Oxidic 3d scaffold structures for wetting-assisted shaping and bonding of polymers
We will exploit wetting-assisted shaping and bonding based on controlled melt imbibition of polymers into porous oxidic 3d scaffolds for thermoplastic processing of intractable polymers as well as for adhesive bonding between polymers and metals/ceramics. As revealed by preliminary works, even melts of highly viscous, intractable polymers such as ultrahigh molecular mass PTFE infiltrate such 3d scaffolds driven by strong adhesion forces. Melt infiltration of an amount of PTFE dimensioned to completely fill the pore system into 3d scaffolds will yield hybrids that combine the advantages of PTFE (chemical stability, low surface energy) with advantages implemented by the 3d scaffold such as mechanical stability, shape persistence and scratch resistance even at elevated temperatures. We will check if even hybrids containing medium molar mass PTFE show this advantageous combination of properties. As use cases we will realize coatings of ultrahigh and medium molecular mass PTFE by wetting-assisted shaping using controlled porous glass as scaffold. As second use case, 3d scaffolds will be exploited as adhesion-mediating layers to bond PTFE and elastomer to ceramics and metals.To fully exploit 3d scaffolds for wetting-assisted shaping and bonding of polymers, predictive understanding of melt imbibition as the fundamental underlying physical process needs to be improved. To enable rational technical imbibition management, we will elucidate how cooperative percolation phenomena (imbibition front broadening, viscous fingering, avalanche-like imbibition front relaxations) as well as single-pore effects (slip, adsorption, capillary rise, precursor film formation, precursor film instabilities) influence imbibition. To meet these objectives, we will develop high-resolution X-ray microscopy (HR-XRM) at the spatial resolution limit of 50 nm as a non-destructive 3d imaging tool for the monitoring of imbibition. HR-XRM overcomes the limitations of destructive state-of-the-art 3d imaging methods such as FIB tomography. HR-XRM routines for studying hybrids with nanoscale feature sizes, for imaging imbibition fronts and for mappings of local filling levels in 3d scaffolds will be developed. We will test whether HR-XRM absorption contrast allows discrimination of filled and empty portions of the 3d scaffolds as different types of effective media even if the pores are smaller than the HR-XRM resolution limit. Moreover, correlative HR-XRM prior to and after infiltration, at different infiltration stages and after mechanical impact will be established, as well as routines for the correlation of HR-XRM data with percolation models. HR-XRM results will moreover be validated by correlation with optical interferometry and results from complementary destructive 3d imaging methods such as FIB tomography. The project will benefit from the complementary expertise of the PIs and from the HR-XRM expertise developed in the XRM center being established in the Wehrspohn group.