An Unconventional Route to Hierarchically Ordered Block Copolymers on a Gradient Patterned Surface through Controlled Evaporative Self-Assembly

摘要

Pinned drying droplets that contain nonvolatile solutes (e.g., polymers, proteins, DNA, microspheres, nanoparticles, etc.) often give dissipative ring-like deposits (e.g., "coffee rings"). Structural evolution of these kinetically trapped surface patterns is primarily governed by the repetitive stick-slip (i.e., pinning-depinning) motion of the three-phase contact line of the drying droplet. However, the formed structures are often stochastically distributed rather than uniform final deposits, largely because of the lack of control over the stick-slip motion and the presence of temperature-gradient-induced convective flux. Therefore, a considerable challenge is the control of drying dynamics and creation of surface patterns of high regularity in a simple and cost-effective manner, thus eliminating the need for external-field and lithography techniques. In this context, a few elegant preparative approaches have emerged, which give highly ordered structures and assemblies by enforcing the drying droplet to evaporate in restricted environments, including "curve-on-flat" geometry, two-plate geometry, and cylindrical tube. The use of these confined geometries provides an effective way to utilize the pinning-depinning process and minimize the possible convective instabilities, which in turn promotes the formation of uniform and well-controlled structures.