In situ characterization on macroscale 3D spatial dispersion of MWCNTs in matrix and interfacial phases of quartz fibers/epoxy composites via fluorescence imaging

To effectively and simply characterize the macroscale dispersion of nanoparticles was vital for understanding the intrinsic connection between the properties and the structure of composites. In this study, fluorescent MWCNTs–FITC was successfully synthesized via grafting fluorescein isothiocyanate on the MWCNTs with protection of polyglycidyl methacrylate, which opened new avenues to in situ visualize the dispersion of carbon-based materials under confocal laser scanning microscopy. With the aid of this noninvasive method, macroscale 3D spatial dispersion of MWCNTs–FITC in both matrix and interfacial phases of quartz fibers/epoxy (QFs/EP) composites was quantitatively evaluated by integrating Morisita’s index, particle spacing probability density theory, 2D fractal dimension and Einstein’s Stokes theory. The results showed that the threshold for uniform dispersion of MWCNTs–FITC was 0.05 wt% due to the interactions of inter-particle van der Waals forces and physical entanglement. The highest particle spacing coefficient of MWCNTs–FITC ( $$\overline{x}/s$$ = 1.69) was achieved curing at 25 °C, which indicated that MWCNTs–FITC was well dispersed in matrix, while for the dispersion in QFs/EP interface, the optimal curing temperature was 40 °C where the actual average diffusion distance ( $$\overline{{l_{{\text{m}}} }}$$ ) was as high as 6.3 µm. The purpose of the established quantification method in this study was to provide viable opportunities and inspirations for quantitatively evaluating the dispersion of nanoparticles.