Diphenylalanine Deposition by Dip-Coating from Acidic Solutions: Fibers and Closed Homogeneous Films

A simple but precisely controllable strategy by molecular assembly that enables the construction of biomaterials is always in the development. Dip-coating deposition of diphenylalanine (FF) onto planar solid substrates from aqueous acidic (acetic, propanoic, formic, and HCl) solutions is studied as a function of the process control parameters (deposition speed, initial concentration of FF and acids, and external gas flow). The results are studied by optical microscopy, AFM, and ellipsometry. For low acidity and low FF concentrations, FF forms microfibers, nanofibers, or stripes of fiber aggregates. For higher acidity and FF concentrations, closed films of FF of remarkably smooth surfaces are found. The thickness of these films can be well-controlled by the FF concentration and the deposition speed and explained by the evaporation regime. These unusual results provide new possibilities to fabricate more abundant structures by a simple strategy and develop a candidate for biological membrane areas.