Silica cluster, solution for producing a coating, method for coating a substrate, coated object, use of the silica cluster, cosmetic product and pharmaceutical product

Abstract

The invention relates to: novel silica clusters which can be produced in a microwave-assisted sol-gel method; a solution for producing a coating; a method for coating a substrate; and a coated object. Here, the silica clusters act as biodegradable film formers and coating agents. Current fields of application are cosmetics, such as hairsprays, and in the fields of agricultural and crop technology, pharmacy, veterinary medicine, medical technology, the food industry, and animal care products. The layer obtained can be biodegraded to give monosilicic acid, is biocompatible, ecologically safe, (micro)plastic-free, transparent, and vegan. The silica clusters are also suitable for use in a cosmetic product or pharmaceutical product.

Description

[0001] FRAUNHOFER SOCIETY eV; IP&PM, Intellectual Property & Project Management

[0002] P149848PC00

[0003] Silica clusters, solution for producing a coating, method for coating a substrate and coated object, use of the silica clusters, cosmetic and pharmaceutical

[0004] The present invention relates to novel silica clusters that can be produced in a microwave-assisted sol-gel process, as well as a

[0005] A solution for producing a coating, a process for coating a substrate, and a coated object. The silica clusters act as biodegradable film formers and coating agents. Current areas of application include cosmetics, such as hairsprays, as well as agricultural and plant technology, pharmaceuticals, veterinary medicine, and medical technology.

[0006] Food industry and pet care products. The resulting layer is biodegradable to monosilicic acid, biocompatible, environmentally safe, (micro)plastic-free, transparent, and vegan. The silica clusters are also suitable for use in cosmetics or pharmaceuticals. Coating agents are thin layers applied to the surface of a substrate to improve or modify specific properties.

[0007] Consumer goods such as cosmetics, personal care and household products, as well as pharmaceutical and industrial products, utilize ingredients that enable them to form a film or coating on various substrates, including keratinous substrates (e.g., hair and skin), hard surfaces (e.g., wood and metal), and other non-keratinous substrates (e.g., fabrics and objects). The components that contribute to the formation of a film or coating on a substrate's surface can be selected from a wide variety of raw materials, such as waxes, polymers (especially acrylate copolymers and polyvinylpyrrolidones), resins (e.g., polyurethane resins and acrylic resins), and oils.

[0008] A disadvantage is their low biodegradability with environmentally harmful effects, so there is an intensive search for toxicologically and ecotoxicologically compatible alternatives that can be made available to the market at a low cost.

[0009] Finally, the pollution of the world's oceans by microplastics poses a major challenge to our society and is omnipresent in daily media reports. Measures, especially a switch to environmentally friendly material alternatives, are necessary. With this goal in mind, consumer goods such as cosmetic products should also be more strictly regulated in the future and be free of microplastics or other polymers that are not biodegradable or only very slowly biodegradable, such as silicones, polyethylene glycols, poly(vinyl) acrylates, polyvinyl alcohols, or synthetic surfactants. Such cosmetic additives currently enter the soil, inland waters, and the world's oceans in enormous quantities via agricultural sewage sludge from wastewater treatment plants, where they are increasingly accumulating.Due to increased environmental awareness, pressure is steadily growing, especially among consumers, to make cosmetic products more environmentally friendly and to avoid microplastics. This is already leading to a noticeable increase in the availability of new natural cosmetic products in drugstores, pharmacies, and beauty salons.

[0010] Nevertheless, the search for functional substitutes proves extremely difficult. While hair cleansing products (shampoos), for example, can now deliver satisfactory results without problematic substances such as silicones or synthetic emulsifiers, the market, especially in the area of ​​hairsprays, is still searching for "green" alternatives. Currently, most state-of-the-art hairsprays use petroleum-based, i.e., non-biodegradable, polyvinylpyrrolidone derivatives or silicones dissolved in water / alcohol mixtures, along with other additives such as surfactants, film improvers, or sunscreens. When sprayed onto the hair, the alcohol evaporates, and the polymers (polyvinylpyrrolidone derivatives or silicones) adhere to each individual hair, resulting in hair stiffening.This hair coating is barely water-soluble, so the polymers, when showering, enter the wastewater and ultimately the environment as "microplastics"—partly as non-biodegradable polymer strands, partly as abrasion in the form of microplastic particles. A replacement with natural organic polymers (e.g., chitosan) does not currently appear to be gaining traction in the market. Furthermore, such natural cosmetic hair-strengthening products are currently only offered as hair tonics and not as hairsprays. It is currently not possible to spray natural organic polymers like chitosan from pressurized bottles over an extended period of use. After just a few applications, these polymers clog the nozzle openings, rendering the product unusable. Customer acceptance can only be expected by developing a "green" hairspray. Another approach is the use of shellac from the lac insect.While such products can deliver satisfactory results as hairsprays, they are less accepted in the natural cosmetics sector due to their animal origin. A vegan alternative is desirable.

[0011] Therefore, developing a natural, vegan, and biodegradable hairspray presents a significant chemical and technological challenge, entailing several development risks. In particular, suitable natural and vegan hairspray substances must be identified that can be sprayed without clogging pressure valves. Furthermore, to improve customer acceptance, new, innovative hair styling products should not only ensure the hairstyle stays in place but also care for the hair and scalp.

[0012] In addition to organic natural substances, inorganic molecules can also be used. For example, the only water-soluble form of silicic acid, monosilicic acid (MKS) - Si(OH)4 -, is bioactive. Scientific studies demonstrate a positive influence not only on skin and hair (Nakanashi et al., Med. Cutan. Iber. Lat. Am. 2017, 45, 29-35; de Auraujo et al., An. Bros. Dermatol. 2016, 91, 331-335), but also on bone formation and a therapeutic potential in terms of preventing Alzheimer's disease (Jurkic et al., Nutrition & Metabolism 2013, 10, 2-12).

[0013] Dissolved calcium carbonate (MC) is naturally absorbed by plants through water and metabolized within the plant to polysilicic acids. For example, polysilicic acids give bamboo and horsetails their high mechanical stability. Various grains (e.g., rice), tubers (e.g., potatoes), and fruits also store higher concentrations of polysilicic acids, which are ingested by humans and animals through the food chain (Currie et al., Annals of Botany, 2007, 100, 1383-1389). Accordingly, silicic acids are ubiquitous in the organisms of humans and animals through food and drinking water intake. After excretion, these polysilicic acids, as dissolved, metabolized MC, re-enter soils and water bodies, thus completing the nutrient cycle.

[0014] There are currently no biodegradable, vegan hairspray products on the cosmetic market. The use of an inorganic silica-based system, which degrades to MKS (microbial sulfate), is particularly novel. Biodegradable, non-vegan hair tonics (i.e., non-pressurized sprays) containing chitosan or shellac are available on the market.

[0015] Other products are based either on non-biodegradable organic polymers, such as polyvinyl alcohols, polyvinylpyrrolidone derivatives, or on non-biodegradable silicones.

[0016] For coating solutions in cosmetics (e.g., hairspray), organic polymers are currently synthesized and purified. Following application, these polymers must be dissolved in a solvent again via a spraying process. During spraying, for example with a pressurized aerosol can, the solvent evaporates, and the polymers are deposited onto the surface (e.g., hair). The individual polymer strands interact only through intramolecular bonds. Therefore, a thick application is necessary for a strong hold, which makes the hair very heavy and lacks volume.

[0017] Furthermore, conventional methods have not succeeded in producing storage-stable, alcoholic, low-molecular-weight silica clusters in sprayable form that, when sprayed onto surfaces, form a uniform, transparent film through condensation reactions as the alcohol evaporates. This has now only been achieved using microwave technology.

[0018] Silica clusters are currently produced via the sol-gel process starting from tetraalkoxysilanes or chlorosilanes. This occurs in a solvent with the addition of water and the aid of a catalyst (acid or base). Temperatures above 80 °C are typically used to promote the condensation of the sol-gel precursors. This reaction is often carried out under pressure in autoclaves. These reaction conditions promote the crosslinking and formation of solids / xerogels by favoring the condensation reactions. This allows, for example, the production of particulate sols that can be used as coating sols. The condensation of silica clusters can be monitored, for example, by NMR. Q4 units are silicon atoms whose four bonding partners are oxo bridges to another silicon atom. Q2 units have only two siloxane bonds and two bonds not to SiO₂. xcondensed units, such as -OH or -OR (R = alcohol residue or CI).

