Sodium Triflate Decreases Interaggregate Repulsion and Induces Phase Separation in Cationic Micelles

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Abstract

Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissociation (a), lower hydration, and higher packing of monomers than other micelles of similar structure. Addition of sodium triflate ([NaTf] > 0.05 M) to DTATf solutions promotes phase separation. This phenomenon is commonly observed in oppositely charged surfactant mixtures, but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the observed phase separation with added salt remain unclear. Thus, we propose an interpretation for the observed phase separation in cationic surfactant solutions. Addition of up to 0.03 M NaTf to micellar DTATf solutions led to a limited increase of the aggregation number, to interface dehydration, and to a progressive decrease in a. The viscosity of DTATf solutions of higher concentration ([DTATf] = 0.06 M) reached a maximum with increasing [NaTf], though the aggregation number slightly increased, and no shape change occurred. We hypothesize that this maximum results from a decrease in interaggregate repulsion, as a consequence of increased ion binding. This reduction in micellar repulsion without simultaneous infinite micellar growth is, probably, the major driving force for phase separation at higher [NaTf].

Details

Authors
  • Filipe S. Lima
  • Iolanda M. Cuccovia
  • Richard Buchner
  • Filipe E. Antunes
  • Björn Lindman
  • Maria G. Miguel
  • Dominik Horinek
  • Hernan Chaimovich
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry
Original languageEnglish
Pages (from-to)2609-2614
JournalLangmuir
Volume31
Issue number9
Publication statusPublished - 2015
Publication categoryResearch
Peer-reviewedYes