Scattering and other miscellanies techniques for the characterization of shape memory polymers

Abstract

Shape memory polymers experience stress-induced macromolecular reorganization like alignment, crystallization, isotropic-to-smectic order, and temperature-induced melting (disorder), crystallization (ordering). The molecular processes involve short and/or long-range order. Hence, there is a need to apply suitable multi-scale characterization techniques to assess the molecular changes occurring during shape memory events. Ideally, the spatial resolution ranges from Å to nm- to μm-scale. This chapter focuses on the application of wide-angle and small-angle X-ray scattering (WAXS and SAXS, respectively), small-angle light scattering (SALS) and optical microscopy techniques which are ideal to get insights into the molecular mechanisms associated to shape memory in polymers. These techniques are ideally suited to enable in situ and time-resolved studies. It is the author’s view that understanding the molecular mechanisms is at the heart of shape memory effects and novel in situ techniques and simultaneous monitoring of microstructure and bulk extensional properties during shape memory cycles need to be implemented. The main body of the chapter focused on fundamentals of X-ray scattering, recording techniques, and applications to the study of shape memory polymers using conventional X-ray sources and synchrotron radiation. WAXS and SAXS enable Å- and nm-scale structure analysis and synchrotron sources enable time-resolved resolution. On the other hand, in situ and time-resolved studies of microstructure at μm-scale are enabled by optical microscopy and SALS. These techniques combined with temperature or uniaxial testing are also a powerful tool to understand molecular mechanisms associated to shape memory behavior.