Dendrimers in Solution of Linear Polymers: Crowding Effects

We study dendrimers embedded in a solution of linear chains with various degrees of polymerization and concentrations. We distinguish the term "crowding", addressing the impact of the polymer environment on the dendrimer, from the term "semidilute", which refers to the state of the polymer environment only. Depending on the length of linear chains, two regimes are observed. Dendrimers in a solution of chains much shorter then their own size display good solvent characteristics at all concentrations. In a dense solution of long chains the dendrimer conformation statistics changes qualitatively. It displays Gaussian scaling with respect to the spacer length instead of the cube root behavior expected for a compact globule. We have found a very good description of the simulation data by using a geometrical ansatz where for crowding given by the matching of the characteristic length scales of the two subsystems; i.e., the ratio of the dendrimer size and the correlation length of the semidilute solution provides the relevant scaling variable. Our study reveals that dendrimer conformations in the strongly crowed state neither are in a compact globular state nor do they correspond to a mean-field theta-state. Instead, a novel scaling variable combining the properties of both species reflects the conformation statistics.