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The specific co-ion effect on gelling and surface charging of silica nanoparticles: Speculation or reality?

Journal article
Authors Isabelle Simonsson
Christian Sögaard
Mark Rambaran
Zareen Abbas
Published in Colloids and Surfaces A: Physicochemical and Engineering Aspects
Volume 559
Pages 334-341
ISSN 09277757
Publication year 2018
Published at Department of Chemistry and Molecular Biology
Pages 334-341
Language en
Keywords Activity coefficients, Co-ion effect, Gel-Times, Ion pairing, Potentiometric titrations, Silica nanoparticles, Silica surface chemistry, Surface charge
Subject categories Inorganic Chemistry, Materials Chemistry


© 2018 Elsevier B.V. Based on extensive experimental investigations on many different oxide nanoparticles, it is now a well-established view that the counter-ions exhibit ion specific effects due to their high charge density and strong interaction with oppositively charged surfaces. On the other hand, studies regarding co-ion effects are scarcely reported in the literature. In this study we have measured the surface charge densities and gel-times of silica nanoparticles in a number of salts which have the same counter-ions but different co-ions, i.e. anions in this case. Gel-times were measured in LiCl, NaCl, NaNO3, NaClO4, NaClO3and Na2SO4as well as in KCl, KNO3, and K2SO4. We have seen clear correlations between the gel-times and the extent of ion pairing in the solutions; salts that have strong ion pairing exhibit longer gel-times than salts having highly dissociated ions. To better understand the mechanisms at work we have determined the surface charging of silica nanoparticles in these salt solutions and we have observed that the surface charging behavior of silica nanoparticles follows the trends seen in the gel-time studies. From our gel-time determinations and potentiometric measurements we can claim that there is a clear co-ion effect on the gelling and surface charging of silica nanoparticles.

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