Method

Abstract

A mechanocaloric method comprising altering a pressure applied to a mechanocaloric material sufficient to induce a phase change in the mechanocaloric material wherein the mechanocaloric material is an

Description

Conventional cooling apparatus such as refrigerators and air conditioners contain a refrigerant fluid which cycles between a liquid phase and a gas phase. A disadvantage of such apparatus is the risk of atmospheric pollution arising from release of gaseous refrigerant into the atmosphere, for example due to a leak during the operational life of the apparatus or after its disposal or during servicing of the apparatus. Many refrigerants are potent greenhouse gases. Alternative cooling methods make use of either a magnetocaloric effect, an electrocaloric effect or a mechanocaloric effect. The elastocaloric effect and the barocaloric effect are types of mechanocaloric effect. The barocaloric effect is described in David Boldrin, "Fantastic barocalorics and where to find them" Appl. Phys. Lett. 118, 170502, 2021 and L. Cirillo, A. Greco and C. Masselli, "Cooling through barocaloric effect: A review of the state of the art up to 2022", Thermal Science and Engineering Progress, Volume 33, 1 August 2022, 101380. Bernet E. Meijer, Richard J. C. Dixey, Franz Demmel, Robin Perry, Helen C. Walker and Anthony E. Phillips, "Dynamics in the ordered and disordered phases of barocaloric adamantane", Phys. Chern. Chern. Phys., 2023, 25, 9282, discloses the barocaloric effect (BCE) of adamantane. Araceli Aznar, Philippe Negrier, Antoni Planes, Lluis Mahosa, Enric Stern-Taulats, et al., "Reversible colossal barocaloric effects near room temperature in 1-X-adamantane (X=CI, Br) plastic crystals", Applied Materials Today, 2021, 23, pp.101023 discloses colossal reversible BCEs of 1-bromo-adamantane and 1-chloro-adamantane. Alejandro Salvatori et al, "Colossal barocaloric effects in adamantane derivatives for thermal management" APL Mater. 10, 111117 (2022) discloses the pressure-induced caloric response at the first-order phase transitions occurring above room temperature of 1-adamantanol, 2-adamantanol, and 2-methyl-2-adamantanol. Paulina Jesionek et al., "Studies on the nature and pressure evolution of phase transitions in 1-adamantylamine and 1-adamantanol", Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 299, 2023,122794, discloses the influence of H-bond strength in l-NH2-adamantane and 1-OH-adamantane. P Negrier et al, "Polymorphism of 1,3-X-adamantanes (X = Br, OH, CHs) and the crystal plastic phase formation ability", CrystEngComm, 2020,22, 1230-1238 discloses the polymorphism of 1,3-dimethyladamantane, 1,3-adamantanediol and 1,3-dibromoadamantane. Mana Barrio, Rafael Levit, Pol Lloveras, Araceli Aznar, Philippe Negrier, et al. "Relationship between the two-component system 1-Br-adamantane + 1-CI-adamantane and the high-pressure properties of the pure components" Fluid Phase Equilibria, 2018, 459, pp.219-229 discloses the temperature-composition phase diagram of the two-component system 1-Br-adamantane and 1-CI-adamantane. WO2018 / 069506 discloses barocaloric cooling using organic materials. EP4407011 discloses use of 2-amino-2-methyl-1,3-propanediol, m-carborane, 1-cyanoadamantane, 2-adamantanone and pentachloronitrobenzene as barocaloric materials used in a solid-state phase change heat storage and release method. SUMMARY The present inventors have found that 2,2-disubstituted adamantanes may provide a large entropy change when undergoing phase transition with little hysteresis. Accordingly, the present disclosure provides a mechanocaloric method comprising altering a pressure applied to a mechanocaloric material sufficient to induce a phase change in the mechanocaloric material wherein the mechanocaloric material is an adamantane substituted with an alkyl group and a halogen. Optionally, the alkyl group and the halogen are the only substituents of the adamantane. Optionally, the alkyl group and the halogen group are both at the 2-position of the adamantane. Optionally, the alkyl group is a Ci-6 alkyl group. Optionally, the alkyl group is methyl. Optionally, the halogen is F, Cl or Br. The present inventors have further found that adamantane-diones may possess more than one solid-solid phase transition, allowing heat pumping across a wide temperature range. The present inventors have further found that an adamantane-diones may undergo a phase transition at a higher temperature than adamantane or adamantanone, allowing for use at an operating temperature closer to ambient temperature. Accordingly, the present disclosure provides a mechanocaloric method comprising altering a pressure applied to a mechanocaloric material sufficient to induce a phase change in the mechanocaloric material wherein the mechanocaloric material is an adamantane-dione. Optionally, the adamantane dione is adamantane-2,6-dione or adamantane-2,4-dione. Optionally, the ketone substituents are the only substituents of the adamantane dione Optionally, the barocaloric method is a heat transfer method. Optionally, the heat transfer method is a cooling method. Optionally, the cooling method is cooling of a fluid of a refrigerator or an air conditioning unit. Optionally, the heat transfer method is a heating method. Optionally, The mechanocaloric method according to any one of claims 1-9 wherein the mechanocaloric method is a thermal storage method. Optionally, the mechanocaloric method is a barocaloric method and the applied pressure is a hydrostatic pressure. Optionally, the mechanocaloric method is an elastocaloric method and the applied pressure is a uniaxial pressure. DESCRIPTION OF THE DRAWINGS Figure 1 schematically illustrates barocaloric apparatus according to some embodiments of the present disclosure. The drawings are not drawn to scale and have various viewpoints and perspectives. The drawings are some