Modification of surface structure and mechanical properties in polyimide aerogel by low-energy proton implantation

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The transport behaviors of proton into nanoporous materials were investigated using different Monte Carlo simulation codes such as GEANT4, Deeper and SRIM. The results indicated that porous structure could enhance the proton scattering effects due to a higher specific surface area and more boundaries. The existence of voids can deepen and widen the proton distribution in the targets due to relatively lower apparent density. Thus, the incident protons would transport deeper and form a wider Bragg peak in the end of the range, as the target materials are in a higher porosity state and/or have a larger pore size. The existence of voids also causes the local inhomogeneity of proton/energy distribution in micro/nano scales. As compared, the commonly used SRIM code can only be used to estimate roughly the incident proton range in nanoporous materials, based on a homogeneous apparent density equivalence rule. Moreover, the estimated errors of the proton range tend to increase with the porosity. The Deeper code (designed for evaluation of radiation effects of nuclear materials) can be used to simulate the transport behaviors of protons or heavy ions in a real porous material with porosity smaller than 52.3% due to its modeling difficulty, while the GEANT4 code has shown advantages in that it is suitable and has been proven to simulate proton transportation in nanoporous materials with porosity in its full range of 0~100%. The GEANT4 simulation results are proved consistent with the experimental data, implying compatibility to deal with ion transportation into homogeneously nanoporous materials.

Section: Experiments Partsupporting

confidence: 75%

Simulation of the Particle Transport Behaviors in Nanoporous Matter

Wang

et al. 2022

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“…All three spectra exhibited bright fluorescent signals, and the spectral bands around 1340 cm −1 can be attributed to the C-N stretching vibration, around 1590 cm −1 to the ring vibration of PI, and around 1740 cm −1 to the stretching vibration of C=O from PI and GO [ 43 , 44 ]. This may be caused by the convergence of the D-band of rGO (1330 cm −1 ) and C-N stretching vibration (1340 cm −1 ) with each other, the overlap of the G-band of rGO (1560 cm −1 ) and the ring vibration of PI (1590 cm −1 ), and the enhancement of the peak signal with an increase in the SiO 2 @GO-NH 2 [ 45 ]. This evidence demonstrates the close association between PI chains and SiO 2 @GO-NH 2 within aerogels.…”

Section: Resultsmentioning

confidence: 99%

Organic–Inorganic Double-Gel System Thermally Insulating and Hydrophobic Polyimide Aerogel

Xiong

Cao

et al. 2022

Aerogel materials are used in various fields, but there is a shortage of aerogel materials with an excellent combination of mechanical properties, thermal stability, and easy preparation. In this study, polyimide aerogel materials with superior mechanical properties, thermal stability, and low thermal conductivity were prepared by forming a double-gel system in the liquid phase. The amino-modified gel, prepared by coating SiO2 nano-microspheres with GO through a modified sol-gel method (SiO2@GO-NH2), was subsequently homogeneously dispersed with PAA wet gel in water to form a double-gel system. The construction of a double-gel system enabled the PI aerogel to shape a unique honeycomb porous structure and a multi-layered interface of PI/SiO2/GO. The final obtained PI aerogel possessed effective thermal conductivity (0.0309 W/m·K) and a high specific modulus (46.19 m2/s2). In addition, the high thermal stability (543.80 °C in Ar atmosphere) and the ability to retain properties under heat treatment proved its durability in high thermal environments. The hydrophobicity (131.55°) proves its resistance to water from the environment. The excellent performance of this PI aerogel and its durability in thermal working environments make it possible to be applied in varied industrial and research fields, such as construction and energy, where heat and thermal insulation are required.

“…Although there have been plenty of reports on the damage behavior and mechanisms of bulk/film polyimides under various particles’ irradiation [ 13 , 14 , 15 , 16 , 17 ], the influence of a three-dimensional porous structure and nanoscale skeleton on radiation effects is still unclear. There have been several studies on the effect of proton irradiation [ 18 , 19 , 20 ] on polyimide aerogels. The Monte Carlo simulation results indicated that a porous structure could enhance the proton-scattering effects due to a higher specific surface area and more boundaries [ 18 ].…”

Section: Introductionmentioning

confidence: 99%

The Discharge Behavior and Mechanism of Polyimide Aerogel under Electron Irradiation

Ju,

Wu,

Wang

et al. 2024

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The response and mechanism of polyimide aerogel under electron irradiations were investigated. The experimental results indicated that electron irradiation could not damage the skeleton polyimide in the aerogel due to its high stability, but could result in a discharge within. The morphology of the discharge shows some dendritic discharge patterns, and the material surrounding the discharge channels was carbonized. The numerical simulation results indicated that the incident electrons, and also large amount induced secondary electrons, would be deposited inhomogeneously within the nano-porous polyimide aerogel. This would result in forming an ultra-high electrical potential of up to about 8.5 × 1010 V/m (which is far higher than the breakdown strength (2 × 108 V/m) of bulk polyimide materials) in a local region. This may be the leading cause of the obvious discharge in the materials. Furthermore, it was found that the actual reason for the discharge is related to the residual gas within the nano-porous structure; namely, the more internal residual gas (as a shorter-time vacuum pumping in the irradiated chamber), the more serious the discharge phenomenon. Correspondingly, the phenomenon may largely consist of both residual-gas discharge and surface flashover due to ultra-high local potentials induced by unevenly deposited charges in the porous aerogel.