Nanoscale Dynamics of Self-Assembled Monolayers on a MHz-Oscillating Solid–Liquid Interface Revealed by Direct Observation

Under dynamic mechanical conditions, temperature and oscillation frequency directly affect the dynamics of soft materials. Specifically, temperature impacts stiffness, while oscillation frequency affects the material response region. The resonant length of a soft material quantitatively reveals the nanoscale dynamics of its main chain in the MHz region, effectively acting as a rheometer. Here, we investigated the nanoscale dynamics of a linear soft material against temperature and oscillation frequency using a quartz crystal microbalance (QCM) and a chemisorbed, self-assembled monolayer. A novel direct analysis based on the Debye process showed that the logarithm of resonant length or molecular weight decreased linearly with that of the QCM angular frequency over the studied temperature range and converged to a single point independently of temperature. Furthermore, the convergence point of molecular weight was independent of the type of bonding/sorption.