Mechanism of Hydration Induced Stiffening and Subsequent Plasticization of Polyamide Aerogel

The mesoporous polyamide (PA) aerogel similar in chemical structure to DuPont's Kevlar is an advanced thermal insulation material tested airspace applications. Unfortunately, the monolithic readily absorbs humidity (from moist air), which dramatically alters its mechanical properties. compressive strength of PA first increases when water content increases, but subsequently decreases following additional hydration. To provide a coherent explanation for this non-monotonic change, hydrated stepwise and hydration mechanism elucidated by multiscale experimental characterization. molecular investigated solid-state liquid-state nuclear magnetic resonance (NMR) spectroscopy, morphology small angle neutron scattering (SANS) at each equilibrium state. physico-chemical changes level nanoscale architecture are reconstructed. molecules bind into vacancies intermolecular H-bonding network macromolecules, strengthens causes concerted morphological changes, leading macroscopic stiffening monolith. Additional disrupts original their increased segmental motion, marking start partial dissolution nanosized fibers backbone. This eventually plasticizes