Surfaces with patterned wettability contrast are important in industrial applications such as heat transfer, water collection, and particle separation. Traditional methods of fabricating such surfaces rely on microfabrication technologies, which are only applicable to certain substrates and are difficult to scale up and implement on curved surfaces. By taking advantage of a mechanical instability on a polyurethane elastomer film, we show that wettability patterns on both flat and curved surfaces can be generated spontaneously via a simple dip coating process. Variations in dipping time, sample prestress, and chemical treatment enable independent control of domain size (from about 100 to 500 μm), morphology, and wettability contrast, respectively. We characterize the wettability contrast using local surface energy measurements via the sessile droplet technique and tensiometry.wettability contrast | creasing instability | domain size | morphology | curved surfaces S urfaces that juxtapose local hydrophilic areas with hydrophobic areas show superior performance compared with surfaces with homogeneous wettability in many industrial applications including heat transfer (1), water collecting (2-6), particle separation (7), and microfluidics (8). For instance, developing enhanced water-collecting efficiency has been inspired by the Namib desert beetle, which was reported (2) to have hydrophilic bumps on an overall wax-covered hydrophobic surface. Although the hydrophilic bumps reduce the nucleation/coalescence energy of microdroplets, the overall hydrophobic character of the surface facilitates the spontaneous shedding of water droplets when they grow beyond a certain size.To achieve surfaces with wettability patterning, traditional fabrication methods such as photolithography and soft lithography have been used. However, these methods are generally not cost-effective, not readily scaled up, require multiple process steps, and are difficult to implement on curved surfaces (3, 9). Recently, mechanical instabilities have been explored as a facile self-assembly approach to endow surfaces with superhydrophobicity (10-12), superhydrophilicity (13), or anisotropic wettability (14). Although mechanical self-assembly provides a low cost route for spontaneous generation of surface patterns, explorations to date have been focused on introducing surface roughness via wrinkling and crumpling instabilities. Here we show that surfaces can be spontaneously patterned with chemical patches with small changes in surface roughness by harnessing a reversible creasing instability (15-17).A creasing instability develops when a soft polymer network is placed under mechanical compression beyond a certain critical strain, at which point sharp folds spontaneously develop and grow on the deformable free surfaces (18). This process has been linked to the morphology development of the brain (19,20), electric breakdown of dielectric elastomers (21), and has also been harnessed to prepare switchable surfaces actuated by temperature (22) or electric ...