Nanomechanics of self-assembled surfactants revealed by frequency-modulation atomic force microscopy

• Published in: Nanoscale Vol. 14; no. 12; pp. 4626 - 4634
• Main Authors: Umeda, Kenichi, Kobayashi, Kei, Yamada, Hirofumi
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 24.03.2022
• Subjects: Atomic force microscopy; Disruption; Energy dissipation; Interfacial energy; Measurement techniques; Micelles; Microscopy; Modulation; Scale formation; Self-assembly; Solvation; Spatial resolution; Surfactants
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/d2nr00369d

Surfactants play a critical role in bottom-up nanotechnologies due to their peculiar nature of controlling the interfacial energy. Since their operational mechanism originates from the molecular-scale formation and disruption processes of molecular assemblies ( i.e. , micelles), conventional static-mode atomic force microscopy has made a significant contribution to unravel the detailed molecular pictures. Recently, we have successfully developed a local solvation measurement technique based on three-dimensional frequency-modulation atomic force microscopy, whose spatial resolution is not limited by jump-to-contact. Here, using this novel technique, we investigate molecular nanomechanics in the formation and disruption processes of micelles formed on a hydrophobic surface. Furthermore, an experiment employing a hetero-nanostructure reveals that the nanomechanics depends on the form of the molecular assembly. Namely, the hemifusion and disruption processes are peculiar to the micellar surface and cause a higher energy dissipation than the monolayer surface. The technique established in this study will be used as a generic technology for further development of bottom-up nanotechnologies. Vertical maps of conservative force, energy dissipation, and adhesion force simultaneously obtained across hemicylindrical micelles and monolayer regions of a surfactant formed on a hydrophobic surface by liquid FM-AFM.