Search for: All records

We report the design and use of calamitic ligands for quantum dot surface modification and nanoparticle assembly. Ligands incorporating a rigid aromatic rod-like core have previously been shown to facilitate the formation of porous nanoparticle-based structures, such as solid-walled capsules and multi-compartment quantum dot foams and networks via liquid crystal phase transition templating—a process in which the host phase is quenched through the isotropic-nematic phase transition. The effect of the calamitic ligand structure on particle dispersion, transport, and subsequent assembly, however, requires further investigation, particularly in the case of anisotropic liquid crystal solvents. In this report, we vary the structure of six new calamitic ligands and characterize quantum dot size and packing into superstructures when modified with each ligand. Dynamic light scattering is used to measure the effective nanoparticle size for each ligand in dilute toluene solution. Transmission electron microscopy reveals nanoparticle distribution in dense drop-cast films for each ligand, and small-angle x-ray scattering is used to measure interparticle separations in the assembled porous structures. Together, these methods provide a full picture of particle packing for each ligand. Notably, our findings demonstrate that while longer, more rigid aromatic cores promote a closer packing structure in drop-cast films (a slow quasi-equilibrium process)—such effects are not evident using a rapid quenching method. This study highlights the fact that when nanoparticles are formed into macroscopic assemblies, both ligand design and the particular method of assembly can contribute significantly to the final packing structure. 

Abstract The authors reveal a thermal actuating bilayer that undergoes reversible deformation in response to low‐energy thermal stimuli, for example, a few degrees of temperature increase. It is made of an aligned carbon nanotube (CNT) sheet covalently connected to a polymer layer in which dibenzocycloocta‐1,5‐diene (DBCOD) actuating units are oriented parallel to CNTs. Upon exposure to low‐energy thermal stimulation, coordinated submolecular‐level conformational changes of DBCODs result in macroscopic thermal contraction. This unique thermal contraction offers distinct advantages. It's inherently fast, repeatable, low‐energy driven, and medium independent. The covalent interface and reversible nature of the conformational change bestow this bilayer with excellent repeatability, up to at least 70 000 cycles. Unlike conventional CNT bilayer systems, this system can achieve high precision actuation readily and can be scaled down to nanoscale. A new platform made of poly(vinylidene fluoride) (PVDF) in tandem with the bilayer can harvest low‐grade thermal energy and convert it into electricity. The platform produces 86 times greater energy than PVDF alone upon exposure to 6 °C thermal fluctuations above room temperature. This platform provides a pathway to low‐grade thermal energy harvesting. It also enables low‐energy driven thermal artificial robotics, ultrasensitive thermal sensors, and remote controlled near infrared (NIR) driven actuators.