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 language | English |
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Pages (from-to) | 424-439 |
Number of pages | 16 |
Journal | Physical Chemistry Chemical Physics |
Volume | 15 |
Issue number | 2 |
Early online date | 2 Nov 2012 |
DOIs | |
Publication status | Published - 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