Two-dimensional self-assembly of amphiphilic porphyrins on a dynamically shrinking droplet surface.

Developing a new field of molecular self-assembly in the sub-micrometer regime-with precision as high as that used to make discrete nano-sized molecular architectures through molecular design-is a major challenge for supramolecular chemistry. At present, however, there is no effective strategy for controlling the assembling molecules when their quantity is greater than one thousand. Herein, we propose a potential solution by exploiting a novel supramolecular system in conjunction with dynamically shrinking oil droplets, enabling more than a thousand component molecules to organize simultaneously into the form of sub-micrometer-scale ring structures. In our developed system, amphiphilic porphyrins, having potential two-dimensional assembling ability, were compartmentalized into droplets with narrow distributions and molecular numbers. These droplets were subsequently transformed into discrete ring-like structures during the process of solvent removal from the inner organic layer, i.e., shrinking the droplets. Unique self-assembled structures, which are not accessible through conventional supramolecular strategies, can be selectively created depending on the initial stage of the droplet.

Hierarchical supramolecular spinning of nanofibers in a microfluidic channel: tuning nanostructures at a dynamic interface.

One of the fundamental problems in supramolecular chemistry, as well as in material sciences, is how to control the self-assembly of polymers on the nanometer scale and how to spontaneously organize them towards the macroscopic scale. To overcome this problem, inspired by the self-assembly systems in nature, which feature the dynamically controlled self-assembly of biopolymers, we have previously proposed a self-assembly system that uses a dynamic liquid/liquid interface with dimensions in the micrometer regime, thereby allowing polymers to self-assemble under precisely controlled nonequilibrium conditions. Herein, we further extend this system to the creation of hierarchical self-assembled architectures of polysaccharides. A natural polysaccharide, ß-1,3-glucan (SPG), and water were injected into opposite "legs" of microfluidic devices that had a Y-shape junction, so that two solvents would gradually mix in the down stem, thereby causing SPG to spontaneously self-assemble along the flow in a head-to-tail fashion, mainly through hydrophobic interactions. In the initial stage, several SPG nanofibers would self-assemble at the Y-junction owing to the shearing force, thereby creating oligomers with a three-way junction point. This unique structure, which could not be created through conventional mixing procedures, has a divergent self-assembly capability. The dynamic flow allows the oligomers to interact continuously with SPG nanofibers that are fed into the Y-junction, thus amplifying the nanostructure along the flow to form SPG networks. Consequently, we were able to create stable, centimeter-length macroscopic polysaccharide strands under the selected flow conditions, which implies that SPG nanofibers were assembled hierarchically in a supramolecular fashion in the dynamic flow. Microscopic observations, including SEM and AFM analysis, revealed the existence of clear hierarchical structures inside the obtained strand. The network structures self-assembled to form sub-micrometer-sized fibers. The long fibers further entangled with each other to give stable micrometer-sized fibers, which finally assembled to form the macroscopic strands, in which the final stabilities in the macroscopic regime were governed by that of the network structures in the nanometer regime. Thus, we have exploited this new supramolecular system to create hierarchical polymeric architectures under precisely controlled flow conditions, by combining the conventional supramolecular strategy with microfluidic science.