INTERFACE DIRECTED SELF-ASSEMBLY OF LIQUID CRYSTAL-NANOPARTICLE HYBRID MATERIALS
The self-assembly of nanoparticles (NPs) has broad applications. This process is controlled by the NP cores and the molecular interactions at the interfaces between ligands and their environments, which impart dynamics to the assembled superlattices (SLs) with temperature changes. Designing and understanding temperature-sensitive interfaces to precisely manipulate NPs is critical in the fabrication of high-quality SLs with desired structures and properties. Liquid crystals (LCs) are promising candidates as thermo-responsive materials. The LC-NP hybrid materials, including NPs with liquid crystalline ligands and NP dopants in LC matrices, have active yet complex interfaces, offering opportunities and challenges to manipulate these nanomaterials' dynamics, structures, and properties. This thesis starts with dried NP aggregates with liquid crystalline ligands and the dynamics of ligand-ligand interfaces. These ligands are also referred to as (pro)mesogenic ligands. Traditional NPs lack mobility in the dried state due to the interdigitation of ligand tails. Tailored dendritic promesogenic ligands with a thermally triggerable lubricating property induce dried NP aggregates to transform from a random state to ordered SLs with preferred orientations by heating or laser illumination. Simulations reveal the promesogenic ligands with flexible chains do not interdigitate, increasing the mobility of NPs. Next, NP dopants in LC matrices and the ligand-environment interfaces are investigated. In an anisotropic LC environment, an ellipsoidal ligand shell on a spherical NP is induced, aligns with the LC orientation, and can be manipulated indirectly with a magnetic field. A novel methodology for growing SLs reversibly from LCs is developed. LCs serve as temperature-responsive solvents to disperse NPs in the isotropic phase and expel NPs in the LC phases. Experiments and simulations demonstrate that the expelled NPs co-crystallize with LC molecules into solid solutions, where LC molecules occupy the voids and diffuse in/out of the SLs with temperature changes. Manipulating the interfaces between promesogenic ligands and LCs can tune the SL growth mode and achieve reversible SL phase transformations. Moreover, a fibrillar network of nanoplate self-assembly can gelate fluidic LCs, highlighting the synergistic and mutual interaction between NPs and LCs.
Materials Engineering, Engineering, Chemistry
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