Evaluation of the exfoliation and stability of Na-montmorillonite in aqueous dispersions

Ali, Samim; Bandyopadhyay, Ranjini

doi:10.1016/j.clay.2015.05.013

Cited by 32 publications

(17 citation statements)

References 44 publications

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“…S11, ESI ‡), reveal that due to the considerable screening of negative charges on the basal surfaces, the face-face aggregation process due to van der Waals attractions becomes dominant under very high salt conditions [52]. Such parallel aggregation of platelets for low clay and high salt concentrations was also observed indirectly using ultrasound attenuation spectroscopy in our earlier study [48]. The face-face aggregation occurs very randomly and leads to elongated and thicker branches known as band structures ( Fig.…”

Section: Resultsmentioning

confidence: 61%

“…In this article, we present our results on the influence of NaCl on the microstructures, viscoelasticity, yielding and stability of Na-montmorillonite gels at a clay concentration, 5% w/v, at which the dispersion is expected to exhibit a glassy phase in the absence of salt [48]. Microscopic observations using cryogenic scanning electronic microscopy (cryo-SEM) reveal that at low salt concentrations, the clay platelets form longer sheet structures (the network branches) through attractive overlapping coin (OC) configurations predicted in a simulation study recently [52].…”

Section: Discussionmentioning

confidence: 99%

“…As a result, tactoids slowly swell and exfoliate, producing laminar flexible platelets with electric double layers (EDLs) on their surfaces [45][46][47][48]. The exfoliated platelets are highly irregular in shape and size (shown in a representative SEM micrograph in Fig.…”

Section: Experimental Section a Materials Structurementioning

confidence: 99%

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Effect of electrolytes on the microstructure and yielding of aqueous dispersions of colloidal clay

Ali

Bandyopadhyay

2016

Soft Matter

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Na-montmorillonite is a natural clay mineral and is available in abundance in nature. The aqueous dispersions of charged and anisotropic platelets of this mineral exhibit non-ergodic kinetically arrested states ranging from soft glassy phases dominated by interparticle repulsions to colloidal gels stabilized by salt induced attractive interactions. When the salt concentration in the dispersing medium is varied systematically, viscoelasticity and yield stress of the dispersion show non-monotonic behavior at a critical salt concentration, thus signifying a morphological change in the dispersion microstructures. We directly visualize the microscopic structures of these kinetically arrested phases using cryogenic scanning electron microscopy. We observe the existence of honeycomb-like network morphologies for a wide range of salt concentrations. The transition of the gel morphology, dominated by overlapping coin (OC) and house of cards (HoC) associations of clay particles at low salt concentrations to a new network structure dominated by face-face coagulation of platelets, is observed across the critical salt concentration. We further assess the stability of these gels under gravity using electroacoustics. This study, performed for concentrated clay dispersions for a wide concentration range of externally added salt, is useful in our understanding of many geophysical phenomena that involve the salt induced aggregation of natural clay minerals.

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Section: Resultsmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 99%

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Effect of electrolytes on the microstructure and yielding of aqueous dispersions of colloidal clay

Ali

Bandyopadhyay

2016

Soft Matter

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“…However, we find the RR–AR transition for S M55_L2 occurs at C P = 0.5%, which is smaller than the theoretical C sat . Recent experiments using dynamic light scattering and ultrasound attenuation spectroscopy techniques have shown that the distribution of laponite ® particles in suspensions in the early time periods is bimodal, and not monodisperse as one would expect. This was attributed to the fact that there may be partially exfoliated weak aggregates/clusters of particles or stacks of two or more laponite ® particles present in the system.…”

Section: Resultsmentioning

confidence: 96%

Multiple dynamic regimes in colloid‐polymer dispersions: New insight using X‐ray photon correlation spectroscopy

Srivastava

Kishore

Narayanan

et al. 2015

J. Polym. Sci. Part B: Polym. Phys.

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We present an X-ray photon correlation spectroscopy (XPCS) study of dynamic transitions in an anisotropic colloid-polymer dispersion with multiple arrested states. The results provide insight into the mechanism for formation of repulsive glasses, attractive glasses, and networked gels of colloids with weakly adsorbing polymer chains. In the presence of adsorbing polymer chains, we observe three distinct regimes: a state with slow dynamics consisting of finite particles and clusters, for which interparticle interactions are predominantly repulsive; a second dynamic regime occurring above the saturation concentration of added polymer, in which small clusters of nanoparticles form via a short-range depletion attraction; and a third regime above the overlap concentration in which dynamics of clusters are independent of polymer chain length. The observed complex dynamic state diagram is primarily governed by the structural reorganization of a nanoparticle cluster and polymer chains at the nanoparticle-polymer surface and in the concentrated medium, which in turn controls the dynamics of the dispersion.

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“…As shown in Table 2, the ζ values of t‐M20, t‐MM20, and t‐MM50 are all around −30 mV, probably because MMT itself has good dispersibility in water, and the improvement of dispersibility at low MCA addition is limited. But it is worth noting that the good dispersibility of MMT itself in water is caused by the formation of tactoids that are composed of more than one layer, meaning the incomplete exfoliation 26 . The t‐MM80 has a minimum ζ value of −52.5 ± 1.1 mV at pH = 7, suggesting the exfoliated MMT monolayer is highly stable in aqueous solution and the aggregation of MMT layers is strongly reduced by MCA.…”

Section: Resultsmentioning

confidence: 99%

Fast prepare exfoliated montmorillonite water suspension with assistance of melamine cyanurate and the superlattice obtained by self‐assembly

Qin

Hao

2021

Polymers for Advanced Techs

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To explore the exfoliation mechanism of montmorillonite (MMT) layers assisted by melamine cyanurate (MCA), the MCA crystal structures based on the concentration of raw materials and the preparation of MMT‐MCA superlattice are investigated. Here, the correlation between MCA crystal growth and concentration of cyanuric acid (CA) and melamine (MA) water solutions on glass substrate are analyzed using XRD and SEM. With the increasing of concentration of CA and MA water solutions, the stacking of MCA layers along [202] axis is enhanced gradually compared with the growth of single MCA layer along (202) plane, resulting in the transform of MCA morphology from sheet to column. The exfoliated MMT monolayers with sizes of hundreds on nanometer can be obtained and well dispersed in the supernatant of MMT‐MCA superlattice. After removing the solvent of the supernatant, the formed coating show that the MCA crystal with columnar structure is well inserted into MMT galleries, which is the main driving force that increases basal spacing (d‐space) of MMT layers. And, the sandwich‐like superlattice is formed by the restacking of MMT and MCA in the coating of MMT‐MCA suspension, where the MMT is single or few layers, and the d‐space of MMT can even be increased to micron‐scale.

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Evaluation of the exfoliation and stability of Na-montmorillonite in aqueous dispersions

Cited by 32 publications

References 44 publications

Effect of electrolytes on the microstructure and yielding of aqueous dispersions of colloidal clay

Effect of electrolytes on the microstructure and yielding of aqueous dispersions of colloidal clay

Multiple dynamic regimes in colloid‐polymer dispersions: New insight using X‐ray photon correlation spectroscopy

Fast prepare exfoliated montmorillonite water suspension with assistance of melamine cyanurate and the superlattice obtained by self‐assembly

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