Visualizing Assembly Dynamics of All-Liquid 3D Architectures

To better exploit all-liquid 3D architectures, it is essential to understand dynamic processes that occur during printing one liquid in a second immiscible liquid. Here, the interfacial assembly and transition of 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (H₆TPPS) over time provides an opportunity to monitor the interfacial behavior of nanoparticle surfactants (NPSs) during all-liquid printing. The formation of J-aggregates of H₄TPPS²⁻ at the interface and the interfacial conversion of the J-aggregates of H₄TPPS²⁻ to H-aggregates of H₂TPPS⁴⁻ is demonstrated by interfacial rheology and in situ atomic force microscopy. Equally important are the chromogenic changes that are characteristic of the state of aggregation, where J-aggregates are green in color and H-aggregates are red in color. In all-liquid 3D printed structures, the conversion in the aggregate state with time is reflected in a spatially varying change in the color, providing a simple, direct means of assessing the aggregation state of the molecules and the mechanical properties of the assemblies, linking a macroscopic observable (color) to mechanical properties.