Over millions of years of evolution, soil animals have developed surface cuticle structures that help avoid soil adhesion at varying moisture levels. [1] In contrast, in materials science, the technical methods that are well known to reduce adhesion with low surface energy textured surfaces in air [2] and hydrophilic-gel coatings in water [3] perform less efficiently in a changing environment. Inspired by biology and natural materials, the low-adhesion principles occurring in nature have led us to the fabrication of a biomimetic nanostructured composite coating consisting of surface-grafted hydrophobic nanoparticles embedded into a hydrophilic polyethylene oxide molecular brush. This responsive coating undergoes reconstruction from the morphology of rigid hydrophobic asperities, which hide the collapsed polymer brush in air, to the morphology of a hydrophilic brush-like layer engulfing the nanoparticles underwater. Due to this reconstruction, the coating demonstrates low adhesion to hydrophilic, hydrophobic, and amphiphilic materials, in both dry and wet environments. This finding is useful for the development of materials with low-adhesive surfaces, to be used in various applications where adsorption of contaminants or binding to other materials must be reduced.
Adhesion [4] arises from the balance of attractive and repulsive forces acting between contacting surfaces. In most cases, the adhesion phenomenon takes place in two major surrounding environments: air with variable humidity (vapors) and liquid water with various solutes (solutions). Both media may carry polar, nonpolar, and amphiphilic molecules and particles at variable concentrations. For the simplified case of a vacuum, adhesion depends on two major contributions: van der Waals and Coulomb interactions. For water vapor, capillary condensation on hydrophilic surfaces usually contributes to enhanced adhesion. In solutions, the situation is much more complex, and many mechanisms strongly affect the variation in adhesion forces from attractive to repulsive.
A regime that allows near exclusion of adhesion between surfaces and potential contaminants plays a key role in microelectromechanical systems (MEMS), [4] self-cleaning coatings in air, [2] and antifouling coatings in solutions. [3a,6] Similar to many living organisms, engineered devices often have to survive and operate in everchanging environments, where cyclical