Phase change materials

Abstract

An organic phase change material comprising one or more amino acids or salts thereof, colloidal silica, and water; wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 35% by weight based on the total weight of the phase change material; and wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material.

Description

[0001] PHASE CHANGE MATERIALS

[0002] Field of invention

[0003] The invention relates to phase change materials, cooling modules and systems, and uses of said modules, systems and materials.

[0004] Background of the invention

[0005] Phase change materials (PCMs) are an important class of material which can have a significant impact on the efficient use and conservation of heat and solar energy. PCMs have been used for many years in cooling, for instance in providing domestic cooling blocks, or commercial cooling such as in shipping containers. Such applications require large spaces to be kept cool over extended periods of time, and often in situations where there is no easy access to a reliable power supply (i.e. during transportation). Thus it is desirable for PCMs to have a high energy density, meaning they can absorb large amounts of energy relative to their volume. Similarly, it is desirable to have PCMs which can be charged quickly and efficiently, without the need for cooling units to be out of use for long periods. Charging, as referred to herein, is the process of reducing the temperature of phase change material such that it changes phase (i.e. freezes). Efficient charging is also a desirable property in areas which do not have access to reliable power supplies.

[0006] Given that PCMs are often used in the transport of consumables, it is also desirable that they are of food grade standard, and thus the risk of spoiling consumables due to leakage is reduced.

[0007] Currently, inorganic PCMs (e.g. PCMs using inorganic salts as the key component) are commonly used. However, these are limited in terms of their energy density and often have high supercooling leading to low charging efficiencies. Further these PCMs can be corrosive and therefore interact poorly with metal containers. This is undesirable as metals can be very efficient heat transfer materials, and are thus efficient as PCM container materials.

[0008] Thus there is a need for PCMs which have high energy density and thus a high cooling capacity; efficient charging; and compatibility with metals and consumables. Summary of the invention

[0009] The present inventors have determined that organic phase change materials comprising one or more amino acids or salts thereof, colloidal silica, and water; wherein the total amount of amino acids or salts thereof in the phase change material phase is from 1% to 35% by weight based on the total weight of the phase change material; and wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phrase change materials, have a particularly high energy density, low supercooling degree (meaning they can be charged efficiently), and are non-corrosive.

[0010] The composition of the PCM of the invention may be tuned to decrease or increase the phase change temperature such that the materials can be used for a wide range of thermal management, including cold chain logistics, air conditioning, electronics cooling, battery management, industrial cooling, off-grid cooling and other low temperature applications.

[0011] Surprisingly the present inventors have found that the interaction between colloidal silica and amino acid salts provide significant improvements on existing PCMs. In particular, the combination of colloidal silica with amino acid salts facilitates physical adsorption and charge interaction, which enhances the uniform dispersion of amino acid salts in the water phase, reducing agglomeration. Amino acid salts typically carry ionic characteristics, allowing them to interact with the surface charges of colloidal silica, thereby increasing the overall stability of the PCM and preventing precipitation and / or crystallization.

[0012] The present invention therefore provides:

[0013] [1] An organic phase change material comprising one or more amino acids or salts thereof, colloidal silica, and water; wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 35% by weight based on the total weight of the phase change material; and wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material. [2] An organic phase material according to

[0001] , wherein said material comprises less than 1% by weight inorganic salt based on the total weight of the phase change material.

[0014] [3] An organic phase change material according to [1] or [2], further comprising an antimicrobial agent in an amount of 0.1% to 10% by weight based on the total weight of the phase change material.

[0015] [4] An organic phase change material according to any one of [1] to [3], wherein the one or more amino acids or salts thereof are selected from glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine acid, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, mixtures of one or more thereof, and salts thereof.

[0016] [5] An organic phase change material according to any one of [1] to [4], wherein the one or more amino acids or salts thereof are selected from alanine, glycine, threonine, glutamine, glutamic acid, lysine, cysteine, arginine, histidine, serine, and tyrosine, mixtures thereof, and salts thereof.

[0017] [6] An organic phase change material according to any one of [1] to [5], wherein the one or more amino acids or salts thereof are selected from alanine, glycine, threonine, cysteine, glutamine and threonine, mixtures thereof, and salts thereof.

[0018] [7] An organic phase change material according to any one of [1] to [6], wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 25% by weight based on the total weight of the phase change material.

[0019] [8] An organic phase change material according to any one of [1] to [7], wherein the specific surface area of the colloidal silica is from 100 m2 / g to 400 m2 / g.

[0020] [9] An organic phase change material according to any one of [1] to [8], wherein the colloidal silica is present in an amount of from 4% to 10% by weight based on the total weight of the phrase change material.

[0021]

[0010] An organic phase change material according to any one of [1] to [9], wherein the phase change material further comprises a thermal conductive additive.

[0022]

[0011] A method for preparing an organic phase change material, wherein said method comprises adding one or more amino acids or salts thereof to a suspension of colloidal silica in water.

[0023]

[0012] The method according to

[0011] , wherein the suspension of colloidal silica is prepared by adding fumed silica to water.

[0024]

[0013] The method according to

[0012] , wherein the fumed silica has an average particle diameter of from 7 nm to 5000 nm.

[0025]

[0014] The method according to

[0013] , wherein the fumed silica has an average particle diameter of from 50 nm to 1000 nm.

[0026]

[0015] A cooling module, wherein the cooling module contains an organic phase change material according to any one of [1] to

[0010] .

[0027]

[0016] A cooling module having an exterior surface, an internal space configured to contain an organic phase change material, and an open channel disposed in the exterior surface, the open channel having a substantially serpentine portion.

[0028]

[0017] The cooling module of

[0016] , wherein the cooling module is substantially cuboidal, wherein two parallel exterior surfaces of the cooling module each have a respective open channel disposed therein, each open channel having a substantially serpentine portion.

[0029]

[0018] A cooling module comprising a plurality of tubes configured to carry an organic phase change material, and at least one tube connecting fin joined to two of said tubes and configured to provide heat transfer between the respective tubes.

[0019] The cooling module of

[0018] , wherein: said tubes are at least partially contained in a housing; the module further comprises a housing connecting fin joined to one of said tubes and to said housing, and configured to provide heat transfer between the tube and the housing.

[0030]

[0020] The cooling module of

[0018] or

[0019] , wherein said two tubes each comprise a plurality of non-connecting fins, each non-connecting fin having a single end joined to the respective tube.

[0031]

[0021] The cooling module of any of

[0018] to

[0020] , wherein at least one of said fins is a substantially flat plate.

[0032]

[0022] The cooling module according to any one of

[0015] to

[0021] , wherein the module is formed of metal or plastic.

[0033]

[0023] A cooling system comprising one or more cooling modules according to any one of

[0015] to

[0022] ,

[0034]

[0024] The cooling system of

[0023] , wherein the system comprises a plurality of modules according to any one of

[0015] to

[0017] , the modules being disposed parallel to each other within a housing.

[0035]

[0025] Use of a cooling module or system according to any one of

[0015] to

[0024] , or an organic phase change material according to any one of [1] to

[0010] , as a cooling means in a refrigeration system.

[0036]

[0026] A method of cooling, maintaining the temperature, or reducing the rate of temperature increase in a defined space, wherein said method comprises providing a module according to any one of

[0015] to

[0022] in said defined space.

[0027] A method of charging a module according to any one of

[0015] to

[0022] , wherein said method comprises reducing the temperature of said module, preferably wherein said temperature reduction causes the organic phase change material to freeze.

[0037]

[0028] A method according to

[0027] , wherein said method uses a cooling means powered by renewable energy, preferably powered by solar energy.

[0038] Brief description of the figures

[0039] The invention will now be described, by way of non-limitative examples only, with reference to the following drawings and figures, in which:

[0040] Figure 1 shows an exemplar structure of a gel-like composite formed by colloidal silica as, wherein a) shows the chemical structure, and b) shows an image of an exemplar structure;

[0041] Figure 2 shows a) the surface structure of hydrophobic silica, and b) the surface structure of hydrophilic silica;

[0042] Figure 3 shows a cooling module according to the present invention;

[0043] Figure 4 shows a cooling system comprising a plurality of cooling modules as shown in in figure 3;

[0044] Figure 5 shows a comparative example cooling module;

[0045] Figure 6 shows relative convention heat transfer coefficient for the cooling modules shown in figures 3 and 5;

[0046] Figure 7 shows a perspective view of a further arrangement of cooling module according to the present invention; and

[0047] Figure 8 shows a plan view of the arrangement of figure 7.

[0048] Figure 9 shows a schematic of the process for formulating a composite PCM

[0049] Figure 10 shows silica dispersions created using fumed silica with an average particle diameter as displayed on the bottle;

[0050] Figure 11 shows the different charging rates of PCMs comprising different sizes of fumed silica, with % crystallinity on the y-axis, and sample holder temperature on the x- axis. Figure 12 shows scanning electron microscopy images of a) fumed silica with an average diameter of 200 to 300 nm, b) a composite PCM formed of fumed silica with an average diameter of 200 to 300 nm, c) fumed silica with an average diameter of 7 nm, d) a composite PCM formed of fumed silica with an average diameter of 7 nm;

[0051] Figure 13 shows differential scanning calorimetry assessments of a) Table 1, Sample 3 (glycine 18.4 wt%), b) Table 2, Sample 6 (serine 18.00 wt%; glutamine 3.50 wt%, threonine 0.90 wt%), c) Table 1, Sample 4 (alanine 2.68 wt%), d) Table 2, Sample 5 (alanine 1.80 wt%; glutamine 0.80 wt%; threonine 1.10 wt%), e) Table 1, Sample 1 (glycine 2.25 wt%), and f) Table 2, Sample 1 (glycine 2.00 wt%; alanine 0.10 wt%; serine 0.13 wt%). Each diagram shows two charging and discharging cycles.

