Research Progress on Confined Assembly of Block Copolymers in China

Block copolymers (BCPs) are a kind of copolymers containing homopolymer blocks that are chemically bonded together. They can undergo microphase separation (i.e., self-assembly) to form well-defined nanostructures (e.g., spheres, cylinders, vesicles, etc.), since their non-compatible blocks are covalently bonded, limiting the macrophase separation. The self-assembled nanostructures possess great potential for various applications in the fields of nanolithography, photonic crystal, data storage, drug delivery and controlled release, diagnostics and others. When imposing spatial constrains on BCPs, where the confining volume has at least one dimension comparable to the period (L-0) of the bulk copolymer phase, a large variety of novel BCP assemblies (e.g., helix, patchy, staking, and other complex structures) can be generated under confined space due to the symmetry breaking, interfacial interactions, structural frustration and confinement-induced entropy loss. Recently, the fabrication of confined assemblies of BCPs and investigation of the BCPs assembly in different confined geometries from experimental and theoretical simulation points have been a topic of great interest in the scientific communities in China. This review aims to summarize some research progress on confined assembly of BCPs in China, including the general concept of confined assembly of BCPs, experimental and simulative investigation of confined assemblies of BCPs through varying factors under different dimensions, and potential applications of confined BCP assemblies. Factors affecting the confined assembly of BCPs, including the degree of confinement (D/L-0, D is the size of confinement space), interfacial interaction (selective or neutral interface), geometry of the confining space, block ratio, topology structure of the BCPs, and others, are also discussed. Moreover, compared with one dimension (1D) and 2D confinement, 3D confinement provides the most tightly confining geometry (i.e., highest confinement degree) and presents an enclosed surface around the BCPs, which may facilitate to easily manipulate new morphologies of the confined assembles and will attract more attention on this topic. To push forward the studies of the confined assembly of BCPs, the conjunction study of simulation and experiment is necessary for promoting the deep and systematic understanding of the phase behavior of BCPs under confinement, and sufficient attention should be paid to the studies of geometrical confinement on properties of the self-assembled polymeric materials.