An extended shoving model for dynamic fluctuation of glass transition in amorphous polymer towards cooperative shape-memory effect

Phase transition theory is a powerful approach to study shape-memory effect (SME) and dynamic relaxation behaviour in amorphous shape-memory polymers (SMPs) undergoing glass transition processes. However, previous studies are mostly limited to building-up of experimental models, mainly due to poor understanding of dynamic fluctuation of glass transition. In this study, the dynamic fluctuation of glass transition in the amorphous SMPs, whose thermodynamic SME is governed by the phase transition theory, was investigated using a shoving model. A constitutive relationship between potential energy and cooperatively rearranging region (CRR) volume is firstly developed to explore the working principle of phase transition in the thermodynamic SME of amorphous SMPs, based on the shoving model and Adam-Gibbs domain size model. The effect of CRR volume on the phase transition is further formulated using the strain function, and then employed to develop a constitutive stress-strain equation based on the extended Maxwell model. The working principles of cooperative SME and dynamic relaxation behaviours have been explored and discussed. Finally, the effectiveness of the analytical results obtained using the proposed model has been verified using the experimental results of amorphous SMPs reported in literature.