Stability of DNA-Linked Nanoparticle Crystals

Three-dimensional ordered lattices of nanoparticles linked by DNA have potential applications in novel devices and materials, but most experimental attempts to form crystals result in amorphous packing. In this thesis, a coarse-grained model is used to address three factors which impact the kinetic and thermodynamic stability of BCC and FCC crystals formed in DNA-linked nanoparticle systems: (i) surface mobility, (ii) the number of attached strands, and (iii) the size of the nanoparticle core. It has been shown experimentally that the surfaces of nanoparticles can have significant mobility, and that polymers attached to nanoparticles are able to reorient themselves on the nanoparticle surface. The model predicts that systems with surface mobility form crystals with lower free energy, but also a lower heat of fusion. When formed in systems with low rather than high surface mobility, FCC crystals have a higher kinetic melting temperature, whereas BCC crystals have a lower kinetic melting temperature. Due to the procedure of functionalization, it is difficult to independently vary the number of attached strands and the size of the core experimentally. The model demonstrates that the kinetic melting temperature of BCC and FCC systems increases with increasing number of strands, but that it decreases with increasing core size. The results presented here are intended to provide guidance for choosing experimentally controllable parameters that will facilitate the formation of crystalline ordered states.