Preparing The Same

References to Related Applications

This application claims priority to Singapore application number 10201808332U filed on 24 September 2018, the disclosure of which is hereby incorporated by reference.

Technical Field

The present invention relates to an encapsulated particle, whereby the encapsulated particle is a thermochromic dye. The present invention also relates to a method for forming the encapsulated particle, a composite comprising the encapsulated dye and uses of the encapsulated dye.

Background Art

Thermochromism is the phenomenon in which a compound undergoes a reversible or irreversible temperature-dependent colour change. Certain compounds exhibit this thermochromic effect as a gradual colour change over a range of temperatures (continuous thermochromism) , while other compounds exhibit a colour change at a distinct transition temperature (discontinuous thermochromism). Thermochromism offers many promising technological applications such as in thermometers, temperature sensors, laser markings, and in certain responsive applications; for instance, in packaging that communicates product temperature changes.

Presently, there are two main classes of thermochromic compounds used in commercial applications: liquid crystals and leuco dyes. Liquid crystals are generally used for higher precision applications, since their transition temperatures can be very precisely engineered. Currently, liquid crystals are mainly used in medical devices such as forehead thermometers; or in displays for electronics such as game devices and smartphones, as well as in food quality indicators. However, more widespread usage and application of liquid crystal thermochromic materials are limited by their instability and complex processing which require highly specialized manufacturing techniques.

Leuco dyes are another important class of thermochromic material. One version of a leuco dye system that is capable of reversible colour change makes use of a colour former (leuco dye), a developer, and a solvent. The temperature at which the reversible colour change occurs is determined by the melting point of the solvent. Two competing reactions take place at the appropriate temperature - reactions between the dye and the developer; and between the solvent and the developer. The reversible formation of aggregates in leuco dye-developer-solvent systems causes the leuco dye to undergo ring-opening or ring-closing reactions, changing between its colourless and coloured forms, thus leading to the observed colour change. Although leuco dyes are easier to work with compared to liquid crystals, the transition temperatures of leuco dyes are less precisely controlled. Common uses for leuco dyes include advertising material, consumer packaging, product labelling/graphics, toys, and quality/process control applications. However, the leuco dye systems are generally sensitive to the composition of the dye and developer, which makes them unstable under harsh conditions. Thus the leuco dyes are generally unsuitable for practical applications which demand high weather and optical stability.

Recently, inorganic and organic-inorganic hybrid thermochromic materials have received considerable attention due to their thermal stability and enhanced mechanical properties. Transition metal oxides have been studied as potential solid-state thermochromic materials, for instance, vanadium oxides display interesting thermochromic properties, which have led them to be considered for potential applications in electrical and optical switching devices. However, vanadium oxides systems show unremarkable colour change and most of the inorganic and hybrid thermochromic materials lack weather stability as they are easily degraded by UV light.

Therefore, there is a need to provide a thermochromic material that will overcome, or at least ameliorate, one or more of the disadvantages described above. This will allow thermochromic materials to be used in more practical applications, particularly as packaging and sensing materials in environments of fluctuating temperature, light and moisture conditions.

Summary

In one aspect, the present disclosure relates to an encapsulated particle comprising an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a polymeric shell that at least partially encapsulates the inorganic core.

The encapsulated dye may be an encapsulated thermochromic dye particle. Advantageously, the encapsulated thermochromic dye particle may have a fast, reversible and distinct colour change over a wide temperature range.

Still advantageously, the encapsulated thermochromic dye particle may be robust against multiple elements of UV light, visible light, high temperature, moisture and their induced degradation.

Further advantageously, the encapsulated thermochromic dye particle may be highly stable to changes in environmental factors such as moisture, visible light, UV light, pH, and presence of chemicals and may only exhibit sensitivity to temperature changes.

Yet further advantageously, the encapsulated thermochromic dye particle may be suitable for a wide variety of practical applications requiring weather stability in harsh environment. This may be due to the presence of the shell that protects the inorganic core from degradation due to external factors or external forces.

In another aspect, the present disclosure relates to a method of forming an encapsulated particle comprising the steps of (a) mixing at least one transition metal precursor with a metal ligand or oxidizing agent in a sol-gel solution in a solvent to form a metal complex inorganic core; and (b) coating the metal complex inorganic core with at least one shell-forming material to form a shell that at least partially encapsulates the metal complex inorganic core, wherein the metal complex comprises at least one central transition metal ion coordinated to at least two ligands .

In another aspect, the present disclosure relates to a composite comprising a plurality of encapsulated particles embedded within a polymer matrix, wherein each of said plurality of encapsulated particles comprises an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates said inorganic core.

The composite may be a thermochromic composite. Advantageously, the thermochromic composite may have a fast, reversible and distinct colour change over a wide temperature range.

Further advantageously, the thermochromic composite may have improved stability owing to the double level protection offered by the shell and the polymeric matrix.

Still advantageously, the thermochromic composite formed in the present disclosure may be robust against multiple elements of UV light, visible light, high temperature, moisture and their induced degradation. Still further advantageously, the thermochromic composite formed in the present disclosure may be suitable for a wide variety of practical applications requiring weather stability in harsh environment.

In another aspect, the present disclosure relates to a method of forming a composite, comprising the step of dispersing a plurality of encapsulated particles into a polymer solution or a polymer precursor solution, wherein each of said plurality of encapsulated particles comprises an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates said inorganic core.

Advantageously, the method may allow for the composite to be formed easily, thus enabling scale- up in manufacturing.

In another aspect, the present disclosure relates to use of an encapsulated particle as an additive in a composition or formulation, wherein said encapsulated particle comprises an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates said inorganic core.

Definitions

The following words and terms used herein shall have the meaning indicated:

The term“thermochromic” as used herein refers to a property of substances where reversible or irreversible colour change occurs with temperature change.

