Adsorption Kinetics in a Dual-Inlet Channel Flow Cell: I. Cetyl Pyridinium Chloride on Hydrophilic Silica

Abstract

A dual-inlet channel flow cell has been developed for the study of the adsorption kinetics of surfactants to solid−liquid interfaces under hydrodynamic control. This cell, with ellipsometric detection of the adsorbed surfactant, has been used to study the adsorption kinetics of cetyl pyridinium chloride (CPC) to hydrophilic silica in 0.1 M KCl and in pure water. The methodology provides detailed insight into the kinetic parameters and casts light on the adsorption mechanisms. The convection−diffusion behavior in the cell was calculated numerically using the backward implicit finite difference (BIFD) method: the CPC monomer and micelle populations were modeled with constant diffusion coefficients and assumed to equilibrate quickly on the time scale of the experiment. A Frumkin model was used to describe the adsorption behavior at the silica surface: the fitting parameters were determined from the equilibrium adsorption isotherm and kinetically limited desorption measurements. The adsorption kinetics in t...