Direct Tensile Testing of Free-Standing Ultrathin Polymer Films on Liquid Surface at High Temperature.

The fragile nature of ultrathin polymer films poses a challenge for precise mechanical property measurements in a free-standing state, despite their critical importance for the fabrication and performance of advanced electronic devices under thermal loading. Here, a novel high-temperature tensile testing method for free-standing ultrathin polymer films using a film on heated liquid (FOHL) platform is proposed. Glycerol is chosen for the thermally stable liquid platform for its high surface tension, high boiling point, miscibility with water, and chemical stability. A defect healing process of the specimen on the heated liquid effectively eliminates preexisting defects of the brittle polymer sample, enabling precise tensile property measurements at elevated temperatures. The methodology is validated through experiments on polystyrene (PS) films of varying thicknesses (50-400 nm) at elevated temperatures of 25-100 °C, demonstrating the influence of temperature and thickness on tensile properties. Decreasing elastic modulus with increasing temperature and decreasing thickness of ultrathin PS films is accurately measured. The proposed method provides a reliable method todirectly evaluate the tensile properties of ultrathin films in high-temperature conditions.