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.

The colloidal state (sol, flocs, gels) of Na-montmorillonite dispersions (from bentonite from Bavaria, Germany) was adjusted by the addition of poly(ethylene oxides) with terminal trimethylammonium groups. The colloidal state of the dispersions changed with the molar mass of these end-capped poly(ethylene oxides). The sol-gel diagrams (up to 4.5% (w/w) montmorillonite) in the presence of TMA-PEO 1500 and TMA-PEO 4000 (up to 40 g/l) were characterized by large fields of gel whereas TMA-PEO 20000 and TMA-PEO 35000 caused peptization by steric stabilization. Even dispersions with the highest montmorillonite content (4.5%) were peptized by >0.2 g/l TMA-PEO 35000. The critical coagulation concentration of NaCl was increased by the polymer addition, but the increase was modest (from 8-12 mmol/l to 50 mmol/l). The changes of the colloidal state, the flow behaviour and the salt coagulation reveal the sensitive interplay between stabilization mechanisms (electrostatic, steric) and destabilization effects (bridging, charge compensation, depletion flocculation).