When working with Quartz Crystal Microbalance technology, QCM, you will often encounter the terms dissipation, damping, and energy loss. In QCM-D, Quartz Crystal Microbalance with Dissipation monitoring, dissipation describes the relative amount of energy lost during each oscillation cycle of the quartz sensor. This information is valuable because the energy loss depends on the material and liquid coupled to the oscillating sensor surface. By monitoring dissipation together with resonance frequency, QSense QCM-D can reveal whether a surface-bound layer is rigid and compact or soft and viscoelastic.
While conventional QCM measurements focus on frequency changes, QCM-D measures both frequency and dissipation. This makes it possible to analyze not only mass changes, but also the mechanical properties of the surface-bound layer.
A QCM sensor is an harmonic oscillator. Like all real-world oscillators, it loses energy over time unless it is continuously driven by an external force. When the driving force is removed, the oscillation amplitude gradually decreases until the sensor stops oscillating. This decrease in amplitude is called damping. The energy lost from the oscillating system is referred to as energy dissipation.
Energy losses can arise from several sources, including internal losses in the quartz crystal and frictional losses in the surrounding medium, such as air or liquid. In QCM-D measurements, however, the most relevant contribution often comes from the material and liquid in contact with and coupled to the oscillating sensor surface. As the sensor oscillates, a soft, hydrated, or viscoelastic layer at the surface can deform and dissipate energy. The more energy that is lost during this deformation, the higher the dissipation. The phenomenon is particularly pronounced in the presence of bulk liquids or at the deposition of soft films, such as biomolecule- or polymer-based layers.
Dissipation is not usually the final parameter of interest by itself. Instead, it acts as a readout of the mechanical and structural properties of the material at the sensor surface. A change in dissipation can reveal whether an adsorbed layer is becoming:
Dissipation is particularly valuable when studying soft, hydrated, or viscoelastic layers, where mass changes alone may not fully describe the behavior of the material at the surface. This is particularly important because two layers can have similar mass responses but very different mechanical properties. A rigid, compact protein layer and a soft, hydrated polymer layer may both adsorb to the surface, but they will dissipate energy differently during the sensor oscillation. By combining dissipation, ΔD, with frequency, Δf, QCM-D provides a more complete picture of what is happening at the interface.
In QCM-D, energy losses are particularly pronounced when the sensor is in contact with liquids or soft surface-bound films. During the oscillation, a liquid or soft film coupled to the moving surface is deformed. This deformation causes energy loss, resulting in higher dissipation. Examples include hydrated polymer films, biomolecular layers, hydrogels, vesicles, and other soft or viscoelastic materials.
By contrast, when the sensor surface is in contact with air or vacuum, the energy losses are comparatively small. The same is generally true for thin, rigid layers that move with the sensor without substantial deformation. As a rule of thumb:
Figure 1. Schematic illustration of two different types of layers at a QCM-D sensor surface which would result in different amount of energy loss. In A), a hydrated and soft viscoelastic layer which would induce a large energy loss, and in B), a thin and rigid layer where the energy loss would be small.
An important parameter describing an oscillator is the quality factor, or Q factor. The Q factor is a dimensionless measure of how weakly or strongly an oscillator is damped. A high Q factor means that relatively little energy is lost during each oscillation cycle. The oscillation therefore persists for a longer time after the driving force is removed. A low Q factor means that more energy is lost during each cycle. The oscillation then decays more quickly.
Dissipation, D, is the inverse of the Q factor:
More specifically, the Q factor relates the energy stored in the oscillator to the energy dissipated during each oscillation cycle. Dissipation therefore increases as the energy loss increases. In practical terms:
A tuning fork is a useful example of an oscillator with low dissipation. Once struck, it keeps vibrating for a relatively long time. A soft material such as gelatin, by contrast, dissipates energy much more quickly when deformed and stops moving shortly after it is set in motion.
Figure 2. A tuning fork has low dissipation and continues oscillating for a relatively long time once set in motion. A soft material, such as gelatin, dissipates energy more quickly and its oscillation decays faster.
In QCM-D measurements, dissipation is monitored together with the frequency response. The combined Δf and ΔD data can be used to understand both mass changes and changes in layer mechanics. Frequency and dissipation are most informative when interpreted together. While Δf provides information about changes in coupled mass, ΔD helps explain whether the associated layer is relatively rigid and compact or soft, hydrated, and viscoelastic.
Figure 3. Schematic examples of how combined frequency, Δf, and dissipation, ΔD, responses can be interpreted in QCM-D analysis. Frequency changes provide information about changes in coupled mass, while dissipation changes provide information about layer softness and viscoelasticity. Together, the signals can help distinguish relatively rigid adsorption, soft or hydrated layer formation, mass loss and compaction, and structural rearrangement.