[0019] An alternative route would be synthesis starting from water glass.

[0020] Syntheses at temperatures below 80 °C are also known, such as the synthesis of precursors for spinning silica gel fibers. To protect these sols and the silica clusters generated from condensing into a solid, the reaction must be very precisely controlled, and the condensation into higher-order clusters must be carried out at temperatures below 10 °C for several weeks. The resulting sol can only be stored at room temperature for a few hours or, at most, a few days. Otherwise, intramolecular condensation into a solid occurs at room temperature.

[0021] The production of silica clusters results in cage-like structures, as schematically depicted in Fig. 1 (taken from Y. Heider et al., Chem. Rev. 2021, 121, 9674-9718). In the silica clusters shown there, each black dot represents a saturated silicon atom with four valences. Each line connecting two dots corresponds to an oxygen bridge between two silicon atoms. In the prior art, this production is carried out using a sol-gel process, in which, in a first step, a hydroxysilane is formed by the hydrolysis of a tetraalkoxysilane under acid catalysis, which then condenses into silica clusters in a second step. The following scheme illustrates the sol-gel process using the hydrolysis and condensation of TEOS (tetraethoxyethylsilane) as an example. TEOS Si(OC₂Hs)₄ is dissolved in water and / or alcohol, and an acid is added as a catalyst. The TEOS molecules hydrolyze and form silanol groups.The silanol groups condense and form silicon-oxygen bonds (Si-O-Si), releasing water or alcohol. This reaction leads to the formation of numerous silica clusters.

[0022] By controlling the reaction conditions, such as pH, temperature, and reactant concentration, the size and properties of the silica clusters can be controlled. Low-molecular-weight silica clusters can only be produced at low temperatures. Current methods are batch processes and take days or weeks.

[0023] It is not possible using conventional methods to produce storage-stable, alcoholic, low-molecular-weight silica clusters in sprayable form that, when sprayed onto surfaces, form a uniform, transparent film through condensation reactions upon evaporation of the alcohol at temperatures below 50 °C, preferably at room temperature. Either the resulting silica clusters are insufficiently cross-linked and do not harden into a solid film at these low temperatures, or the silica clusters are too reactive and cannot be stored in solution. Removing the solvent and storing the clusters in a dry state is not feasible. In this case as well, the clusters react with each other and cannot subsequently be dissolved into solution as silica clusters.

[0024] The object of the present invention is therefore to provide low-molecular-weight silica clusters that are stable in alcohol for months and only polymerize in situ to higher-molecular-weight compounds after application to a substrate, forming closed films on surfaces or coating hair for hair strengthening, and to specify possible applications. In particular, it is an object of the present invention to modify silica clusters so that they can be used as film formers or coatings on a variety of substrates. When sprayed onto surfaces, the silica clusters should form homogeneous, thin, and transparent layers on materials through in-situ condensation reactions. Furthermore, the coatings should be biodegradable and, after degradation, comprise only monosilicic acid (MCA) as a degradation product.The coating should also exhibit improved biocompatibility, in particular as determined according to DIN ISO 10993-5:2009.

[0025] This problem is solved by novel silica clusters that can be produced via a continuous process and differ from silica clusters produced by classical sol-gel synthesis without microwave action. In the process according to which the silica clusters according to the invention can be produced, a mixture containing a) one or more tetraalkoxysilanes of the general formula Si(0R)4, where R is the same or different for each occurrence and represents a linear, branched, or cyclic alkyl or alkylene group, wherein the alkyl groups orthe alkylene residues may contain primary, secondary amines, carboxylates or thiols, b) at least one solvent suitable for dissolving and mixing one or more tetraalkoxysilanes of the general formula Si(0R)4, c) water and d) at least one acidic catalyst is reacted in a monomodal microwave apparatus under electromagnetic microwave irradiation of a standing wave.

[0026] In this context, "continuous process" means that a reaction medium is passed through a reactor at a constant flow rate.

[0027] “Biodegradability” within the meaning of the present invention means the property that the coating is biocompatible (determined according to DIN ISO 10993-5:2009) and is degraded under physiological conditions.

[0028] Viscosity measurement is performed using a Brookfields viscometer with the LV-1 spindle at 80 rpm at 23 °C.

[0029] For the purposes of the present invention, a "monomodal microwave system" (also "mono-mode microwave system") is understood to be a microwave system characterized by the fact that it contains a microwave reactor and a standing electromagnetic wave propagating in one direction. Monomodal refers to the propagation or excitation of exactly one single mode in a wave or resonance system. A mode is a defined solution of the wave equation with a characteristic field or oscillation pattern, which is determined by the boundary conditions of the system. Monomodal operation thus means that only this one intrinsic solution exists or is energetically excited, while all other possible modes are suppressed.

[0030] The method according to the invention is carried out such that a "standing wave" is formed, or already exists, at least in certain areas of the microwave system. A standing wave is created by the superposition of two counter-propagating waves of the same frequency and amplitude. This results in stationary nodes, where destructive interference occurs, and antinodes, where the waves oscillate in phase and constructive interference generates maximum amplitudes.

[0031] In particular, the process is carried out in a cavity resonator of a monomodal microwave system. Here, the incident monomode microwaves, which are not directly absorbed by the reaction mixture, are reflected at the end of the cavity resonator, forming a standing wave. A short-circuit damper allows the reflection to be adjusted so that the reflected wave and the originally incident wave have the same phase. Being in phase means that the originally incident wave and the reflected wave reach their maxima and minima simultaneously. Their antinodes and nodes are located at the same points (due to spatial superposition). This doubles the wave maxima, making very efficient use of the microwave energy and thus improving the efficiency of the process.This is particularly advantageous in a particularly preferred continuous process in which the reaction mixture is passed (pumped) through a reaction tube, the tube being located in the center of the standing wave.

[0032] Surprisingly, it was found that the silica clusters according to the invention, which can be produced using the method described above, are true clusters and are therefore characterized by film-forming properties and high reactivity: After the clusters are applied to a substrate (as described below), they crosslink further, thus producing a homogeneous and consistently chemically crosslinked coating that differs fundamentally from a layer formed by nanoparticles. In the described microwave-assisted synthesis, mixtures of partially hydrolyzed and condensed alkoxysilanes are formed, which react to form the silica clusters.

[0033] The reaction time requires only seconds to minutes and is therefore significantly shorter than equivalent sol-gel processes from the state of the art.

[0034] The process yields silica clusters according to the invention, whose structural features differ from those of silica clusters produced by conventional synthesis methods known from the prior art (without the use of microwave radiation). NMR studies confirmed that the silica clusters obtained in this way surprisingly contain a higher proportion of Q2 units and remain storable even at room temperature. The ratio of Q2 to Q3 units is therefore higher in the silica clusters according to the invention. The designations "Q2" and "Q3" describe the environment of silicon atoms in a silicon-oxygen network. A Q2 unit is bonded to two other silicon atoms and has two non-bridging oxygen atoms. A Q3 unit is bonded to three other silicon atoms and has only one non-bridging oxygen atom (see also Fig. 1).

[0035] The silica clusters produced according to the invention in a microwave-assisted reaction process exhibit excellent properties as film formers and can be used as surface coating agents and film formers, as well as for the microencapsulation of active ingredients. Furthermore, other ingredients can be integrated into the coating sol, which are ultimately encapsulated in the formed layer.

[0036] According to the process for producing the silica clusters according to the invention, silica clusters can be produced that are storable in dispersion but are nevertheless reactive enough to chemically crosslink in situ, i.e., only during the coating process, without a subsequent annealing step, forming a homogeneous film on various surfaces. This results in stable silica clusters that are stable for storage for months and only crosslink to form higher molecular weight silica clusters and films upon application. Due to the amorphous nature of the layer, it is completely biodegradable to molecular weight silica (MBS) upon contact with aqueous solution. Therefore, only a natural molecule, MBS, is released into the environment after degradation. For the material to be biodegradable, the SiO₂ should be... xThe cross-linking degree of the layer must be high enough for the layer to form. However, the cross-linking degree should be low and contain only a few fully condensed Si atoms so that the hydrolysis to MKS proceeds more quickly.

[0037] Surprisingly, it has also been shown that coatings produced with the silica clusters according to the invention can be manufactured on virtually any substrate that meets the aforementioned requirements. The layers are biotoxic and degrade upon contact with water / moisture to MKS – a completely harmless biological degradation product. The cytocompatibility of the coatings can be demonstrated in accordance with DIN ISO 10993-5:2009, and the degradation to MKS in accordance with DIN 38405-21:1990.

