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In the past recent years, various micro-and nano-rings have received great attentions due to unique properties and applications in magnetics, optics, optoelectronic devices. Among them, ring-shaped magnetic ferric oxide became a great hot in a comprehensive range of disciplines because of its wide applications including magnetic recording materials, catalysts, and logic devices, catalysts, and magnetic fluid, magnetic sensors, as well as detection, bio-separation, medical imaging and targeted drug. Generally, the micro-and nano-rings can be obtained by using either physical or chemical routes such as electron-beam lithography, molecular-beam epitaxy, chemical modification, porous polymer membrane template, and colloidal monolayer template, etc. Most of these routes, however, required either sophisticated instruments or involved complicated procedures that could be limited for large scale production of nanorings from technical or economic perspectives. Here we demonstrated a convenient and low-cost method for the preparation of ferric oxide micro-and nano-rings via an evolution from droplets to bubbles to rings.In experimental, cleaned glass substrates were dipped into SiO2sol with solved ferric nitrate, then a thin SiO2gel film was gained after low-temperature heating. The thin film was heated on a using a KER3100-08S precision thermostatic table and the process was observed simultaneously by a BK-POL/BK-POLR polarization microscope with magnifying certain times. We observed the evolution of droplets from bubble to brings. Bubble and rings formed in the droplets could grow up with droplets and liquid under SiO2gel film supplying raw materials, slip, merge, even spray from droplets, and rupture to small bubble and rings. We also found that the lost of crystal water can promote hydrolysis of ferric nitrates, which generated gases to inflate droplet together with evaporated crystal water. Based on these results, we propose a mechanism underlying the formation of ferric oxide micro-and nano-rings.Surfaces with different wettabilities are fabricated with two kinds of method:heating and lauric acid modifying. And the influence of wettabilities on formation of ferric oxide nanorings with analogous experimental program is also investigated. It is found that the rings gained from heating method on surfaces of glasses with different wettabilities are uniform in sizes and morphologies and could easily be fabricated. We also found out that the more hydrophobic surfaces of glasses gained from lauric acid modifying method were, the smaller the size of rings was. In total, without damaging wettabilities of substrates, the more hydrophobic the substrates are, the more uniform the size and morphologies are and the smaller the size of rings is.
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