Preparation of Patterned Ultrathin Polymer Films.

Thoughpatterned ultrathin polymer films (<100 nm) are of greatimportance in the fields of sensors and nanoelectronic devices, thefabrication of patterned ultrathin polymer films remains a great challenge.Herein, patterned ultrathin polymer films are fabricated facilelyon hydrophobic substrates with different hydrophilic outline patternsby the pinning of three-phase contact lines of polymer solution onthe hydrophilic outlines. This method is universal for most of thewater-soluble polymers, and poly(vinyl alcohol) (PVA) has been selectedas a model polymer due to its biocompatibility and good film-formingproperty. The results indicate that the morphologies of ultrathinpolymer films can be precisely adjusted by the size of the hydrophilicoutline pattern. Specifically, patterned hydrophilic outlines withsizes of 100, 60, and 40 μm lead to the formation of concave-shapedultrathin PVA films, whereas uniform ultrathin PVA films are formedon 20 and 10 μm patterned substrates. The controllabilitiesof morphologies can be interpreted through the influences of the sliplength and coffee ring effect. Theoretical analysis shows that whenthe size of the hydrophilic outline patterns is smaller than a criticalvalue, the coffee ring effect disappears and uniform patterned ultrathinpolymer films can be formed for all polymer concentrations. Theseresults provide an effective methodology for the fabrication of patternedultrathin polymer films and enhance the understanding of the coffeering effect. [ABSTRACT FROM AUTHOR]