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Nano fibrous materials - structure, design and application

Final Report Summary - NANOFIB (Nano fibrous materials - structure, design and application)

The project NANOFIB focused on the understanding of the electrospinning process, the creation of polymer fibres of nanometer diameters from liquid solution filaments that get stretched and dry in a strong electric field. For this the project investigated in detail the breaking dynamics of liquid filaments, in particular what causes a sufficient stabilisation of such a complex solution jet, so that it does not simply disintegrate into droplets as, for example, water would do. Throughout the project several mechanisms have been identified, just to name a few: viscous stresses, viscoelasticity and the relaxation time and extensibility of a polymer, but also the interfacial properties of the liquid nanofilaments or the embedding of nanoparticles.
The investigation of these phenomena required and has led to the discovery and development of several novel experimental techniques: a technical platform for the investigation of ultra-fast thinning and breaking dynamics of filaments at the boundaries of the resolution of optical microscopy, or a method to measure how far a polymer molecules will stretch in the thin filament. Amongst others this led to the fastest measurement of a polymer relaxation reported so far. Only with this precise experimentation was it possible, in combination with numerical simulations of the filament dynamics, to development new scaling laws that allow predicting the occurrence and production of smooth polymeric nanofilaments.
The outcome of this project in terms of actual applications that resulted from the experimental and theoretical investigations are numerous. So was it possible for the first time to electrospin crosslinking hydrogels into nanofibres at length scales that would make them suitable for tissue engineering. Furthermore, we have created electrospun nanorods with Janus-like metallic coatings, that exhibit sideways self-propulsion in reactive solutions. We have shown that the alignment of nanofibres can lead to affordable superhydrophobic membranes for oil/water separations with extremely high water retentions properties.
Apart from the direct applications to electrospinning, the project results have a much broader application: the six-dimensional parameter space for free-surface flows of complex fluids has already stirred interest from food industries to ink-jet printing to apply this concept to general dispensing operations. As another example, the investigations of nanoliter filaments of mucus of the carnivorous sundew plant drosera helped to unravel the secrets of its insect catching mechanism.