Enhancement of light scattering and photoluminescence in electrospun polymer nanofibers

Poly(methyl methacrylate) nanofibers with desired fiber diameters that ranged from 336 to 896 nm were electrospun as light scattering and propagation materials. The light scattering behavior of these samples as a function of the fiber diameter and fiber deposition thickness was examined by UV-vis spectrophotometry, which revealed the scattering bands in the absorption spectra. The scattering bands of these nanofibers were linearly proportional to the fiber diameter, which shows good agreement with a scattering model based on the Mie theory. The light scattering and prolonged light path lengths in the nanofiber scaffolds were monitored and quantified by the photoluminescence of a fluorescent dye, Coumarin 6, which was preloaded into the polymer nanofibers. The photoluminescence after proper normalization showed a second-order dependence on the dye loading per unit area, which is significantly different from the spin-coated thin-film samples following a first-order relationship. Nonlinear photoluminescence enhancements indicated prolonged light path lengths and multiple light absorptions within the fiber scaffolds as a result of light scattering. Even with relatively broad scattering band widths, the light scattering and photoluminescence of the electrospun nanofibers exhibited considerable wavelength selectivity, especially as the scattering bands overlapped with the excitation wavelengths of the fluorescence reagent.