I prepared a composite material. SEM images & EDX showed that there is a large change in the surface properties and also the chemical composition. Whereas by FTIR analysis, the peaks remained intact at position but the magnitude of the peaks changed noticably. What can be inferred from that?
Dear Roy,
The working principle of FTIR is based on infamous Beer- Lambert's Law, the change in the intensity is related to molar absorbtivity, concentration and path length. Any change of these factors will change the intensity of the incident radiation. In your sample either the path length or the concentration is changing.
Regards
Dear Roy,
If all your samples are in same composition I am agree with Dr. Rather, it means either the concentration or path length is higher. However, change in intensity definitely indicates some changes based on the sample composition which can be bonds or crystallinity in different compositions. You may know that temperature can also affect the FTIR peaks intensity.
Best,
Hello Dear Rokhsareh, I could understand that intensity varies with some changes in the sample. Regarding the chemical bonding, the peak positions would have shifted towards right or left which did not happen. So if there is no shifitng of the peaks then it means that there is no new chemical bonding in the sample. How can the intensities of peaks change then?
Hi Roy, these are the basic conditions that can change the intensity in FTIR. Now, other factors like the operating conditions, doping, composite formation change the value of above said factors. For example if you are doing your samples in ATR mode, even the difference of cantilever press over diamond or germanium cell can vary the intensity.
After composite formation the decrease in intensity is mainly due to suppression of certain specific vibrations or rotations modes of the material. These can be further inferred by doing the Raman of the same sample. Yes, you are right the situation is valid for a peak where there is no change in the wave number.
In FTIR the reflection of incident wave extends into the sample. The penetration depth of these waves is between 0.3 and 2.0 micrometres. By forming the composite the penetration depth may vary and some specific vibrational modes are restricted thus decreasing the intensity.
These are just assumptions, the original results are with you making you better to judge what is actually happening. But my suggestion is to go for the Raman.
Regards
Dear Roy, to get a detailed answer to your question you need to explain what exactly is in your sample and how you did the experiment, including how you made the IR measurements. Otherwise, everyone is guessing what might be happening!
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