From amorphous aggregates to polymer bundles: The role of stiffness on structural phases in polymer aggregation

We study the aggregation transition of a finite theta-polymer system in dependence on the bending stiffness $\kappa$ with the help of parallel multicanonical simulations. In order to distinguish amorphous aggregates from polymer bundles we introduce an order parameter, measuring the correlation of the end-to-end vectors. With the help of this order parameter, we construct generic $T$-$\kappa$ phase diagrams for systems with $2$ and $8$ polymers and discuss the occurring phases from amorphous aggregates to bundle structures. For an intermediate stiffness range we find multiple aggregated phases which change with increasing number of polymers and discuss their nature with the help of microcanonical analyses. We show that the stiffness of semiflexible theta polymers is the distinguishing parameter for the emergent structural motifs.