[0052] Figure 14 depicts the experimental set-up for assessing the charging and discharging process of a phase change material, as described in Example 4.

[0053] Figure 15 depicts the charging and discharging process of a PCM of Example 4, with temperature on the y-axis, and time on the x-axis. When the line is roughly parallel to the x-axis, this indicates a phase change.

[0054] Detailed description of the invention

[0055] Definitions

[0056] A phase change material is a material which releases or absorbs a high amount of energy at a phase transition, i.e. has a high energy density or energy capacity at the phase transition, such as greater than 100 kJ / kg. Phase change materials are therefore useful in cooling or heating applications as they can maintain their phase transition temperature for a long period of time while absorbing energy or releasing energy into its surrounding.

[0057] Energy capacity, or energy density refers to the amount of energy which can be stored by a material per unit volume. A high energy density means that a large amount of energy (e.g. thermal energy) can be absorbed by a small volume of material.

[0058] Phase change temperature is the temperature at which a material transitions from one state of matter to another. For example, a phase change temperature may be the temperature at which a material transitions from liquid / gel to solid (i.e. freezing or crystallisation), or the temperature at which a material transitions from a solid to a liquid / gel (i.e. melting). Supercooling degree or supercooling temperature as referred to herein relates to the difference between the temperature needed to charge (i.e. freeze) the material and the temperature at which a material is discharged (i.e. melts). The lower the supercooling temperature the more efficient a PCM is, as less excess energy is needed to cool the material below its discharge temperature. A lower supercooling temperature can also increase a PCM charging rate, and therefore decrease the charging time. As a representative example, a decrease in supercooling temperature from 5°C to 0.5°C could increase the energy efficiency of the charging process by up to 90%.

[0059] Charging, as referred to herein, is the process of reducing the temperature of phase change material such that it changes phase (i.e. freezes). The solid phase change material then has the capacity to absorb large amounts of energy from its surroundings while maintaining a constant temperature. Discharging of the PCM occurs as the temperature increases and is discharge is complete once the PCM temperature has increased such that it has undergone a phase transition from solid to liquid. The PCM may then be recharged. Recharging may occur either after complete discharge of the PCM, or after partial discharge (i.e. when the PCM has not fully changed to liquid phase)

[0060] Cycling is the name given to the process of charging and discharging of a phase change material. For example, one cycle includes charging of the phase change material and use or discharge, such that it needs charging again. The next cycle then comprises recharging and a second use or discharge of the phase change material.

[0061] An organic phase change material as used herein refers to a phase change material that has organic substances or materials as its major component (i.e. more than 50% by weight), although some amounts of inorganic material, e.g. inorganic salts, may be present. Typically, an organic phase change material comprises less than 15% by weight inorganic salt based on the total weight of the material. An organic phase change material may therefore comprise less than 10%, less than 5%, less than 2%, less than 1% or less than 0.1% inorganic salt by weight based on the total weight of the phase change material. Preferably an organic phase change material as described herein comprises from 0% to 5% inorganic salt, or more preferably from 0% to 1% inorganic salt based on the total weight of the phase change material. Typically, an organic phase change material comprises from 0% to 0.1% inorganic salt by weight based on the total weight of the phase change material. The organic phase change material of the invention may comprise substantially no inorganic salt (i.e. less than 0.01% by weight, or no inorganic salt).

[0062] An inorganic salt may be any inorganic salt, or a mixture of inorganic salts. Inorganic salts as referred to herein do not include salts of organic compounds, e.g. salts of amino acids. An inorganic salt typically does not contain any C-H bonds. Typically an inorganic salt is an alkali metal or alkali earth metal salt, such as a sodium salt, a magnesium salt, a potassium salt or a calcium salt. An inorganic salt may be a carbonate, a bicarbonate, a phosphate, a sulfate, a sulphite, a halide (e.g. a fluoride, a chloride, a bromide or an iodide) or an oxide. For example, an inorganic salt may be sodium chloride. Therefore an organic PCM as described herein may comprise less than 5% by weight sodium chloride by total weight of the PCM, preferably less than 1% by weight sodium chloride by total weight of the PCM, such as less than 0.5% by weight sodium chloride based on the total weight of the PCM.

[0063] An amino acid, as described herein, may be any amino acid. Typically the amino acid is a naturally occurring amino acid (i.e. glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine acid, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, and histidine).

[0064] Colloidal silica, as described herein, is a suspension of silica particles in a liquid phase. Typically said silica particles are substantially spherical, for example, spherical. The liquid suspension may be an aqueous suspension. Therefore, colloidal silica may be silica suspended in water.

[0065] Organic Phase Change Material

[0066] The organic phase change material (“PCM”) of the invention comprises one or more amino acids or salts thereof, colloidal silica, and water. The organic phase change material comprises one or more amino acids or salts thereof, colloidal silica and water, in defined weight percentages and concentrations. The % by weight of each component is described herein with reference to the total weight of the phase change material.

[0067] Thus the present invention provides an organic phase change material comprising one or more amino acids or salts thereof, colloidal silica, and water; the one or more amino acids or salts thereof are present in an amount of from 1% to 35% by weight based on the total weight of the phase change material; and wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material.

[0068] An organic phase change material has the advantage of being less abrasive than similar materials comprising greater amounts of inorganic salt. The present inventors have found that the less abrasive material means that modules (such as those described herein) comprising an organic phase change material of the present invention can experience longer usage lifetimes, as they are not subject to abrasion from the PCM. In particular, the present inventors have found that the present PCM provides a significant reduction in abrasion of metals and metal alloys compared to materials comprising larger amounts of inorganic salts. This means that metal and metal alloys modules and units comprising the PCM of the invention may have significantly elongated lifetimes, need less regular maintenance, and modules need replacement less frequently.

[0069] The reduction in abrasion facilitates the use of metal and metal alloys as the modules for containing the phase change material. This is beneficial, as these materials are typically very good thermal conductors. This makes them ideal materials for creating modules designed to transfer or conduct heat (i.e. to cool objects, such as to refrigerate consumables).

[0070] The one or more amino acids are typically one or more naturally occurring amino acids. The one or more amino acids may be selected from glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine acid, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, and mixtures of one or more thereof. Often, the one or more amino acids may be selected from alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine acid, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, and mixtures of one or more thereof.

[0071] Typically, the one or more amino acids may be selected from alanine, glycine, threonine, glutamic acid, lysine, arginine, histidine, serine, and tyrosine, and mixtures thereof. Often, the one or more amino acids may be selected from alanine, threonine, glutamic acid, lysine, arginine, histidine, serine, and tyrosine, and mixtures thereof. Such amino acids are typically used due to their good solubility in water. The amino acid concentration in the PCM of the invention can be used to control the phase change temperature. Good solubility of amino acids used means that the concentration can easily be adjusted without saturation, leading to flexibility in terms of variation in phase change temperature.

[0072] The amino acid may be provided as a free acid or in the form of a salt. References herein to the amino acid include the amino acid either in free acid or salt form, unless otherwise specified. An amino acid salt is an organic salt (i.e. not an inorganic salt). Often the salt is an alkali metal or alkali earth metal salt, such as a sodium, calcium, potassium or magnesium salt, which can significantly improve the phase change temperature of PCMs. For example, a 5% glycine-1% NaCl solution as a PCM has a phase transition temperature of -5.94 °C, a latent heat of phase change (AH) of 291.15 J / g, and a thermal conductivity of 0.58 W / (m-K). These chloride solutions can effectively adjust and optimize the phase change temperature while enhancing the thermal conductivity, contributing to more efficient thermal energy storage and release.

[0073] Typically, the one or more amino acids include less than 5% glycine, such as less than 3% glycine, such as no glycine.

[0074] In some preferred embodiments, the one or more amino acids consist of threonine, alanine, glycine, serine, cysteine, glutamine and mixtures thereof. More preferably the one or more amino acids consist of threonine, alanine, serine, cysteine, glutamine and mixtures thereof.

[0075] The one or more amino acids or salts thereof are present in the PCM in an amount of from 1% to 35% by weight based on the total weight of the PCM. Preferably, the one or more amino acids or salts thereof are present in the PCM in an amount of from 1% to 25% by weight based on the total weight of the PCM, such as from 1% to 20%, from 1% to 15% or preferably from 1% to 5%. The one or more amino acids or salts thereof in the PCM are preferably present in an amount of from 1% to 25% by weight of the total weight of the PCM, with the proviso that, when one of the amino acids (or the only amino acid) is glycine, the glycine is present in an amount of less than 5%, preferably less than 3% by weight of the total weight of the PCM.

[0076] The one or more amino acids or salts thereof may be one amino acid or salt thereof, such as one amino acid selected from glycine, alanine, cysteine, glutamine, serine and threonine. Typically, one amino acid may be selected from alanine, cysteine, glutamine, serine, and threonine. Often, when there is one amino acid it is present in the PCM in an amount of from 1% to 35% by weight based on the total weight of the PCM. Preferably, when there is one amino acid it is present in the PCM in an amount of from 1% to 25% by weight based on the total weight of the PCM, such as from 1% to 20%, from 1% to 15% or preferably from 1% to 5%. When there is only one amino acid in the PCM it is preferably present in an amount of from 1% to 25% by weight of the total weight of the PCM, with the proviso that, when there is only one amino acid present and the amino acid is glycine, glycine is present in an amount of less than 5%, preferably less than 3% by weight of the total weight of the PCM. Alternatively, if there is one amino acid present and it is glycine it may be present in an amount of greater than 17% by weight, preferably greater than 20% by weight based on the total weight of the PCM.

