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Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Griffin, LR 
Browning, KL 
Lee, SY 
Skoda, MWA 
Rogers, S 

Abstract

Using specular neutron reflection, the adsorption of sodium and calcium salts of the surfactant bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT or AOT) has been studied at the mica/water interface at concentrations between 0.1 and 2 CMC. The pH dependence of the adsorption was also probed. No evidence of the adsorption of Na(AOT) was found even at the critical micelle concentration (CMC) while the calcium salt was found to adsorb significantly at concentrations of 0.5 CMC and above. This interesting and somewhat unexpected finding demonstrates that counterion identity may be used to tune the adsorption of anionic surfactants on anionic surfaces. At the CMC, three condensed bilayers of Ca(AOT)2 were adsorbed at pH 7 and 9 and four bilayers adsorbed at pH 4. Multilayering at the CMC of Ca(AOT)2 on the mica surface is an unusual feature of this surfactant/surface combination. Only single bilayer adsorption has been observed at other surfaces at the CMC. We suggest this arises from the high charge density of mica which must provide an excellent template for the surfactant.

Description

Keywords

0306 Physical Chemistry (incl. Structural)

Journal Title

Langmuir

Conference Name

Journal ISSN

0743-7463
1520-5827

Volume Title

32

Publisher

American Chemical Society
Sponsorship
We thank BP for funding the work and our industrial colleagues, Isabella Stocker and Peter Salino, for their scientific contributions to the work (RG63491).