1. Core Physics: Capillary Pressure (Laplace Pressure)
     · During drying, liquid–gas interfaces form menisci inside nanopores, exerting negative capillary pressure on the fragile skeleton:

P=2γcos⁡θrP = \frac{2 \gamma \cos \theta}{r}
    · γ\gamma: surface tension of solvent
    · θ\theta: contact angle (for hydrophilic surfaces, θ≈0∘\theta \approx 0^\circ, cos⁡θ≈1\cos \theta \approx 1)
    · rr: pore radius (smaller pore → higher stress)
    · Magnitude example (hydrophilic case):
       o Ethanol: γ≈0.022 N/m,r=10 nm⇒P≈4.4 MPa\gamma \approx 0.022\ \text{N/m}, r=10\ \text{nm} \Rightarrow P \approx 4.4\ \text{MPa}
       o Water: γ≈0.072 N/m,r=10 nm⇒P≈14.4 MPa\gamma \approx 0.072\ \text{N/m}, r=10\ \text{nm} \Rightarrow P \approx 14.4\ \text{MPa}

    Such stress is far above the yield strength of the “wet” silica skeleton, leading to elastic–plastic deformation, pore collapse, shrinkage, densification, or even cracking.

2. Structural & Chemical Factors
    · Smaller pores / narrow distribution → stronger capillary stress.
    · Insufficient neck growth (weak skeleton) due to poor aging → prone to irreversible plastic shrinkage.
    · Surface state: hydrophilic Si–OH surfaces (low θ\theta) → high stress; hydrophobic surfaces (high θ\theta) reduce stress.
    · Solvent: high γ\gamma (e.g., water) increases stress.
    · Sample geometry: thick monoliths develop drying gradients → cracks; thin films/felts are less prone.
    · Pre-shrinkage (syneresis) during gelation/aging can set the stage for further collapse.

Summary: Shrinkage mainly comes from capillary pressure; small pores, hydrophilic surfaces, high-γ\gamma solvents, weak skeletons, and thick parts all worsen it.

1. How is the pore structure of aerogel formed?

    Aerogels are typically produced using the sol–gel process, and their pore structure develops through three main steps:

    (1)Sol Formation

        a. A precursor (e.g., tetraethyl orthosilicate, TEOS) undergoes hydrolysis and condensation reactions in solution.

        b. This generates a large number of uniformly dispersed silica nanoparticles.

    (2) Gelation

        a. As condensation continues, these nanoparticles connect via chemical or hydrogen bonds, forming a 3D interconnected network.

        b. The pores are still filled with solvent (alcohols or water) — this is called a "wet gel."

    (3) Drying

        a. The critical step is to remove the solvent without collapsing the fragile network.

        b. Simple evaporation causes capillary forces and collapse.

        c. Therefore, supercritical drying or surface modification + controlled drying is used to replace liquid with gas while retaining the network.

        d. The result is a solid with a nanostructured porous network (pore size ~10–100 nm, porosity 80–99%).

    In summary: the aerogel's pore structure is formed by a nanoparticle network from sol–gel chemistry, preserved by a special drying process.

2. If we use 3D printing to create a similar porous structure, is it also an aerogel?

    Strictly speaking, no.

    (1) Essential difference

        a. Aerogel pores are naturally self-assembled at the nanoscale via chemical reactions.

        b. Most 3D printing technologies today can only fabricate pores at the microscale or larger, not true nanostructures.

        c. The printed object would be a porous scaffold, but not classified as an aerogel.

    (2) Definition issue

        a. The widely accepted definition of aerogel is: a material derived from a sol–gel process, dried to preserve its nanostructured porous network.

        b. If a material does not come from this process, even if it looks similar, it usually isn't considered an aerogel.

3. Interesting frontier

    · If future 3D printing technologies can build structures with nanoscale precision, high porosity, and ultralow density, then we might achieve “aerogel-like” materials.

    · Some researchers are already combining 3D printing inks with sol–gel precursors to print wet gels and then dry them into true 3D-printed aerogels.

