The specific work of flow as a universal parameter to control the formation of shish-kebab morphology in polymers

Model bidisperse linear-linear hydrogenated polybutadiene blends as well as an industrial material (low-density polyethylene) have been investigated by both small-angle X-ray scattering (SAXS) and birefringence methods. It has been found that two parameters are responsible for the formation of shish-kebab morphology by flow-induced crystallization: a minimum shear rate reciprocal to the longest Rouse time of molecules present in a polymer ensemble and a specific work of flow applied to the polymer. The magnitude of the specific work required to create oriented (shish) nuclei to form shish-kebab structures depends on parameters responsible for relaxation times of polymer (chemical structure of the polymer, molecular weight distribution and thermodynamic conditions of shearing). It has been also found that shish nuclei can be formed and exist at temperatures above the nominal melting points of the studied polymers. The phenomenon of elastic turbulence has been identified in semicrystalline polymers crystallized under shear where complex oriented structure caused by elastic instabilities is pinned by the process of crystallization and persists down to room temperature.