Increased thickness uniformity of large-area nanofibrous layers by electrodynamic spinning

This paper studies the causes of thickness inhomogeneities in continuously deposited large-area nanofibrous layers, introduces a new method of their rapid analysis and suggests technical measures to ensure greater thickness uniformity of produced nanofibrous layers. The thickness uniformity of nanofibrous layers over large surface areas and its testing have recently appeared as very important issues following the scale up of the production of nanofibrous layers from laboratory to industrial levels, i.e. from point-to-plate arrangement to roll-to-roll processing. The basic electrostatic spinning method produces layers with thickness distribution corresponding to the bivariate Gaussian distribution. However, increasing production and scaling-up processes often results in variations in the thickness of deposited nanofibrous layers even up to the order of tens of percent. But for most applications, inhomogeneities in the thickness are a critical and even limiting factor. Our results show that by using the method of electrodynamic spinning with moving electrodes, we were able to achieve 30% greater thickness uniformity within the observed area (100 x 26) cm2 than with the electrostatic method. Electrodynamic spinning can therefore be considered a very promising technology for the industrial production. We also demonstrated the digital image analysis as a new and efficient tool to optically determine the thickness uniformity of electrospun layers by analyzing the intensity of transmitted light through the layer on 26 x 22 cm2 sample area. This unique approach brings benefits of non-destructive, rapid and reproducible evaluation of the thickness uniformity of the nanofibrous layers over decimeter-square surface areas at the same time.