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Stabilizing Colloidal Particles against Salting-out by Shortening Surface Grafts

Journal article
Authors Kristin Jonsson
Jeanette Ulama
Rasmus Persson
Malin Zackrisson Oskolkova
Michael Sztucki
Theyencheri Narayanan
Johan Bergenholtz
Published in Langmuir
Volume 35
Issue 36
Pages 11836−11842
ISSN 0743-7463
Publication year 2019
Published at Department of Chemistry and Molecular Biology
Pages 11836−11842
Language en
Links https://doi.org/10.1021/acs.langmui...
Keywords colloids, small-angle X-ray scattering, colloidal stability, PEG, steric stabilization, aggregation, wetting
Subject categories Surface and colloid chemistry

Abstract

A dramatic improvement is reported in the stability of colloidalparticles when stabilizing surface grafts are systematically shortened from small polymers to single monomers. The colloidal dispersions consist of fluorinated latex particles, exhibiting a weak van der Waals attraction, with grafted steric layers of poly(ethylene glycol) (PEG) of different chain lengths. Using an effective salting-out electrolyte, Na2CO3, particle aggregates are detected above a threshold salt concentration that is independent of the particle concentration. The results are interpreted in terms of a sudden onset of nondispersibility of single particles, triggered by the solvent not completely wetting particle surfaces. By decreasing the PEG chain length, the threshold salt concentration is found to increase sharply. For grafts with just a single ethylene glycol group, dispersions remain stable up to exceedingly high concentrations of Na2CO3. However, on removal of the surface coverage altogether, the classical stability behavior of charge-stabilized dispersions is recovered. The behavior can be captured by a simple model that incorporates effective polymer−solvent interactions in the presence of an electrolyte.

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