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Surface modification of bentonites. VI. Sol-gel transitions of sodium and calcium montmorillonite dispersions in the presence of anionic end-capped poly(ethylene oxides)

Institute of Inorganic Chemistry, University of Kiel, D-24098 Kiel, Germany

^* E-mail: lagaly{at}ac.uni-kiel.de

(Received 10 May 2007; revised 9 October 2007)

Poly(ethylene oxides) (PEOs) with sulphonate groups attached at both chain ends (S-PEOs) were strongly adsorbed by dispersed Na- and Ca-montmorillonite particles. The amounts adsorbed were very similar to those of cationic end-capped poly(ethylene oxides). In both cases bilayers of PEO chains were intercalated so that the basal spacing of the particles reached the same plateau values of ~1.73 nm. In contrast, the influence of anionic PEOs on the colloidal behaviour of the Na- and Ca-montmorillonite dispersions was very different from the effect of the cationic PEOs. The shorter chain S-PEOs (S-PEO 1500, 4000) destabilized the Na-montmorillonite dispersions by coagulation due to the Na⁺ ions introduced as counterions to the S-PEOs. The longer chain S-PEO 20000 and S-PEO 35000 did not coagulate the Na-montmorillonite sols because the corresponding Na⁺ concentration did not reach the critical coagulation value. The slightly enhanced salt tolerance indicated that the long-chain PEOs exerted a weak steric stabilization. In contrast, bridging of the particles by S-PEO molecules and Ca²⁺ ions played an important role in destabilizing the Ca-montmorillonite dispersions in the form of flocs and formation of gels.

KEYWORDS: coagulation, colloids, flocculation, gel, montmorillonite, poly(ethylene oxides)