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

Abstract

Changes in the microphase-separated structure of the poly­(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer (13 wt % polystyrene (PS) block) were investigated during mechanical deformation. In situ synchrotron radiation small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS) measurements were successfully performed for SEBS under equi-biaxial deformation as well as under uniaxial deformation. In situ SAXS/WAXS measurements revealed changes in (1) the shape of spherical PS domains, (2) the spacing of PS domains packed in the body-centered cubic structure in the initial state, (3) their ordering, and (4) the orientation of PEB chains during deformations. In terms of the microdomain structure, affine deformation was kept below a certain strain (εd‑A), which are 4 and 1.2 for uniaxial and equi-biaxial deformation, respectively. In contrast, the ordering of the arranged PS domains decreased from the initial strain region. Above the εd‑A value, deviation from affine deformation started to occur. This deviation is related to contact of PS domains under mechanical deformation. Uniaxial stretching still showed the plane-independent behavior, while equi-biaxial stretching did not. Moreover, the εd‑A value for equi-biaxial deformation was smaller than that for uniaxial deformation and further smaller than expected. This might be because the entanglement effect was enhanced for equi-biaxial deformation. Furthermore, after contact of PS domains at around strains of 6 and 2, during uniaxial and equi-biaxial deformation, respectively, the ordering of PS domains suddenly increased with an increase in strain. It is inferred that the locked state between the PS domains and the extended PEB chains formed during deformation may have been released and repacked at a certain strain.

Molecular Characterization of Polymer Networks

“…Recently, scattering coupled with in situ rheological measurements has become more popular to aid in the development of structure–property relationships. − Rheo-small-angle-neutron scattering (rheo-SANS, Figure ) is most common in polymer networks due to the contrast selectivity as mentioned for static SANS, and it provides a direct correlation between the structure and the macroscopic rheological response. There are a number of flow devices compatible with in situ neutron scattering measurements (flow-SANS or rheo-SANS), most notably, Couette cells, capillary flow cells, 1–2 shear cells, and even entire oscillatory rheometers .…”

“…Capillary and microfluidic flow devices, , for low sample volume experiments under arbitrary deformation fields, are also available. Such rheo-SANS experiments have given insights into the interplay of chain branching and alignment with the formation/breakage of reversible cross-links under different shear conditions. − Further, rheo-SAXS has shown that the glassy styrene domains (within a microphase-separated poly­(styrene- b -ethylene- co -butylene- b -styrene) (SEBS) triblock thermoplastic elastomer) change shape, spacing, and ordering while undergoing uniaxial or biaxial stretching …”

“…218−221 Further, rheo-SAXS has shown that the glassy styrene domains (within a microphase-separated poly(styrene-b-ethylene-cobutylene-b-styrene) (SEBS) triblock thermoplastic elastomer) change shape, spacing, and ordering while undergoing uniaxial or biaxial stretching. 222…”

Specific deformation behavior of isotactic polypropylene films under a multiaxial stress field

“…The importance of multiaxial deformation, such as biaxial, [13][14][15][16][17][18][19][20] compression, 21 bulge, 22 lateral indentation, 23 and flow, 24 in terms of understanding the physical properties of polymers is well known. This is because (1) the polymers have a string-shaped structure, (2) they can become entangled, and (3) the strain density energy function of the materials can be obtained.…”

In Situ SAXS Observation of Transient Network Behavior in Ionically Cross-Linked Polydimethylsiloxane Elastomer with Slow and Fast Stretching

“…For a precise and deep understanding of the behavior of transient networks, in situ observations of the internal structure of specimens under deformation are important. For elastomers and gels, in situ small-angle X-ray scattering (SAXS) is frequently employed. ,,− For example, Winey et al observed the morphological changes in precise acid polyethylenes and their metal-neutralized ones using in situ SAXS with stretching. − Sakurai et al reported the deformation of a glassy polystyrene spherical domain in a polystyrene- block -poly­(ethylene- co -butylene)- block -polystyrene elastomer with uniaxial stretching . Kojio et al investigated the deformation behavior of polythiouretane elastomers using the combination of in situ SAXS, in situ wide-angle X-ray scattering (WAXS), and in situ X-ray absorption fine structure methods with stretching .…”