I am using DMSO as a solvent while coating nanoparticles with PEI. I maintain the solution at 95 C for 6 h, and after a few hours I notice that the solution turns from clear to brown. The reaction is exposed to the atmosphere. I am thinking this color change means that the DMSO has reacted but am not sure whether this affects the synthesis of the PEI-coated nanoparticles. Is a moisture-free and oxygen-free environment needed when working with DMSO?
If anyone with experience in nanoparticles/DMSO has any insight on what's going on, I'd appreciate it. Thanks in advance for your help!
Hello dear, DMSO can be employed in inert atmosphere, there are some reports where this solvent has been employed under oxygen atmosphere and high temperature (> 120 °C).
DMSO on long standing at room temperature or exposure to air or heating at elevated temperature turns brown possible due to transformation of dimethylsulfoxide to dimethylsulfide by oxidizing the impurities present in dimethylsulfoxide.
PEI (branched?) is prone to actively react with air components - with CO2 binding to carbamate, with H2O to hydrates, and with O2 to oxidation products. Last compounds are the reason of browning.
DMSO and products of its autodismutation (Me-S-Me and Me-SO2-Me) are colorless.
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