Highly porous nanoparticle layers from the gas phase - stabilization through mechanical compression to withstand capillary forces during imbibition

In order to expand the field of application of highly porous nanoparticle layers from the gas phase to liquid environments, the effect of mechanical compression on the structure and on the stability of the layers is investigated. Furthermore, the capillary rising process within the complex pore structure of the layers is determined with imbibition measurements. These analyses enable an approximation of the detaching forces on the nanoparticle layer and a predetermination of the layer stability during imbibition. For mechanical compression of the layers, a novel two-step layer transfer process is developed that applies a low pressure lamination step. The results show a shift of the pore size distribution to smaller pores and an increase of the amount of particle-particle contact points within the nanoparticle layer with an increasing lamination pressure. This significantly increases the resistance of the layer against elastic deformation. To analyze the influence of the mechanical compression on the stability of the layers during imbibition, the occurring forces on the nanoparticles were approximated with capillary rising experiments. The results demonstrate a deviation of the imbibition process from the classical capillary rising theory (Bell, Cameron, Lucas and Washburn). Therefore, a new capillary rising model is developed that is capable to predetermine the imbibition process into the complex pore structure of highly porous layers of aggregated particles. Measurements of the particle removal reveal that the occurring capillary forces play the major role for the layer stability while friction forces mainly lead to a removal of detached particles. The results demonstrate the possibility of mechanical compression to stabilize highly porous layers from the gas phase for applications in liquid environments.