Assembly of clay mineral platelets, tactoids, and aggregates: Effect of mineral structure and solution salinity

Maoz Dor, Yael Levi-Kalisman, Ruarri J. Day-Stirrat, Yael Mishael*, Simon Emmanuel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Clay mineral properties, together with solution chemistry, control the assembly of clay platelets into hierarchical structures, including tactoids and aggregates. We studied the effect of salinity on the assembly of kaolinite, illite, and montmorillonite at three critical scales: platelet, tactoid, and aggregate, using cryogenic scanning electron microscopy (cryo-SEM), atomic force microscopy (AFM) and cryo-transmission EM (cryo-TEM), respectively. Cyro-SEM images coupled with original alignment analysis indicate that the degree of aggregate alignment in an ionized solution was significantly higher than in deionized water. Furthermore, upon increasing platelet-platelet bonding energy (montmorillonite > illite > kaolinite), tactoid size increased, packing was less ordered, and aggregate alignment decreased. AFM measurements showed that an increase in ionic-strength caused a decrease in the Young's modulus of the clays, indicating higher tactoid alignment, since, disordered structures, comprising various platelet orientations, are stiffer than highly-aligned structures. We successfully measured distances <1 nm, for both kaolinite and montmorillonite by cryo-TEM, directly demonstrating that increasing ionic-strength reduces platelet-platelet distances. The outcome of this study offers a new approach and methodology to study fundamental colloid-assembly which will trigger future studies investigating additional parameters affecting assembly such as, temperature, solution pH, natural organic matter, and anthropogenic activity.

Original languageAmerican English
Pages (from-to)163-170
Number of pages8
JournalJournal of Colloid and Interface Science
StatePublished - 15 Apr 2020

Bibliographical note

Publisher Copyright:
© 2020 Elsevier Inc.


  • Alignment
  • Atomic force microscopy
  • Clay mineral aggregate
  • Clay mineral assembly
  • Cryogenic electron microscopy
  • Salinity


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