Sol–gel transitions of sodium montmorillonite dispersions by cationic end-capped poly(ethylene oxides) (surface modification of bentonites, IV)
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- Lagaly, G. & Ziesmer, S. Colloid Polym Sci (2006) 284: 947. doi:10.1007/s00396-006-1477-8
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Poly(ethylene oxides), PEO, end-capped with hexadecyl dimethylammonium, HDDMA+, and trimethylammonium hexyldimethylammonium, THA2+, changed distinctly the sol–gel transition of sodium montmorillonite dispersions. In the presence of HDDMA+-PEO 1,500 and 4,000, domains of sol with increased salt tolerance (ck=550–1,000 mmol NaCl/l) were found at high polymer and low montmorillonite contents. The corresponding PEO of higher molar mass (20,000 and 35,000) led to extended fields of flocs. THA2+-PEO 1,500 formed attractive gels at polymer concentrations >2–5 g/l and montmorillonite contents >0.5%. These gels showed very high yield values. THA2+-PEO of higher molar mass acted as stabilizing agents. The salt tolerance was highest (300–750 mmol/l) in the presence of THA2+-PEO 20,000. The observed sol–gel diagrams reveal the interplay between polymer end-group fixation on the clay mineral particles, polymer conformation, and colloidal stabilization and destabilization mechanisms.