It is a widespread notion that performing AFM in liquids is a fairly complicated research approach. In fact, several tasks connected to the study of molecular structures and complexes in a liquid environment have high demands on the SPM equipment. The following image depicts an AFM scan of surfactant molecules that are dynamically self-assembled into parallel, hemicylindrical micelles on a hydrophobic graphite surface.
In this case, it was difficult to observe dynamically self-assembled molecular structure. The "soft contact mode" is the imaging mode used — that is scanning with constant force using a very low set point. The probe’s vertical force must be kept as close as possible to the set point — in this case — ~100 pN. The force exceeding this value will disturb the native molecular assembly (the periodicity of the micelles is ~5 nm.). The contrast disappears for lower forces. It must be noted that the vertical topography modulation is only 0.1-0.2 nm, but it is still considerably above the noise level. This example also demonstrates that NTEGRA nanolaboratory offers enough stability and sensitivity to investigate dynamic molecular structures in an aqueous environment.
Materials and Equipment Used
10 mM aqueous solution of cetyltrimethylammonium bromide surfactant in contact with HOPG.
AFM Equipment and Probe
AFM Probe — CSG01, 0.03 N/m
AFM Equipment — NTEGRA Prima, Constant force imaging mode in liquid cell using a very low set point ("so contact mode"- force ~100 pN).
Source: "Surfactant micelles in aqueous solution: critical resolution in AFM" by Hannes Schniepp, The College of William and Mary, Williamsburg, VA, USA
This information has been sourced, reviewed and adapted from materials provided by NT-MDT Spectrum Instruments.
For more information on this source, please visit NT-MDT Spectrum Instruments.