Probe three-dimensional structure of soft organized surfactants at solid–liquid interface with an AFM in MAC Mode and contact mode

Abstract

Atomic force microscopy provides a unique direct-visualization tool to study the three-dimensional structure of adsorbed surfactants on solid surfaces. Ionic surfactant molecules spontaneously adsorbed onto hydrophilic surfaces from aqueous solution above the critical micelle concentration (cmc) have been imaged using an atomic force microscope in magnetic ac mode (MAC Mode) and contact mode. It was found that the soft organized surfactants were highly compressible and therefore showed a wide range of corrugations depending on imaging forces. When using gentle MAC Mode, corrugations of the organized surfactants around half of the estimated height of the proposed surfactant aggregate cylinders on mica have been stably observed. Traditional contact mode operating in the pre-contact double-layer electrostatic interaction region, however, showed significantly reduced height of the organized molecules.