THE RHEOLOGICAL AND COLLOIDAL PROPERTIES OF BENTONITE DISPERSIONS IN THE PRESENCE OF ORGANIC-COMPOUNDS .5. BENTONITE AND SODIUM MONTMORILLONITE AND SURFACTANTS

The influence of surfactants on the flow behavior of sodium montmorill onite dispersions (2% w/w) was studied for a cationic (cetylpyridinium chloride, CPCl) and an anionic surfactant (sodium dodecylsulfate, SDS ). When the dispersion pHs were > 3.5 and < 7, CPCl concentrations > 1 0(-4) M increased the shear stress but the Bingham yield value remaine d virtually unchanged (tau(o) approximate to 100 mPa). At pH approxima te to 7, the shear stress and yield point decreased with increasing CP Cl concentration (tau(o) from 430 to 100 mPa). The flow properties of sodium calcium bentonite dispersions were independent of pH and CPCl c oncentrations less than or equal to 10(-4) M; they increased modestly at higher concentrations. At pH < 4, SDS addition to the sodium montmo rillonite dispersions increased the shear stress and yield value to a maximum value (tau(o) = 2100 mPa) at 10(-3) M SDS; higher SDS concentr ations reduced the shear stress and yield value. At pH > 4, the flow v alues decreased to a minimum value at 10(-2) M SDS (tau(o) from 430 to 50 mPa). The flow of the sodium calcium bentonite dispersions at pH > 4 was independent of SDS concentrations less than or equal to 10(-3) mole/liter; at higher SDS concentrations, the flow values increased mo re strongly in sodium calcium bentonite than in sodium montmorillonite dispersions. Surfactants influence the flow behavior of sodium montmo rillonite dispersions by their action on the card-house networks in st rongly acidic medium and, at higher pH, by the electroviscous effect. At the highest surfactant concentrations without flocculation, the she ar stress and yield value are increased by interacting chains of oppos ed particles. Addition of the surfactants increases the salt (NaCl) st ability of the dispersions because the adsorbed surface active agents influence the counterion distribution between the Stern and the diffus e ionic layer.