The term“composite” its used herein refers to a material made of two or more constituent components that are of different physical and/or chemical properties such that when combined, the resulting material has characteristics different and superior to those from the constituent components and the individual components remain separate and distinct within the finished structure.

The term“encapsulate” or grammatical variants thereof such as“encapsulated” or“encapsulating” as used herein refers to enclosing or entrapping a material within a shell-like material or layers of shell- like material or within a system to provide protection.

The term“disperse” as used herein refers to the distribution of a substance or phase over another substance or phase.

The term“distinct” as used herein in relation to colour change refers to easily distinguishable colour difference when viewed by the human eye.

The term“ligand” as used herein refers to an ion or molecule that binds to a central metal atom to form a coordination entity made up of two or more component entities.

The term“matrix” as used herein refers to a host substance which is the primary phase and has a continuous character functioning as a support to hold together or bind the discontinuous phase(s) together.

The term“sol-gel” as used herein refers to a specific type of colloidal processing where desired solid particles are dispersed in a liquid forming the sol, which gradually forms a gel.

The term“stable” or“stability” as used herein refers to the unlikeliness of physical and/ or chemical deterioration or degradation that will affect the thermochromic properties of the substance. Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and sub-generic groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Detailed Disclosure of Embodiments

Exemplary, non-limiting embodiments of an encapsulated particle will now be disclosed.

The encapsulated particle comprises: an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates the inorganic core.

The encapsulated particle may be an encapsulated thermochromic dye particle.

The metal complex may be capable of thermochromism.

The at least one central transition metal ion comprises at least one transition metal selected from Group 3 to Group 12 of the Periodic Table of Elements. The at least one transition metal may be selected from the group consisting of nickel, cobalt, molybdenum, tungsten, copper, gold, silver, chromium, mercury and combinations thereof.

The at least two ligands may be independently selected from the group consisting of nitrogen containing organic molecules, phosphate containing organic molecules, sulphur containing organic molecules, chloride, bromide, iodide, perchlorate, boron fluoride, hydroxide, cyanide and isocyanine.

The ligands may be independently selected from the group consisting of oxide, hydroxide, potassium iodide, diisopropylammonium chloride, diphenyl ethyltriethoxysilane phosphine, diphenyl propyl-phosphine, 3,3’-thiodipropionic acid, diethylammonium chloride, N,N- diethylethylenediamine, diphenylethyl triethoxysilanephosphine, bis(N-isopropyl-5,6- benzos alicy lideneiminato), N-(3-propyltrimethoxysilane)imidazole, and thiosemicarbazones. The number of ligands forming a coordination complex with the at least one transition metal may be from 2 to 9.

The shell may be an inorganic shell or a polymeric shellor a combination of inorganic and polymeric shell.

Where the shell is an inorganic shell, the shell may be selected from the group comprising of metal oxides such as silica, alumina, titania, zinc oxide, and zirconium dioxide.

Where the shell is a polymeric shell, the polymeric shell may comprise a monomer selected from the group consisting of alkyl acrylate, styrene, ether, ketone, vinylidene (di)fluoride, cyclic ether, butylene terephthalate, acrylic acid, alkenyl benzene, alkylacrylamide, alkyleneglycol acrylate and combinations thereof. The polymeric shell may comprise a polymer selected from the group consisting of poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(ether-ether ketone) (PEEK), poly( vinylidene fluoride) (PVDF), poly(tetrahydrofuran) (PTHF), poly (butylene terephthalate) (PBT), poly(methacrylic acid) (PMAA), poly(divinylbenzene) (PDVB), polyacrylic acid (PA A), poly(N-isopropylacrylamide) (PNIPAM), poly (ethyleneglycol dimethacrylate)

(PEGDMA), PEGDMA-based copolymers, copolymers therefrom (such as PMMA -based copolymers, PS-based copolymers, PEEK-based copolymers, PVDF-based copolymers, PTHF-based copolymers, PBT-based copolymers, PMAA-based copolymers, PDVB-based copolymers, PAA-based copolymers, PNIP AM-based copolymers, or PEGDMA-based copolymers) and copolymers thereof.

The polymeric shell may be a plurality of layers, wherein each layer independently may be selected from the group consisting of poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(ether-ether ketone) (PEEK), poly( vinylidene fluoride) (PVDF), poly(tetrahydrofuran) (PTHF), poly (butylene terephthalate) (PBT), poly(methacrylic acid) (PMAA), poly(divinylbenzene) (PDVB), polyacrylic acid (PA A), poly(N-isopropylacrylamide) (PNIPAM), poly (ethyleneglycol dimethacrylate)

(PEGDMA), PEGDMA-based copolymers, copolymers therefrom (such as PMMA -based copolymers, PS-based copolymers, PEEK-based copolymers, PVDF-based copolymers, PTHF-based copolymers, PBT-based copolymers, PMAA-based copolymers, PDVB-based copolymers, PAA-based copolymers, PNIP AM-based copolymers, or PEGDMA-based copolymers) and copolymers thereof.

The encapsulated particle may be in the form of a solid powder.

The encapsulated particle may have a particle size in the range of about 1 x 10 ⁹ m to about 1 x 10 ⁶ m, about 1 x 10 ⁹ m to about 1 x 10 ⁷ m, about 1 x 10 ⁹ m to about 1 x 10 ⁸ m, about 1 x 10 ⁶ m to about 1 x 10 ⁷ m, about 1 x 10 ⁶ m to about 1 x 10 ^s m, about 1 x 10 ⁷ m to about 1 x 10 ⁸ m, about 1 x 10 ⁸ m to about 1 x 10 ⁹ m, about 5 x 10 ⁹ m to about 5 x 10 ⁷ m, about 5 x 10 ⁹ m to about 5 x 10 ⁸ m, or about 5 x 10 ⁸ m to about 5 x 10 ⁷ m.

