The "Invisible Armor" under the Test of Heat and Humidity: How Does Aerogel Resist Moisture Erosion?

### I. Thermal Insulation Mechanism in Nanopores

The excellent thermal insulation performance of aerogels stems from the following three key elements:

1. Gas Locking in Nanopores: With a porosity of over 90%, air or nitrogen is confined within the nanopores, completely suppressing macroscopic convection and microscopic diffusion heat transfer.

2. Sparse Skeleton Resisting Heat: The solid skeleton only accounts for 10% of the total volume, significantly cutting off the heat conduction path, and the thermal conductivity can be as low as 0.015 W·m⁻¹·K⁻¹.

3. Filling with Low - Thermal - Conductivity Media: The air (0.026 W·m⁻¹·K⁻¹) or nitrogen filling the pores is the most efficient thermal insulation medium, greatly reducing the heat transfer efficiency.

### II. Multiple Damages Caused by Moisture Invasion

When aerogels encounter a high - humidity environment, moisture can damage the thermal insulation system through ways such as gaseous diffusion, capillary condensation, or liquid impact:

- Replacement of the Gas Phase by High - Thermal - Conductivity Liquid Phase: The thermal conductivity of liquid water is 0.6 W·m⁻¹·K⁻¹, approximately 23 times that of air. Research shows that for silica - based aerogels at a relative humidity of 80%, the thermal conductivity can soar from 0.015 W·m⁻¹·K⁻¹ to 0.05 W·m⁻¹·K⁻¹, and the thermal insulation performance decays by more than 200%. Science Express.

- Reconstruction of the Heat Transfer Network by the Liquid Bridge Effect: The water condensed by capillary action forms "bridges" in the nanopores, connecting areas originally isolated by the skeleton, resulting in a local "thermal short - circuit" phenomenon, which is particularly evident during the condensation of aircraft outer shells.

- Structure Softening and Pore Collapse: After hydrophilic silica aerogels absorb moisture, the skeleton softens and shrinks due to hydrogen - bond interactions. When the moisture absorption rate exceeds 5%, its compressive strength decreases by 40%, the thermal diffusion rate increases by 200%, and some pores undergo irreversible collapse.

### III. Performance Degradation under Hygro - Thermal Coupling

The synergistic effect of moisture and heat will further exacerbate the degradation of aerogels:

- Non - linear Thermal Spots: Under sunlight, the surface temperature of a locally wet area can be 15℃ higher than that of a dry area, forming "thermal spots" and accelerating moisture migration.

- Stress Caused by Moisture Migration Hysteresis: In a hot - cold alternating environment, the moisture content gradient with surface condensation and inner - layer dryness can generate stress of the order of 10 MPa, leading to the expansion of micro - cracks and skeleton fatigue.

- Damage from Condensation - Drying Cycles: After undergoing 10 hygro - thermal cycles, the porosity of some aerogels decreases by 30%, the thermal conductivity increases by 50%, and the thermal insulation performance deteriorates significantly.

### IV. Technical Routes to Combat Moisture

To delay or even reverse the hygro - thermal degradation, the scientific and technological community has proposed several innovative strategies:

1. Surface Hydrophobic Chemical Modification

- Using methyltrimethoxysilane (MTMS) and fluorosilanes to achieve surface C - H and C - F modifications, making the contact angle exceed 150° (the profile angle can reach 168°), and the water absorption rate can be reduced to less than 2%.

2. Composite Moisture - Barrier Physical Barriers

- Combining aerogels with PTFE films, closed - cell foams, and resin layers to form a double - layer protection of "outer - layer moisture - resistance + inner - layer thermal insulation". After the aerospace - grade thermal insulation cover adopts this design, the hygro - thermal cycle life exceeds 3000 hours.

3. Synergistic Enhancement by Functional Fillers

- Introducing super - hydrophobic hexagonal boron nitride (h - BN), graphene, or carbon nanotubes. With an addition amount of 0.01%, the increase in thermal conductivity in a hygro - thermal environment can be reduced by 10%.

4. Intelligent Self - Healing Design

- Relying on dynamic covalent bonds or hydrogen - bond networks, more than 90% of the porosity can be restored through heat treatment (120℃/1h) after being affected by moisture, and the strength can be maintained at 85% after 5 cycles.

### V. Future Prospects: Aerogels Entering Daily Life

With the reduction of costs and the maturity of large - scale production technologies, aerogels will go beyond the laboratory and integrate into our daily lives:

- Architecture and Home Furnishings: Ultra - thin aerogel insulation boards (thermal conductivity 0.018 W·m⁻¹·K⁻¹, water absorption rate < 3%) will be popularized in new energy - efficient buildings and smart homes.

- Polar Regions and Deep Sea: Biomimetic super - hydrophobic surfaces (contact angle > 160°) and adaptive humidity - responsive aerogels will become the preferred thermal insulation and protective materials for polar exploration suits and deep - sea detectors.

- Smart Wearables: Lightweight, breathable, and moisture - proof aerogel fibers can be used in high - end outdoor sports clothing and electronic skin, integrating thermal insulation, antibacterial, and sensing functions.

- Green Processes: In the future, water - based hydrophobic agents will replace organic solvents, and biomimetic pore arrangement technologies and low - carbon preparation routes will make aerogels more environmentally friendly and sustainable.