Effect of solvent chain length on the colloidal behavior of alkylamine-protected silver nanoparticles in alkanes: Insights from solvent relaxation NMR.

HYPOTHESIS

The dispersion of apolar-ligand-protected nanoparticles (NPs) in alkanes is a complex process diverging from the "like dissolves like" principle, making its prediction beyond the capability of the Hansen solubility parameter (HSP) sphere method. This necessitates experimental investigation at the molecular level to understand dispersion behavior, particularly the role of solvent-ligand interactions.

EXPERIMENTS

Solvent relaxation NMR was applied for the first time to investigate solvent-ligand interactions in the dispersion/agglomeration of hexadecylamine-protected silver nanoparticles (C16-Ag NPs) in alkanes. The dispersibilities in different alkanes were determined from the localized surface plasmon resonance (LSPR) and compared with those predicted from the HSPs.

FINDINGS

The colloidal behavior of C16-Ag NPs in alkanes was notably affected by the length of the solvent chain. LSPR analysis demonstrated that while C16-Ag NPs remained dispersed in pentane, hexane, and octane, they exhibited agglomeration in decane, dodecane, and tetradecane, contradicting the HSP theory predictions. Solvent relaxation NMR revealed that this unexpected agglomeration stems from the strong bonding of longer-chain solvents to surface C16 ligands, leading to significant interaction. In contrast, shorter-chain solvents exhibited weaker bonding, promoting better dispersion. These findings emphasize the importance of solvent choice in NP applications and offer valuable insights into ligand-shell dynamics, furthering the development of NP technologies.