Spatially Resolved Molecular Structural Evolution during Crack-Tip Plasticity in Polyrotaxane Glasses

Abstract

Polymer fracture is governed by plastic deformation around crack tips, yet its underlying molecular processes remain difficult to observe in amorphous polymers. Polyrotaxane glasses provide a rare opportunity to probe these processes because the orientation and intermolecular distance of the constituent ring molecules can be directly evaluated by X-ray scattering. Here, simultaneous synchrotron microbeam small- and wide-angle X-ray scattering (SAXS/WAXS) measurements were used to spatially resolve crack-tip structural evolution from molecular to mesoscale dimensions. WAXS revealed spatially continuous ring orientation and phase separation from axle chains extending away from crack tips, suggesting that these structural changes constitute key molecular processes underlying crack-tip plastic deformation, whereas SAXS detected spatially discrete nanovoids and craze-like structures. The distinct SAXS/WAXS distributions suggest that ring orientation and phase separation can develop prior to, or independently of, localized mesoscale damage. These findings provide molecular insight into crack-tip plasticity relevant to fracture resistance and molecular design of tough polymers.