3D printable thermal management composite for flexible wireless communication electronic devices

Abstract

The current invention relates to an ink formulation for additive manufacture, the ink formulation comprising a photocurable siloxane polymer, a photocurable silane, and one or more fillers, wherein the one or more fillers comprises particles of a core-shell material, where the core is formed from a phase change material and the shell is formed from a silane, and optionally a 2D MXene

Description

[0001] 3D PRINTABLE THERMAL MANAGEMENT COMPOSITE FOR FLEXIBLE WIRELESS COMMUNICATION ELECTRONIC DEVICES

[0002] Field of Invention

[0003] The current invention relates to an ink formulation for additive manufacture, a resin composition comprising the cured ink formulation, and a method of providing a product using additive manufacture.

[0004] Background

[0005] The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

[0006] Electronic devices, such as power electronic devices, highly integrated devices, and wireless communication devices, consume immense electrical power. Most of the power consumption is converted into heat energy, leading to thermal stress in the electronic devices. Efficient heat dissipation from the electronic devices is crucial to maintain the reliability of the devices.

[0007] Traditionally, metal-based heat sinks, such as copper (Cu) and aluminium (Al), have been employed for the heat dissipation from the electronic devices. Owing to the high thermal conductivity of metal (~102W / mK), the metal-based heat sinks have shown outstanding heat dissipation performances. However, due to the rigidity of the metal-based heat sinks, their application in deformable or flexible electronic devices is limited.

[0008] Metal filler / polymer composite has been adopted to overcome this issue. These conventional thermal management composites, such as thermal paste or pad, are composed of metal oxide-based particle and silicone-based polymer. Typical thermal conductivity (-10° W / mK) and low dielectric properties (dielectric constant: ~5, tangent loss: ~10'3) of metal filler / polymer composites makes it suitable to use in flexible electronic devices. However, the conventional materials have lower thermal conductivity (~7 W / mK). There are also other issues, such as leakage occurred in the paste-like composite and lower thermal conductivity of the pad-like composite, limiting its utilisation on high power electronic devices.

[0009] Accordingly, there appears to be a need to address the abovementioned issues to obtain effective thermal management materials for flexible electronics. Summary of Invention

[0010] It has been surprisingly found that resin compositions formed from an ink formulation that can be printed into any suitable shape and design by additive manufacture can be useful as a thermal management solution in an electronic device that suffers from heat management issues. These resin compositions may be formed from a polymeric material that has flexibiilty and may contain phase change material particles and provide improved heat-management performance. These resin composites may also contain 2D MXenes.

[0011] Also, it has been surprisingly found that photo-curable polydimethylsiloxane (PDMS)Zphase change material (PCM)-SiO2 (core-shell) / 2D material filler composite resolves the mentioned issues related to flexible thermal management composites.

[0012] The current invention has demonstrated that photo-curable PDMS is a good polymer matrix for thermal management materials. This is especially so because thermal management materials with specific designs can be obtained by employing selective photo-curing. In other words, photo-assisted 3D printing technique can be practical with the material fabrication.

[0013] On top of that, the PCM-SiO2 (core-shell) / 2D material filler composites are good thermal conductive materials. At higher temperature, the solid PCM is converted into liquid PCM, which implies that the thermal energy is stored in the PCM. The stored thermal energy will be transported out of the composites through the 2D materials, thus achieving the desired heat dissipation.

[0014] In summary, the current invention relates to 3D printable and thermally conductive composite with low dielectric properties. In addition, the photo-curable polymer matrix (photo-curable PDMS) enabled the fabrication of specifically designed features via 3D printing technique.

[0015] Aspects and embodiments of the invention will now be described by reference to the following numbered clauses.

[0016] 1 . An ink formulation for additive manufacture, the ink formulation comprising: a photocurable siloxane polymer; a photocurable silane; and one or more fillers, wherein the one or more fillers comprises particles of a core-shell material, where the core is formed from a phase change material and the shell is formed from a silane, and optionally a 2D MXene. 2. The ink formulation according to Clause 1 , wherein: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation.

