Silica Aerogels

Jang D, et al. Polymer Testing, 2024, 137, 108534.

The study assessed the sensing performance of nanocomposites with silica aerogel contents ranging from 0.5% to 2%, revealing significant effects on sensor conductivity below the percolation threshold, but no impact above this threshold. The research underscores the influence of silica aerogels on CNT-based PDMS composites, suggesting significant potential in sensor development and material design.

The nanocomposites were synthesized using PDMS and its curing agent, incorporating multi-walled CNTs from Hyosung Inc. (diameter: 12-40 nm, length: 10 μm) as conductive fillers. To enhance CNT dispersion, sodium poly(styrene sulfonate) (PSS) was added in a ratio equivalent to the CNT content. The specific mixing proportions are summarized in Table 1. The percolation threshold was identified by varying CNT concentrations from 0% to 4% by PDMS weight, and after determining the optimal CNT content, silica aerogel was introduced at concentrations between 0% and 2% by PDMS weight.

The results showed that the introduction of silica aerogels hindered the formation of conductive networks, leading to reduced conductivity. The interaction between silica aerogels and CNT particles also affected electron mobility. Modified theoretical models, including the effective medium theory, successfully predicted the conductivity of the nanocomposites. The CNT@aerogel nanomixed clusters exhibited enhanced strain sensitivity and linearity under tensile stress, with a strain coefficient of 1.15, indicating their potential as strain sensors for various applications.

Pantaleo S, et al. Developments in the Built Environment, 2024, 20, 100576.

This study explores a novel approach to improving the thermal conductivity and mechanical properties of silica aerogel composites by utilizing a water-based latex matrix and chemical bonding enhancements. This method involves the use of silane coupling agents to chemically bond silica aerogel particles to the latex matrix, thereby improving the overall performance of the composite material.

The process begins with treating acrylic latex under magnetic stirring in ethanol for 5 minutes, followed by the addition of dodecyltriehosilane and stirring for another 10 minutes. Silica aerogel particles are then incorporated, and the mixture is manually stirred to ensure uniform dispersion. Notably, no additional water is added during the preparation, avoiding phase separation issues that commonly occur when water is introduced. The final solid content is balanced to maintain appropriate flowability and dispersion of the aerogel particles within the latex.

Key findings of the study include the observation that the silica aerogel particles significantly influence the thermal conductivity of the composites, with values around 0.02–0.03 W m^-1K^-1, slightly higher than that of pure silica aerogel (0.012 W m^-1K^-1). Furthermore, the use of silane coupling agents enhanced not only the mechanical properties but also the physical response of the composites, making them more cohesive and less brittle. These improvements contribute to a more durable material with better overall quality. Environmental testing under varying humidity conditions showed that the samples exhibited low moisture absorption, but even slight increases in humidity affected thermal conductivity, highlighting the need to optimize moisture resistance.

Yan Y, et al. Radiation Measurements, 2024, 177, 107259.

This study investigates the optical and temporal characteristics of silica aerogels used as Cherenkov radiators for high-energy pulsed electron source time spectrum measurements. Silica aerogels with varying densities and thicknesses were prepared and analyzed for their transmittance, refractive index, absorption, and scattering lengths. The refractive index was measured under a 632.8 nm laser, revealing values of 1.005 for 30 mg/cm³ and 1.028 for 120 mg/cm³ aerogels. These values were used in conjunction with a one-pole Sellmeier function to fit the refractive index curve.

The time response of silica aerogels was then simulated using Geant4 software, with results indicating the intrinsic luminescence time of the aerogels. Experimental measurements on a picosecond electron accelerator demonstrated that the rise time of the silica aerogel was below 54.32 ps, and the rise time of the measurement system did not exceed 180 ps, with an uncertainty of less than 3.3%. These results confirm that silica aerogels can be effectively used as Cherenkov radiators, capable of detecting and measuring the time spectrum of high-energy pulsed electron sources.

This work contributes to the development of precision measurement systems for radiation sources, particularly in applications requiring time characterization of high-energy electron beams.

