Smart Surfaces with Tunable Wettability

Modification of surface wettability (ranging from complete wetting to complete non-wetting) of various surfaces is often required in many applications. Conventionally, it is done using a coating of suitable materials as per the requirement. In this approach, the old coating needs to be replaced every time by a new appropriate one. Alternatively, smart responsive surfaces can show tunable wettability with external stimulus. Electric field, temperature, light, pH, mechanical strain, etc. can be effectively used as external stimuli, and a suitable coating can be incorporated, which responses to the respective stimulus. These surfaces can be used to tune the surface wettability to any extent based on the magnitude of the stimulus. The primary role of the external stimulus is to vary the liquid-solid interfacial energy, which subsequently changes the surface wettability. The biggest advantage of this approach is that the surface wettability can be reversibly tuned. Each of the techniques mentioned above has many advantages along with certain limitations, and the combination of advantages and limitations helps users to choose the right technique for their work. Many recent studies have used this approach to quantify the tuning of the surface wettability and have also demonstrated its potential in various applications

Electric Field Driven Reversible Spinodal Dewetting of Thin Liquid Films on Slippery Surfaces

Abstract The stability of thin liquid films on a surface depends on the excess free energy of the system involving various short‐range and long‐range interactions. When forced to wet an unfavorable surface, thin liquid films dewet into multiple small‐sized droplets via spinodal, homogeneous, or heterogeneous nucleation process. However, if the total excess free energy of the system can be manipulated using external stimuli, for example, electric field, temperature, or light, one can control the stability of thin liquid films on demand. Here the electric‐field induced reversible dewetting and rewetting of thin liquid films underneath aqueous drops on slippery surfaces is studied. Upon applying voltage, hundreds of nanometer thick stable liquid films dewet in a manner identical to the spinodal dewetting of few nanometer‐thick liquid films following the linear stability analysis. Upon removing the applied voltage, the dewetted droplets spread, coalesce with neighboring ones, and form a uniform film again, albeit taking significantly longer times. The characteristic features defined via spatial and temporal evolution of the dewetting and rewetting processes are present over multiple cycles suggesting the complete reversibility of the process

Waldschadensinventur Baden-Wuerttemberg 1983 mit Infrarot-Farbluftbildern Ergebnisse und Erfahrungen

Available from Forstliche Versuchs- und Forschungsanstalt Baden-Wuerttemberg, Freiburg im Breisgau (DE) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Surface wettability of an atomically heterogeneous system and the resulting intermolecular forces

We present the effect of 0.5 keV Ar+ beam irradiation on the wetting properties of metallic thin films. Observations reveal a transition from hydrophilic to hydrophobic nature at higher beam fluences which can be attributed to a reduction in net surface free energy. In this low-energy regime, ion beams do not induce significant surface roughness and chemical heterogeneity. However, they cause implantation of atomic impurities in the near surface region of the target and thus form a heterogeneous system at atomic length scales. Interestingly, the presence of implanted Ar atoms in the near surface region modifies the dispersive intermolecular interaction near the surface but induces no chemical modification due to their inert nature. On this basis, we have developed a theoretical model consistent with the experimental observations that reproduces the effective Hamaker constant with a reasonable accuracy