Effect of Calamitic Ligands on Quantum Dot Size and Packing

We investigate the use of calamitic ligands in quantum dot (QD) dispersion and assembly. Six different mesogenic ligands were designed for their ability to connect and stabilize nanoparticles into macroscopic structures. The structures are templated by the liquid crystal (LC) isotropic-to-nematic phase transition and include capsules, and foams. The molecular structure of the host LC phase influences particle distribution, and this distribution can also be tuned depending on the size and surface chemistry of the particle. Ligands play an important role in the self-assembly process. They promote particle dispersion and tune the strength with which the moving phase boundary transports the particles. Particle dispersion can be very challenging because they do not readily incorporate into the host. Our ligands must be able to both promote dispersion and facilitate assembly. We used dynamic light scattering (DLS) to measure effective particle size in dilute solution. Transmission electron microscopy (TEM) analysis using pair autocorrelation functions was used to measure particle separation in dense drop-cast films. XRD was used to measure interparticle separation in 3D assemblies (i.e capsules). Using TEM, we observed that the most calamitic ligands (rod-like) produced a closer packing structure compared to more flexible, shorter ligands. This may be due to stronger short-range attractive interactions. DLS showed that particle radii vary similarly in magnitude. These results help us to understand the role of ligand design for applications that rely on nanoparticle transport in anisotropic fluids.