[0077] When the one or more amino acids or salts thereof are more than one amino acid or salt thereof, it is typically a mixture of two or more amino acids or salts thereof, and more typically a mixture of three amino acids or salts thereof. For example, the PCM may comprise exactly three amino acids selected from glycine, alanine, serine, cysteine, glutamine and threonine. When there is more than one amino acid present in the PCM the total amount of all amino acids in the PCM is typically from 1% to 35% by weight based on the total weight of the PCM. Preferably, when there is more than one amino acid present in the PCM the total amount of all amino acids in the PCM is typically from 1% to 25% by weight based on the total weight of the PCM, such as from 1% to 20%, from 1% to 15%, 3% to 15%, or preferably from 1% to 5%. The more than one amino acids or salts thereof may be present in any combination and in any ratio. Often, however, the amount of glycine present is less than 5% by weight based on the total weight of the PCM, such as less than 3%, or there is no glycine. Alternatively, the amount of glycine present may be greater than 17% by weight, such as greater than 20% by weight based on the total weight of the PCM. Some preferred combinations of amino acids include glycine, alanine and serine; cysteine, glutamine and threonine; alanine, glutamine and threonine; and serine, glutamine and threonine.

[0078] In some embodiments, the PCM comprises a first amino acid or salt thereof in an amount of from 10% to 20% by weight based on the total weight of the PCM (typically 12% to 18%), a second amino acid or salt thereof in an amount of from 1% to 4% by weight based on the total weight of the PCM (typically from 1.7% to 3.5%), and a third amino acid or salt thereof in an amount of from 0.5% to 1% based on the total weight of the PCM (typically from 0.7% to 0.9%). Alternatively, the PCM may comprise a first amino acid or salt thereof in an amount of from 1% to 3% by weight based on the total weight of the PCM (typically from 1.8% to 2%), a second amino acid or salt thereof in an amount of from 0.05% to 1% by weight based on the total weight of the PCM (typically from 0.1% to 0.8%), and a third amino acid or salt thereof in an amount of from 0.05% to 1.5% by weight based on the total weight of the PCM (typically from 0.13% to 1.1%).

[0079] The first amino acid is typically selected from glycine, cysteine, alanine or serine, preferably cysteine, alanine or serine. The second amino acid is typically selected from alanine or glutamine. The third amino acid is typically selected from serine or threonine. Typically each of the amino acids are different. Therefore if, for example, the first amino acid is selected as serine, the third amino acid will typically be threonine.

[0080] The PCM as described herein, comprising a combination of amino acids and colloidal silica is defined amounts, has been found to improve energy storage capacity, supercooling and cycling performance of the PCMs. As discussed above, each of these properties are extremely desirable for PCMs.

[0081] In particular, the present inventors have found that, while the typical supercooling degree of a PCM using an inorganic salt is around 10°C, the organic based PCMs of the invention can have supercooling degree of below 1.5°C. Thus the charging of the organic PCMs is much more efficient.

[0082] Also, the energy density / energy storage capacity of organic PCMs of the invention has been found to be nearly 15% higher than inorganic PCMs. Similarly, the charging efficiency of inorganic PCMs may be up to around 35% lower, and the charging rate may be around 60% slower. Increased energy density / storage capacity, means that the PCMs of the invention are suitable for use in smaller, e.g. portable, modules. This means that when PCMs of the invention are used in a cooling system, they do not take up too much space, so there is more space in storage containers for products which are actually being cooled.

[0083] Further, the invention is beneficial in terms of health risks and environmental safety. Compared with toxic inorganic salts, the amino acid containing PCMs of the invention are much safer in terms of concerns around their proximity with consumables.

[0084] The composition of the phase change material determines the phase change temperature. Variation of the amounts of amino acid may therefore be used to alter the phase change temperature. Usually, increasing the concentration of amino acid will lower the phase change temperature. Thus, PCMs with a concentration of amino acid from 4 mol / L to 10 mol / L, often from 4 mol / L to 6 mol / L, e.g. about 25 to 35 weight% amino acid, have a phase change temperature of from -60°C to -40°C. Such a phase change temperature may be desirable for transportation of sensitive organic material, such as biobased vaccines (e.g. mRNA vaccines) or research materials such as ice cores.

[0085] Typically, the phase change temperature of the PCMs described herein may vary between -60°C to 10°C, typically -50°C to 0°C, or typically -30°C to 10°C. In some embodiments the PCMs described herein may preferably have a phase change temperature of -30°C to 10°C, such as -30°C to 0°C.

[0086] When the storage temperature is desirably from -30°C to -10°C the total amount of amino acids or salts thereof in the phase change material may preferably be from 10% to 25% by weight based on the total weight of the PCM.

[0087] When the storage temperature is desirably from -10°C to 10°C the total amount of amino acids or salts thereof in the phase change material may preferably be from 1% to 10% by weight based on the total weight of the PCM.

[0088] While increasing the concentration of amino acid in the PCM decreases the phase change temperature, it may also increase the supercooling temperature. Thus the PCMs of the invention are carefully designed to provide optimal phase change temperatures without sacrificing the low supercooling degree. Therefore, in one preferred embodiment, the one or more amino acids or salts thereof are present in an amount of 25% of less by weight of the total weight of the phase change material.

[0089] The silica may be provided as a suspension of fumed silica in water (i.e. colloidal silica). Silica acts as a nucleating agent for crystallisation of the salts present in the phase change solution. It also acts as a thickener to increase the viscosity of the solution. Fumed silica is beneficial as it provides good stability once in suspension and a reduced tendency to settle out of the solution. Silica also has a dual role as both nucleating agent and thickener, which is beneficial to provide a simple and easy to manufacture PCM, which does not require multiple additives.

[0090] In existing PCMs, borax is commonly used as a nucleating agent. Borax is highly toxic, and thus difficult to handle during manufacture. It also can make the PCMs it is used for unsuitable for use in the food industry, and a broken PCM module could leak toxic material. The thickening role of silica means that fewer thickening additives such as carboxymethyl cellulose are needed in the PCMs of the invention. A high amount of additional thickener can decrease the energy storage density of a PCM significantly. Thus in some embodiments, the PCM of the invention includes less than 5 wt% additional thickening agent based on the total weight of the PCM, typically less that 2 wt%, and more typically no additional thickening agent is included in the PCM.

[0091] Silica also has a long-life, and provides long-term suspension stability, which is important as PCM-containing elements may be in use for long periods of time.

[0092] Preferably, hydrophilic silica is used. Hydrophilic silica is preferable as silica particles with a hydrophilic surface may bridge with other silica particles, for example via hydrogen bonding. This creates a more stable, gel like composite than similar materials. An exemplar structure of the composite is shown in Figure 1. Hydrophilic silica refers to silica particles with a hydrophilic surface, and in particular to silica with a surface capable of forming hydrogen bonds. For example the surface of hydrophobic silica comprises a higher proportion of bridged silica (see e.g. Figure 2a), whereas the surface of hydrophilic silica may comprise a higher proportion of hydroxyl groups (see e.g. Figure 2b). It has been found that hydrophobic silica does not dissolve in water, or only a very small portion dissolves after ultrasonic agitation and stirring. Further, measurements indicate that if a small portion does dissolve, this small amount of silica does not affect the overall characteristics of the PCM.

[0093] In the method of the invention, the colloidal silica (which may be fumed silica following treatment, or commercially available colloidal silica) may have an average particle diameter of from 0.1 nm to 5000 nm, such as 0.1 nm to 1000 nm. For example the average particle diameter may be from 0.1 nm to 100 nm, such as from 1 nm to 100 nm, typically from 5 nm to 100 nm, or preferably from 10 nm to 50 nm. In some preferred embodiments, the average particle diameter of the colloidal silica may be from 5 nm to 200 nm, such as from 10 nm to 80 nm, or preferably from 10 nm to 50 nm. Often the average particle diameter is from 5 nm to 100 nm, preferably from 10 nm to 50 nm. Average particle diameter is measured using Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM), both of which provide high-resolution imaging for precise particle size analysis. In the method of the invention, the colloidal silica may have a specific surface area of from 10 m2 / g to 1000 m2 / g, such as 50 m2 / g to 1000 m2 / g. For example the average particle diameter may be from 50 m2 / g to 600 m2 / g, such as from 50 m2 / g to 500 m2 / g, typically from 80 m2 / g to 500 m2 / g, or preferably from 100 m2 / g to 400 m2 / g. In some preferred embodiments, the specific surface area of the colloidal silica may be from 80 m2 / g to 600 m2 / g, such as from 100 m2 / g to 400 m2 / g, 150 m2 / g to 350 m2 / g, or preferably from 200 m2 / g to 300 m2 / g. Preferably the specific surface area is from 100 m2 / g to 400 m2 / g. Specific surface area is measured using BET (Brunauer-Emmett-Teller) method.

[0094] Typically, the colloidal silica used has a specific surface area of at least 10 m2 / g, preferably at least 50 m2 / g, preferably at least 80 m2 / g, more preferably at least 100 m2 / g.

[0095] Typically, the colloidal silica used has a specific surface area of up to 1000 m2 / g, preferably up to 600 m2 / g, more preferably up to 500 m2 / g, such as 400 m2 / g.

[0096] In some embodiments the silica particles of the colloidal silica suspension are joined together in a web-like structure.

[0097] The present inventors have surprisingly found that introduction of colloidal silica in a PCM, as described by the present invention, can increase the charging rate of the PCM, thus reducing the time required between uses. The inventor have further found that increasing the average particle diameter of the colloidal or fumed silica used to produce a compound of the invention can further increase the charging rate of the PCM.

[0098] The inclusion of colloidal silica in a PCM, as described herein, has also been found by the present inventors to decrease the supercooling temperature of the PCM. As discussed above, a low supercooling degree is desirable as this means that less energy is required to reduce the temperature below the phase change temperature, thus making the PCM more efficient. As shown in Example 2, a PCM with colloidal silica may have a stable supercooling temperature over many charge / discharge cycles. In some embodiments, the colloidal silica is formed of fumed silica. Further, the present inventors have shown that by increasing the average particle diameter of the fumed silica used to produce the colloidal silica used in the invention can also reduce the supercooling temperature, with PCMs maintaining this reduced temperature for many cycles.

