Unveiling the Creep Recovery Behavior of Pseudo-Free-Standing Polymer Thin Films for Wearable Electronics

Polymer thin films in wearable electronics undergo creep recovery during operation as on-body devices, resulting in unrecoverable strain that subsequently induces mechanical instability in the films. However, the creep recovery behavior of polymer thin films has not been investigated due to their intrinsic fragility and the difficulty in controlling ultralow loads for the films. We evaluate the creep recovery behavior of pseudo-free-standing polymer thin films as a function of creep stress, developing direct creep recovery testing with a feedback-based ultralow-load control system. Polystyrene (PS) thin films exhibit a sharp increase in unrecoverable strain with the onset of crazing. While poly(3-butylthiophene) (P3BT) thin films show a linear increase in the relative ratio of unrecoverable strain with increasing creep stress, poly(3-hexylthiophene) (P3HT) thin films exhibit a viscoelastic strain larger than unrecoverable strain. This work reveals the creep recovery behavior of polymer thin films and proposes a direct creep recovery testing method.