Acceleration of Crazing on Polyacrylonitrile Through Solid or Liquid Coating

Since crazes have a porous structure in the order of tens of nanometers, if they could be generated periodically in polyacrylonitrile (PAN), which is a raw material for carbon fiber, we can create new porous carbon materials (e.g., carbon films with periodic porous layers). However, according to Wu, PAN is a polymer that predominant yield behavior than craze behavior. Therefore, in this study, to generate crazes in polymers with predominant yield behavior, such as PAN, we used a method that focuses on the entanglement of molecular chains on the film surface, which is the starting point of craze generation (solid coating), as well as a method that focuses on the interfacial free energy (liquid coating). The results clarified that crazes can be generated in even polymers with predominant yield behavior, such as PAN, by sufficiently lowering at least one of the following: the entanglement density of the film surface, which is the starting point of craze generation, or the interfacial free energy of the film surface. Additionally, it is concluded that Wu's indexes (see the manuscript for details) should be applied to the surface rather than the bulk because the surface properties are crucial for craze generation. Moreover, it was confirmed that a craze can continue to grow in the direction of the film thickness once it has been generated, even if the inside of the film with predominant yield behavior according to Wu's indexes and the interfacial free energy of the craze tip is about several tens of mJ/m(2).