Janus Polymer Single Crystal Nanosheet via Evaporative Crystallization.

We show that liquid/liquid interface can guide polymer chain folding during crystallization. Evaporation-induced crystallization of telechelic dicarboxyl end-functionalized poly(ε-caprolactone) (COOH-PCL-COOH) at a water/pentyl acetate interface produced millimeter-scale, uniform polymer single crystal (PSC) films. Due to the asymmetric nature at the interface, the PSC nanosheets exhibited a Janus structure: the two surfaces of the crystal showed distinct water contact angle, which are quantitatively confirmed by in situ nanocondensation using environmental scanning electron microscopy (ESEM).