Aramid Colloidal Aerogels: Architecting Nanofibers via Dynamic Sol–Gel Transition for Multifunctional Applications

Abstract

Conspectus Aerogels have long captivated materials scientists with their extreme properties─ultralow density, high porosity, and enormous specific surface area. Yet for nearly a century, their fabrication has remained trapped in a static paradigm: the sol–gel transition of small-molecule precursors requires prolonged standing times, which is fundamentally incompatible with the rapid, continuous processing of modern manufacturing. The root cause is intrinsic─precursors and gelation-inducing agents possess comparable molecular dimensions and thus similar diffusion coefficients. In dynamic environments, precursors diffuse away before the gel network can form, leading to structural inhomogeneity and poor shape fidelity. Our breakthrough came from a simple insight: by deliberately enlarging the precursor size to suppress its diffusion, one creates a diffusivity disparity with rapidly diffusing gelation agents. This simple kinetic consideration led us to propose the dynamic sol–gel transition─a colloidal approach that transforms aerogel manufacturing from a static, batch-wise process into a continuous, versatile platform capable of meeting the demands of modern industrial production. Aramid nanofibers (ANFs) emerged as ideal building blocks, inheriting the mechanical strength, thermal stability, and flame retardancy of bulk aramid while offering excellent colloidal processability and rapid proton-triggered gelation. This Account chronicles our systematic development of aramid colloidal aerogels across all dimensional architectures─from one-dimensional fibers to two-dimensional films and three-dimensional stereoscopic materials. We first solved the building-block bottleneck through microfluidic deprotonation, reducing ANF production from days to minutes while enabling continuous, scalable manufacturing with precise control over nanofiber dimensions. We then extended the dynamic sol–gel transition to fibers via wet, liquid crystal, centrifugal, and gas-blows-liquid spinning─achieving spinning speeds up to 300–700 m/s─and to films through blade coating, roll-to-roll, and electrochemical methods, each yielding distinct internal architectures ranging from isotropic to vertically aligned to horizontally layered. For three-dimensional architectures, we developed microgel-directed suspended printing for programmable spatial structuring and a twice-coagulated strategy, inspired by traditional Chinese folk arts, for configuration-editable aerogels with tensile elongation exceeding 7000%. These materials demonstrate broad application potential: thermal insulation from −196 to 300 °C, infrared stealth, electromagnetic shielding (54.4 dB), on-demand emulsification/demulsification with 99.97% efficiency, VOC adsorption (438.0 mg/g), rapid hemostasis, high-security information storage, shape-memory actuation, and wearable oxygen-generating microreactors validated at 4998 m altitude. Together, these demonstrations illustrate how the same underlying material platform can be adapted to distinct functional requirements across multiple domains. The dynamic sol–gel transition constitutes a general platform extendable to cellulose, chitosan, polyimide, and other nanofibrous systems─transforming aerogels from scientific curiosity into manufacturable, multifunctional materials poised to address pressing challenges in energy efficiency, environmental sustainability, personal protection, and human health.