Spontaneous fracturing and self-healing in electrospun microfibers of block copolymers

The formation of patterns through fracturing is prevalent in both natural and synthetic systems and has a significant effect on the mechanical and physical properties of the system. In particular, the fracturing of thin films due to in-plain tensile stresses is a well-studied phenomenon. In such systems, the fractures generation depends on the stress inside the film, its thickness, the residual strain, and the elastic properties of the film and of the substrate. Tuning these parameters allows controlling the fracturing process and manipulating the obtained patterns.

Here, we present the extension of this concept towards one-dimensional systems and demonstrate the self-fracturing of electrospun microfibers fabricated from custom-made amphiphilic tri-block copolymers. Upon deposition of the fibers on different substrates during their fabrication, the fibers spontaneously fracture into relatively uniform microscale partitions. The fracture frequency and the average fragment length are dictated by the thickness of the fibers, allowing us to form cylindrical fragments with lengths ranging from hundreds of nanometers to hundred microns depending on the fiber thickness. Upon exposure to humid conditions, the amphiphilic nature of the copolymer promotes the adsorption of water and the swelling of the fragments. In their contact region, the swollen fragments coalesce, leading to self-healing of the fibers into their original, un-fractured form.

The presented work extends the ideas of 2D thin films fracturing systems towards 1D systems and displays a new mechanism for obtaining size-controlled micro and nano polymeric particles. The system enables the comprehensive study and detailed examination of the different parameters and conditions that affect the fracturing process and will allow further deciphering of the physical principals that control fracturing and self-healing in the microscale level.