Modifying the structure and flow behaviour of aqueous montmorillonite suspensions with surfactant

Abstract

Colloidal suspensions of plate-like particles undergo a variety of phase transitions. The predicted isotropic/ nematic transition is often pre-empted by a sol/gel transition, especially in suspensions of the most commonly used natural swelling clay montmorillonite (MMT). A number of factors, including charge interactions, flexibility and salt concentration, may contribute to this competition. In this study, the effect of surfactant adsorption on suspensions of MMT was studied using rheology, small-angle X-ray scattering, static light scattering and optical microscopy. The addition of a polyetheramine surfactant reduced the moduli of the system and shifted the sol/gel transition to a much higher clay concentration, compared with suspensions of bare clay particles. Yet, scattering data revealed no change in suspension structure on length scales up to around a micrometre. Primary aggregates remain at this length scale and no nematic phase is formed. There is, however, a change in structure at large length scales (of order 20 µm) where light scattering indicates the presence of string-like aggregates that disappear on addition of surfactant. Microscope images of dried suspensions also revealed a string-like structure. The dried strings show strong birefringence and may consist of concentric cylinders, self-assembled from clay sheets.

Smectite clay – inorganic nanoparticle mixed suspensions: phase behaviour and rheology

“…There have been signicant developments in the ability to study the structure of clay dispersions using techniques such as cryo-TEM, 80 ultra small angle X-ray scattering, 81 X-ray uorescence microscopy, 82 environmental scanning electron microscopy, 83 transmission X-ray microscopy, [84][85][86] and differential interference contrast microscopy. 87 This has led to some convergence of the views on the structure of clay gels. It appears that the house of cards structure is limited to the regime of low pH and moderate to high electrolyte concentration where the positive edge charge is not screened by the extent of the double layer from the large negative face charge.…”

Spontaneous evolution of self-assembled phases from anisotropic colloidal dispersions

“…Recently, we have reported the sol-gel transition behavior in laponite-MMT mixed clay dispersions 6 . On the other hand, visco-elastic properties of many clay suspensions have been extensively probed [7][8][9][10] . For instance, …”

“…Recently, we have reported the sol-gel transition behavior in laponite-MMT mixed clay dispersions 6 . On the other hand, visco-elastic properties of many clay suspensions have been extensively probed [7][8][9][10] through face (−)/edge (+) (FE) attraction form "house of cards" structures in acidic medium and band-like structures are formed through cation-mediated face (−)/face (−) (FF) attraction in alkaline medium 13 . The nature and mechanical strength of these microstructures formed are shown to be influenced by the structure and nature of the adsorbed additives 14 .…”

New frontiers in anisotropic fluid–particle composites

“…Jeroen van Duijneveldt [10] the montmorillonite plates was described as one possible reason, charge separation could be another ( figure 6). Henk Lekkerkerker [11] brought the session to a close with a brief, but educating and entertaining, history of mineral colloidal liquid crystals.…”