Abstract
HypothesisThe interaction of Aerosol OT (AOT) surfactant with systems of model colloids in nonaqueous solvents (water-in-oil microemulsions, surfactant-stabilized silica organosols, and sterically-stabilized PMMA latexes) is expected to be system specific. Two limiting cases are expected: adsorption, with surfactant located at the particle surfaces, or absorption, with surfactant incorporated into the particle cores. ExperimentsTwo approaches have been used to determine how AOT is distributed in the colloidal systems. The stability of the colloids in different alkanes (heptane to hexadecane, including mixtures) has been studied to determine any effects on the colloid surfaces. Contrast-variation small-angle neutron scattering (SANS) measurements of the colloid cores and of AOT-colloid mixtures in colloid-matched solvent have also been performed. Normalization to account for the different scattering intensities and different particle radii have been used to enable a system-independent comparison. FindingsAOT in water-in-oil microemulsions and surfactant-stabilized silica organosols is determined to be adsorbed, whereas, surprisingly, AOT in sterically-stabilized PMMA latexes is found to be absorbed. Possible origins of these differences are discussed.
Highlights
Colloids in nonpolar solvents are crucial in many industries and applications; this motivates the extensive research into their properties
Silica organosols consist of surfactant-coated nanoparticles which have been transferred into organic solvent [15,24]
Three ternary systems of nonaqueous colloids have been considered in this study, consisting of a polar core, a nonpolar solvent, and added surfactant
Summary
Colloids in nonpolar solvents are crucial in many industries and applications; this motivates the extensive research into their properties. Novotny reviewed the applications of nonaqueous colloids, identifying four technologies making significant use of such systems: magnetic recording media, ceramics in electronic components, reprographic printing, and electrophoretic displays [12]. These high technology applications show the importance of colloids in nonpolar solvents. Due to the properties of nonpolar solvents, the interparticle interactions are reduced as compared to aqueous colloids. Unless charging agents are added, there is little electrostatic interaction between colloids, a consequence of the reduced relative permittivity
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