Influence of ionic strength and shear rate on the desorption of polystyrene particles from a glass collector as studied in a parallel-plate flow chamber

Abstract

The residence-time-dependent desorption during the deposition of polystyrene particles 736 nm in diameter on glass was studied in situ using a parallel-plate flow chamber and automated image analysis. Comparison of successively grabbed images yielded the initial desorption rate coefficient, and final desorption rate coefficient and a relaxation time for the transition from the initial to the final desorption state, i.e. ageing of the bonds. Desorption experiments were performed from suspensions with different potassium nitrate concentrations (1, 10 and 50 mM) and at varying shear rates (15–200 s −1. The initial desorption rate coefficient β 0 ranging from 1 × 10 −3 to 20 × 10 −3s −1, and the final desorption rate coefficient β ∞, ranging from 0.01 × 10 −3 to 0.65 × 10 −3s −1 were both larger than the desorption rate coefficients calculated neglecting a possible residence time dependence. These desorption rate coefficients, β, ranged from 0.005 × 10 −3 to 0.40 × 10 −3s −1. The relaxation times, at which the adhesion of the polystyrene particles entered a more irreversible state of adhesion compared with their initial state of adhesion, varied from 100 to 1000 s. The desorption rate coefficients as well as the relaxation time showed major variations with the shear rate and the ionic strength of the suspension. At high ionic strength, the initial and final desorption rate coefficients increase and the relaxation time decreases with increasing shear rate, whereas at low ionic strength the desorption rates decrease and the relaxation time increases with increasing ionic strength. This study provides direct evidence that the interaction forces between adhering particles and a collector surface change over time.