Direct preparation of silver nanoparticles and thin films in CO2-expanded hexane

•Ag nanoparticles and films were prepared in CO2-expanded hexane.•The CO2 pressure needs to be sufficient for the nanoparticles to precipitate.•The pressurization rate of CO2 is influential to the precipitation rate.•The heating rate in annealing needs to be slow to prevent film defects.•Annealing temperature is lower than softening point of a polymer.

Small, uniform and suspended silver nanoparticles were directly prepared in CO2-expanded hexane by reducing a synthesized metal precursor, silver isostearate, with hydrogen but without introducing additional capping agents. By increasing CO2 pressure, the suspended silver nanoparticles could be further deposited on a solid substrate to form silver thin film via gas antisolvent and the subsequent supercritical drying processes. The silver thin films prepared by the aforementioned method possessed a uniform thickness of about 150 nm without surface cracking and low electrical resistivity (5.64 × 10−6 Ω cm) after applying an annealing process. Due to the deposition of nano-sized silver particles, the annealing temperature could be as low as 175 °C that is lower than the softening points of many transparent polymeric substrates used for fabrication of flexible conductive films.

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