Behavior of polyethylene glycol molecules at an oscillating solid-liquid interface

The behavior of polyethylene glycol (PEG) molecules at an oscillating solid-liquid interface was examined using a quartz crystal microbalance (QCM). The number-average molecular weights (Mn) of PEG molecules were systematically varied. This study revealed that the shift in the energy dissipation factor, ΔD, of the QCM against square root of the density-viscosity product of the PEG solution is linear and has an intercept. Moreover, the systematical analysis revealed that the ΔD slope rapidly decreases with Mn, and the ΔD intercept becomes constant above 1.1×10(4) g/mol. Those results indicated that the resonant length of PEG molecules moving with the oscillating plate at 9 MHz is 97.6 Å. We also found that the difference between the resonant lengths calculated from ΔD and series resonance-frequency shift, ΔF, is related to the density of the thin PEG layer formed on the gold electrode.