A STUDY OF THE PARTITIONING OF COLLOIDAL PARTICLES BASED ON THEIR SIZE DURING ELECTROSTATIC IMMOBILIZATION AT THE AIR-WATER-INTERFACE USINGFATTY AMINE MONOLAYERS

We have recently demonstrated that carboxylic acid derivatized silver and gold colloidal particles can be immobilized through electrostatic interaction with fatty amine Langmuir monolayers at the air-water inte rface and that good quality multilayer films of the clusters can be de posited by the Langmuir-Blodgett(LB) technique. In this paper, we exte nd our study on the electrostically controlled immobilization process through an investigation of the partitioning of carboxylic acid deriva tized clusters based on their size. Simultaneous immobilization of gol d and silver clusters (130 +/- 30 and 70 +/- 12 Angstrom diameter, res pectively) from the same colloidal subphase at the air-water interface using octadecylamine Langmuir monolayers has been followed by pi-A is otherm measurements as well as optical absorption, quartz crystal micr ogravimetry (QCM), and X-ray fluorescence (XRF) analysis of the built- up LB films. Even for small concentrations of gold relative to silver clusters in the subphase, the density of the larger gold clusters in t he LB films was found to be surprisingly high in relation to the small er silver clusters. While the pi-A isotherms stabilized within 3 h of spreading the fatty amine monolayer, the cluster density at the air-wa ter interface continued to increase, taking up to 12 h to reach equili brium. The larger gold clusters reached an equilibrium density at the interface much faster than the smaller silver clusters. The ''reverse' ' fractionation of clusters observed is discussed in terms of an elect rostatic model.