In the last few years, the creation of new 1D single crystalline molecular materials has attracted much attention due to promising applications in fields such as optics and electronics. Much research effort is currently devoted to obtain long nanowires and nanotubes in a reproducible manner. Most approaches to influence the morphology of nanostructures are based on modifications of the chemical composition of the building blocks and optimization of preparative conditions, such as concentrations, solvents, and temperature. Furthermore, in order to obtain high-quality homogeneous micro-and nanostructures from molecular units in solution, a number of deposition techniques has been developed including zone-casting, self-assembled monolayers (SAMs), Langmuir-Blodgett (LB) films, stamping, electrochemical methods, and thermal evaporation. Although these techniques and their combination facilitate the fabrication of soft-matter devices with low manufacturing costs, large-area coverage on surfaces, and high molecular order, it is still challenging to obtain anisotropic structures and to influence the crystalline structure.
Recent studies, however, have indicated that microfluidic systems could provide unique advantages in order to promote the formation of micro-and nanometer-scaled structures. In particular, the formation of crystals and nanoparticles was achieved in microchannels in superior quality due to the excellent handling of small fluid volumes of nano-and even picolitres. Several studies report the formation of polymer fibers, metal wires, and tubular structures in simple planar microfluidic networks. One important difference of microfluidic systems compared to conventional large-scale manufacturing processes is the reproducible, well-controlled supply of reagents due to the laminar flow regime present in microfluidic channels. In the absence of turbulence, two co-flowing streams carrying the reagents form a very well defined interface. Reaction and assembly take place directly at the interface as well as in the diffusion cone of the reactants.