Microscale thermomechanical characterization of environmentally conditioned shape memory polymers

摘要

Shape memory polymers (SMPs) are an emerging class of active polymers that have dual-shape capability and are, therefore, candidate materials for reconfigurable structures. However, the durability of SMPs has not been fully investigated to ensure they function properly in relevant environments. In this study, epoxy-based SMPs were conditioned separately in simulated service environments designed to be reflective of anticipated performance requirements, namely, (1) exposure to UV radiation for 125 cycles, (2) immersion in lube oil at ambient temperature, (3) immersion in water at 49 °C. A novel high-temperature indentation method was used to evaluate the shape recovery ability and mechanical properties of the conditioned SMPs. Results show that environmentally conditioned SMPs generally exhibit decreased glass transition temperatures and higher moduli and strain rate sensitivities in comparison to an unconditioned one. Environmental conditioning affects the shape recovery abilities of the SMPs if the recovery temperatures are set low. In particular, the UV exposed and water immersed SMPs exhibit noticeable lower shape recovery ratios compared to the unconditioned material. When the recovery temperature is above T_g, the material's ability to regain shape remains relatively unchanged with conditioning.