Langmuir−Blodgett Films of Carboxylic Acid Derivatized Silver Colloidal Particles:  Role of Subphase pH on Degree of Cluster Incorporation

In this paper, we demonstrate that reasonably ordered multilayer films of silver clusters can be deposited by the Langmuir−Blodgett (LB) technique. The approach consists of electrostatically immobilizing negatively charged carboxylic acid derivatized silver colloidal particles at the air−water interface using positively charged fatty amine Langmuir monolayers. The degree of cluster incorporation into the Langmuir monolayer has been controlled by varying the charge on the amine molecules through the colloidal subphase pH. Pressure−area isotherms were used to follow adsorption of the silver colloidal particles at the amine surface, while quartz crystal microgravimetry (QCM), optical absorption spectroscopy, infrared spectroscopy, contact angle measurements, and optical interferometry were used to characterize the multilayer LB films. The films were found to grow in the classical Y-type mode. Optical interferometry indicated a bilayer thickness of 106 Å, which yields a cluster size of ∼55 Å, in reasonable agreement with a mean cluster size of 73 Å determined from transmission electron microscopy. Incorporation of clusters into inorganic matrices as outlined in the paper shows promise for the growth of superlattice structures, mixed cluster systems, etc., which are not realizable by currently used experimental methods.

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