Size Dispersion of the Filler Particles and Its Consequences on the Light-Extinction Properties of TiO2/PET Nanocomposite Fibers

Titanium dioxide (TiO₂) nanoparticles have been extensively used to modify the optical properties of various types of materials. In particular, they have been intensively loaded onto polymer fibers to quench the light reflection. In situ polymerization and online addition are two common strategies for fabricating TiO₂-loaded polymer nanocomposite fibers. The former does not require separate preparation of masterbatches as the latter does and therefore has its advantages in terms of decreasing the fabrication steps and economic costs. Moreover, it has been found that in situ-polymerized TiO₂-loaded polymer nanocomposite fibers (e.g., TiO₂/poly(ethylene terephthalate) fibers) usually have enhanced light-extinction properties over those prepared by the online addition process. Intuitively, there should be a difference in the filler particle dispersion for the two fabrication processes. This hypothesis has not yet been tackled due to the technical difficulty in acquiring the three-dimensional (3D) filler morphology inside the fiber matrix. In this paper, we report a study using the powerful focused ion beam-scanning electron microscopy (FIB-SEM) with a resolution of 20 nm to directly acquire the 3D microstructure of TiO₂/poly(ethylene terephthalate) nanocomposite (TiO₂/PET) fibers. This microscopy technique allows us to characterize the particle size statistics and the dispersion inside TiO₂/PET fibers. We have found that the particle size of TiO₂ inside the fiber matrix can be well modeled by Weibull statistics. Surprisingly, we find that TiO₂ nanoparticles form more significant agglomeration in the in situ-polymerized TiO₂/PET fibers. This observation is contrary to our common understanding of the two fabrication processes. Namely, slightly altering the particle dispersion with increased TiO₂ filler size helps improve the light-extinction properties. The slightly increased filler size may have altered the Mie scattering between the nanoparticles and the incident visible light, leading to enhanced light-extinction properties of in situ-polymerized TiO₂/PET nanocomposite fibers.