Surface tension reduction (STR) in aqueous solutions of anionic surfactants with cobalt(III) complexes

Sieng Sovanna, Takayoshi Suzuki, Masaaki Kojima, Satoshi Tachiyashiki, Masakazu Kita

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


It has been observed that, at 25.0 ± 0.1 ° C, [Co(NH3)6](ClO4)3, [Co(en)3](ClO4)3, [Co(bpy)3](ClO4)3, and [Co(phen)3](ClO4)3 in the regions of 1.25-5.00 mM aqueous solutions cause a significant surface tension reduction (STR) of water by the surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SBS), suggesting the formation of the 1:1 and 1:2 association complexes, {[complex]3+(S-)}2+ and {[complex]3+(S-)2}+ where [complex]3+ = [Co(NH3)6]3+, [Co(en)3]3+, [Co(bpy)3]3+, or [Co(phen)3]3+, S- = DS- or BS-. The effect of [Co(en)3]3+ on STR in SDS-water system is the largest due to a strong hydrophilic interaction between amino protons of [Co(en)3]3+ and sulfate oxygen atoms of DS-. The effects of [Co(en)3]3+, [Co(bpy)3]3+, and [Co(phen)3]3+ on STR in SBS-water system are significant and almost same, meaning that the hydrophilic interaction between [Co(en)3]3+ and the sulfonate group is comparable to the hydrophobic interaction between [Co(bpy)3]3+ or [Co(phen)3]3+ and the phenyl group of BS-. The Co(III) complexes of 1.25-5.00 mM are precipitated as {[complex]3+(S-)3} at 0.0295-0.173 mM of S-. The precipitates, {[Co(bpy)3]3+(S-)3} and {[Co(phen)3]3+(S-)3} can be dissolved at higher molar ratio of [S-]/[complex3+] than 3.5 for SDS and 4.0 for SBS. This observation suggests that the aggregated premicelle [Co(bpy or phen)3]2(DS)-7 or aggregated premicelle [Co(bpy or phen)3](BS)-4 is formed.

Original languageEnglish
Pages (from-to)194-200
Number of pages7
JournalJournal of Colloid And Interface Science
Issue number1
Publication statusPublished - Apr 1 2009


  • Co(III) complexes
  • Hydrophilic interaction
  • Hydrophobic interaction
  • Sodium dodecylbenzenesulfonate
  • Sodium dodecylsulfate
  • Surface tension

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry


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