Understanding the Colloidal Stability of Nanoparticle-Ligand Complexes: Design, Synthesis, and Structure-Function Relationship Studies of Amphiphilic Small-Molecule Ligands.

For effective application of nanoparticles, their amenability to in-solution processing must be addressed, and stable, homogeneous solvent conditions are required. Although organic ligands have been used as surface-modifying reagents for nanoparticles to increase their colloidal stability and homogeneity in solution, the structure-function relationships of nanoparticle-ligand complexes remain elusive and controversial. Herein, a series of novel amphiphilic small-molecule ligands were designed, synthesized, and applied as surface-modifying reagents for aqueous, transparent TiO2 and ZrO2 nanoparticles. The colloidal stability of the resulting nanoparticle-ligand complexes was found to depend not only on the chain length, but also on the relative balance between hydrophobicity and hydrophilicity. The structure of the ligands can be fine-tuned to achieve "flexible colloidal stability", thus significantly increasing complex stability in a variety of organic solvents.