In Situ Wetting State Transition on Micro- and Nanostructured Surfaces at High Temperature

We studied the in situ transition of the droplets' wetting state on the heated solid surfaces. The wetting behaviors of four micro- and nanostructured surfaces with different chemical components were studied. These parameters included the maximum contact areas (MCA), the maximum evaporation areas (MEA) and the wetting transition temperature (T(trans)). The reduction in MEAs has a specific transition process from wetting (Wenzel state) or partial wetting (Wenzel-Cassie intermediate state) to nonwetting (Cassie State) as the surface temperature rises. When the MEAs drop to zero at a critical temperature (T(trans)), the droplets rebound from the heated surfaces to complete the wetting transition process. The chemical compounds and the surfaces' rough structure play an important role in the droplets' wetting transition behavior. Before FAS-modification, microstructures can increase the MCAs, MEAs, and T(trans). However, the microstructures are less effective at increasing the MEAs and T(trans) than changes to nanostructures. After FAS-modification, both the nano- and microstructures reduce the T(trans). On the FAS-MNSi surfaces, the MEAs are always zero--the droplets rebounded at room temperature, and the wetting transition did occur. We propose two high-temperature mechanisms to explain these transition phenomena.