[0017] 3. The ink formulation according to Clause 2, wherein: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

[0018] 4. The ink formulation according to Clause 2, wherein: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0019] 5. The ink formulation according to any one of the preceding clauses, wherein the photocurable siloxane polymer has a formula I: where each R is independently H or CH3.

[0020] 6. The ink formulation according to any one of the preceding clauses, wherein the photocurable silane has a formula II:

[0021] II. where R is H or CH3.

[0022] 7. The ink formulation according to any one of the preceding clauses, wherein the 2D MXene is Ti3C2Tx, where T is at least one functional group selected from F, O or OH and x is the number of terminal groups.

[0023] 8. The ink formulation according to any one of the preceding clauses, wherein the one or more fillers consists of:

[0024] (i) 100 wt% of the total amount of the fillers are particles of the core-shell material; or

[0025] (ii) from 10 to 90 wt% of the total amount of the fillers are particles of the core-shell material and from 10 to 90 wt% of the total amount of the fillers are the 2D MXene, such as from 15 to 85 wt% of the total amount of the fillers are particles of the core-shell material and from 15 to 85 wt% of the total amount of the fillers are the 2D MXene, such as from 25 to 75 wt% of the total amount of the fillers are particles of the core-shell material and from 25 to 75 wt% of the total amount of the fillers are the 2D MXene.

[0026] 9. The ink formulation according to any one of the preceding clauses, when subjected to additive manufacture using a digital light processing printer and subsequent photocuring, has one or more of the following properties:

[0027] (ai) a through plane thermal conductivity of from 4 to 10 W / mK, such as about 6.2 W / mK;

[0028] (aii) an in-plane thermal conductivity of from 10 to 32 W / mK, such as about 16 W / mK;

[0029] (aiii) a dielectric constant of from 2 to 8, such as about 4.5 at 10 MHz;

[0030] (aiv) a tangent loss of about 0.01 at 10 MHz.

[0031] 10. A resin composition comprising a cured ink formulation according to any one of

[0032] Clauses 1 to 8, wherein the resin composition has one or more of the following properties: (bi) a through plane thermal conductivity of from 4 to 10 W / mK, such as about 6.2 W / mK; (bii) an in-plane thermal conductivity of from 10 to 32 W / mK, such as about 16 W / mK;

[0033] (biii) a dielectric constant of from 2 to 8, such as about 4.5 at 10 MHz;

[0034] (biv) a tangent loss of about 0.01 at 10 MHz. 11. A method of providing a product using additive manufacture, the method comprising the steps of:

[0035] (a) providing an ink formulation according to any one of Clauses 1 to 9 to a suitable additive manufacturing device; and

[0036] (b) causing the additive manufacturing device to generate a product according to a set of computer-readable instructions, where at least some of the product is formed using the ink formulation according to any one of Clauses 1 to 9.

[0037] 12. The method according to Clause 11 , wherein the method further comprises subjecting the resulting product to a further curing step to provide a fully-cured product.

[0038] Drawings

[0039] FIG. 1 depicts the synthesis procedure of (a) photo-curable PDMS and (b) photo-curable silane.

[0040] FIG. 2 depicts the scanning electrode microscopy (SEM) images of the synthesized paraffin wax-SiC>2 (core-shell) particles.

[0041] FIG. 3 depicts (a) the 3D printed prototype with different printed features and (b) the rendered images of the printed samples.

[0042] FIG. 4 depicts (a) the through-plane thermal conductivity and (b) the in-plane thermal conductivity of printed Samples A-F. (A: PDMS only and no filler, B: 4 wt% core-shell as filler, C: 3 wt% core-shell / 1 wt% MXene as filler, D: 2 wt% core-shell / 2 wt% MXene as filler, E: 1 wt% core-shell / 3 wt% MXene as filler, F: 4 wt% MXene as filler).

[0043] FIG. 5 depicts the characterisation of dielectric properties of the printed samples: (a) dielectric constant; and (b) tangent loss.

[0044] FIG. 6 depicts the infrared (IR) images of Joule heater deposited composites during heat dissipation at the 300 s (heater on) to 350 s (heater off).

