Financial support from Ministerio de Ciencia, Innovación y Universidades (Spain) ( GC2018-098770-B-I00 ), and Junta de Andalucía (Spain) and European Funds for Regional Development ( BF-FQM-141-UGR18 , PI20-00233 ) is gratefully acknowledged.Financial support from Ministerio de Ciencia, Innovación y Universidades (Spain) (GC2018-098770-B-I00), and Junta de Andalucía (Spain) and European Funds for Regional Development (BF-FQM-141-UGR18, PI20-00233) is gratefully acknowledged.Because of their singular phenomenology, the so-called salt-free colloids constitute a special family of dispersed
systems. Their main characteristic is that the dispersion medium ideally contains only the solvent and the ions
compensating exactly the surface charge of the particles. These ions (often called released counterions) come into
the solution when the surface groups responsible for the particles charge get ionized. An increasing effort is
nowadays dedicated to rigorously compare theoretical model predictions for ideal salt-free suspensions, where
only the released counterions are supposed to be present in solution, with appropriately devised experiments
dealing with colloids as close as possible to the ideal salt-free ones. Of course, if the supporting solution is
aqueous, the presence of atmospheric contamination and any other charged species different from the released
counterions in the solution must be avoided. Because this is not an easy task, the presence of dissolved atmospheric CO2 and of H+ and OH− from water dissociation cannot be fully discarded in aqueous salt-free solutions
(often denominated realistic in such case). Ultimately, at some point, the role of the released counterions will be
comparable or even larger in highly charged concentrated colloids than that of added salts. These topics are
covered in the present contribution. The model results are compared with experimental data on the dynamic
mobility and dielectric dispersion of polystyrene spheres of various charges and sizes. As a rule, it is found that
the model correctly predicts the significance of alpha and Maxwell-Wagner-O'Konski relaxations. Positions and
amplitudes of such relaxations are well predicted, although it is necessary to assume that the released counterions are potassium or sodium instead of protons, otherwise the frequency spectra of experimental mobility and
permittivity differ very significantly from those theoretically calculated. The proposed electrokinetic evaluation
is an ideal tool for detecting in situ the possible contamination (or incomplete ion exchange of the latexes). A
satisfactory agreement is found when potassium counterions are assumed to be in solution, mostly if one considers that the comparison is carried out without using any adjustable parameters.Ministerio de CienciaMinisterio de Ciencia, Innovación y Universidades
GC2018-098770-B-I00European Regional Development Fund
BF-FQM-141-UGR18, PI20-00233Junta de Andalucí
