Porous Polyimide Aerogel Shrinkage Control
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Solution Overview
Problem
Existing methods for producing three-dimensional porous polyimide and carbon networks face challenges such as high energy costs, shrinkage issues, and limitations in achievable density and morphological stability, which affect their mechanical properties and applications.
Innovation Solution
A method involving the reaction of dianhydrides with diisocyanates at room temperature to form sol-gel materials, followed by supercritical, subcritical, or freeze drying, which allows for the production of polyimide aerogels with fibrous morphology that can be converted to carbon aerogels with retained morphological characteristics, reducing shrinkage and increasing density range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional methods are used to produce three-dimensional porous polyimide and carbon networks, then production is achieved, but high energy costs and shrinkage issues occur
Solution Approach 1:
The patent employs parameter changes by conducting the polyimide synthesis at room temperature rather than high temperatures, and by using supercritical or subcritical drying conditions to control the pore structure formation. These parameter modifications reduce energy consumption while maintaining structural integrity and minimizing shrinkage during the drying process.
Solution Approach 2:
The patent utilizes phase transitions in the drying process, specifically employing supercritical or subcritical conditions where the liquid solvent transitions to a supercritical or subcritical fluid state. This phase transition allows for removal of the liquid component without causing capillary stresses that would lead to shrinkage, thereby maintaining the porous structure while reducing energy requirements compared to conventional high-temperature drying.
2Quantity of substance
If conventional production methods are used, then porous networks are formed, but limitations in achievable density and morphological stability occur
Solution Approach 1:
The patent applies preliminary action by forming the complete three-dimensional porous polyimide network structure before the drying process. The gel structure is fully developed while the polymer is in the wet state, and this pre-formed structure is then preserved through careful control of the drying process. This preliminary formation of the network structure ensures morphological stability and allows for a broader range of achievable densities without structural collapse.
Solution Approach 2:
By using supercritical or subcritical drying, the patent avoids the liquid-vapor phase transition that occurs in conventional drying. Instead, the solvent is brought to supercritical or subcritical conditions where menisci are eliminated and capillary pressures are removed, preventing structural collapse. This phase transition approach preserves the morphological stability of the porous network across a wider density range.
3Loss of energy
If room temperature synthesis is used, then energy cost is reduced, but production time may increase
Solution Approach 1:
The patent maintains continuity of useful action by conducting the polyimide synthesis at room temperature without interrupting the reaction to apply external heating. The reaction proceeds continuously under ambient conditions, and the gelation process occurs uninterrupted. This continuous process at room temperature reduces energy input while the extended reaction time is offset by the elimination of heating/cooling cycles and simplified process steps.
Solution Approach 2:
The patent leverages the phase transition properties of the solvent system during room temperature synthesis and subsequent supercritical/subcritical drying. The room temperature synthesis allows adequate time for complete polymerization and gelation, while the phase transition during drying provides a rapid and efficient solvent removal mechanism. This combination balances the extended reaction time at room temperature with a streamlined drying process, overall reducing energy costs without excessive production time extension.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the production of polyimide and carbon aerogels with reduced shrinkage, higher density, and retained morphological stability, enhancing their mechanical properties and expanding their application in thermal insulation, impact dampening, and electronic dielectrics.
Implementation Method 1
Drying may be performed supercritically, subcritically, or by freeze drying
Implementation Method 2
Drying may be performed supercritically, subcritically, or by freeze drying
Implementation Method 3
the aerogel may be subjected to a pyrolysis step, giving rise to a carbon skeleton in the aerogel
Data Source
AI summary
Porous three-dimensional networks of polyimide and porous three-dimensional networks of carbon and methods of their manufacture are described. For example, polyimide aerogels are prepared by mixing a dianhydride and a diisocyanate in a solvent comprising a pyrrolidone and acetonitrile at room temperature to form a sol-gel material and supercritically drying the sol-gel material to form the polyimide aerogel. Porous three-dimensional polyimide networks, such as polyimide aerogels, may also exhibit a fibrous morphology. Having a porous three-dimensional polyimide network undergo an additional step of pyrolysis may result in the three dimensional network being converted to a purely carbon skeleton, yielding a porous three-dimensional carbon network. The carbon network, having been derived from a fibrous polyimide network, may also exhibit a fibrous morphology.