Single-Sided NMR of Paint Films After Climate Cycling: Conclusion

This will be my last Monroe blog post. Fortunately, the chemistry department gave me additional funding to continue research for the remainder of the summer. But as of now, here is where my research stands:

The NMR climate cycling data is intriguing. Each pigment is consistent with itself, but across several experiments doing the same thing to the same sample yielded different changes. However, I did notice an interesting trend in the measurements. Every paint sample returned to its initial T2 value after climate cycling if it was left alone for a few hours. This has lead us to hypothesize the existence of an “equilibrium” T2 value that the paint films want to return to.

For one memorable day in the lab, I measured the T2 values of a sample as it warmed after being dipped in liquid Nitrogen. (Yes, you heard me right. I took a paint sample and dipped it in liquid nitrogen. -195.8 degrees Celsius) This confirmed the trend I had seen of a return to an “equilibrium” T2 value. After doing some research I believe this might have something to do with the expansion and contraction of the paint film as it is pulled by the glass. Like a rubber band, it returns to its original state after being stretched, due to crosslinks between the molecules.

I’ve also been doing differential scanning calorimetry experiments on paint samples to try to find glass transition temperatures. Differential scanning calorimetry measures heat flow into a small amount of sample to locate phase transitions, such as crystallization, melting, and glass transitions. (It can also be used to look at reactions and melting points and other things, but I’m not doing that.) The glass transition of a polymer is the temperature where it goes from a flexible material to a brittle material. You can look up videos of people dipping things like roses and rubber bands into liquid nitrogen, and then pulling them out and smashing them with a hammer. This can happen because the material is at a temperature below its glass transition temperature. Our results are bizarrely bumpy however, but the bumps are in the same place for each sample. I think this may be caused by high levels of plasticizers in the paint samples, by metal soaps in the paint samples, or by inhomogeneous curing throughout the thickness of the paint film.

The next steps that I will be taking involve trying to correlate NMR data with DSC data and the physical conditions of the paint films. I also plan to take FTIR (Fourier Transform Infrared) measurements of the paint films to determine if there are metal soaps. I also might end up developing a method to use single-sided NMR to identify glass transitions of materials, because some of the data I got from the liquid nitrogen experiment looked promising.

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