[0045] FIG. 7 depicts temperature profile over time of the Joule heating operation (from 0 to 300 s heater on, -500 s heater off). FIG. 8 depicts the Fourier Transform Infrared (FTIR) spectra of (a) NH2PDMS-NH2; (b) monosubstituted photo-curable PDMS; and (c) di-substituted photo-curable PDMS.

[0046] Description

[0047] It has been found that an ink that can be subjected to additive manufacture can be used to provide a thermally conductive composite material (i.e. a resin) with low dielectric properties and good heat management characteristics.

[0048] In a first aspect of the invention, there is provided an ink formulation for additive manufacture, the ink formulation comprising: a photocurable siloxane polymer; a photocurable silane; and one or more fillers, wherein the one or more fillers comprises particles of a core-shell material, where the core is formed from a phase change material and the shell is formed from a silane, and optionally a 2D MXene.

[0049] In embodiments herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components / features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of” or “consists essentially of”). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of’ or the phrase “consists essentially of’ or synonyms thereof and vice versa.

[0050] The phrase, “consists essentially of’ and its pseudonyms may be interpreted herein to refer to a material where minor impurities may be present. For example, the material may be greater than or equal to 90% pure, such as greater than 95% pure, such as greater than 97% pure, such as greater than 99% pure, such as greater than 99.9% pure, such as greater than 99.99% pure, such as greater than 99.999% pure, such as 100% pure.

[0051] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an oxygen carrier” includes mixtures of two or more such oxygen carriers, reference to “the catalyst” includes mixtures of two or more such catalysts, and the like. As noted herein, the one or more fillers must include particles of a core-shell material. In addition, the one or more fillers may also include a 2D MXene. As noted herein, the core-shell material is one where the core is formed from a phase change material and the shell is formed from a silane.

[0052] The term “phase change material” means a material that can change from one state of matter (i.e. a “phase”) to a different state of matter when an environment undergoes a change. For example, a phase change material may be a material capable of changing from a solid phase to a liquid phase in response to an external stimulus (e.g. heat) and may then return to a solid phase when the external stimulus is removed. As will be appreciated, the phase change material will be selected so that it undergoes a phase change at a sufficiently different stimulus value (e.g. temperature) compared to the silane shell. Any suitable phase change material with suitable properties may be used herein. Examples of phase change materials that may be used herein include, but are not limited to, a hydrocarbon-based phase change material (e.g. (CnH2n+2)), such as a paraffin wax. It will be appreciated that the phase change material may be selected to be a material that will convert from a solid to a liquid at a temperature greater than room temperature.

[0053] In embodiments of the invention, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation.

[0054] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

[0055] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0056] In embodiments of the invention, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

[0057] In embodiments of the invention, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation.

[0058] In embodiments of the invention, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0059] In embodiments of the invention, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0060] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation.

[0061] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

[0062] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0063] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0064] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0065] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation. In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation.

[0066] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

[0067] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

[0068] In particular embodiments, the ink formulation may be one in which: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

[0069] Any suitable the photocurable siloxane polymer may be used herein. For example, the photocurable siloxane polymer may be a photocurable polydimethylsiloxane or any similar kind of material. As will be appreciated, the photocurable aspect may be achieved through the addition of a suitable photocurable group to the termini of the polysiloxane chains. An example of such a material includes, but is not limited to a photocurable siloxane polymer has of formula I: where each R is independently H or CH3. In particular embodiments of the invention R may be CH3.

[0070] Any suitable the photocurable silane may be used herein. For example, the photocurable silane may be a photocurable polydimethylsiloxane or any similar kind of material. As will be appreciated, the photocurable aspect may be a silane of formula II:

[0071] II. where R is H or CHg. In embodiments of the invention, R may be CHg.

[0072] As noted above, the one or more fillers may include a 2D MXene. Any suitable 2D MXene may be used herein. As will be appreciated, 2D MXenes are a class of two-dimensional inorganic compounds that are formed from atomically thin layers of transition metal carbides, nitrides or carbonitrides, and which have a variety of hydrophilic terminations. An example of an MXene that may be used herein includes, but is not limited to, Ti3C2Tx, where T is at least one functional group selected from F, O or OH and x is the number of terminal groups (as will be appreciated the number of terminal groups.