The encapsulated thermochromic dye particle may have a transition temperature where the particle changes colour in response to a change in temperature. The transition temperature may be about 50 °C to about 180 °C, about 50 °C to about 160 °C, about 50 °C to about 140 °C, about 50 °C to about 120 °C, about 50 °C to about 100 °C, about 50 °C to about 80 °C, about 50 °C to about 60 °C, about 160 °C to about 180 °C, about 140 °C to about 180 °C, about 120 °C to about 180 °C, about 100 °C to about 180 °C, about 80 °C to about 180 °C, about 60 °C to about 180 °C, about 60 °C to about 80 °C, about 60 °C to about 100 °C, about 60 °C to about 120 °C, about 60 °C to about 140 °C, about 60 °C to about 160 °C, about 80 °C to about 100 °C, about 80 °C to about 120 °C, about 80 °C to about 140 °C, about 80 °C to about 160 °C, about 100 °C to about 120 °C, about 100 °C to about 140 °C, about 100 °C to about 160 °C, about 120 °C to about 140 °C, about 120 °C to about 160 °C or about 140 °C to about 160 °C.

The encapsulated particle may comprise:

from about 15 % to about 50 % by weight of the transition metal;

from about 10 % to about 45 % by weight of the ligand; and from about 30 % to about 80 % by weight of the shell.

Therefore, the encapsulated particle may have a transition metal content of about 15 % to about 50 % by weight, about 15 % to about 40 % by weight, about 15 % to about 30 % by weight, about 20 % to about 50 % by weight, about 30 % to about 50 % by weight, about 40 % to about 50 % by weight, about 20 % to about 30 % by weight, about 20 % to about 40 % by weight, or about 30 % to about 40 % by weight.

The encapsulated particle may have a ligand content of about 10 % to about 45 % by weight, about 10 % to about 40 % by weight, about 10 % to about 35 % by weight, about 10 % to about 30 % by weight, about 10 % to about 25 % by weight, about 10 % to about 20 % by weight, about 10 % to about 15 % by weight, about 15 % to about 45 % by weight, about 20 % to about 45 % by weight, about 25 % to about 45 % by weight, about 30 % to about 45 % by weight, about 35 % to about 45 % by weight, about 40 % to about 45 % by weight, about 15 % to about 20 % by weight, about 15 % to about 25 % by weight, about 15 % to about 30 % by weight, about 15 % to about 35 % by weight, about 15 % to about 40 % by weight, about 20 % to about 25 % by weight, about 20 % to about 30 % by weight, about 20 % to about 35 % by weight, about 20 % to about 40 % by weight, about 25 % to about 30 % by weight, about 25 % to about 35 % by weight, about 25 % to about 40 % by weight, about 30 % to about 35 % by weight, about 30 % to about 40 % by weight, or about 35 % to about 40 % by weight.

The encapsulated particle may have a shell content of about 30 % to about 80 % by weight, about 30 % to about 75 % by weight, about 30 % to about 70 % by weight, about 30 % to about 65 % by weight, about 30 % to about 60 % by weight, about 30 % to about 55 % by weight, about 30 % to about 50 % by weight, about 30 % to about 45 % by weight, about 30 % to about 40 % by weight, about 30 % to about 35 % by weight, about 35 % to about 80 % by weight, about 40 % to about 80 % by weight, about 45 % to about 80 % by weight, about 50 % to about 80 % by weight, about 55 % to about 80 % by weight, about 60 % to about 80 % by weight, about 65 % to about 80 % by weight, about 70 % to about 80 % by weight, about 75 % to about 80 % by weight, about 35 % to about 40 % by weight, about 35 % to about 45 % by weight, about 35 % to about 50 % by weight, about 35 % to about 55 % by weight, about 35 % to about 60 % by weight, about 35 % to about 65 % by weight, about 35 % to about 70 % by weight, about 35 % to about 75 % by weight, about 40 % to about 45 % by weight, about 40 % to about 50 % by weight, about 40 % to about 55 % by weight, about 40 % to about 60 % by weight, about 40 % to about 65 % by weight, about 40 % to about 70 % by weight, about 40 % to about 75 % by weight, about 45 % to about 50 % by weight, about 45 % to about 55 % by weight, about 45 % to about 60 % by weight, about 45 % to about 65 % by weight, about 45 % to about 70 % by weight, about 45 % to about 75 % by weight, about 50 % to about 55 % by weight, about 50 % to about 60 % by weight, about 50 % to about 65 % by weight, about 50 % to about 70 % by weight, about 50 % to about 75 % by weight, about 55 % to about 60 % by weight, about 55 % to about 60 % by weight, about 55 % to about 65 % by weight, about 55 % to about 70 % by weight, about 55 % to about 75 % by weight, about 60 % to about 65 % by weight, about 60 % to about 70 % by weight, about 60 % to about 75 % by weight, about 65 % to about 70 % by weight, about 65 % to about 75 % by weight, or about 70 % to about 75 % by weight. The shell may be silica or titania and therefore the silica shell content or titania shell content may be as above.

Exemplary, non-limiting embodiments of a method of forming an encapsulated particle will now be disclosed.

The method of forming an encapsulated particle may comprise the steps of:

(a) mixing at least one transition metal precursor with a metal ligand or oxidizing agent in a sol-gel solution in a solvent to form a metal complex inorganic core; and

(b) coating the metal complex inorganic core with at least one shell forming material to form a shell that at least partially encapsulates the metal complex inorganic core, wherein the metal complex comprises at least one central transition metal ion coordinated to at least two ligands.

The transition metal precursor may be a transition metal salt having a transition metal cation selected from Group 3 to 12 of the Periodic Table of Elements and an anion selected from the group consisting of chloride (Cl ), bromide (Br ), iodide (I ), acetate (CH ³ COO ), sulfate (S0 ₄ ² ), perchlorate (00 ₄ ), nitrate (N0 ₃ ), carbonate (C0 ₃ ² ), boron fluoride (BF ₄ ), hydroxide (OH ), cyanide (CN ), and isocyanine (SCN ). Therefore, the transition metal cation may be selected from the group consisting of nickel, cobalt, molybdenum, tungsten, copper, gold, silver, chromium and mercury, and the anion selected from the group consisting of chloride (Cl ), bromide (Br ), iodide (I ), acetate (CH ³ COO ), sulfate (S0 ₄ ² ), perchlorate (C10 ₄ ), nitrate (N0 ₃ ), carbonate (C0 ₃ ² ), boron fluoride (BF ₄ ), hydroxide (OH ), cyanide (CN ), and isocyanine (SCN ).

