In-fiber composite nanostructures formed through filamentation instability during the thermal drawing process.

Long and flexible fibers with composite nanostructures have impactful applications in sensing, energy harvesting, biomedicine, and healthcare. Recent progress on in-fiber nanostructures from the perspective of filamentation instability is reviewed. The physical mechanism of filamentation instability is revealed by considering both the stretching effect and van der Waals forces, and theoretical predictions reach a close agreement with experimental results. Then, it is shown that using textured films in the preform with varying template thickness, the filamentation instability can be controlled to obtain a prescribed diameter and periodicity of ordered nanowire arrays in fibers. The filamentation instability of multilayer sheets has been investigated to get fibers with multilayer and multimaterial nanostructures. Lastly, second-order nonlinear stability analysis could provide guidance on the diameters of the main nanowires and satellite nanowires in fibers. This review could motivate more work in the future to obtain various multifunctional and multimaterial fibers through filamentation instability.