Phase equilibriums, self-assembly and interactions in two-, three- and four medium-chain length component systems

Jarl B. Rosenholm*

*Corresponding author for this work

Research output: Contribution to journalReview Article or Literature Reviewpeer-review

17 Citations (Scopus)

Abstract

The Scandinavian surface (surfactant) and colloid science owes much of its success to Per Ekwall and Björn Lindman. In this review the main topics shared by their research groups at Åbo Akademi University in Finland and at Lund University in Sweden are described. The nature of surface active substances (cosolvents, co-surfactants and surfactants) and microemulsions are evaluated. It is shown that the properties of medium-chain length surfactants differ dramatically from long-chain surfactants. The phase equilibriums of binary systems are related to the phase equilibriums of ternary and quaternary systems referred to as microemulsions or more recently also as nanoemulsions. A distinction is made between hydrotrope liquids, detergentless microemulsions, surfactant mixture systems and microemulsions. Three component systems are assembled to "true" quaternary microemulsions. An exceptionally comprehensive network of thermodynamic parameters describing molecular site exchange and micelle formation are derived and related mutually. Gibbs free energy, enthalpy, entropy, volume, heat capacity, expansivity and compressibility can be used to illustrate the degree of aggregation cooperativity and to evaluate whether micelle formation is of a first-, second- or intermediate order phase transition. Theoretical simulations and experimental results show that the associate structures of medium-chain length surfactants are quite open and may be deformed due to small aggregation numbers. The self-assembly occurs over a number of distinct steps at a series of experimentally detectable critical concentrations. Despite the low aggregation tendency their phase behavior equals those of long-chain homologs in surfactant mixture and microemulsion systems. A number of models describing the self-assembly are reviewed. Nuclear magnetic resonance (shift, relaxation rate and diffusion), Laser Raman and infrared spectroscopies were chosen as key instruments for molecular interaction characterization since they were used in the collaboration between the research groups in Åbo and in Lund. A new method is introduced in order to evaluate the traditional procedure for extracting limiting parameters which also enables an illustration of the degree of cooperativity. The focus is laid mainly on aqueous, alcoholic, saline and, to a limited extent oil phases of one-, two-, three- and four component systems of water-sodium carboxylates-alcohol-oil. The extensive thermodynamic characterization of these liquid phases and liquid crystalline phases is left out due to space restrictions.

Original languageEnglish
Pages (from-to)9-47
Number of pages39
JournalAdvances in Colloid and Interface Science
Volume205
DOIs
Publication statusPublished - Mar 2014
MoE publication typeA2 Review article in a scientific journal

Keywords

  • Cooperativity
  • Hydrotrope-, surfactant mixture- and solvent systems
  • New model for molecule interaction and self-assembled structure
  • NMR-Laser-Raman-FTIR spectroscopy
  • Order of phase transition
  • Phase equilibriums
  • Theoretical simulations
  • Thermodynamic models for microemulsion formation
  • Two-, three- and four component microemulsions

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