Beta-Lactoglobulin for Water-Based and Tunable Nanostructure Templating of Printed Titania Thin Films: The Influence of pH Value and Protein Concentration

An environmentally friendly as well as scalable synthesis route of nanostructured titania thin films is of interest for many state-of-the-art devices, from solar cells to battery materials. Beta-lactoglobulin (ß-lg) enables water-based and tunable titania thin film templating, allowing for different domain sizes, porosities, and morphologies. When printed with a slot-die coater, the titania films can be tailored to specific applications with simple changes to the solution chemistry. Films printed at acidic pH conditions form significantly different final morphologies than films printed at a neutral pH value. The protein concentration plays a more limited role in the final nanostructure. With in situ grazing incidence small-angle/wide-angle X-ray scattering (GISAXS/GIWAXS), the structure formation is followed with an excellent time resolution during the printing process. From the GISAXS measurements, the size evolution of the titania clusters is understood, showing significant differences for different pH values. Crystal phases and corresponding crystal orientations are investigated with GIWAXS. The combination of a water-based titania synthesis with the scalable film deposition via slot die coating makes the presented results interesting for potential environmentally friendly mass production of nanostructured titania films.