Composite solar control coating based on tungsten bronze nanocrystals dispersed in a silica-based sol-gel matrix

Abstract

The present invention relates to a sol formulation that can be used to form a coating that shields UV and NIR irradiation, in particular a solar control coating comprising at least one or more silica-based sol-gel matrix precursors and doped tungsten bronze nanocrystals homogeneously and individually dispersed in a protic solvent medium. The invention also relates to a method for forming a solar control coating on the surface of a support using such a sol formulation, as well as to a structure comprising at least one support, preferably a transparent support having such a solar control coating on at least one of its faces.

Description

Technical Field

[0001] The present invention relates to the field of developing coatings for solar control that enable effective cutting of sunlight irradiation in various ranges. More particularly, the present invention relates to the formation of coatings based on tungsten bronze-type plasmonic nanocrystals having improved optical performance that enable effective shielding of ultraviolet and / or near-infrared light. These coatings can be used in a wide variety of applications, for example, they can be used on glass.

Background Art

[0002] In the development of glass materials having protective properties against ultraviolet (UV) irradiation and / or near-infrared (NIR) irradiation while maintaining transparency, there has been increasing interest in manufacturing a wide range of applications, particularly building and vehicle windows, greenhouses in the agricultural sector, etc.

[0003] In particular, among all the rays contained in sunlight, ultraviolet (UV) rays are undesirable because they can cause damage to human skin, accessories or equipment installed in or on vehicles, while near-infrared (NIR) rays significantly increase the internal temperature.

[0004] In particular, in today's situation where energy-efficient building renovation has become a major environmental and technical issue, the development of solar control glass, i.e., glass that enables cutting of sunlight irradiation in various wavelength ranges, is regarded as an important technical means for restricting heating and air-conditioning energy consumption. Therefore, when the climate is cold, it is important that the heat generated by heating appliances indoors or in vehicles can be stored generally within the mid-infrared (MIR) range of 3 to 18 μm [1]. On the other hand, when the climate is hot, the problem is whether it is possible to shield the near-infrared irradiation of sunlight, which is in the wavelength range of 780 to 2500 nm and corresponds to 50% of solar radiation.

[0005] Therefore, it is desirable for glass to have good transparency, that is, to have at least partial transmission of electromagnetic rays within the visible range of sunlight (denoted as Vis), and also to be able to shield the ultraviolet and near-infrared ranges to protect the interior and provide heat insulation.

[0006] Several coating technologies for glass, such as windows, windshields, verandas, and greenhouses, have already been proposed to shield ultraviolet and / or near-infrared irradiation. The most commonly used thermal screens are based on metal layers or low-emissivity coatings that effectively reflect MIR [2]. However, in order to effectively shield NIR, it is necessary to use a complex laminated structure of several functional layers. Unfortunately, these approaches are expensive, typically at least ten times more expensive than the cost of uncoated glass, and generally enable the selectivity that should be achieved in terms of wavelength transmission / extinction (this selectivity can be evaluated by the ratio of T Vis ) in the visible wavelength range to T UV and T NIR ) in the respective wavelength ranges of UV and NIR, i.e., the ratio of T Vis :T UV and T Vis :T NIR ).

[0007] "Plasmonic" particles with high absorption (high optical density) in a small amount of material and very high selectivity in their absorption wavelength range have emerged as a promising solution for NIR protection.

[0008] Conventional metals such as silver and gold have a high density of free carriers (10 22 cm -3) and when these are confined on the nanometer scale, it leads to collective oscillations of those free electrons, also known as localized surface plasmon resonance (LSPR). The phenomenon of LSPR in metals has been extensively studied over the past few decades and has applications in a wide range of optical fields ([3]). However, their absorption ranges are limited to the ultraviolet and visible regions, and the NIR range remains largely inaccessible to metals, except for complex structures such as highly anisotropic core-shell nanowires ([4]).

[0009] In this context, highly doped semiconductor nanocrystals have been gaining increasing interest as absorptive materials [5]. Their free carrier density can be adjusted to 10 18 ~10 22 cm -3 by changing their doping levels ([6]), directly during synthesis ([7]), or by subsequent processing (post-treatment) ([8]). In addition to known parameters for metals such as shape, size, or surrounding medium, and a large number of compositional possibilities, this tool enables extremely precise control of their LSPR positions from the visible to the mid-infrared (MIR) [9]. As a result, their unique features are being utilized in a number of applications, such as LSPR detection (

[10] ); bioimaging and biotherapy (

[11] ); and the development of smart windows

[12] . In particular, semiconductor nanocrystals that enable high absorption in the NIR while maintaining transparency in the visible region are thus seen as good candidates for obtaining coatings for solar control.

[0010] In particular, in many studies, indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO) nanoparticles have been used to produce active or passive devices (

[13] ). However, their LSPR located in the wavelength region of 1500 - 2500 nm remains highly transmissive to electromagnetic waves in the wavelength range of 780 - 1500 nm.

[0011] More recently, the development of novel nanocrystalline compositions such as rare earth metal hexaborides (RB6, R = La, Ce, Pr, Nd, Gd)(

[14] ) and tungsten bronzes (M x WO3, M = K, Na, Cs)(

[15] ,

[16] ,

[17] ,

[18] ,

[19] ) has enabled LSPR, and thus electromagnetic wave absorption achieved within the NIR wavelength range.

[0012] Unfortunately, there remain challenges in incorporating these nanocrystals into solid thin films without sacrificing their own LSPR intensity and selectivity. In particular, in situations where these nanocrystals are used with conventional methods for forming surface coatings, the coupling effect related to the bonding of nanocrystals at the level of a compact film structure causes a decrease in LSPR intensity and a red shift, while the aggregation of nanocrystals within the formed coating increases scattering in the visible region (

[20] ).

[0013] Among the methods proposed for the preparation of semiconductor nanocrystal-based coatings, the publication by Zeng et al.

[21] describing the production of thin films of composite resins incorporating Cs 0.33 WO3 nanoparticles prepared by a bulk milling method that provides limited control over size and shape can be cited.

[0014] The publication by T. Mattox et al.

[14] proposing a means of dispersing colloidal LaB6 in a polymer or sol-gel silica matrix by incorporating a ligand during the solvent-based synthesis of sodium borohydride can also be cited. However, this method cannot be applied to most plasmonic metal oxide semiconductors, and in its synthetic route, it uses precursors of organometallic complexes that react at high temperatures in nonpolar solvents. By varying various parameters, these syntheses enable precise control of particle size and shape, but they remain capped with nonpolar ligands, making dispersion in most polymer or silica media difficult. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] Therefore, there is still a need for means to utilize the advantageous optical properties of tungsten bronze-type plasmonic nanocrystals when used in surface coatings.

[0016] More specifically, there is still a need for a method to produce a coating based on tungsten bronze-type plasmonic nanocrystals that maintains high attenuation of electromagnetic waves, particularly in the UV and NIR ranges, while simultaneously maintaining good transparency in the visible range without impairing the properties of these nanocrystals.

[0017] The present invention is specifically directed to meeting these needs.

Means for Solving the Problems

[0018] Accordingly, the present invention provides a thin film coating based on doped tungsten bronze nanocrystals without degrading the inherent properties of these nanocrystals, particularly in terms of the intensity and selectivity of the LSPR of these nanocrystals, and as a result, proposes means for enabling the formation of a solar control coating that exhibits high attenuation of electromagnetic waves in the UV and NIR ranges while simultaneously maintaining high transparency in the visible range.

[0019] More specifically, the inventors have discovered that a coating having the required optical properties, which can effectively shield UV and near-infrared irradiation in particular, can be obtained by a method of homogeneously and individually dispersing doped tungsten bronze nanocrystals, preferably doped tungsten bronze nanocrystals with a controlled morphology and size, in a silica-based sol-gel matrix.

[0020] Such a composite coating for solar control can be produced more specifically from a sol formulation comprising a mixture of one or more precursors of a silica-based sol-gel matrix and doped tungsten bronze nanocrystals homogeneously and individually dispersed in a protic solvent medium.

[0021] Thus, according to a first aspect thereof, the present invention is a sol formulation useful for forming a solar control coating, particularly a coating for shielding UV and NIR irradiation, comprising at least, - one or more silica-based sol-gel matrix precursors, and - M called doped tungsten bronze nanocrystals homogeneously and individually dispersed in a protic solvent medium x WO 3-y type (wherein M represents potassium (K), sodium (Na) or cesium (Cs), x ranges from 0.05 to 0.33, and y ranges from 0 to 0.4) of nanocrystals relates to a sol formulation containing.

[0022] Preferably, as detailed later in the text, the doped tungsten bronze nanocrystals are advantageously surface-functionalized so that their dispersion within the sol formulation and within the composite coating formed therefrom is promoted.

