Effect of sodium pyrophosphate and understanding microstructure of aqueous LAPONITE^®dispersion using dissolution study

Abstract

In this work, we investigate physical origin of ergodicity breaking in an aqueous colloidal dispersion of synthetic hectorite clay, LAPONITE ® , at pH 10 by performing dissolution and rheological experiments with monovalent salt and tetrasodium pyrophosphate solution. We also study the effect of interface, nitrogen and paraffin oil on the same. Dissolution experiments carried out for dispersions with both the interfaces show similar results. However, for samples with nitrogen interface, all the effects are observed to get expedited in time compared to paraffin oil interface. When kept in contact with water, 1.5 wt. % and 2.8 wt. % colloidal dispersion at pH 10 swell at small ages, while do not swell at large ages. The solution of tetrasodium pyrophosphate, interestingly, dissolves the entire colloidal dispersion samples with pH 10 irrespective of the concentration of clay. Experiments carried out on colloidal dispersions prepared in water having pH 13 demonstrate no effect of water as well as sodium pyrophosphate solution on the same suggesting a possibility of the presence of negative charge on edge at that pH. We believe that all the behaviors observed for samples at pH 10 can be explained by an attractive gel microstructure formed by edgeto-face contact. Furthermore, the absence of swelling in old colloidal dispersion at pH 10 and dissolution of the same by sodium pyrophosphate solution cannot be explained by merely repulsive interactions. This behavior suggests that attractive interactions originating from edge-to-face contact play an important role in causing ergodicity breaking in the colloidal dispersions at pH 10 at all the ages irrespective of the clay concentration. We further substantiate the presence of fractal network structure formed by interparticle edge-face association using rheological tools and cryo-TEM imaging. We also conduct a comprehensive study of the effect of tetrasodium pyrophosphate in the sol-gel transition of LAPONITE ® dispersion.

Phase-Selective Gelation of the Water Phase in an Oil–Water Mixture: An Approach Based on Oil-Activated Nanoparticle Assembly in Water

“…When the BA enters the water, the acidinduced reduction in pH to about 7 imparts cationic charges to the edges of the LAP disks, while the faces retain their anionic charges. 20,21 Further, we speculate that some of the P123 desorbs from the faces of the LAP disks, which is consistent with previous reports showing that the interaction of polymers with laponite is pH-dependent. 31−33 At this point, the cationic edges of LAP disks bind to the anionic faces of adjacent disks (Figure 6).…”

“…When LAP (3 wt %) is added to water, the particles initially form a stable suspension (sol). Over time (around a day), the particles aggregate to form a three-dimensional network (gel) due to interactions between the edges and faces of the disks. ,, This type of network is termed a “house-of-cards” structure. If the water contains a “stabilizer”, however, gel formation of LAP can be prevented. , Typical stabilizers for LAP are the triblock copolymers from the Pluronic family .…”

“…Over time (around a day), the particles aggregate to form a three-dimensional network (gel) due to interactions between the edges and faces of the disks. 18,20,21 This type of network is termed a "house-ofcards" structure. If the water contains a "stabilizer", however, gel formation of LAP can be prevented.…”

Improving Colloidal Stability of Sepiolite Suspensions: Effect of the Mechanical Disperser and Chemical Dispersant

“…It was expected that this compound could act as a good dispersing/stabilizing agent in the studied range. It is important to highlight that phosphates are traditionally used as dispersing agents for clay suspensions [36]. However, for sepiolite 1, it seems that the highly negative charge density of the polyphoshate did not favor the interaction with the clay, unless ultrasonication is applied in the system.…”

Mixture design applied to the rheology of clay gel mixtures

“…This is to insure that the product will be stable for a long enough time without being too As shown by the plots, the pH has a significant effect on the blending behaviour with a lower pH favouring higher values of G ′ and hence stronger gels. The isoelectric point of bentonite is around 7 (Benna et al 1999), and around 10.5 for raw Laponite (Suman et al 2020). Therefore, at pH 4, both bentonite and Laponite feature positively charged edges.…”