[0099] Therefore the fumed silica used (before treatment) typically has a diameter of at least 1 nm, preferably at least 10 nm, preferably at least 50 nm, more preferably at least 100 nm. When the fumed silica used has an average particle diameter which is too large, the silica may be unable to form a stable suspension in gel, and thus the benefits of silica in the PCM cannot be enjoyed.

[0100] Therefore the fumed silica used (before treatment) typically has a diameter of up to 20000 nm, preferably up to 10000 nm, more preferably up to 2000 nm, such as 1000 nm, or 600 nm.

[0101] Overall, the fumed silica (before treatment) may have an average particle diameter of from 1 nm to 5000 nm, such as 7 nm to 5000 nm. For example the average particle diameter may be from 5 nm to 2000 nm, such as from 50 nm to 1000 nm, typically from 50 nm to 1000 nm, or preferably from 50 nm to 400 nm. In some preferred embodiments, the average particle diameter of the fumed silica may be from 50 nm to 600 nm, such as from 100 nm to 400 nm, 150 nm to 350 nm, or preferably from 200 nm to 300 nm. Often the average particle diameter is from 50 nm to 400 nm, preferably from 100 nm to 400 nm. Most preferably the fumed silica has an average particle diameter of from 200 to 300 nm. Average particle diameter is measured using Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM), both of which provide high-resolution imaging for precise particle size analysis. Preferably food grade silica is used, which minimises any potential toxicity concerns in the event of leakage of the phase change material from a module in which it is used.

[0102] Colloidal silica is present in the PCM in an amount of from 1 to 35% by weight, preferably in an amount of from 1% to 25 %, 1% to 20%, 1% to 15%, 1% to 10%, 2% to 10% or 4% to 10% by weight. More preferably, the colloidal silica is present in the phase change material in an amount of from 2% to 10%, typically from 2% to 8% by weight. The colloidal silica may be present in the phase change material from 2% to 4% by weight. The colloidal silica may be present in the phase change material from 2% to 8% by weight, such as from 6% to 8% by weight. In some preferred embodiments, the colloidal silica may be present in the phase change material from 5% to 10% by weight, preferably from 6% to 8%.

[0103] The present inventors have found that if the percentage weight of colloidal silica in the PCM is less than as described above, the viscosity and nucleating effects of the silica are weakened. However, if the amount is higher, the energy storage density of the PCM decreases and the silica is not soluble. The present inventors have found that the percentage weight as specified in the present invention provides a good balance of the benefits of high energy storage density, desirable viscosity, low supercooling, and high charging rate. For example, increasing the percentage weight of silica by around 10%, has been found to decrease the energy storage capacity by up to 20%, and reduce charging rate by up to 50%.

[0104] Silica acts as a thickener in the PCM. In some embodiments, no further thickener is included in the PCM. However, a second thickener may also incorporated. The second thickener is typically a food grade thickener. Suitable food grade thickeners include carboxymethyl cellulose or salts thereof. Other suitable food grade thickeners include gelatine or starch. . The second thickener may be a combination of two or more different thickener materials, but is preferably a single thickener material. Typically a salt of carboxymethyl cellulose is used. Preferred salts are sodium, potassium, calcium and magnesium salts. Sodium salts of carboxymethyl cellulose are preferred. The second thickener is typically present in an amount of from 0.1 to 20% by weight, for example from 0.1 to 15%, 0.1 to 10% or preferably 0.1 to 5% by weight. Typically, the second thickener is present in an amount of 0.1 to 1% by weight, most preferably from 0.1 to 0.5% by weight, or from 0.2 to 0.5% by weight.

[0105] The phase change material may comprise one or more additives. The one or more additional additives may include, for example an antimicrobial agent and / or a thermally conductive agent. The nature and amount of each additive is described herein, the amounts being indicated in % by weight, with reference to the weight of the phase change material.

[0106] Therefore, in some embodiments, the PCM of the invention preferably also comprises an antimicrobial agent. The antimicrobial agent is typically water soluble. The antimicrobial agent may comprise two or more different antimicrobial materials in combination, or a single antimicrobial material. Typically, a single antimicrobial material is used.

[0107] The antimicrobial agent may comprise a biological food preservative, nisin, s- polylysine, a lactate (e.g. sodium lactate), a propionate (e.g. calcium propionate), a diacetate (e.g. sodium diacetate), a paraben, benzoic acid or a salt thereof, sorbic acid or a salt thereof, dehydroacetic acid or a salt thereof, or a mixture of one or more thereof (e.g. calcium propionate and sodium lactate). Typically salts as mentioned above, are alkali metal or alkali earth metal salts, such as sodium, magnesium, potassium or calcium salts, preferably sodium salts.

[0108] A biological food preservative, as described herein, may be any suitable biological food preservative. For example, salts of benzoic acid, i.e. benzoate salts may be used. Such salts are examples of suitable antimicrobial agents, and the antimicrobial agent may therefore comprise one or a mixture of benzoate salts. Sodium benzoate is an example of a preferred antimicrobial agent, as it is suitable for use as a preservative in PCM for food cold chain applications. Sodium benzoate is effective in inhibiting the growth of bacteria, yeast, and fungi, especially in acidic conditions. The compatibility of sodium benzoate with PCM compositions makes it a reliable choice for maintaining the safety and quality of food during cold storage. s-polylysine is a further example of a preferred antimicrobial agent, s-polylysine is a food grade additive, which means it is especially suitable for cold chain storage of consumables.

[0109] The antimicrobial agent has an antiseptic effect on the PCM. The antimicrobial agent, preferably sodium benzoate and / or s-polylysine, is preferably present in the material in an amount of 0.1% to 10% by weight, for example from 0.1% to 8% by weight, 0.1% to 5% by weight, preferably from 0.1% to 2% by weight. Preferably, the antimicrobial agent, typically sodium benzoate and / or s-polylysine, is present in the PCM in an amount of from 0.1% to 0.8% by weight, e.g. from 0.2% to 0.6% by weight, such as about 0.4% by weight.

[0110] In one preferred embodiment, the PCM therefore comprises one or more amino acids or salts thereof, colloidal silica, water, and an antimicrobial agent (typically sodium benzoate and / or £-polylysine). Typically, the PCM may comprise one or more amino acids or salts thereof, colloidal silica, water, and an antimicrobial agent; wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 35 % by weight based on the total weight of the phase change material; wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material; and wherein the antimicrobial agent is present in an amount of from 0.1% to 10% by weight based on the total weight of the phase change material.

[0111] The phase change material may additionally comprise a thermal conductive agent. A thermal conductive agent is beneficial in increasing the thermal conductivity of the

[0112] PCM, such that, for example, cooling of the PCM to force it into the solid state may occur more quickly. Indeed it has been found that the use of a thermal conductive additive can both accelerate the charging and discharging rate of a PCM. An increase to the charging rate can be especially helpful in locations with limited power supply, where there is high demand for limited energy sources. An increase to the charging rate is similarly desirable in transport, where there are quick transition times, such as the short period of time between unloading and reloading a shipping container. An increase to discharging rate can be especially desirable in the cooling of good which are quick to spoil, i.e. goods that may melt if not cooled quickly (e.g. ice cream), and goods which may spoil in heat (e.g. fresh fruit and vegetables).

[0113] Any suitable thermal conductive material, or combination of materials, may be used, including, preferably carbon materials and / or metal particles. For example, the thermal conductive agent may comprise graphite, expanded graphite, graphene, carbon nanotubes, or a combination thereof e.g. graphite or carbon nanotubes. Suitable metal particles include copper, nickel, aluminium, stainless steel, or a combination thereof. Copper has a high thermal conductivity of approximately 398 W m-1 K-l, and copper powder may be particularly effective for enhancing the thermal conductivity of PCMs. Nickel offers thermal conductivity of around 91.4 W m-1 K-l and has been shown to effectively improve heat transfer in PCM composites. Aluminum has a thermal conductivity of about 237.0 W m-1 K-l, making it suitable for improving thermal conductivity in PCM systems. Stainless Steel has a thermal conductivity of approximately 16.3 W m-1 K-l, and stainless steel powder can be suitable for applications where moderate enhancement is acceptable.

[0114] These metal powders can significantly improve the effective thermal conductivity of PCM composites and optimize the phase change period of the system. However, it should be noted that while the thermal conductivity increases, the overall latent heat of the composite may decrease due to the lack of phase change within the metal matrix itself. Additionally, the performance may be influenced by factors such as the porosity and particle size distribution of the metal powder used. Typically, the thermal conductive agent is provided in powdered form, with a particle size of 10 ~ 500nm. Typically, a single material is used as the thermal conductive agent. For example, copper (Cu) nanoparticles with a purity of 99.9% can have a diameter of around 25 nm and a specific surface area of 30-50 m2 / g may be used. These fine particle sizes provide an increased surface area, enhancing their thermal conductivity properties when incorporated into PCM composites.

[0115] The thermal conductive agent, is preferably present in the material in an amount of 0.1% to 15% by weight, for example from 2% to 10% by weight, preferably from 3% to 8% by weight. Preferably, the thermal conductive agent, is present in the PCM in an amount of from 3% to 8% by weight, e.g. from 4% to 6% by weight, such as about 5% by weight. When the thermal conductive agent is present in an amount as described herein the charging or discharging rates of the PCM may increase by up to 30%.

[0116] In one preferred embodiment, the PCM therefore comprises one or more amino acids or salts thereof, colloidal silica, water, and a thermal conductive agent. Typically, the PCM may comprise one or more amino acids or salts thereof, colloidal silica, water, and a thermal conductive agent; wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 35% by weight based on the total weight of the phase change material; wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material; and wherein the thermal conductive agent is present in an amount of from 3% to 8% by weight based on the total weight of the phase change material.

