Macroscopic Self‐Assembly Realized by Polymer Brush─A Thickness‐Dependent Rule for Rapid Wet Adhesion

Macroscopic self‐assembly of µm‐to‐mm components (dimension from 100 µm to millimeters), is meaningful to realize the concept of “self‐assembly at all scales” and to understand interfacial phenomena such as adhesion, self‐healing, and adsorption. However, self‐assembly at this length scale is different from molecular self‐assembly due to limited collision chances and binding capacity between components. Long‐time contact between components is requisite to realize µm‐to‐mm assembly. Even though the recent idea of adding a compliant coating to enhance the molecular binding capacity is effective for such self‐assembly, a trade‐off between coating thickness (several micrometers) and assembly efficiency exists. Here a new compliant coating of surface‐initiated polymer brush to address the above paradox by both realizing fast assembly and reducing the coating thickness to ≈40 nm by two magnitudes is demonstrated. Millimeter‐sized quartz cubes are used as components and grafted with oppositely charged polyelectrolyte brushes, enabling assembly in water by electrostatic attraction and disassembly in NaCl solutions. A rule of thickness‐dependent assembly chance is obtained and understood by in situ force measurements and a multivalent theory. The polymer brush strategy pushes the thickness limit of requisite compliant coating to the nanoscale for fast µm‐to‐mm self‐assembly and provides insights into rapid wet adhesion. Surface‐initiated (SI) polyelectrolyte brush is used as a compliant coating to promote interfacial binding and realize fast self‐assembly of µm‐to‐mm hard materials (quartz) in seconds. Owing to the flexibility of the SI brush, the lower thickness limit of requisite compliant coatings is reduced by two magnitudes from 3–4 µm to 40 nm, which is meaningful for fast wet adhesion.