Kinetics of fluorescent latex particle deposition at polyelectrolyte monolayers determined by in situ measurements

A new flow cell was constructed for studying in situ kinetics of particle and macromolecule adsorption using fluorescence microscopy. Using the cell, calibration experiments were performed for fluorescent latex particles on mica coated by cationic polyelectrolytes: polyallylamine hydrochloride (PAH) and poly(diallyldimethylammonium chloride) (PDADMAC). Formation of polyelectrolyte monolayers was controlled via streaming potential measurements in the flow cell. The bulk latex properties were determined by dynamic light scattering (DLS) and microelectrophoresis. The hydrodynamic diameter of particles varied in the range 528–574 nm, depending on ionic strength. The electrophoretic mobility measurements revealed that the zeta potential of particles was negative varying between −56 mV for I = 10−4 M, and −42 mV for I = 0.15 M. The kinetics of latex particle deposition at mica coated by saturated polyelectrolyte layers was studied in situ as a function of ionic strength under diffusion-controlled conditions. The coverage was determined by direct enumeration of particles using the fluorescent microscopy and AFM. The experimental results were adequately interpreted in terms of numerical solutions of the mass transport equation with the blocking function derived from the random sequential adsorption (RSA) approach. Additionally, the dependence of integrated fluorescence intensity on particle coverage was determined, which enables a quasi-continuous measurements of particle deposition kinetics. It was concluded that the cell is versatile tool for determining mechanism of particle deposition at interfaces.