Nanoparticles can be assembled into large arrays, but currently we do not possess control over forces governing self–assembly at the nanoscale. It has been observed that alkyl chain molecules passivating nanocrystal surfaces have an important role in dictating particle interactions. These ligands go through an order–disorder phase transition on a CdS surface<sup> </sup>as temperature is increased. Simulations show that the alkyl chains arrange in an alternating gauche–eclipsed pattern, but this alternation gets destroyed closer to the phase transition. It is unclear if the defects in the ligand pattern are essential for the disorder transition to occur. Hence, we are investigating their role by performing biased simulations. Umbrella sampling on the ligands is used to determine the free energy surface as a function of their average alignment. As a result, the equilibrium behavior at a given temperature has been obtained with the Weighted Histogram Analysis Method (WHAM). Using this information, we are also working to describe the order–disorder phase transition by postulating a coarse–grained model with an effective Hamiltonian inspired by Landau–Ginzburg theory.

Field theory for ligand alignment on nanoparticles: Prospects for self–assembly driven by phase transitions

253rd National Meeting (2017)

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