[0117] In one preferred embodiment, the PCM therefore comprises comprising one or more amino acids or salts thereof, colloidal silica, water, an antimicrobial agent (typically sodium benzoate and / or s-polylysinc), and a thermal conductive agent. Typically, the PCM may comprise one or more amino acids or salts thereof, colloidal silica, water, an antimicrobial agent, and a thermal conductive agent; wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 35% by weight based on the total weight of the phase change material; wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material; wherein the antimicrobial agent is present in an amount of from 0.1% to 10% by weight based on the total weight of the phase change material; and wherein the thermal conductive agent is present in an amount of from 3% to 8% weight based on the total weight of the phase change material.

[0118] It is preferred to minimise the number of additives present in the PCM described herein. Thus, silica is an essential element for achieving effective nucleation and thickening. An antimicrobial agent is also preferably added. A thermal conductive agent may be added, if desired. Preferably, however, the PCM consists of the organic phase change material of the invention and from two to five, more preferably from two to four additives, the additives preferably including an antimicrobial agent and / or a thermal conductive agent and / or a second thickening agent, such as an antimicrobial agent and a second thickening agent, or a thermal conductive agent and a second thickening agent, or, preferably, a antimicrobial agent and a thermal conductive agent.

[0119] In one preferred embodiment, the phase change material contains three additives, including an antimicrobial agent, a thermal conductive agent, and a second thickener.

[0120] Phase Change Material Precursor

[0121] It can be advantageous to supply the PCM in the form of a precursor, which corresponds to the PCM described herein, but is a dry material and does not contain water. This substantially reduces both the volume and weight of the material, which is beneficial in enabling cheaper and more convenient transportation. Water can be added to the precursor prior to use and shaking and / or stirring, typically shaking, is used to mix the precursor with water, thus providing a PCM as described herein.

[0122] The PCM precursor accordingly corresponds to the PCM as described herein, but in the absence of water. The dried materials are provided in the same relative ratios as described herein for the PCM, such that on addition of the appropriate amount of water, the resulting micture forms a PCM as described herein.

[0123] The precursor accordingly comprises one or more amino acids. These amino acids are typically provided in the forms of salts. Any salt may be used. Often the salt is an alkali metal or alkali earth metal salt, such as sodium, calcium, potassium or magnesium salt. The one or more amino acids or salts thereof are present in the precursor. The the amount of amino acid salts to be used in the precursor may be from 5% to 35% by weight, relative to the total weight of the precursor. This range may provide a balance between achieving optimal phase change properties and maintaining the structural integrity of the PCM. For specific applications requiring higher thermal storage capacity, a range of 10% to 25% by weight is preferred.

[0124] The precursor may alternatively contain and amino acid and a separate salt. The amino acid is present in an amount of from 5% to 35% by weight, relative to the total weight of the precursor. The salt may be present in an excess amount (15 to 40%, for example 15% to 30% by weight relative to the total weight of the precursor), to enable amino acid salt formation on mixing of the precursor with water.

[0125] The salt may be an alkali or alkaline earth metal with a suitable anion. The alkali or alkaline earth metal may preferably be sodium, calcium, potassium or magnesium. The anion may preferably be a nitrate or chloride. Preferred salts may therefore be nitrate or chloride salts of alkali or alkaline earth metals. Sodium, calcium, potassium or magnesium chlorides or nitrates may be most preferred. Nitrate salts often achieve very low phase change temperatures, providing effective thermal performance. However, considering food safety, chloride salts are generally preferred as the primary choice for use in PCMs intended for food-related applications.

[0126] The precursor additional comprises fumed silica with an average particle diameter as described herein.

[0127] The precursor may additionally comprise one or more additives, as described herein. Silica microparticles are present in the precursor in an amount of from 0.3 to 95% by weight, relative to the total weight of the one or more amino acids or salts thereof. Preferably, the silica microparticles are present in an amount of 0.5 to 75% by weight, 0.5 to 50% by weight, 0.5 to 40% by weight, or 0.5 to 20% by weight, relative to the total weight of the one or more amino acids or salts thereof. More preferably, silica microparticles are present in the precursor in an amount of from 0.5 to 4% by weight, e.g. from 0.7 to 4% by weight or from 1 to 4% by weight, relative to the total weight of the one or more amino acids or salts thereof.

[0128] The precursor preferably also comprises an antimicrobial agent. The antimicrobial agent is as described herein for the PCM. The antimicrobial agent, preferably sodium benzoate and / or s-polylysinc, is preferably present in the precursor in an amount of 0.3 to 75% by weight, for example from 0.5 to 50% by weight, 0.5 to 40% by weight, preferably from 0.5 to 20% by weight, relative to the total weight the one or more amino acids or salts thereof. Preferably, the antimicrobial agent, typically sodium benzoate, is present in the precursor in an amount of from 0.3 to 4% by weight, e.g. from 0.5 to 4% by weight, e.g. from 1 to 4% by weight.

[0129] In one preferred embodiment, the precursor comprises the one or more amino acids or salts thereof, the fumed silica and further comprises one or more additives, the additives comprising sodium benzoate and / or s-polylysinc in an amount of from 0.3 to 4% by weight relative to the total weight of the one or more amino acids or salts thereof.

[0130] The precursor may additionally comprise a thermal conductive agent (1% to 10% by weight relative to the total weight of the one or more amino acids or salts thereof). If present, the thermal conductive agent is as described herein for the PCM.

[0131] A second thickener may also be present in the precursor, the second thickener being as described herein for the PCM. The second thickener is typically present in the precursor in an amount of from 0.3 to 75% by weight, for example from 0.5 to 50%, 0.5 to 40% or preferably 0.5 to 20% by weight, relative to the total weight of the one or more amino acids or salts thereof. Typically, the second thickener is present in an amount of 0.3 to 4% by weight, from 0.5 to 4% by weight, most preferably from 0.5 to 0.4% by weight, or from 1 to 4% by weight, relative to the total weight of the one or more amino acids or salts thereof.

[0132] In some embodiments, the precursor consists of one or more amino acids or salts thereof, fumed silica and from one to five, preferably two, three or four, additives, the additives including an antimicrobial agent, as described herein. Most preferably, the precursor consists of one or more amino acids or salts thereof, fumed silica, an antimicrobial agent and optionally a thermal conductive agent, as described herein.

[0133] The precursor can be produced simply by mixing the dry materials. The precursor may optionally be compressed.

[0134] Preparation method for the PCM

[0135] The present invention also provides a method for preparing an organic phase change material.

[0136] Typically the method comprises adding one or more amino acids or salts thereof to a colloidal suspension of silica in water.

[0137] The colloidal silica may be initially provided in the form of colloidal silica. In such instances the colloidal silica may have a specific surface area of from 10 m2 / g to 1000 m2 / g, such as 50 m2 / g to 1000 m2 / g. For example, the average particle diameter may be from 50 m2 / g to 600 m2 / g, such as from 50 m2 / g to 500 m2 / g, typically from 80 m2 / g to 500 m2 / g, or preferably from 100 m2 / g to 400 m2 / g. In some preferred embodiments, the specific surface area of the colloidal silica may be from 80 m2 / g to 600 m2 / g, such as from 100 m2 / g to 400 m2 / g, 150 m2 / g to 350 m2 / g, or preferably from 200 m2 / g to 300 m2 / g. Preferably the specific surface area is from 100 m2 / g to 400 m2 / g. Specific surface area is measured using BET (Brunauer-Emmett-Teller) method.

[0138] The colloidal silica may be commercially available silica, for example LUDOX® LS colloidal silica.

[0139] The method may further comprise a step of preparing the colloidal suspension of silica. For example, the method may comprise adding fumed silica to water.

[0140] Therefore, in some embodiments, the methods comprises:

[0141] - forming a colloidal suspension of silica in water;

[0142] - adding one or more amino acids or salts thereof to the mixture.

[0143] Alternatively, the method may comprise adding colloidal silica to water to form a colloidal suspension. In such embodiments, the method may comprise: adding colloidal silica to water; adding one or more amino acids or salts thereof to the mixture.

[0144] In the method of the invention, the steps of adding colloidal silica to water, and adding one or more amino acid salts to water may be carried out in any order.

[0145] Optionally, such a method may comprise a further step of mixing the colloidal silica in the water, and / or mixing the mixture of colloidal silica, water and one or more amino acids or salts thereof. The mixing may occur using any suitable method such as manually, using a magnetic stirrer, vortex mixer, ball mill mixer.

[0146] In the method of the invention, the colloidal silica may have an average particle diameter of from 0.1 nm to 5000 nm, such as 0.1 nm to 1000 nm. For example the average particle diameter may be from 0.1 nm to 100 nm, such as from 1 nm to 100 nm, typically from 5 nm to 100 nm, or preferably from 10 nm to 50 nm. In some preferred embodiments, the average particle diameter of the colloidal silica may be from 5 nm to 200 nm, such as from 10 nm to 80 nm, or preferably from 10 nm to 50 nm. Often the average particle diameter is from 5 nm to 100 nm, preferably from 10 nm to 100 nm, preferably from 10 nm to 50 nm. Average particle diameter is measured using Transmission Electron Microscopy (TEM). TEM allows for direct observation and accurate measurement of particle size distribution by capturing high-resolution images of the colloidal silica particles, enabling analysis of their average diameter. In the method of the invention, the colloidal silica may have a specific surface area of from 10 m2 / g to 1000 m2 / g, such as 50 m2 / g to 1000 m2 / g. For example the average particle diameter may be from 50 m2 / g to 600 m2 / g, such as from 50 m2 / g to 500 m2 / g, typically from 80 m2 / g to 500 m2 / g, or preferably from 100 m2 / g to 400 m2 / g. In some preferred embodiments, the specific surface area of the colloidal silica may be from 80 m2 / g to 600 m2 / g, such as from 100 m2 / g to 400 m2 / g, 150 m2 / g to 350 m2 / g, or preferably from 200 m2 / g to 300 m2 / g. Preferably the specific surface area is from 100 m2 / g to 400 m2 / g. Specific surface area is measured using BET (Brunauer-Emmett-Teller) method.

