Resonant Properties of Chemisorbed Soft Materials on a MHz-Oscillating Solid-liquid Interface

In terms of resonant lengths, the behavior of chemisorbed soft materials on a MHz-oscillating solid-liquid interface was investigated using a quartz crystal microbalance (QCM). As chemisorbed materials, we used self-assembled monolayers (SAMs) formed from three types of mercapto oligo(ethylene oxide) methyl ethers, each with a single molecular weight: HS(CH₂CH₂O)₅CH₃, HS(CH₂CH₂O)₂₇CH₃, and HS(CH₂CH₂O)₄₃CH₃. Systematic variation in the concentrations of sucrose solutions resulted in corresponding changes in their viscosity and density. In addition, it is well known that the Kanazawa equation can qualitatively explain the relationship between the resonant frequency shift (ΔF) of the QCM and the solution's viscosity and density. Therefore, we investigated the relationship between the ΔF of the QCM, both without and with a SAM, and the concentrations of sucrose solutions. The attempt showed that, for the ratios of SAM thicknesses to resonant lengths below 50 %, the experimental results of ΔF quantitatively corresponded to the Kanazawa equation. The experimental results suggest that the equation describing the resonant length could appropriately evaluate the experimental data. Based on those results, the applicability of the QCMs with the SAMs of HS(CH₂CH₂O)₅CH₃ and HS(CH₂CH₂O)₂₇CH₃ to a bubble-free nonlinear chemical oscillator led to quantitative analysis.