Role of Entropy-Enthalpy Competition on the Thermochemically Driven Shape Memory Effect in Amorphous Polymer Films.

The application of thermochemically responsive polymer films in the biomedical field is a promising direction, particularly for controllable drug delivery. However, the mechanism governing the shape memory effect (SME) remains poorly understood due to the complex interactions between solvent molecules and polymer chains. Herein, we integrate the Flory-Huggins theory with the transition state model to investigate the plasticization effect of solvent on the thermodynamic behavior of polymers. By introducing the concept of phase transition, the dependences of the glass transition temperature, thermomechanical properties, and shape memory behavior of polymer films on the thermochemical stimuli are discussed. Our theoretical analysis reveals that the entropy of mixing promotes the occurrence of the SME, while the enthalpy of mixing exerts an inhibitory effect on this process. Consequently, the competition between the entropy of mixing and the enthalpy of mixing is the critical factor determining whether polymers exhibit the SME under different thermochemical conditions. The effectiveness of the proposed model is further validated by applying it to predict the shape memory behavior of acrylate copolymer films under different thermochemical conditions. This study is expected to provide a practical methodology for understanding the working mechanism of the thermochemically driven SME in polymer films.