Transparent glazing material, assembly containing glazing material, and method for forming them.

Abstract

Transparent glazing materials, assemblies containing glazing materials, and methods for forming and using glazing materials and assemblies are provided. An exemplary glazing material includes an aerogel comprising a network of cellulose nanofibers and silicon functional groups bonded to the surface of the cellulose nanofibers.

Description

[Technical Field]

[0001] Cross-references to related applications This application claims priority to U.S. Provisional Application No. 63 / 450,286, titled "Highly Transparent Silanized Cellulose Aerogels for Boosting Energy Efficiency of Glazing in Buildings," filed on 6 March 2023, the contents of which are incorporated herein by reference.

[0002] Statements regarding federally supported research or development. This invention was developed with government support under authorization number DE-AR0000743 issued by the U.S. Department of Energy. The U.S. Government has certain rights in this invention. [Background technology]

[0003] To provide desirable indoor conditions with little to no additional energy supply, regardless of the outdoor environment, building exteriors are generally configured to mitigate energy exchange between the interior and exterior through heat conduction, convection, and emission. Achieving this using glazing is particularly challenging due to the typically stringent requirements regarding visible light transmittance and haze. Current approaches to this challenge utilize insulated glass units (IGUs) filled with air or gas, but the high thermal insulation performance of such IGUs requires a large gap thickness between the glass panes, which is limited by gas convection, the number of panes, and structural constraints. On the other hand, the use of much thinner vacuum insulated glass units is limited by seal integrity and high cost. Low emissivity silver and other coatings allow for limiting energy loss due to blackbody-like electromagnetic radiation originating from the interior of a building at room temperature, but such coatings can only capture a small fraction of the escaping energy at the expense of reduced visible light transmittance. Aerogels, highly insulating materials used in a wide range of applications from pipe insulation to Mars rovers, stand out as a class of materials that can perform superiorly as more efficient insulating barriers than still air and other gas-filled materials, and have therefore been highly valued as a solid material alternative for gas-filled materials inside IGUs. However, conventional aerogels are typically mechanically brittle and strongly scatter light. Manufacturing aerogels with low haze, high transparency, and mechanical robustness at building-related scales and costs remains a challenge. The development of transparent aerogels, such as cellulose-based aerogels, remains limited to small scales and, while featuring haze and transparency properties, is still insufficient for use in most types of glazing. Technological solutions for controlling emissivity in the thermal range are suitable for some applications, and the emergence of recent novel electrochromic methods can address the needs of solar radiation gain and privacy control, but the lack of good transparent insulating materials significantly limits the energy efficiency of window technology.Therefore, improved glazing materials, assemblies containing glazing materials, and methods for forming and using glazing materials and assemblies are desirable.

[0004] Any discussions, including those relating to the problems and solutions described in this section, are included in this disclosure solely for the purpose of providing context for this disclosure and should not be construed as admitting that any or all of the discussions were known at the time the invention was made, or otherwise constitute prior art. [Overview of the project]

[0005] This summary may introduce several concepts in a simplified form, which may be explained in more detail below. This summary is not intended to necessarily identify any very important or essential features of the subject matter described in the claims, nor is it intended to be used to limit the scope of the subject matter described in the claims.

[0006] Examples of the present disclosure disclose a technology for the scalable production of highly transparent silane-cellulose aerogel (SiCellA) having material properties suitable for glazing applications, and the aerogel itself. By sandwiching these highly insulating SiCellA materials between glass plates, a high thermal resistance R (e.g., R-5 and above, where R is h·ft) is achieved. 2It can enable windows with a geometric form factor (expressed in units of °F·Btu) and conventional double-pane IGUs, as well as glazing for daylighting and skylights, and has the potential to exceed current standards and targets not only for windows but also for building walls. The deployment of IGUs using air or other gas fillers is limited by convection in the large gaps between the panels and reflection of light from the glass-air interface of multi-pane IGUs, but SiCellA-based IGUs do not have such inherent limitations. This aerogel-based glazing material makes it possible to design building exterior walls to better utilize external conditions and provide natural comfort for occupants. As described in more detail below, SiCellA films can replace inner glass panels when used as IGU fillers and in multi-pane IGU designs and are fully compatible with existing solutions for thermal range emissivity and solar radiation gain control. The aerogels described herein can provide a holistic solution to the energy management challenges facing building technology and furthermore, help next-generation buildings utilize energy from the environment.

[0007] Embodiments of the present disclosure provide transparent glazing materials. Examples of transparent glazing materials include a network of cellulose nanofibers and an aerogel comprising silicon functional groups bonded to the surface of the cellulose nanofibers, wherein the thermal conductivity of the transparent glazing material is less than 26 mW / (K·m), less than 20 mW / (K·m), or less than 15 mW / (K·m). According to examples of these embodiments, the haze of the transparent glazing material is less than 2.5%, less than 2%, less than 1.5%, or less than 1%. In further examples, the transparency of the transparent glazing material is greater than 97% in the visible light spectrum. In even further examples, the transparent glazing material exhibits superhydrophobicity. In even further examples, the average width of the cellulose nanofibers is less than 15 nm, less than 10 nm, between approximately 4 nm and approximately 6 nm, between 1 and 15 nm, or between 1 and 10 nm. Additionally or alternatively, the average length of cellulose nanofibers is greater than 100 nm, greater than 1000 nm, between approximately 200 nm and approximately 2000 nm, between 100 and 2000 nm, or up to 5000 nm. Further examples show that aerogels are optically anisotropic. Further examples show that the average pore size of aerogels is less than 100 nm or between approximately 2 nm and approximately 50 nm.

[0008] According to further embodiments of the present disclosure, the assembly comprises a transparent glazing material and a first (e.g., glass and / or transparent) plate. An exemplary assembly may include a substrate attached to the transparent glazing material. The substrate may be one or more of, for example, plastic and glass, or may include both. According to an example of the present disclosure, the transparent glazing material is attached to the substrate by electrostatic charge. According to a further example, the assembly includes a low emissivity coating between the substrate and the transparent glazing material. According to a further example, the assembly includes a second (e.g., glass) plate, where the transparent glazing material is inserted between the first and second plates. An exemplary assembly may include three or more plates. The assembly may further include an inert gas. In some cases, the transparent glazing material is a self-supporting transparent glazing material.

[0009] Further embodiments of the present disclosure provide a method for forming a transparent aerogel and / or assembly. An exemplary method for forming a transparent aerogel includes the steps of: forming cellulose nanofibers having an average diameter of less than 10 nm and an average length of more than 100 nm; functionalizing the cellulose nanofibers with carboxylic acid anions to form functionalized cellulose nanofibers; forming a hydrogel from a network of functionalized cellulose nanofibers; forming an aerogel from the hydrogel; and silanizing the surface of the functionalized cellulose nanofibers. In an example of the present disclosure, the step of silanizing the surface includes gas-phase silanization of the aerogel. In some cases, the step of silanizing the surface includes silanizing the functionalized cellulose nanofibers of the hydrogel. In a further example, the step of silanizing the surface includes exposing the surface to a chlorine-free silanizing agent (e.g., using a silane such as SiH4, or a higher-order silane, or an organosilicon compound). In a further example, the transparent aerogel is formed on the surface of a windable substrate. In such cases, the substrate and transparent aerogel can be wound onto a roll having a diameter of less than approximately 1 centimeter.

[0010] It should be understood that the elements in the figures are shown for brevity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated relative to others to aid in understanding the illustrated embodiments of this disclosure.

[0011] The exemplary embodiments of this disclosure may be better understood by referring to the detailed description and claims, in conjunction with the following exemplary drawings. [Brief explanation of the drawing]

