In the present work, aggregation of two oppositely charged hydrophobic colloidal particles (sulphate and amidine functionalized polystyrene latices) were investigated in the presence of simple electrolytes and ionic liquids by electrophoresis and time-resolved dynamic light scattering.
In order to maintain the charge of particles and to avoid disturbing CO2 absorption, all measurements have been performed at pH 4.0. As for the coagulating agents the anions as well as the cations were varied systematically to study their effects comprehensively. Experiments of four different series such as sodium (Na+) and 1-butyl-3-methylimidazolium (BMIM+) for the different anions while chloride (Cl-) and dicyanamide (DCA-) for the different cations have been compared. The results reflect the Hofmeister effect in an excellent way; in case of highly charged sulphate latex particles one can observe a smaller shift in the critical coagulation concentrations when varying the simple electrolytes, while in case of positive particles this effect is more pronounced. Moreover, the constituents of Ionic Liquids (ILs) show interesting behavior. Depending if they act as counterions or co-ions in case of cations specific adsorption can be observed, while varying the anions similarities to simple electrolytes can be seen. The electrophoretic mobility measurements confirm the stability behaviors. Accordingly, screening, neutralization and overcharging but no restabilization can be observed at the concentration range investigated even in the presence of ILs which is in good agreement with previous results [1]. This behavior was found for both particles, hence it can be considered as generic. The results are summarized in an extended Hofmeister series.
[1] I. Szilagyi et al. Phys. Chem. Chem. Phys., 2014, 16, 9515-9524
