Light-reducible dissipative nanostructures formed at the solid-liquid interface.

Dissipative structures are macroscopic or even larger ordered structures that emerge under conditions far from thermodynamic equilibrium. In contrast, molecular self-assembly has been investigated near at the thermodynamic equilibrium, which provides basically smaller, nano-to-micron sized structures. In terms of the formation principles, there exists an essential gap between the dissipative structures and molecular self-assemblies. To fill this gap, molecular self-assembly of light-reducible organic-inorganic ion pairs was investigated under far-from-equilibrium conditions. When solid films of tetraalkylammonium hexafluorophosphate were immersed in aqueous Au(OH)4(-) and immediately photoirradiated, gold nanowires are formed at the solid-aqueous interface. On the other hand, such nanowires were not formed when the photoirradiation was conducted for the specimens after a prolonged immersion period of 60 min. These observations indicate spontaneous growth of dissipative nanofibrous self-assemblies consisting of light-reducible ion pairs [tetraalkylammonium ion][Au(OH)4(-)] at the interface and their photoreduction to give developed nanowires. These nanowires are not available by the photoreduction of Au(OH)4(-) ions under conditions near at the thermodynamic equilibrium. A picture for the dissipative nanostructures is obtained: the formation of amphiphilic light-reducible nanowire structures is based on the static self-assembly near at the thermodynamic equilibrium, whereas their spontaneous, anisotropic growth from the interface to the aqueous phase is directed by dynamic, dissipative self-assembly phenomena under the far-from-equilibrium conditions. Thus, the both elements of dissipative self-assembly (dynamic) and static molecular self-assembly fuse together at the nanoscale, which is an essential feature of the dissipative nanostructures.