The ligands may be independently selected from the group consisting of nitrogen containing organic molecules, phosphate containing organic molecules, sulphur containing organic molecules, chloride, bromide, iodide, perchlorate, boron fluoride, hydroxide, cyanide and isocyanine.

The ligand may be independently selected from the group consisting of oxide, hydroxide, potassium iodide, diisopropylammonium chloride, diphenyl ethyltriethoxysilane phosphine, diphenyl propyl-phosphine, 3,3’-thiodipropionic acid, diethylammonium chloride, N,N- diethylethylenediamine, diphenylethyl triethoxysilanephosphine, bis(N-isopropyl-5,6- benzos alicy lideneiminato), N-(3- propyltrimethoxysilane)imidazole, and thiosemicarbazones.

The sol-gel solution may be a silica sol-gel solution or a titania sol-gel solution.

The sol-gel precursor forming the resultant sol-gel solution may be selected from the group consisting of tetraethoxysilane, trimethoxy(propyl)silane, 3-(trimethoxysilyl)propyl methacrylate, n- Propyltriethoxysilane, trimethoxy(3,3,3-trifluoropropyl)silane, triethoxy(octyl)silane, isobutyl(trimethoxy)silane, triethoxy(ethyl)silane, trimethoxy(octadecyl)silane, trimethoxy[3- (methylamino)propyl] silane, trimethoxy(octyl)silane, lh, lh, 2h, 2h-perfluorooctyltriethoxysilane, (pentafluorophenyl)triethoxysilane, lh, lh, 2h, 2h-perfluorodecyltriethoxysilane, lh, lh, 2h, 2h- perfluorodecyltrimethoxysilane, titanium(IV) ethoxide, tetraethyl orthotitanate, titanium(IV) butoxide, titanium(IV) isopropoxide, and zirconium(IV) propoxide solution.

In order to form the sol-gel solution, the sol-gel precursor may be exposed to a sol-gel catalyst. The sol-gel catalyst may be selected from the group comprising of mineral acids and inorganic bases. The sol-gel catalyst may be hydrochloric acid, nitric acid, sodium hydroxide or ammonia solution. The normality of the acid or base may be in the range of about IN to about 6N, or about IN to about 2N.

The solvent may be selected from the group consisting of isopropyl alcohol, diethyl ether, tetrahydrofuran, ethanol, water, dimethylformamide, ethyl acetate, dimethyl sulphoxide, acetonitrile and methylene chloride.

The at least one shell-forming material used in the coating step may result in the formation of an inorganic shell or a polymeric shell. Where the shell is an inorganic shell, this may be formed using the sol-gel precursor and sol-gel catalyst mentioned above. Where the shell is a polymeric shell, the shell forming material may be a monomer selected from the group consisting of alkyl acrylate, styrene, ether, ketone, vinylidene (di)fluoride, cyclic ether, butylene terephthalate, acrylic acid, alkenyl benzene, alkylacrylamide, alkyleneglycol acrylate and combinations thereof. The polymer shell coating may then be formed using surface-initiated polymerization, emulsion or co-precipitation techniques.

Exemplary, non-limiting embodiments of a composite will now be disclosed. The composite may comprise a plurality of encapsulated particles embedded within a polymer matrix, wherein each of the plurality of encapsulated particles comprises an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates the inorganic core. The composite may be a thermochromic composite. The encapsulated particles may be homogeneously dispersed within the polymer matrix.

The encapsulated particles are as described above.

The polymer matrix may be selected from the group consisting of poly acrylates, polycaprolactone, low-density polyethylene, high-density polyethylene, polyvinylidene floride, and copolymers thereof.

The thermochromic composite may be photo-stable under exposure to continuous UV light and visible light of about 15 watts to 150 watts for up to about 30 days, where the thermochromic DE values for colour difference of the said composite at transition temperature, remain essentially unchanged after the continuous visible light exposure.

The thermochromic composite may be thermal- stable under exposure to high temperature of about 100 °C to about 150 °C, about 100 °C to about 140 °C, about 100 °C to about 130 °C, about 100 °C to about 120 °C, about 100 °C to about 110 °C, about 110 °C to about 150 °C, about 120 °C to about 150 °C, about 130 °C to about 150 °C, about 140 °C to about 150 °C, about 110 °C to about 120 °C, about 110 °C to about 130 °C, about 110 °C to about 140 °C, about 120 °C to about 130 °C, about 120 °C to about 140 °C, or about 130 °C to about 140 °C, for up to about 15 minutes, where the thermochromic DE values for colour difference of the said composite at transition temperature, remain essentially unchanged after the high temperature exposure.

The thermochromic composite may be weather- stable under exposure to moisture of about 30 °C to about 95 °C, about 30 °C to about 90 °C, about 30 °C to about 80 °C, about 30 °C to about 70 °C, about 30 °C to about 60 °C, about 30 °C to about 50 °C, about 30 °C to about 40 °C, about 40 °C to about 95 °C, about 50 °C to about 95 °C, about 60 °C to about 95 °C, about 70 °C to about 95 °C, about 80 °C to about 95 °C, about 90 °C to about 95 °C, about 40 °C to about 50 °C, about 40 °C to about 60 °C, about 40 °C to about 70 °C, about 40 °C to about 80 °C, about 40 °C to about 90 °C, about 50 °C to about 60 °C, about 50 °C to about 70 °C, about 50 °C to about 80 °C, about 50 °C to about 90 °C, about 60 °C to about 70 °C, about 60 °C to about 80 °C, about 60 °C to about 90 °C, about 70 °C to about 80 °C, about 70 °C to about 90 °C, or about 80 °C to about 90 °C, for up to about 2 minutes, where the thermochromic DE values for colour difference of the said composite at transition temperature, remain essentially unchanged after the moisture exposure.