[0023] The nanocrystals can preferably be functionalized with at least one ligand capable of promoting good dispersion of the nanocrystals within the sol formulation.

[0024] Such ligands may be, for example, those retaining a hydroxyl functional group, polyglycerol ligands (e.g., especially hyperbranched polyglycerol type polyglycerol ligands), or polyphosphate or organofunctional silane ligands (e.g., gamma-glycidoxypropyltrimethoxysilane (GLYMO) and (3-aminopropyl)triethoxysilane (APTES), etc.), and in particular the ligand may be hyperbranched polyglycerol.

[0025] According to another aspect, the present invention relates to the use of a sol formulation according to the invention for forming a solar control coating, in particular a solar control coating that shields UV and NIR irradiation, on the surface of a support, in particular a transparent support, more specifically a support made of glass or a transparent polymer.

[0026] In particular, the present invention relates to a method for forming a solar control coating, in particular a solar control coating that shields UV and NIR irradiation, on the surface of a support, in particular the surface of a glass or transparent polymer support, comprising at least (i) providing a sol formulation according to the invention comprising one or more silica-based sol-gel matrix precursors and doped tungsten bronze nanocrystals homogeneously individually dispersed in a protic solvent medium (preferably doped tungsten bronze nanocrystals surface-functionalized with at least one ligand as defined above, in particular a ligand bearing a hydroxyl functional group); (ii) depositing a layer of said sol formulation on the surface of said support; and (iii) drying the layer formed in step (ii) to obtain said silica-based sol-gel matrix. The invention relates to a method comprising the steps thus constituted.

[0027] According to another aspect, the present invention relates to a structure comprising at least one support, preferably transparent, in particular made of glass or a transparent polymer, having on at least one of its surfaces a solar control coating that shields UV and NIR irradiation, in particular formed from a sol formulation according to the invention as defined above, more specifically by a method according to the invention as defined above. Such a coating more specifically comprises a silica-based sol-gel matrix in which the doped tungsten bronze nanocrystals are homogeneously dispersed in an individualized manner.

[0028] In the context of the present invention, "in a given medium, such as in a sol formulation or a coating, " Individualization in a given manner or Individually"Dispersed nanocrystals" and " Individualization The terms "nanocrystals being dispersed" and "nanocrystals that are dispersed" are intended to indicate the fact that the nanocrystals do not aggregate, in other words, do not exist in the form of aggregates. In particular, the distance between two individualized nanocrystals is strictly greater than its maximum dimension, especially at least 1-fold its maximum dimension.

[0029] The aggregates of nanocrystals under consideration according to the present invention may, in some cases (from the point of view of the formed dispersion or coating), contain nanocrystals that do not conform to this feature, provided that at least 60%, especially at least 70%, of the number of nanocrystals in the aggregate meet the non-aggregation criteria. Preferably, at least 80%, especially at least 90%, preferably at least 95% of the number of nanocrystals in the aggregate under consideration are individualized.

[0030] The term "homogeneously" means that the nanocrystals are homogeneously spread on the scale of about 100 nanometers throughout the volume of the formed dispersion or coating. The homogeneity of the nanocrystal dispersion in the coating formed according to the present invention can be evaluated, as detailed in the following examples, especially by analyzing the images obtained by 3D tomography transmission electron microscopy using the Voronoi cell algorithm.

[0031] As will be explained in the subsequent examples, the inventors have found that the intrinsic optical properties of doped tungsten bronze nanocrystals are advantageously preserved in a hard and highly protective silica-based sol-gel matrix, especially in terms of the intensity and position of its LSPR.

[0032] Advantageously, the optical properties of the coating can thus be easily adjusted, especially the selectivity of attenuation in the UV and NIR ranges, by controlling the composition of the nanocrystals used, especially the level, size and morphology of the doping treatment.

[0033] Thus, as shown above, doped tungsten bronze nanocrystals may simultaneously have localized surface plasmon resonance (LSPR), strongly absorb NIR irradiation by the bandgap energy at the visible-UV boundary, and also strongly absorb UV irradiation.

[0034] The term "ultraviolet irradiation" is intended to refer to the portion of the electromagnetic spectrum within the wavelength range of 200 nm to 390 nm, while the term "near-infrared irradiation" is intended to refer to the portion of the electromagnetic spectrum within the wavelength range of 780 nm to 2500 nm. The visible spectrum means the portion of the electromagnetic spectrum within the wavelength range of 390 nm to 780 nm.

[0035] Advantageously, the doped tungsten bronze nanocrystals used have a controlled size and morphology so as to adjust the spectral position of their localized surface plasmon resonance (LSPR) peaks, thereby adjusting their NIR absorption selectivity.

[0036] It is also possible to vary the degree of doping of the tungsten bronze nanocrystals used with an alkali metal so as to control the position of the bandgap absorption within the UV range.

[0037] Thus, by adjusting the inherent properties of the nanocrystals used, it is possible to provide a coating with optimized optical properties, particularly effectively shielding UV and NIR irradiation. The ability of a coating to act as a screen against UV and NIR irradiation can be measured, for example, by measuring the attenuation spectrum of the film using a spectrophotometer, as detailed in the following examples.

[0038] In particular, the coating may have an NIR absorption rate denoted as 60% or more, particularly 70% or more, and / or a selectivity of solar energy transmission known as "SETS" of 0.70 or more, particularly 0.75 or more. NIR and may have a selectivity of solar energy transmission known as "SETS" of 0.70 or more, particularly 0.75 or more.

[0039] Selectivity of solar energy transmission (SETS)

[18] , and NIR absorption rate (A NIR ) can also be calculated from the convolution of the attenuation spectrum of the film with sunlight irradiation for the transmittance regarding the visible range setting at 80%. It can be calculated from the convolution of the attenuation spectrum of the film with sunlight irradiation for the transmittance regarding the visible range setting at 80%.

[0040] In particular, the NIR absorption rate is defined as follows

[29] .

[0041]

Equation

[0042] (In the formula, I NC represents the irradiation amount after being cut through a medium containing nanocrystals, especially a coating, and I solar represents the solar irradiation amount, and λ represents the wavelength.)

[0043] In particular, the selectivity of solar energy transmission is defined as follows

[29] .

[0044]

Equation

[0045] (In the formula, I NC , I solar and λ are as defined above.)

[0046] Furthermore, the coating is highly transparent and has an aesthetically pleasing color in the visible range. In particular, the formed coating preferably has a transmittance of 70% or more, particularly 80% or more, particularly 90% or more, and more specifically 95% or more over the entire visible spectrum.

[0047] The transmittance represents the intensity of light passing through the coating within the visible spectrum. This can be measured, for example, by UV-Vis spectroscopic analysis using, for example, a Shimadzu UV-3100 spectroscopic analyzer.

[0048] More advantageously, the coatings obtained according to the invention have a dispersion in which the doped tungsten bronze nanocrystals are homogeneously individualized in a silica-based sol-gel matrix, even when the volume fraction of the nanocrystals is high, in particular up to a volume fraction of 20%.

[0049] Thus, it is possible to obtain a coating having optimized solar control properties, in particular blocking both UV and NIR irradiation, while at the same time maintaining good transparency in the visible range.

[0050] Thus, according to another aspect, the invention relates to the use of a sol formulation according to the invention for imparting solar control properties to a support, in particular for blocking UV and NIR irradiation.

[0051] Furthermore, the formation of the coatings according to the invention has proven to be simple and inexpensive, especially compared to the coating technologies proposed to date based on complex stacks of metal layers, as previously discussed. This is because the coatings according to the invention can be produced by conventional liquid phase deposition techniques, such as spin coating.

[0052] Finally, the composite coatings formed according to the invention, in particular in the form of thin films, in particular with a thickness of less than 3 μm, have good mechanical properties, especially in terms of film flexibility and resistance to breakage.

[0053] Also, the coatings based on chemically / thermally stable inorganic oxides formed according to the invention have good durability, in particular better durability than the coatings already proposed in the prior art based on organic polymers or metal deposits.

[0054] The coatings formed according to the present invention with optimized solar control properties may have a wide range of applications. These can be used, for example, in glass structures, such as building windows, especially for reducing energy consumption in eco-buildings, vehicle glass for motor vehicles, greenhouses in agriculture, technical glass, etc.

[0055] According to another aspect, the present invention thus relates to an article comprising at least one structure as defined above, in particular to an article which is, for example, a building window, a veranda, a porthole, a motor vehicle front glass, a train glass window, a glass for a greenhouse or a solar panel used in agriculture.

[0056] Other features, variations and advantages of the coatings according to the present invention, their preparation and their properties will become even more apparent upon reading the following description, examples and drawings, which are given as a non-limiting illustration of the present invention.

