Novel liquid crystal phase transition of linear defects in an epitaxial layer of DNA-nanoparticle superlattices

We use Monte Carlo simulations and mean-field theory to study a lattice model system in which DNA-coated nanoparticles form an epitaxial layer onto a patterned bcc (100) template. If nanoparticles only attach to the so-called ``center'' sites, each of which is the center of a unit cell in the square lattice template, it would result in a perfect bcc epitaxial layer. However, defects arise due to attachment to ``edge'' sites and ``corner'' sites. In simulation, we show that edge-binding defects prefer to form linear clusters in horizontal and vertical directions. These linear defects can undergo a second-order isotropic-nematic phase transition in some regimes. A mean-field approach is introduced to provide theoretical descriptions for the system in each of the phases and predict the critical phase transition conditions. Striking agreement is observed between the theory and simulation.