Wang S, et al. Energy and Buildings, 2024, 323, 114817.

This study investigates the preparation of a novel bio-based thermal insulation material using corn cobs as the primary raw material, with foam clay polymer as the binder, and silica aerogels and silicone oil as additives. The developed insulation material offers a promising alternative for energy-efficient construction. The optimal composition of the material was achieved with corn cob particles of 20 mesh size, a silica aerogel to foam clay polymer mass ratio (A/G) of 1.71%, and a silica aerogel to silicone oil mass ratio (A/O) of 0.2. The resulting material demonstrated impressive thermal conductivity (0.111 W/(m·K)), compressive strength (2.2 MPa), density (350 kg/m³), water absorption rate (7.1%), moisture absorption rate (9.4%), and water contact angle (133°), making it a viable candidate for building applications.

The preparation process involved several key steps. First, the corn cobs were pretreated with an alkali activator and different combinations of silica aerogel and silicone oil to ensure good adhesion. Next, a foam clay polymer slurry was prepared by mixing kaolinite clay with an alkali activator solution, followed by the addition of a surfactant and foaming agent. The pretreated corn cob was then incorporated into the foam clay slurry, and the mixture was cast into silicone molds and cured under specific temperature conditions. The final product was dried at 40°C for one week.

Zhu C, et al. Applied Thermal Engineering, 2024, 255, 123915.

This study investigates a novel strategy to improve the thermal performance of silica aerogels by incorporating opacifier particles with surface protrusions. While silica aerogels are renowned for their exceptional thermal insulation properties, their infrared transparency limits their performance at high temperatures. To mitigate this issue, the introduction of micron-sized opacifiers with surface protrusions designed based on the structural absorption' mechanism is proposed. This mechanism relies on surface features that induce multiple light scattering, thereby enhancing the opacifier's extinction capacity and reducing the radiative heat transfer in the aerogel.

The study examines three types of opacifiers—spherical, rectangular, and cylindrical protrusions—and evaluates their impact on the radiative thermal conductivity of silica aerogels. Results indicate that the presence of protrusions significantly enhances the opacifier’s extinction capability, with cylindrical protrusions proving most effective in reducing radiative heat transfer. Notably, the optimal design consists of opacifiers with 12 cylindrical protrusions, which reduced the radiative thermal conductivity by 22.6% at 1300 K compared to silica aerogels without protrusions.

Further analysis reveals that increasing the height of cylindrical protrusions while maintaining a constant diameter reduces the radiative thermal conductivity, although the effect becomes less pronounced beyond a certain height. This research provides valuable insights into the design of opacifiers for improving the thermal insulation of silica aerogels, particularly in high-temperature applications.

Li Z, et al. Construction and Building Materials, 2024, 438, 137161.

This study presents a novel approach to the development of silica aerogel slurries by incorporating a binary surfactant mixture of polyether L62 and CTAC (cetyltrimethylammonium chloride) in a 1:4 ratio to optimize the slurry’s properties. The research focuses on enhancing the dispersion and performance of silica aerogel in composite materials, aiming to improve thermal insulation and hydrophobic characteristics. Extensive testing reveals that this surfactant mixture significantly reduces the surface tension to 24.25 mN/m, leading to an exceptional thermal conductivity of 26.7 mW/m·K while maintaining a high degree of hydrophobicity, with a contact angle exceeding 125°.

The slurry exhibited a wet density of 0.48 g/cm³ and a dry density of 0.098 g/cm³, underscoring the lightweight nature of the aerogel composites. The study also demonstrates that although increasing surfactant concentration improves aerogel dispersion, excessive surfactant levels negatively impact the insulation properties. Microscopic analysis further confirms that the binary surfactant mixture effectively modifies the aerogel surface, overcoming the dispersal limitations imposed by the aerogel's hydrophobic groups.

The findings from this research provide a critical engineering solution for developing high-performance silica aerogel-based composites with superior thermal insulation and waterproof properties.