Investigation of microdomain deformation of thermoplastic elastomer based on in situ synchrotron radiation X-ray scattering

Microphase separation occurs in polystyrene (PS)-b-poly(ethylene-co-butylene)-b-PS (SEBS), leading PS domains to serve as physical crosslinking points. To investigate behaviors of PS domains, well-ordered SEBS films with low PS content were measured during uniaxial, biaxial and compression testing using in situ SAXS in SPring-8, Japan. After annealing, characteristics of spherical microdomain of PS packed in body-centered cubic lattice were observed in structure and form factors. During uniaxial testing, a shift of structure factor reveals an increase in domain spacing in parallel to stretching direction (SD) while it decreased in the perpendicular to SD. Furthermore, the shift of form factor implies to the deformation of PS spherical domains to egg-like ellipsoidal shape. For biaxial testing, a shift of structure factor indicates an increase in domain spacing as strain increased. In compression testing, the experiment was observed from the edge of sample. It was found that structure factor indicates a decrease in domain spacing in the parallel to compressing direction (CD) while it increased in the perpendicular to CD. The results of form factor observed in biaxial and compression testing suggest the deformation of PS domain, which the sphere became asymmetry in three dimension.