 
Conclusion

    · Aerogel pore structures are formed by sol–gel chemistry + special drying methods.

    · Simply 3D printing a porous structure ≠ aerogel; it would be called a porous material.

    · But if 3D printing is combined with sol–gel methods, then 3D-printed aerogels are possible.

1. Fundamental Differences

    Silica Aerogel

        · Preparation: Produced by the sol–gel process followed by supercritical drying.

        · Structure: A three-dimensional, continuous nanoporous network with porosity as high as 80–99%.

        · Properties:

        o Extremely low density (0.003–0.2 g/cm³)

        o Very high surface area (500–1200 m²/g)

        o Ultra-low thermal conductivity (as low as 0.012–0.016 W/m·K)

        o High optical transparency (up to >80% visible light transmittance)

    Fumed Silica (Pyrogenic Silica)

        · Preparation: Produced mainly by hydrolysis of silicon tetrachloride (SiCl₄) in a hydrogen-oxygen flame (chemical vapor process).

        · Structure: Amorphous nanoparticles (7–40 nm), loosely aggregated, not forming a continuous porous network.

        · Properties:

        o White, lightweight powder

        o High surface area (200–400 m²/g)

        o Strong rheological and thickening effects

        o High adsorption capacity

2. Application Differences

    Silica Aerogel

        · Building & Construction: Super-thin insulation for walls, roofs, curtain walls, and retrofitting of historical buildings

        · Energy & Batteries: Thermal management and fire protection for lithium-ion batteries and energy storage systems

        · Petrochemical/Industrial: High-temperature pipeline and equipment insulation

        · Aerospace: Spacecraft thermal insulation (famously used by NASA for Mars missions)

        · Optics & Acoustics: Transparent insulating glass, sound-absorbing and wave-absorbing materials

        · Environmental: Oil-spill sorbents, air-filtration materials

    Fumed Silica

        · Rubber/Plastics: Reinforcing filler to improve strength and wear resistance (especially in silicone rubber)

        · Coatings/Inks: Thickener, anti-settling agent, rheology modifier

        · Adhesives/Sealants: Improves flow control and stability

        · Pharma/Food: Anti-caking agent, excipient, carrier

        · Cosmetics: Enhances texture, spreadability, and stabilit

3. Summary
    Nature
        · Aerogel → A nanoporous 3D solid network (lightweight, super-insulating)

        · Fumed Silica → A nanoparticle powder (rheology modifier, reinforcing agent)

    Applications

        · Aerogel → High-performance insulation, optics, aerospace, specialty uses (high-value functional material)

        · Fumed Silica → Commodity additive across many industries (cost-effective, broad usage)

    You can think of fumed silica as a nano-powder “additive” to tune system performance, while silica aerogel is a nano-sponge “structural material” with unique functional properties.

1. Drying Methods of Aerogels and Their Differences

    Drying is the most critical step in aerogel fabrication. The goal is to remove solvents while preserving the 3D nanoporous network. Main methods include:
    （1）Ambient Pressure Drying (APD)
        · Low cost, but large shrinkage and uneven pore distribution result in degraded performance.
    （2）Freeze Drying (FD)
        · Removes solvent by sublimating ice; however, large pores or collapse may occur.
    （3）Supercritical CO₂ Drying (CO₂-SCD)
        · Mild conditions, decent pore retention, but requires multiple solvent exchanges and pore uniformity is limited.
    （4）Supercritical Ethanol Drying (EtOH-SCD)
        · Directly dries under ethanol supercritical conditions, eliminating capillary stress.
        · Produces the most uniform nanopore distribution, high porosity, large surface area, and excellent thermal stability.
        · Silica aerogels remain intact even at 500–1000℃.

    In summary: Aerogels prepared by EtOH-SCD have the most uniform nanoporous structure and best thermal stability, making them the top choice for high-end applications.

