Transfer of highly porous nanoparticle layers to various substrates through mechanical compression

A new two-step layer transfer process is introduced that is capable of fabricating mechanically stabilized highly porous nanoparticle layers on various substrates. In a first step titanium dioxide nanoparticles were synthesized with Flame-Spray-Pyrolysis and accumulated on a filter paper in the gas phase. In a second step this highly porous filter cake is subsequently transferred to a final substrate via low pressure lamination at room temperature. This leads to mechanical restructuring and stabilization of the porous layer. Pore size analysis indicates homogenization of the layers through rearrangement of the aggregates inside the layers that increases with applied pressure. Additionally, the Young's moduli of the layers were quantified through Colloidal-Probe-Technique indentation measurements with an Atomic-Force-Microscope. The highest lamination pressure of 2.5 MPa resulted in triplication of the Young's modulus. The results show that our novel two-step layer transfer process leads to mechanically stabilized layers that preserve their high porosity. Through the decoupling of the high temperature nanoparticle synthesis and the final substrate the process also enables the possibility to apply temperature sensitive substrates such as polypropylene foil.