[0057] In the following text, the expressions “... to...” (between... and...), “ranging from... to...” and “varying from... to...” are equivalent and are intended to mean that the boundaries are included unless otherwise specified.

Brief Description of the Drawings

[0058]

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DETAILED DESCRIPTION OF THE INVENTION

[0059] Doped tungsten bronze nanocrystals The nanocrystals used in accordance with the present invention are M x WO 3-yDoped metal oxide nanocrystals known as type (where M represents potassium (K), sodium (Na) or cesium (Cs), x ranges from 0.05 to 0.33, and y ranges from 0 to 0.4).

[0060] It is understood that the coating formed according to the present invention may use one type of nanocrystal or a mixture of at least two different nanocrystals.

[0061] In certain embodiments, the nanocrystals are cesium-doped tungsten bronze nanocrystals, or in other words, nanocrystals of the above formula (where M is cesium).

[0062] Advantageously, the nanocrystals are single crystals.

[0063] Advantageously, as described above, M x WO 3-y The characteristics of the nanocrystals are controlled and adjusted so that the desired UV and NIR absorption selectivity is achieved, particularly in terms of composition, particularly the density of free charge carriers, morphology and size.

[0064] In particular, the degree of doping of the doped tungsten bronze nanocrystals used according to the present invention with an alkali metal, such as cesium, can be adjusted relative to the desired UV bandgap position to obtain the desired absorption selectivity at the desired UV wavelength.

[0065] In particular, the degree of doping with an alkali metal, particularly cesium, can be from 0.05 to 0.33, and / or the free carrier density can be from 1×10 18 ~9×10 22 cm -3 It can be.

[0066] Advantageously, the nanocrystals have a controlled morphology, in particular a controlled shape and size, so as to tune the spectral position of their localized surface plasmon resonance (LSPR) peaks and to obtain an optimized absorption selectivity at NIR wavelengths.

[0067] Preferably, the nanocrystals are in the form of nanorods. These nanocrystals can have an aspect ratio ((AR), defined as the ratio of the longest dimension of the particle to its shortest dimension) of from 0.1 to 20, in particular from 0.4 to 12. In particular, these nanocrystals can have an aspect ratio of from 1.2 to 20, more specifically from 1.2 to 3.5, especially from 1.5 to 2.5.

[0068] These nanocrystals preferably have a length of from 4 nm to 100 nm and a width of preferably from 5 nm to 100 nm, in particular from 5 nm to 30 nm.

[0069] The nanocrystal size can be evaluated by transmission electron microscopy or X-ray diffraction analysis. It should be noted that for the purpose of characterizing the maximum dimension of the nanocrystals, the direction along the crystal growth direction, in particular the (001) direction of the crystal, is usually preferred.

[0070] In particular, the nanocrystals can have a hexagonal prism morphology.

[0071] Nanocrystal synthesis The nanocrystals can be synthesized by synthesis methods known to those skilled in the art.

[0072] Advantageously, the nanocrystals are obtained using a "bottom-up" synthesis method. The "bottom-up" synthesis method is a chemical synthesis method based on the assembly of small chemical species (atoms or molecules) to produce large objects, in this case nanocrystals. Thus, this type of synthesis is different from the method of producing nanocrystals by powder grinding.

[0073] Advantageously, bottom-up nanocrystal synthesis enables precise control of the size and morphology of the nanocrystals.

[0074] More specifically, the doped tungsten bronze nanocrystals can be obtained by synthesis from precursors in a solvent medium, particularly from tungsten hexacarbonyl (W(CO)6) and a precursor of metal M.

[0075] In certain embodiments, as described in Example 1.2, for example, the nanocrystals of cesium-doped tungsten bronze can be obtained by synthesis from tungsten hexacarbonyl (W(CO)6) and an oleate of an alkali metal M, such as cesium oleate, in oleic acid.

[0076] Such a synthetic route is described, for example, in reference

[19] . More specifically, it includes the steps of mixing a powder of W(CO)6 and a precursor of the metal oleate, particularly cesium oleate, in oleic acid, and subsequently heating to a temperature of at least 200 °C, particularly 300 °C, for a period of at least 1 minute, particularly 30 minutes.

[0077] Surface functionalization of nanocrystals As described above, the doped tungsten bronze nanocrystals are preferably surface-functionalized, and their individual dispersion within the sol formulation used to form the solar control coating according to the present invention and within the coating formed according to the present invention is promoted.

[0078] According to certain embodiments, the doped tungsten bronze nanocrystals are surface-functionalized with a ligand that retains a hydroxyl functional group.

[0079] Without wishing to be bound by theory, the interaction between the hydroxyl functional group of the ligand grafted onto the nanocrystal surface and the silanol functional group of the silica-based sol-gel matrix precursor promotes the individual dispersion of each nanocrystal within the silica-based sol-gel network formed according to the present invention, as described in the following text.

[0080] Preferably, the doped tungsten bronze nanocrystals are surface-functionalized with a polymeric ligand, preferably a branched polymer, more preferably a hyperbranched polymer bearing hydroxyl functional groups.

[0081] The term "hyperbranched polymer" is intended to denote a branched polymer structure comprising at least two, particularly at least three, polymer branches.

[0082] Hyperbranched polymers generally result from the polycondensation of one or more monomers of the ABx type (where A and B are reactive groups capable of reacting together and x is an integer of 2 or more), although other preparation methods are conceivable.

[0083] Advantageously, the doped tungsten bronze nanocrystals are surface-functionalized with a branched polyglycerol ligand, preferably hyperbranched polyglycerol.

[0084] The nanocrystals can be directly functionalized with polyglycerol on the nanocrystal surface by polymerizing polyglycerol, for example by ring-opening polymerization of glycidol.

[0085] Thus, in a preferred embodiment, the doped tungsten bronze nanocrystals, preferably surface-functionalized with a ligand, such as a ligand bearing hydroxyl functional groups, before being used in the sol formulations according to the invention, - the bottom-up synthesis of the nanocrystals from tungsten hexacarbonyl (W(CO)6) and a metal M precursor, particularly in a solvent medium as described above, more specifically in oleic acid, from tungsten hexacarbonyl (W(CO)6) and an oleate of an alkali metal M, such as cesium oleate, the step of bottom-up synthesis of said nanocrystals, and preferably, - the step of functionalizing the surface of the synthesized nanocrystals with a ligand selected from at least one ligand, particularly at least one hydroxyl-bearing ligand, particularly a hyperbranched hydroxyl-bearing polymer, more specifically the hyperbranched polyglycerol described above It is prepared by

[0086] Other nanocrystal surface functionalizations that promote the dispersion of individual nanocrystals during the formation of the sol-gel matrix according to the present invention are also conceivable.

[0087] As an example, the nanocrystals can be surface-functionalized with functional polyphosphates or organic-functional silane-type ligands (such as gamma-glycidoxypropyltrimethoxysilane (GLYMO) or (3-aminopropyl)triethoxysilane (APTES), etc.).

[0088] Coatings based on nanocrystals dispersed in a silica-based sol-gel matrix As shown above, the present invention is based on a dispersion of individual doped tungsten bronze nanocrystals in a silica-based sol-gel matrix.

[0089] Dispersion of silica-based sol-gel matrix precursors As shown above, the coating is more specifically at least - Said nanocrystals of doped tungsten bronze (in particular as defined above, preferably nanocrystals of doped tungsten bronze surface-functionalized with the aforementioned ligands, especially ligands retaining a hydroxyl functional group, such as hyperbranched polyglycerol), individually and homogeneously dispersed in a protic solvent medium, and - One or more precursors of said silica-based sol-gel matrix are obtained from a sol formulation containing

[0090] When this sol formulation is deposited on the surface, the precursors are condensed by evaporation of the solvent to form a network trapped in the solvent. By these polymerization reactions, further condensed species are formed, resulting in colloidal particle-forming gels. When these gels are dried and densified at a temperature of about several hundred °C, a solid composite coating formed from a sol-gel matrix incorporating said nanocrystals is obtained.

[0091] The silica-based sol-gel matrix formed according to the present invention can be a silica sol-gel matrix or a sol-gel matrix of a mixed silica / titanium oxide or silica / zirconium oxide.

[0092] More specifically, the precursor of the silica-based sol-gel matrix includes at least an organosilane containing a hydrolyzable functional group that forms a silica network or matrix.

[0093] Generally, the organosilane has the formula R n SiX (4-n) (wherein, n is equal to 0, 1, 2, 3, the groups X may be the same or different and represent a hydrolyzable group selected from alkoxy, acyloxy or halide groups, preferably alkoxy, the groups R may be the same or different and represent a non-hydrolyzable organic group bonded to silicon by a carbon atom) and can be.

