Activation energies of colloidal particle aggregation: towards a quantitative characterization of specific ion effects

Abstract

A quantitative description of specific ion effects is an essential and focused topic in colloidal and biological science. In this work, the dynamic light scattering technique was employed to study the aggregation kinetics of colloidal particles in the various alkali ion solutions with a wide range of concentrations. It indicated that the activation energies could be used to quantitatively characterize specific ion effects, which was supported by the results of effective hydrodynamic diameters, aggregation rates and critical coagulation concentrations. At a given concentration of 25 mmol L(-1), the activation energies for Li(+) are 1.2, 5.7, 28, and 126 times as much for Na(+), K(+), Rb(+), and Cs(+), respectively. Most importantly, the activation energy differences between two alkali cation species increase sharply with decrease of electrolyte concentrations, implying the more pronounced specific ion effects at lower concentrations. The dominant role of electrolyte cations during the aggregation of negatively charged colloidal particles was confirmed by alternative anions. Among the various theories, only the polarization effect can give a rational interpretation of the above specific ion effects, and this is substantially supported by the presence of strong electric fields from montmorillonite surfaces and its association mainly with electrolyte cations and montmorillonite particles. The classical induction theory, although with inclusion of electric field, requires significant corrections because it predicts an opposite trend to the experimentally observed specific ion effects.

Impact of electric field on Hofmeister effects in aggregation of negatively charged colloidal minerals

“…19,20,53 This implies that properties of colloidal surface and cations are equally important in the aggregation of colloidal minerals. Furthermore, similar Hofmeister effects in charged particle interactions were also found by Liu et al 34 and Tian et al 33 In their work, ionic polarization in strong electric field was regarded as the origin of Hofmeister effects in ion-surface interactions. But the experimental materials in their work were merely pure minerals (i.e., illite and montmorillonite), which are the dominant components of the colloidal minerals in our work, implying that ionic polarization and electric field arising from the charged colloidal minerals may also be an important contributor to Hofmeister effects in our study.…”

“…The hydrated layers of the cations and colloidal mineral surfaces may overlap, resulting in the center of the cations moving further close to the edge of the hydration layers of the particle surfaces. 33 Accordingly, strongly hydrated cation species, Na + and Mg…”

“…The cation species with larger main and angular quantum numbers have "softer" electron cloud which then exhibit much stronger quantum fluctuation, resulting in a stronger polarization effect when interacting with the negatively charged particle surface. 33 The higher the polarizability of cations, higher is the propensity for the particle surface, 14,30 indicating that these cation species can be more effective to precipitate the colloidal minerals, and this is the production of Hofmeister effects in aggregation of colloidal minerals.…”

“…3,14,[28][29][30][31][32] In addition, Hofmeister effects are found to be more pronounced at very dilute concentration, 11,31,33,34 but classical theories including hydration effects, ionic size and dispersion force could not give a reasonable interpretation to this phenomenon. 34 Fortunately, several recent studies [33][34][35] have disclosed the essential role of polarization effect played in Hofmeister effects at interface surfaces, and these results provided motivation for us. Furthermore, some investigations 8,29,32 along with the present work pointed out that quite a different Hofmeister series were observed at relatively low and high ionic concentration.…”

Unraveling the size distributions of surface properties for purple soil and yellow soil

“…Moreover, ingestion of fine-sized soil particles associated with many trace metals Madrid et al, 2008) and organic contaminants (Luo et al, 2011) through the water or air can even pose special risks to human health. Therefore, there is an increasing interest in extraction and characterization of colloidal-sized particles, especially natural nanoparticles in soils (Bakshi et al, 2014;Calabi-Floody et al, 2011;Li et al, 2010b;Li et al, 2012;Tian et al, 2014). For example, Calabi-Floody et al (2011) extracted nanomaterials from the clay fraction of an Andisol and compared the zeta potential of these particles.…”