Controlling Clusters of Colloidal Platelets: Effects of Edge and Face Surface Chemistries on the Behavior of Montmorillonite Suspensions

Abstract

The structural and rheological consequences of adsorbing pyrophosphate anions to the edges and polyetheramines to the faces of montmorillonite platelets in aqueous suspension were investigated. Oscillatory rheology and scattering experiments showed that the two surface treatments act in different regions of the phase diagram and that this can be attributed to modifications of local particle interactions resulting in changes to the behavior and morphology of platelet clusters. The polyetheramine was found to neutralize surface charge, reducing electrostatic repulsion between platelets and therefore allowing them to come into closer proximity. This reduces the effective volume fraction of the clusters and reverses jamming in low ionic strength arrested phases. Conversely, the adsorption of pyrophosphate was found to introduce a high concentration of negative charge to the particle edge, resisting the formation of bonded percolating gels at high ionic strength. The two separate surface chemistries can be applied in parallel with no adverse effects and thus have the potential to be applied to dual functionalization of two-dimensional colloids such as platelets. This has implications for finer formulation design where targeted rheology modification could be achieved by careful selection of chemistry at one surface accompanied by an additional function at the other.

Short- and Long-Range Attractive Forces That Influence the Structure of Montmorillonite Osmotic Hydrates

“…delaminate [also seen by Pignon and Ganley and van Duijneveldt using small-angle neutron scanning (SANS)/static light scattering (SLS)] (33,34). At intermediate q (0.01 < q < 0.05), the power law slope for SWy-2 suspended in water or 0.1 M NaCl is I(q) ∼ q -2 , characteristic of scattering from two-dimensional particles or sheets.…”

Steady-state droplet size in montmorillonite stabilised emulsions

“…This is unlikely here as Fig. 1 and 2 show that the particles are adsorbed as a single monolayer and although the montmorillonite platelets have been reported to form particle clusters in suspension 31,37 it has also been shown in high shear rotational rheometry that the particles behave hydrodynamically as single disk-like particles. 38,39 Finally there is the possibility that particles may desorb during high shear mixing.…”

“…Additionally this could be combined with previous work on rheology control using montmorillonite platelets 16,18,31 to produce a system where the minority component acts as a dual emulsion stabiliser and rheology modifier. This improvement in the understanding of platelet stabilised droplets in turbulent flow can be used to optimise the design of tightly controlled and efficient emulsion-based formulations for example Fig.…”

“…Montmorillonite dispersions were prepared as previously reported. 31 45 g L À1 powdered clay was added to deionised water and stirred for 24 hours. The suspension was then dialysed against aqueous NaCl (1 M) for 1 week changing the solution everyday, to remove unwanted ions such as Ca 2+ , and then dialysed against deionised water, changing water every day, until the conductivity of the dialysate was below 5 mS cm À1 .…”

Three-Phase Coexistence in Colloidal Rod–Plate Mixtures

“…To gauge the clay content in the isotropic phase, the transmission of light (632.8 nm) through the isotropic phase was measured using a setup described previously. 25 The transmission was compared to a blank cell filled with deionised water and the transmissions of known concentrations of pure clays were measured to create a Beer-Lambert plot (Supplementary Information).…”