Coarse Grain Dynamics Simulation of Dendrimers

Tahir Cagin

Materials and Process Simulation Center, Caltech, Pasadena, CA 91125

Dendrimers and hyperbranched polymers represent a novel class of structurally controlled macromolecules derived from a branches-upon-branches structural motif. The synthetic procedures developed for dendrimer preparation permit nearly complete control over the critical molecular design parameters, such as size, shape, surface/interior chemistry, flexibility, and topology. Dendrimers are well defined, highly branched macromolecules that radiate from a central core and are synthesized through a stepwise, repetitive reaction sequence that guarantees complete shells for each generation, leading to polymers that are monodisperse. This property of dendrimers makes it particularly natural to coarsen interactions in order to simulate dynamic processes occuring at larger length and longer time scales. The coarse grain interaction parameters are obtained from atomic interaction parameters to represent the interaction between supramolecular assemblies. The self assembly problem of globular dendritic molecules such as PAMAM can be reduced to a limited number of center-center interactions between them rather than millions of interactions between the individual atoms of a PAMAM dendrimers. We will demonstrate the use of the coarse grained force fields derived by this method in a molecular dynamics simulation of bulk generation 7 PAMAM dendrimers in periodic boundary conditions. Furthermore, this approach by eliminating the high frequency modes leads orders of magnitude larger simulation times.