[0038] Dissolved calcium carbonate (MC) is naturally absorbed by plants through water and metabolized within the plant to polysilicic acids. For example, polysilicic acids give bamboo and horsetails their high mechanical stability. Various grains (e.g., rice), tubers (e.g., potatoes), and fruits also store higher concentrations of polysilicic acids, which are ingested by humans and animals through the food chain (Currie et al., Annals of Botany, 2007, 100, 1383-1389). Accordingly, silicic acids are ubiquitous in the organisms of humans and animals through food and drinking water intake. After excretion, these polysilicic acids, as dissolved, metabolized MC, re-enter soils and water bodies, thus completing the nutrient cycle.

[0039] When living organisms, e.g. mammals including humans, come into contact with the manufactured coatings, no substances enter the organism that are not virtually ubiquitous in nature, namely FMD.

[0040] The toxicological and ecotoxicological compatibility of this class of substances is advantageous.

[0041] The coatings do not require the incorporation of additives, such as plasticizers, which are necessary, for example, in polymer coatings.

[0042] In particular, it is advantageous that the formed layers degrade completely to microplastics upon contact with aqueous solution, and that the base coating does not release any microplastics or other organic matter (except for traces of ethanol). This allows for the generation of biodegradable layers for many applications.

[0043] Another advantage is that the resulting layers are transparent and UV-resistant. Layers made of organic material often have a yellowish tint, which is particularly undesirable in cosmetics. Organic layers discolor over time when used outdoors under UV radiation. The inorganic layers developed here remain transparent even under UV irradiation.

[0044] Another important advantage is the storability of the brine despite the continued reactive nature of the silica clusters, which, after application to a substrate, enables crosslinking to form a homogeneous layer.

[0045] Surprisingly, the silica clusters according to the invention also exhibit a narrow molecular weight distribution (polydispersity), which is preferably in the range of 1 to 8, preferably 1 to 5, and particularly preferably 1 to 3.

[0046] As described above, the silica clusters according to the invention are not nanoparticles, but rather clusters. According to the invention, this term refers to an accumulation of atoms or molecules that lies in the boundary region between individual molecules and solids. The number of constituent building blocks is small, often only a few to a few hundred, and their properties depend strongly on their precise number and arrangement. Such clusters therefore exhibit quantized electronic or catalytic effects that cannot be easily derived from the behavior of the macroscopic material. Nanoparticles, on the other hand, are significantly larger, typically in the range of 30 to 100 nm, and possess an internal structure that corresponds to that of the solid. Clusters are still strongly characterized by the discrete nature of individual atoms, whereas nanoparticles can be understood as miniaturized pieces of the bulk material.The silica clusters according to the invention thus preferably have a mean particle diameter (number mean) of <30 nm, more preferably 2 to 25 nm, more preferably 3 to 20 nm, particularly preferably 4 to 15 nm, and especially preferably 4 to 10 nm. The mean particle diameter can be determined using conventional analytical methods, e.g., dynamic light scattering (DLS, e.g., with a ZetaSizer, Malvern). The individual diameters of a statistically representative number of clusters (e.g., several hundred) are measured and summarized in a size distribution. The number mean is calculated by taking the arithmetic mean of the measured diameters.

[0047] Examples of the solvent mentioned in b) are linear or branched aliphatic alcohols with 1 to 18 carbon atoms, in particular methanol, ethanol, n-propanol, i-propanol, and mixtures thereof. If the R group in the Si(OR)4 used is derived from a linear, branched, or cyclic alkyl or alkylene group (and the Si(OR)4 is thus a tetraalkoxysilane), it is preferred that the solvent is an alcohol of the formula ROH, in which case R of the solvent and R of the Si(OR)4 are identical.

[0048] Preferably, the silica clusters according to the invention are low molecular weight. A silica cluster is defined as low molecular weight if the number (N) of bound Si atoms is greater than or equal to 3 but less than or equal to 64.

[0049] With reaction times of just a few minutes, low-viscosity, low-molecular-weight silica clusters can be produced that are stable in alcohol for months and only polymerize in situ to higher-molecular-weight silica clusters during the spraying process, forming closed films on surfaces.

[0050] For the purposes of this invention, “low viscosity” means silica clusters whose dynamic viscosities at 21 °C range from 0.1 mPa-s to 10 mPa-s, preferably from 0.2 mPa-s to 7 mPa-s, particularly preferably from 1 mPa-s to 4 mPa-s, and most preferably from 1.5 mPa-s to 3 mPa-s.

[0051] "Highly viscous" silica clusters within the meaning of the invention are understood to be silica clusters characterized by a viscosity greater than 0.110 mPa-s and less than or equal to 100,000 mPa-s at 21°C.

[0052] The viscosities are measured of reaction products obtained as such according to the process for producing the silica clusters according to the invention and which do not undergo any work-up, such as separation of solvent (b), water (c) and catalyst (d).

[0053] The process for producing the silica clusters according to the invention significantly reduces reaction times for the production of silica clusters. The process according to the invention is characterized by considerable energy savings and a significant reduction in CCh compared to existing processes.

[0054] In a preferred embodiment of the invention, the residues R of the general formula Si(OR)4 are selected from linear or branched alkyl residues with 1 to 16 carbon atoms and / or alkenyl residues with 3 to 16 carbon atoms, wherein the residues R may be the same or different.

[0055] According to this embodiment, transparent low-viscosity to high-viscosity silica clusters are obtained.

[0056] In a further preferred embodiment of the process for producing the silica clusters according to the invention, the residues of the general formula Si(OR)4 are the same and represent the ethyl residue.

[0057] The tetraalkoxysilane particularly preferred in the process for producing the silica clusters according to the invention is tetraethoxyethylsilane (TEOS).

[0058] The silica clusters according to the invention can be applied to the surfaces of substrates, e.g. sprayed on, and cross-link there to form higher molecular weight silica clusters and a transparent film.

[0059] Another preferred embodiment of the process for producing the silica clusters according to the invention is characterized in that the acidic catalyst used has a pKa value (negative decadic logarithm of the acid dissociation constant) of pKa < 2 and is preferably selected from the group consisting of methanesulfonic acid, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and mixtures and combinations thereof.

[0060] This yields silica clusters with a narrow distribution of weight-average molecular weights in the range of 200 g / mol to 5,000 g / mol, preferably from 360 g / mol to 4,000 g / mol, and particularly preferably from 500 g / mol to 2,000 g / mol. A further preferred embodiment of the process for producing the silica clusters according to the invention is characterized in that the at least one solvent is selected from the group consisting of organic solvents, preferably alcohols, in particular ethanol.

[0061] This results in faster cross-linking to higher molecular weight silica clusters with film formation when the obtained silica clusters are sprayed onto surfaces.

[0062] Another preferred embodiment of the process for producing the silica clusters according to the invention is characterized in that the molar ratio of the totality of the tetraalkoxysilanes to the totality of the solvents is from 0.1 to 10, preferably from 0.5 to 2.0, and particularly preferably from 0.6 to 1.1.

[0063] Another preferred embodiment of the process for producing the silica clusters according to the invention is characterized in that the molar ratio of the totality of the acidic catalysts to the totality of the tetraalkoxysilanes is from 0.01 to 0.1, preferably from 0.02 to 0.05.

[0064] Another preferred embodiment of the process for producing the silica clusters according to the invention is characterized in that the temperature of the mixture during microwave irradiation is between 20°C and 100°C, preferably between 50°C and 90°C, particularly preferably between 60°C and 80°C, and especially between 60°C and 70°C. Particularly in continuous process operation, the temperature can be controlled by adjusting the intensity of the irradiated microwave energy and the flow rate. Continuous process operation enables upscaling while maintaining consistent product quality.

[0065] No decomposition of reactants and products occurs in this temperature range.

[0066] Another preferred embodiment of the method for producing the silica clusters according to the invention is characterized in that the microwave irradiation is carried out over a period of 10 seconds to 120 minutes, preferably over a period of 2 minutes to 60 minutes, particularly preferably 5 minutes to 50 minutes, and most preferably 10 minutes to 40 minutes.

[0067] In the electromagnetic field of a standing wave, hydrolysis and condensation reactions for the synthesis of low-molecular-weight silica clusters are significantly accelerated and occur within seconds to minutes. Hydrolysis and condensation reactions cease immediately upon the mixture leaving the electromagnetic field, resulting in the formation of low-molecular-weight silica clusters.

