Lamellar Langmuir–Blodgett films of hydrophobized colloidal gold nanoparticles by organization at the air–water interface

Abstract

The organization of hydrophobically modified colloidal gold nanoparticles at the air–water interface and the formation thereafter of lamellar, multilayer films of the nanoparticles by the Langmuir–Blodgett (LB) technique is described in this paper. The hydrophobization of the gold colloidal particles was accomplished by the electrostatic extraction of carboxylic acid derivatized gold particles (synthesized in an aqueous medium, 35 Å in size) from solution into thermally evaporated fatty amine films by a simple immersion procedure. The acid–base complex formed by the association of the carboxylic acid groups bound to the colloidal particle surface and the amine groups in the lipid matrix leads to the formation of a strongly-bound hydrophobic sheath of fatty amine molecules around the particles. The colloidal gold particles can thereafter be dissolved in different organic solvents, dried and redispersed repeatedly without significant aggregation of the gold particles. The hydrophobic gold particles were dissolved in a spreading solvent and organized on the surface of water. The organization of the particles and the formation of multilayer films by the Langmuir–Blodgett technique was followed by surface pressure–area isotherm measurements of the colloidal particle Langmuir monolayer, quartz crystal microgravimetry, ultraviolet-vis spectroscopy and Fourier transform infrared spectroscopy. It was observed that a close-packed monolayer of the colloidal particles was formed on the surface of water and that excellent multilayer films of the colloidal nanoparticles can be grown on different supports by sequential transfer by the LB technique.