Aggregation of semiflexible polymers

In the following, we will discuss the aggregation of interacting semiflexible polymers by analyzing the order and hierarchy of subphase transitions that accompany the aggregation transition.

Cluster formation and crystallization of polymers are processes that are interesting for technological applications, e.g., for the design of new materials with certain mechanical properties or nanoelectronic organic devices and polymeric solar cells. From a biophysical point of view, the understanding of oligomerization, but also the (de)fragmentation in semiflexible biopolymer systems like actin networks is of substantial relevance. This requires a systematic analysis of the basic properties of the polymeric cluster formation processes, in particular, for small polymer complexes on the nanoscale, where surface effects are competing noticeably with structure-formation processes in the interior of the aggregate.

A further motivation for investigating the aggregation transition of semiflexible homopolymer chains derives from the intriguing results of the similar aggregation process for peptides [254, 255] discussed in Chapter 11, which were modeled as heteropolymers with a sequence of two types of monomers, hydrophobic (A) and hydrophilic (B). By specializing the previously employed heteropolymer model to the apparently simpler homopolymer case, we now, by comparison, aim at isolating those properties that were driven mainly by the sequence properties of heteropolymers. In fact, while in both cases the aggregation transition is a first-order-like phase-coexistence process, it will turn out that for the homopolymer model considered in the following, aggregation and crystallization (if any) are separate conformational transitions, if the bending rigidity of the interacting homopolymers is sufficiently small. This was different in the example of heteropolymer aggregates that we discussed in the previous chapter, where these transitions were found to coincide [254, 255].