[0068] The high energy efficiency of the process for producing the silica clusters according to the invention is very advantageous, resulting from very short reaction times of seconds to minutes compared to conventional processes with reaction times of days and weeks. In conventional processes, the mixture of tetraalkoxysilane, solvent, water and acidic catalyst must be cooled to below 0 °C, which requires additional energy.

[0069] Another preferred embodiment of the method for producing the silica clusters according to the invention is characterized in that the mixture is subjected to microwave irradiation with a power of 0.1 W / cm³ related to a volume of a reaction chamber. 3 up to 10 W / cm 3 preferably 1.0 W / cm² 3 up to 7.5 W / cm 3 , preferably 2.5 W / cm 3 up to 4.5 W / cm 3 is suspended.

[0070] This preferred embodiment leads to increased energy efficiency.

[0071] Another preferred embodiment of the method for producing the silica clusters according to the invention is characterized in that the reaction of the mixture is carried out by irradiating the mixture with microwaves with an energy input of 100 W to 5000 W, preferably from 200 W to 3000 W, particularly preferably from 300 W to 2000 W, and most preferably from 350 W to 1500 W.

[0072] The advantage is improved energy efficiency.

[0073] In particular, the silica clusters according to the invention can be produced by continuous process operation. In continuous operation, the starting materials are fed into the system without interruption, and the products are simultaneously and continuously discharged. The process runs in a steady state, meaning that temperature, pressure, and concentrations remain largely constant over extended periods. For example, the (reaction) mixture can be continuously conveyed through a reaction tube of a monomodal microwave system, in which a standing wave of electromagnetic microwave irradiation is generated, at least in some areas. The microwave system can be operated either in flow mode (i.e., passing the reaction mixture through the system only once) or in recirculation mode (i.e., passing the reaction mixture through the system multiple times).

[0074] Another preferred embodiment of the method for producing the silica clusters according to the invention is characterized in that the mixture is exposed in a continuous process in a mono-mode microwave system to the electromagnetic field of a standing wave with TEIO mode and thereby absorbs 10% to 99% of the supplied microwave energy.

[0075] The advantage is further improved energy efficiency.

[0076] According to a preferred embodiment of the method for producing the silica clusters according to the invention, the mixture is converted in a continuous process in a monomodal microwave system, wherein the mixture is transported in a cavity parallel to the propagation direction of a standing electromagnetic wave in TE10 mode or perpendicular to the propagation direction of a standing electromagnetic wave in TE10 mode through a rectangular waveguide.

[0077] The abbreviation "TE" in "TE10 Mode" stands for "Transverse Electric," meaning that the electric field has no component in the direction of propagation (longitudinal direction of the waveguide). The electric field is only present in the two transverse directions (in the cross-section of the waveguide). The subscripts 1 and 0 indicate how many nodes (zeros) the electric field has in the two transverse directions of the rectangular waveguide: The first subscript 1 represents the number of nodes in the broad direction of the rectangular waveguide. A value of 1 means that there are half a wavelength of nodes along the width of the waveguide (a maximum field strength in the center and nodes at the walls). The second subscript 0 represents the number of nodes in the narrow direction of the waveguide. A value of 0 means that the electric field is constant along this axis, i.e., there are no nodes in this direction.

[0078] The monomodal microwave system used in the process for producing the silica clusters according to the invention is preferably characterized in that standing waves are formed in the rectangular waveguide and the length of the waveguide is between half a wavelength and up to 20 wavelengths, preferably 2 to 10 wavelengths, particularly preferably 3 to 6 wavelengths of the standing wave. Typically, the cross-section of the waveguide has a width of half a wavelength and a height of one quarter of the wavelength of the standing electromagnetic wave, so that it forms a TE10 mode.

[0079] The advantage is a further improvement in energy efficiency.

[0080] For example, the mixture is processed continuously in a monomodal microwave system, whereby the mixture is irradiated with microwaves in a reaction tube whose longitudinal axis is located in the direction of propagation of the microwaves in a monomodal microwave applicator.

[0081] Preferably, the mixture is irradiated with microwaves in a largely microwave-transparent reaction tube located inside a waveguide connected to a microwave generator. Preferably, the reaction tube is axially aligned with the central axis of symmetry of the waveguide.

[0082] The waveguide, which functions as a microwave applicator, is preferably configured as a cavity resonator. Furthermore, microwaves not absorbed in the waveguide are preferably reflected at its end. By configuring the microwave applicator as a reflection-type resonator, a local increase in electric field strength is achieved for the same power supplied by the generator, resulting in increased energy utilization.

[0083] The cavity resonator is preferably operated in EOln mode.

[0084] The designation "E" in the term "EOln mode" stands for the electric mode—in contrast to magnetic modes, which are designated "H." "0" refers to the number of nodes in the radial direction. A value of 0 means there are no nodes in the radial direction. "1" represents the number of nodes in the azimuthal direction, i.e., around the circumference of the waveguide. Here, 1 means there is one node. n is an integer and indicates the number of field maxima of the standing microwave along the central axis of symmetry of the resonator. In this operation, the electric field is directed along the central axis of symmetry of the cavity resonator. It has a maximum in the region of the central axis of symmetry and decreases to zero towards the surface. This field configuration is rotationally symmetric about the central axis of symmetry.Depending on the desired flow rate of the reactant through the reaction tube, the required temperature, and the required residence time in the resonator, the length of the resonator is selected relative to the wavelength of the microwave radiation used. Preferably, n is an integer from 1 to 20, more preferably from 2 to 14, and particularly preferably from 4 to 6.

[0085] Another preferred embodiment of the process for producing the silica clusters according to the invention is characterized in that the conversion of the mixture takes place in a continuous process in a mono-mode microwave plant, wherein the number of field maxima of the standing wave in the microwave reactor is 1 to 20, preferably 2 to 10, particularly preferably 3 to 6.

[0086] The advantage is the further optimization of energy efficiency.

[0087] The microwave energy is introduced into the waveguide, which functions as a microwave applicator, through suitably dimensioned holes or slots. In a particularly preferred embodiment according to the invention, the ammonium salt is irradiated with microwaves in a reaction tube located within a waveguide with a coaxial microwave transition. Microwave devices particularly preferred for this method consist of a cavity resonator, a coupling device for coupling a microwave field into the cavity resonator, and openings on two opposing end walls for guiding the reaction tube through the resonator. The microwaves are preferably coupled into the cavity resonator via a coupling pin projecting into the cavity resonator. Preferably, the coupling pin is configured as an inner conductor tube, preferably made of metal, and functioning as a coupling antenna.In a particularly preferred embodiment, this coupling pin projects through one of the end-face openings into the cavity resonator. Particularly preferably, the reaction tube connects to the inner conductor tube of the coaxial transition and, more specifically, is guided through its cavity into the cavity resonator. Preferably, the reaction tube is axially aligned with a central axis of symmetry of the cavity resonator, for which purpose the cavity resonator preferably has a central opening on each of two opposing end walls for guiding the reaction tube through.

[0088] The microwaves are fed into the coupling pin or into the inner conductor tube, which acts as a coupling antenna, for example by means of a coaxial connecting line. In a preferred embodiment, the microwave field is fed to the resonator via a waveguide, wherein the end of the coupling pin protruding from the cavity resonator is guided into an opening in the wall of the waveguide, extracts microwave energy from the waveguide, and couples it into the resonator.

[0089] Preferably, the process for producing the silica clusters according to the invention is carried out as a continuous process in a monomodal microwave reactor for the production of silica clusters, wherein the reaction medium is transported in a cavity parallel to the propagation direction of a standing electromagnetic wave in TE10 mode or perpendicular to the propagation direction of the standing wave in TE10 mode through a rectangular or circular waveguide, wherein the standing wave has formed in the waveguide and the length of the waveguide is between half a wavelength and six wavelengths of the standing electromagnetic wave. The cross-section of the waveguide has a width of half a wavelength and a height of one quarter of the wavelength, so that it forms a TE10 mode.

