Molecular simulation of dendrimers under shear

In this work flow properties of dendrimers are studied with the aid of molecular simulations. For the first time the results of the nonequilibrium molecular dynamics simulations of the dendrimers in the melt are reported. Molecules are modelled at the coarse-grained level using the bead-spring model. The objective of this research is to analyse the influence of the molecular topology in the macroscopic flow behaviour of the melts. Systems of dendrimers of generations 1 to 4 undergoing planar shear are compared to the melts composed of linear chain polymers. The internal structure and shape of dendrimers is extensively analysed. The response of the molecules to the shearing in the form of stretching and alignment is studied. The correlation between the onset of shear thinning and the onset of deformation of molecules is observed. The changes in the fractal dimensionality of dendrimers due to shearing are also analysed. Dendrimers, due to their highly branched structure and compact globular conformations in the melt, are found to behave differently when sheared, compared to traditional linear polymers. Unlike linear polymers, they do not undergo transition form the Rouse to the reptation regimes. This effect is explained in terms of the suppressed entanglement between molecules. Moreover, dendrimers when compared to linear chain systems exhibit lower Newtonian viscosity, onset of the shear thinning at higher strain rates, and less pronounced shear thinning in the non-Newtonian regime. They can be used as rheology modifiers, as it is shown in the preliminary results obtained from the simulations of the dendrimers-linear polymer blends. In agreement with other theoretical and experimental studies, dendrimers in the melt are found to have compact space-filling structure with terminal groups distributed throughout the interior of the molecule. Suggestions for the further study of dendrimers via molecular simulations are made