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Thermodynamics of

Yasuhiro Umebayashi1, Mari Shin, Ryo Kanzaki

  • 1Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan

Journal of Colloid and Interface Science
|May 4, 2001
PubMed
Summary

The study investigated cobalt(II)-thiocyanato complex formation in nonionic surfactant solutions, revealing that micelles have a heterogeneous structure. Thermodynamic analysis indicates distinct interactions at ethylene oxide and octylphenyl moieties within the micelles.

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Area of Science:

  • Coordination Chemistry
  • Surfactant Science
  • Thermodynamics

Background:

  • Nonionic surfactants of the poly(ethylene oxide) type are widely used in various chemical applications.
  • Understanding the complexation behavior of metal ions within surfactant micelles is crucial for optimizing processes.
  • Cobalt(II)-thiocyanato complexes serve as model systems for studying ion-surfactant interactions.

Purpose of the Study:

  • To investigate the formation of cobalt(II)-thiocyanato complexes in poly(ethylene oxide) nonionic surfactant solutions.
  • To elucidate the role of varying poly(ethylene oxide) chain lengths on complex formation.
  • To determine the thermodynamic parameters associated with complexation in aqueous and micellar phases.

Main Methods:

  • Titration spectrophotometry was employed to monitor complex formation.

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  • Calorimetry was used to determine the enthalpy changes associated with complexation.
  • Data analysis involved assuming the formation of ternary complexes and calculating overall formation constants.

    • Main Results:

    • Cobalt(II)-thiocyanato complexes form in both aqueous and micellar phases, with specific species identified (Co(NCS)(+), Co(NCS)(2), and Co(NCS)(4)Y(2-)).
    • The ratio of complex formation constants (beta(41)/beta(20)) increased with longer poly(ethylene oxide) chains.
    • Thermodynamic parameters revealed a heterogeneous micellar structure, with distinct contributions from ethylene oxide and octylphenyl moieties.

    Conclusions:

    • The inner structure of nonionic surfactant micelles is heterogeneous, comprising both ethylene oxide and octylphenyl groups.
    • The ethylene oxide moiety interacts with water via hydrogen bonding, influencing the solvation of the cobalt complex.
    • Thermodynamic data provide insights into the specific interactions governing cobalt-thiocyanato complexation within surfactant systems.