[0090] Preferably, the silica clusters according to the present invention are in the form of an alcoholic solution with dynamic viscosities at 20 °C of 0.1 mPa-s to 10 mPa-s, preferably 0.2 mPa-s to 7 mPa-s, particularly preferably 1 mPa-s to 4 mPa-s, and most preferably 1.5 mPa-s to 3 mPa-s. According to a further aspect, the present invention relates to silica clusters containing Si(OR)2 groups (Q2 units) and Si(OR)3 groups (Q3 units), wherein R is the same or different in each occurrence and represents a linear, branched or cyclic alkyl group, alkylene group or hydrogen, wherein the alkyl groups or the alkylene groups may contain primary or secondary amines, carboxylates or thiols, characterized by a ratio of the total number of Q2 units to the total number of Q3 units of greater than or equal to 50:50, preferably from 80:20 to 50:50, more preferably from 70:30 to 55:45.

[0091] The number of Q2 and Q3 units, as well as their ratio to each other, can be determined cumulatively for a sample, for example, by 29 Si-NMR measurement and integration of the respective signals attributable to the Q2 and Q3 units will be determined.

[0092] These silica clusters according to the present invention are surprisingly characterized by a higher ratio of Q2 to Q3 units than would be achievable using the classical sol-gel synthesis method known from the prior art. This appears, on the one hand—without being bound to theory—to be partly responsible for the higher reactivity of the silica clusters, enabling them to rapidly crosslink into higher molecular weight structures even at room temperature as soon as they are applied to a substrate surface. On the other hand, the higher Q2 / Q3 ratio also seems to be responsible for the increased storage stability. Both findings are extremely surprising.

[0093] For example, and particularly preferably according to the invention, these silica clusters can be produced according to the method described above.

[0094] The silica clusters of the present invention are characterized in particular by a number (N) of bound Si atoms greater than or equal to 3 to less than or equal to 64.

[0095] Preferred polydispersities of the silica clusters according to the invention are in the range of 1 to 8, preferably 1 to 5, particularly preferably 1 to 3.

[0096] The silica clusters according to the invention are further characterized by a preferred weight-average molecular weight in the range of 200 g / mol to 5,000 g / mol, preferably from 360 g / mol to 4,000 g / mol, and particularly preferably from 500 g / mol to 2,000 g / mol.

[0097] Furthermore, the present invention relates to a solution containing silica clusters according to the invention, as described above and / or producible by the above-described method, dissolved in an alcohol or a mixture of several alcohols. The solution is particularly suitable for coating substrates. In connection with the present invention, the term "solution" is used for both true solutions and brines.

[0098] According to a preferred embodiment, the solution has a viscosity of 0.1 mPa-s to 10 mPa-s, preferably 0.2 mPa-s to 7 mPa-s, particularly preferably 1 mPa-s to 4 mPa-s, and most preferably 1.5 mPa-s to 3 mPa-s.

[0099] The alcohol that constitutes the solvent for dissolving the silica clusters according to the invention is preferably a monohydric, dihydric or trihydric, branched or unbranched alcohol, which may be aliphatic or aromatic and which is preferably selected from the group consisting of ethanol, propanol, butanol, ethylene glycol, phenol and mixtures thereof, wherein ethanol is preferred.

[0100] The solution may further preferably contain, in addition to the silica clusters, at least one active ingredient, in particular an active ingredient selected from the group consisting of pharmaceutical active ingredients or excipients, cosmetically active substances, plant protection products, in particular herbicides, fungicides, insecticides, pesticides, preservatives, food additives, flavorings, fragrances, colorants, chelating additives, in particular carboxylic acid derivatives, pheromones and other attractants, natural products, in particular poly- and oligosaccharides, proteins and protein fragments, resins, oils, fats, fatty acids and derivatives, lignins and lignin derivatives, (partially) functionalized natural products, in particular cellulose ethers such as methylhydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose. The active ingredient is preferably present in an amount, based on the total amount of the solution, of 0.01 to 40% by weight, preferably of 0.5 to 20% by weight.-%, particularly preferably from 1 to 20 wt.%.

[0101] In addition to the silica clusters according to the invention, the present invention also relates to a method for producing the silica clusters. The method is carried out in the manner described above.

[0102] The invention further relates to a method for coating a substrate, in which a solution according to the invention, as described above, is applied at least partially or completely to a surface of a substrate, whereby a post-condensation step of the silica clusters is excluded, so that a coating is formed.

[0103] The solution can be applied, for example, by spray coating, dip coating, rotary coating, plasma coating, roller coating, doctor blade coating, brushing, pouring, drum coating process, doctor blade coating, spin coating, doctor blade coating, slot nozzle application, drum coating, fluid bed coating or by means of the Wurster process.

[0104] Preferably, the process is carried out such that after the application of the solution a drying step is performed in which heating of the coating to above 120 °C, preferably above 100 °C, particularly preferably above 80 °C is excluded.

[0105] Drying can be achieved, for example, by the solvent, e.g., alcohol, evaporating spontaneously without any further intervention (e.g., at ambient temperature). Alternatively, drying can be carried out using a gas stream (e.g., an air stream) directed onto the applied coating. It is also possible to perform drying at slightly elevated temperatures within the aforementioned range.

[0106] Exemplary substrates that can be coated using the coating process according to the invention can be selected from the group consisting of

[0107] Hair, fur and pelts, human and animal body parts, tissues and cells, such as skin, fingernails and toenails, hooves, feathers,

[0108] Plant substrates, in particular seeds, seedlings, fruit, vegetables, salad, nuts, plants, plant parts, in particular leaves and roots, algae, lichens,

[0109] Insects, especially pest insects such as aphids, tortrix moths and oak processionary caterpillars,

[0110] Mushrooms

[0111] Single-celled organisms, such as bacteria

[0112] Unprocessed and processed foods as well as pet food

[0113] Pharmaceutical products, especially tablets, such as film-coated tablets,

[0114] Medical devices, in particular implants or contact lenses

[0115] Scaffolds for in-vitro cell culture,

[0116] Washing and cleaning products, in particular dishwasher tablets and laundry detergent tablets,

[0117] Biodegradable (disposable) products, especially plates, bowls, cups and cutlery.

[0118] The silica clusters according to the invention can, in addition to applications in cosmetics, such as hairspray, hair gel, or nail polish, also find applications in other fields. Due to their biocompatible and ecotoxicologically safe nature, these layers can also be used, for example, in pharmaceuticals (e.g., coating of dosage forms), agricultural technology (e.g., coating of plants and other living organisms, but also fruits, nuts, vegetables, and produce), medical technology (coating of non-, partially, and fully resorbable implants), insect control (coating of and against pest insects), the food industry (coating of food or ingredients), or animal care / feed (coating of body parts such as hooves, claws, feathers, etc.), or as spray-on plasters. The coating is preferably produced in a layer thickness of 10 nm to 1 mm, more preferably from 100 nm to 200 µm, and particularly preferably from 1 µm to 100 µm.

[0119] Furthermore, the present invention relates to a coated object comprising a substrate and a coating applied at least partially to the substrate, produced according to a method according to the invention for coating a substrate as described above.

[0120] In a particularly preferred embodiment of the invention, the silica clusters according to the invention are used as film formers in hairstyling products, which are characterized in that they contain water and ethanol as a further component.

[0121] In a particularly preferred embodiment of the invention, the silica clusters according to the invention are used as film formers in hairstyling products, which are characterized in that they contain water, ethanol and citric acid esters as a further component.

[0122] In a particularly preferred embodiment of the invention, the silica clusters according to the invention are used as film formers in hairstyling agents in weight amounts of 0.1 wt.% to 10 wt.%, preferably from 0.5 wt.% to 75 wt.%, particularly preferably from 2 wt.% to 5 wt.%, based on the finished hairstyling agent.

[0123] In particular, the silica clusters according to the invention can be used as a layer in the following application areas, among others:

[0124] Cosmetics: Hairspray (pump spray and pressurized spray bottles), nail polish and more.

[0125] Pharmacy (human and veterinary medicine): Coating of tablets and other dosage forms such as soft capsules, hard capsules, granules, melt-in-the-mouth films, lozenges and others.

[0126] Medical technology: Coating of non-, partially, and fully resorbable implants; coating of living organs and tissues; and other applications. Environmental technology / plant protection: Coating of plant parts, e.g., leaves, wood, etc.; coating of plants, lichens, fungi, algae, mosses, and other organisms; coating of substrates for the attachment of algae, fungi, lichens, mosses, and plants; and other applications.

[0127] Insect protection: Coating of insects, especially pest insects, and other areas of application

[0128] Food industry: Coating of unprocessed foods (such as fruits, vegetables, nuts, berries, meat, eggs), but also processed and highly processed foods (meat alternatives (in-vitro, fermented cider plant-based) and processed ingredients.

