Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 296, Issue 1, Pages 342-349Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2005.08.060
Keywords
molecular dynamics simulations; cationic surfactants (C(12)TAB); structure and shape of micelles; mechanical properties of micelles; hydrophobic (graphite) surface; hydrophilic (silica) surface; AFM
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Cationic surfactants are important for a wide range of applications, including controlled drug delivery systems, emulsifiers, and chemical mechanical polishing. It is therefore important to better understand surfactant Structure and properties at the solid-liquid interface. Here, classical molecular dynamics simulations with empirical potentials are used to compare the Structures and mechanical properties of cationic surfactant micelles at hydrophobic (graphite) and hydrophilic (silica) surface-water interfaces. In particular, the morphology of monolayers and bilayers of C(12)TAB (n-dodecyltrimethylammoniumbromide) at these interfaces, and their responses to atomic force microscopy indentation, are examined. The simulations predict that surfactant monolayers and bilayers on silica evolve into a spherical micelle Structure, in agreement with theoretical models Of surfactant morphology. In contrast, surfactant monolayers on graphite evolve into a hemi-cylindrical structure, in agreement with experimental findings. In the simulated indentation of the micelle/silica system, the spherical micelle breaks apart and forms a surfactant monolayer. The indentation force Curve has a maximum value of 2.25 nN. On the other hand, the simulated indentation of the micelle/graphile system causes the hemi-cylindrical micelle Structure to break apart and the surfactant tails to wrap around the graphite indenter. The indentation force curve has a maximum value of 13 nN. (c) 2005 Elsevier Inc. All rights reserved.
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