Curvature-induced 45°-Tilted long-range order in constrained crystallization of Poly(1-butene)

Abstract

Curvature fundamentally alters self-assembly principles in Euclidean space, enabling the formation of unique and more complex structures. The curvature-induced self-assembly of molecular chains under confinement generates novel long-range nanostructures, distinct from the micron-scale spherulites formed in bulk free crystallization. However, few reports have focused on investigating the effect of symmetry on by crystallizing molecular chains at the curved surfaces under nano-confinement, in particular the incompatibility of traditional crystal translational symmetry and curved surface geometry. Here, using poly(1-butene) with 3₁- or 11₃-helical chains as a model system, we investigate the impact of chain and unit cell symmetry on curvature-assisted self-assembled nanostructures in cylindrical confinement. The curvature-assisted self-assembled polymer nanostructures have been prepared by infiltrating polymer melts to nanoporous alumina. Two types of ordered nanostructures of poly(1-butene) have been identified via two-dimensional wide-angle X-ray diffraction experiments: trigonal and tetragonal. On one hand, we found that the long-range ordered 45°-tilted tetragonal nanostructures along the cylinder-axis self-assembled with 11₃ helices in nano-curved spatial constraints. This 45°-tilted crystals are most likely to be epitaxially grown from the a∗-axis crystal (parent crystal) in poly(1-butene). On the other hand, there is no crystal branching for trigonal nanostructure self-assembled with 3₁ helices under cylindrical confinement. In this case, the a∗-axis of the [001] zone trigonal crystals of poly(1-butene) are consistent with rod-long axis. Our research demonstrates that chain self-assembly in geometrically confined space is an effective method to generate novel long-range ordered polymer nanostructures. The topological constraints imposed by geometric surfaces contribute to the formation of specific long-range ordered nanostructures of polymers, which are closely related to the symmetry of the chains and unit cells in the polymer crystal structure.