[0094] In particular, the sol formulation according to the present invention, as a silica-based sol-gel matrix precursor, may include at least one organosilane of the above formula R n SiX (4-n) (wherein n is 0 or 1), that is, an organosilane known as a "sol-gel precursor" capable of forming a three-dimensional network, and forms a sol-gel matrix.

[0095] In particular, the sol formulation according to the present invention may include at least one organosilane precursor, all of whose groups are hydrolyzable.

[0096] This sol-gel precursor preferably has the following formula:

[0097]

Chemical formula

[0098] (wherein, R1, R2, R3 and R4 may be the same or different, preferably the same, preferably a linear C1-C5, preferably a C1-C3 alkyl chain) is a silicon alkoxide or alkoxysilane of.

[0099] In a particular embodiment, especially when the tungsten bronze nanocrystals are surface-functionalized with polyglycerol, the sol formulation uses at least tetramethoxysilane of the formula Si(O-CH3)4, i.e., TMOS, as the sol-gel precursor.

[0100] Advantageously, the alkoxysilane type sol-gel precursor in which all the groups are hydrolyzable is combined with at least one different sol-gel precursor that retains at least one non-hydrolyzable group.

[0101] The sol-gel precursor more specifically has at least one non-hydrolyzable group, preferably of the following formula:

[0102]

Chemical formula

[0103] (wherein, R1', R2', R3' and R4' may be the same or different, preferably the same, preferably a linear C1-C5, preferably a C1-C3 alkyl chain, more preferably a methyl group) and may be of the silicon alkoxide or alkoxysilane type containing.

[0104] In a particular embodiment, the sol-gel precursor that retains the non-hydrolyzable group is methyltrimethoxysilane of the formula H3C-Si(O-CH3)3, i.e., MTMOS.

[0105] The addition of such sol-gel precursors, especially MTMOS, can affect the mechanical properties of the coating formed by loosening the formed silica sol-gel network. In particular, the destruction of the coating film formed after cooling to room temperature is avoided.

[0106] According to certain embodiments, the dispersion for forming the coating according to the invention thus uses, as precursors of the silica-based sol-gel matrix, at least one alkoxysilane sol-gel precursor in which all groups are hydrolyzable and at least one alkoxysilane sol-gel precursor in which at least one group is non-hydrolyzable.

[0107] Advantageously, this dispersion uses at least a mixture of TMOS and MTMOS.

[0108] Preferably, the sol-gel precursor containing non-hydrolyzable functional groups (e.g., MTMOS) is present in the dispersion in a molar ratio not exceeding that of the sol-gel precursor in which all groups are hydrolyzable (e.g., TMOS).

[0109] Advantageously, the molar ratio between the alkoxysilane sol-gel precursor in which all groups are hydrolyzable and the alkoxysilane sol-gel precursor in which at least one group is non-hydrolyzable, in particular the molar ratio TMOS:MTMOS, is strictly greater than 1, in particular from 6:4 to 9:1, preferably 7.5:3.5.

[0110] In particular, the organosilane-type precursor, especially alkoxysilane, is present in the sol formulation according to the invention in a content of 0.12 mol / L to 9 mol / L, in particular 1 mol / L to 5 mol / L, in the sol formulation.

[0111] Needless to say, the present invention is not limited to the aforementioned sol-gel precursors, and other precursors may be considered as long as they result in the formation of a silica-based sol-gel matrix.

[0112] In particular, when forming a mixed silica / titanium oxide or silica / zirconium oxide sol-gel matrix, the sol formulations according to the invention may comprise a mixture of one or more of the above-described organosilane sol-gel precursors, in particular alkoxysilanes, and one or more titanium alkoxides or zirconium alkoxides.

[0113] Preferably, the molar amount of said precursor of the titanium alkoxide type (or the molar amount of said precursor of the zirconium alkoxide) can be from 0 to 100%, in particular from 0 to 30%, of the amount of silane.

[0114] Furthermore, the sol formulations according to the invention may comprise one or more sol-gel precursors comprising at least one non-hydrolyzable functional group capable of imparting specific properties to the formed sol-gel matrix, such as properties of color, hydrophobicity, oleophobicity, antifouling, anti-icing, etc. In particular, the sol formulations according to the invention may use, as sol-gel precursors comprising at least one non-hydrolyzable functional group, gamma-glycidoxypropyltrimethoxysilane (GLYMO) in order to improve the resistance of the coatings formed, in particular in relation to the problem of cracking that may occur during drying or heat treatment.

[0115] Similarly, the coatings formed according to the invention, based on sol formulations and thus on silica-based sol-gel matrices, may optionally contain, in addition to the said nanocrystals according to the invention, other particles, such as pigments and / or photocatalytic systems.

[0116] The protic solvent medium of the sol formulation used to form the solar control coating according to the invention can be formed from a single protic solvent or a mixture of protic solvents.

[0117] More specifically, said solvent can be selected from water, alcohols containing from 1 to 5 carbon atoms such as methanol, ethanol or propan-1-ol, and mixtures thereof.

[0118] According to certain embodiments, the sol formulation according to the present invention contains water and a mixture of one or more C1-C5 alcohols. Preferably, the protic solvent medium is a mixture of water and methanol.

[0119] The protic solvent medium advantageously occupies 40% to 99% by volume, particularly 60% to 99% by volume, of the sol formulation according to the present invention.

[0120] The nanocrystals can be used in the sol formulation at a ratio of 1 to 50 mg / mL, particularly 1 to 15 mg / mL.

[0121] The sol formulation according to the present invention can be formed by mixing the various components at room temperature. Advantageously, the mixture is subjected to stirring, for example ultrasonic stirring, to enable accurate homogenization and dispersion.

[0122] Preferably, the sol formulation is ultrasonically treated for 10 to 90 minutes, for example 30 minutes, before application.

[0123] Coating formation According to another aspect thereof, the present invention relates to the use of a sol formulation as defined above for forming a coating on the surface of a support.

[0124] In the context of the present invention, the term "support" refers to a solid underlying structure on at least one side of which a coating according to the present invention is formed.

[0125] The support can be of various types depending on the desired application.

[0126] The support can be a flexible support or a rigid support. The support can be modified in shape and surface structure according to the application for which the coating is intended. The support can be flat or non-flat.

[0127] Preferably, the support has good transparency. Advantageously, the support has a transmittance of 70% or more, particularly 80% or more, especially 90% or more, and more specifically 95% or more across the entire visible spectrum.

[0128] The transmittance represents the intensity of light passing through the support within the visible spectrum. This can be measured, for example, by UV-Vis spectroscopic analysis using, for example, a Shimadzu UV-3100 spectroscopic analyzer.

[0129] Thus, the support can be made of glass or a transparent polymer such as polycarbonate, polyolefin, polyethersulfone, polysulfone, phenolic resin, epoxy resin, polyester resin, polyimide resin, polyetherester resin, polyetheramide resin, polyvinyl acetate, cellulose nitrate, cellulose acetate, polystyrene, polyurethane, polyacrylonitrile, polytetrafluoroethylene (PTFE), polyacrylate, such as polymethyl methacrylate (PMMA), polyarylate, polyetherimide, polyetherketone, polyetheretherketone, polyvinylidene fluoride, polyester, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polyamide, zirconia, or derivatives thereof.

[0130] In certain embodiments, the support is made of glass. The silica-based sol-gel matrix coating according to the present invention advantageously has good affinity with the glass support.

[0131] The support, among other things, has a thickness of 500 nm to 1 cm, particularly 10 μm to 5 mm.

[0132] By way of example, the support can be in the form of sheet glass that is imparted with solar control properties to maintain good transparency in the visible range while particularly blocking UV and near-infrared irradiation.

[0133] The present invention also relates to a support, preferably a transparent support having a coating formed from the sol formulation according to the invention on at least one side.

[0134] The method for preparing the coating according to the invention is of course adapted to the shape of the support to be coated.

[0135] Generally, as described above, the formation of the coating includes (ii) a step of depositing a layer of the dispersion on the surface of the support and (iii) a step of drying the layer to form a coating based on the silica-based sol-gel matrix.

[0136] The sol formulation can be applied to the surface of the substrate to be coated by any liquid-phase precipitation technique known to those skilled in the art. For example, the deposition in step (ii) of the sol formulation is carried out by spin coating, slot die coating, blade coating, spraying, dip coating, etc.

[0137] In a particular embodiment, the sol formulation is applied by spin coating.

[0138] The deposited dispersion layer can have a thickness of 20 nm to 10 μm, particularly 100 nm to 5 μm.

[0139] The deposited layer preferably has a uniform thickness.

[0140] Therefore, the deposited layer is preferably homogeneous in composition and thickness.

