Production of nanofibers by atto-incubator-assisted assembly of urea using the particle array

We exploited three approaches to fabricate urea nanofibers by using an array of core-shell particles as a template. Core-shell particles were prepared by seeded polymerization and used as an atto-liter scale incubator (atto-incubator) to form nanofibers of urea crystal. Firstly, the mixture of the particle suspension and a urea aqueous solution was spin-coated to promote arrangement of core-shell particles and urea crystallization simultaneously (mix-spin method). Secondly, core-shell particles were arranged by a Langmuir-Blodgett apparatus and then the spin-coating of a urea aqueous solution was performed (LB-spin method). Then, the nano-network of urea crystals was produced by heat treatment at 80 °C. The interparticle distance and the amount of the remaining solution were important to determine the shapes, orientation and amounts of urea crystals. In the LB-natural drying method, one-directionally oriented nanocrystals were obtained over the wide range of the interparticle distance. As preliminary attempts, the obtained nanofibers were used as a template for the production of nanoscale metallic materials. Au nanofibers, nanotubes and nanorods could be obtained by gold sputtering deposition on the urea nanofiber and dissolving urea crystals. Ag-urea hybrid nanofibers were also produced using a mixture of urea and Ag nanoparticles by the modified LB-spin method.