Coupling layer-by-layer assembly and multilayer transfer to fabricate flexible transparent film heater

Flexible transparent film heaters (f-TFH) were prepared on a polysulfone (PSU) film with a multilayer transfer of silver nanowires (AgNWs) coated on glass substrates via layer-by-layer (LBL) deposition. First, as-received AgNWs were functionalized with carboxylic acid (AgNW-COOH) and amine (AgNW-NH₂) moieties to obtain negatively and positively charged nanowires, respectively. Second, functionalized AgNWs were sequentially coated on a glass substrate via the LBL deposition, which was followed by subjecting the multilayer film to annealing at 125 °C for 30 min to improve the electrical conductivity. Third, the multilayer was transferred from the glass substrate to the polymer film by coating and detaching the PSU. The multilayer film provided optical transmission of 84% and sheet resistance of 12 Ω/□ with 5 bilayer sample, which is comparable to indium tin oxide (ITO) film. The f-TFH reached maximum temperature of 128 °C at 7 V with a response time of 45 s. Moreover, it exhibited good defrosting capability by applying 7 V for 20 s. Cyclic bending test results indicated that the sheet resistance of the flexible multilayer film does not demonstrate any change until 300 cycles, while adhesion test 3-M tapes exhibited no sheet resistance change even after 20 peel cycles showing the superior performance of the multilayer film. In addition, the film showed stable heating performance at 128 °C for 5 h.