[0141] The sol-gel coating is obtained by curing the dispersion, and thus contains the silica-based sol-gel matrix, in particular the product resulting from the hydrolysis and condensation of the precursor of the organosilane as described above, optionally as a mixture with one or more titanium alkoxides or zirconium alkoxides.

[0142] Drying is carried out under conditions that promote the condensation of the sol-gel precursor and the removal of the solvent, forming a silica-based sol-gel network.

[0143] In particular, drying can be carried out at a temperature of 40 °C to 250 °C, especially about 100 °C, and for a period of 1 hour to 48 hours, especially 3 hours to 24 hours.

[0144] Thus, the obtained film or coating is based in particular on a silica-based sol-gel matrix formed from a sol-gel precursor as defined above, and the doped tungsten bronze nanocrystals are dispersed in an individualized and homogeneous manner.

[0145] The coating can have a thickness of 10 nm to 25 μm, especially 30 nm to 10 μm, more specifically 100 nm to 7 μm.

[0146] The nanocrystals can be present in the formed composite coating at a volume fraction in the range of 0.1% to 30% by volume, especially 0.5% to 15% by volume.

[0147] Preferably, the volume fraction of the nanocrystals in the composite coating is 5% or less, especially 3% or less, for example 0.5% to 2.7%.

[0148] Advantageously, the distance between the nanocrystals in the coating formed according to the invention is strictly greater than the maximum dimension of the nanocrystals. In particular, the distance between the nanocrystals can be strictly longer than 4 nm and shorter than 100 nm, especially 10 nm to 50 nm. This distance can be evaluated by analyzing the images obtained by 3D tomography transmission electron microscopy, as described in the following examples.

[0149] It is also understood that a structure according to the invention comprising at least one support holding the solar control coating according to the invention on at least one of its surfaces can also include one or more additional layers, for example an anti-scratch layer, an anti-reflection layer, a multilayer stack such as a Bragg mirror type, depending in particular on the intended use.

[0150] In particular, the structure according to the invention may also include a protective layer on the surface of the solar control coating. The solar control coating may in particular be sandwiched between the support and the protective layer.

[0151] In particular, the protective layer is amorphous silicon; Si t N x O y C z H u (where t is from 0 to 1, x is from 0 to 4 / 3, y is from 0 to 2, z is from 0 to 1, and u is from 0 to 4), in particular Si t N x (where t is from 0 to 1 and x is from 0 to 4 / 3), or SiO2, preferably Si3N4 or SiO2; Al2O3; ZrO2; ZnO; Ag; Al; in particular polymers selected from polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polymethyl methacrylate (PMMA) and poly(butyl acrylate) (PBA); or mixtures thereof. Preferably, the protective layer can be made of Si3N4, SiO2, Al2O3 or mixtures thereof. The protective layer can be made of a polymer selected from PVA, PVP, PMMA and PBA. Advantageously, the protective layer can be made of a highly transparent material. For example, the protective layer can be deposited by evaporation, chemical vapor deposition (CVD), cathodic sputtering or liquid deposition.

[0152] As described above, the solar control coating according to the invention can be adapted to a wide variety of objects in a wide range of applications.

[0153] The structure according to the invention can more specifically be used, for example, for windows such as building windows, verandas, the front glass of motor vehicles, the glass windows of trains such as portholes, or the glass equipped on the surface of greenhouses or solar panels used in agriculture.

[0154] Needless to say, the use of the solar control coating according to the invention is not limited to the above applications, and other applications of the sol formulation and / or coating according to the invention can also be envisaged.

[0155] The present invention is herein described by the following examples and drawings, which are of course given as a non-limiting illustration of the present invention.

Example

[0156] In the following examples, the property evaluations were performed as follows.

[0157] X-ray analysis (XRD) An X-ray diffraction (XRD) pattern was obtained using a Bruker D8 Advance diffractometer with Cu Kα X-rays operating at 40 kV and 40 mA. Data were collected from 2θ = 5° to 2θ = 90° with a step size of 0.02° and a scan speed of 0.9 s / step. For analysis, nanocrystals were deposited on an oriented silicon wafer substrate (400) by the drop casting technique.

[0158] Fourier transform near-infrared spectroscopy (FTIR) Fourier transform near-infrared (FTIR) spectroscopy measurements were performed using a Bruker Equinox 55 spectroscopic analyzer in transmission mode with nanocrystal pellets (2 mass%) in KBr.

[0159] Dynamic light scattering method (DLS) Measurements were performed three times in total for each sample using a Zetasizer Nano ZS instrument.

[0160] Scanning electron microscopy (SEM) Films were imaged on silicon wafers (surface and cross-section) using a Hitachi 4800 SEM scanning electron microscope (SEM).

[0161] Attenuation spectrum of the film The attenuation spectrum of the film was measured using a LabSpec 4 ASD spectrophotometer connected by an optical fiber in a glove box.

[0162] Reflectivity measurement Reflectivity measurements were performed using the UMA instrument of an Agilent Cary 5000 spectrophotometer with a detector placed at 10° at an incident angle of 5°.

[0163] Image processing The obtained reconstructions were processed using ImageJ software. First, a 3D hybrid median filter was applied to reduce noise, and subsequently, the volume was binarized using a common threshold calculated using the maximum entropy method. A further 3D median filtering step was used on the binary volume using a structured object size of 2×2×2 nm 3 Segmentation / labeling was performed using the "3D Object Counter" plugin, which also enables extraction of the centroid coordinates and volume of the nanocrystals, by binarizing the volume using the threshold calculated from the image using the Otsu method. The Voronoi diagram was calculated using the centroid positions with the "Tess library on Pithon". This creates 3D polyhedra (called Voronoi cells) each containing a particle. The faces of these polyhedra are defined as a set of points by the tangential distance between two adjacent particles.

[0164] (Example 1) 1.1 Synthesis of nanocrystals with various aspect ratios These nanocrystals were synthesized using the Schlenk line technique. Oleic acid (technical grade, 90%, from Sigma-Aldrich) was used as the solvent and degassed at 120 °C for 3 hours before synthesis.

[0165] To obtain aspect ratios of 0.5 and 0.8, 652 mg (2 mmol) of WCl4 was mixed with 10 mL of oleic acid (0.2 M) and degassed at 120 °C for 30 minutes to prepare a tungsten oleate precursor. In another bottle, for aspect ratios of 0.5 and 0.8, 56 mg (0.33 mmol) and 1060 mg (6 mmol) of CsCl (Sigma-Aldrich) were respectively mixed with 45 mL of oleic acid. The mixture was degassed at 120 °C for 30 minutes, then heated to 300 °C under a nitrogen atmosphere, and then 5 mL (1 mmol) of the tungsten oleate precursor was rapidly injected.

[0166] To obtain aspect ratios of 1.8 and 2.9, a cesium oleate precursor was prepared by degassing a 0.2 M Cs2CO3 solution (Sigma-Aldrich) in oleic acid at 120 °C for 30 minutes. Next, for aspect ratios of 1.8 and 2.9, 156 mg (0.44 mmol) of W(CO)6 (Sigma-Aldrich) was respectively mixed with 73 μL (0.015 mmol) and 36.5 μL (0.007 mmol) of the cesium oleate precursor and 20 mL of oleic acid. The mixture was degassed for 30 minutes and then heated to 300 °C.

[0167] To obtain an aspect ratio of 6.2, a tungsten oleate precursor was prepared by leaving 10 mL of a 0.1 M W(CO)6 solution in oleic acid in an oil bath at 180 °C overnight under a nitrogen stream. 1 mL of this solution was injected into a 0.75 mM cesium oleate precursor solution in oleic acid at 300 °C.

[0168] For all aspect ratios, the reaction mixture was maintained at 300 °C for 30 minutes and then cooled to room temperature. The reaction flask was transferred to a glove box under a nitrogen atmosphere, and the nanocrystals were washed by centrifugation and then dispersed in toluene at a concentration of 10 mg / mL.

[0169] The obtained nanocrystals were analyzed by transmission electron microscopy (TEM), and their dimensions measured for over 200 particles are reported in Table 1 below. Their morphology is also shown in Figure 1a.

[0170]

Table 1

[0171] The attenuation spectra of various nanocrystals were measured in a solution in tetrachloroethylene (TCE) and are shown in Figure 1a. It is observed that the aspect ratio of the nanocrystals enables the adjustment of the position and spectral shape of the localized surface plasmon resonance (LSPR) peak.

[0172] 1.2 Cs x WO 3-y Synthesis of nanocrystals (also denoted as “h-Cs:WO3”) (hexagonal structure) Nanorod-shaped Cs having a hexagonal structure denoted as h-Cs:WO3 with an aspect ratio (AR) of 1.9 (width 6.8 ± 1.5 nm and length 12.7 ± 4.5 nm) x WO 3-y type nanocrystals were synthesized using a method of heating a cesium oleate precursor obtained from W(CO)6 powder and cesium carbonate (Cs2CO3) in oleic acid according to the following protocol.