[0012] [Figure 1]Figure 1 shows SiCellA-based window modifications and IGUs according to examples of the present disclosure. a, b. Schematic diagrams of a window modified with SiCellA film (a) and an IGU (b) with SiCellA film inserted between glass plates. c. 1 square meter of 1.5 mm thick SiCellA with 99.2% porosity, bonded to an optically clear plastic film. d, e. Photographs of double-pane IGUs measuring 36 cm × 51 cm (d) and 1 square meter (e), with one glass plate coated with LoE-366 and a 3 mm thick SiCellA film attached to the surface of the other glass plate. Note that the slight coloration in d and e results from the LoE-366 coated glass used in these IGUs. f. A single-pane window modified with a 72.1cm × 71.4cm 1.5mm thick SiCellA film (indicated by the arrow and enclosed by the dashed line) inside a building on the University of Colorado campus, photographed from the outside using both a conventional photographic camera (left) and a thermal imaging camera (right). Temperature is coded according to the color scale. g, h. Infrared thermal images of various types of fenestrations installed in the openings of 0.78m × 0.68m × 0.43m high-temperature (g) or low-temperature (h) boxes, with internal temperatures set to 40°C (g) and -20°C (h). "SiCellA-IGU" indicates a double-pane IGU with SiCellA aerogel film. "IGU" indicates a double-pane IGU without SiCellA. "Modified" indicates a 3mm thick single glass panel modified with SiCellA film. "Single Panel" indicates a 3mm thick single glass panel. [Figure 2]Figure 2 shows the fabrication of superhydrophobic silane-treated cellulose aerogel on a window scale. a. A 1 square meter gel is gelled, followed by solvent exchange in a 40 L bath. A 3 mm thick red rubber spacer forms the edge of the flat mold. b, c. A 1 square meter hydrogel film on a supporting white Mylar sheet (b), photographed before being wound onto a roll for drying in a critical point dryer, and a 3 mm thick SiCellA film tightly wound onto the Mylar sheet after drying (c). d, e. A 3 mm thick hydrogel shown in b (outlined by a dashed line) suspended in water (d), and the corresponding 3 mm thick aerogel after drying (outlined by a dashed line). f. Schematic diagram of gas-phase silanization of the aerogel. g. Infrared transmission spectra of unmodified and modified aerogels. After surface modification, the carboxylate rate in the aerogel is significantly reduced at 1712 cm⁻¹. h. A photograph of a water droplet on the surface of a SiCellA film, with a contact angle measured at approximately 155° and marked on the image. [Figure 3a] Figure 3 shows the nanoscale morphology of aerogels according to an example of the present disclosure. a, b. TEM images of sonicated TEMPO-oxidized cellulose nanofibers in an aqueous dispersion negatively stained with 1% phosphotungstic acid (a) and unmodified nanocellulose aerogel (b). c, d. TEM image of silane-treated aerogel (c) and corresponding tomographic TEM visualization of SiCellA (d). e. Density of modified and unmodified aerogels depending on porosity. The red line is a visual guideline. f. N2 adsorption and desorption isotherms at 77K for modified and unmodified aerogels. The solid line connects the measurement data represented by symbols. The inset shows the distribution of pore volume difference depending on the pore width of the modified aerogel. g. Distribution of pore surface area difference depending on the pore width of SiCellA. The inset shows the cumulative surface area depending on the pore width. h. Schematic diagram of SiCellA formed by a network of thin cellulose nanofibers having a silane surface. [Figure 3b] Same as above [Figure 3c] Same as above [Figure 3d] Same as above [Figure 3e] Same as above [Figure 3f] The same as above [Figure 3g] The same as above [Figure 3h] The same as above [Figure 4a] Figure 4 shows the optical properties of the SiCellA material. a, b. Visible spectral dependence of the total transmittance and diffuse transmittance of the 1 mm thick film (indicated by the dashed line) (a) and SiCellA films of different thicknesses (b) shown in the inset. The inset in b shows the transmittance and haze as a function of the thickness of the SiCellA film, the experimental data points are shown by symbols with error bars, and the solid lines are visual guides. c. A 5 mm thick triangular SiCellA prism. d. Spectral dispersion of the refractive index calculated from absorption measurements using the Kramers–Kronig relation. The dashed line shows the refractive index of 1.0025 determined at 632 nm by measuring the minimum deviation angle of the laser beam. e. Visible to near-infrared spectral dependence of the transmittance and absorption coefficient of the 2 mm thick SiCellA film shown in the inset. f. A 25 mm thick SiCellA prism, through which a 532 nm laser beam passes without deviation because the refractive index is close to that of air. g–j. 4 mm thick SiCellA prisms having star (g), pentagon (h), hexagon (i) and octagon (j) shapes. [Figure 4b] The same as above [Figure 4c] The same as above [Figure 4d] The same as above [Figure 4e] The same as above [Figure 4f] The same as above [Figure 5a]Figure 5 shows the thermal properties of SiCellA. a. Temperature dependence of the thermal conductivity of SiCellA at different porosities. The solid line is a visual guideline. b. Dependence of the thermal conductivity of SiCellA to porosity at 5°C and 25°C. The inset shows the dependence of R per 2.54 cm (1 inch) on the porosity of SiCellA. Symbols with error bars indicate experimental data points. c. Infrared thermal images of SiCellA films of different shapes placed on a hot plate: (top left, bottom right) 4 mm thick triangle, square, pentagon, hexagon, heptagon, star, University of Colorado logo, 8 mm thick triangle, 10 mm thick disk and rectangle. d, e. Raw infrared transmittance (d) and mean infrared transmittance (e) weighted by blackbody radiation at 300 K of unmodified cellulose-based aerogels of various thicknesses (solid line). For comparison, spectra of silane-modified aerogel and unmodified aerogel of the same 2.5 mm thickness are provided. [Figure 5b] Same as above [Figure 5c] Same as above [Figure 5d] Same as above [Figure 5e] Same as above [Figure 6] Figure 6 shows the mechanical properties of cellulose-based aerogels. a. Tensile stress-strain dependence of silane-modified aerogels (solid line) and unmodified aerogels (dashed line) with different porosities. The inset shows a SiCellA sample held between tensile mechanical clamps during measurement. b. Compressive stress-strain dependence of aerogels with different porosities. The inset shows a SiCellA sample held between compression mechanical clamps during measurement. c. Compression cycle loop of 10 cycles. The number of cycles is represented by color according to the color scale. The inset shows compressive stress-strain plots for the 1st and 10th cycles. d, e. SiCellA sample (d) and three-point bending of SiCellA sample (e) placed in three-point clamps. f. Bending stress-strain dependence of a 25mm × 5mm × 3mm aerogel sample. g. Photograph of a 2mm thick aerogel film with an area of ​​100mm × 100mm bent / folded, exhibiting rubber-like flexibility. [Figure 7a]Figure 7 shows the durability, stability, and condensation resistance of SiCellA and window products. a. Thermogravimetric analysis of silane-modified nanocellulose aerogel and unmodified nanocellulose aerogel showing the percentage of weight loss with respect to temperature. The inset shows the DTG analysis of TGA. b. Differential scanning calorimetry of unmodified nanocellulose aerogel and silane-modified nanocellulose aerogel. c. Dependence of indoor surface temperature to outdoor temperature for SiCellA-based window products compared to single glass panes. Tc indicates the outdoor temperature when condensation formed on the indoor surface of the glass at indoor relative humidity of 50%. d-f. Optical performance of triple-pane IGU with a 3 mm thick SiCellA layer in the center before and after chemical fogging test (d), 80-80 durability test (e), and 30-day 500W UV irradiation test (f). Insets d-f show the IGU (d) of a 15cm x 15cm area after a chemical fogging test, the IGU (e) of a 10cm x 10cm area after an 80-80 durability test, and the IGU (f) of a 10cm x 10cm area inside a chamber under UV irradiation, respectively. [Figure 7b] Same as above [Figure 7c] Same as above [Figure 7d] Same as above [Figure 7e] Same as above [Figure 7f] Same as above [Figure 8a]Figure 8 shows window products containing SiCellA. a. U and R values ​​(inset) of single-pane windows modified with SiCellA of various thicknesses on a 100 mm thick support substrate attached to a glass plate. Lines and symbols indicate calculated and measured data, respectively. b. U and R values ​​against aerogel thickness, calculated for a fixed triple-pane IGU with a total thickness of 32 mm, and for SiCellA used instead of an intermediate layer and a low-E coating applied to one of the glass plates. c. U and R values ​​against SiCellA thickness, calculated for a triple-pane IGU with a SiCellA film in the center and a 12 mm gap between the glass plate and the SiCellA. Solid and dashed lines are calculated for average thermal range infrared transmittance at 0% and 16%. d. Photograph of a 15 cm × 15 cm triple-pane IGU made using a 3 mm thick SiCellA film as an intermediate plate and a fixed 12 mm gap between the glass plate and the SiCellA. e. Calculated (lines) and measured (symbols) U and R for the triple-layer IGU shown in (d). f. Calculated R values ​​for air, argon, and krypton-filled triple-layer aerogel IGUs, having two clear glass plates (IGU1) or one clear glass plate and LoE-180 (IGU2) or LoE-366 (IGU3) coatings, with a 3mm thick SiCellA film as an intermediate plate. g. Spectral dependence of total transmittance and diffuse transmittance of triple-layer IGUs with a 3mm thick SiCellA film as an intermediate plate. The inset on the right shows a photograph of the corresponding IGU. The spectral dependence of the total visible light transmittance of the following: a triple-layer IGU (1) having a 3mm thick SiCellA between two 3mm thick clear glass plates with a 14mm gap; a double-layer IGU (2) having two 3mm thick clear glass plates and a 31mm gap; a 3mm thick glass plate modified with a 2mm thick SiCellA (3); a 2mm thick self-supporting SiCellA (4); and air (5). [Figure 8b] Same as above [Figure 8c] Same as above [Figure 8d] Same as above [Figure 8e] Same as above [Figure 8f]Same as above [Figure 8g] Same as above [Figure 8h] Same as above [Figure 9a] Figure 9 shows modified products based on SiCellA and their properties. a-c. Photographs of (a) 15cm × 15cm, (b) 20cm × 25cm, and (c) 1 square meter 1.5mm thick SiCellA layers on a transparent plastic film. d. Photograph of a 36cm × 51cm 3mm thick single glass plate modified with a 3mm thick SiCellA film. e. Spectral dependence of the transmittance of a 1.5mm thick hydrogel. f. Spectral dependence of the transmittance and absorbance of a 1.5mm thick SiCellA film bonded to a transparent polyester film. g. Spectral dependence of the visible light transmittance of a 1.5mm thick SiCellA film bonded to a transparent polyester film. The inset shows the window of a single plate modified with this SiCellA-polyester composite film having dimensions of 72.1cm × 71.4cm × 0.15cm. [Figure 9b] Same as above [Figure 9c] Same as above [Figure 9d] Same as above [Figure 9e] Same as above [Figure 9f] Same as above [Figure 9g] Same as above [Figure 10] Figure 10 shows IGUs in which SiCellA can be used and their visible light transmittances. a. A 1 square meter IGU with 3 mm of SiCellA between a flat glass and LoE-180 coated glass facing the Rocky Mountains. b. Transmittances of different IGUs studied. d-f. Photographs of a 36 cm × 51 cm double-plate IGU with 3 mm thick SiCellA between (d) two 3 mm thick clear glass plates, (e) one clear glass and one LoE-180 glass, and (I) one clear glass and one LoE-366 glass plate. [Figure 11]Figure 11 shows the processing of hardwood pulp into TEMPO-oxidized cellulose nanofibers. a. Poplar wood as a bioresource for pulp in Colorado, USA. b. Photographs of softwood and hardwood pulp used in the production of TEMPO-oxidized cellulose nanofibers. c. Chemical structure of cellulose biopolymer molecules with active hydroxyl groups of each unit highlighted. d. Schematic diagram including details of the reaction of cellulose and TEMPO-oxidized cellulose nanofibers. e. Hardwood cellulose pulp in an oxidation chamber. f. Cellulose pulp under blender-assisted TEMPO oxidation. g. TEMPO-oxidized cellulose nanofibers after the first oxidation and blending. h. Cellulose nanofibers after a second oxidation at 60°C for 72 hours. i. TEMPO-oxidized cellulose nanofibers with a width of 4-10 nm in a blender after the second oxidation (Figure 3a). j. 1 L of TEMPO-oxidized nanofibers in 1 wt.% water after sonication at 20% amplitude for 30 minutes using a Branson sonicator and filtration. [Figure 12] Figure 12 shows an exemplary procedure for the fabrication of SiCellA. a. Photograph of 1 L of TEMPO-oxidized cellulose nanofibers dispersed at 1 wt.% in water. b. Photograph (red) of a homogeneous aqueous dispersion of 1 wt% cellulose nanofibers supported by 1 cm × 0.3 cm rubber spacers at the bottom and on all four sides of the glass. c. Tank in which a hydrogel was formed by acid gelation (0.5 M HCl), followed by washing away trace amounts of acid and exchanging the solvent from water to ethanol in the hydrogel. d. Alcogel using ethanol as the solvent thereafter. e. Silanation of the hydrogel stage with vinylsilane before drying. f. Silanation of the alcogel in ethanol before drying by CPD. g. Drying of the alcogel by CPD using liquid CO2 in a drying chamber. h. Vinylsilane-modified SiCellA. i. Unmodified nanocellulose-based aerogel. j. Gas-phase silanation of an aerogel using 1H,1H,2H,2H-perfluorooctyltriethoxysilane. k. Fluorosilane modification SiCellA. [Figure 13]Figure 13 shows the conversion from a large alcohol gel to an aerogel. a. The alcohol gel is rolled up with a protective layer, which will be placed inside the large CPD chamber shown in (c). The alcohol gel is safely and carefully protected with layers of foam and plastic mesh for rolling and subsequent drying. b. One square meter of alcohol gel tightly rolled up before drying with the CPD. c. A CPD with a 16.5 cm × 104 cm cylindrical chamber suitable for drying one square meter and larger alcohol gels. d. One square meter of aerogel dried in the CPD and tightly rolled up. e. One square meter of aerogel spread out after drying and bonded to a clear plastic film. f. A photograph of a 0.09 square meter (1 square foot) of aerogel rolled up after drying. [Figure 14] Figure 14 shows the experimental setup for measuring the thermal properties of the IGU. a. Photograph of the high / low temperature box and data acquisition setup for measuring the thermal performance of a 1 square meter single-pane window modified with 1.6 mm thick SiCellA film. Heat flux and temperature sensors are shown. b. Typical experimentally measured heat flux and corresponding temperature over time are shown. [Figure 15] Figure 15 shows a. Brunauer-Emmett-Teller (BET) plots of unmodified aerogel and silane-modified aerogel, b. isotherms of unmodified aerogel, c. absolute isotherms of unmodified aerogel, d. pore size distribution of unmodified and modified aerogel based on density functional theory models, e. isotherms of modified aerogel, and f. absolute isotherms of modified aerogel. [Figure 16] Figure 16 shows a. stress-strain plots and b. force-strain plots for a 2% elongation cycle, and c. stress-strain plots and d. force-strain plots for a 4% elongation cycle. [Figure 17]Figure 17 shows: a. Stress-strain plot for a 2% compression cycle. Insets show the sample at the alcogel stage and the characterized aerogel on the compression pan. b. Compression and recovery of the aerogel at 2% strain within 10 cycles. c. Stress-strain plot for a 4% compression cycle. d. Compression and recovery of the aerogel at 4% strain within 10 cycles. e. Stress-strain plot for a 6% compression cycle. f. Compression and recovery of the aerogel at 6% strain within 10 consecutive cycles. [Figure 18] Figure 18 shows thermal images of a heat radiation source taken through glass or SiCellA. a. Uncoated glass, b. LoE-180 glass, c. LoE-366 glass, and d. 6.5 mm thick SiCellA are shown. The images were taken at 40°C using a FLIR E60 camera with a blackbody radiation source having an emissivity of 0.95 or higher. The radiation surface of the Model GM-01A blackbody radiation source (IKTech) used was 10 mm away from the nearest surface of the glass or SiCellA, and the measurements were performed in a vacuum chamber to avoid heat exchange by conduction and convection through air. The measured surface temperatures suggest that the radiative heat shielding capability of thickness-dependent SiCellA slabs may be superior to that of low-emissivity coated glass used in the glass industry. [Figure 19] Figure 19 shows the assembly of the IGU of triple-layer SiCellA and its numerically calculated thermal properties. [Figure 20] Figure 20 shows a three-panel assembly according to a further example of the present disclosure.

