A coarse-grained model for polyphenylene dendrimers:: Switching and backfolding of planar three-fold core dendrimers

In this paper, we present a mesoscopic model for melt of polyphenylene dendrimers. The coarse-graining force field is built on the basis of the distribution functions derived from atomistic simulations, and thus it takes into account the chemical details of the system. Owing to the reduced number of particles, simulations of melts longer than 0.1 mu s for dendrimer generation up to the fourth have been carried out to investigate both bulk and single molecule properties. In the bulk, it has been shown that these dendrimers do not acquire orientational order. Single molecule geometrical analysis has been performed by computing the radius of gyration, hydrodynamic radius, and small-angle neutron scattering profile. All the computed parameters compare favorably with experimental data and with previous atomistic simulations. It is concluded, in agreement with previous atomistic studies, that polyphenylene dendrimers present a substantially rigid structure that does not allowed for a remarkable back-folding even in the melt phase. Interestingly, the switching between a collapsed and open global shape found in previously isolated-molecule atomistic simulations occurs also in the melt phase.