[0129] Animal care / feeding: Coating of animal care products and animal body parts (hooves, claws, feathers, scales, etc.), coating of animal feed

[0130] The silica clusters according to the invention have a firming effect on twisted hair curls and waves in hairstyling products.

[0131] In addition to the silica clusters according to the invention, hairstyling products contain other components such as water, solvents, surfactants, emollients, emulsifiers, viscosity regulators, pH regulators, stabilizers and fragrances.

[0132] Preferred components are selected from water, ethanol, triisopropylamine, aminomethyl propanol, propylene glycol, isopropyl myristate, triethyl citrate, PEG-12 dimethicone, dimethyl ether, glycerin, jojoba oil, PEG-60 hydrogenated castor oil, sunflower oil, PEG-3 methyl ether and polysorbate 20.

[0133] Further objectives, features, advantages, and applications will become apparent from the following description of exemplary embodiments that do not limit the invention. All described features, individually or in any combination, constitute the subject matter of the invention, even independently of their compilation in the claims or their cross-references. They show

[0134] Fig. 1 Stable silica clusters according to the state of the art,

[0135] Fig. 2 a schematic representation of the TEOS-based synthesis, Fig. 3 an application example of the silica clusters according to the invention as hairspray

[0136] Fig. 4 29 Si-NMR spectra of the silica clusters according to the invention in comparison with silica clusters produced by sol-gel synthesis (without the use of microwave radiation).

[0137] Figure 1 shows stable silica clusters containing Si atoms Q2 (green residues) and Q3 (blue residues). Figure 1 (left) provides an overview of the basic building blocks of stable silica clusters (from: Chem. Rev. 2021, 121 (15), 9674-9718). Each Si atom is saturated and 4-coordinate. For clarity, reactive terminal silanol and ethoxy groups are not shown. Figure 1 (right) illustrates reactive terminal groups on two selected silica clusters, which can undergo intermolecular crosslinking reactions. These low-molecular-weight silica clusters mainly contain reactive terminal functional groups, -Si-OH or -Si-OR, where R represents an alkyl group (linear, branched, saturated, unsaturated) that can react with each other to form high-molecular-weight silica clusters.

[0138] The TEOS-based synthesis is schematically depicted in Figure 2. Figure 2 shows a reaction scheme for the production of reactive silica species in ethanol cider or bioethanol. A defined reaction process controls the parallel hydrolysis and condensation reactions starting from the liquid sol-gel precursor TEOS. The process can be controlled to produce defined silica clusters by adjusting parameters such as temperature, time, concentration, or the use of microwave technology.

[0139] The in-situ crosslinking on the hair surface according to the invention for layer formation is shown schematically in Figure 3: Fig. 3 shows the functional principle of the intended MOSINA development. Dissolved silica clusters are applied to the hair via a pressurized spray can. As the solvent evaporates, the individual silica clusters on the hair surface approach each other and crosslink in-situ to form a hair coat that strengthens the hair.

[0140] Fig. 4 shows the results of liquid- 29 Si-NIVIR studies of A) a TI

[0141] Borosilicate glass NMR tube (background), B) of a sol synthesized according to the invention (see synthesis example 1 above) and C) of a sample prepared according to EP3692191B1 without microwave.

[0142] In sols produced using microwave technology, the Q2 content is significantly higher. The intensities of the Q2 signals are at least identical, and preferably higher, than the intensities of the Q3 signals. All measurements were performed in the same (identical) NMR tube, so that the integrals of the signals originating from the Q2 and Q3 units can be determined by subtracting the background signal of the NMR tube (A).

[0143] Surprisingly, despite the higher Q2 content, the storage stability of sols produced using the microwave method was also higher (Table 1). The dry residue obtained from the sols produced using the microwave method ranged from 23.7 to 31.1 wt%. The dry residue of the sample produced without microwaves was 25.1%. Storage took place at room temperature (22°C ± 1°C).

[0144] All brines and solutions produced using the microwave process are stable for > 49 days. A brine synthesized for 30 minutes at 20% microwave power is even stable for > 98 days. The reference brine (without microwave) was fully gelled after only 35 days and, as the rheological analysis of the gelation of the produced brines shows, already had a viscosity too high for spray coatings (20.9 Pa s) after only 28 days.

[0145] Table 1

[0146] Examples of implementation

[0147] Conducting the DLS measurements: To determine the mean particle size (number mean), the samples were

[0148] The solution was diluted 1:10 with ethanol and filtered through a syringe filter (pore size 200 nm). The mean particle diameter of the clusters was determined by dynamic light scattering (DLS) using a ZetaSizer ZS (Malvern Instruments, UK). Measurements were performed as a triplet analysis with at least 12 runs per measurement at 20 °C.

[0149] The DLS laser had a wavelength of 633 nm, and the scattered light was measured at 173° in polystyrene cuvettes (No. 67.754, Sarstedt AG & Co. KG, Germany). The data were analyzed using OriginPro 2021 software (OriginLab Corporation, United States).

[0150] Example:

[0151] For the reference without microwave (according to EP3692191B1), a sol was prepared according to EP3692191B1 and condensed at 40 °C for 18 h. Immediately after this synthesis, the sol was not yet film-forming. Therefore, the sol was subjected to rotation according to EP3692191B1 and allowed to mature to a viscous solution. This mixture was then diluted with ethanol to a dry residue of 25.1 wt%.

[0152] The dry residue of B) is comparable to 26.0 m%.

[0153] The cytocompatibility of the layers has been demonstrated in accordance with DIN ISO 10993-5:2009. Degradation to FMD is based on DIN 38405-21:1990.

[0154] The microwave-assisted reaction took place in an apparatus containing a borosilicate glass tube (length: 160 cm, inner diameter: 1.0 cm) as the reaction tube. This tube was axially symmetrical within a cylindrical cavity resonator (90 cm x 10 cm) (irradiation zone). At one end face of the cavity resonator, this borosilicate glass tube passed through the cavity of an inner conductor tube that served as a coupling antenna. The microwave field, generated by a magnetron with a frequency of 2.45 GHz, was coupled into the cavity resonator via the coupling antenna (E01 cavity applicator; single-mode), where a standing wave was formed. The microwave system was located under a λ-atmosphere.

[0155] The microwave power was adjusted throughout the experiment to maintain a constant temperature of the reaction mixture at the end of the reaction tube. The stated microwave power represents the time-averaged value of the applied microwave power. The temperature of the reaction mixture was measured directly at the end of the reaction tube.

[0156] Microwave energy not directly absorbed by the reaction mixture was reflected at the end face of the cavity resonator opposite the coupling antenna; microwave energy not absorbed by the reaction mixture even during the return flow and reflected back towards the magnetron was directed into a water-filled vessel using a prism system (circulator). The microwave energy introduced into the reaction mixture was calculated from the difference between the radiated energy and the power loss (determined by the heating of the water).

[0157] The starting materials and their ratios in the synthesis are governed by EP3692191B1:

[0158] Synthesis example 1:

[0159] In a 2-liter reactor equipped with a gas inlet tube, stirrer, internal thermometer, and pressure equalization, a mixture of 729.0 g (3.5 mol) of tetraethoxysilane, 204.5 g (4.4 mol) of ethanol, and the slow addition of 114.5 g of aqueous 0.1 N methanesulfonic acid solution was prepared under atmospheric pressure and subjected to a continuous flow of 450 watts of microwave energy for 30 minutes. The temperature of the reaction mixture upon exiting the reactor was 72°C. After exiting the reaction tube, the mixture was cooled to 21°C in a heat exchanger.

[0160] The result is a colorless liquid with a viscosity of 1.2 mPa s, which can be used without further processing. The mean particle diameter, determined by DLS, was 7.13 nm. The polydispersity index (Pdl) of the DLS measurement was 0.292.

[0161] Synthesis example 2:

[0162] In a 2-liter reactor equipped with a gas inlet tube, stirrer, internal thermometer, and pressure equalization, a mixture of 729.0 g (3.5 mol) of tetraethoxysilane, 204.5 g (4.4 mol) of ethanol, and the slow addition of 114.5 g of aqueous 0.1 N nitric acid solution was prepared under atmospheric pressure and subjected to a continuous flow of 450 watts of microwave energy for 30 minutes. The temperature of the reaction mixture upon exiting the reactor was 72°C. After exiting the reaction tube, the mixture was cooled to 21°C in a heat exchanger. The result is a colorless liquid with a viscosity of 1.2 mPa·s, which can be used without further work-up.