[0147] Typically, the colloidal silica used has a specific surface area of at least 10 m2 / g, preferably at least 50 m2 / g, preferably at least 80 m2 / g, more preferably at least 100 m2 / g.

[0148] Typically, the colloidal silica used has a specific surface area of up to 1000 m2 / g, preferably up to 600 m2 / g, more preferably up to 500 m2 / g, such as 400 m2 / g.

[0149] The step of forming a colloidal suspension of silica in water, may comprise adding fumed silica to water, and treating the fumed silica and water such that a colloidal suspension of silica is formed.

[0150] Thus the invention provides a method for preparing an organic phase change material, wherein said method comprises:

[0151] - adding fumed silica to water;

[0152] - treating the fumed silica and water such that a colloidal suspension of silica is formed;

[0153] - adding one or more amino acids or salts thereof to the mixture.

[0154] The step of treating the fumed silica and water such that a colloidal suspension is formed may comprise mixing. Mixing may occur using any method known to the skilled person, such as those mentioned above.

[0155] Preferably, the step of treating to fumed silica is a step of treating the fumed silica with ultrasound (i.e. ultrasonication).

[0156] Therefore preferably, the method of the invention comprises:

[0157] - adding fumed silica to water;

[0158] - treating the fumed silica with ultrasound;

[0159] - adding one or more amino acids or salts thereof to the mixture.

[0160] Given this, the method of the invention may preferably comprise:

[0161] - adding fumed silica to water;

[0162] - treating the fumed silica and water with ultrasound such that a colloidal suspension of silica is formed;

[0163] - adding one or more amino acids or salts thereof to the mixture.

[0164] The ultrasonication process enhances the dispersion of fumed silica within the phase change material (PCM) solution through the application of high-frequency sound waves. These sound waves generate cavitation — rapid formation and collapse of microbubbles — which creates intense localized shear forces. These forces break down the agglomerates of fumed silica particles into smaller, uniformly dispersed individual particles. This mechanical effect has been demonstrated to improve the material properties of the PCM solution in several scientifically validated ways:

[0165] Reduction in Agglomerate Size: Ultrasonication (e.g. 200-500 kJ over 30-minute) reduces the size of silica agglomerates, typically breaking them down from, for example, an initial 200-300 nm size range (average particle diameter) to dispersed particles with an estimated size below 100 nm, depending on the energy input and duration of the sonication process. The cavitation forces directly impact the interparticle Van der Waals forces, reducing agglomeration and resulting in a stable suspension with well-dispersed particles.

[0166] Increase in Surface Area Utilization: Ultrasonication enhances the effective surface area of the dispersed fumed silica by preventing large clusters from forming. For example, fumed silica pre-sonication may have an accessible surface area of 50 m2 / g, which could increase up to 100-150 m2 / g post-sonication, depending on the specific conditions such as power input and solvent viscosity. This increased surface area enhances thermal interaction with the PCM matrix, improving the rate of heat absorption and release during phase transitions.

[0167] Enhanced Thermal Conductivity: The formation of a finely dispersed silica network post-ultrasonication has been shown to improve the thermal conductivity of the PCM. Incorporating ultrasonicated silica nanoparticles into PCM can lead to a conductivity enhancement of up to 20-30% compared to non-sonicated samples, directly contributing to faster and more efficient thermal energy storage and release. The thermal conductivity of the phase change materials (PCMs) in this invention generally falls within the range of 0.1 to 0.5 W / m-K, depending on the specific composition and structure of the PCM. Thermal conductivity is measured using the Thermal Bridge Method, which involves creating a controlled temperature difference across the sample and measuring the resulting heat flow. This method allows for an accurate assessment of the PCM’s ability to conduct heat by directly analyzing the thermal bridge created between two points at different temperatures.

[0168] Prevention of Sedimentation: Due to the more uniform dispersion and smaller particle size post-ultrasonication, the fumed silica remains suspended in the PCM for a longer duration. Sedimentation analysis shows that ultrasonicated samples exhibit up to a 50% reduction in sedimentation rates over a 30-day period, compared to samples processed using traditional mechanical stirring. The sedimentation rates for the phase change materials (PCMs) in this invention are generally low, typically within the range of 0.01 to 0.1 mm / day under standard conditions, depending on the particle size and dispersion stability of the PCM composition. Sedimentation rates are commonly measured using a visual observation method or a gravimetric analysis over time. In these methods, the PCM sample is placed in a transparent container, and the height of the settled layer is periodically recorded to determine the rate. Alternatively, sedimentation can be quantified by measuring the mass of settled particles after a specific duration.

[0169] Precise Control of Dispersion Parameters: Ultrasonication provides precise control over dispersion parameters, such as energy input (measured in kJ) and sonication time. This tunability allows for adjustments to fit specific application needs, improving overall process efficiency.

[0170] No Chemical Modifiers Required: Ultrasonication may eliminate the need for additional chemical dispersants, which could otherwise interfere with the PCM’s phase transition behaviour. Common chemical dispersants such as sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and silica nanoparticles are typically added in other systems to improve dispersion. However, by relying solely on mechanical forces to achieve dispersion, the integrity of the PCM remains intact, ensuring that no additional thermal mass or unwanted chemical interactions are introduced into the system. Therefore, the present invention may preferably comprise no chemical dispersants.

[0171] In the method of the invention, the energy input of ultrasonication may be from 50 kJ to 1000 kJ, typically from 100 kJ to 600 kJ. Preferably the energy input for ultrasonication is from 200 kJ to 500 kJ. For example, the energy input may be from 50 kJ, from 100 kJ or from 200 kJ. The energy input may be up to 1000 kJ, up to 600 kJ, or up to 500 kJ. The ultrasonication may occur over a time period of from 5 minutes to 120 minutes, such as from 10 minutes to 60 minutes, such as from 20 minutes to 40 minutes, such as from 25 minutes to 35 minutes, preferably about 30 minutes. For example, ultrasonication may be for from 5 minutes, from 10 minutes, from 20 minutes or from 25 minutes. Ultrasonication may occur for up to 120 minutes, up to 60 minutes, up to 40 minutes or up to 35 minutes. Preferably ultrasonication occurs for from 20 minutes to 40 minutes.

[0172] Therefore, treating with ultrasound (ultrasonication) may be treatment with an energy input of from 50 kJ to 1000 kJ over a duration of 5 minutes to 120 minutes. Often treating with ultrasound (ultrasonication) may be treatment with an energy input of from 100 kJ to 600 kJ over a duration of from 10 minutes to 60 minutes. Preferably, treating with ultrasound (ultrasonication) is treatment with an energy input of from 200 kJ to 500 kJ over a duration of from 20 minutes to 40 minutes.

[0173] For instance, using an energy input of 200-500 kJ over a 30-minute duration has been shown to optimize particle size reduction and suspension stability in PCM formulations.

[0174] In the method of the invention, the fumed silica (before treatment) may have an average particle diameter of from 1 nm to 5000 nm, such as 7 nm to 5000 nm. For example the average particle diameter may be from 5 nm to 2000 nm, such as from 50 nm to 1000 nm, typically from 50 nm to 1000 nm, or preferably from 50 nm to 400 nm. In some preferred embodiments, the average particle diameter of the fumed silica may be from 50 nm to 600 nm, such as from 100 nm to 400 nm, 150 nm to 350 nm, or preferably from 200 nm to 300 nm. Often the average particle diameter is from 50 nm to 400 nm, preferably from 100 nm to 400 nm. Most preferably the fumed silica (before treatment) has an average particle diameter of from 200 to 300 nm. Average particle diameter is measured using Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM), both of which provide high-resolution imaging for precise particle size analysis.

[0175] The present inventors have found that fumed silica within these parameters (before treatment) offers excellent dispersibility and provides an appropriate specific surface area following treatment to ensure material stability and performance. Typically, the fumed silica (before treatment) used has a diameter of at least 1 nm, preferably at least 10 nm, preferably at least 50, more preferably at least 100 nm.

[0176] Typically, the fumed silica (before treatment) used has a diameter of up to 20000 nm, preferably up to 10000 nm, more preferably up to 2000 nm, such as 1000 nm.

[0177] The preparation method of the invention typically occurs at room temperature (typically from 15 °C to 25 °C) and atmospheric pressure (approximately 100000 Pa).

[0178] Thermal Energy Storage Elements

[0179] The present invention also provides thermal energy storage elements which contain the phase change material, or phase change material precursor, of the invention. The phase change material of the present invention (or a precursor thereof) may be used with any suitable thermal energy storage element, such as a cooling module.

[0180] Exemplary arrangements of cooling module are described below. However, it will be understood that the cooling modules with which the phase change material can be used is not limited to these arrangements, and may be used with any suitable arrangement of cooling module.

[0181] In some arrangements, the thermal energy storage element comprises a compartment arranged to contain the PCM or PCM precursor. The compartment may have a heat transfer surface which is arranged to transfer heat to and from the PCM, e.g. between the PCM and the external environment. As used herein, the term “external environment” may indicate the environment, e.g. the air or another fluid, surrounding the compartment, typically the environment, e.g. the air or another fluid, surrounding the thermal energy storage element. In such arrangements, the inner surface of the heat transfer surface is in contact with the PCM such that heat is transferred to or from the PCM via the heat transfer surface.

[0182] The heat transfer surface may comprise ridges or undulations to increase the surface area of the surface, and thereby increase the transfer of heat. For instance, the thermal energy storage element may act as a heat exchanger, to maximise heat transfer to or from the PCM.

