Subdiffusion in Dendrimer Melts

Describing molecular mobility in a crowded environment is one of the challenges of modern science, as it often leads to non-Markovian processes and anomalous diffusion, which cannot be captured by classical theories. A relevant example of such an environment is a melt of dendrimers, which are tree-like, highly branched macromolecules. We study the mechanisms of dendrimer mobility in a melt, which were found to lead to subdiffusion. The center-of-mass mobility of dendrimers was found to be consistent with an fBm-like Gaussian, ergodic subdiffusive regime over the investigated time window, which can be observed in an environment with long-term memory. To determine the causes of the long-term memory of the environment, we investigated the motion of the macromolecular structure itself. This motion includes two processes: the random walk of atoms along the geometric surface defined by the dendrimer shape, and the relaxation of branches as a whole. It was found that the combination of these processes with the topology of the melt leads to negative correlations in the dendrimer center-of-mass motion, which is consistent with the observed fBm-like anomalous subdiffusion. Notably, in the case of a dendrimer in solution, these motions do not lead to anomalous center-of-mass motion of the dendrimer.