Macroscopic graphene structures such as graphene papers and fibers can be manufactured from individual 2D graphene oxide sheets by fluidics-enabled assembly followed by high temperature carbonization and graphitization. However, challenges exist to achieve high thermal-mechanical and electrical properties due to non-optimized microstructures and morphology. Here, we report the fabrication of highly thermally/electrically conductive and mechanically strong graphene fibers with a unique inner fiber structure, consisting of large-sized graphene sheets forming a highly ordered fiber arrangement intercalated with small-sized graphene sheets filling the space/micro-voids. The graphene fibers exhibited a sub-micron crystallite domain size through high temperature treatment, achieving an enhanced thermal conductivity up to 1290 Wm-1K-1, outperforming the best carbon fibers.
In addition, multiscale graphene structures with tunable graphene sheet alignment and orientation order are achieved by microfluidics design with strong size and geometry confinements and varied flow patterns. The microfluidics-enabled control of orientation order and microstructure accompanied with superior thermal-mechanical properties may enable their immense potentials in diverse technological applications, including thermal managements for effective heat transfer and reinforced fillers in structural composites.