implementations and examples. Additionally, some components and / or operations may be separated into different blocks or combined into a single block for the purposes of discussion of some of the embodiments of the disclosed technology. Moreover, while the technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the technology to the particular implementations described. On the contrary, the technology is intended to cover all modifications, equivalents, and alternatives falling within the scope of the technology as defined by the appended claims. DETAILED DESCRIPTION Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. References to a chemical element include any isotope of that chemical element unless stated otherwise. The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements. These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims. To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details. The present disclosure provides mechanocaloric materials which undergo a first-order phase change. Mechanocaloric materials described herein exhibit a reversible thermal response ( / .e., a change in temperature or entropy) caused by a pressure-induced first- order phase change. The first-order phase change may be a transition from a solid crystalline phase to a plastic crystal phase; a transition between two different plastic crystal phases; or a transition between two solid crystalline phases. Preferably, the mechanocaloric materials described herein have a crystalline phase and a plastic crystal phase. Preferably, the difference in the phase transition temperatures between a first to a second phase transition and the reverse second to first phase transition is no more than about 20°C, more preferably no more than about 10°C. Optionally, the mechanocaloric compound has a plurality of phase changes, each phase change occurring at a different pressure. A cumulative mechanocaloric effect may be obtained by subjecting these materials to a pressure change sufficient to induce at least two of the phase changes. Preferably, the additive mechanocaloric effect (change in temperature or change in entropy) across the phase changes is greater than the mechanocaloric effect of a single phase change. Mechanocaloric materials as described herein may be used in a heat transfer method in which pressure is applied to the mechanocaloric material sufficient to induce a phase change in the mechanocaloric material resulting in one of heat being released by the material (mechanocaloric effect) or heat being absorbed by the material (inverse mechanocaloric effect). Reduction of pressure sufficient to induce a reversal of this phase change results in the other of heat release by the material or heat absorption by the material. Mechanocaloric materials as described herein may be used in a barocaloric method in which hydrostatic pressure is applied to the material or in an elastocaloric method in which a uniaxial pressure is applied to the material. References to a "pressure" herein includes both a hydrostatic pressure and a uniaxial pressure unless specifically stated otherwise. The mechanocaloric compounds described herein are in the solid state at the operating temperature and pressure. It will be understood that the operating temperature will depend on the temperature of the environment in which the mechanocaloric material is used, and the mechanocaloric material may be selected accordingly. The pressure applied to a mechanocaloric compound described herein depends on the application and the operating temperature, i.e., temperature of the external environment. Optionally, the phase transition temperature is in the range of about -30-50°C, or about 10-40°C. Preferably, the pressure applied to the mechanocaloric material is less than 1,000 Bar optionally at least 1 bar. Preferably, the mechanocaloric materials described herein have a melting point of at least 200°C, preferably at least 300°C or at least 400°C at atmospheric pressure. Alkyl-Halo-adamantanes A preferred class of mechanocaloric materials are adamantanes substituted with an alkyl substituent and a halogen substituent. Preferably, the alkyl substituent and the halogen substituent are the only substituents of the adamantane. The adamantane may be, without limitation: a 1,3-disubstituted adamantane wherein the 1-position 3-position is the halogen or vice-versa; a 2,2-disubstituted adamantane; a 1,2-disubstituted adamantane wherein the 1-position 2-position is the halogen or vice-versa; a 2,4-disubstituted adamantane wherein the 2-position 4-position is the halogen or vice-versa; a 2,6-disubstituted adamantane wherein the 2-position 6-position is the halogen or vice-versa; or a 1,4-disubstituted adamantane wherein the 1-position 4-position is the halogen or vice-versa. is the alkyl group and the is the alkyl group and the is the alkyl group and the is the alkyl group and the is the alkyl group and the l-alkyl-3-halo-adamantanes, adamantanes are preferred. l-halo-3-alkyl-adamantanes and 2-alkyl-2-halo The halogen may be F, Br, Cl or I, preferably F, Cl or Br in the case where the alkyl and halo substituents are provided on different C atoms of the adamantane, and preferably F or Cl in the case where the alkyl and halo substituents are provided on the same C atom of the adamantane. The alkyl may be a Ci-6 alkyl group, preferably a methyl group. Adamantane-diones A preferred class of mechanocaloric materials are adamantane-diones. Exemplary adamantane diones are adamantane-2,6-dione and adamantane-2,4-dione. Preferably, the ketone groups are the only substituents of the adamantane dione. Without wishing to be bound by any theory, the reduction in symmetry (including symmetry axes, planes of symmetry and rotation-reflection axes) due to the presence of two or more substituents as compared to no or only one substituent may increase the magnitude of entropy