Publication Title: Load Impedance of Immersed Layers on the Quartz Crystal Microbalance: A Comparison with Colloidal Suspensions of Spheres

Journal:  Langmuir 2020, 36, 31, 9225–9234

Communication Type: Scientific Publication

By: Marc Meléndez, Adolfo Vázquez-Quesada, and Rafael Delgado-Buscalioni

UAM, Spain



The analytical theories derived here for the acoustic load impedance
measured by a quartz crystal microbalance (QCM), due to the presence of layers of
different types (rigid, elastic, and viscous) immersed in a fluid, display generic
properties, such as “vanishing mass” and positive frequency shifts, which have been
observed in QCM experiments with soft-matter systems. These phenomena seem to
contradict the well-known Sauerbrey relation at the heart of many QCM measurements,
but here, we show that they arise as a natural consequence of hydrodynamics. We
compare our one-dimensional immersed plate theory with three-dimensional
simulations of rigid and flexible submicron-sized suspended spheres and with
experimental results for adsorbed micron-sized colloids, which yield a “negative
acoustic mass”. The parallel behavior unveiled indicates that the QCM response is
highly sensitive to hydrodynamics, even for adsorbed colloids. Our conclusions call for a
revision of existing theories based on adhesion forces and elastic stiffness at contact,
which should, in most cases, include hydrodynamics.