[0073] The one or more fillers may consist of:

[0074] (i) 100 wt% of the total amount of the fillers are particles of the core-shell material; or

[0075] (ii) from 10 to 90 wt% of the total amount of the fillers are particles of the core-shell material and from 10 to 90 wt% of the total amount of the fillers are the 2D MXene, such as from 15 to 85 wt% of the total amount of the fillers are particles of the core-shell material and from 15 to 85 wt% of the total amount of the fillers are the 2D MXene, such as from 25 to 75 wt% of the total amount of the fillers are particles of the core-shell material and from 25 to 75 wt% of the total amount of the fillers are the 2D MXene. The ink formulation disclosed herein may have particularly good properties that are realised upon use of the ink formulation to make a composite material. Thus, when the ink formulation is subjected to additive manufacture using a digital light processing printer and subsequent photocuring, the resulting material may have one or more of the following properties:

[0076] (ai) a through plane thermal conductivity of from 4 to 10 W / mK, such as about 6.2 W / mK;

[0077] (aii) an in-plane thermal conductivity of from 10 to 32 W / mK, such as about 16 W / mK;

[0078] (aiii) a dielectric constant of from 2 to 8, such as about 4.5 at 10 MHz;

[0079] (aiv) a tangent loss of about 0.01 at 10 MHz.

[0080] It is noted that the properties of (aiii) and (aiv) may be obtained my measurement of a metalinsulator-metal formation, where the metal may any suitable metal (e.g. silver) and may be in the form of a paste and the insulator may be the cured ink formulation. Further details of this measurement may be found in the examples section below.

[0081] As noted ink formulation upon curing provides a resin composition that has good properties. Thus, in a further aspect of the invention, there is provided a resin composition comprising a cured ink formulation as described hereinbefore, wherein the resin composition has one or more of the following properties:

[0082] (bi) a through plane thermal conductivity of from 4 to 10 W / mK, such as about 6.2 W / mK;

[0083] (bii) an in-plane thermal conductivity of from 10 to 32 W / mK, such as about 16 W / mK;

[0084] (biii) a dielectric constant of from 2 to 8, such as about 4.5 at 10 MHz;

[0085] (biv) a tangent loss of about 0.01 at 10 MHz.

[0086] Similarly, the properties (biii) and (biv) may be measured as described above for (aiii) and (aiv).

[0087] As will be appreciated, the ink formulation may be suited for use in additive manufacture so as to provide a resin composition with a particular shape and size. Thus, in a further aspect of the invention, there is provided a method of providing a product using additive manufacture, the method comprising the steps of:

[0088] (a) providing an ink formulation as described herein to a suitable additive manufacturing device; and

[0089] (b) causing the additive manufacturing device to generate a product according to a set of computer-readable instructions, where at least some of the product is formed using the ink formulation as described herein. While not necessary to do so, the method may further comprise subjecting the resulting product to a further curing step to provide a fully-cured product.

[0090] As noted hereinbefore, conventional thermal management composites tend to be composed of silicone-based polymer / metal oxide particles. However, the conventional materials have lower thermal conductivity (~7 W / mK).

[0091] In contrast, the current invention may make use of phase change particles as a filler material (e.g. a paraffin wax-SiO2 (core-shell structure)) in a photocurable ink formulation, which, when cured, has improved properties due to the presence of the phase change particles. In certain embodiments, these properties may be enhanced further by the inclusion of a second filler material (a 2D MXene). The filler(s) are dispersed within a photocurable siloxane polymer (e.g. a photocurable PDMS) and a photocurable silane to provide an ink that can be readily used by an additive manufacture device (e.g. a commercial 3D printer). Owing to the flexibility of the resulting cured material (e.g. due to the cured siloxane polymer and silane), the resulting resin composite can be flexible, with superior thermal conductivity (e.g. approximately 16 W / mK of thermal conductivity), which provides the resin composite with good heat dissipation performance. In addition, the dielectric properties of the resin composite may also be good (e.g. -5 of dielectric constant and -0.01 of tangent loss at 10 MHz, in certain embodiments).

