I did UV-Vis of PANI with DMSO. During UV-Vis I found the graph line of absorption from 800 to 500 nm goes in a downward trend and finally goes below the zero line and moves in negative axis and again near about 400 nm it moves upward and gives out good characteristics peak of PANI. Why does the negative movement take place and why does this negative shift change with increase in concentration?
PANI salts have a metallic character. Penetration/absorption is thus limited to the very surface and most of the light is reflected; the collected spectrum is a combination of absorption and reflection thatr varies with wavelength.
It has been demonstrated that PANI doped by large sized organic sulfonic acids, such as DBSA have a good solubility and processibility in common organic solvents. It is due to the enlarge interchain distance, which means weaker interchain reaction, and strong interaction between dopant and solvent. In the present work the synthesized PANI-DBSA is soluble in mixture of toluene and 2-propanol, chloroform, DMSO and DMF.
http://iopscience.iop.org/1742-6596/439/1/012002/pdf/1742-6596_439_1_012002.pdf
You are probably using a commercial UV-Vis spectrometer where the measurement method is done by differentiating two signals. One signal comes from a reference sample (for example a cuvette with solvent only) and one signal comes from your test sample (for example a cuvette with PANI in DMSO).
Since the instrument is calculating the absorption by differentiation between your sample and a reference, every now and then you will have a negative absorption. Check the manual of the system to see how you can calibrate the instrument and avoid going into the negatives.
It depends on the blank of your system. THis only means that your simple is more "transparent" than your reference at that given wavelength.
Thank you :Thierry Dubroca you are 100% correct. I think science has this great thing that the soul reason remain same irrespective of where you are working.
I would try to follow your instruction for better result next time.
With regards
PANI salts have a metallic character. Penetration/absorption is thus limited to the very surface and most of the light is reflected; the collected spectrum is a combination of absorption and reflection thatr varies with wavelength.
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