Controlling colloid charge in nonpolar liquids with surfactants

Gregory Smith, Julian Eastoe

Research output: Contribution to journalArticle (Academic Journal)peer-review

70 Citations (Scopus)
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Abstract

The formation of ions in nonpolar solvents (with relative permittivity εr of approximately 2) is more difficult than in polar liquids; however, these charged species play an important role in many applications, such as electrophoretic displays. The low relative permittivities of these solvents mean that charges have to be separated by large distances to be stable (approximately 28 nm or 40 times that in water). The inverse micelles formed by surfactants in these solvents provide an environment to stabilize ions and charges. Common surfactants used are sodium dioctylsulfosuccinate (Aerosol OT or AOT), polyisobutylene succinimide, sorbitan oleate, and zirconyl 2-ethyl hexanoate. The behavior of charged inverse micelles has been studied on both the bulk and on the microscopic scale and can be used to determine the motion of the micelles, their structure, and the nature of the electrostatic double layer. Colloidal particles are only weakly charged in the absence of surfactant, but in the presence of surfactants, many types, including polymers, metal oxides, carbon blacks, and pigments, have been observed to become positively or negatively charged. Several mechanisms have been proposed as the origin of surface charge, including acid–base reactions between the colloid and the inverse micelle, preferential adsorption of charged inverse micelles, or dissolution of surface species. While most studies vary only the concentration of surfactant, systematic variation of the particle surface chemistry or the surfactant structure have provided insight into the origin of charging in nonpolar liquids. By carefully varying system parameters and working to understand the interactions between surfactants and colloidal surfaces, further advances will be made leading to better understanding of the origin of charge and to the development of more effective surfactants.
Original languageEnglish
Pages (from-to)424-439
Number of pages16
JournalPhysical Chemistry Chemical Physics
Volume15
Issue number2
Early online date2 Nov 2012
DOIs
Publication statusPublished - 14 Jan 2013

Keywords

  • REVERSE MICELLE FORMATION
  • SMALL-ANGLE NEUTRON
  • ELECTRICAL DOUBLE-LAYER
  • AEROSOL-OT
  • APOLAR MEDIA
  • ELECTROPHORETIC MOBILITY
  • NONAQUEOUS MEDIA
  • ORGANIC-SOLVENTS
  • LIGHT-SCATTERING
  • ELECTROSTATIC INTERACTIONS

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