Glass Formation and Dynamical Heterogeneity of Star Polymers

While glass formation of linear chain polymers has been widely explored, comparatively little is known about glass formation of star polymers. We study the segmental structure and dynamics, contrast to those of the star core, and particularly focus on the dynamical heterogeneity and cooperative nature of segmental motion via molecular dynamics simulations. We quantify how the architecture of star polymers, i.e., the number of arms and the length of those arms, affect the glass transition temperature Tg, the non-Gaussian nature of molecular displacements, and the collective string-like motion of monomers. We find that, while the star geometry can significantly affect the size and time scale of collective motions, the relationship between the size scale of the collective motions and the overall relaxation time follows the same Adam-Gibbs like relationship previously found to describe simple linear polymers. Thus, while star polymers offer an opportunity to significantly alter material properties relative to their linear polymer counterparts, the fundamental physics governing their relaxation is unchanged.