Exemplary, non-limiting embodiments of a method of forming a composite will now be disclosed.

The method of forming the composite may comprise the step of dispersing a plurality of encapsulated particles into a polymer solution or a polymer precursor solution, wherein each of the plurality of encapsulated particles comprises an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates the inorganic core.

The encapsulated particles are as described above.

The dispersing step may comprise the step of solution blending, melt blending, or extruding.

Where solution blending is used, the encapsulated particles may be mixed with one or more polymer solution or polymer precursors and then solidified through evaporation or photo-polymerization. Where melt blending or extrusion is used, the encapsulated particles may be dispersed into the polymer matrix by hot blending or screw extruder. The melting temperature used in the melt blending or extrusion may be of about 120 °C to about 200 °C, about 120 °C to about 190 °C, about 120 °C to about 180 °C, about 120 °C to about 170 °C, about 120 °C to about 160 °C, about 120 °C to about 150 °C, about 120 °C to about 140 °C, about 120 °C to about 130 °C, about 130 °C to about 200 °C, about 140 °C to about 200 °C, about 150 °C to about 200 °C, about 160 °C to about 200 °C, about 170 °C to about 200 °C, about 180 °C to about 200 °C, about 190 °C to about 200 °C, about 130 °C to about 140 °C, about 130 °C to about 150 °C, about 130 °C to about 160 °C, about 130 °C to about 170 °C, about 130 °C to about 180 °C, about 130 °C to about 190 °C, about 140 °C to about 150 °C, about 140 °C to about 160 °C, about 140 °C to about 170 °C, about 140 °C to about 180 °C, about 140 °C to about 190 °C, about 150 °C to about 160 °C, about 150 °C to about 170 °C, about 150 °C to about 180 °C, about 150 °C to about 190 °C, about 160 °C to about 170 °C, about 160 °C to about 180 °C, about 160 °C to about 190 °C, about 170 °C to about 180 °C, about 170 °C to about 190 °C, or about 180 °C to about 190 °C.

The extrusion may be carried out at a temperature of about 120 °C to about 200 °C, about 120 °C to about 180 °C, about 120 °C to about 160 °C, about 120 °C to about 140 °C, about 140 °C to about 200 °C, about 160 °C to about 200 °C, about 180 °C to about 200 °C, about 140 °C to about 160 °C, about 140 °C to about 180 °C, or about 160 °C to about 180 °C, and at a pressure of about 200 bar to 1000 bar, about 200 bar to 800 bar, about 200 bar to 600 bar, about 200 bar to 400 bar, about 400 bar to 1000 bar, about 600 bar to 1000 bar, about 800 bar to 1000 bar, about 400 bar to 600 bar, about 400 bar to 800 bar, or about 600 bar to 800 bar.

When forming the composite, the encapsulated particle may be present in a concentration in the range of about 0.5 % to about 20 % by weight, about 0.5 % to about 18 % by weight, about 0.5 % to about 15 % by weight, about 0.5 % to about 13 % by weight, about 0.5 % to about 10 % by weight, about 0.5 % to about 8% by weight, about 0.5 % to about 5 % by weight, about 0.5 % to about 3% by weight, about 0.5 % to about 1 % by weight, about 1 % to about 20 % by weight, about 3 % to about 20 % by weight, about 5 % to about 20 % by weight, about 8 % to about 20 % by weight, about 10 % to about 20 % by weight, about 13 % to about 20 % by weight, about 15 % to about 20 % by weight, about 18 % to about 20 % by weight, about 1 % to about 3 % by weight, about 1 % to about 5 % by weight, about 1 % to about 8 % by weight, about 1 % to about 10 % by weight, about 1 % to about 13 % by weight, about 1 % to about 15 % by weight, about 1 % to about 18 % by weight, about 3 % to about 5 % by weight, about 3 % to about 8 % by weight, about 3 % to about 10 % by weight, about 3 % to about 13 % by weight, about 3 % to about 15 % by weight, about 3 % to about 18 % by weight, about 5 % to about 8 % by weight, about 5 % to about 10 % by weight, about 5 % to about 13 % by weight, about 5 % to about 15 % by weight, about 5 % to about 18 % by weight, about 8 % to about 10 % by weight, about 8 % to about 13 % by weight, about 8 % to about 15 % by weight, about 8 % to about 18 % by weight, about 10 % to about 13 % by weight, about 10 % to about 15 % by weight, about 10 % to about 18 % by weight, about 13 % to about 15 % by weight, about 13 % to about 18 % by weight, or about 15 % to about 18 % by weight of the total composite.

The formed thermochromic composite may exhibit colour changes distinctly and reversibly at the transition temperature of about 50 °C to about 180 °C, wherein the thermochromic DE value between room temperature and transition temperature is in the range of 10 to 90.

The encapsulated thermochromic dye particle may be applied as an additive in a composition or formulation, wherein the encapsulated particle comprises an inorganic core comprising a metal complex having at least one central transition metal ion coordinated to at least two ligands; and a shell that at least partially encapsulates said inorganic core.

The encapsulated particles are as described above.

There is also provided the use of a thermochromic composite in temperature sensing or indicating applications as well as use of the thermochromic composite as a green building material. Brief Description of Drawings

The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

Fig.lA

[Fig. 1A] is a schematic illustration of the structure of an encapsulated thermochromic dye particle 600 having an inorganic core 200 comprising a metal complex having at least one central transition metal ion 300 coordinated to at least two ligands 400; and a shell 100 that at least partially encapsulates the inorganic core 200.

