How do small particle silica sols achieve a balance between high light transmittance and strong thermal insulation in ultra-thin, transparent thermal insulation coatings?
Publish Time: 2025-08-27
With the growing emphasis on energy-saving and green, low-carbon building concepts, transparent thermal insulation coatings, a new material that can be applied directly to glass surfaces and combines both light-collecting and energy-saving properties, are attracting widespread attention. An ideal transparent thermal insulation coating must maintain high visible light transmittance while effectively blocking near-infrared radiation from solar radiation, which accounts for over 50% of heat and is the primary source of indoor temperature rise. However, traditional materials often struggle to achieve both transparency and thermal insulation. Adding insulating fillers can easily cause light scattering, reducing light transmittance; pursuing high light transmittance compromises thermal insulation. Small particle silica sols, with their unique nanoscale effects and chemical properties, are a key component in achieving this conflicting balance.1. Nanoscale: Breaking the Physical Limits of Light ScatteringThe key to transparency lies in reducing light scattering. According to the Rayleigh scattering law, the light scattering intensity of a particle is proportional to the sixth power of its particle size. When the particle size is significantly smaller than the wavelength of incident light (visible light is 400–700 nm), the scattering effect is dramatically reduced. The average particle size of small-particle silica sol is generally less than 20 nm, well below the wavelength of visible light. Therefore, after film formation, the dispersed phase in the coating causes virtually no visible light scattering, ensuring excellent transparency and visual clarity even in extremely thin layers, without haze or whitening.2. Building a Stable Transparent Matrix and Improving Coating DurabilitySmall-particle silica sol is not only a functional filler but also an excellent inorganic film-forming substance. Its surface is rich in silanol (Si-OH) groups, which form a continuous Si-O-Si three-dimensional network structure through polycondensation during the drying and curing process, creating a transparent silica (SiO₂) matrix with high hardness, high wear resistance, and strong weather resistance. This inorganic network not only boasts high light transmittance itself but also effectively encapsulates and secures other functional thermal insulation components (such as antimony-doped tin oxide (ATO), indium tin oxide (ITO) nanoparticles, or near-infrared absorbers), preventing aggregation or precipitation and maintaining the long-term stability and optical uniformity of the coating.3. Synergistic Enhancement: Serving as an "Enabling Platform" for Thermal InsulationSmall particle size silica sol itself has some near-infrared reflection and scattering properties, but its greatest value lies in its role as a "functional carrier" to enhance overall thermal insulation performance. Its high specific surface area and surface activity make it easy to combine with near-infrared shielding materials such as ATO and ITO to form a uniformly dispersed nanocomposite system. The silica matrix of the silica sol reduces direct contact between metal oxide nanoparticles, inhibiting their visible light absorption due to plasmon resonance. This enhances near-infrared rejection (reaching over 80%) while maximizing visible light transmittance. Furthermore, the SiO₂ network inherently has low thermal conductivity, further enhancing the coating's thermal barrier capabilities.4. Process Compatibility: Supports Ultra-Thin, Uniform CoatingSol systems formed with small particle size silica sol offer excellent stability, low viscosity, and excellent leveling, making them ideal for ultra-thin coating processes such as spin coating, spray coating, and dip coating. Their rapid film-forming properties help form dense, uniform, and defect-free films on glass surfaces, avoiding optical distortion or localized thermal stress caused by uneven coating thickness, ensuring consistent and aesthetically pleasing application over large areas.5. Environmental and Durability AdvantagesTransparent thermal insulation coatings based on small particle size silica sol are mostly water-based, VOC-free, and environmentally friendly. Their inorganic components impart excellent resistance to UV aging, high temperatures, and chemicals, making them less susceptible to yellowing and chalking. Their service life far exceeds that of organic polymer-based coatings, making them suitable for a variety of applications, including architectural curtain walls, automotive glass, and greenhouses.Small particle size silica sol, through its low light scattering properties at the nanoscale, excellent film-forming ability, and its role as a synergistic platform for functional materials, successfully resolves the technical contradiction between transparency and thermal insulation. It is not only the "transparent skeleton" of ultra-thin transparent thermal insulation coating, but also the "optical control engine" for achieving high efficiency and energy saving.
