Nanoindentation of surfactant aggregates

Surfactants are important for a wide range of applications dealing with one-dimensional nanoscale materials, including dispersion of carbon nanotubes, as organic templates in mesoporous silica thin films, and for the fabrication of silica nanowires. There is therefore great interest in better understanding the structure and properties of surfactant aggregates 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 that are being indented with carbon nanotubes and silica nanowires at the silica–water interface. The findings are compared to the results of bulk indentation with graphite and silica surfaces, and the influence of nanometer-scale curvature on the results is described.

Graphical abstractSurfactant-covered carbon nanotube indenting adsorbed CTAB micelle on silica by molecular dynamics simulation.Figure optionsDownload full-size imageDownload high-quality image (74 K)Download as PowerPoint slideResearch highlights►Classical molecular dynamics simulations provide predictions about the morphology of surfactant aggregates at hydrophobic and hydrophilic solid–liquid interfaces of varying curvature. ►Adsorbed surfactants on carbon nanotubes create steric repulsion between the nanotubes that exceed the van der Waals forces of attraction. ►Nanoindentation of a micelle with a tip of sharp curvature shows a steady rise in force as the escaped surfactant monomers climbed up the indenter. ►Nanoindentation with a surfactant-covered tip of the same sharp curvature is predicted to have the same separation distance to break the micelle and comparable mechanical breakdown mechanisms as a tip that is not surfactant-covered.