Fig.lB

[Fig. IB] is a schematic illustration of a structure of a thermochromic composite 700 comprising a plurality of encapsulated thermochromic dye particles 600 embedded within a polymer matrix 500.

Fig.2

[Fig. 2] is UV-vis absorption spectra of the PAC thermochromic composites at room temperature and at 55°C, where the corresponding thermochromic colour change was calculated to be 13.8.

Fig.3A

[Fig. 3A] shows the photo-stability test setup for the PAC thermochromic composite at room temperature of 25 °C.

Fig.3B

[Fig. 3B] shows the comparison of the PAC thermochromic composite sample (a) before and (b) after 30 days illumination under the fluorescent lamp in the photostability test.

Fig.4

[Fig. 4] is UV-vis absorption spectra of the PAC thermochromic composite after subjection to photo-stability test at room temperature and 55°C, where the corresponding thermochromic colour change was calculated to be 14.7.

Fig.5A

[Fig. 5A] is UV-vis absorption spectra of the 100°C thermal-treated PAC thermochromic composite after subjection to thermal-stability test at room temperature and 55°C, where the corresponding thermochromic colour change was calculated to be 15.8.

Fig.5B

[Fig. 5B] is UV-vis absorption spectra of the 150°C thermal-treated PAC thermochromic composite after subjection to thermal-stability test at room temperature and 55°C, where the corresponding thermochromic colour change was calculated to be 13.5.

Fig-6

[Fig.6] shows the LDPE thermochromic composite sample for photo-stability test at room temperature of 25°C, where the LDPE thermochromic composite 1000 had exposed surface area 800 and aluminium-wrapped surface area 900.

Fig-7

[Fig.7] is UV-vis absorption spectra of the LDPE thermochromic composite before (PS-B) and after (PS-A) subjection to 30 days of photo- stability test, where the corresponding thermochromic colour change was calculated to be 1.03. Fig.8

[Fig.8] is UV-vis absorption spectra of the LDPE thermochromic composite before (TS-B) and after (TS-A) heating at 100°C for 15 minutes, measured at room temperature in comparison with the LDPE thermochromic composite at 55°C (TS-C). The thermochromic colour changes for the LDPE thermochromic composite were calculated to be 1.26, 47.61 and 46.97 for TS-A versus TS-B, TS-B versus TS-C and TS-A versus TS-C respectively.

Fig.9

[Fig.9] is a UV-vis absorption spectra of the LDPE thermochromic composite before (WS-B) and after (WS-A) the water submersion procedure for the weather-stability test, in comparison with the LDPE thermochromic composite at 55°C (WS-C). The thermochromic colour changes for the LDPE thermochromic composite were calculated to be 2.62, 49.80 and 47.90 for WS-A versus WS-B, WS-B versus WS-C and WS-A versus WS-C respectively.

Examples

Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Materials and Methods

All the reagents were obtained from commercial suppliers and used without further purification. Commercially available (3-aminopropyl)triethoxysilane (APTES), isopropyl alcohol, glacial acetic acid, nickel(II) perchlorate hexahydrate, copper(II) chloride dihydrate, copper(II) perchlorate hexahydrate, absolute ethanol, N,N-diethylethylenediamine, N,N-dimethylethylenediamine, sodium hydroxide, hydrochloric acid, (pentafluorophenyl)triethoxysilane, tetraethylorthosilicate (TEOS), and poly-a-caprolactone (PCL) were purchased from Sigma-Aldrich (of St. Louis, Missouri of the United States of America). Characterization of the samples was done using the UV-vis spectrophotometer from Perkin Elmer (model LAMBDA 1050).

Example 1: Synthesis of encapsulated thermochromic dye particle 1

Encapsulated thermochromic dye particles 1 were synthesized in a base-catalysed sol-gel mixture followed by polymerization. Briefly, an isopropyl alcohol solution containing tetraethoxysilane (0.1 M) in the presence of ammonium hydroxide (pH of solution adjusted to 11) was stirred at room temperature overnight to obtain the sol-gel solution. An equivalent molar ratio of nickel chloride and diethylammonium chloride were mixed into the sol-gel solution and ultrasonicated in an ice -water bath for 30 minutes, followed by constant stirring at room temperature for 8 hours. The solution was transferred to an ice water bath and the precipitation induced was collected by suction filtration. The collected precipitate was washed with isopropyl alcohol twice to remove any free ligands.

The collected thermochromic dye particles 1 were dried in a vacuum oven at 80 °C for 8 hours. The transition temperature was determined at 72 °C, with colour change from yellow to blue. The dried thermochromic particles 1 (5 g) were dispersed in 500 ml of anhydrous toluene under strong stirring. Thereafter, 0.5 ml of APTES was added and the solution was ultra-sonicated by using a ultrasonicator (model Esquire Biotech, 500W) with pulse amplitude level of 40 % for a total operation time of 40 minutes with each pulse and cooling step at 15 seconds, for 80 cycles of ultrasonication. The solution was stirred for 30 minutes at 800 rpm at room temperature. Thereafter, 10 ml ethanol and 0.2 ml of 1 N HN0 ₃ solution were added to each 2.5 ml of pre -hydrolysed solution containing the thermochromic dye particles 1. The solution was stirred at room temperature for 24 hours and the precipitate was collected by suction filtration. The precipitate was washed with anhydrous ethanol twice and then dried under vacuum for 2 hours. A schematic representation of the structure of the synthesized encapsulated thermochromic dye particle is depicted in Fig. 1A.