[0183] Figure 3 depicts (as an example of a thermal energy storage element) a cooling module 101 having an exterior surface and an internal space configured to contain an organic phase change material (such as, but not limited to, the phase change material of the present invention). The cooling module 101 has an open channel 102 disposed in its exterior surface. As shown in figure 3, the open channel has a substantially serpentine shape. That is, at least a portion of the open channel 102 has a serpentine shape. In other words, the channel has a series of straight sections which are parallel to each other, with subsequent straight sections being joined at being joined by curved sections, so as to make a series of conjoined S shapes. The serpentine channel may increase heat exchange between the surface of the cooling module and the external environment, and thus between the PCM and the external environment.

[0184] It will be understood that the open channel is formed by an indentation in the exterior surface of the cooling module, and does not perforate the cooling module so as to expose the internal space. All or part of the exterior surface may have a serpentine open channel. The serpentine channel may have breaks rather than being continuous, thus forming a plurality of serpentine channels in one surface.

[0185] As shown in figure 3, the cooling module may further comprise an opening 103 in one end, to allow the phase change material, water, a PCM precursor, or a combination thereof, to be provided to the internal space.

[0186] The shape of the cooling module shown in figure 3 is substantially cuboidal. However, it will be understood that other shapes are possible.

[0187] In some arrangements, more than one surface of the cooling module may have a serpentine open channel. For example, although not visible in figure 3, two parallel exterior surfaces of the cooling module may have a respective open channel 102. The shapes of the open channel on different surfaces may be the same or may be different from each other.

[0188] Figure 4 shows a cooling system comprising a plurality of the cooling modules shown in figure 3. In this particular example, eight cooling modules are depicted, disposed parallel to each other. However, any suitable number or arrangement of cooling modules 101 may be used. The cooling system may have a housing in which the cooling modules are accommodated, with an inlet 202 and an outlet 203. Air or another fluid may flow from the inlet, past the cooling modules 101, and to the outlet, thus allowing heat to be exchanged between the cooling modules and the fluid, thus changing the temperature of the fluid. As a comparative example, figure 5 depicts a comparative example cooling module 301 which does not include an open channel with a serpentine shape. Rather, the cooling module is a cuboid with flat surfaces. Figure 6 provides a comparison between the convective heat transfer coefficient (HTC) achieved by the cooling modules of figure 3 (the upper set of points, labelled “Actual TES plate”) and figure 5 (the lower set of points, labelled “Rectangular TES plate”). It will be seen that the cooling module of figure 3 provides a significantly higher HTC over a wide range of inlet velocities.

[0189] Figure 7 and 8 show a further arrangement of cooling module according to the invention. In particular, two tubes 401 are provided, with the tubes being configured to carry a phase change material, (which may be, but is not limited to, the phase change material of the present invention). The phase change material may flow through the tubes.

[0190] As shown in figures 7 and 8, two tube connecting fins 402 are provided. Each tube connecting fin 402 is joined to the two tubes 401. In other words, one end of tube connecting fin 402 is joined to one tube 401, and the other end of tube connecting fin 402 is joined to the other tube 401. Thus, the tube connecting fins are configured to provide heat transfer between the respective tubes. It will be noted, that as depicted in figure 7, the tube connecting fins 402 are substantially flat plates, and are solid. That is, they do not contain any void through which fluid can flow, and heat is transferred between the two tubes 402 by conduction. This may help to avoid large temperature differences between tubes which are joined by the fins.

[0191] As also shown in figures 7 and 8, the tubes are partially contained within a housing 403. The module further comprises housing connecting fins 404, which join the tubes 401 and the housing 403. In other words, one end of housing connecting fin 404 is joined to one tube 401, and the other end of housing connecting fin 404 is joined to the housing 403. In the particular arrangement set out in figures 7 and 8, each tube is provided with two housing connecting fins. Similarly to the tube connecting fins, the housing connecting fins are substantially flat plates. The housing connecting fins are thus configured to provide heat transfer by conduction between the respective tubes and the housing 403. This may help to avoid large temperature differences between tubes which are joined by the fins.

[0192] As further depicted in figures 7 and 8, the module may further comprise a plurality of non-connecting fins, each of which has one end connected to one of the tubes. The other end of the fin is a free end (i.e. not connected to the housing or to another tube). In the arrangement shown in figures 7 and 8, each tube has two sets of twelve non-connecting fins 405. However, it will be understood that any suitable arrangement of fins may be provided. The non-connecting fins may provide heat transfer to or from the tube (and thus to or from the fluid disposed therein), by a combination of conduction, and other heat transfer mechanisms such as radiation or convection.

[0193] As shown in figures 7 and 8, the housing may also further comprise one or more housing fins 406, which are joined at one end to the housing and have a free end.

[0194] The cooling modules described above may be formed of any suitable material. However, metals or plastics materials may be particularly suitable. In a preferred example, the cooling modules are formed of aluminium, which may be preferred due to its high thermal conductivity, lightweight nature, and cost-effectiveness. Stainless steel is also preferred.

[0195] Although the arrangements described above are described as cooling modules, it will be understood that these arrangements may equally apply to other thermal energy storage elements.

[0196] In one embodiment, the heat transfer element contains a PCM precursor. The compartment of the heat transfer element may comprise an opening (as described above in relation to figure 3) and a closure means configured to close the opening. The opening may be arranged such that water can be added to the compartment such that it mixes with the PCM precursor within the compartment. The closure means may be arranged to seal the opening, e.g. before and after addition of water. The compartment may be provided with an indicator mark, showing a user the volume of water which needs to be added to the PCM precursor to produce a PCM according to the invention.

[0197] In one embodiment, therefore, the invention provides a thermal energy storage element containing a PCM precursor as described herein, and a method for producing a PCM as described herein which comprises adding water to the compartment, e.g. in a predetermined amount, and mixing the precursor with the added water.

[0198] Thermal Energy Storage Systems

[0199] The thermal energy storage elements may be provided within a thermal energy storage system. Thus, the present invention also provides a thermal energy storage system comprising one or more thermal energy storage elements. May systems are known in the art which incorporate PCMs into thermal energy storage systems and such systems are envisaged also for use with the PCMs of the invention.

[0200] Given the phase transition temperatures of the PCMs of the invention, which typically lie in the range of -30°C to 10°C, the PCMs and thermal energy storage elements of the invention are particularly suitable for cool thermal energy storage systems and may therefore be used in any cooling device. An example of a cool thermal energy system is a cooling container for storing or transporting refrigerated or frozen goods. For example the system may be a domestic cooling block, a refrigeration unit, such as a refrigerated shipping container or a cold storage container. The PCM may alternatively be used for cooling buildings.

[0201] Use of PCM

[0202] The PCM described herein, or a thermal energy storage element containing the PCM, may be used as a heat absorber in a cooling system. Where used as a cooling system, the PCM is first charged by cooling to below the phase transition temperature such that the PCM is in the solid state. In this form, the PCM effectively absorbs heat from the surroundings and can be used in refrigeration devices or as domestic cooling systems. Any means of cooling to charge the PCM may be used. Advantageously, the PCM can be used in solar cold storage where solar power is used for charging, or marine cold storage where wind energy is used for charging.

[0203] Non-limiting examples of cooling techniques include:

[0204] Passive cooling: The materials could be charged inside a warehouse or freezer, the charging rate is slower as there is no forced heat transfer.

[0205] Heat transfer fluid: Use of air or liquid (silicone oil, water solution, such as salt solution, ethylene Glycol Aqueous Solution) to charge the materials via heat exchanger. This method required a separate chiller to provide the cooling fluid, but the charging rate will be quicker (from around 2 to 20 times quicker).

[0206] Thermoelectric cooling: Pasting thermoelectric cooling film on to the materials container surface, and supplying electricity such that the film generates cooling and charges the materials. The materials can be used for a wide range of thermal management, including cold chain logistics, air conditioning, electronics cooling, battery management, industrial cooling, off-grid cooling and other low temperature applications.

[0207] One area where the PCMs of the invention may be especially effective is in battery storage systems, which currently use very high cost materials.

[0208] Examples

[0209] Example 1: Preparation method of PCMs

[0210] PCMs of the invention were prepared by adding 3.6 g (20% of the total weight of the fumed silica) to 702 g water, at room temperature and pressure.

[0211] The mixture was then stirred, using a magnetic stirrer, typically at a stirring speed of from 30 rpm to 50 rpm.

[0212] The remaining fumed silica (14.4 g) was added slowly. If any agglomeration occurred, feeding of the silica to the mixture was paused, and continued when agglomerates dissolved.

[0213] The silica water mixture was subject to ultrasonic dispersion for 6 hours, at approximately 40-60 °C.

[0214] After the silica had fully dispersed, the one or more amino acids or salts thereof, and any additional additive (e.g. optionally antimicrobial agent and / or thermal conductive agent) were added.

[0215] After all of the further additives were added, the mixture was stirred, typically at a stirring speed of from 50 to 120 rpm, for approximately 1 hour.

[0216] The whole solution was subsequently subjected to ultrasonic dispersion for 3 hours, at approximately 40-60 °C.

[0217] The schematic diagram of the formulation of the composite PCMs is illustrated in Figure 9.

[0218] Example 2: Preparation of PCMs using different sizes of fumed silica

[0219] PCMs were prepared according to Example 1 above, except in that different sizes of fumed silica were used, covering a nanometer to a micrometer range (7 nm, 20 nm, 200 to 300 nm and 20000 nm). The method of Example 1 was followed up to the point at which the silica had dispersed (i.e. no amino acids or further additives were added). The resulting colloidal silica dispersions are shown in Figure 10.

[0220] It was found that use of fumed silica with an average particle diameter of 100 to 1000 nm produced a colloidal silica dispersion with a preferable viscosity. As can be seen in Figure 10, the larger silica may not fully dissolve, and the smaller silica may not form a viscous gel.

