Sulfometuron incorporation in cationic micelles adsorbed on montmorillonite

Yael Golda Mishael, Tomas Undabeytia, Giora Rytwo, Brigitte Papahadjopoulos-Sternberg, Baruch Rubin, Shlomo Nir*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


The aim of this study was to understand the interactions between alkylammonium cations present as monomers and micelles and a clay mineral, montmorillonite, to develop slow release formulations of anionic herbicides, such as sulfometuron (SFM) whose leaching in soils is an environmental and economic problem. In the proposed formulation the herbicide is incorporated in positively charged micelles of quaternary amine cations, which in turn adsorb on the negatively charged clay. The adsorption of hexadecyltrimethylammonium (HDTMA) and octadecyltrimethylammonium (ODTMA) on montmorillonite was studied above and below their critical micelle concentrations (CMC). At concentrations above the CMC, the loading exceeded the clay's cation exchange capacity (CEC) and indicated higher affinity of the cation with the longer alkyl chain. An adsorption model could adequately simulate adsorption at concentrations below the CMC, and yield fair predictions for the effect of ionic strength. The model indicated that above the CMC adsorbed micelles contributed significantly to the amount of ODTMA adsorbed. Evidence for adsorption of ODTMA micelles on montmorillonite was provided by X-ray diffraction, freeze-fracture electron microscopy, and dialysis bag measurements. SFM was not adsorbed directly on the clay mineral, and adsorbed at low levels, when the organic cation was adsorbed as monomers. In contrast, a large fraction of SFM adsorbed on the clay mineral when incorporated in micelles that adsorbed on the clay.

Original languageAmerican English
Pages (from-to)2856-2863
Number of pages8
JournalJournal of Agricultural and Food Chemistry
Issue number10
StatePublished - 8 May 2002


  • Adsorption model
  • Freeze-fracture electron microscopy
  • Hexadecyltrimethylammonium
  • Micelles
  • Montmorillonite; sulfometuron
  • Octadecyltrimethylammonium
  • X-ray diffraction


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