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.