Investigation of the nanostructure-thermal properties correlation in functionally gradient aerogels synthesized via a monolithic and controllable method
摘要
This research work introduces a method for fabricating functionally graded (FG) phenolic aerogels with enhanced thermal insulation properties using a thermal gradient device. The approach involved a continuous, one-step sol–gel polymerization process, enabling precise control over monolithic structures of the aerogels. By adjusting the processing device speed (i.e., 1, 1.5, 2, and 2.5 mm/min), FG aerogels were synthesized with varying structures and properties. Physical characteristics such as porosity, density, and structure were evaluated along the length of the samples. Analysis revealed gradual changes in density and porosity, as evidenced by FESEM and mercury porosimetry results. The aerogel samples exhibited gradients in thermal conductivity (k) and thermal diffusivity (α) along their length, attributed to variations in pore size and density. Thermal imaging was used to assess the performance of both homogeneous and FG aerogel samples synthesized under identical conditions. Thermal performance tests indicated that the FG aerogels, when heated, displayed a thermal gradient, with the upper layers heating more rapidly due to their higher values of k and α paremeters. This behavior was attributed to the larger colloid particles and pores in the upper layers, resulting from the concentration gradient. Specifically, the upper layers have a reduced concentration compared to the lower layers, which had an increased concentration relative to the initial solution. In contrast, the homogeneous aerogels demonstrated uniform heating along their entire length. Notably, thermal conductivity coefficients at the two ends of a FG aerogel sample differed significantly, with a nearly sixfold increase from 0.03 W·m⁻1·K⁻1 at the 0 mm point to 0.23 W·m⁻1·K⁻1 at the 80 mm point.
Graphical abstract