[0221] Cycle testing was conducted by testing the entire PCM in an environmental chamber and observing melting and freezing temperatures of the PCM. As shown in Table 1 below, it was found that not only did the use of colloidal silica decrease the supercooling degree of the PCM, but that super cooling degree was maintained at a low temperature after many cycles.

[0222] Table 1

[0223] PCM Cycling Freezing Melting latent Melting Freezing latent Super-cooling number temperature (°C) heat(kJZkg) temperature (°C) heat(kJ / kg) Degree

[0224] 0 -19.28 216.86 -15.50 216.85 3.78

[0225] Pure PCM

[0226] 200 -20.34 212.79 -15.46 213.68 4.88

[0227] 0 -19.19 208.60 -15.43 208.46 3.76

[0228] PCM

[0229] @0-007pm200-19.212()6 54_15 53 2()6 4g 3 6g

[0230] 0 -16.08 207.11 -15.55 207.07 0.53

[0231] PCM

[0232] @0.2-0.3|im20Q-16.11 206.97 _15 53 2Q6 g6 Q 5gAnalysis was also done to assess the effect of the size of the silica on charging rate.

[0233] Specifically, the PCMs were cooled such that they began to freeze (i.e. crystallize). Percentage crystallinity is equivalent to the extent to which the PCM is charged.

[0234] Crystallinity was observed and calculated using scanning electron microscopy (SEM) and the results provided in Figure 11. Results set out in Figure 11 provide an analysis of individual droplets of PCM, as opposed to the cycle testing above which analyses the PCM as a whole.

[0235] As shown in Figure 11, the increase in crystallinity of the PCM comprising fumed silica with an average diameter of 7 nm (i.e. 0.007 pm) is significantly greater than that of a pure PCM, indicating more rapid charging. Further the crystallinity of the PCM comprising fumed silica with an average diameter of 200 to 300 nm (i.e. 0.2 to 0.3 pm) increases at an even greater rate, indicating even more rapid charging over the same temperature range.

[0236] The difference in crystallinity can also be seen in the SEM images of Figure 12.

[0237] Example 3: Analysis of PCMs

[0238] PCMs were prepared according to the method of Examples 1. Varying amounts of amino acid or salts thereof were used to afford different percentage weights.

[0239] The melting temperature, freezing temperature, latent heat of each PCM were measured with the results displayed in the table below.

[0240] For temperature measurement, a thermocouple is consistently inserted into the PCM, ensuring it does not contact the container walls to avoid errors. To calculate latent heat, DSC (Differential Scanning Calorimetry) is used. The latent heat is determined by integrating the area under the phase change curve obtained from the DSC analysis.

[0241] Table 2 shows the results of PCMs prepared using a single type of amino acid and Table 3 shows the results of PCMs prepared using a mixture of more than one type of amino acid.

[0242] able 2

[0243] Table 3

[0244] As can be seen from the above, tables, increasing and decreasing the amino acid content of the PCM can be used to tune the phase change temperature such that the PCM is suitable for a different use, such as chilling, freezing or deep freeze.

[0245] Phase change temperatures were assessed using differential scanning calorimetry (DSC). Graphs showing the DSC analysis are shown in Figure 13 of the application as filed. The peaks observed in the DSC graphs represent endothermic melting events, while the troughs correspond to exothermic freezing events. The troughs are observed at temperatures lower than the typical freezing point due to supercooling, a common phenomenon in phase change materials without nucleating agents, which delays crystallization until a lower temperature. The temperature values on the right-hand axis indicate the programmed temperature of the DSC environment, which does not exactly match the specific transition temperatures noted in the captions. The onset, peak, and area temperatures in the captions are measured directly from the DSC curve, providing precise thermal transition points for each sample.

[0246] Example 4 - PCMs with lower phase change temperatures

[0247] PCMs were prepared according to the method of Example 1. Up to 25-35% of amino acid was used.

[0248] The materials were charged using a cold bath, and chiller, which decreased the temperature of the material to around -60°C. The material was then discharged by leaving to warm to room temperature.

[0249] Throughout the charging and discharging process, the temperature of the PCM was monitored to assess the phase change temperature. Figure 14 depicts the experimental setup.

[0250] As shown in Figure 15, it was found that the PCM of Example 1 charged at a temperature of around -54°C, and discharged at a temperature of around -50°C. This is a remarkably small supercooling degree for a PCM with such a high concentration of amino acid.

[0251] PCMs with a phase change temperature around -50°C can be used for example for transporting and preserving ice cores. Example 5 - Comparing organic versus non-organic PCMs

[0252] A PCM of the invention was prepared using 15—20% of amino acid. The material was charged and discharged in a calorimeter, and differential scanning calorimetry was used to assess the phase change temperature, and the energy density of the composition. Two commercially available PCMs, which comprise 19.5 wt% ammonium chloride solution, also underwent the same procedure.

[0253] The results of the test are displayed in Table 4 below, and in Figure 16. As can be seen in Figure 16, the difference between the freezing temperature of the PCM and the melting temperature of the PCM is significantly reduced in the PCM of the invention compared to the commercial PCMs. Thus showing that the PCMs of the invention charge more efficiently.

[0254] Table 4

[0255] Phase change point Energy storage

[0256] Number Materials / °cdensity / J / g

[0257] Melting Freezing As can be seen in the above table, the supercooling temperature of the Exemplar PCM is much smaller than that of the commercial PCMs, and the energy density is much greater. Thus this example demonstrates that the PCMs of the invention are much more energy efficient and have greater storage capacity than existing PCMs.

Claims

CLAIMS1. An organic phase change material comprising one or more amino acids or salts thereof, colloidal silica, and water; wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 35% by weight based on the total weight of the phase change material; and wherein the colloidal silica is present in an amount of from 1% to 25% by weight based on the total weight of the phase change material.

2. An organic phase material according to claim 1 , wherein said material comprises less than 1% by weight inorganic salt based on the total weight of the phase change material.

3. An organic phase change material according to claim 1 or claim 2, further comprising an antimicrobial agent in an amount of 0.1% to 10% by weight based on the total weight of the phase change material.

4. An organic phase change material according to any one of claims 1 to 3, wherein the one or more amino acids or salts thereof are selected from glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine acid, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, mixtures of one or more thereof, and salts thereof.

5. An organic phase change material according to any one of claims 1 to 4, wherein the one or more amino acids or salts thereof are selected from alanine, glycine, threonine, glutamine, glutamic acid, lysine, cysteine, arginine, histidine, serine, and tyrosine, mixtures thereof, and salts thereof.

6. An organic phase change material according to any one of claim 1 to 5, wherein the one or more amino acids or salts thereof are selected from alanine, glycine, threonine, cysteine, glutamine and threonine, mixtures thereof, and salts thereof.

427. An organic phase change material according to any one of claims 1 to 6, wherein the total amount of amino acids or salts thereof in the phase change material is from 1% to 25% by weight based on the total weight of the phase change material.

8. An organic phase change material according to any one of claims 1 to 7, wherein the specific surface area of the colloidal silica is from 100 m2 / g to 400 m2 / g.

9. An organic phase change material according to any one of claims 1 to 8, wherein the colloidal silica is present in an amount of from 4% to 10% by weight based on the total weight of the phrase change material.

10. An organic phase change material according to any one of claims 1 to 9, wherein the phase change material further comprises a thermal conductive additive.

11. A method for preparing an organic phase change material, wherein said method comprises adding one or more amino acids or salts thereof to a suspension of colloidal silica in water, preferably wherein the suspension of colloidal silica is prepared by adding fumed silica to water.

12. The method according to claim 11, wherein the suspension of colloidal silica is prepared by adding fumed silica to water, and wherein the fumed silica has an average particle diameter of from 7 nm to 5000 nm, preferably from 50 nm to 1000 nm.

13. A cooling module, wherein the cooling module contains an organic phase change material according to any one of claims 1 to 10.

14. A cooling module having an exterior surface, an internal space configured to contain an organic phase change material, and an open channel disposed in the exterior surface, the open channel having a substantially serpentine portion.

15. The cooling module of claim 14, wherein the cooling module is substantially cuboidal, wherein two parallel exterior surfaces of the cooling module each have a respective open channel disposed therein, each open channel having a substantially serpentine portion.

16. A cooling module comprising a plurality of tubes configured to carry an organic phase change material, and at least one tube connecting fin joined to two of said tubes and configured to provide heat transfer between the respective tubes.

17. The cooling module of claim 16, wherein: said tubes are at least partially contained in a housing; the module further comprises a housing connecting fin joined to one of said tubes and to said housing, and configured to provide heat transfer between the tube and the housing.

18. The cooling module of claim 16 or 17, wherein said two tubes each comprise a plurality of non-connecting fins, each non-connecting fin having a single end joined to the respective tube.

19. The cooling module of any of claims 16 to 18, wherein at least one of said fins is a substantially flat plate.

20. The cooling module according to any one of claims 13 to 19, wherein the module is formed of metal or plastic.

21. A cooling system comprising one or more cooling modules according to any one of claims 13 to 20.

22. The cooling system of claim 21 , wherein the system comprises a plurality of modules according to any one of claims 13 to 20, the modules being disposed parallel to each other within a housing.

23. Use of a cooling module or system according to any one of claims 13 to 22, or an organic phase change material according to any one of claims 1 to 10, as a cooling means in a refrigeration system.

24. A method of cooling, maintaining the temperature, or reducing the rate of temperature increase in a defined space, wherein said method comprises providing a module according to any one of claims 13 to 20 in said defined space.

25. A method of charging a module according to any one of claims 13 to 20, wherein said method comprises reducing the temperature of said module, preferably wherein said temperature reduction causes the organic phase change material to freeze; optionally wherein said method uses a cooling means powered by renewable energy, preferably powered by solar energy.

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