Dynamic Reversible Tuning of the Geometry of Responsive Hybrid Nanostructured Surfaces

Adaptive behavior, intrinsic to natural systems, is becoming a key requirement for advanced artificial materials and devices, presenting a real scientific and engineering challenge. Here we describe two original responsive hybrid architectures, which are based on integrating high-aspect-ratio silicon nanocolumns either substrate-attached or free-standing - with a hydrogel layer that acts as an actuator upon exposure to humidity. The resulting response of the hybrid structures is a dramatic reversible transition of the surface microtopography: the heights of the exposed nanocolumns change from 8 to 0 m, and their tilt - from 15˚ to 90˚, in the two designs, respectively. Such unprecedented dynamic control over the surface geometry at the submicron scale allows the tuning of various nanostructure-dependent interfacial properties. In particular, we demonstrate reversible switching of the surface wetting behavior and controlled reversible micropattern formation. These "smart" surfaces may, therefore, find exciting applications as artificial responsive materials.