Spectroscopic investigation of highly-scattering nanofiber mats during drying and film formation

Electrospun nanofiber mats show a very high surface-to-volume ratio as well as good mechanical properties and are thus typically used as filters or wound dressings, for drug delivery or as catalysts. Their optical properties, however, are only scarcely investigated. Due to the fine fibers with typical diameters of a few hundred nanometers, they tend to scattering visible light strongly. When wetted, however, they can become nearly invisible due to index-matching with the solvent and benefiting from the low thickness of the mats of usually only few microns. Here we report on polyacrylonitrile nanofiber mats, electrospun solely or blended with biopolymers, ceramics and other materials to modify their morphological and optical properties. Spectroscopic investigations of wetted nanofiber mats revealed different drying processes for different nanofiber morphologies and materials. On the other hand, some nanofiber mats were dissolved and the nano-mat forming process was evaluated spectroscopically, underlining the significant difference in the optical properties of nanofiber mats and nano-membranes of identical areal weights. With that we show the capability of the nanofiber mats for reversible transmission as well as permanent transmission tuning.