change between phases, in particular crystalline and plastic crystal phases. Applications A mechanocaloric cycle includes: application of pressure to the mechanocaloric material resulting in one of (i) absorption of heat by the mechanocaloric material and (ii) release of heat from the mechanocaloric material; and reduction or removal of the pressure resulting in the other of (i) absorption of heat by the mechanocaloric material and (ii) release of heat from the mechanocaloric material. In some applications, the absorbed or released heat may be transferred away from the mechanocaloric material to provide heating or cooling, for example heating or cooling for an air conditioning unit or a refrigerator. Heat may be transferred using any known heat transfer fluid. Figure 1 illustrates barocaloric apparatus 100 arranged to cycle a barocaloric material between a high-pressure state and a low-pressure state. The apparatus comprises a pressure vessel 101 containing a fluid, more preferably a liquid, in which a barocaloric material 105 is dispersed. The fluid may be selected according to its compatibility with the mechanocaloric material; in particular, the fluid is suitably inert to the mechanocaloric material and the mechanocaloric material is suitably insoluble in the fluid at the operating temperature and pressure ranges of the apparatus. Exemplary fluids include, without limitation, water, alcohols and mixtures thereof; and oils. The barocaloric material may be in any suitable form, for example a powder dispersed in the fluid. The apparatus comprises a mechanism 103, such as a piston, arranged to apply a hydrostatic pressure to the barocaloric material 105; and a heat transfer loop 107 arranged for flow of a heat transfer fluid into and out of the pressure vessel and including a heating element 109 and a cooling element 111. In the case of a material exhibiting the barocaloric effect, the temperature of the barocaloric material 105 increases upon application of hydrostatic pressure sufficient to induce a phase change of the barocaloric material, heating a heat transfer fluid in the heat transfer loop 107. The applied hydrostatic pressure is preferably less than 1000 Bar. Heated fluid is delivered by a first valve arrangement 113 from the pressure chamber 101 to a heating element 111 and then returned via a second valve arrangement 115 to the pressure chamber 101. The temperature of the barocaloric material reduces upon reduction of pressure sufficient to induce a phase change of the barocaloric material, cooling the heat transfer fluid flowing through the pressure chamber 101 in the heat transfer loop 107. Cooled fluid is delivered by the first valve arrangement 113 from the pressure chamber 101 to a cooling element 109 and then returned via the second valve arrangement 115 to the pressure chamber. The operation of the apparatus of Figure 1 is described above with reference to the barocaloric effect. It will be understood that the apparatus may also be used with a material exhibiting the inverse barocaloric effect. Figure 1 illustrates apparatus in which heating or cooling is achieved through the barocaloric or inverse barocaloric effect. The same apparatus may be used for heating or cooling using an elastocaloric material in which pressure vessel 101 and mechanism 103 are replaced with a container for containing the elastocaloric material a mechanism arranged to apply uniaxial pressure to the elastocaloric material. The heat transfer loop 107 may form a coil within the pressure chamber. The heating element 111 may be in the form of a coil. The cooling element 109 may be in the form of a coil. The mechanocaloric apparatus may be used to provide cooling in any object requiring cooling, for example a refrigerator or an air conditioner. The mechanocaloric apparatus may be used in any object requiring heating, for example a radiator. In some applications, the absorbed heat may be stored. Mechanocaloric materials as described herein may also be used in thermal batteries in applications such as waste heat management. In these applications, heat may be absorbed during a pressure-induced endothermic phase transition and delivered by a pressure-induced exothermic phase transition. EXAMPLES Differential scanning calorimetry (DSC) was performed for various compounds as shown in Tables 1 and 2. DSC measurements were performed on a Perkin Elmer DSC8500 using l-5mg of the compound and a scan rate of 5°C I minute. The hysteresis value of a compound as given herein is the difference between the heating and cooling peak values taken from the compound's DSC measurements. 5 As set out in Table 1, 2-bromoadamantane provides a large (>100 J / K / Kg) entropy change arising from a phase transition, however this material also has a large (>10K) hysteresis. 2-methyladamantane does not show any phase transition without elevated (9 kbar) pressure as disclosed in Kimihiko Hara et al, "Pressure-induced phase transition in 2-10 methyladamantane and 2-bromoadamantane", Chemistry Letters, Volume 9, Issue 7, July 1980, Pages 803-806. In contrast, each of 2-bromo-2-methyl adamantane and 2-chloro-2-methyl adamantane provides both a large entropy change and a small hysteresis. Table 1 Compound Mp(K) Heating (K) Cooling (K) Hysteresis (K) Entropy change (JK-lKg-1) Adamantane 543 209 207 2 118 2-Bromo-Adamantane 413 272 259 13 185 2-Chloro-Adamantane 467 242 231 11 202 2-Chloro-2-Methyl-Adamantane 440 275 273 2 199 Table 2 Compound Mp(K) Heating (K) Cooling (K) Hysteresis (K) Entropy change (JK-lKg-1) Adamantane 543 209 207 2 118 Adamantan-2-one* 523 221 178 43 250 Adamantan-2,6-dione -transition 1 596 285 260 15 40 Adamantan-2,6-dione -transition 2 316 306 10 55 5 * As reported by Ian S. Butler et al, "Differential scanning calorimetric studies of the phase transition in adamantanone", J. Chem. Soc., Faraday Trans. 2,1986,82,535-539. 10

