A Molecular and Thermodynamic View of the Assembly of Gold Nanoparticles in Nematic Liquid Crystal

The molecular interactions driving the assembly of gold nanoparticles (AuNPs) in a nematic liquid crystal (LC) are directly detected by nuclear magnetic resonance (NMR) spectroscopy and thermodynamically analyzed. The orientational orders of the selectively deuterated LC matrix and AuNP ligands, each separately followed by variable temperature (2)H NMR as a function of particle concentration, were observed to be strongly correlated. The mechanism of the reversible formation of long-range, quasi-periodic nanoparticle structures is attributed to the coupling of the AuNP ligands to the LC matrix, inducing an isotropic-nematic biphasic state. Experimentally validated thermodynamic modeling shows that, in contrast to colloidal nematics that are dominated by elastic forces, nematic dispersions of nanoparticles self-organize through a subtle balance of entropic forces and excluded volume, interface-mediated mesogen and nanoparticle molecular interactions, and couplings between conserved and nonconserved order parameters. Fine-tuning of these interactions through ligand and mesogen chemistry, together with mesoscale modeling, provides a route for materials innovations by merging structured fluid physics and nanoscience.