Temperature Dependence of Dynamic Properties of Poly(ethylene glycol) Molecules on a MHz-Oscillating Solid-Liquid Interface

The temperature dependence of resonant molecular weights and resonant lengths of soft materials was investigated at the nanoscale for a viscous penetration depth region and a physisorption region using a quartz crystal microbalance (QCM). Poly(ethylene glycol) (PEG) was used as a model for soft materials. The study revealed that, in the viscous penetration depth and physisorption regions, the logarithmic values of the resonant molecular weights decreased linearly with those of the QCM angular frequencies and converged to a single point of 1360 g/mol at 416 MHz independently of temperature. The convergence point was consistent with that of chemisorption. In addition, in the regions of the viscous penetration depth and physisorption at each temperature, the slopes of logarithms of the resonant lengths decreased linearly with the logarithms of the QCM angular frequencies and were equal to those of chemisorption. As a result, a convergence point of the resonant length appeared at 2.87 nm and 416 MHz, where its frequency was equivalent to that of the chemisorption. These results enabled us to quantitatively establish the behavior of the resonant molecular weight and resonant length as a function of temperature and frequency.