Anisotropic polyimide aerogels fabricated by directional freezing

Wu, Pingbo; Zhang, Bin; Yu, Zhi; Zou, Huawei; Liu, Pengbo

doi:10.1002/app.47179

Cited by 25 publications

(24 citation statements)

References 39 publications

(52 reference statements)

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“…By repeating this operation, a five-layer sample was obtained. After freeze drying and thermal imidization, [44,45] the gradient PI aerogel was thus obtained. The final thickness of every layer of five-layer PI aerogel was about 4 to 5 mm.…”

Section: Preparation Of Pi Aerogels Via Layer-by-layer Assembly Methodsmentioning

confidence: 99%

Properties of gradient polyimide aerogels prepared through layer‐by‐layer assembly

Yuan

et al. 2020

Polymer Engineering & Sci

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A series of density gradient polyimide (PI) aerogels were prepared using layer‐by‐layer assembly and radial freezing method. Briefly, a layer of poly(amic acid) (PAA) ammonium salt aqueous solution was first radially frozen. Then, the second layer of PAA ammonium salt (PAS) aqueous solution of different concentration was added on the top of the first PAS layer and radially frozen. A multilayer gradient PAS solid sample could therefore be fabricated by repeating this similar procedure. The density gradient PI aerogels were obtained after freezing drying and final thermal imidization treatment. Each layer of gradient PI aerogels had anisotropic pore structure, which consisted of tube‐like pores along the radial direction and toward the center axis of the cylindrical samples. The compressive strength of five‐layer gradient PI aerogel was higher than that of three‐layer gradient and single‐layer PI aerogels with the same density. The gradient PI aerogels exhibited anisotropic heat transfer behavior in the direction of density gradient, and heat transfer from the higher density side to the lower density side was faster.

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Section: Preparation Of Pi Aerogels Via Layer-by-layer Assembly Methodsmentioning

confidence: 99%

Properties of gradient polyimide aerogels prepared through layer‐by‐layer assembly

Yuan

et al. 2020

Polymer Engineering & Sci

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“…As we can see, most species of poly(amic acid) (PAA) are immiscible with water. In order to settle this issue, PAA ammonium salt (PAS) was made, which was a kind of hydrosoluble PI precursor . For realizing the unidirectional freezing, the bottom of cylindrical mold containing PAS aqueous solution was placed in contact with dry ice slightly.…”

Section: Introductionmentioning

confidence: 99%

“…In order to settle this issue, PAA ammonium salt (PAS) was made, which was a kind of hydrosoluble PI precursor. 8 For realizing the unidirectional freezing, the bottom of cylindrical mold containing PAS aqueous solution was placed in contact with dry ice slightly. The ice crystals would grow from the bottom to top of mold (along the freezing direction).…”

Section: Introductionmentioning

confidence: 99%

“…[9][10][11] The dosage of TEA was dependent on the content of carboxyl in PAA. 8 Similarly, PAS aqueous solutions with 1.5, 3, 8, 10, and 12 wt % PAA content were also made. The TEA would have been totally eliminated during thermal imidization process; as a result, the PAA content of PAS aqueous solution was defined as mass ratio of PAA to PAA and water in this work.…”

Section: Introductionmentioning

confidence: 99%

“…The TEA would have been totally eliminated during thermal imidization process; as a result, the PAA content of PAS aqueous solution was defined as mass ratio of PAA to PAA and water in this work. 8…”

Section: Introductionmentioning

confidence: 99%

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Fabrication and properties of anisotropic polyimide aerogels with aligned tube‐like pore structure

Chen

et al. 2019

J of Applied Polymer Sci

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Polyimide (PI) aerogels with highly aligned tube‐like pores were fabricated by unidirectional ice crystal‐induced self‐assembly method. During this process, the mold bottom contacted with the freezing medium, the aqueous solution of poly(amic acid) (PAA) ammonium salt in the mold was unidirectionally frozen, the ice crystals grew from the bottom to top of PAA ammonium salt (PAS) solution along the freezing direction, which endowed PI aerogels with aligned tube‐like pores after sublimation of ice crystals and thermal imidization of PAS. The obtained aerogels had low densities (0.077–0.222 g cm−3) and high porosities (83.8–94.2%) and exhibited anisotropic morphology and properties. Their compression strength in vertical direction (parallel to freezing direction) was higher than that in horizontal direction (perpendicular to freezing direction). Their heat transport in horizontal direction was much slower than that in vertical direction; the aerogels had better thermal insulating property in horizontal direction. This facile approach contributed to prepare new type of PI aerogel materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48769.

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Nanocellulose‐Based Ultralight Porous Material for Various Environmental Applications

Mathew,

Poulose,

Gopakumar

et al. 2024

Nanomaterials for Air‐ and Water Purification

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Anisotropic polyimide aerogels fabricated by directional freezing

Cited by 25 publications

References 39 publications

Properties of gradient polyimide aerogels prepared through layer‐by‐layer assembly

Properties of gradient polyimide aerogels prepared through layer‐by‐layer assembly

Fabrication and properties of anisotropic polyimide aerogels with aligned tube‐like pore structure

Nanocellulose‐Based Ultralight Porous Material for Various Environmental Applications

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