Polymer aerogels derived from engineering thermoplastics provide good mechanical properties and high chemical and thermal stability through highly-porous, low-density monolithic structures. Poly(phenylene sulfide) (PPS) aerogels were fabricated via a thermally-induced phase separation (TIPS) process. Initially, the  thermoreversible gels consist of a semi-crystalline network entrapping solvent in an expanded morphology of interconnected axialites. Exchanging and removing solvents yields low-density aerogels (0.11-0.24 g/cm<sup>3</sup>). USAXS/SAXS scattering profiles reveal complex, hierarchical morphologies. Power law scaling of aerogel modulus over a range of densities suggests a tendency of the well-connected strut-like crystallites to bend in compression rather than just collapse and compress, common with mass fractal cellular solids.<br/>Annealing has been shown to improve the toughness of PPS by increasing crystallinity, allowing amorphous chains to relax into more thermodynamically-favorable conformations, and by the potential to induce chemical cross-linking. PPS aerogels of various concentrations were annealed at different temperatures to explore the effect of annealing on morphology and properties. Microscopy appears to reveal that annealing increases crystallite connectivity. Annealing decreased the power law scaling of density with modulus, suggesting a greater bending-moment character in compression, attributed to higher network connectivity. Consequently, toughness increased with annealing temperature, which may expand the practical applicability of PPS aerogels as a structural material.

Influence of thermal annealing on the morphology and toughness of poly(phenylene sulfide) aerogels

ACS Fall 2021

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