Local Dielectric Spectroscopy as a Scanning Probe Method for Nanoscale Crystallinity Mapping in Semicrystalline Polymers and Polymeric Nanocomposites

Determining crystal size, typology, and distribution in the amorphous matrix in semicrystalline polymers becomes challenging when the crystal size is reduced to the nanometric scale. Spatially resolved diffraction techniques, like electron diffraction in transmission electron microscopy, demand high crystalline order, often not present in polymers, where crystalline structures can be somewhat disordered. Furthermore, functional properties of crystals in contrast to those of the surrounding amorphous material can be of interest, for instance, the dielectric constant and the role in establishing Maxwell-Wagner-Sillars or interfacial polarization that is at the base of nanodielectrics [1]. Another relevant issue is how the properties of the polymer are perturbed at the interface with inclusions in nanocomposites. Measurement methods to access directly to these properties, at least at the outer surface of specimens, are represented by scanning probes with sensitivity to electrical properties. Notably, Local Dielectric Spectroscopy (LDS) [2] allows obtaining local dielectric spectra with the same spatial resolution as electrostatic force microscopy, that is, a few nanometers [3], with a frequency range of up to 8 decades [4], not far from that of Broadband Dielectric Spectroscopy (BDS). In this work, we illustrate progress in the application of LDS to discriminate crystalline regions from surrounding amorphous ones in semicrystalline polymers like poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as well as natural polysaccharides as chitosan. On materials with specific spectral features that can be derived from studies of the bulk, discrimination of different phases can be possible, for instance, by exploring the dependence on temperature of such spectral features, related, e.g. to the amorphous or the crystalline state.<br/><br/>References.<br/>[1] Lewis, T. J. (1994). Nanometric dielectrics. <i>IEEE Transactions on Dielectrics and Electrical Insulation</i>, <i>1</i>(5), 812-825.<br/>[2] P.S. Crider, M.R. Majewski, J. Zhang, H. Oukris, N.E. Israeloff, “Local dielectric spectroscopy of polymer films,” Appl. Phys. Lett. 91, 013102 (2007).<br/>[3] M. Labardi, A. Bertolla, C. Sollogoub, R. Casalini, S. Capaccioli, “Lateral resolution of electrostatic force microscopy for mapping dielectric interfaces in ambient conditions,” Nanotechnology 31, 335710 (2020).<br/>[4] M. Labardi, M. Lucchesi, D. Prevosto, S. Capaccioli, “Broadband local dielectric spectroscopy,” Appl. Phys. Lett. 108, 182906 (2016).<br/><br/>Acknowledgements. Financial support from the Office of Naval Research Global (NICOP N62909-23-1-2003 research grant) is acknowledged.