[0173] These nanocrystals were synthesized using the Schlenk line technique (vacuum gas trap).

[0174] Oleic acid (technical grade, 90%, from Sigma-Aldrich) was used as the solvent and degassed at 120 °C for 3 hours before synthesis. 236 mg (1 mmol) of Cs2CO3 was mixed with 10 mL of oleic acid (0.2 M cesium), and degassed at 120 °C for 30 minutes under vacuum to prepare the cesium oleate precursor.

[0175] Next, 156 mg (0.44 mmol) of W(CO)6 was mixed with 326 μL (0.06 mmol) of cesium oleate and 39.67 mL of oleic acid. The mixture was degassed under vacuum for 30 minutes, then heated to 300 °C under a nitrogen atmosphere, maintained for 30 minutes, and cooled to room temperature.

[0176] The reaction flask was transferred to a glove box, washed with 2-propanol, and the nanocrystals were dispersed in toluene.

[0177] Figure 1b is a transmission electron microscope (TEM) photograph of the obtained nanocrystals. Analysis by high-resolution transmission electron microscopy (HRTEM) confirms that the obtained nanocrystals are indeed single crystals, but from the image by X-ray analysis (XRD) (Figure 2), the hexagonal phase of tungsten bronze is confirmed.

[0178] (Example 2 (comparative)) Preparation of a film based on nanocrystals surface-functionalized with a DMOAP ligand 2.1. Preparation of nanocrystals surface-functionalized with a DMOAP ligand (referred to as NC@DMOAP) After the synthesis described in Example 1.2, visual inspection of the nanocrystals stored in toluene shows a tendency to strongly aggregate and loosely aggregate over time. To prevent this phenomenon, the oleic acid ligand surrounding the nanocrystals is exchanged with a DMOAP (N,N-dimethyl-N-[3-(trimethoxysilyl)propyl]-1-octadecanaminium chloride) ligand according to the following protocol.

[0179] 10 mg of nanocrystals (2.5 mg / mL in toluene) was mixed with 100 μL of DMOAP (42% in methanol), sonicated for 1 hour, and then washed with ethanol.

[0180] When the oleic acid ligand is exchanged with a DMOAP-type ligand, their colloidal stability is enhanced in non-polar solvents such as toluene or tetrachloroethylene.

[0181] Figure 3 shows the attenuation spectra of nanocrystals coated with oleic acid (aggregated state) and DMOAP (dispersed state) at the same concentration (0.0667 mg / mL). Aggregated particles have a high attenuation coefficient in the visible region due to aggregation diffusion, but their LSPR is not very strong due to the coupling effect between nanocrystals

[11] .

[0182] This test shows that the dispersed state of plasmonic nanocrystals has a significant impact on their optical properties.

[0183] 2.2. Preparation of Films Based on NC@DMOAP Nanocrystals A film based on NC@DMOAP nanocrystals was prepared by spin-coating a 60 mg / mL solution of NC@DMOAP nanocrystals in toluene at 1000 rpm for 90 seconds. A dense and homogeneous NC@DMOAP film was obtained.

[0184] Figure 4 shows a scanning electron microscope (SEM) image of the cross-section of the obtained film.

[0185] Figure 5 shows the spectra of the attenuation coefficient ε of nanocrystals dispersed in solution and in the film, calculated according to the Beer-Lambert law.

[0186] [Equation 1] A = ε.I.f V (where A represents the absorption (absorption maximum) at a specific wavelength, I represents the optical path length passing through the sample (corresponding to the film thickness), f V represents the volume fraction of nanocrystals (set at 70% for the film

[12] ,

[20] ).)

[0187] This figure is normalized by the total amount of nanocrystals and the sample shape, making it possible to easily compare between different arrangements.

[0188] When the nanocrystals overlap, due to the expected LSPR coupling effect, the characteristics of the film from the perspective of LSPR are inferior compared to the solution, and it may be observed that the transparency in the visible region is also inferior.

[0189] By convoluting their spectra with sunlight irradiation (Figure 5), and their selectivity of solar energy transmission (SETS)

[18] , and for a visible transmittance set at 80%, their NIR absorption rate (A NIR ) can be calculated to evaluate the selectivity for near-infrared irradiation (NIR) for solar protection applications. The SETS and A NIR values calculated according to SI are collated in Table 2 below.

[0190]

Table 2

[0191] The transfer from nanocrystals dispersed in solution to a compact film results in a 36% loss of A NIR and a 58% loss of the attenuation coefficient.

[0192] Also, for a well-dispersed solution, the values obtained for the selectivity of solar energy transmission and the NIR absorption rate, SETS = 0.778 and A NIR = 75.6% prove the good selectivity obtained with Cs 0.33 WO3 powder (SETS = 0.713 and A NIR = 72.6%)

[18] compared to Cs with an exact morphology (aspect ratio of 1.9) x WO 3-y nanocrystals. These results highlight the advantage of using bottom-up synthesis to accurately control the particle size and shape, and thus the position of their LSPR.

[0193] The loss of transparency in the visible range is due to the refractive index of the nanocrystals, causing the film to reflect (Figure 6). The film also reflects in the NIR and accounts for 25% of the complete attenuation in this wavelength range.

[0194] The impact on absorption by stacking nanocrystals as a dense layer can be estimated by subtracting the reflectance from the attenuation.

[0195] It can be seen that the LSPR coupling between nanocrystals in the formed dense film is responsible for a 72% decrease in NIR absorption.

[0196] (Example 3) Preparation of a composite film according to the invention based on nanocrystals surface-functionalized with polyglycerol 3.1. Preparation of nanocrystals surface-functionalized with hyperbranched polyglycerol (denoted as "hyperbranched NC@polyglycerol") According to the protocol described below, adapting references

[22] ,

[23] , the nanocrystals synthesized with oleic acid as described in Example 1.2 were surface-functionalized with polyglycerol ligands.

[0197] 1 mL of a solution of nanocrystals in toluene synthesized in Example 1.2 was added to 1.25 mL of glycidol in a glass tube with a Teflon (registered trademark) seal. This tube was placed in a microwave oven, the temperature was raised to 120 °C and maintained for 2 hours. After the reaction, the mixture was cooled to room temperature, washed with acetone, and the free polymer was removed by repeating ultrafiltration (10,000 Daltons) in methanol.

[0198] Microwave heating enables the initiation of ring-opening polymerization of glycidol on the surface of the nanocrystals, and the resulting hyperbranched polyglycerol polymer retains a large number of hydroxyl groups (Figure 7), ensuring good solubility in water and methanol by establishing hydrogen bonds.

[0199] Results Nanocrystals surface-functionalized with polyglycerol have the same shape and dimensions (7.2±1.7nm×13.7±4.9nm) before and after functionalization, demonstrating that the reaction does not attack the nanocrystal surface and that the ligand shell surrounds individual nanocrystals.

[0200] By Fourier transform near-infrared (FTIR) spectroscopy (Figure 8), the grafting effect of the polyglycerol ligand was confirmed, and the absorption band at 1700 cm -1 due to oleic acid (C=O valence vibration) disappears after grafting. On the other hand, the absorption band at 1096 cm -1 (C-O-C valence vibration), the absorption band at 2900 cm -1 (C-H2 valence vibration) and the absorption band at 3380 cm -1 (hydrogen-bonded -OH valence vibration) are characteristic of polyglycerol.

[0201] The absorption band in the 500~1030 cm -1 region corresponds to the W-O unit of h-CsWO3 particles.

[0202] Thermogravimetric analysis (Figure 9) suggests that the glycerol shell represents 56% of the total mass of the sample. The density of the ligand bound to the surface of the nanocrystals can be estimated to be about 40 monomers / nm 2 which corresponds to a lower density of the polyglycerol molecular chains and varies as a function of the polymer chain length.

[0203] The accurate dispersion of the functionalized nanocrystals in methanol was verified by the visual appearance of the solution that does not scatter light (Figure 10) and by TEM imaging (Figure 11) showing well-dispersed nanocrystals on the grid.

[0204] Furthermore, by dynamic light scattering (DLS) measurement, a monodisperse particle distribution with a hydrodynamic radius of 20.8±0.7 nm was confirmed, which is consistent with the dimensions of the nanorods and the radius (18.1±3.1 nm) obtained for DMOAP-functionalized nanocrystals (NC@DMOAP) in toluene.

