Study On Supramolecular Hierarchical Self-assembly Behavior Of Aromatic Oligoamides

Supramolecular hierarchical self-assembly is an effective way of constructing functional materials based on non-covalent bonds.The supramolecular hierarchical self-assembly in aqueous solution has great potential in constructing functional materials with the biological application but the existing related researches mainly focus on realizing primary self-assembled structures such as tubes through non-covalent bonds.However,little literature is reported on further organization of higher ordered structures through primary self-assemblies such as the formation of 2D lyotropic columnar phase or even a 3D columnar crystal phase by tubular self-assemblies.Based on this background,the pathway and kinetics of hierarchical self-assembly of aromatic oligoamides in aqueous solution as well as the two-dimensional and three-dimensional order of the forming 3D columnar crystal phase were studied here.The detailed contents and results are listed below:(1)The pathway and kinetics of hierarchical self-assembly of aromatic oligoamides in aqueous solution were studied at different scales using in-situ Small Angle X-ray Scattering,Cryo-TEM,etc.Aromatic oligoamides can self-assemble into hollow cylinders which further arrange into columnar phases in water.In-situ investigation suggests a multiple-step pathway of the supramolecular assembly via dispersed molecular aggregates followed by a less ordered intermediate phase before the columnar phase are formed.This part of the work provides in-situ evidence of the multi-step pathway in supramolecular hierarchical self-assembly process,which helps to understand how to construct high-order structures by supramolecular self-assembly.(2)The two-dimensional and three-dimensional order of the assembled structures by aromatic oligoamides at different concentration were studied by both Small Angle and Medium Angle X-ray Scattering as well as Cryo-TEM,etc.While highly ordered liquid crystal hexagonal columnar phase is found in a wide concentration range,the inter-columnar axial order shows obvious concentration dependence.Medium Angle X-ray Scattering on the highly oriented sample displays convolution of contribution from the column's shape and Bragg peaks which gradually evolves from form-factor like pattern to powder diffraction.Such transformation is attributed to the emergence of interlock between columns and the appearance of three-dimensional crystalline order in the columnar phase.This part of the work suggests the possibility to obtain directional 3D crystalline order in the lyotropic system through supramolecular assembly and helps to understand the process of the spontaneous formation of ordered structures by rigid rods.