title: Surfactants with colloids: adsorption or absorption?
abstract: OBJECTIVE
  The 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.
  
  
  METHODS
  Two 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.
  
  
  RESULTS
  AOT 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.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Smith
authors.affiliation: Institut Max-von-Laue-Paul-Langevin, BP 156-X, F-38042 Grenoble Cedex, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Grillo
authors.affiliation: ISIS-STFC, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, United Kingdom.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Rogers
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom. Electronic address: julian.eastoe@bristol.ac.uk.
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe
keywords: Colloids; Nonpolar solvents; Small-angle neutron scattering