Fast and scalable production of crosslinked polyimide aerogel fibers for ultrathin thermoregulating clothes

Polyimide aerogel fibers hold promise for intelligent thermal management fabrics, but their scalable production faces challenges due to the sluggish gelation kinetics and the weak backbone strength. Herein, a strategy is developed for fast and scalable fabrication of crosslinked polyimide (CPI) aerogel fibers by wet-spinning and ambient pressure drying via UV-enhanced dynamic gelation strategy. This strategy enables fast sol-gel transition of photosensitive polyimide, resulting in a strongly-crosslinked gel skeleton that effectively maintains the fiber shape and porous nanostructure. Continuous production of CPI aerogel fibers (length of hundreds of meters) with high specific modulus (390.9 kN m kg−1) can be achieved within 7 h, more efficiently than previous methods (>48 h). Moreover, the CPI aerogel fabric demonstrates almost the same thermal insulating performance as down, but is about 1/8 the thickness of down. The strategy opens a promisingly wide-space for fast and scalable fabrication of ultrathin fabrics for personal thermal management.

radius R (R = 1.0σ), the two nearest cross-linkable beads have the chance to react with each other at a certain probability Pr to form a new (covalent) bond.The reaction probability Pr can also be used as a parameter that controls the reactivity determined by the nature of the reactive groups.In this work, the reaction probability Pr is set to be 0.001.
The MD simulations include both bonding Ubond and nonbonding potentials Uij in the interaction potential.Any pair of ith and jth beads has a nonbonding potential Uij which can be calculated using the modified Lennard-Jones 12:6 (LJ126) potential.
where the εij is the interaction parameter between beads i and j.When rij is truncated and shifted to zero energy and force, this distance is known as rij c .In the modified LJ126 potential, the cutoff distance (rij c ) determines the attractive (rij c > 2 1/6 σ) or repulsive (rij c ≤ 2 1/6 σ) interaction between i and j beads, where the σ represents the distance unit in the MD simulations.To mimic the corresponding experimental system, the strength and cutoff distance for the interactions between beads i and j is fixed at 1.0ε and 2.5σ (attractive), respectively, where the ε represents the unit of energy in the MD simulations.
where kb = 20ε/σ 2 and R0 = 1.5σ is the elastic coefficient and the maximum extensible bond length, respectively.We used a cosine harmonic function (angle potential) to further constrain the linearly rigid chain structure of polyimide, written as where ka = 20ε is the angle spring constant and θ0 = 180° is the equilibrium angle.
In the present MD simulation, the total number of CG MD beads is 48000, containing 834 polyimide molecules (each polyimide molecule chain includes LP = 23 beads, i.e., the mass fraction of polyimide is 834LP / 48000 × 100% ≈ 40%).All the MD simulations were carried out by the large scale atomic/molecular massively parallel simulator (LAMMPS), developed by Sandia National Laboratories 1 .In the MD simulations, to generate the initial configurations, we constructed a large system with low volume fraction in a cubic box, which was compressed to the volume fraction of 0.45.Based on the initial configurations, the MD simulations were performed in the isothermal-isobaric (NPT) ensemble by using the Nose-Hoover barostat and thermostat.
During the MD simulations, the periodic boundary conditions were imposed with a time step Δt = 0.001τ (τ denotes the unit time).
(c) 1 H NMR spectrum of PI.(d) 13 C NMR spectrum of PI.(e) 19 F NMR spectrum of PI.
Structure of the PI was determined by 1 H NMR, 13 C NMR, 19 F NMR and FT-IR spectra.
The FT-IR spectra of PI showed two peaks assigned to the carbonyl group, 1355 cm -1 (C-N stretching) and 1784 cm -1 (C=O asymmetric stretching), which represented the characteristic peaks of the polyimides.The absorption peak near 1145 cm -1 was assigned to the C-F bond, while the strong peaks appearing at 1100 cm -1 is assigned to the ether bond vibration peaks.The peaks at 1498 cm -1 and 1451 cm -1 were assigned to the C-C stretching of the aromatic rings

Table 5
13 The 1 H NMR spectrum of PI showed the main chain proton signals for aromatics at 7.2-8.25 ppm.Characteristic signals of the carboxyl group (166.6 ppm), the imide ring (166.3 and 166.1 ppm), the C-F and the benzene ring (140-120 ppm) are clearly observed in the13C NMR pattern.And in 19 F Solubility of PI.++: soluble at room temperature, +-: partially swelling at room temperature.Summary of temperature difference/thickness (|ΔT|/T) values for commercial materials and reported aerogel fibers.