Shape memory polymers (SMPs) are thermo-rheologically complex materials showing significant temperature and time dependences. Their segments often undergo cooperative phase transitions and conformational relaxations simultaneously along with shape memory effect (SME). In this study, a cooperative domain model is proposed to describe the composition dependence, multiple phase transitions and conformational relaxations of SMPs within their glass transition zones. Variations in local-area compositions and cooperative domains of the amorphous SMPs cause significant differences in their segmental relaxation. At a fixed domain size, both intermolecular activation energy and relaxation time significantly influence the SME and thermomechanical properties of the SMPs. Finally, the model is successfully applied to predict the shape memory behavior of SMPs with one stage SME and triple-SME, and the theoretical results have been validated by the experimental ones. This model could be a powerful tool to understand the working mechanisms and provide a theoretical guidance for the designs of multi-SME in SMPs.

Sequential glass and melting transitions in semi-crystalline shape memory polymers (SMPs) provide great opportunities to design and generate multiple shape-memory effects (SMEs) for practical applications. However, the complexly dynamic confinements of coexisting amorphous and crystalline phases within the semi-crystalline SMPs are yet fully understood. In this study, an interfacial confinement model is formulated to describe dynamic relaxation and shape memory behavior in the semi-crystalline SMPs undergoing sequential phase/state transitions. A confinement entropy model is first established to describe the glass transition behavior of amorphous phase within the SMPs based on the free volume theory, where the free volume is critically confined by the crystalline phase. An extended Avrami model is then formulated using the frozen volume theory to characterize the melting and crystallization transitions of the crystalline phase in the SMPs, whose interfacial confinement with the amorphous phase has been identified as the driving force for the supercooled regime. Furthermore, an extended Maxwell model is formulated to describe the effect of dynamic confinement of two phases on the multiple SMEs and shape recovery behaviors in the semi-crystalline SMPs. Finally, the effectiveness of the newly proposed model is verified using the experimental data reported in the literature. This study aims to provide a new methodology for the dynamic confinements and cooperative principles in the semi-crystalline SMP towards multiple SMEs.

Smart materials with self-growing and tailorable mechanical strength have wide-range potential applications in self-healing, self-repairing, self-assembly, artificial muscle, soft robots and intelligent devices. However, their working mechanisms and principles are not fully understood yet and mathematically and physical modeling is a huge challenge, as traditionally synthesized materials cannot self-grow and reconstruct themselves once formed or deformed. In this study, a phenomenological constitutive model was developed to investigate the working mechanisms of self-growing and tailorable mechanical strength in double-network (DN) hydrogel composites, induced by mechanochemical transduction of dynamic-modal mechanophore. An extended Maxwell model was firstly employed to characterize the mechanical unzipping of hydrogel composites, and then mechanochemically induced destruction and reconstruction processes of brittle network in the hydrogel composite were formulated. The enhanced mechanical

Entanglement plays a critical role in determining dynamic properties of polymer systems, e.g., resulting in slip links and pulley effects for achieving their large deformation and high strength. Although it...

In this study, a cooperative model has been proposed for the double network (DN) hydrogel, which synchronously undergoes heuristic swelling and inhibitive micellization by the ionic dissociation of polyelectrolyte. Flory-Huggins solution theory is initially employed to identify the working mechanism of dielectric constants on swelling behavior of the DN hydrogel. Then a free-energy function is introduced to formulate the constitutive relationship of the DN hydrogels, in which the first hydrotropic network undergoes a heuristic swelling and the second hydrophobic network undergoes an inhibitive micellization. Finally, the proposed model has been verified using the experimental results reported in the literature. A good agreement between the theoretical results and experimental ones has been achieved. This study provides a fundamental approach to formulate the constitutive relationship and to understand the cooperative dynamics of two types of networks in DN hydrogels induced by the polyelectrolyte.