (EC) efficiency and applicable temperature range are 50% wider than the best performing smectic ferroelectric LCs.

[0222] · Improved efficiency – 32 times higher than the best performing smectic ferroelectric LC.

[0223] More than three times more efficient than PST ceramic multilayers, with the widest reported temperature range.

[0224] The peak electric calorific temperature change ΔT is approximately 0.6K, which is good.

[0225] Being a liquid, the electrocaloric cooling process is not subject to frequency limitations like solid electrocaloric materials.

[0226] The electrocaloric temperature range is highly advantageous for technical applications, e.g. microelectronics cooling.

[0227] N F The applicable temperature range can be expanded by mixing LC.

[0228] ·

number

Claims

1. 1. An electrocaloric device comprising: two or more electrodes for generating an electric field within a spatial volume distributed between the at least two electrodes; and a liquid dielectric material at least partially disposed within the spatial volume, an electrocaloric device wherein the dielectric material comprises one or more liquid crystalline (LC) materials having a ferroelectric nematic phase;

2. 10. The electrocaloric device of claim 1, wherein the dielectric material exhibits a ferroelectric response to an applied electric field within the operating temperature range of the device.

3. 3. An electrocaloric device according to claim 1 or 2, wherein the device is an electrocaloric heat pump or a cooling device.

4. 4. An electrocaloric device according to any one of claims 1 to 3, wherein the device further comprises a pumping mechanism for transporting the dielectric material within the spatial volume between the electrodes.

5. Electrocaloric device according to any one of claims 1 to 4, wherein the one or more LC materials comprise at least two compounds having the molecular structure of formula I: 【Chemistry 1】 (In the formula, A １ teeth, 【Chemistry 2】 represents A ２ teeth, 【Transformation 3】 represents A ３ teeth, 【Chemistry 4】 or a single bond, R １ is an alkyl group having 1 to 12 C atoms (but in addition, one or more CH ２ The groups may be in each case independently of one another, such that the O / S atoms are not directly linked to one another, such as -C≡C-, -CF ２ -O-, -OCF ２ -, -CH=CH-, 【Transformation 5】 or represents H, and X is CN, F, CF ３ , -OCF ３ , -NCS, Cl, preferably CN or F, L １ is H or CH ３ and Z １ is CF ２ O or —(CO)—O— or a single bond, and Z ２ is CF ２ O, —(CO)—O—, or a single bond.

6. The LC material has a ferroelectricity of 1000 nC / cm at the upper transition temperature of the ferroelectric nematic phase range. －２ The spontaneous polarization P ｓ The electrothermal device according to any one of claims 1 to 5, wherein

7. 7. An electrocaloric device according to any one of claims 1 to 6, wherein the device comprises a loop for liquid LC liquid crystal material, the volume of the loop comprising the spatial volume of the electric field between electrodes, and the volume of the loop configured to be thermally coupled to a heat load.

8. 8. An electrocaloric device according to any one of claims 1 to 7, wherein the spatial volume between the electrodes coincides with the heat sink.

9. 9. An electrocaloric device according to any preceding claim, comprising a controlled voltage source connected to the electrodes.

10. 10. An electrocaloric device according to any one of claims 1 to 9, having an operating temperature range lying in the range of 15 to 60°C.

11. A method for cooling an object using the electrocaloric response of a ferroelectric nematic liquid crystal.

12. A method of cooling an object using an electrocaloric device according to any one of claims 1 to 10.

13. 1. Use of a liquid crystal material having a ferroelectric nematic liquid crystal phase as an electrocaloric dielectric in a heat pump or cooling device.

14. Use of an electrocaloric device according to any one of claims 1 to 10 as a cooling device for electronic equipment.

15. 1. A method for preparing an electrocaloric device comprising two or more electrodes for generating an electric field within a spatial volume distributed between at least two of the electrodes, the method comprising: The method includes at least partially inserting into said spatial volume a dielectric material comprising one or more liquid crystal (LC) materials having a ferroelectric nematic phase.

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