In situ Investigation of Structural Changes during Deformation and Fracture of Polymers by Synchrotron SAXS and WAXS

Abstract

For many applications of polymers, their mechanical properties play an important role. These properties are strongly dependent on processing (thermal and deformation (mainly shear) history), by which the chain orientation and morphology are formed. To improve the mechanical properties of soft materials, a deeper understanding of the processes of deformation and failure is necessary. In this context, mechanisms at different length scales play a role, whose interaction and interplay must be understood and tailored.X-ray scattering is sensitive to differences in the electron density on scales above the wavelength of the X-rays. Thus, by wide-angle X-ray scattering (WAXS), crystallites, and their internal order and orientation are detectable. By small-angle X-ray scattering (SAXS), phase structures (including microcracks and voids) can be investigated in the range of up to about 100 nm (dependent on the wavelength, the sampleto-detector distance and the detector resolution).Coupling mechanical testing and synchrotron x-ray scattering enables a simultaneous investigation of the mechanical and structural features of materials. In this way, damage mechanisms of polymers involving cavitation and fibrillation can be investigated. Local deformation mechanisms can be identified, such as shear yielding. Individual failure events can be followed with a spatial resolution in the micrometer range. A better understanding of the processes in the crack zone of the polymer is achieved by local structural investigations. On this basis, models for structure-properties relationships can be established or verified. Experimental PartOnline-structural characterisation during deformation was performed by the following strategy. To get local structural information, a well-defined local-deformation geometry must be realised. Therefore, waisted specimens with the dimensions shown in Figure 1 were used: the thickness was 1.0 AE 0.1 mm. The dimensions could be scaled up or down. In this way, miniaturised specimens were also possible. The local strain in the middle of the specimen was estimated optically, by marks or by an optical-grating technique. A miniaturised tensile rig with two, parallel, moving grips held the specimen in such a way that the middle of the specimen was always in place during deformation. Using this sample geometry, necking started in the middle of the specimen and passed directly into strain hardening. Comparison of the mechanical data obtained by the classical dog-bone and the waisted specimens shows good agreement.The local structure was characterised by SAXS and WAXS measurements. The whole experimental set-up is shown in Figure 2 (see also Davies et al. [1] ). The experiments were performed at the European Synchrotron Radiation Facility, Grenoble (ESRF), ID13, with beams with a diameter of about 5 mm, and a photon energy of 12.6 keV or wavelength of 0.997 Š(without WAXS) and at the Hamburg Synchrotron Radiation Laboratory HASYLAB, BW4, with beams of 0.3 mm  0.3 mm, and a photon energy of 9.06 keV or wavelength of 1...

Deformation and orientation in filled rubbers on the nano‐ and microscale studied by X‐ray scattering

“…For USAXS, a MarCCD 165 detector was used; for WAXD, we used a Pilatus 300K. The quasistatic tensile experiments were performed on a self‐developed miniature tensile testing machine in the beamline in a step‐hold technique to allow for sufficient exposure time 12–14. The average strain rate was 0.005 s −1 (0.01 s −1 actual strain rate interrupted by 30 s holding periods for pattern acquisition).…”

Mechanical properties of water desalination and wastewater treatment membranes

“…In addition, time resolved X-ray diffraction, including wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) is also an effective technique for investigating the structure-property relationship of materials. WAXS detects chain orientation, orientation-induced crystallization and crystal destruction for polymer samples [197] and SAXS investigate phase structures and cavitation up to ~ 100 nm depending on the wavelength, the sample-to-detector distance and the detector resolution [198] and [199]. Similar to the 3D imaging approaches, the acquisition time, resolution and data treatment technique are the main challenges for the real-time investigations.…”

Hierarchical Nanomaterials Assembled from Peptoids and Other Sequence-Defined Synthetic Polymers

“…Thus, X-ray scattering at a broad range of scattering angles (from small to large angles) could be used to study information about the hierarchical structures at different length scales. 231 SAXS includes both the diffraction of large lattice spacing (at the order of tens to even thousands of interatomic distances) and the scattering by perturbed or nonperiodic structures. SAXS has been widely used to study neutral or charged biological macromolecules.…”