[0013] It should be understood that the elements in the figures are shown for brevity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated relative to others to help improve understanding of the illustrated embodiments of this disclosure. [Modes for carrying out the invention]

[0014] While certain embodiments and examples are disclosed below, it will be understood by those skilled in the art that this disclosure extends beyond the specifically disclosed embodiments and / or uses of the disclosure, as well as obvious modifications and equivalents thereof. Therefore, the scope of this disclosure is not intended to be limited by the specific embodiments described herein.

[0015] Unless otherwise indicated, the figures presented herein are not necessarily actual representations of any particular material, assembly, structure, or device, but are merely illustrative and used to illustrate embodiments of the present disclosure.

[0016] Buildings consume approximately 40% of the energy generated worldwide to maintain a comfortable indoor environment. Windows and skylights remain the least efficient parts of building exteriors, as achieving high transparency and thermal insulation simultaneously remains a challenge. Here, we describe transparent cellulose-based aerogels (glazing materials) fabricated from the most abundant biopolymers on Earth, utilizing techniques such as colloidal self-assembly and roll-to-roll processes. Cellulose-based aerogels are suitable for scalable manufacturing because they have a visible light transmittance of 97–99% (better than glass), a haze of approximately 1%, and a thermal conductivity lower than still air. With a mass density hundreds of times that of glass, these lightweight materials can be used as panels in multi-pane insulated glass units or for modifying existing windows. Exemplary aerogels have the potential to improve energy efficiency, enable entirely new technological solutions for insulated glass units, skylights, daylighting, and facade glazing, and enhance the role of glazing in future building exteriors.

[0017] Specific example Specific examples are provided below. These examples are for illustrative and descriptive purposes only. Unless otherwise indicated, these examples should not be taken as limiting. Similar methods and materials may be used in other plasmonic nanoparticles, nematic liquid crystals, functionalized coatings, and / or chemical coatings described herein.

[0018] Fabrication of nanostructured SiCellA materials for window-scale thermal insulation The ultra-thermal transparent SiCellA material improves the efficiency of existing windows on a window-related scale and enables new window products, as demonstrated using SiCellA-based modified films and IGUs (Figures 1c-e, as well as Figures 9 and 10).

