Preparation of polyimide/multi‐walled carbon nanotubes composite aerogels with anisotropic properties

Abstract

In this study, a series of polyimide/multi‐walled carbon nanotubes (PI/MWCNTs) composite aerogels with anisotropic properties were fabricated. First, the poly(amic acid) ammonium salt (PAS)/MWCNTs suspension was prepared by blending poly(amic acid), deionized water, triethylamine, MWCNTs, and CNT dispersant with the aid of ultrasonication treatment. Afterwards, the aqueous PAS/MWCNTs suspension was unidirectionally frozen at −65 ± 5°C, then followed by freeze‐drying. Subsequently, the PI/MWCNTs composite aerogels were obtained after thermal imidization treatment. Morphology observations revealed that PI/MWCNTs composite aerogels exhibited a “hive‐like” structure while viewed along the freezing direction, whereas a typical channel‐like pore structure was observed perpendicular to the freezing direction. This typical structure rendered PI/MWCNTs composite aerogels with anisotropic properties such as heat conduction, electrical conductivity as well as electromagnetic interference shielding effectiveness when the aerogels were characterized at different directions.

Anisotropic and Lightweight Carbon/Graphene Composite Aerogels for Efficient Thermal Insulation and Electromagnetic Interference Shielding

“…To be specific, when the electromagnetic waves entered the samples along the freezing direction, that is, parallel to the tubular pore, they would penetrate the aerogels more easily and thus reduce the dissipation of incident electromagnetic waves. As for the incident electromagnetic waves perpendicular to above direction, they would get trapped in the pores and bounce back and forth among the pore walls until the electromagnetic waves were totally dissipated in the form of heat. ,, As a result, the CG aerogels showed better shielding against electromagnetic interference in the radial direction than that in the axial direction.…”

“…As for the incident electromagnetic waves perpendicular to above direction, they would get trapped in the pores and bounce back and forth among the pore walls until the electromagnetic waves were totally dissipated in the form of heat. 29,49,50 As a result, the CG aerogels showed better shielding against electromagnetic interference in the radial direction than that in the axial direction.…”

Carbonization of Graphene-Doped Isocyanate-Based Polyimide Foams to Achieve Carbon Foams with Excellent Electromagnetic Interference Shielding Performance

“…It is known that the apparent density of carbon foams was d termined by the doping content of GR particles and carbonization process. Figure shows that the apparent density of pure PI foams derived carbon foams was higher th that of 0.5GR doped counterparts, which was related to the higher volume shrinkage pure PI foams than 0.5GR doped counterparts [44]. The apparent density of pure PI an 0.5GR doped PI foams reached 37 and 26 kg/m 3 when the carbonization temperature w 800 °C.…”

“…It is known that the apparent density of carbon foams was determined by the doping content of GR particles and carbonization process. Figure 5b shows that the apparent density of pure PI foams derived carbon foams was higher than that of 0.5GR doped counterparts, which was related to the higher volume shrinkage of pure PI foams than 0.5GR doped counterparts [44]. The apparent density of pure PI and 0.5GR doped PI foams reached 37 and 26 kg/m 3 when the carbonization temperature was 800 • C. Moreover, there was an incremental decrease of foam density with increasing temperature up to 1100 • C. In this scenario, it was induced that the rate of mass loss was higher than that of the volume shrinkage during the thermal treatment process.…”

Polyimide-Based Foams: Fabrication and Multifunctional Applications

“…Polymer foams are ubiquitous in the world we live in and have been used as cushioning materials for furniture, membranes for separation, packing materials for fragile products, and dielectric layers for electronics industry . Usually, polymer foams can be divided into open-cell foams and closed-cell foams, which correspond to thermoplastic foams with flexibility and thermosetting foams with rigidness, respectively. − With regard to polyimide (PI) foams, they were first invented by Du Pont Company and Monsanto Company in the 1960s, and then they gained interest by domestic and foreign academic communities as well as industrial circles for their excellent performance. − …”