Abstract
Hofmeister effects have been recognized as important as Mendel’s work was to genetics while remain largely controversial, especially for the mechanistic aspects. Here we demonstrated that complex colloids in electrolyte solutions show resembling aggregation kinetics as model colloid, and then quantitatively evaluated the resulting Hofmeister effects. Mechanism for the aggregation of complex colloids has been proposed that is closely associated with the charges of their constituents; despite that, electrostatic interactions play a minor role while polarization effect is evidenced to be the driving force for the aggregation processes. Polarization effect is further ascribed to arouse the resulting Hofmeister effects, which is supported by the fine correlation of activation energies vs. polarizability data of different alkali ions and the calculations of dipole moments for minerals with different charges and adsorbed alkali ions. Because of neglecting polarization effect, the prevailing DLVO theory is not sufficient to describe Hofmeister effects that are ubiquitous in nature. We speculate that polarization effect should also be responsible for Hofmeister effects of other charged systems such as proteins and membranes.
Highlights
Proteins, membranes, clays and colloids carry a plethora of surface charges that result in strong electric fields and particular adsorption behaviors [1,2,3]
Interactions between colloidal particles can lead to aggregation, and electrolytes dissolved in aqueous solutions have an eminent influence on such aggregation processes, which are known to be Hofmeister effects [4,5,6,7]
We speculate polarization effect should be responsible for Hofmeister effects of other charged systems that are ubiquitous in nature, such as proteins and membranes
Summary
Membranes, clays and colloids carry a plethora of surface charges that result in strong electric fields and particular adsorption behaviors [1,2,3]. Interactions between colloidal particles can lead to aggregation, and electrolytes dissolved in aqueous solutions have an eminent influence on such aggregation processes, which are known to be Hofmeister effects (specific ion effects) [4,5,6,7]. It is evident that Hofmeister effects are associated with surface charges, mechanistic understanding remains a subject of burgeoning debates [1, 6, 10,11,12,13]. A number of previous studies focused on the aggregation of mono-dispersive synthetic colloids (small and spherical particles) [14,15,16,17]. We have used the dynamic light scattering technique to quantitatively characterize the Hofmeister effects for the aggregation of (polydispersive) montmorillonite particles in electrolyte solutions [18]. The PLOS ONE | DOI:10.1371/journal.pone.0128602 July 22, 2015
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