Homogeneity of Needleless Electrospun Nanofiber Mats
Nanofiber mats can be electrospun by different techniques, usually subdivided into needle-based and needleless. The latter allow for producing large-area nanofiber mats, e.g., with a width of 50 cm and lengths of several meters, if electrospinning proceeds for several hours, depending on the required thickness. Even spinning smaller samples, however, raises the question of homogeneity, especially if defined mechanical properties or a defined thickness is required, e.g., for filtration purposes. Very often, only the inner parts of such electrospun nanofiber mats are used to avoid too high variation of the nanofiber mat thickness. For this study, we used wire-based electrospinning to prepare nanofiber mats with slightly varying spinning parameters. We report investigations of the thickness and mass per unit area, measured on different positions of needleless electrospun nanofiber mats. Martindale abrasion tests on different positions are added as a measure of the mechanical properties. All nanofiber mats show unexpectedly strong variations of thickness, mass per unit area, and porosity, as calculated from the apparent density of the membranes. The thickness especially varied by nearly one order of magnitude within one sample, while the apparent density, as the most uniform parameter, still showed variations by more than a factor of two within one sample. This shows that even for apparently highly homogeneous areas of such nanofiber mats, variations cannot be neglected for all potential applications.