Review on Solvent-Free Nanofluids in Fibers: Progress, Applications, and Prospects

Solvent-free nanofluids (SNFs) are a charming existence form of nanoparticles for the 21st century that consist of nanoscale cores with a crown and canopy structure. The corona molecules connected directly or via a neck layer simultaneously reduce nanoparticle aggregation and provide a "solvent" effect, leading to a stable structure under physical disturbances for superior liquid-like fluidity, hydrodynamic stability, and thermal stability. The draw of SNFs lies in their nonvolatility, stable nanoparticle dispersion, tunable rheology, and adjustable structures. The internal and external compatibility of SNFs is optimized in composites processing, allowing significant functional modification potential (for example, it is difficult to maintain mechanical performance for filling exceeding a 20% content of heterogeneous particles in high-performance fiber). This Review summarizes the research progress and preparation strategies of SNFs and discusses the effects of five factors on their rheological behavior (corona layer molecules, nanoparticle cores, core-corona interactions, corona layer chain length, and external fields). The applications of fibers composited with SNF is also reviewed for fiber preparation and processing, fabric comfort, fiber reinforcement, antibacterial properties, separation and purification, and energy. Finally, this Review addresses the challenges in studying the performance and stability of SNFs in fibers, highlighting vital issues that need resolution.