[0019] Figure 1a shows an assembly 100 comprising a substrate 102 and a transparent glazing material 104 (e.g., a SiCellA film, or simply SiCellA, or sometimes an aerogel) as described herein. Figure 1b shows an assembly 200 comprising plates 202 and 206, and the transparent glazing material 204 placed between plates 202 and 206. As shown, gaps 208, 210 may exist between the transparent glazing material 204 and one or more plates 202, 206.

[0020] Figure 20 shows a three-plate assembly 300 according to a further example of the present disclosure. The assembly 300 may include plates or substrates 302, 304, 306 and one or more transparent glazing materials 308, 310 between and / or on the plates or substrates 302, 304, 306. In some cases, gaps may exist between the plates and the transparent glazing materials, as will be described in more detail below. Furthermore, the assembly may include one or more coatings 312-318 on one or more plates and / or on one or more transparent glazing materials, as will be described below.

[0021] SiCellA films (also referred to herein as transparent glazing materials, e.g., transparent glazing materials 104, 204) readily adhere to the surface of substrates such as substrates 102 and / or plates 202, 206, which may be formed from, for example, plastic films and / or glass plates, due to electrostatic charging. When used as a laminated modification on the inner surface of a single-pane window, a thin film of SiCellA (Figure 1c) can improve the thermal insulation performance of a single-pane window, as is evident from the thermal image of the outdoor glass surface temperature in winter (Figure 1f). The temperature of the outer surface of the modified plate has been measured to be lower than that of a similar unmodified plate, because the introduction of the SiCellA modification can more effectively block heat transfer from the window (Figure 1f). High-temperature and low-temperature boxes, which mimic the internal and external heat exchange in summer and winter, respectively, exhibit similarly excellent thermal insulation performance when the SiCellA aerogel described herein is laminated on a single pane of glass or inserted into the gap between two IGUs (Figure 1g, h).

[0022] An exemplary method for producing SiCellA material involves the step of oxidizing natural cellulose by treating wood pulp-derived cellulose nanofibers or other suitable cellulose nanofibers with an oxidizing agent such as 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) mediated (see Figure 11). Other exemplary cellulose nanofibers can be obtained by chemically or mechanically treating various natural sources, such as cotton, softwood pulp, hardwood pulp, tunicates, and bacterial cellulose, as well as similar materials. In some cases, nanorods and nanofibers can be obtained from multiple sources, such as any combination of the above sources. The surface charge associated with carboxylic acid anions relaxes the aggregation of nanofibers, allowing the nanofibers to form stable aqueous colloidal dispersions at various concentrations, which can be poured into molds of desired shape and size (see Figure 12). By adding an acid (such as hydrochloric acid or HF), the nanofibers are interconnected via hydrogen bonds between carboxyl groups, and the colloidal dispersion is converted into a hydrogel with a sparse network of nanofibers (Figure 12b). Next, the fluid medium within the gel is replaced by replacing water with isopropanol or ethanol (see Figures 2a, b and 12c, d), and then the gel is formed into an aerogel by, for example, supercritical drying (Figure 2c). These fabrication procedures are highly scalable and can be combined with simple steps such as molding to define the desired hydrogel volume, solvent exchange at a moderately elevated temperature (see Figure 12), and winding and drying the gel onto rolls (Figures 2a-c). Furthermore, such techniques allow for the mitigation of cellulose nanofiber aggregation during gelation or drying so that the colloidal dispersion, which was initially transparent, maintains its transparency even in the hydrogel and aerogel states (Figures 2d, e, 13). According to an example in this disclosure, the cellulose surface is silanized, and silanization can be carried out by gas-phase functionalization at the hydrogel stage after and / or before supercritical drying (Figure 2f), details of both methods are provided below, see, for example, Figures 2f and 12e-k.Silanization is revealed by analyzing the presence or intensity of a specific absorption line using infrared spectroscopy (Figure 2g). This procedure makes SiCellA superhydrophobic (note that the water droplet contact angle shown in Figure 2h is greater than 150°), which is a highly desirable property for window applications.

[0023] Nanoscale characterization provides insights into the formation and structure of SiCellA materials (Figure 3). According to examples of this disclosure, individual cellulose nanofibers are well-defined rod-shaped particles having a width of 4–6 nm or other widths as described herein, and a length of several hundred to several thousand nanometers as described herein (Figure 3a). Through fabrication procedures of gelation, surface modification, solvent exchange, and drying, an initial colloidal dispersion of such nanorods is converted into a gel having a nanoscale morphology featuring a network of fine fibers, with interfiber pores typically smaller than 100 nm (Figures 3b–d). By controlling the initial concentration of cellulose nanofibers, the porosity of SiCellA can be varied in the range of 97.5%–99.25% or 90%–99.5% (Figure 3e), which is linearly related to the mass density of the material.

[0024] Nitrogen absorption-desorption analysis is consistent with direct nanoscale imaging and provides quantitative analysis of the porous morphology of SiCellA related to the interconnected nanofiber network (Figure 3h) (Figures 3f, g, and 15).

[0025] Optical, thermal, and mechanical properties of SiCellA material Modern windows and skylights are expected to perform a primary function made possible by transparency, while simultaneously effectively separating the controlled indoor environment from the building's exterior. The transparent SiCellA material described herein exhibits a desirable combination of optical, thermal, and mechanical properties, thereby making it suitable for applications in window products. Exemplary freestanding slabs of SiCellA feature extremely high visible light transmittance, ranging from 97% to 99%, far exceeding the approximately 92% of glass (Figures 4a-c, Figure 9, and Table 1).

[0026] [Table 1]

[0027] In addition, the haze coefficient is low, typically within 1–3% depending on the thickness of the SiCellA slab (Figure 4a, b). Slabs of various thicknesses with low scattering and high transparency can be fabricated (Figure 4b). This extremely high light transmittance stems from the nanoscale properties of SiCellA (Figure 3), where all length scales of the aerogel form are much smaller than the wavelengths of light in the visible spectral range. SiCellA is highly porous, with a solid content of only about 1% and an air content of about 99%, resulting in similar effective refractive indices for these materials and air (Figure 4d). This low refractive index of about 1.0025 (compared to about 1.0003 for air and about 1.52 for glass) means that the SiCellA-air interface reflects far less light than the glass-air interface, resulting in high light transmittance of SiCellA across the entire visible and near-infrared spectral range (Figure 4a–c, e). Due to the refractive index matching of SiCellA and air, prisms made of these materials exhibit a very small deflection angle at the aerogel-air interface, while the light follows Snell's law (Figure 4f). The color rendering index, which quantifies the effect of the material or window on the perception of natural colors, is very high at approximately 99%, resulting in the preservation of natural colors. Furthermore, SiCellA material can be cut into desired shapes using, for example, a regular razor or knife while maintaining high transparency (Figures 4c, f), and / or molded to adopt a wide variety of geometric shapes and dimensions from a few millimeters to several meters while preserving low haze and high transparency (Figures 1 and 4g~j).

[0028] SiCellA minimizes its impact on visible light transmittance (Figure 4) while simultaneously functioning as an excellent insulator (Figure 5), increasing the thermal resistance R of windows and reducing the U coefficient, which measures how well a window insulates. U = 1 / R. The thermal conductivity and R of transparent glazing materials depend on porosity and change with temperature (Figures 5a, b). When porosity is appropriately selected, SiCellA significantly outperforms the thermal insulation of still air, and its performance does not involve the convection-related problems characteristic of air and other gas fillers, as discussed below in the context of window products. The superior insulation is clearly demonstrated by placing slabs of aerogel of different thicknesses and shapes on a high-temperature stage (Figure 5c). The nanoscale morphology of SiCellA is such that air molecules collide with the cellulose network more frequently than with each other, resulting in significantly lower gaseous heat conduction compared to bulk air, while poor thermal contact between fibers in the cellulose network minimizes heat conduction through the solid component (approximately 1% by volume). In addition to these two factors and the low thermal conductivity measured differently from air, the exemplary transparent glazing materials described herein obstruct the transmission of radiation in the thermal range, resulting in reduced radiative heat transfer (Figures 5d, e). While exemplary transparent glazing materials based on pure cellulose are somewhat transparent in some parts of the thermal range, this transparency is significantly reduced by silanizing the surface of the material (Figure 5d), thus further improving the thermal barrier properties of the transparent glazing material, as quantified using transmittance weighted across the spectrum of thermal blackbody radiation at room temperature (Figure 5e). While many aerogels may exhibit fairly low thermal conductivity, SiCellA uniquely combines this property with very high visible transparency and low haze, desirable for window applications. Because SiCellA aerogel (transparent glazing material) is prepared by gelling a nematic colloidal dispersion of oxidized cellulose nanofibers, it is optically anisotropic (the difference between the anomalous and normal refractive indices is approximately 4 × 10⁻⁶). -3(Birefringence). Although not directly related to window applications, birefringence reveals nematic-like structures of polydomains and monodomains in nanofiber structures where the spatial orientation of nanofibers changes gradually. This is desirable for maintaining a spatially uniform distribution of the effective refractive index and reducing light scattering associated with such changes.

