The difference between QCM-D and traditional QCM
The difference between QCM-D and traditional QCM
Regarding the technique of detecting surface sensitivity, you often encounter the QCM real-time detection method. The three letters QCM are abbreviations for quartz crystal microbalances and are for the detection of very small material mass balances. If you are concerned about more instrumental knowledge, you may have noticed that there are many types of QCM series, such as QCM-D. So what is the difference between them? Unlike the traditional QCM, an additional parameter D is added to QCM-D as the dissipation factor. The dissipation factor provides real-time information on the softness of the adsorption layer on the surface of the chip, also known as viscoelasticity. This means that QCM-D can provide more information about the research system than traditional QCM.
- What is dissipation?
QCM-D measures dissipation, but what is this parameter, what is it made of, and what does it mean? Sometimes dissipation is also referred to as damping of the chip in oscillation. The strict definition of dissipation is the sum of the energy losses of the system during each oscillation period. If described by an equation, it can be written as 1/Q, where Q is the quality factor of the oscillator used. Another way to define dissipation is to divide the energy loss per oscillation period by the total energy in the system.
Having said so many conceptual things, but what does it have to do with actual experiments? As mentioned earlier, dissipation is related to the softness of the adsorption layer on the surface of the chip. A rigid material deposited on the surface of the chip will vibrate with the chip without deformation. In this case, the rigid material does not inhibit oscillation and the detected dissipation value will be low. On the other hand, the soft film will not completely follow the chip to vibrate together. This means it will deform during the test. The soft film suppresses oscillation and produces high dissipation. Therefore, the dissipation parameter provides real-time properties of the softness or viscoelasticity of the film deposited on the surface of the chip, which makes it possible to monitor conformational changes.
2. Why is it important to measure energy dissipation?
It is certainly beneficial to collect as much information as possible about the system under study, but is dissipative information really necessary?
There are three important aspects to the dissipation parameter:
First , dissipation reveals the relationship of the studied system over time.
Second , it provides key information on the adsorbed material, such as quantified mass, thickness and viscoelastic properties.
Third , dissipation reveals whether a model of a viscoelastic or rigid film should be used. The quality of the rigid membrane can be calculated using the Sauerbrey equation, requiring only a single harmonic resonance frequency to be input; multi-parametric fitting requires at least a period of variation of the F and D values ​​with respect to time. In general, the more the frequency multiplication, the better the fitting result.
A more in-depth discussion of the first point just mentioned is to qualitatively understand the time-resolved behavior of the system under study. The dissipation parameter will supplement the information of the adsorbed material from the collected frequency-doubling frequency. The two parameters F and D captured at the same time will plot the state of the adsorbed material on the surface and how the arrangement changes with time; the frequency response of a QCM chip reflects the change in the coupling quality on its surface, including being trapped in the molecular layer. The quality of the solvent between. Dissipation reflects the softness of the film. Monitor these two parameters as a function of time, ie whether the molecule lies flat on the surface (less rigid membrane and hydration); or stretched configuration (high membrane and hydration); and if there is rearrangement, such as swelling These changes are detected (from flat to extended) or collapsed (from extended to lying).
3. QCM-D is better than QCM's three points
In summary, the dissipation parameter provides three important advantages over traditional QCM:
1. It qualitatively provides information on the softness of the film of the adsorbent material and information on the softness and hardness as a function of time.
2. It provides key information about the quantitative model.
3. It provides the basic elements of the model of viscoelastic film.
What value can the D value also help you with your understanding of your experiment? Can you fully understand the solvent content, nanostructure or arrangement of the films in the system under study? Explore the potential of dissipating and share your stories and questions in the comments below.
4. Below is a review from one of our users:
"I can tell you that for every electron moved, this amount of mass changed. That's powerful. You can't really get that with any other system."
Jodie Lutkenhaus, Associate Professor, Texas A&M University
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