Coarse-grained simulations of poly(propylene imine) dendrimers in solution

Abstract

The behavior of poly(propylene imine) (PPI) dendrimers in concentrated solutions has been investigated using molecular dynamics simulations containing up to a thousand PPI dendrimers of generation 4 or 5 in explicit water. To deal with large system sizes and time scales required to study the solutions over a wide range of dendrimer concentrations, a previously published coarse-grained model was applied.Simulation results on the radius of gyration, structure factor, intermolecular spacing, dendrimer interpenetration and water penetration are compared with available experimental data, providing a clear concentration dependent molecular picture of PPI dendrimers. It is shown that with increasing concentration the dendrimer volume diminishes accompanied by a reduction of internalized water, ultimately resulting in solvent filled cavities between stacked dendrimers. Concurrently dendrimer interpenetration increases only slightly, leaving each dendrimer a separate entity also at high concentrations. Moreover, we compare apparent structure factors, as calculated in experimental studies relying on the decoupling approximation and the constant atomic form factor assumption, with directly computed structure factors. We demonstrate that these already diverge at rather low concentrations, not because of small changes in form factor, but rather because the decoupling approximation fails as monomer positions of separate dendrimers become correlated at concentrations well below the overlap concentration.

A Comparative Study of Intramolecular Mobility of Single Siloxane and Carbosilane Dendrimers via Molecular Dynamics Simulations

“…Along with single dendrimers in dilute solutions [14,15,16,17,18,19,20,21,22,23], much attention is attracted nowadays to concentrated solutions and melts [24,25,26,27,28,29,30,31,32,33,34], where intermolecular interactions of dendrimer molecules are significant. It is expected that the tree-like molecular morphology of dendrimers would distinguish their behavior from that of conventional linear polymers.…”

Linear Viscoelasticity of Carbosilane Dendrimer Melts

“…[16,20,21] Dendrimer melts with other chemistry were simulated in Ref. [22,23] and the coarse-grained non-equilibrium MD simulations were used for studies of the shear viscosity of dendrimer melts [24,25] and of the rheological properties of dendrimer melts undergoing planar elongational flow. [26] None of these studies investigated the dynamical shear-stress relaxation modulus.…”

Multivalency in a Dendritic Host–Guest System

“…Furthermore, the G 4 and G 5 PPI models provided a clear concentration-dependent molecular picture in simulations of up to 1430 dendrimers in water from dilute to melt conditions and compared well with experimental SANS data. 36 It demonstrated that even at high concentrations each dendrimer remains a distinct entity and that structure factors computed using the approximations and assumptions experimenters need to employ start to diverge at rather low concentrations from structure factors derived directly from the simulation data.…”