Humidity Responsive Asymmetric Free-Standing Multilayered Film

A humido-responsive free-standing film has been created using layer-by-layer assembly technique. Polyethylenimine(PEI) at high was assembled with poly(acrylic acid) (PAA) at low pH on a Teflon substrate to yield a micro-nanostructured surface that can be made superhydrophobic after being coated with a low surface energy compound. The resulting asymmetric freestanding film with one surface being superhydrophobic while the Other is hydrophilic after detachment from the substrate can undergo reversible bending/unbending shape transitions when the environmental humidity is changed. The bending, unbending movement of the free-standing film can be ascribed to the different responses of these two surfaces to humidity.