Visualizing Molecular-Scale Adsorption Structures of Anti-freezing Surfactants on Sapphire (0001) Surfaces at Different Concentrations by 3D Scanning Force Microscopy

Abstract

Anti-freezing surfactants form an adsorption layer at the solid–water interface to inhibit the nucleation and growth of ice. However, this mechanism has not been elucidated at the molecular scale because of the difficulties in visualizing such adsorption structures. In this study, we overcome this limitation by directly visualizing the three-dimensional (3D) adsorption structures of anti-freezing surfactants, hexadecyltrimethylammonium bromide (C16TABs), on sapphire (0001) surfaces through 3D scanning force microscopy. We present molecularly resolved two-dimensional/3D images of the adsorption structures in solutions of 1, 10, and 100 ppm. At 1 ppm, the molecules form a monolayer with a flat-lying configuration. At 10 ppm, the molecular orientation is closer to the upright configuration, with a relatively large tilt angle. At 100 ppm, the molecules form a bilayer with almost upright configurations, providing excellent screening of the sapphire surface from water. Owing to the steric and electrostatic repulsion between adjacent molecular head groups, the surface of the bilayer exhibits relatively large fluctuations, inhibiting the formation of stable ice-like structures. The understanding of molecular-level mechanisms provides important guidelines for improving the design of anti-freezing surfactants for practical applications such as car coolants.

Dynamics of Molecular Self‐Assembly of Short Peptides at Liquid–Solid Interfaces – Effect of Charged Amino Acid Point Mutations

“…The FM‐AFM technique has recently emerged as a highly effective tool for obtaining unique structural information at molecular and atomic scales, offering unprecedented detail for a wide range of surfaces, interfaces, and nanostructures. [ 36–39 ] In the present study, the peptides are assembled in pure water, with pH ≈7.0, and therefore, the hydropathy and pI values shown in Figure 1 are expected to be the true values of the peptides. In general, the broad traits of the self‐organization are similar for each of the peptides, i.e., first forming monomolecular‐thick nanowires, oriented at 60° and 120° to each other, following homogeneous nucleation (i.e., isolated locations on the surface) and subsequent growth, both longitudinally and transverse to the peptide nanowire.…”

Visualizing the inside of three-dimensional self-organizing systems by three-dimensional atomic force microscopy

“…3D-SOSs) may be visualized by 3D-AFM. Recently, we have made tremendous efforts to explore this possibility and succeeded in demonstrating it for various 3D-SOSs, including the hydration structures on the CNCs, 21) the molecular adsorption structures of the anti-freezing surfactants, 27) the cellular components inside the living cells, 28) and the charge distributions inside the EDLs. 29) These examples demonstrated the effectiveness of this method in various in-liquid sciences, including interface sciences, life sciences and electrochemistry.…”

“…Among our recent 3D-AFM studies on the interfacial molecular structures, here we review the study on molecular-scale adsorption structures of anti-freezing surfactants on sapphire (0001) surface. 27) Car coolant is used to remove the heat generated by the engine from the car system. For using a car in a cold area, the car coolant's freezing point (T fp ) should be kept at less than −35 °C.…”

“…Recently, we have made tremendous efforts to explore such possibilities and demonstrated direct 3D imaging of various 3D-SOSs, including hydration structures, 21) swollen polymers, 19) adsorbed molecules, 27) intra-cellular structures 28) and potential distribution inside an EDL. 29) Here, we review recent progresses in our 3D-AFM studies on various 3D-SOSs.…”