[0092] The resin composite can be readily employed for heat dissipation applications in soft / f lexible electronics. This may be a practical and elegant solution, as since the ink formulation can be subjected to additive manufacture, the resulting resin composite can be provided with any desired shape and size, so as to match a specific use-case without the need for a mold or castin process. In addition, as the resin composite has low dielectric properties, it can also be used readily in wireless communication electric devices such as antennae or satellites.

[0093] Some advantages of the ink formulation and resulting resin composite may include one or more of the following:

[0094] 1. being able to provide thermal management materials having any suitable size or shape through additive manufacture;

[0095] 2. effective thermal transport due to the use of phase change material particles and, when present, 2D MXenes, as filler material, thereby enhancing thermal conductivity;

[0096] 3. being able to provide a free-standing elastomeric thermal management material due to the use of a photocurable siloxane polymer (e.g. a photocurable PDMS); and

[0097] 4. owing to the low dielectric properties, the resin composite can be used for heat dissipation in high-power wireless communication electric devices. Further aspects and embodiments of the invention will now be described by reference to the following non-limiting examples.

[0098] Examples

[0099] The following examples are provided for understanding the present invention more easily. For example, methacrylate terminated PDMS and silane was used as the photo-curable polymer matrix, whereas fillers comprising paraffin wax-SiOz (core-shell) and / or 2D MXene were employed as the thermally conductive matter. The fillers were dispersed in the photo-curable PDMS matrix, and the prepared composite was successfully printed via commercial 3D printer. However, the contents of the present invention are not limited thereto.

[0100] Materials

[0101] Aminopropyl terminated polydimethylsiloxane (NH2-PDMS-NH2, DMS-A21 , Mw 5000 g / mol) was purchased from Gelest. 2-lsocyanatoethyl methacrylate was purchased from Tokyo Chemical Industry. 3-Aminopropyltrimethoxysilane, paraffin wax, tetraethyl orthosilicate (TEOS), cetyltrimethylammonium bromide (CTAB), ammonium hydroxide solution (30-33% NH3 in H2O), lithium fluoride, hydrochloric acid (37% HCI, ACS reagent), and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide (TPO) were purchased from Sigma-Aldrich. Titanium aluminium carbide (TisAICz) powder was purchased from Carbon-Ukraine, whereas commercial silver (Ag) paste was purchased from TED Pella.

[0102] Example 1. Preparation of Photo-Curable PDMS and Silane

[0103] Synthesis of Photo-Curable PDMS

[0104] The synthesis procedure of the photo-curable PDMS is illustrated in FIG. 1 (a). 100 g of aminopropyl terminated polydimethylsiloxane (NH2-PDMS-NH2, DMS-A21 , Mw 5000 g / mol, Gelest) was dissolved in 300 mL chloroform, followed by inert gas (Ar or N2) purging for 10 min at room temperature. Then, 5 mL of the 4-methoxyphenol solution (10 mg / mL in chloroform) was added dropwise to the solution. Next, 6.206 g of 2-isocyanatoethyl methacrylate (155.15 g / mol, Tokyo Chemical Industry) was added slowly (dropwise), followed by stirring for 1 hour at room temperature. Lastly, the resulting precipitates were collected by filtration, and the residual chloroform was removed by rotary evaporation. Synthesis of Photo-Curable Silane

[0105] The synthesis procedure of the photo-curable silane is illustrated in FIG. 1 (b). In the case of photo-curable silane, 3-aminopropyltrimethoxysilane (179.29 g / mol, Sigma-Aldrich) was used. Typically, 5 g of 3-aminopropyltrimethoxysilane was dissolved in 150 mL chloroform, followed by inert gas (Ar or N2) purging for 10 min at room temperature. Next, 250 pL of 4-methoxyphenol solution (10 mg / mL in chloroform) was added dropwise to the solution. Then, 4.327 g of 2-isocyanatoethyl methacrylate (155.15 g / mol, Tokyo Chemical Industry) was added slowly (dropwise) , followed by the stirring for 1 hour at room temperature. Lastly, the resulting precipitates were collected by filtration, and the residual chloroform was removed by rotary evaporation.

