Using The Quartz Crystal Microbalance To Study Macro- And Nanoscale Bubbles At Solid-Liquid Interfaces

We show here that macro-and nanoscale bubbles can be detected by Quartz Crystal Microbalances (QCM) submerged in liquids. QCM's are high quality factor oscillators that generate a shear wave when submerged in a fluid. The damping of the oscillation by the fluid causes the resonance frequency of the QCM to shift, and a viscosity can be calculated from the frequency shift. Since the shear wave generated is so short, this is a near-surface viscosity as opposed to a bulk viscosity. When bubbles cling to the QCM face the viscosity of the liquid as measured by the QCM will be reduced from the true bulk viscosity of the liquid. In this study we have submerged QCM's with both hydrophilic (gold or silicon dioxide) and hydrophobic (octadecanethiol) surfaces in water distilled to varying degrees, including seltzer water and vacuum distilled DI water. The seltzer water has visible macroscale bubbles, and so we were able to correlate video acquired of the QCM submerged in the seltzer water with the viscosity data to directly link the presence or absence of a bubble to a change in the measured viscosity.