[0205] 3.2 Formation of Composite Films According to the Invention with Functionalized Nanocrystals in a Sol-Gel Matrix A mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMOS) is selected as the precursor for the formation of the sol-gel composite. Methanol is produced by the hydrolysis of TMOS and MTMOS.

[0206] A silica sol-gel matrix incorporating hyperbranched NC@polyglycerol nanocrystals is formed as follows.

[0207] 0.75 molar equivalents of TMOS were mixed with 0.35 molar equivalents of MTMOS and 4 molar equivalents of H2O at pH 1. The solution was stirred for 1 hour, diluted to the desired concentration in methanol, and then added to the hyperbranched NC@polyglycerol nanocrystals.

[0208] For all samples, the nanocrystal concentration was set to 9 mg / mL and the amount of silica was increased. The solution was sonicated for 30 minutes to initiate condensation, and then deposition was carried out by spin coating at 1000 rpm for 90 seconds.

[0209] Thereafter, the film was placed on a hot plate at 100 °C overnight.

[0210] On the one hand, films were formed on silicon wafers for electron microscopy analysis and on the other hand on glass for optical measurements.

[0211] Without wishing to be bound by theory, the individual dispersion of each nanocrystal within the network is preferred due to the strong interaction between the numerous -OH groups of the ligands grafted on the nanocrystal surface and the silanol functional groups of the silica precursor.

[0212] The addition of MTMOS enables the improvement of the mechanical properties of the layer by relaxing the silica network. The molar ratio of TMOS:MTMOS that advantageously enables the avoidance of layer cracking after cooling to room temperature is 7.5:3.5.

[0213] The FTIR spectrum of the composite film (Figure 8) shows a strong absorption band (asymmetric Si-O-Si valence vibration) at 1063 cm -1 in combination with weak bands at 960 cm (Si-OH valence vibration) and 3470 cm -1 for -OH valence vibration, which corroborates a high degree of condensation

[24] . -1

[0214] (Example 4) Characterization of silica sol-gel matrix films incorporating hyperbranched NC@polyglycerol nanocrystals As described in Example 3, several composite coatings with varying volume fractions of nanocrystals (0.9% - 14.6% f V ) in the silica matrix were prepared and the influence of their structures on their optical properties was investigated.

[0215] The exact structure was studied by electron tomography. Films with volume fractions of nanocrystals f V = 1.1% and f V = 2.7% were thinned to 200 nm thickness by FIB (focused ion beam).

[0216] 2D projections (Figure 12) by TEM analysis at an angle of 0° show good dispersion of nanocrystals in all cases.

[0217] The high - speed Fourier transform method highlights the presence of edge contrast corresponding to a family of crystal planes of the P63 / mcm space group with a hexagonal lattice, related to h-Cs x WO 3-y nanocrystals.

[0218] ​Figure 13 shows the segmented 3D model for each volume fraction extracted from the tomography data. The elongation of the nanocrystals in the z-direction

[25] caused by the "loss of vertices" in the acquisition of the tilt series can be observed, which induces a loss of resolution in the direction parallel to the beam direction and thus deforms the nanocrystals. Their volume distributions were extracted from the analyzed volumes and compared with their distributions by standard TEM of the nanocrystals deposited by the technique of droplet attachment onto the carbon lattice. The resulting 33% difference may be due to this deformation, which supports the reliability of current image processing and emphasizes the individual dispersion of the nanocrystals.

[0219] The homogeneity of the nanocrystal dispersion was analyzed using the Voronoi cell algorithm and compared with a random arrangement of particles of the same particle density. In many cases, this calculation is used to characterize granular dispersions, thereby making it possible to explain the local environment of each particle. The nanocrystals are defined by the position of their centroids rather than their surface areas, and artifacts of elongation in the z-direction are removed.

[0220] Three parameters were extracted from the Voronoi partition and summarized in Table 3 below.

[0221] N neighbors The number of nearest neighbor crystals of each nanocrystal, denoted as, which corresponds to the number of self-faces in the Voronoi partition, shows a monodisperse distribution in all cases (Figure 14), meaning that each nanocrystal has the same local environment. Furthermore, the distribution is centered around a neighborhood of about 14 - 15, which corresponds to a random stacking of individual spheres in the literature. Furthermore, the histogram of the local volume fraction f V,local (defined as the average volume of the nanocrystals divided by the cell volume) is also monodisperse, having an average value corresponding to the macroscopic volume fraction and a standard deviation corresponding to the nanocrystal size. The good agreement between these two elements and between the experiment and the simulation suggests a homogeneous dispersion for both samples. Furthermore, d N-NThe histogram of the nearest-neighbor inter-crystalline distances, denoted as, has the same shape between the experiment and the simulation (Figure 15). The slight difference in the average values may be due to the electrostatic repulsive force between the nano-crystals in the experiment.

[0222]

Table 3

[0223] For the experiments and simulations, parameters were extracted from the Voronoi tessellation for samples with nano-crystal volume fractions of 1.1% and 2.7%.

[0224] In conclusion, the coating formed according to the present invention does indeed have an individual and homogeneous dispersion of nano-crystals, at least up to a nano-crystal volume fraction f V = 2.7% (corresponding to 200 mg / mL).

[0225] Therefore, the main difference related to the structure of the various films with f V ≦ 2.7% is the distance between the nano-crystals.

[0226] (Example 5) Effect of the volume fraction of film nano-crystals on the optical properties The normalized attenuation spectra of composite films with various nano-crystal volume fractions prepared as described in Example 3 are shown in Figure 16. It can be confirmed that as f V decreases, the transparency in the visible region increases. This effect is due to the decrease in the reflectivity of the film as the silica content increases. Furthermore, when the nano-crystals are further diluted, the NIR attenuation becomes narrower and further blue-shifts.

[0227] By examining only the absorption, the effect on the nano-crystal LSPR of the film structure was analyzed (taking attenuation - reflectivity). Due to the combined effect of LSPR coupling and the change in the refractive index of the medium surrounding the nano-crystals, f VAs it increases, the peak position redshifts.

[0228] In addition to the redshift of the LSPR position, LSPR coupling also has an impact on the attenuation coefficient of the nanocrystals. At a nanocrystal volume fraction greater than 2.7%, as the attenuation coefficient decreases, it deviates from the linearity of the Beer-Lambert law (Figure 17). Here, the slope of the reference line is the attenuation coefficient of the nanocrystals in a well-dispersed solution. This deviation starts at a center-to-center distance of the nanocrystals of 20.0 ± 4.6 nm, which corresponds to a surface-to-surface distance of 10.0 ± 2.3 nm corresponding to the average size of the nanocrystals. This corresponds to the plasmon hybridization model established for metal nanoparticles, suggesting that when the surface-to-surface distance between two particles is approximately equal to the particle diameter, LSPR coupling between the two particles begins to occur.

[0229] Therefore, the optimal nanocrystal content in the film to maintain good NIR selectivity and a good attenuation coefficient is f V <2.7%. The reason is that the coating with f V = 1.1% has an optical parameter A NIR = 74.2% for NIR absorbance, a selectivity for solar energy transmission SETS = 0.770, and an attenuation coefficient ε = 15.3 μm -1 (Figure 18).

[0230] These results are very close to the parameters in a well-dispersed solution and higher than those obtained with crushed powder dispersed in silica (SETS = 0.757 and A NIR = 71.4%)

[18] . Furthermore, A NIR is calculated for 80% visible transmittance, which is achieved with a coating thickness of 6.0 μm corresponding to a two-layer structure where one is spin-coated on top of the other.

[0231] (Example 6) Effect of the protective layer on the stability of the attenuation spectrum As described in Example 1.1, nanocrystals with an aspect ratio of 0.5 were synthesized.

[0232] Following the same protocol as detailed in Example 3, the nanocrystals were surface-functionalized with hyperbranched polyglycerol and dispersed in methanol.

[0233] Gamma-glycidoxypropyltrimethoxysilane (GLYMO) was selected as the precursor for forming the sol-gel composite. A composite incorporating functionalized nanocrystals with an aspect ratio of 0.5 was formed as follows.

[0234] 0.97 mL of water was added dropwise to 4 mL of GLYMO at pH = 1.0 (HCl), and the mixture was left under stirring for 2 hours for hydrolysis. Then, 0.172 g of aluminum acetylacetonate (Al(acac)3) was added, and the solution was stirred until dissolution was complete. A solution of polyglycerol-functionalized nanocrystals dispersed in methanol at a concentration of 10 mg / mL was added in an amount that gave a final volume fraction f v = of approximately 1.1% of the nanocrystals in the matrix. After 30 minutes of sonication, the solution was spin-coated onto a glass substrate pre-cleaned by piranha treatment at 1000 rpm for 90 seconds. The resulting layer was dried at 100 °C for 3 hours to form a solar control coating.

