Effects of supercritical drying media on structure and properties of silica aerogel

Tajiri, Koji; Igarashi, Kazuo; Nishio, Tomoko

doi:10.1016/0022-3093(95)00038-0

Cited by 77 publications

(43 citation statements)

References 5 publications

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“…When NMP and CO 2 are in a single phase state, the pressure difference at the NMP-CO 2 interface is almost zero and the capillary force also becomes almost zero because there is essentially no liquid-gas interface. [15][16][17][18] The NMP in the gel can be displaced by CO 2 without capillary force under supercritical CO 2 of 16 MPa and 80 8C in which NMP and CO 2 are in a single phase state. [19] When CO 2 is released after NMP is displaced with CO 2 , there is no air-CO 2 interface.…”

Section: Resultsmentioning

confidence: 99%

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Superior Nanoporous Polyimides via Supercritical CO₂ Drying of Jungle‐Gym‐Type Polyimide Gels

Kawagishi

Saito

Furukawa

et al. 2007

Macromol. Rapid Commun.

104

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We report novel nanoporous polyimides formed from jungle‐gym‐type rigid polyimide gels by supercritical CO2 drying. By virtue of supercritical CO2 drying to avoid the collapse of nanostructure, porosity above 90 vol.‐% was achieved. We found a rich variety of nanoporous structures in the range of 50–800 nm such as crisp fragments, minute network, and highly‐connected beads. These characteristic structures were formed by the competitive progress of liquid‐liquid phase separation and crystallization induced due to the two chemical reactions of end‐crosslinking and thermal imidization during gelation.magnified image

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Section: Resultsmentioning

confidence: 99%

“…This procedure is called supercritical CO 2 drying. [15][16][17][18] As shown in Figure 2, nanoporous polyimides having characteristic structures in 50-800 nm were obtained by supercritical CO 2 drying of the polyimide gels. Distinct structures of the dried gels are clearly observed.…”

Section: Resultsmentioning

confidence: 99%

Superior Nanoporous Polyimides via Supercritical CO₂ Drying of Jungle‐Gym‐Type Polyimide Gels

Kawagishi

Saito

Furukawa

et al. 2007

Macromol. Rapid Commun.

104

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“…The ZAC condition can be reached at ρ CO2 ¼ 1.39 g/cm 3 if the density of silicon matrix of the porous material is taken to be equal to the density of amorphous silica ρ SiO2 ¼ 2.2 g/cm 3 . The skeletal density of silica in aerogel strands is smaller than that of the amorphous silica (ρ SiO2 ffi 2.0 g/cm 3 [34]) and the calculated ZAC condition in this case corresponds to ρ CO2 ¼ 1.27 g/cm 3 . Representative SANS curves obtained from aerogel at different CO 2 densities are shown in Fig.…”

Section: Silica Aerogelsmentioning

confidence: 97%

Supercritical Fluids in Confined Geometries

Melnichenko

2016

Small-Angle Scattering From Confined and Interfacial Fluids

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Understanding the influence of confinement on the structure and thermodynamic properties of supercritical fluids in pores of different surface chemistry and topology is fundamental to the successful development and optimization of the variety of technologies involving fluid-solid interactions. Adsorption behavior of supercritical fluids (SCFs) is fundamentally different from that of subcritical vapors and this chapter begins with a general description of the specifics of the supercritical adsorption. Presented examples illustrate the capability of SAS methods to deliver unique, pore-size-dependent information on the properties of supercritical CO 2 , hydrogen, methane, and other fluids confined in pores of different engineered and natural porous solids. Applications of SAS for studying pore interconnectivity and structural stability of porous materials under pressure are also discussed.

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“…Small pores are thus filled, and particle necks are strengthened. As a consequence, the resulting aerogels have a lower specific surface area, a narrow pore radius distribution (elimination of microporosity), and a stiffer network [167][168][169][170]. Organic groups may be destroyed during drying [171].…”

Section: Drying In Organic Solventsmentioning

confidence: 99%

Aerogels

Hüsing

Schubert

2006

Ullmann's Encyclopedia of Industrial Chemistry

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The article contains sections titled: 1. Introduction 2. Synthesis 2.1. Network Formation and Structure 2.1.1. Inorganic Aerogels 2.1.1.1. SiO 2 Aerogels 2.1.1.2. Metal Oxide Aerogels 2.1.2. Inorganic/Organic Hybrid Aerogels 2.1.3. Organic Aerogels 2.2. Drying Methods 2.2.1. Supercritical Drying 2.2.1.1. Drying in Organic Solvents 2.2.1.2. Supercritical Drying with CO 2 2.2.2. Freeze Drying 2.2.3. Ambient Pressure Drying 2.3. Modification of Aerogels after Drying 3. Properties 3.1. Structural Properties 3.2. Physical and Chemical Properties 3.2.1. Optical Properties 3.2.2. Mechanical and Acoustic Properties 3.2.3. Thermal Conductivity 3.2.4. Hydrophobicity 4. Applications 4.1. Çerenkov Detectors 4.2. Thermal Insulation 4.3. Catalysis 4.4. Application as Storage Media 4.5. Electrical and Electronic Applications 4.6. Acoustic and Mechanical Applications 4.7. Optical Applications 4.8. Other Applications 5. Future Perspectives Aerogels are unique among solid materials. They have extremely low densities (up to 95 % of their volume is air), large open pores, and a high inner surface area. This combination of properties results in interesting physical properties, e.g., for silica aerogels extremely low thermal conductivities and low sound velocities are combined with optical transparency. Aerogels are typically prepared via wet chemical processes, such as sol – gel processing, and thus their pore system is initially filled with liquid. Only special drying techniques allow for exchange of the pore liquid against air while maintaining the filigrane solid framework. The most common drying technique is supercritical extraction, and sometimes chemical modification of the inner surface can be used to facilitate drying. The structure of the gel network, and thus the physical properties of aerogels, decisively depends on the choice of the precursors and the chemical reaction parameters for preparing the gels. Therefore, the later materials properties can be deliberately designed in the starting reaction solution.

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Effects of supercritical drying media on structure and properties of silica aerogel

Cited by 77 publications

References 5 publications

Superior Nanoporous Polyimides via Supercritical CO₂ Drying of Jungle‐Gym‐Type Polyimide Gels

Superior Nanoporous Polyimides via Supercritical CO₂ Drying of Jungle‐Gym‐Type Polyimide Gels

Supercritical Fluids in Confined Geometries

Aerogels

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Effects of supercritical drying media on structure and properties of silica aerogel

Cited by 77 publications

References 5 publications

Superior Nanoporous Polyimides via Supercritical CO2 Drying of Jungle‐Gym‐Type Polyimide Gels

Superior Nanoporous Polyimides via Supercritical CO2 Drying of Jungle‐Gym‐Type Polyimide Gels

Supercritical Fluids in Confined Geometries

Aerogels

Contact Info

Product

Resources

About

Superior Nanoporous Polyimides via Supercritical CO₂ Drying of Jungle‐Gym‐Type Polyimide Gels

Superior Nanoporous Polyimides via Supercritical CO₂ Drying of Jungle‐Gym‐Type Polyimide Gels