[0163] In a 2-liter vessel equipped with a gas inlet tube, stirrer, internal thermometer, and pressure equalization, a mixture of 729.0 g (3.5 mol) of tetraethoxysilane was prepared.

[0164] 204.5 g (4.4 mol) of ethanol and 114.5 g of aqueous 0.1 N nitric acid solution were prepared under normal pressure and subjected to a continuous flow of 450 watts of microwave energy for 1 h. The temperature of the reaction mixture was 72°C immediately upon exiting the reactor. After leaving the reaction tube, the reaction mixture was cooled to 21°C in a heat exchanger.

[0165] The result is a colorless liquid with a viscosity of 1.3 mPa s, which can be used without further processing.

[0166] Synthesis example 4:

[0167] In a 2-liter vessel equipped with a gas inlet tube, stirrer, internal thermometer, and pressure equalization, a mixture of 729.0 g (3.5 mol) of tetraethoxysilane was prepared.

[0168] 204.5 g (4.4 mol) of ethanol and 114.5 g of aqueous 0.1 N methanesulfonic acid solution were prepared under normal pressure and subjected to a continuous flow of 450 watts of microwave energy for 30 minutes. The temperature of the reaction mixture was 72°C immediately upon exiting the reactor. After leaving the reaction tube, the reaction mixture was cooled to 21°C in a heat exchanger.

[0169] The result is a colorless liquid with a viscosity of 1.2 mPa s, which can be used without further processing. An additive, the antibiotic octenidine hydrochloride, was then stirred into this solution at a concentration of 1% by mass. The liquid remained stable and storable.

[0170] Synthesis example 5:

[0171] In a 2-liter vessel equipped with a gas inlet tube, stirrer, internal thermometer, and pressure equalization, a mixture of 729.0 g (3.5 mol) of tetraethoxysilane was prepared.

[0172] 204.5 g (4.4 mol) of ethanol and 114.5 g of aqueous 0.1 N methanesulfonic acid solution were prepared under normal pressure and subjected to a continuous flow of 450 watts of microwave energy for 30 minutes. The temperature of the reaction mixture was 72°C immediately upon exiting the reactor. After leaving the reaction tube, the reaction mixture was cooled to 21°C in a heat exchanger.

[0173] The result is a colorless liquid with a viscosity of 1.2 mPa s, which can be used without further processing. Two additives, ethyl citrate (1 wt%) and glycerol (1 wt%), are then stirred into this solution. The liquid remained stable and storable for at least 200 days at room temperature (22 °C).

[0174] Synthesis example 6

[0175] 1458.24 g [7 mol] of TEOS were dissolved in 406.49 g [8.75 mol] of ethanol and 228.97 g of 0.1 N methanesulfonic acid were added. 2 L of the sol were continuously pumped through the apparatus at a flow rate of 10 L / h at a working pressure of 1 bar and exposed to a microwave power of 450 watts, of which 90% was absorbed by the reactant. The residence time of the reaction mixture in the reaction tube was 12 minutes. At the end of the reaction tube, the reaction mixture had a temperature of 71 °C. After exiting the reaction tube, the reaction mixture was cooled to 21 °C in a heat exchanger.

[0176] A colorless liquid with a viscosity of 1.2 mPa·s was obtained, which could be used without further processing. The mean particle diameter, determined by DLS, was found to be 3.07 nm.

[0177] Application example 1: Hairspray

[0178] 20.0 wt% of the silica cluster product according to synthesis example 1 was stirred into a mixture of 78.0 wt% ethanol and 2.0 wt% triethyl citrate at room temperature, filled into a spray bottle and sprayed onto hair.

[0179] The silica clusters according to the invention were investigated with regard to their strengthening effect on hair by means of so-called curl retention tests.

[0180] For this purpose, the length of a hair strand sprayed with hairspray 1 and curled was compared to a hair strand sprayed with water or the market products Einett from L'Oreal and Wellaflex from Wella and curled, as a function of time. The hair length at time 0 and the hair length at time X were determined, and the curl retention (CR) was calculated using the following formula.

[0181] Lf - Lt(i)

[0182] CR X 100

[0183] Lf - Lt(G)

[0184] CR Curl Retention in %

[0185] Hair length, uncurled, in cm

[0186] Lt(i) Hair length of the curl at time i in cm

[0187] Lt(O) Hair length of the curl at time t = 0 minutes in cm

[0188] To determine the CR, two strands of hair tied together (each approx. 0.4-0.5 g / 26 cm free length) are used; 3 strands are sprayed with water without any product and 3 strands each are sprayed with the applied product (hairspray 1 according to the invention containing silica cluster according to Example 1) or, for comparison, the market products Einett from L'Oreal and Wellaflex from Wella.

[0189] The hair strands are weighed before treatment. The hairspray is then applied in five sprays from a distance of 20 cm, carefully distributed over all the hair in the strand with the hands, and the strand is dried with a hairdryer. The strand is then weighed again to determine the amount of product used. The amount of product applied is approximately 1 g.

[0190] The hair strand is wound onto a spiral roller (13 mm diameter). One end of the hair strand is weighted, while the other end is clamped and suspended from a device inside the climate chamber. The hair strands are then dried with a hairdryer.

[0191] The hair strand is carefully developed and suspended in the climate chamber in front of a mirror scale. The reading must be taken without parallax error. This means the reading must be taken so that the lower hair strand bundles are at eye level and do not overlap with the mirror image. Zero-point correction is mandatory. The lower edge of the upper hair strand bundle is usually below the zero point. This difference must be subtracted from the determined length of the curled hair strand.

[0192] The climate chamber in which the test takes place is set to a relative humidity of 75% and a temperature of 25°C. The length of the curled hair strands is measured every 5 minutes from 0 to 20 minutes and every 10 minutes from 20 to 60 minutes, and the CR is calculated according to the formula above.

[0193] Table 2 shows the curl retention values ​​(CR) for hair strands that were sprayed and curled with water, the market products Wellaflex, Einett and the formulation according to the invention.

[0194] Table 2

[0195] Result: The hairspray according to the invention surpasses the firming effect of the market products Einett from L'Oreal and Wellaflex from Wella.

[0196] Application example 2: Nail polish

[0197] A sol prepared according to synthesis example 2 was applied to fingernails with a brush. After evaporation of the solvent, a homogeneous film remained on the fingernail, which could be removed after thorough cleaning with water.

[0198] Application example 3: Film coating on tablets

[0199] A sol produced according to synthesis example 1 was applied to tablets using a fluidized bed system (Glatt, Mini). For this purpose, 70 g of tablets (diameter: 6 mm) were processed at an oven temperature of 50 °C with a fluidized bed pressure of 55 m. 3 The tablets were coated at a rate of 1 / h and a nozzle pressure of 1.5 bar for 20 minutes. Sol consumption was 20 g. The result was a homogeneous coating of the entire tablet surface. The layer thickness was approximately 10 µm.

[0200] Application example 4: Coating of plant leaves

[0201] A sol prepared according to synthesis example 1 was filled into a commercially available spray bottle (pump spray) and sprayed onto the leaves of a hazelnut tree. This resulted in the formation of a layer on the leaf.

[0202] Application example 4: Coating of insects

[0203] A sol, as described in synthesis example 2, was sprayed onto aphids. The aphids were enveloped by the material and mechanically trapped.

Claims

FRAUNHOFER SOCIETY eV; IP&PM, Intellectual Property & Project Management P149848PC00 Patent claims 1. Silica clusters, producible by a process in which a mixture containing a) one or more tetraalkoxysilanes of the general formula Si(OR)4, wherein R is the same or different in each occurrence and denotes a linear, branched or cyclic alkyl group or alkylene group, wherein the alkyl groups or the alkylene groups may contain primary or secondary amines, carboxylates or thiols, b) at least one solvent suitable for dissolving and mixing the one or more tetraalkoxysilanes of the general formula Si(OR)4, c) water and d) at least one acidic catalyst is reacted in a monomodal microwave apparatus under electromagnetic microwave irradiation of a standing wave.

2. Silica cluster according to claim 1, characterized in that the residues R of the general formula Si(0R)4 are selected from linear or branched alkyl residues with 1 to 16 carbon atoms and / or alkenyl residues with 3 to 16 carbon atoms, wherein the residues R may be the same or different.

3. Silica cluster according to one of the preceding claims, characterized in that the residues of the general formula Si(0R)4 are the same and represent the ethyl residue.