[0029] While the low mechanical stability of conventional aerogels hinders many technical applications, SiCellA materials are mechanically robust, and their properties are partially improved by silanization (Figure 6). Compression and bending deformations demonstrate that such materials can withstand the significant mechanical loads expected during the manufacture and use of various window products (Figures 6a-f). Periodic compression cycles clearly showed no degradation of mechanical performance over time (Figures 6c, 16, and 17). SiCellA films and slabs with thicknesses ranging from millimeters to centimeters can be bent and even wound while maintaining high transparency (Figures 6c-g) without cracking or performance degradation. Since the mechanical properties depend on porosity, the desired mechanical behavior can also be tuned by preparing samples with different porosity and solid content (Figures 6a, b, f).

[0030] Window products and their durability For window applications, many stringent properties are desirable, far beyond the optical, thermal, and mechanical characterizations described above. Some desirable properties relate to the durability of the material itself and the durability of the entire glazing product in which these materials are used. Thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTG), and differential scanning calorimetry (DSC) characterization of salt-treated cellulose aerogels and unmodified cellulose aerogels reveal that they are thermally stable at ambient and moderately elevated temperatures (Figures 7a, b). While such materials may degrade when heated well above 200°C, such high temperatures are irrelevant for window and skylight applications. Exemplary SiCellA aerogels, whether used as modifications or within IGUs, improve window condensation resistance (Figure 7c), and single-pane glass modified with SiCellA exhibits a condensation resistance coefficient (quantifying the ability to suppress water condensation on the window surface at low temperatures) comparable to commercially available double-pane IGUs. Thin double-walled IGUs with the air filler replaced by SiCellA exhibited a condensation resistance coefficient of 82, which is far better than the 35–50 known for commercially available double-walled IGUs. SiCellA did not show any detectable performance degradation after chemical fogging tests of SiCellA IGUs (Figure 7d), which is related to the superhydrophobic properties of SiCellA (Figure 2h). Two weeks of 80 / 80 humidity and UV exposure tests did not reveal any significant degradation in the optical or thermal properties of SiCellA IGUs (Figure 7e). Testing according to ASTM2189 and ASTM2190-19 standards using IGUs containing SiCellA in the gaps (see Figure 1b) did not reveal any condensation inside the IGUs, nor any significant changes in light transmittance and thermal performance in response to factors such as chemical processes and UV irradiation (Figures 7d–f, and Table 2). As expected (Figures 1a, b), SiCellA significantly improves the condensation resistance of window products and IGUs when aerogel-based film is applied to window products, including single-pane windows, and when the aerogel is inserted into the gap between double-pane IGUs (Figure 7c).

[0031] [Table 2]

[0032] To create robust modified products, exemplary SiCellA were bonded to a protective clear plastic or thin glass substrate and then laminated onto the inner surface of a single-pane window (Figures 1c, f, and 9). The R-value of the subsequent modified single-pane window may depend on the thickness of the SiCellA, as revealed by combining numerical models and experimental measurements (Figure 8a) using both actual windows and high / low temperature box prototypes (Figures 1f-h and 14). Here, the single-pane window with such improved efficiency can perform comparably to or even surpass the performance of a double-pane window (Figure 8a). Since single-pane windows still constitute approximately 40% of all windows, as multi-pane IGUs often do not fit structurally or architecturally with the design of older historical buildings, these modified products could play a significant role in compensating for window-related energy losses in existing buildings (Figure 12).

[0033] IGUs containing a new type of SiCellA intended for new construction can take many different embodiments, where glass plates can be used with or without various low-emissivity coatings, and the thickness of the aerogel filler relative to the overall gap thickness can be varied along with the thickness of air or other filling gases. The results of numerical modeling of such SiCellA-IGUs (Figures 8b, c) are consistent with experimental measurements performed on a series of fabricated prototypes (Figures 8d-h), demonstrating that general principles commonly applied to the design of glass-based multi-pane IGUs can be appropriately adapted to the use of SiCellA plates and fillers. The R value can be further increased even when aerogel fills only a portion of the gaps by filling some of the gaps in the SiCellA-containing IGU with an inert gas such as krypton and / or argon (Figure 8f, Table 3 in Figure 19). Due to the very high transmittance of SiCellA, adding SiCellA to window products does not degrade the overall optical properties of the IGU (Figures 8g, h, 9, and 10), and therefore, transmitted light loss mainly arises from the glass and the various coatings on it. In this regard, SiCellA is an excellent candidate for an intermediate plate in IGUs because it enables higher transmittance than glass, and therefore, IGUs with multiple intermediate plates can be developed while maintaining high overall transmittance (Figures 8g, h, 9, and 10).

[0034] Moderately transparent cellulose, silica, organic-inorganic hybrids, and other aerogels have been demonstrated over the past several decades and initially attracted the interest of window manufacturers. However, numerous challenges related to the stringent requirements for glazing products have hindered their mainstream application in windows, skylights, and other parts of building exteriors. The glazing materials and assemblies of the present invention overcome these major challenges as follows.

[0035] 1) SiCellA has been demonstrated to be mechanically robust even on a square meter scale related to windows. 2) Low haze and high clarity meet the requirements for window applications. 3) Silanation makes SiCellA superhydrophobic, improving its durability.

[0036] 4) By adhering SiCellA to plastic films, it becomes possible to use it in a wide range of glass products. 5) Simple manufacturing steps and low-cost raw materials are helpful for deployment. The fundamental difference between SiCellA and conventional aerogels is that the size of pores (less than 100 nm) and nanofibers (less than 10 nm) that form networks (Figure 3) are controlled to be much smaller than the visible light wavelengths on a (square meter) scale related to windows, guaranteeing a visible light transmittance of 97-99% (considerably better than the transmittance of general-purpose clear glass, which is about 92%) and a haze of about 1%. These lightweight materials, with a mass density of about 1% of glass density, are mechanically robust and take the form of self-supporting films exhibiting a thermal conductivity of only about 14 mW / (K·m), which is lower than that of still air.

[0037] The exemplary SiCellA described herein can be manufactured in a low-cost and highly scalable manner and is expected to enable the design of entirely new types of TGUs, skylights, daylights, and even window frames containing SiCellA. The abundant raw material, which is undried wood pulp in this study, can also be obtained from waste from the food and beer production industries by utilizing the bacteria and / or other materials described herein, and the cost of the final SiCellA film is approximately $1 per 0.09 square meters (1 square foot) in both cases.

[0038] In addition, there is a potential possibility that solar radiation acquisition can be controlled by using a reflective cholesteric filter based on nanocellulose. Therefore, in some cases, the assembly may include a cholesteric nanocellulose filter.

[0039] The deployment of SiCellA could potentially increase the use of glazing in building exteriors, as aerogel-reinforced windows can exceed current and near-future targets for the R-value of glazing.

[0040] Combining extremely high transparency and low thermal conductivity at the building material scale, iCellA is groundbreaking, opening up unique opportunities to utilize and control the solar energy supplied to buildings in accordance with climate and seasonal needs. Its low mass density (approximately 1% or less of glass) is desirable for structural compatibility, the renovation of older windows, and, most importantly, for new multi-panel IGU designs. The improved performance of SiCellA-based IGUs is directly related to the low thermal conductivity and high visible light transmittance of these materials when used as interlayers in IGUs. The reflectance coefficient at the air-SiCellA interface is approximately one-tenth that at the glass-air interface; therefore, multi-panel assemblies using SiCellA-based interlayers exhibit less light loss due to reflection compared to their standard counterparts. For example, in a quadruple-panel IGU assembly, replacing two interlayer glass panes with SiCellA counterparts can reduce light loss by approximately 16% (Figure 8). Each new SiCellA plate reduces light transmittance by less than 1%, and therefore, even a 10-plate IGU might be possible (a 10-plate glass-based IGU is not possible with an intermediate glass plate because reflections at 20 interfaces block almost all light from passing through). Thus, exemplary assemblies according to this disclosure may include 2, 3, 4, 5, 6, 7, 8, 9, 10, or more, e.g., self-supporting transparent glazing material sheets or layers. In a SiCellA-based IGU, the plates may be separated by gaps of varying thickness in the range of about 6 to 16 mm, and these gaps can be optimized depending on the gas filler (Figures 8b-f, Figure 19). For example, by making the outer glass about 3 mm thick and using a SiCellA plate as the intermediate layer, a triple-plate IGU with an overall thickness of about 21 mm, the same as a standard double-plate IGU, can be fabricated to replace a standard double-plate IGU while providing better thermal insulation with equivalent light transmittance. In IGU designs, it is possible to mix self-supporting SiCellA interlayers with interlayers bonded to glass plates on their inner surfaces.Since the thermal conductivity of still air is less than approximately 26 mW / (K·m) and there is no convection, SiCellA-based IGUs can achieve better thermal insulation per 2.54 cm (1 inch) than conventional double-pane windows with air gaps (Figures 8, 9, and 10). Low emissivity coatings can be applied to glass surfaces such as the inner surface of outdoor glass panes (Figure 8), but for SiCellA-based IGU assemblies with an intrinsic radius greater than 9, low-e coatings do not provide a significant further improvement in thermal insulation.

