Surface Reconstruction in Hierarchically Organized Strutures Composed of Block Copolymers Crafted from Controlled Evaporative Self-Assembly

摘要

Pinned drying droplets containing nonvolatile solutes (e.g., polymers, viruses, DNAs, microspheres, nanoparticles, carbon nanotubes, etc.) yield intriguing one- or two-dimensional patterns (e.g., “coffee rings”, fingering instabilities, cellular structures, etc.) after complete evaporation of solvent. These patterns, however, often lack the regularity required for many technological applications. To date, there have been a few impressive studies of the exploitation of evaporation to form well-ordered structures rapidly and cheaply over large areas by deliberately controlling the evaporation process. Among them, controlled evaporative self assembly in a restricted geometry has been shown as a simple, rational preparation route for the creation of microscopic structures having high fidelity and regularity. Block copolymers composed of two or more chemically different blocks that are covalently linked are thermodynamically driven to self-assemble into various ordered structures including spheres, cylinders, and lamellae, depending on the volume fraction of the blocks. This self-assembly process occurs to reduce the interfacial energy between immiscible blocks and to maximize the conformational entropy of chains. The size of the structures governed by the molecular weight of the polymer is typically on the scale of 10 to 100 nm. As such, self-assembly of block copolymers offers a facile route to nanofabrication with an areal density of 1013 nanostructures per square inch for critical application in areas such as nanodevices, biosensor arrays, and nanotechnology.