4. Silica cluster according to one of the preceding claims, characterized in that the acidic catalyst used in the process has a pKa value of pKa < 2 and is preferably selected from the group consisting of methanesulfonic acid, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and mixtures and combinations thereof.

5. Silica cluster according to one of the preceding claims, characterized in that the at least one solvent suitable for dissolving and mixing one or more tetraalkoxysilanes of the general formula Si(0R)4 is selected from the group consisting of linear or branched aliphatic alcohols having 1 to 18 carbon atoms, in particular methanol, ethanol, n-propanol, i-propanol and mixtures thereof.

6. Silica cluster according to one of the preceding claims, characterized in that in the process the molar ratio of the totality of the tetraalkoxysilanes to the totality of the solvents is from 0.1 to 10, preferably from 0.5 to 2.0, particularly preferably from 0.6 to 1.

1.

7. Silica cluster according to one of the preceding claims, characterized in that in the method the microwave irradiation is carried out in a period of 10 seconds to 120 minutes, preferably in a period of 2 minutes to 60 minutes, particularly preferably 5 minutes to 50 minutes, and most preferably 10 minutes to 40 minutes.

8. Silica cluster according to one of the preceding claims, characterized in that in the method the mixture is subjected to microwave irradiation with a power of 0.1 W / cm³ related to a volume of a reaction chamber. 3 up to 10 W / cm 3 preferably 1.0 W / cm² 3 up to 7.5 W / cm 3 , preferably 2.5 W / cm 3 up to 4.5 W / cm 3 is suspended.

9. Silica cluster according to one of the preceding claims, characterized in that the process is carried out continuously.

10. Silica cluster according to one of the preceding claims, characterized in that in the process the mixture is exposed to the electromagnetic field of a stationary microwave system in a monomodal microwave system. is exposed to the wave with TE10 mode and absorbs 10% to 99% of the injected microwave energy.

11. Silica cluster according to one of the preceding claims, characterized in that in the process the conversion of the mixture takes place in a continuous process in a monomodal microwave system, wherein the mixture is transported in a cavity parallel to the propagation direction of a standing electromagnetic wave in TE10 mode or perpendicular to the propagation direction of a standing electromagnetic wave in TE10 mode through a rectangular waveguide, wherein standing waves have formed in the rectangular waveguide and the length of the waveguide is between half a wavelength and up to 20 wavelengths, preferably 2 to 10 wavelengths, particularly preferably 3 to 6 wavelengths of the standing wave.

12. Silica cluster according to the preceding claim, wherein the cross-section of the waveguide has a width of half the wavelength and a height of one quarter of the wavelength of the standing electromagnetic wave, such that it forms a TE10 mode.

13. Silica cluster according to one of the preceding claims, characterized in that in the process the conversion of the mixture takes place in a continuous process in a monomodal microwave plant, wherein the number of field maxima of the standing wave in the microwave reactor is 1 to 20.

14. Silica cluster according to one of claims 1 to 12, characterized in that the process is carried out in a monomodal microwave reactor plant for the production of silica clusters, wherein the reaction medium is transported in a cavity parallel to the propagation direction of a standing electromagnetic wave in TE10 mode or perpendicular to the propagation direction of the standing wave in TE10 mode through a rectangular or round waveguide, wherein the standing wave has formed in the waveguide and the length of the waveguide is between half a wavelength and six Wavelengths of the standing electromagnetic wave.

15. Silica cluster according to the preceding claim, wherein the cross-section of the waveguide has a width of half the wavelength and a height of one quarter of the wavelength, such that it forms a TE10 mode.

16. Silica clusters, particularly according to one of the preceding claims, comprising Si(OR)2 groups (Q2 units) and Si(OR) groups (Q3 units), wherein R is the same or different in each occurrence and represents a linear, branched or cyclic alkyl group, alkylene group or hydrogen, wherein the alkyl groups or the alkylene groups may contain primary or secondary amines, carboxylates or thiols, characterized by a ratio of the total number of Q2 units to the total number of Q3 units of greater than or equal to 50:50, preferably from 80:20 to 50:50, more preferably from 70:30 to 55:

45.

17. Silica cluster according to one of the preceding claims, characterized in that the number (N) of the bound Si atoms is greater than or equal to 3 to less than or equal to 64.

18. Silica cluster according to one of the preceding claims, characterized by a polydispersity of 1 to 8, preferably 1 to 5, particularly preferably 1 to 3.

19. Silica cluster according to one of the preceding claims, characterized by a mean particle diameter of <30 nm, preferably of 2 to 25 nm, more preferably of 3 to 20 nm, particularly preferably of 4 to 15 nm, especially preferably of 4 to 10 nm.

20. Silica cluster according to one of the preceding claims, characterized by a weight-average molecular weight in the range of 200 g / mol to 5,000 g / mol, preferably from 360 g / mol to 4,000 g / mol, particularly preferably from 500 g / mol to 2,000 g / mol.

21. Solution containing silica clusters according to any of the preceding claims, dissolved in an alcohol or a mixture of several alcohols.

22. Solution according to one of the preceding claims, characterized by a viscosity of 0.1 mPa-s to 10 mPa-s, preferably 0.2 mPa-s to 7 mPa-s, particularly preferably 1 mPa-s to 4 mPa-s, extraordinarily preferably 1.5 mPa-s to 3 mPa-s, or greater than 0.110 mPa-s and less than or equal to 100,000 mPa-s at 21°C.

23. Solution according to the preceding claim, characterized in that the alcohol is a monohydric, dihydric or trihydric, branched or unbranched alcohol, which may be aliphatic or aromatic and which is preferably selected from the group consisting of ethanol, propanol, butanol, ethylene glycol, phenol and mixtures thereof, wherein ethanol is preferred.

24. Solution according to one of the preceding claims, characterized in that it comprises at least one active ingredient, in particular an active ingredient selected from the group consisting of pharmaceutical active ingredients or excipients, cosmetically active substances, plant protection products, in particular herbicides, fungicides, insecticides, pesticides, preservatives, food additives, flavorings, fragrances, colorants, chelating additives, in particular carboxylic acid derivatives, pheromones and other attractants, natural substances, in particular poly- and oligosaccharides, proteins and protein fragments, resins, oils, fats, fatty acids and derivatives, lignins and lignin derivatives, (partially) functionalized natural substances, in particular cellulose ethers such as methylhydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose.

25. Solution according to the preceding claim characterized in that the at least one active ingredient is contained in an amount, based on the total amount of the solution, of 0.01 to 40 wt.%, preferably of 0.5 to 20 wt.%, particularly preferably of 1 to 20 wt.%.

26. Method for coating a substrate, in which a solution according to one of claims 22 to 25 is applied at least partially or over the entire surface of a substrate, wherein a post-condensation step of the silica clusters is excluded, so that a coating is formed.

27. Method according to the preceding claim, characterized in that after the application of the solution a drying step is carried out in which heating of the coating to above 120 °C, preferably above 100 °C, particularly preferably above 80 °C is excluded.

28. Method according to one of the two preceding claims, characterized in that the substrate is selected from the group consisting of Hair, fur and pelts, human and animal body parts, tissues and cells, such as skin, fingernails and toenails, hooves, feathers, Plant substrates, especially seeds, fruit, vegetables, salad, nuts, plants, plant parts, especially leaves and roots, algae, lichens, Insects, especially pest insects such as aphids, tortrix moths and oak processionary caterpillars, Mushrooms Single-celled organisms, such as bacteria Unprocessed and processed foods as well as pet food Pharmaceutical products, especially tablets, such as film-coated tablets, Medical devices, in particular implants or contact lenses Scaffolds for in-vitro cell culture, Washing and cleaning products, in particular dishwasher tablets and laundry detergent tablets, Biodegradable (disposable) products, especially plates, bowls, cups and cutlery.

29. Method according to one of claims 26 to 27, characterized in that the coating is produced in a layer thickness of 10 nm to 1 mm, preferably from 100 nm to 200 pm, particularly preferably from 1 pm to 100 pm.

30. Coated article comprising a substrate and a coating applied at least partially to the substrate, manufactured according to a method according to one of claims 26 to 29.

31. Use of the silica clusters according to any one of claims 1 to 20, for coatings as well as cosmetic and pharmaceutical products.

32. Cosmetic product containing silica clusters according to one of claims 1 to 20 and at least one cosmetic substance and / or at least one cosmetic excipient.

33. Pharmaceutical product containing silica clusters according to any one of claims 1 to 20 and at least one pharmaceutically active substance.

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