Nanoscale Analysis of Large Deformation of Tough Microparticle-Based Polymer Films Revealed by Atomic Force Microscopy and Small-Angle X-ray Scattering

For understanding the mechanical properties of polymer materials and establishing design guidelines, elucidation of nanoscale structural changes under deformation is crucial. This study focused on microparticle-based polymer films exhibiting high fracture energies of several tens of MJ/m3 without additives, and the influence of intraparticle crosslinking on nanoscale deformation was investigated using atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The improvement of an AFM equipped with a stretching device enabled nanoscale observation of films under strain conditions of up to 700%. As intraparticle crosslinking increased, a trade-off was observed in which the Young's modulus increased while the fracture strain decreased. AFM observations showed that, although the increase in intraparticle crosslinking density did not significantly affect the deformation of each microparticle or particle clusters constituting the assembly, their surface roughness increased with increasing crosslinking density. SAXS measurements under tensile deformation revealed that the strain-induced structural anisotropy decreased with increasing intraparticle crosslinking density, suggesting suppressed nanoscale deformation within highly crosslinked microparticles. These results suggest that the trade-off in macroscopic mechanical properties is associated with a change in nanoscale deformation, from smooth elongation to surface roughening, highlighting that particle design is an important factor contributing to tough microparticle-based film properties.