Rational Synthesis of Large-Area Periodic Chemical Gradients for the Manipulation of Liquid Droplets and Gas Bubbles

Synthetic approaches based on the patterned deposition of volatile molecules from the vapor phase are used extensively in the creation of surface-chemical gradients; however, the ability to generate diffusion-controlled 1D and 2D gradients from multiple sources remains a challenge. The current work reports a one-step approach to the synthesis of continuous and periodic chemical gradients with simple and intricate geometries using multiple sources within custom reaction chambers. Specifically, this approach provides precise, simultaneous control over the physicochemical conditions (e.g., concentration, evaporation rate, and direction of diffusion flux of the chemical moieties) and the geometrical parameters (e.g., size, shape, and position) during surface functionalization, thus enabling materials with predictable surface-chemical gradients applicable to the manipulation and/or organization of liquid droplets and that can generate assemblies of functional solids (e.g., silver nanoparticles) that are transferrable via stamping. These surfaces can be useful to various fields, for example, molecular diagnostics and microfabrication. Furthermore, this work extends the application of these surfaces to the precise placement and manipulation of gas bubbles that can have potential use in, for example, controlling bubble nucleation in processes designed to manage heat transfer.