[0235] Thereafter, a 50-nm-thick amorphous silicon protective layer was deposited on the solar control coating by plasma-enhanced chemical vapor deposition (PECVD). Then, the resulting structure was left in ambient air, and the attenuation spectrum of the coating was measured over time. After subtracting the contribution of amorphous silicon, these are shown in Figure 19. No decrease in absorption was observed over a period of 26 hours, indicating that the protective layer is effective in preventing the oxidation of the nanocrystals, especially when exposed to air. (References) TIFF2025521665000008.tif250163

Claims

1. A sol formulation useful for forming a solar control coating, particularly an ultraviolet (UV) and near-infrared (NIR) irradiation shielding coating, comprising at least, - one or more silica-based sol-gel matrix precursors, and - M, called doped tungsten bronze nanocrystals, individually and homogeneously dispersed in a protic solvent medium x WO 3-y type nanocrystals (wherein M represents potassium (K), sodium (Na) or cesium (Cs), x ranges from 0.05 to 0.33, and y ranges from 0 to 0.4) A sol formulation comprising

2. The doped tungsten bronze nanocrystals are surface-functionalized with at least one ligand capable of promoting good dispersion of the nanocrystals within the sol formulation, The ligand is particularly selected from ligands retaining a hydroxyl functional group (e.g., polyglycerol ligand), polyphosphate, or organofunctional silane ligands (e.g., gamma-glycidoxypropyltrimethoxysilane (GLYMO) and (3-aminopropyl)triethoxysilane (APTES)), and in particular, the ligand is selected from hyperbranched polyglycerol, characterized in that the sol formulation according to claim 1.

3. The sol formulation according to claim 1 or 2, characterized in that the nanocrystals are cesium-doped tungsten bronze nanocrystals.

4. The sol formulation according to any one of claims 1 to 3, characterized in that the nanocrystals are pre-obtained by a bottom-up synthesis route.

5. The sol formulation according to any one of claims 1 to 4, characterized in that the nanocrystals have a hexagonal prism morphology.

6. The sol formulation according to any one of claims 1 to 5, characterized in that the nanocrystals are in the form of nanorods.

7. The doped tungsten bronze nanocrystals have a size and morphology controlled to adjust the spectral position of their localized surface plasmon resonance (LSPR) peak, and in particular, the nanocrystals are in the form of nanorods having an aspect ratio of 0.1 to 20, particularly 0.4 to 12, characterized in that the sol formulation according to any one of claims 1 to 6.

8. The doped tungsten bronze nanocrystals have a degree of doping treatment with an alkali metal (especially cesium) of 0.05 to 0.33 and / or a free carrier density of 1×10 18 ~9×10 22 cm -3 The sol formulation according to any one of claims 1 to 7, characterized in that it has a free carrier density of

9. The sol formulation according to any one of claims 1 to 8, characterized in that the doped tungsten bronze nanocrystals are present in the sol formulation in an amount of 1 to 50 mg / mL, particularly 1 to 15 mg / mL.

10. As the silica-based sol-gel matrix precursor, the formula: R n SiX (4-n) (wherein, n is equal to 0 or 1, Group X may be the same or different and represents a hydrolyzable group selected from an alkoxy, acyloxy or halide group, preferably an alkoxy, Group R may be the same or different and represents a non-hydrolyzable organic group bonded to silicon via a carbon atom) The sol formulation according to any one of claims 1 to 9, characterized by containing at least one organosilane of.

11. As the silica-based sol-gel matrix precursor, at least a mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMOS), in particular, strictly greater than 1, in particular a molar ratio of TMOS:MTOS of 6:4 to 9:1, preferably 7.5:3.5 The sol formulation according to any one of claims 1 to 10, characterized by containing a mixture of TMOS and MTOS.

12. The protic solvent medium is formed by one or more solvents selected from water and alcohols containing 1 to 5 carbon atoms, such as methanol, ethanol or propan-1-ol, preferably a mixture of water and methanol. The sol formulation according to any one of claims 1 to 11, characterized by being.

13. Use of the sol formulation according to any one of claims 1 to 12 for forming a solar control coating, in particular a solar control coating that shields UV and NIR irradiation, on the surface of a support, in particular a transparent support, more specifically a support made of glass or a transparent polymer.

14. A method of forming a solar control coating, in particular a solar control coating that shields UV and NIR irradiation, on the surface of a support, in particular a support made of glass or a transparent polymer, comprising at least (i) A sol formulation according to any one of claims 1 to 12, comprising at least one or more silica-based sol-gel matrix precursors and doped tungsten bronze nanocrystals (preferably doped tungsten bronze nanocrystals surface-functionalized with a ligand as defined in claim 2, in particular a ligand retaining a hydroxyl functional group), the doped tungsten bronze nanocrystals being homogeneously and individually dispersed in a protic solvent medium, providing a sol formulation containing the doped tungsten bronze nanocrystals, (ii) Depositing a layer of the sol formulation on the surface of the support, and (iii) Drying the layer formed in step (ii) to obtain the silica-based sol-gel matrix A method comprising the steps so configured. **Claim 15** The doped tungsten bronze nanocrystals, preferably doped tungsten bronze nanocrystals surface-functionalized with a ligand, - The step of bottom-up synthesis of said nanocrystals from tungsten hexacarbonyl (W(CO) 6 ), and a precursor of metal M, especially in a solvent medium, more specifically, the step of bottom-up synthesis of said doped tungsten bronze nanocrystals by synthesis in oleic acid from tungsten hexacarbonyl (W(CO) 6 ), and an oleate of an alkali metal M, such as cesium oleate, and preferably, - Functionalizing the surface of the synthesized nanocrystals with at least one ligand as defined in claim 2, in particular a ligand retaining a hydroxyl functional group, in particular a ligand selected from hyperbranched polymers retaining a hydroxyl functional group, more specifically hyperbranched polyglycerol The method according to claim 14, prepared in advance by **Claim 16** The deposition in step (ii) of the sol formulation is carried out by spin coating, slot die coating, dip coating, blade coating or spraying, preferably by spin coating, the method according to claim 14 or 15. **Claim 17** The drying in step (iii) is carried out at a temperature of 40°C to 250°C, in particular about 100°C, in particular for a period of 1 hour to 48 hours, in particular 3 hours to 24 hours, the method according to any one of claims 14 to 16. **Claim 18** At least one support (preferably transparent, in particular a support made of glass or a transparent polymer), having on at least one of its surfaces a solar control coating formed from the sol formulation according to any one of claims 1 to 12 (in particular obtained via the method according to any one of claims 14 to 17, in particular a solar control coating that shields UV and NIR irradiation). **Claim 19** The solar control coating according to claim 18, having a thickness of 10 nm to 25 μm, in particular 30 nm to 10 μm, more specifically 100 nm to 7 μm. **Claim 20** The solar control coating according to claim 18 or 19, having a volume fraction of the doped tungsten bronze nanocrystals of 0.1% to 30%, in particular 0.5% to 15%, more specifically 5% or less, preferably 3% or less. **Claim 21** The distance between the doped tungsten bronze nanocrystals in the solar control coating is strictly greater than 4 nm and 100 nm or less, in particular 10 nm to 50 nm, the structure according to any one of claims 18 to 20. **Claim 22** The structure according to any one of claims 18 to 21, wherein the solar control coating has a transmittance of 70% or more, particularly 80% or more, over the entire visible spectrum.

23. The solar control coating has an NIR absorption rate of 60% or more, particularly 70% or more of A NIR and / or a selectivity of solar energy transmission known as "SETS" of 0.70 or more, particularly 0.75 or more, the structure according to any one of claims 18 to 22.

24. The structure according to any one of claims 18 to 23, further including a protective layer on the surface of the solar control coating. wherein the protective layer is particularly amorphous silicon; Si t N x O y C z H u (wherein t is from 0 to 1, x is from 0 to 4 / 3, y is from 0 to 2, z is from 0 to 1, and u is from 0 to 4), particularly Si t N x (wherein t is from 0 to 1 and x is from 0 to 4 / 3), or SiO 2 , preferably Si 3 N 4 or SiO 2 ; Al 2 O 3 ; ZrO 2 ; ZnO; Ag; Al; a polymer, particularly a polymer selected from polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polymethyl methacrylate (PMMA), and poly(butyl acrylate) (PBA); or a mixture thereof, Preferably Si 3 N 4 , SiO 2 , Al 2 O 3 or a mixture thereof The structure according to any one of claims 18 to 23, which is made of...

25. An article comprising at least one of the structures according to any one of claims 18 to 24, particularly a glass structure (e.g., a building window, a veranda, a porthole, a front glass of a motor vehicle, a glass window of a train, a greenhouse used in agriculture or a glass structure for a solar panel).

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