[0041] Initial deployments of SiCellA-based glazing products are likely to focus on conventional windows, but SiCellA can also be designed to be semi-transparent and backscatter for other glazing uses such as skylights and privacy windows, in which case SiCellA can be intentionally made more frosted. The high R value makes SiCellA-based IGUs attractive for integration with electrochromic and other technologies for privacy and solar heat gain control, particularly in new types of multi-pane IGU designs (Figure 8), thus enabling an all-in-one solution for high energy efficiency. Glazing that can utilize SiCellA allows building exteriors to better utilize external conditions while providing natural comfort to occupants and potentially utilizing energy from the environment. [Examples]

[0042] Raw materials and oxidation of cellulose. Undried hardwood cellulose pulp was obtained from Nine Dragons Paper (Rumford Division, USA). This hardwood kraft pulp, with a moisture content of 92%, was maintained in the wet stage after bleaching. The pulp was desalted by stirring in HCl (0.1 M) solution for 1 hour, washed with deionized (DI) water by filtration, and then stored at 4°C without drying. TEMPO oxidation of the cellulose pulp was initiated in a basic medium at pH 10 (Figure 11e). TEMPO (28.92 mg, 0.094 mmol) and NaBr (317.64 mg) were added to the suspension, followed by the addition of 10 ml of 1 M NaOCl solution. When the pH decrease was less than 0.01 per minute, the solution was transferred to a blender and blended at 1500 rpm for several minutes (Figure 11f). This breaks down the aggregates of cellulose fibers, allowing the oxidizing agent to penetrate more deeply. After a total blending time of approximately 15 minutes, the solution was returned to the stirring plate and the pH was adjusted back to 10. This process was repeated until the pH of the blended solution decreased to less than 0.5. The reaction was considered complete when the pH of the solution on the stirring plate decreased to less than 0.03 in one hour. Next, the solution was placed in a centrifuge at 9000 rpm for 20 minutes to filter out excess chemicals from the cellulose solution. This process was repeated several times, with the waste liquid replaced with DI water each time, to remove residual chemicals from the solution until only pure oxidized cellulose fibers remained. Next, the oxidized nanocellulose was recovered by centrifugation, thoroughly washed with water, then mechanically ground with a 1500W grinder (Figure 11g), followed by sonication with a Branson sonicator at 30% amplitude for 15 minutes. Furthermore, the oxidation of unreacted C6 hydroxyl groups to C6 carboxylate groups of cellulose was carried out using NaClO2 as the main oxidizing agent in water at pH 4.8-6.8 with catalytic amounts of TEMPO and NaClO. TEMPO again enabled the selective and efficient conversion of C6 hydroxyl groups. 1 g of TEMPO-oxidized cellulose nanofiber solution was added to 1 M disodium hydrogen phosphate (2.35 ml) and 1 M monosodium hydrogen phosphate (2.65 ml) solutions (Figure 11h) to act as buffers during the reaction.This was stirred at 500 rpm for approximately 5 minutes, then 20 mL was taken out and set aside, and later added to the reaction vessel after diluting sodium hypochlorite. Next, TEMPO (25 mg) and sodium chlorite (1.13 g) were added to the oxidized cellulose nanofiber dispersion, and the mixture was stirred at 500 rpm for approximately 20 minutes until these additives were completely dissolved. Next, sodium hypochlorite (0.455 mL) was added to another 20 mL of solution. Next, the diluted sodium hypochlorite was added to the nanocellulose dispersion, and the reaction vessel was immediately sealed with a tightly fitting screw cap. The solution was placed in a water bath at room temperature and stirred at 500 rpm for approximately 30 minutes. Next, the water bath was heated to approximately 60°C, and the reaction was allowed to run continuously for 72 hours. Next, the solution was placed in a centrifuge at 9000 rpm for 20 minutes to filter out excess chemicals from the cellulose solution. This process was repeated several times, with the waste liquid replaced with DI water each time to wash away residual chemicals until only pure oxidized cellulose fibers remained. Next, the dispersion was sonicated for 30 minutes using a Branson sonicator and filtered through Whatman filter paper 2 to obtain the final aqueous dispersion of oxidized cellulose nanofibers.

[0043] Preparation of aerogel Aqueous dispersions of TEMPO-oxidized cellulose nanofibers with concentrations ranging from 0.5% to 2% were poured into plastic molds of desired thicknesses ranging from 1.5 mm to 25 mm (Figure 12a, b). To initiate gelation, 0.5 M HCl was sprayed onto the dispersion for several seconds using a fine sprayer. The sprayed HCl was allowed to stand for 30 minutes without stirring, with the dispersion remaining spread evenly. The resulting hydrogel was then transferred to a 0.1 M HCl solvent bath and left for 24 hours to ensure complete gelation. The hard hydrogel was then removed from the mold, washed away with DI water to remove the acid, and then transferred to a mixture of water and ethanol (50 vol.%), followed by replacement of the solvent with ethanol (Figure 12b-d). The temperature was increased (60°C) during the water-to-ethanol exchange because ethanol forms an azeotropic mixture with water (Figure 124c, d). Next, the subsequent alcohol gel was rolled and moved to a critical point dryer (CPD) chamber, where the chamber's initial temperature was set to 5°C and the pressure to 800 psi for drying (Figures 12g and 13a-c). In the next step, the ethanol was purged from the chamber and replaced with liquid CO2. The temperature was then increased to 40°C and the pressure to 1500 psi, and the remaining ethanol from the supercritical phase was purged for 30 minutes. The final step of the process, the removal of supercritical CO2, was then slowly started at 25 psi / min, and the chamber was gradually depressurized over approximately 1 hour. The resulting aerogel was held at 60°C for 1 day before characterization and functionalization (Figures 12i, h). Depending on the size of the SiCellA to be dried, CPD chambers with cylindrical internal volumes of two different dimensions (diameter × height 16.5 cm × 2.5 cm and 16.5 cm × 10⁴ cm) were used (Figures 12g-k and 13c-f).

[0044] Silaneization of cellulose gel Most commonly (and for all SiCellA samples characterized in Figures 1-8), silanation of cellulose molecules was performed after aerogel preparation, as illustrated in Figures 2f and 12g-k; however, modification can also be performed at the hydrogel stage (Figures 4e, f, h). Silanation at the aerogel stage was carried out using 1H,1H,2H,2H-perfluorooctyltriethoxysilane as a coupling agent (Figure 2f), where the aerogel was functionalized with 1H,1H,2H,2H-perfluorooctyltriethoxysilane in a sealed container at 100°C for 2 hours (Figure 2f). The aerogel sample and silane were placed in a vacuum oven for heating, and the reaction was completed at optimized reaction time, amount of silane, and temperature (Figure 2f) (Figure 12). The resulting superhydrophobic aerogel (Figure 2h) retained the desired optical and thermal properties. Alternatively, to obtain similar results, vinyltrimethoxysilane was used as a coupling agent to silane the cellulose molecules of the fabricated hydrogel (Figures 12d-f). The fabricated hydrogel was immersed for 4 hours in a circulating bath of a 60:40 ethanol / water mixture containing an optimized concentration (5%) of the coupling agent. The pH of the solution was maintained between 3.5 and 4 by using METREPAK Phydrion buffer to efficiently coat the exposed individual cellulose fibers with the vinyltrimethoxysilane coupling agent. The ethanol-water mixture was then drained and replaced with pure ethanol by repeated washing. The subsequent salt-treated nanocellulose alcohol gels were dried in a CPD chamber (Figures 12f-h).

[0045] Thermal characterization The thermal conductivity k of the aerogel was characterized by two methods, depending on the dimensions of the sample: using a commercially available heat flow meter, Netzsch HFM 446, or measuring the heat flux passing through the sample using a sensor (FluxTeq). In the former case, the aerogel was prepared with dimensions ranging from 10 cm × 10 cm to 20 cm × 20 cm in the lateral dimensions specified in the instrument guidelines, while the latter method was used for samples ranging in size from square inches to square meters.

