A 3D thermodynamic model in adapted to 2D ultrathin polymer films. Compression isotherms of various polymers are fitted without adjustable parameters. The model predicts polymer film thickness agrees with experiments.

This work aims to model the thermodynamic behavior of ultrathin polymer films. A mean-field thermodynamic model, originally developed for 3D polymers and parametrized by fitting the 3D pressure–volume–temperature data, is adapted to the 2D case. Remarkably, without any adjustable parameters, the 2D model successfully describes the experimental pressure–area isotherms for a wide range of polymers (polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polytetrahydrofuran, and polybutadiene) with varying hydrophobic–hydrophilic balances. Furthermore, it allows for the prediction of ultrathin film thickness, yielding values consistent with available experimental data for different polymers (PDMS, PMMA, and polybutadiene, especially). This 2D model remains applicable across different phases of the phase diagram, provided the film is in a dense state.