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

Abstract

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.

Computational Study of Mechanochemical Activation in Nanostructured Triblock Copolymers

“…Overall, the stressstrain curves follow the expected behavior, with the stress increasing with the fraction of the glassy A component in the sample. Consistent with prior results from simulations 20,58 and experiments 27,60 , the absolute stress is highest for the lamellar morphology, followed by cylindrical morphology, with the spherical morphology having the lowest stress.…”

In Situ Synchrotron Radiation X-ray Scattering Investigation of a Microphase-Separated Structure of Thermoplastic Elastomers under Uniaxial and Equi-Biaxial Deformation Modes

“…The orientation of the PEB chains during sample deformation is also crucial for understanding the mechanical properties of the material. In situ small-angle X-ray scattering (SAXS) − and wide-angle X-ray scattering (WAXS) techniques − are powerful methods to investigate the arrangement and deformation behavior of PS domains as well as the orientation state of the PEB chains. Many studies have reported on the deformation behavior of various types of thermoplastic elastomers based on these techniques.…”

“…They concluded that the interdomain distance increased with increasing strain in the stretching direction, as observed from a change in the scattering intensity distribution from the SAXS results. Sakurai et al investigated the quantitative deformation of PS domains containing in thermoplastic elastomers under uniaxial elongation using simultaneous SAXS measurements . They clarified that the glassy domains deformed to prolate spheroids during uniaxial stretching.…”

Thinning Approximation for Calculating Two-Dimensional Scattering Patterns in Dissipative Particle Dynamics Simulations under Shear Flow

“…For block copolymer systems, 2DSPs were extensively observed to study structural changes due to shear or uniaxial deformations [32,33,34,35,36,37,38,39,40,41,42]. For example, Betes et al [32] reported the dependence of the order–disorder transition in poly(ethylene-propylene)–poly(ethylethylene) (PEP–PEE), a diblock copolymer, on the shear rate; two-dimensional contour plots of the two phases show changes corresponding to those in scattering patterns.…”

“…Krishnamoorti et al conducted neutron scattering experiments to examine 2DSPs during a cylinder-to-sphere order–order transition in block copolymers [37]. Sakurai and co-workers examined 2DSPs of strain-induced deformation of glassy spherical micro-domains in elastomeric triblock copolymers [38,39,40]; they also measured the stress as a function of strain in these systems. Mao et al and McCready and Burghardt reported changes in 2DSPs corresponding to deformation of re-oriented micro-domains in a hexagonally ordered styrene–ethylene–butylene–styrene (SEBS) triblock copolymer under uniaxial extensional flow [41,42].…”