Example 2: Synthesis of encapsulated thermochromic dye particle 2

Encapsulated thermochromic dye particles 2 were synthesized in an acid-catalysed sol-gel mixture followed by polymerization. Briefly, a tetrahydrofuran (THF) solution was mixed with trimethoxy(octadecyl)silane (TMOS), tetraethoxysilane (TEOS) and HC1 solution with ratio of THF/TM0S/TE0S/HC1/H ₂ 0 = 100 : 0.75 : 2.25 : 2 x 10 ³ : 2, and the solution was stirred at room temperature for 24 hours to obtain the sol-gel solution. In separate flask, the nickel and copper nitrate salts (1: 100 in mole) were rapidly mixed with N, N-diethylethylenediamine in anhydrous tetrahydrofuran in an ice water bath. The formed mixture was slowly transferred into the prepared sol- gel solution with continuous stirring at room temperature. After 2 days of reaction, the compounds were collected by centrifugation and washed with isopropyl alcohol, water, and isopropyl alcohol alternatively to remove unreacted compounds.

The thermochromic dye particles 2 were dried in a vacuum oven at 80 °C for 8 hours. The transition temperature was determined at 55 °C, with colour change from red to purple. The encapsulation of the thermochromic dye particles 2 was done through surface polymer grafting by adding APTES. The mixture of thermochromic dye particles 2 (10 g) and APTES (0.5 ml) was stirred at 50 °C for 2 hours. Thereafter, a pre -hydrolysed poly-s-caprolactone (5 mg/ ml) solution (500 ml) was added and the mixture was stirred at 70 °C for 5 hours. The mixture was suction filtered and washed thoroughly with absolute ethanol. The encapsulated thermochromic dye particles 2 were dried in vacuum oven for 8 hours.

Example 3: Synthesis and characterization of pol acrylate (PAC) thermochromic composite by solution blending

PAC thermochromic composite was synthesized by solution blending in the following procedures: mixing of the following compounds to obtain a 100 % final weight based on di(ethylene glycol) diacrylate (65 % by weight), 1,6-Hexanediol diacrylate (33.5 % by weight), phenylbis (2, 4, 6-trimethylbenzoyl) phosphine oxide (0.5 % by weight) and the encapsulated thermochromic dye particle 2 (1 % by weight). The mixture was stirred at room temperature for 8 hours in the dark. The resultant solution was transferred into a glass mould and solidified under UV light at 365 nm for 15 minutes to obtain the PAC thermochromic composite. A schematic representation of the structure of the synthesized thermochromic composite is depicted in Fig. IB.

The absorption spectrum of the freshly prepared, room temperature samples of PAC thermochromic composite were measured with a UV-vis spectrophotometer. The transmittance was calculated and the transmittance value near 1000 nm was subtracted from all other wavelength values as a baseline correction. The PAC thermochromic composite samples were heated to the transition temperature of 55 °C for 5 minutes, and immediately placed in the UV-vis spectrophotometer to measure the absorption spectrum. The absorption spectra obtained were used to calculate CIEXYZ colour coordinates, where the CIE 2006 xyz (2 degree) colour matching function and the D65 reference illuminant spectrum were used for calculation. The CIEXYZ coordinates were used to calculate CIELAB values, L, a*, and b* values. The difference in colour of the PAC thermochromic composite samples at room temperature and transition temperature of 55 °C was determined by the calculating the thermochromic DE value according to the formula as follows:

Thermochromic AE =

The resultant UV-vis spectra of the PAC thermochromic composite samples at room temperature and at the transition temperature of 55 °C as well as the thermochromic DE are as depicted in Fig. 2. Based on Fig. 2, there is a distinct UV-vis absorption difference in the visible spectrum range from 400 nm to 800 nm at transition temperature of 55 °C as compared to room temperature and the corresponding thermochromic DE value of 13.8 to indicate the sharp and distinct thermochromic effect of the PAC thermochromic composite.

Photo-stability test of the synthesized PAC thermochromic composite

Photo-stability of the synthesized PAC thermochromic composite samples was determined by comparison of the UV-vis absorption spectra change before and after continuous illumination of the samples with an indoor fluorescent lamp of 40 watts for 30 days. The controls were prepared as such where half the surface areas of each of the PAC thermochromic composite were covered with aluminium foil. Triplicate experiments were conducted. The photo-stability test setup as depicted in Fig. 3A and the corresponding average colour change of the samples as depicted in Fig. 3B. As observed in Fig. 3B, the PAC thermochromic composite samples did not show any visible colour change after 30 days of continuous illumination. To further confirm the photo-stability of the PAC thermochromic composite samples, the UV absorption spectra values of the samples before and after 30 days illumination were measured and the corresponding thermochromic DE calculated as shown in Fig. 4. Based on the results of Fig. 4, there was no significant change in the thermochromic DE values before and after photo treatment in relation to the transition temperature. The synthesized PAC thermochromic composite samples retained their sensitivity to temperature change at the transition temperature of 55 °C and the thermochromic colour change after 30 days illumination did not reduce the sharpness of colour change. Flence, the synthesized PAC thermochromic composite samples were shown to be photo-stable.

Thermal-stability test of the synthesized PAC thermochromic composite

Thermal-stability of the synthesized PAC thermochromic composite samples was determined by comparison of the UV-vis absorption spectra change before and after subjecting the samples to high temperatures of 100 °C and 150 °C for 15 minutes.

The UV-vis absorption spectra of the freshly prepared room temperature samples were first measured. The samples were subjected to heating to transition temperature of 55 °C for 5 minutes, and immediately placed in the UV-vis spectrophotometer to measure the absorption spectrum. The results obtained were used to calculate the thermochromic DE before thermal treatment.

The samples were tested for thermal-stability by placing in an oven at high temperatures of 100 °C and 150 °C for 15 minutes and the absorption spectra were measured immediately thereafter. Subsequently, the thermal-treated samples were cooled to room temperature before heating to the transition temperature of 55 °C for 5 minutes, and immediately placed in the UV-vis spectrophotometer to measure the absorption spectra. Triplicate experiments were conducted. The results obtained were used to calculate the average thermochromic DE after thermal treatment.