[0046] The thermal conductivity of the large-area aerogel film and the U-value of the SiCellA aerogel prototype were determined by measuring the heat flux passing through the sample. To study the heat exchange between the indoor environment and the outdoor environment separated by the window retrofitted with the SiCellA film and measure its U-value, an environmental high-temperature / low-temperature box system (Figure 14) was constructed. The overall dimensions of the box are 1.3 m × 1.3 m × 0.5 m, and a double-insulated wall was constructed using commercially available polystyrene foam (FOAMULAR NGX) with a wall thickness of 38 mm and R = 10. The high-temperature / low-temperature box can be adapted to samples with various aspect ratios and areas up to 1 m 2 To mimic the heat exchange between the indoor and outdoor environments of a building under various conditions, the inside of the box was heated with an electronically controlled heating band or cooled by the supply of dry ice. Thus, the internal temperature of the box corresponding to the ambient outdoor temperature can be varied within a wide range from -70 °C to +100 °C. The inside air temperature T e and the outside air temperature T i , as well as the temperature of the window surface, were continuously monitored with thermocouples. A heat flux sensor (FluxTeq) was used to measure the heat flux q passing through the measured assembly or IGU. Data from the heat flux sensor and thermocouples were collected by a computer using automatic data acquisition software (Figure 14). The heat flow passing through the characterized SiCellA material, assembly or IGU can be monitored over several hours or days as required. Using this system, the thermal conductivity, thermal conductance, U-value and R-value were measured. For example, the U-value of a window retrofitted with an aerogel film or IGU was calculated as U = q / (T i -T e [[ID=I2]]) using the measured values of q, T i and T e . <00OO303>

[0047] Optical Characterization A Cary 500 scan spectrophotometer was used to measure spectra from ultraviolet to visible and near-infrared in transmission mode. Total transmittance and diffuse transmittance spectra of the aerogel film in the visible region (400–800 nm) were recorded using an integrating sphere (Labsphere DRA-CA-5500). The haze coefficient value, which quantifies the amount of scattered light, was calculated using the integrating sphere based on the measured total transmittance and diffuse transmittance according to ASTM D1003 (Standard Test Method for Haze and Luminous Transmittance), which is commonly used for haze measurement in window applications. For light transmittance and haze measurements, the sample was mounted in the input port of the integrating sphere and calibrated using a diffuse reflectance standard. For freestanding modified samples, samples with an area of ​​10 cm × 10 cm, and for triple-plate IGUs, samples with an area of ​​10 cm × 10 cm × 3.6 cm were typically inserted into the instrument's standard sample compartment. To accommodate these medium-sized samples, the cover of the standard sample compartment was removed and a custom-made light-shielding housing was used.

[0048] Fourier transform infrared (FTIR) spectroscopy experiments are performed using a DTGS detector (4000-400 cm²). -1 The analysis was performed in the mid-infrared (2.5–25 μm) region using a Nicolet 6700 FTIR spectrometer equipped with ) in transmission mode. A gold-coated 3-integrating sphere (PIKE Technologies, Mid-IR Upward-looking InegratIR) was used in a broadband (4000–500 cm²) range. -1 A mercury-cadmium telluride detector was used, employing both reflection and transmission modes. These measurements allowed us to characterize the thermal infrared transmittance of various unmodified aerogels and SiCellA aerogels shown in Figure 5d. Weighted transmittance emissivity (W / m 2 The ratio of thermal transmittance from the aerogel to the radiation from an ideal blackbody at the same temperature (μm) was calculated by multiplying the blackbody emissivity at 300K by the average transmittance of the aerogel at each wavelength (Figure 5e). These data were used as input data to model the thermal performance of the glazing product.

[0049] Optical microscopy observations of hydrogel, alcogel, and aerogel samples were performed using an Olympus BX-51 upright microscope. Using a Nikon D50 digital camera mounted on the microscope and a low-magnification (2x or 4x) Olympus objective lens, photographs of water droplets on the SiCellA film surface were taken. The contact angle was then measured using ImageJ software (freeware, National Institutes of Health) to determine the surface wettability. The refractive index of SiCellA aerogel was obtained by measuring the minimum deflection angle using a prism fabricated from this material. Here, a laser beam from a 632 nm helium-neon laser (Edmund Optics) was deflected by an aerogel prism (Figure 4f) mounted on a rotating holder (Olympus). The refractive index of the transparent aerogel was determined with high precision by measuring the minimum beam deflection angle and the corresponding incident angle.

[0050] In addition, the spectral dispersion of the refractive index (Figure 4d) was obtained by using the Kramers-Kronig relation from the measured absorption data of the aerogel film. To measure the optical birefringence of a 12 mm thick aerogel sample with 99.1% porosity, a Berek compensator U-CTB (Olympus) was used, mounted on a microscope in the optical path immediately after the SiCellA sample. The appearance of colors of materials and objects viewed through the IGU can be an important property and can be quantitatively described by the color rendering index (CRI). The CRI of the SiCellA film and SiCellA-IGU was determined based on the light transmittance measured by a Cary 500 scan spectrophotometer according to ASTM standards and was found to exceed 99%, meeting the requirements of the IGU.

[0051] Mechanical characterization Tensile mechanical measurements were performed using a DMA850 instrument (TA Instruments) equipped with a standard tension clamp attachment. Compression, three-point bending, and compression and extension cycles were recorded using an RSA-G2 solid analyzer. During these measurements, the forces and displacements applied to the clamps were recorded. Using the initial dimensions of the sample, these measurements were converted to stress and strain using TRIOS software (TA Instruments). For silane aerogels, the mechanical properties were also investigated under tensile / compression cycles up to a maximum strain of 6% (Figures 6c and 17). In each cycle, the stress increased linearly with increasing strain, and when the load was removed after reaching the maximum value, the stress typically returned to its original value (Figures 16 and 17), indicating no hysteresis behavior with respect to compression and extension up to 6% strain. Below 6% strain, the maximum stress remained constant even with increasing cycle count, confirming the overall robust mechanical properties of the SiCellA material (Figures 6, 10, and 11).

[0052] Material stability and durability of window products Thermogravimetric analysis (TGA) was performed on both unmodified and silane-modified aerogels at 25–500°C in an N2 atmosphere. TGA was performed using a Netsch STA 449 Fl Jupiter thermogravimeter with an alumina crucible at a heating rate of 10°C / min in an argon atmosphere. Thermal stability was characterized using the basic mass loss rate, dm / dt, normalized by the total mass loss. Differential scanning calorimetry (DSC) was performed using a Q1000 instrument (TAI instruments) with an aluminum sealed crucible. All tests were performed in an N2 environment, with heating and cooling rates set to 10°C / min, and the temperature was increased between 30°C and 250°C for the entire cycle.

[0053] IGUs are typically placed in high relative humidity (RH) environments, especially when installed in tropical or subtropical climate regions. Excess moisture and oxygen in the air can react with, for example, secondary silicone sealants, accelerating their aging process and degrading the performance of the IGU. A high-RH environment test chamber was used to create a temperature regime of 80°F (27°C) with 80% high RH. IGUs containing SiCellA were placed in the chamber for 14 days. The properties of the IGUs were then measured before and after the test, revealing robust performance (Figure 7e). Another common test, the fogging test (also known as the "chemical gas release test"), is intended to determine the fogging resistance of pre-assembled, sealed IGUs, which can be caused by the release of chemical gases from materials and assembly components within the IGU. This test was conducted for 14 days in a dedicated box equipped with an ultraviolet light source, air circulation fan, and cooling plate according to the ASTM E2189 standard, and the results showed no degradation of physical properties (Figure 7d). In the UV exposure test, the IGU was placed in a UV irradiation chamber at 40 W / m². 2 Alternatively, exposure to a 500W MLU ultraviolet irradiator at a higher output, where the ultraviolet exposure photons have an energy comparable to the dissociation energy of polymer bonds (300-1000 kJ / mol), was performed. When IGUs containing SiCellA were left exposed in a chamber at 50±3°C for 30 days and then characterized, no substantial degradation of properties was observed (Figure 7f).

[0054] Condensation resistance If the temperature of the inner surface of a window is low, and these temperatures are below the dew point, indoor moisture may condense on the surface as water droplets. High indoor RH increases the likelihood of condensation, which can affect window clarity and indoor humidity, thereby degrading indoor air quality. To compare the condensation resistance of SiCellA-based window products and their equivalents, the Condensation Resistance Factor (CRF) was measured to quantify how well the window can withstand condensation on its indoor-facing surface. Typical CRF values ​​are 5–15 for single-pane IGUs, 35–50 for double-pane IGUs, and 60–80 for triple-pane IGUs. A homemade cryogenic box chamber was used to measure the CRF (Figure 14a). The temperature inside the chamber, representing the external ambient environment and outdoor temperature, was lowered using dry ice, and the total surface temperature of the IGU was continuously monitored by a thermocouple (FluxTeq). Figure 7c shows the dependence of the indoor panel surface temperature on the outdoor temperature for various characterized window configurations. The condensation resistance coefficient is CRF = 100(T c -T e ) / (T i -T e )(in the formula, T c , T i and T e The following were calculated as the temperature of the interior surface of the IGU facing the room, the internal room temperature, and the external temperature, respectively, which were experimentally measured when water condensed on the IGU. Condensation was also detected visually and by measuring the decrease in intensity of a 632 nm laser beam (Edmund Optics) passing through the center of the IGU.