2.  IBIH is a global leader in using ethanol supercritical drying technology to mass-produce high-quality aerogels.
     IBIH employs advanced EtOH-SCD technology with proprietary large-scale horizontal drying equipment.
     Achieved industrial-scale production from lab to tens of thousands of metric square metres, with full intellectual property rights.
    Performance Highlights:
        · Porosity up to 85–99% with narrow pore size distribution.
        · Thermal conductivity as low as 0.016 W/(m·K).
        · Structural stability maintained at 500–1000℃
        · Visible light transmittance >80%, suitable for translucent  insulation.
        · Excellent compressive resilience and long service life.

Overall Evaluation:
    IBIH’s EtOH-SCD silica aerogels combine ultralow thermal conductivity, exceptional thermal stability, and optical transparency, representing the global top level. They are especially suited for high-end applications in energy-efficient buildings, new energy batteries, and aerospace.

1. Definition & Structure
    Aerogel: A three-dimensional nanoporous solid material produced by the sol–gel process, with extremely high porosity (80%–99%), large surface area, and a continuous solid skeleton filled with nanoscale pores of air.
    Aerosol: A dispersed system of solid or liquid particles suspended in a gas medium, such as fog, smoke, or spray. Essentially a two-phase system: dispersed particles/droplets + continuous gas phase.

2. Preparation
    Aerogel: Sol–gel method → Drying (supercritical or ambient) → Preserved porous network. Common types include silica aerogel, carbon aerogel, and polymer aerogel.
    Aerosol: Formed by mechanical atomization, chemical reaction, combustion, spraying, or condensation.

3. Physical Properties
    Aerogel: Solid, ultralow density (down to 0.001 g/cm³), ultralow thermal conductivity (as low as 0.013 W/m·K), high transparency, and tunable mechanical properties. IBIH's aerogel granules feature exceptional optical performance, with visible light transmittance exceeding 80%.
    Aerosol: Suspension with particle diameters from 1 nm to 100 μm, showing Brownian motion, light scattering, and sedimentation.

4. Applications
    Aerogel:
        （1） Building insulation (heritage restoration, near-zero energy buildings).
        （2）Aerospace (thermal protection tiles, Mars dust collection).
        （3）Batteries & electronics (thermal management, fireproof layers).
        （4）Petrochemical & industrial pipeline insulation.
        （5） Medicine & environment (drug delivery, oil–water separation).
    Aerosol:
        （1）Meteorology & environment (smog, climate studies).
        （2）Medicine (inhaled drug delivery).
        （3）Daily life (sprays, perfumes, insecticides).
        （4）Industry (spray coating, combustion, dust control.

5. Key Differences Summary

1. Definition

     The Sol–Gel Process is a versatile chemical method that transforms a system from a liquid (solution or sol) into a solid network (gel) through hydrolysis and condensation reactions.
        · Sol: A colloidal suspension of nanoparticles (1–100 nm) uniformly dispersed in a liquid.
        · Gel: As reactions proceed, particles aggregate and interconnect, forming a three-dimensional network that traps liquid inside the pores.

In essence, it is a liquid → colloid → solid porous network transformation.

2. Role in Aerogel Preparation

    Aerogel preparation involves three main stages:
        （1）Sol formation: Precursors such as metal alkoxides (e.g., TEOS) undergo hydrolysis and condensation to form a nanoparticle-containing sol.
        （2）Gelation: The sol gradually evolves into a three-dimensional gel network, with liquid still occupying the pores.
        （3）Drying: The liquid in the pores is removed by supercritical drying or ambient pressure drying, preserving the fragile gel network and yielding a highly porous solid — the aerogel.

    In aerogel synthesis, the sol–gel process is the foundation that builds the nanoporous skeleton, directly influencing pore size, surface area, and performance.

3. Other Applications
    Beyond aerogels, the sol–gel process is widely applied in advanced materials:

        · Optical & electronic materials: optical coatings, antireflective films, waveguides, semiconductor oxides.
        · Ceramics: high-purity, ultrafine ceramic powders and ceramic coatings.
        · Catalysts & adsorbents: porous oxides with large surface area for catalysis and pollutant removal.
        · Biomedical materials: drug delivery systems, bioactive glasses.
        · Protective coatings: high-temperature coatings, thermal barrier layers, and fire-retardant coatings.