Carbon-deposited hexagonal boron nitride filler orientational state evaluation in polyrotaxane composites via electron spin resonance

Electric-field-applied filler orientation has been investigated as a strategy for developing flexible composite materials with enhanced thermal conductivity. However, evaluating orientational states remains challenging. In this study, angle-dependent electron spin resonance (ESR) spectroscopy was used to analyze the orientational state of carbon-deposited hexagonal boron nitride (hBN) fillers in polyrotaxane composites. Directional ordering and orientation direction were assessed from g -value variations. This approach enabled the analysis of both the hBN particles and their carbon-coating layers, which are difficult to characterize using conventional techniques. These results demonstrate that ESR provides a method for characterizing the orientational state of anisotropic fillers in composites.