The UV-vis absorption spectra and the corresponding thermochromic DE values of the fresh samples and thermally treated samples were compared as in Fig. 5 A and Fig. 5B. Based on these results, there were no significant changes in the thermochromic DE values before and after thermal treatment at 100 °C and 150 °C in relation to the transition temperature. The synthesized PAC thermochromic composite samples retained their sensitivity to temperature change at the transition temperature of 55 °C and the thermochromic colour change after thermal treatment at 100 °C and 150 °C did not reduce the sharpness of colour change. Flence, the synthesized PAC thermochromic composite samples were shown to be thermal-stable. Example 4: Synthesis and characterization of low-density polyethylene (LDPE) thermochromic composite by melting blending

LDPE thermochromic composite was synthesized by melting bending in the following procedures: briefly, 98.5 grams of LDPE grains were mixed with 1.5 grams of the encapsulated thermochromic dye particle 2 in a beaker. The mixture was poured into a hot blender with heating temperature at 130 °C, and rotation rate of 100 rpm for 10 minutes. The formed composites were peeled off from the blender, cooled to room temperature and crushed by milling into a powdered form for easy moulding. The powdered composite containing thermochromic dye particles 2 was moulded into composite sheets using the injection machine at 130 °C and 600 bar.

The LDPE thermochromic composite samples synthesized were heated to the transition temperature of 55 °C. The LDPE thermochromic composite samples before and after heating to 55 °C show visible colour change at room temperature compared to the transition temperature of 55 °C.

Photo-stability test of the synthesized LDPE thermochromic composite

Photo-stability of the synthesized LDPE thermochromic composite samples was determined by comparison of the UV-vis absorption spectra change before and after continuous illumination of the samples with an indoor fluorescent lamp of 40 watts for 30 days, similar to the procedures for PAC thermochromic composite samples as described in Example 3. The controls were prepared as such where half the surface area of the LDPE thermochromic composite was covered with aluminium foil. The photo-stability test setup as depicted in Fig. 6. Triplicate experiments were conducted. The UV absorption spectra values of the samples before and after 30 days illumination were measured and the corresponding average thermochromic DE calculated as shown in Fig. 7. Based on the results of Fig. 7, there was no significant change in the thermochromic DE values before and after photo treatment in relation to the transition temperature. The synthesized LDPE thermochromic composite samples retained its sensitivity to temperature change at the transition temperature of 55 °C and the thermochromic colour change after 30 days illumination did not reduce the sharpness of colour change. Hence, the synthesized LDPE thermochromic composite sample was shown to be photo - stable.

Thermal-stability test of the synthesized LDPE thermochromic composite

Thermal-stability of the synthesized LDPE thermochromic composite sample was determined by comparison of the UV-vis absorption spectra change before and after subjecting the sample to high temperatures of 100 °C for 15 minutes, similar to the procedures for PAC thermochromic composite samples as described in Example 3.

The UV-vis absorption spectra and the corresponding thermochromic DE values of the fresh sample and thermally treated sample were compared as in Fig. 8. Based on these results, there were no significant changes in the thermochromic DE values before and after thermal treatment at 100 °C in relation to the transition temperature. The synthesized LDPE thermochromic composite sample retained its sensitivity to temperature change at the transition temperature of 55 °C and the thermochromic colour change after thermal treatment at 100 °C did not reduce the sharpness of colour change. Hence, the synthesized LDPE thermochromic composite sample was shown to be thermal- stable.

Weather-stability test of the synthesized LDPE thermochromic composite

Weather-stability of the synthesized LDPE thermochromic composite sample was determined by comparison of the UV-vis absorption spectra change before and after subjecting the sample to full and repeated cycles of submersion in water according to the following conditions: submersion in water at 30 °C for 30 seconds, followed by submersion in water at 95 °C for 30 seconds followed by submersion in water at 95 °C for 30 seconds, and followed by a final submersion in water at 30 °C for 30 seconds.

The UV-vis absorption spectrum of the freshly prepared room temperature sample was first measured. The sample was subjected to heating to transition temperature of 55 °C for 5 minutes, and immediately placed in the UV-vis spectrophotometer to measure the absorption spectrum. The results obtained were used to calculate the thermochromic DE before weather treatment.

The sample was tested for weather-stability by subjecting to full and repeated cycles of submersion in water in the sequence: submersion in water at 30 °C for 30 seconds, followed by submersion in water at 95 °C for 30 seconds followed by submersion in water at 95 °C for 30 seconds, and followed by a final submersion in water at 30 °C for 30 seconds. In the weather stability test, the LDPE thermochromic composite showed a lighter red colour when submerged in water at 30 °C compared to a dark purple colour when submerged in water at 95 °C, indicating the difference in temperature of the water. The absorption spectrum was measured immediately thereafter. Subsequently, the weather- treated sample was heated to the transition temperature of 55 °C for 5 minutes, and immediately placed in the UV-vis spectrophotometer to measure the absorption spectra. Duplicate experiments were conducted. The results obtained were used to calculate the average thermochromic DE after weather treatment.

The UV-vis absorption spectra and the corresponding thermochromic DE values of the fresh samples and weather treated samples were compared as in Fig. 9. Based on these results, there were no significant changes in the thermochromic DE values before and after weather treatment in relation to the transition temperature. The synthesized LDPE thermochromic composite sample retained its sensitivity to temperature change at the transition temperature of 55 °C and the thermochromic colour change after weather treatment did not reduce the sharpness of colour change. Elence, the synthesized LDPE thermochromic composite sample was shown to be weather-stable.

Industrial Applicability

The encapsulated particle or composite may be used in a wide variety of applications such as in temperature sensing or indicating applications, in areas of intelligent building and packaging, infra red filtering, defence, medical, textile and consumer goods.

The encapsulated particle or composite may be suitable for smart applications to monitor the temperature change through optical switches and indicative ink for food industry to reduce waste, semi -conducting device, and medical applications.

The encapsulated particle or composite may be suitable for improving energy efficiency of building when applied to windows or other surfaces to reflect light and heat at a higher temperature while allowing light to pass at lower temperatures.

The method used to form the encapsulated particle or composite may allow for large-scale manufacturing.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.