Study on pore size distribution and thermal conductivity of aramid nanofiber aerogels based on fractal theory

Aramid nanofiber aerogels (ANFAs) have been considered as ideal thermal insulation materials due to their low bulk density, hierarchical porous structure, high thermal insulation, and thermal stability. Thermal conductivity of ANFAs is highly determined by their complicated porous structure. Fractal geometry theory can effectively simulate pore size distribution, but it is rarely used in the study of the thermal conductivity of aerogels. In this work, the Sierpinski carpet model and two modified Sierpinski carpet models were established to study the pore size distribution of ANFAs, and then the equivalent resistance method was used to transform the models into series and parallel fractal resistance networks, which were applied for the calculation of the effective thermal conductivity of ANFAs. Results show that the calculated results are closer to the experimental data, with a minimum error of 0.78%, indicating the thermal conductivity prediction model is effective and reliable.