Spontaneously spread polymer thin films on the miscible liquid substrates

Compared with the deposition of thin films on a solid substrate, using a liquid substrate provides an atomic level roughness and extra degree of freedom in manipulating the system conditions such as interfacial tension, which can be preferred for the fabrication of high-performance films. Herein, we develop a liquid-substrate-based spontaneous spreading (LSBS) technology that applies miscible liquids of high surface tension as the substrate and spreads the polymer solution under capillary forces for thin-film processing. We demonstrate the LSBS technology using a conductive polymer, poly (3,4-ethylenedioxythiophene)/poly (styrenesulfonate) (PEDOT/PSS), and the spread thin films were then transferred to various untreated substrates. LSBS technology uses a miscible liquid substrate for the first time and mediates the spreading, solvent removal, and ion exchange process between the liquid substrate and PEDOT/PSS, increasing the crystallinity of the PEDOT/PSS, thereby significantly improving its electrical conductivity. The LSBS mechanism is investigated through the time–space relationship between spreading and solvent removal, from which we confirm the operating window. Our LSBS technology exhibits a spontaneous, scalable, and versatile process for forming polymer thin films with thicknesses from nano to micron scales on liquid substrates, providing an easy route to control the geometry and presenting universally applicable to different materials.