Brownian Force Profile Reconstruction of Interfacial 1-Nonanol Solvent Structure

Abstract

Using Brownian force profile reconstruction (BFPR), we measured the solvent structure force profile of interfacial 1-nonanol between graphite and methyl terminated alkane thiol SAM surfaces. BFPR harnesses the thermal motion of the cantilever to accurately and precisely reconstruct force profiles that may be stiffer than the intrinsic cantilever stiffness. Novel methods to compensate instrument noise and seamlessly stitch together subsections of the force profile significantly improve upon previous reconstruction techniques using thermal noise. The increased accuracy and precision of BFPR could enable the measurement of stiff or rough energy landscapes such as solvent structure or ligand-protein binding. The force profile for interfacial 1-nonanol solvent structure was well fit by an exponentially decaying sinusoid function with a period of 4.5 A for distances greater than four molecular layers, revealing liquid behavior. Distances shorter than four molecular layers displayed solid behavior with interlayer transitions being 3.9 A and possible crystal orientation rearrangements causing submolecular steps upon subsequent confinement.