Strain-Induced Deformation of Glassy Spherical Microdomains in Elastomeric Triblock Copolymer Films: Simultaneous Measurements of a Stress–Strain Curve with 2d-SAXS Patterns

Thermoplastic elastomers are elastomeric materials which contain hard domains as physical cross-linking for rubbery chains. Therefore, the hard domains are required permanently rigid. Nevertheless, we have found experimentally deformation of the hard domains upon uniaxial stretching of the thermoplastic elastomer films. In this paper, we report experimental results of deformation of glassy spherical microdomains in elastomeric triblock copolymer films upon uniaxial stretching, as revealed by two-dimensional small-angle X-ray scattering (2d-SAXS) measurements. Actually, shifts of the peak position of the particle scattering toward lower and higher q-regions were detected for q directions parallel and perpendicular to the stretching direction (SD), respectively, where q stands for the scattering vector. By assuming that spheres simply deformed into prolate spheroids with its major axis parallel to SD, 1d-SAXS profiles measured at several strains were successfully reproduced with model calculation of the 1d-SAXS profile. From the results of model calculation, radii of the prolate spheroids were appropriately determined. Since the extent of the deformation of microdomains was found to increase as the initial size of microdomains decreased, it is concluded that the deformation of glassy microdomains may be due to a high extent of the stress concentration at microdomains. Upon unloading, the deformed particle scattering peak in the 2d-SAXS pattern was found to retrieve almost a round shape. At a glance, this fact implies that the deformed sphere (prolate spheroid) recovers an isotropic shape. However, this kind of the elastic behavior cannot be the case for the glassy domain. Alternatively, we have tried to explain the change of the 2d-SAXS pattern by orientational relaxation of the prolate spheroids without changing the shape of the prolate spheroids. It was found that such trial was sound.