[0106] Fourier Transform Infrared (FTIR) Spectroscopy measurement

[0107] To characterize the functional groups on the prepared polymer, FTIR spectroscopy (Frontier, Perkin Elmer) was employed. Viscous sample was dropped on a KBr pallet and the spectrum was obtained by transmittance mode.

[0108] Results and Discussions

[0109] FIG. 8 depicts the Fourier Transform Infrared (FTIR) spectra of (a) NH2PDMS-NH2; (b) monosubstituted photo-curable PDMS; and (c) di-substituted photo-curable PDMS. As shown in FIG. 8, appearance of the signature peaks related to amide at the region of 1574-1720 cm-1and the broad peak at 3340 cm1for NH confirms the successful substitution of the photo- curable methacrylate components at the terminal amines of the NH2PDMS-NH2

[0110] Example 2. Preparation of Paraffin Wax-SiO2 (Core-Shell) Particles and 2D TiaCzTx

[0111] Preparation of Paraffin Wax-SiOz (Core-Shell) Particles

[0112] 7.5 g of paraffin wax (Sigma-Aldrich) was melted at 348 K, followed by addition of 5 g of tetraethyl orthosilicate (TEOS, Sigma-Aldrich) to the melted paraffin wax. The mixture was then added to a solution of CTAB, which has the composition of 0.82g CTAB, 140 mL H2O, and 70 mL of absolute ethanol, followed by high-speed shear mixing at 10000 rpm for 10 min at 338 K. Then, 1 mL of ammonium hydroxide solution (30-33% NH3 in H2O, from Sigma- Aldrich) was added dropwise to the solution and stirred for 12 hours at 338 K. The resulting particles were washed by diethyl ether and ethanol with centrifuge. After centrifuge, supernatants were disposed and precipitate was dried at 353 K in vacuum oven for 24 hours. Preparation of 2D Ti3C2Tx

[0113] 1.98 g of lithium fluoride (LiF, Sigma-Aldrich) was dissolved in 30 mL of 9.4 M HCI aqueous solution (HCI - hydrochloric acid, ACS reagent, Sigma-Aldrich). Next, 3 g of Ti3AIC2powder was slowly added to the solution. Then, the mixture was stirred for 24 hours at 313 K. The resulting precipitate was washed by water (H2O) with centrifuge. After centrifuge, supernatants were disposed and precipitate was dried at 353 K for 24 hours in vacuum oven.

[0114] Characterisation by Scanning Electrode Microscopy (SEM)

[0115] Prepared core-shell particles were dispersed in ethanol, and the dispersion was dropped on an aluminum oxide membrane to distinguish the particles readily.

[0116] Results and Discussions

[0117] FIG. 2 show the SEM images of the synthesised paraffin wax-SiO2(core-shell) particles.

[0118] Example 3. 3D Printing Test

[0119] Composites comprising photo-curable polymer matrix and fillers were prepared to demonstrate their 3D printability. The photo-curable polymer matrix and fillers used herein were prepared by following the protocols disclosed in Examples 1 and 2. Several examples of such 3D-printable composites have been prepared, such as those shown in Table 1 .

[0120] Table 1. Composition of 3D-Printable Composites Comprising Photo-Curable Polymer Matrix and Fillers.

[0121] The preparation of 3D-printable composites is demonstrated as the following, taking Sample D as an example. The preparation of the other samples follow the same protocol presented below.

[0122] To demonstrate 3D printing, photo-curable PDMS / paraffin wax-SiO2(core-shell) / 2D MXene composite was prepared. The composition of the composite was 91 wt% of photo-curable PDMS / 5 wt% of photo-curable silane / 4 wt% of fillers. In the case of fillers, 4 wt% core-shell, 3 wt% core-shell / 1 wt% MXene, 2 wt% core-shell / 2 wt% MXene, 1 wt% core-shell / 3 wt% MXene were prepared for 3D printing (Table 1 ). For example, 91 wt% photo-curable PDMS / 5 wt% photo-curable silane / 2 wt% core-shell / 2 wt% MXene is prepared as below.

