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Surface modification of bentonites. V. Sol-gel transitions of Ca-montmorillonite in the presence of cationic end-capped poly(ethylene oxides)

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

(Received 8 November 2006; revised 17 January 2007)

The colloidal state of aqueous Ca²⁺-montmorillonite dispersions was modified with three types of cationic end-capped poly(ethylene oxides). The macromolecules were not only adsorbed at the external surfaces but were also intercalated into the dispersed montmorillonite particles. The amounts adsorbed and the basal spacings (1.7 nm) were comparable to the corresponding Na⁺-montmorillonite dispersions. The poly(ethylene oxides) protruding out of the interlayer spaces or adsorbed at the external surface determined the colloidal behaviour of the dispersions. The phase diagrams (sol-gel diagrams) of the Ca²⁺-montmorillonite dispersions differed from those of the corresponding Na⁺-montmorillonite because of the different colloidal states of both dispersions (Ca²⁺-montmorillonite particles vs. delaminated Na⁺-montmorillonite). The phase diagrams of the poly(ethylene oxide) containing Ca²⁺-montmorillonite dispersions showed fields of sol and flocs. Attractive gels were formed in a few cases only (TMA⁺-PEO 1500 and 4000, THA²⁺-PEO 1500, 4000 and 20,000) and with distinctly lower gel strength than in the presence of Na⁺ ions. On the basis of the sol-gel diagrams, conditions (type and concentration of poly(ethylene oxides), montmorillonite content) can be selected which lead to peptization of the Ca²⁺-montmorillonite particles into stable colloidal dispersions (sols). Addition of cationic poly(ethylene oxides) can enhance the salt tolerance up to 1000 mmol/l NaCl.

KEYWORDS: colloidal clay dispersions, montmorillonite, poly(ethylene oxides), polymer adsorption, sol-gel diagrams, steric stabilization

This article has been cited by other articles:

				S. ZIESMER and G. LAGALY Surface modification of bentonites. VI. Sol-gel transitions of sodium and calcium montmorillonite dispersions in the presence of anionic end-capped poly(ethylene oxides) Clay Minerals, December 1, 2007; 42(4): 563 - 573. [Abstract] [Full Text] [PDF]