[0055] Nanoscale characterization Transmission electron microscopy (TEM) characterization was performed using a Titan Krios G3i by recording a tilt series at 300 kV under low-dose conditions. The tilt series was recorded using a SerialEM, and tomographic data was reconstructed using IMOD. Individual cellulose nanofibers in aqueous dispersions were negatively stained with 1% phosphotungstic acid before TEM imaging with a Tecnai ST20 200 kV TEM (Figures 3a-d). Thin aerogels were fabricated on a 300-mesh Au carbon film TEM grid for imaging and dried to avoid potential changes in internal structure during transfer and processing. Nanoscale porosity of the aerogels was also characterized using nitrogen absorption-desorption measurements, performed at 77 K with a Quantachrome NOVA contact pore analyzer. Prior to these measurements, aerogel samples (approximately 50 mg each) were maintained at 60°C for 48 hours, followed by gas release at 50°C under vacuum for at least 24 hours, and then pressed into tubular sample holders. Using ASiQwin software, specific surface area was calculated based on the Brunauer-Emmett-Teller (BET) multipoint method, and then the pore size distribution was evaluated according to the density functional theory model implemented in the instrument's software. Specific surface area was determined from the linear region of isotherms at relative pressures (P / P0) in the range of 0.03–0.3 by the BET method. Total pore volume was estimated from the amount of adsorbed N2 at P / P0 = 0.99, given that the porosity of the studied aerogels was in the range of 99.3–97.5%. Adsorption isotherms, total surface area, individual pore surface area, and cumulative pore surface area were characterized for unmodified and silane-modified aerogels (Figures 3f, g, and 15).

[0056] Modeling and characterization of SiCellA-based window products. Numerical simulations of the SiCellA insulated glass unit (Figure 19) were performed using Berkeley Lab WINDOW 7.7 software, assuming a lateral dimension of 1000 mm × 1000 mm and a thermal conductivity of SiCellA of approximately 0.014 W / (m·K) (Figures 5a, b). All spectral characteristics were experimentally obtained using a spectrometer as described above, and then Berkeley Lab Optics 6 was used to define the optical layer and calculate the spectral data, which was imported into the user-defined input of the International Glazing Database (IGDB). Unless otherwise indicated, it was assumed that the glass plate was made from general-purpose clear glass (3 mm thick). For the modification, either general-purpose thin glass (0.5 mm thick) or 0.2 mm thick polyethylene terephthalate (PET) film was used as the back support protective layer of the SiCellA-based modification prototype. SiCellA was fabricated and bonded to a plastic substrate used as a mold during fabrication and as a protective layer for the modified product. Alternatively, a self-supporting SiCellA film can be easily electrostatically bonded to the glass substrate and plastic support layer during the modification, resulting in only the edges of the modified window needing to be sealed. For the low-emissivity coated glass plates, Cardinal Glass Industries' 3mm thick LoE-180, 272, and 366 window products with physical properties available at IGDB were used. IGUs with various lateral dimensions ranging from 10cm×10cm to 100cm×100cm, and with a number of glass or SiCellA plates, were fabricated and experimentally characterized. A 3mm thick self-supporting SiCellA aerogel was used as an intermediate plate in SiCellA-based triple-plate IGUs. The thickness of the gap between the glass and SiCellA plate was defined by 6.3mm and 12.7mm wide Super Spacer SS1466 Gray Edgetech spacers. The IGU boundary was hermetically sealed with silicone foam and metal spacer IG sealant (CR Laurence Co., Inc.). [Industrial applicability]

[0057] Technoeconomic analysis A technoeconomic analysis was conducted to study the full-load production costs of commercial mass production of SiCellA for monolithic layers as window insulation products. The production cost analysis estimates a provisional upper limit of full-load production costs, including bulk material shipping costs, as well as plant utilization and capital expenditures, including direct and indirect labor, labor burden, production and auxiliary energy, waste management, building leases, production equipment, equipment maintenance, plant design and installation, and building expansion costs. Quantitative assumptions used in the model include a baseline annual production of 92,903 square meters (1 million square feet) of SiCellA with a thickness of 3.2 mm and a density of 150 μg / ml. Both wood pulp-derived and bacterially synthesized cellulose sources are used in the production cost analysis. While the results presented in this work correspond to the wood-derived cellulose source, bacterial synthesis is a promising method for obtaining cellulose nanofibers, and therefore, a bacterial initial film source obtained using Acetobacter hansenii was also used in the analysis. In this model, the capacity of the production equipment was scaled to meet the aforementioned production volume and to manufacture aerogel products in sheets of approximately 1m x 2m. The model implements the heavy use of chemicals and the recycling of solvents. Assuming a straight-line depreciation of capital expenditures over 5 years, the estimated full-load production cost of SiCellA is $17.20 / m when using a wet wood pulp source. 2 And if using a bacterially synthesized cellulose source, the cost is $17.31 / m². 2 Therefore, the maximum possible cost calculated is approximately $53.76 / m 2 The lowest possible cost is approximately $10.75 / m 2 This estimated cost range takes into account direct labor costs, material shipping costs, aerogel cellulose density, and variations in cellulose production efficiency.

Claims

1. Aerogel containing a network of cellulose nanofibers, and Silicon functional groups bonded to the surface of cellulose nanofibers A transparent glazing material including, A transparent glazing material having a thermal conductivity of less than 26 mW / (K·m), less than 20 mW / (K·m), or less than 15 mW / (K·m).

2. The transparent glazing material according to claim 1, wherein the haze of the transparent glazing material is less than 2.5%, less than 2%, less than 1.5%, or less than 1%.

3. The transparent glazing material according to claim 1 or 2, wherein the transparency of the transparent glazing material exceeds 97% in the visible light spectrum.

4. A transparent glazing material according to any one of claims 1 to 3, which exhibits superhydrophobicity.

5. A transparent glazing material according to any one of claims 1 to 4, wherein the average width of the cellulose nanofibers is less than 10 nm or between approximately 4 nm and approximately 6 nm.

6. A transparent glazing material according to any one of claims 1 to 5, wherein the average length of the cellulose nanofibers is greater than 100 nm, greater than 1000 nm, or between about 200 nm and about 2000 nm.

7. The transparent glazing material according to any one of claims 1 to 6, wherein the aerogel is optically anisotropic.

8. A transparent glazing material according to any one of claims 1 to 7, wherein the average pore size of the aerogel is less than 100 nm or between approximately 2 nm and approximately 50 nm.

9. A transparent glazing material according to any one of claims 1 to 8, and First glass plate An assembly that includes this.

10. The assembly according to claim 9, further comprising a substrate attached to a transparent glazing material.

11. The assembly according to claim 10, wherein the base material comprises one or more of plastics or glass.

12. The assembly according to any one of claims 10 and 11, wherein the transparent glazing material is attached to the substrate by electrostatic charge.

13. The assembly according to any one of claims 10 to 12, further comprising a low emissivity coating between the substrate and the transparent glazing material.

14. The assembly according to any one of claims 9 to 13, further comprising a second glass plate, wherein a transparent glazing material is inserted between the first glass plate and the second glass plate.

15. The assembly according to any one of claims 9 to 14, further comprising an inert gas.

16. The assembly according to any one of claims 9 to 15, comprising three or more glass plates.

17. The assembly according to any one of claims 9 and 13 to 16, wherein the transparent glazing material is a self-supporting transparent glazing material.

18. A method for forming a transparent aerogel, The steps include forming cellulose nanofibers having an average diameter of less than 10 nm and an average length of more than 100 nm, The steps include functionalizing cellulose nanofibers with carboxylic acid anions to form functionalized cellulose nanofibers, The steps include forming a hydrogel from a network of functionalized cellulose nanofibers, The steps of forming an aerogel from a hydrogel, The step of silaneizing the surface of functionalized cellulose nanofibers Methods that include...

19. The method according to claim 18, wherein the step of silanizing the surface includes gas-phase silanization of the aerogel.

20. The method according to claim 18, wherein the step of silanizing the surface includes silanizing the functionalized cellulose nanofibers of the hydrogel.

21. The method according to any one of claims 18 to 20, wherein the step of silanizing the surface includes exposing the surface to a chlorine-free silanating agent.

22. The method according to any one of claims 18 to 21, wherein a transparent aerogel is formed on the surface of a rollable substrate.

23. The method according to claim 22, wherein the combination of the substrate and the transparent aerogel can be wound onto a roll having a diameter of less than about 1 centimeter.

24. A combination of a base material and a transparent glazing material according to any one of claims 1 to 8, wherein the combination is windable.

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