[0123] Preparation of Sample D (91 wt% photo-curable PDMS / 5 wt% photo-curable silane / 2 wt% core-shell / 2 wt% MXene)

[0124] 91 g of photo-curable PDMS and 5 g of photo-curable silane were dissolved in 300 mL chloroform. Then, 2 g of core-shell particles and 2 g of MXene were dispersed in the solution for 15 min by using bath type ultrasonic. Next, 1 g of diphenyl(2,4,6-trimethylbenzoyl)- phosphine oxide (TPO, Sigma-Aldrich) was added in the mixture. Lastly, chloroform was removed by rotary evaporation.

[0125] The commercial digital light processing (DLP) based 3D printer was employed for 3D printing of the prepared composite. (FIG. 3)

[0126] Parameters used:

[0127] • layer thickness: 0.05 mm

[0128] • exposure time: 15 s for the initial two layer, 7 s for the subsequent layers

[0129] • light intensity: 10 mW / cm2

[0130] Results and Discussions

[0131] Owing to the flexibility of PDMS matrix, the 3D printed result was flexible.

[0132] Example 4. Thermal Conductivity of Printed Composite

[0133] Thermal conductivity of the 3D printed samples was characterized by ASTM 5470-06 (through- plane thermal conductivity) and Angstrom method (in-plane thermal conductivity). In this example, the thermal conductivity of the composite was characterized depending on the ratio between core-shell particles and 2D MXene.

[0134] ASTM 5470-06 (Through-Plane Thermal Conductivity)

[0135] To characterize temperature information, data acquisition (DAQ6510, Keithley) was employed.

[0136] Also, T-type thermocouples were used. Angstrom Method (In-Plane Thermal Conductivity)

[0137] To characterize temperature information, data acquisition (DAQ6510, Keithley) was employed. Also, T-type thermocouples were used.

[0138] Results and Discussions

[0139] In the case of 1 wt% core-shell / 3 wt% MXene (Sample E), the through-plane and in-plane thermal conductivity showed 6.2 and 16 W / mK, respectively. (FIG. 4) In the case of photocured PDMS (Sample A), the thermal conductivity of through-plane and in-plane showed 0.21 and 0.26 W / mK, respectively. The thermal conductivities were increased after the incorporation of core-shell particles and MXene. For example, thermal conductivity of through- plane and in-plane with 4 wt% core-shell (Sample B) showed 5.74 and 9.7 W / mK, respectively. When the MXene was added to the composite, both through-plane and in-plane thermal conductivities were increased. For example, thermal conductivity of through-plane and inplane with 2 wt% core-shell / 2 wt% MXene (Sample D) showed 8.07 and 14.44 W / mK, respectively.

[0140] Example 5. Dielectric Properties of Printed Composite

[0141] Preparation of Printed Composites with Metal-lnsulator-Metal (MIM) Structure

[0142] Metal-insulator-metal (MIM) structure was prepared for the dielectric properties characterization of the 3D printed composites. The commercial Ag paste was employed as a metal layer. Briefly, a printed composite was prepared. Then, the Ag paste was pasted on top and bottom faces of the printed composition (1 x 1 cm2).

[0143] Dielectric Properties Characterisation of the 3D Printed Composite

[0144] The dielectric properties of the 3D printed composite were characterized by impedance analyzer (Agilent 4294A). As a function of frequency, the capacitance and tangent loss of the samples were measured. And, the capacitance was converted into a dielectric constant.

[0145] Results and Discussions

[0146] The printed composites showed ~4.5 of dielectric constant and -0.01 of tangent loss at 10 MHz. (FIG. 5). FIG. 5 shows that the prepared material is a dielectric material. The result indicates that the prepared materials can be applied in thermal management of wireless communication device. Example 6. Heat Dissipation Performance of the Printed Composites

[0147] Characterisation of Heat Dissipation Performance

[0148] Printed composites with dimensions of 30 mm x 30 mm x 0.25 mm (widthxlengthxthickness) were prepared for the determination of their heat dissipation performance. Joule heating device with 200 nm of Au was deposited on the samples using a thermal evaporator in order to generate heat on the samples. Then, 200 mW of power was applied to the device, and the temperature information was characterized by IR camera (Ti200, Fluke). The temperature at the reference point, located 2 mm from the heater, was recorded.