Claims

1. A mechanocaloric method comprising altering a pressure applied to a mechanocaloric material sufficient to induce a phase change in the mechanocaloric material wherein the mechanocaloric material is an adamantane substituted with an alkyl group and substituted with a halogen.

2. The mechanocaloric method according to claim 1 wherein the alkyl group and the halogen are the only substituents of the adamantane.

3. The mechanocaloric method according to claim 1 or 2 wherein the alkyl group and the halogen group are both at the 2-position of the adamantane.

4. The mechanocaloric method according to any one of the preceding claims wherein the alkyl group is a Ci-6 alkyl group.

5. The mechanocaloric method according to any one of the preceding claims wherein the alkyl group is methyl.

6. The mechanocaloric method according to any one of the preceding claims wherein the halogen is F, Cl or Br.

7. A mechanocaloric method comprising altering a pressure applied to a mechanocaloric method sufficient to induce a phase change in the mechanocaloric material wherein the mechanocaloric material is an adamantane-dione.

8. The mechanocaloric method according to claim 7 wherein the adamantane dione is adamantane-2,6-dione or adamantane-2,4-dione.

9. The mechanocaloric method according to claim 7 or 8 wherein the ketone substituents are the only substituents of the adamantane dione10. The mechanocaloric method according to any one of the preceding claims wherein the barocaloric method is a heat transfer method.

11. The mechanocaloric method according to claim 10 wherein the heat transfer method is a cooling method.

12. The mechanocaloric heat transfer method according to claim 11 wherein the cooling method is cooling of a fluid of a refrigerator or an air conditioning unit.

13. The mechanocaloric method according to any one of claims 1-9 wherein the heat transfer method is a heating method.

14. The mechanocaloric method according to any one of claims 1-9 wherein the mechanocaloric method is a thermal storage method.

15. The mechanocaloric method according to any one of the preceding claims wherein the mechanocaloric method is a barocaloric method and the applied pressure is a hydrostatic pressure.

16. The mechanocaloric method according to any one of the preceding claims wherein the mechanocaloric method is an elastocaloric method and the applied pressure is a uniaxial pressure.s

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