Probing size-dependent electrokinetics of hematite aggregates.
Aqueous particle suspensions of many kinds are stabilized by the electrostatic potential developed at their surfaces from reaction with water and ions. An important and less well understood aspect of this stabilization is the dependence of the electrostatic surface potential on particle size. Surface electrostatics are typically probed by measuring particle electrophoretic mobilities and quantified in the electrokinetic potential (ζ), using commercially available Zeta Potential Analyzers (ZPA). Even though ZPAs provide frequency-spectra (histograms) of electrophoretic mobility and hydrodynamic diameter, typically only the maximal-intensity values are reported, despite the information in the remainder of the spectra. Here we propose a mapping procedure that inter-correlates these histograms to extract additional insight, in this case to probe particle size-dependent electrokinetics. Our method is illustrated for a suspension of prototypical iron (III) oxide (hematite, α-Fe2O3). We found that the electrophoretic mobility and ζ-potential are a linear function of the aggregate size. By analyzing the distribution of surface site types as a function of aggregate size we show that site coordination increases with increasing aggregate diameter. This observation explains why the acidity of the iron oxide particles decreases with increasing particle size.
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Karolina
K
Kedra-Królik
Pacific Northwest National Laboratory, Richland, WA, United States.
Kevin M
KM
Rosso
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland. Electronic address: zarzycki.piotrek@gmail.com.
Piotr
P
Zarzycki
-Fe(2)O(3); Central Limit Theorem; Electrical double layer; Electrokinetics; Electrophoresis; Electrophoretic mobility; Hematite; Iron oxide/electrolyte interface; Particle size; Zeta potential