[0149] Results and Discussions

[0150] Notably, by employing paraffin wax-SiC>2 (core-shell) / 2D Ti3C2Tx(MXene) filler, effective heat dissipation was achieved.

[0151] When the heater was operated, the temperature of the reference point increased rapidly with core-shell / MXene composite. (FIG. 6 and FIG. 7). The rapid increase of temperature indicates that generated heat from Joule heating device was delivered fast through the PDMS / core- shell / MXene layer, (higher thermal conductivity)

Claims

Claims1 . An ink formulation for additive manufacture, the ink formulation comprising: a photocurable siloxane polymer; a photocurable silane; and one or more fillers, wherein the one or more fillers comprises particles of a core-shell material, where the core is formed from a phase change material and the shell is formed from a silane, and optionally a 2D MXene.

2. The ink formulation according to Claim 1 , wherein: the photocurable siloxane polymer is present in an amount of from 80 to 95 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 2 to 10 wt%, of the total weight of the ink formulation.

3. The ink formulation according to Claim 2, wherein: the photocurable siloxane polymer is present in an amount of from 85 to 93 wt%; the photocurable silane is present in an amount of from 3 to 10 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of from 4 to 5 wt%, of the total weight of the ink formulation.

4. The ink formulation according to Claim 2, wherein: the photocurable siloxane polymer is present in an amount of about 91 wt%; the photocurable silane is present in an amount of about 5 wt%; and the one or more fillers are present, and as a combined amount if two or more fillers are present, in an amount of about 4 wt%, of the total weight of the ink formulation.

5. The ink formulation according to any one of the preceding claims, wherein the photocurable siloxane polymer has a formula I:where each R is independently H or CH3.

6. The ink formulation according to any one of the preceding claims, wherein the photocurable silane has a formula II:II. where R is H or CH3.

7. The ink formulation according to any one of the preceding claims, wherein the 2D MXene is Ti3C2Tx, where T is at least one functional group selected from F, O or OH and x is the number of terminal groups.

8. The ink formulation according to any one of the preceding claims, wherein the one or more fillers consists of:(i) 100 wt% of the total amount of the fillers are particles of the core-shell material; or(ii) from 10 to 90 wt% of the total amount of the fillers are particles of the core-shell material and from 10 to 90 wt% of the total amount of the fillers are the 2D MXene, such as from 15 to 85 wt% of the total amount of the fillers are particles of the core-shell material and from 15 to 85 wt% of the total amount of the fillers are the 2D MXene, such as from 25 to 75 wt% of the total amount of the fillers are particles of the core-shell material and from 25 to 75 wt% of the total amount of the fillers are the 2D MXene.

9. The ink formulation according to any one of the preceding claims, when subjected to additive manufacture using a digital light processing printer and subsequent photocuring, has one or more of the following properties:(ai) a through plane thermal conductivity of from 4 to 10 W / mK, such as about 6.2 W / mK; (aii) an in-plane thermal conductivity of from 10 to 32 W / mK, such as about 16 W / mK;(aiii) a dielectric constant of from 2 to 8, such as about 4.5 at 10 MHz;(aiv) a tangent loss of about 0.01 at 10 MHz.

10. A resin composition comprising a cured ink formulation according to any one of Claims 1 to 8, wherein the resin composition has one or more of the following properties:(bi) a through plane thermal conductivity of from 4 to 10 W / mK, such as about 6.2 W / mK;(bii) an in-plane thermal conductivity of from 10 to 32 W / mK, such as about 16 W / mK;(biii) a dielectric constant of from 2 to 8, such as about 4.5 at 10 MHz;(biv) a tangent loss of about 0.01 at 10 MHz.

11. A method of providing a product using additive manufacture, the method comprising the steps of:(a) providing an ink formulation according to any one of Claims 1 to 9 to a suitable additive manufacturing device; and(b) causing the additive manufacturing device to generate a product according to a set of computer-readable instructions, where at least some of the product is formed using the ink formulation according to any one of Claims 1 to 9.

12. The method according to Claim 1 1 , wherein the method further comprises subjecting the resulting product to a further curing step to provide a fully-cured product.

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