For example, Fig. 3:
Plotting dissipation as a function of frequency, often referred to as a ΔD versus Δf plot, can help reveal structural transitions or multiple stages in an adsorption or rearrangement process.
QCM-D measurements can be recorded at several harmonics. Comparing the responses at multiple harmonics can provide additional insight into layer uniformity, viscoelasticity, and whether a simple rigid-film interpretation is appropriate.
Dissipation is particularly important and provides key information when the surface-bound layer is soft, hydrated, viscoelastic, or undergoing structural change. In these cases, frequency data alone may not distinguish mass uptake or loss from changes in layer mechanics, hydration, or conformation. Examples include studies of:
Applications where soft matter and the surface and interface phenomena listed above frequently occur include, for example:
Biomolecular layers and biointerfaces
Dissipation is useful for studying proteins, lipid membranes, hydrogels, polymer brushes, and other biomolecular layers because these materials are often soft and highly hydrated. Changes in dissipation can help distinguish between rigid adsorption, formation of a soft viscoelastic layer, membrane restructuring, swelling, collapse, or conformational changes.
Polymers, coatings, and thin films
In polymer films, multilayers, responsive coatings, and hydrogel-like materials, dissipation helps characterize how the mechanical properties of a layer change during build-up, solvent uptake, crosslinking, collapse, degradation, or removal. This can be important when film performance depends not only on how much material is present, but also on whether the layer is flexible, hydrated, compact, or mechanically stable.
Cleaning, detergency, and residue removal
During cleaning, dissipation can reveal whether a deposited soil or residue layer first swells or softens before it is removed. This helps distinguish direct removal from multi-step processes involving detergent penetration, hydration, restructuring, breakup, and rinsing.
Surfactant and formulation studies
Dissipation helps compare surfactant layers that may have similar adsorbed mass but different structures. For example, one surfactant may form a rigid, compact layer, while another forms a softer, more hydrated, or more viscoelastic layer. This is useful in cleaning, pharmaceutical formulations, biopharmaceutical material compatibility studies, CMP, mining, and other applications involving surface-active molecules.
EQCM-D and electrochemical energy applications
Dissipation is also valuable in electrochemical QCM-D, or EQCM-D, where frequency and dissipation data are measured together with electrochemical signals such as current and potential. This combined information can help reveal how electrochemical processes affect not only electrode mass, but also the mechanical and viscoelastic properties of surface layers. In battery research, this can be relevant when studying the formation and evolution of soft or mechanically complex interfacial layers. In fuel cells, corrosion studies, electrodeposition, and other electrochemical energy applications, dissipation can help assess how electrode surfaces and interfacial films change as a function of potential, electrolyte composition, or operating conditions.
High dissipation does not necessarily mean that more dry material is present at the surface. It can also reflect a softer, more hydrated, or more viscoelastic layer.
Dissipation is most informative when interpreted together with Δf. The relationship between frequency and dissipation helps reveal whether a layer is rigid, soft, compact, hydrated, swelling, collapsing, or restructuring.
Comparing several harmonics can provide additional information about layer uniformity, viscoelasticity, and whether a simple rigid-film model is appropriate.
When dissipation is significant, the layer may not meet the assumptions required for rigid-film analysis. In these cases, viscoelastic modeling is often more appropriate for estimating thickness and mechanical properties.
Dissipation is influenced not only by the surface-bound layer, but also by conditions such as liquid viscosity, liquid density, liquid temperature, and the properties of the sensor surface. Well-controlled baselines and reference measurements are therefore important for reliable interpretation.
Dissipation, damping, and energy loss are closely related concepts in QCM-D. Dissipation describes the energy lost from the oscillating sensor during each cycle, and this energy loss is strongly influenced by the material and liquid coupled to the sensor surface. For QCM-D analysis, dissipation is valuable because it provides information about the mechanical and structural properties of surface-bound layers. Together with frequency data, it can reveal whether a layer is rigid or soft, compact or hydrated, stable or restructuring. Dissipation is therefore relevant across a wide range of QCM-D and EQCM-D applications, from biomolecular layers, polymers, coatings, and cleaning processes to battery interfaces and electrochemical energy-conversion materials. By following changes in dissipation over time, QSense QCM-D helps make interfacial layer properties visible during adsorption, swelling, collapse, film formation, degradation, and other dynamic surface processes.
Download the overview to learn more about dissipation, why it is important in QCM-D measurements, and how the information of energy loss can be used to characterize surface-bound layers.
Malin graduated in engineering physics in 2006, where her research focused on the QCM-D technology. Since then, she has been scrutinizing the how’s and why’s of the world in general, and the world of QCM-D in particular.
