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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