[SY-M1] Memory effects in functional polymers: The interplay between entropic elasticity and kinetic arrest
In contrast to metallic alloys, the shape memory effect in polymers is not based on a change of crystalline phases but on the interplay between entropic elasticity and kinetic arrest. Consequently, the shape recovery process, during which chains start to recover their entropically most favorable conformation, strongly depends on preparation protocol, frozen stresses and the selected recovery temperature. In this work, we study these issues via molecular dynamics simulations with a special focus on aging processes and the effects arising from the presence of small molecules. It is shown that aging leads to irreversible plastic rearrangements and a resulting increase of residual strain during shape recovery. At a fixed temperature, this process is enhanced if small molecules are added to the system. Interestingly, the triggering temperature depends in a non-monotonic way on the size of added molecules. This observation is rationalized in terms of diffusion coefficient of added molecules and the strength of their coupling to the polymer matrix.